Compactación

Professor Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss

Compaction Technology in Earthwork, Highway and Transportation Engineering Volume 1

Basic Principles of Vibratory Compaction Compaction of Soil and Rock Compaction of Asphalt

Professor Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss

Compaction Technology in Earthwork, Highway and Transportation Engineering

Professor Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss

Compaction Technology in Earthwork, Highway and Transportation Engineering Volume 1

Basic Principles of Vibratory Compaction Compaction of Soil and Rock Compaction of Asphalt

Specialist book of BOMAG GmbH & Co. OHG, Germany, 1st edition 2001 Published by BOMAG GmbH & Co. OHG

Impressum © BOMAG GmbH & Co. OHG, Germany, all rights reserved Publisher: BOMAG GmbH & Co. OHG, Boppard Project Management: Dipl. Ing. H.-J. Kloubert, BOMAG GmbH & Co. OHG, Boppard Prof. Dr.-Ing. Dr.-Ing. E. h. Rudolf Floss, Munich Layout: Schray – Grafisches Atelier, Weissach Translation: Techtrans GmbH, Boppard Print: Druckerei Seyl & Hohn, Koblenz Publisher‘s notes: The publication in its entirity is protected by copyright. All details, data, results etc. contained in this book have been reviewed by the project management according to the best of knowledge under utmost care. At the same time, errors

Preface Mechanical compaction technology with vibratory compaction equipment has reached a high level of development. It has matured to an economical and technically indispensable construction technology used all over the world for the construction of permanently stable and deformation resistant highways, transportation routes, earth work, embankments and foundations of buildings, bridges, sealing layers and waste disposal sites.

Systematic fundamental investigations in the Research and Development Centre of BOMAG as well as application oriented investigations on large scale construction sites were the essential prerequisites for this progress. The author of this first edition of the BOMAG specialist book, University Professor Dr. Ing. Dr. Ing. e.h. Rudolf Floss, has scientifically contributed on these researches and developments over many years.

These engineering projects are characterised by increasing output, a strong weighting of economical aspects and high quality demands. Compaction equipment must be powerful, economical and versatile in use and contribute to a surface covering quality assurance by means of an immediate work integrated control.

Purpose and goal of this specialist book is the presentation of the know-how about BOMAG compaction technology in connection with the scientific state of fundamental knowledge in a comprehensive publication. Volume 1 available in German and English and the planned successive volume shall be available for all those who are interested in BOMAG equipment. The experience contained therein shall help civil engineering contractors, authorities, and consulting engineers in the planning and execution of compaction tasks in earthwork, Transportation routes and landfill site construction, but shall also provide fundamental knowledge for experts in research and science.

BOMAG has recognised these trends and development objectives and already in the eighties thoroughly investigated compaction processes when using vibratory rollers and the interaction between drum vibration and the soil reaction force changing with increasing compaction. The push in innovation resulting from this led to the development of automatic measuring and recording systems. With these roller integrated systems the compaction processes can be controlled and optimised and provide a surface covering recording of the compaction. In recent years further research and development activities led to the successful launch of intelligent BOMAG compaction systems such as VARIOMATIC and VARIOCONTROL, which automatically adapt the compaction amplitude to the actual operating conditions. These controlled rollers particularly stand out in terms of compaction performance, depth effect, uniform compaction and suitability for universal use. Last but not least, the demand for more powerful padfoot rollers for fine grain and rockfill materials, as used on large scale civil engineering projects of the German Railway, led to the development of new padfoot designs.

Boppard, March 2001 BOMAG Management

Introduction Research and development in the field of compaction technology concentrates on enhancing the performance capacity of machines, on user friendly and environmentally compatible designs and on extending the functional structural range of application. These improvements, which are achieved in a continuous process, occur temporally parallel with the development of electronic measuring and computing technology as well as the use of micro-processor controls. An important radical change and milestone in this respect is the introduction of automatic measuring and recording systems as well as EDP and GPS based machine controls. These machine integrated systems enable an almost automatic control of compaction work and an optimisation of the use of equipment as well as a surface covering assurance of the compaction quality. The application of the construction machine as a “measuring and testing unit” and the use of the machine parameters for process control is essential for large area projects, because it is the only way to achieve a uniform placement quality and the reliability of the quality assurance in accordance with the required construction progress. A development leap in control automation of vibratory rollers has been in fact achieved by the possibility to combine data of compaction quality and compaction management with DGPS-information (Differential Global Position Systems) about the position of the roller. Further developments aim at the possibility to localise the roller position exactly via a position system suitable for practical applications and to specify, control and record the number of roller passes. The further development of the machine integrated measuring and recording systems as well as the localisation of the roller by means of satellite navigation will also enable the linkage of the position data with the compaction data and the real time presentation in a 3 D-model. Furthermore, poking interfaces for DGM planning software (digital terrain models) are planned, so that the actual position can be compared with the nominal data during the compaction process in a work integrated manner.

The great present and future challenges of engineering technology induce BOMAG and the author of this specialist book to communicate, in form of a compendium, the state-of-the-art concerning the optimisation and automation of equipment engineering and compaction technology gained by research and investigating to the public and especially to those persons interested in BOMAG compaction technology. Volume one of this specialist book is divided into three parts. The first part contains the fundamental principles of vibratory compaction, the characteristic equipment technological parameters as well as the design types of and applications for BOMAG vibratory compactors. The second part deals with the compaction of soil and rock in connection with the operative range of the BOMAG compaction technology in earthwork and embankment construction, describing the soil and rock mechanical principles of compaction and subsequently the recommendations for vibratory equipment with performance data. The third part contains, in a similar way, experiences and equipment recommendations for the compaction of asphalt pavements as applied in highway and transportation engineering and for sealing layers. The appendix contains several conversion tables and reference lists as general assistance for the user of this book. For the intended sequential volume special subjects and special applications for the BOMAG compaction technology are planned. This includes subjects such as the compaction of unbonded and hydraulically bonded base courses and soil-binder mixes in highway and transportation engineering, the compaction of recycling materials, industrial wastes and household refuse, the compaction of cable and pipeline trenches, construction backfills and embankments, as well as the compaction of sanitary landfill constructions and mineral sealing layers. Furthermore, special chapters will deal with fundamental principles and information for the calculation of output and costs of compaction work, as well as measuring, testing and recording systems for quality assurance of compaction work.

The author would like to thank BOMAG for the publication of this specialist book, namely Mr. Dipl.Ing. Hans-Josef Kloubert, who has made a significant contribution with their engineering knowledge and editorial support. The author would also like to thank BOMAG executives in the research and engineering department for the useful discussions. BOMAG and author wish all users of this specialist book many inspirations and beneficial information for their daily work.

Munich, March 2001 Univ. Prof. Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss

2

Table of Contents Part 1 Fundamental principles of vibratory compaction 1

Principles of dynamic vibration

1.1 1.2 1.3 1.4 1.5

Basic vibrations ............................................................................................................................. 7 Natural and resonance vibrations .................................................................................................. 8 Harmonic and subharmonic vibrations .......................................................................................... 9 Propagation of vibrations ............................................................................................................... 9 Dynamic forces and resilient stiffness of the subsoil ................................................................... 10

2

Vibration and movement performance of the system types

2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.2 2.3 2.4 2.5

Vibration exciter systems for vibratory rollers .............................................................................. 11 Vibrator (circular vibrator) ............................................................................................................ 11 Oscillator ...................................................................................................................................... 11 Comparative compaction effect of vibrator and oscillator ............................................................ 12 BOMAG directed vibration systems ............................................................................................. 13 Parameters of vibration generation .............................................................................................. 17 Static axle load and vibrating mass ............................................................................................. 17 Centrifugal force, frequency, amplitude........................................................................................ 17 Energy transfer............................................................................................................................. 20

3

Design types and applications for BOMAG compaction technology

3.1 3.2 3.3 3.4 3.5 3.6 3.7

Vibratory tampers......................................................................................................................... 23 Vibratory plates / hydraulic plates ................................................................................................ 23 Hand guided vibratory rollers ....................................................................................................... 25 Tandem rollers ............................................................................................................................. 26 Single drum rollers with smooth drum.......................................................................................... 28 Single drum rollers with padfoot drum ......................................................................................... 30 Towed vibratory rollers ................................................................................................................. 32

1

Table of Contents Part 2 Compaction of soil and rock in earthwork 1

Soil

1.1 Soil groups under engineering aspects........................................................................................ 33 1.2 Earth engineering classification ................................................................................................... 38 1.3 Geotechnical suitability of the soil types ...................................................................................... 40 1.3.1 Material and engineering properties ............................................................................................ 40 1.3.2 Geotechnical suitability for earthwork .......................................................................................... 43 1.3.2.1 Clays and silts ............................................................................................................................. 43 1.3.2.2 Sands and gravel......................................................................................................................... 44 1.3.2.3 Mixed particle soils ...................................................................................................................... 45 1.4 Compaction characteristics of the soils........................................................................................ 46 1.4.1 Compaction parameters............................................................................................................... 46 1.4.2 Compaction characteristics.......................................................................................................... 48 1.4.2.1 Functional interrelationship.......................................................................................................... 48 1.4.2.2 Coarse particle soils .................................................................................................................... 49 1.4.2.3 Fine particle soils......................................................................................................................... 50 1.4.2.4 Mixed particle soils ...................................................................................................................... 51 1.4.3 Relations between compaction and deformation parameters ...................................................... 51 1.4.3.1 Test dependent deformation parameters ..................................................................................... 51 1.4.3.2 Soil specific interrelationships ..................................................................................................... 54 1.4.3.3 Relationships to international soil classifications......................................................................... 56 2

Rock

2.1 2.1.1 2.1.2 2.1.3 2.2 2.3 2.4 2.5 2.5.1 2.5.2 2.5.3

Classification of rock (overview)................................................................................................... 57 Congealed rock (magmatic rock) ................................................................................................. 57 Sedimentary rock ......................................................................................................................... 57 Metamorphic rock ........................................................................................................................ 57 Description of rock ....................................................................................................................... 58 Parting plane structure of rock ..................................................................................................... 58 Strength and deformation properties of rocks.............................................................................. 59 Suitability of rock .......................................................................................................................... 60 Exploitation of rock as filling material........................................................................................... 60 Rock classes ................................................................................................................................ 60 Placement and compaction.......................................................................................................... 61

2

3

Application and performance of the BOMAG compaction technology

3.1 3.2 3.3 3.4 3.5 3.6 3.6.1 3.6.2 3.6.3 3.6.4 3.6.5 3.7 3.8

Applications.................................................................................................................................. 64 Calculation of compaction output................................................................................................. 66 Trial compaction ........................................................................................................................... 68 Placement and compaction water content ................................................................................... 70 General equipment and soil specific recommendations .............................................................. 72 Special machine specific compaction effects............................................................................... 75 Static smooth drum rollers ........................................................................................................... 75 Pneumatic tired roller ................................................................................................................... 76 Smooth drum vibratory roller ....................................................................................................... 76 Padfoot rollers with and without vibration..................................................................................... 76 Single drum rollers with special padfoot drums ........................................................................... 77 Compaction of marginal zones (slopes, embankment shoulder) ................................................. 78 Compaction of layers on elastic base .......................................................................................... 79

3

Table of Contents

Part 3 Compaction of asphalt 1

Asphalt pavements in highway and transportation engineering ........................................ 81

2

Bitumen and bituminous binders

2.1 2.2 2.3 2.4 2.4.1 2.4.2

Types and manufacturing ............................................................................................................. 83 Chemical-physical properties....................................................................................................... 84 Tests............................................................................................................................................. 85 Material specific requirements ..................................................................................................... 87 Paving bitumen ............................................................................................................................ 87 Special bitumens and bituminous binders ................................................................................... 88

3

Asphalt

3.1 3.2 3.3 3.3.1 3.3.2 3.3.3 3.3.4 3.3.5 3.3.6 3.3.7 3.3.8 3.3.9 3.4

Mineral aggregates ...................................................................................................................... 89 Asphalt for base courses.............................................................................................................. 91 Asphalt for surfacing .................................................................................................................... 92 General requirements .................................................................................................................. 92 Binder coarse asphalt .................................................................................................................. 94 Asphalt concrete .......................................................................................................................... 95 Stone mastic asphalt.................................................................................................................... 96 Gussasphalt ................................................................................................................................. 97 Asphalt mastic.............................................................................................................................. 98 Combined surface - base - courses ............................................................................................. 98 Natural asphalt and modified asphalt........................................................................................... 98 Asphalts for special construction methods................................................................................... 98 Asphalt veneer coats ................................................................................................................... 99

4

Compaction characteristics of asphalt

4.1 4.2 4.2.1 4.2.2 4.3 4.3.1 4.3.2

Fundamentals ............................................................................................................................ 100 Tests methods............................................................................................................................ 101 Marshall stability and flow .......................................................................................................... 101 Compactibility............................................................................................................................. 102 Influencing factors ...................................................................................................................... 103 Composition of mixture .............................................................................................................. 103 Influence of the temperature ...................................................................................................... 104

4

5

Application and performance of BOMAG compaction technology in asphalt engineering

5.1 5.2 5.3 5.4 5.4.1 5.4.2 5.4.3 5.4.4 5.4.5 5.4.5.1 5.4.5.2 5.4.5.3 5.4.5.4 5.4.5.5 5.4.6 5.4.7 5.5 5.5.1 5.5.2

Planning and fields of application.............................................................................................. 105 Influences caused by ambient laying and compaction conditions............................................. 107 Areal output and volumetric output of the machines ................................................................. 109 Compaction equipment ............................................................................................................. 113 Pre-compaction during pavin .................................................................................................... 113 Selection criteria ....................................................................................................................... 113 Static smooth drum rollers ........................................................................................................ 114 Pneumatic-tired rollers .............................................................................................................. 115 Vibratory rollers......................................................................................................................... 116 Effectiveness in asphalt compaction ......................................................................................... 116 Hand guided vibratory rollers .................................................................................................... 116 Tandem vibratory rollers............................................................................................................ 117 Combination rollers ................................................................................................................... 118 Plates and tampers ................................................................................................................... 119 Applicational advantages of the directed vibration system BOMAG VARIOMATIC................... 119 List of recommendations for the use of BOMAG vibratory rollers ............................................. 120 Basic rules for rolling technique ................................................................................................ 122 Rolling pattern........................................................................................................................... 122 Monitoring of quality influences................................................................................................. 125

Appendices A 1 Conversion tables............................................................................................................................ 129 A 2 Compaction parameters (soil) ......................................................................................................... 131 A 2 Conversion of compaction parameters............................................................................................ 133 A 3 Characteristics of rock..................................................................................................................... 134 A 4 Standards, regulations, guidelines .................................................................................................. 135 Literature ............................................................................................................................................. 141 Glossary ............................................................................................................................................. 147

5

6

Part 1

Fundamental principles of vibratory compaction

1

Principles of dynamic vibration

1.1

Basic vibrations

The temporal change of harmonic vibrations is defined and described by sine or cosine functions (Fig. 2).

With their rotating eccentric masses (unbalanced masses) mounted on one or several drive shafts, depending on the system, the vibratory machines designed for vibratory compaction generate uniform, stable rotary vibrations. These vibrations are transferred to the substrate via contact areas (special padfeet, plates, roller drum), either flat or linear. They act as dynamic forces in a spatially distributed manner, compact the medium by means of pressure and vibration and, with these volume reducing deformations, increase the physical-mechanical stiffness characteristics. The interaction between vibration exciter and medium to be compacted - e.g. a soil layer - can be schematically presented using a dynamic substitution model.

Compactor

suspendet machine mass exciter mass resonant vibrating soil mass machine damping soil damping resilience value of machine resilience value of soil exciter force

Compactor - soil - substitution model

A stationary vibration is a vibration with temporally constant characteristic functions. Temporary vibration processes (transient and dying processes) are transient vibrations, which will either dissipate in the course of time or change over to a stationary condition. Deterministic vibrations are vibrations that do not occur by chance; their momentary vibration magnitude can be mathematically exactly described on the basis of the previous course of time. In contrast to this, random or stochastic vibration processes showing irregular variations of time, can only be described with the help of statistic or probabilistic parameters. Fig. 2 shows a sinusoidal oscillation process as time function of the vibration displacement a‘ = f(t). The sequence of movement of this vibration type is generally characterised by the following definition and mathematical derivations: T

Soil

M m1 m2 r1 r2 k1 k2 Fo

The vibration is periodic if it is continuously repeated after a certain period of time. A periodic vibration can be graphically presented as a superimposition of several sine or cosine oscillations, the frequency of which is a multiple of the basic frequency.

Fig. 1

The basic vibrations of the exciter system normally have harmonic, periodic attributes, (fundamentals Lit. 1, 2, 5, 6):

f

Frequency, reciprocal value of the vibration period T (duration of period) T f = 1 [Hz = s-1]

ω

Radian frequency, number of vibrations in 2 π seconds ω = 2 π . f = 2πT

a

Amplitude [mm]

a‘

Vibration displacement: a‘ = a . sin (2 π . f . t)

7

Part 1

Vibration path a‘ T Amplitude a

Time t

T

Sinosoidal vibration process: Path-time-diagram

Fig. 2

Vibration speed v and vibration acceleration b are temporal derivations from the vibration displacements a‘: Vibration speed: v = da‘ = a (2 π . f) . cos (2 π . f . t) dt v = v sin (2 π . f . t + 2π )) v=a.2π.f Vibration acceleration: b = dtdv = a (2 π . f)2 . sin (2 π . f . t) b = b . sin (2 π . f . t + π) b = v . 2 π . f = a (2 π . f)2 Parameters of vibration generation for the system types, Fig. 16.

the natural frequency f multiplied by 2 π is called natural radian frequency ω0. If a vibration system possesses several natural frequencies (e.g. compaction machine and dynamically coupled soil mass), each of these natural frequencies also has its own type of vibration. When exciting such a system with a frequency which is more or less identical with one of the natural frequencies, resonance frequencies with high amplitudes will occur. According to the resonance theory (Hertwig 1933, Lit. 1) the optimal compaction effect is obtained in the range of the natural frequency of the system machine - substrate (resonance frequency). Under this condition the substrate responds elastically, similar to a spring, whereby the natural radian frequency ω02 depends in a linear relation on the spring stiffness C and the total vibrating mass m of the system: ω02 = c . m Depending on substrate and machine parameters, the natural frequencies are located in the range between 13 and 27 Hz (800 - 1.600 vibrations/ minute). Investigations reveal that the natural frequency of the system drops with increasing nominal amplitude (Lit. 3).

1.2 Natural and resonance vibrations Natural vibrations characterise system inherent vibrations, which solely depend on the properties of the system (e.g. the properties of the compaction machine: dimensions, material parameters, contact as well as marginal conditions) and adjust themselves after a short excitation period independently from the excitation magnitude. As far as these natural vibrations are characterised by harmonic vibration features, basic terms as in part 1, section 1.1 are used: Each vibration magnitude reappears after the system inherent period duration T (duration of natural vibration). The reciprocal value of the system inherent period duration T0 is the natural frequency f0 = 1/T0. The value of

8

Change of frequency in connection with amplitude eccentric mass (Machet 1976)

Fig. 3

Fundamental principles of vibratory compaction

1.3 Harmonic and subharmonic vibrations Vibration exciters and oscillating masses of the substrate to be compacted form a coupled vibration system. During the compaction process the basic vibration of the machine’s exciter system is changed or disturbed by the stiffness of the dynamically coupled mass. These changes in the periodic sequence of movement result in harmonic vibrations, which are a multiple of the basic vibration generated by the exciter. The magnitude of these harmonic vibrations increases with progressing compaction or with the stiffness of the substrate and is therefore an indirect measure for the dynamic change in stiffness. This process reaches a limit condition when the machine lifts off the substrate or “jumps” at a very high stiffness. In this jump condition so-called subharmonic vibrations, half the size of the basic vibration, occur besides the basic vibrations generated by the exciter. For example, on vibratory rollers used in earthwork with a normal vibration frequency of approx. 30 Hz, the harmonic vibrations reach 60 Hz and the subharmonic vibrations 15 Hz.

Wave propagation of the vibration energy

Fig. 4

The transferred vibrations dissipate with increasing distance from the source of excitation. This is caused by the geometric decrease of the amplitudes as a result of the reduction in energy density and by the material damping caused by the frequency dependent absorption of vibration energy. Vibrations with higher frequencies are thereby dampened more than vibrations with low frequencies (Lit. 9). Locally the propagation of vibrations may be considerably disturbed or obstructed, e.g. by extreme division of layers, building density, clefts in the terrain and the interaction of several vibration sources. In case of distinct layer borders with high density differences, existence of groundwater or loads not applied to the ground the propagation of vibration concentrates along the surface.

1.4 Propagation of vibrations In the dynamically coupled strata the introduced vibration energy spreads in form of space waves (compression and shearing waves) and surface waves or even as a combination of both wave types (Fig. 4). The magnitude of these wave types depends on the type of vibration exciter and the introduction of the energy. Since the source of excitation for the vibratory compaction of layers described hereunder is located near the surface, the vibrations mainly spread in form of surface waves. Depending on the distance from the source of excitation, these surface waves have higher vibration amplitudes than the space waves.

Compared with vibrations originating from blasting activities the propagation of waves from vibration excitation introduced by vibratory equipment on the surface is only of minor significance. However, during the compaction process the fact must be taken into consideration that both surface waves as well as space waves have an effect on buildings (pipes, wall and shaft constructions); example Fig. 5.

9

Part 1

Vibration speed at a foundation [mm/sec]

5 4 3 2 1

200kg-700kg Vibratory plates 10m distance

2t 6t 9t Tandem-vibratory rollers 5 m distance

17t

18t 19t Single drum rollers

Compaction equipment

2 m distance

Effects of vibrations generated by vibratory compaction equipment on a hall building

Fig. 5

1.5 Dynamic forces and resilient stiffness of the subsoil Forces, which are variable with respect to their effective duration and direction, are known as dynamic forces. If the effective duration of the force is short in relation to the periodic duration of the natural vibration of the system, the force acts as a blow and depends on the size of the impulse. Vibration magnitudes (speed, acceleration, amplitude) are measured as function of time by acceleration measurements on the compaction machine. From the measured accelerations a force-way-function can be derived by mathematical evaluation of the soil contact force and the integration of the accelerations and presented as a so-called indicator diagram. The released energy or power is an

10

indirect measure for the dynamic stiffness of the subsoil. The increase of the contact force in relation to the respective assigned vibration displacement corresponds with the momentarily achieved dynamic stiffness of the subsoil achieved by compaction; see T 1, para. 2.5 and Fig. 21.

Fundamental principles of vibratory compaction

2

Vibration and movement performance of the system types Overview of the system types (matrix) as in Fig. 6

Vibratory rollers work with various types of vibration exciters which, depending on design and system produce non-directed or directed rotational vibrations by eccentric masses. 2.1.1 Vibrator (circular vibrator)

Circular vibrator

Directed vibrator

Circular vibrator

Oscillator

Directed vibrator (Variomatic 1)

The exciter system consists of a central drive and exciter shaft with an attached unbalanced mass. The fast rotation of the exciter shaft generates centrifugal forces rotating 360° with undirected rotation vibrations. This type of vibration exciter is also known under the name single shaft rotation vibrator (Fig. 7).

Directed vibrator (Variocontrol)

Vibration exciter systems

Fig. 6

Circular vibrator 2.1 Vibration exciter systems for vibratory rollers The vibration and movement performance of vibratory rollers change with increasing stiffness of the soil layers which develops in the course of compaction. This interaction between the reactive performance of the roller and the stiffness of the soil depends on soil specific and machine characteristic influence magnitudes. When weighting these influencing parameters a distinction must be made as to their effect on the compaction process. T 1, para. 2 describes the substantial vibration and equipment parameters which interact in an accumulated way, depending on the type of machine.

Fig. 7

2.1.2 Oscillator The exciter system consists of a central drive shaft and two rotating exciter shafts with the same sense of rotation. The unbalanced masses of these toothed belt driven exciter shafts are 180° offset to each other, thereby generating a varying moment around the central axis. This exciter system generates an oscillating, i.e. rotary movement of the drum, whereby the drum is permanently in contact with the soil, without any blows and impact (Fig. 8).

11

Tooth belt

Part 1

Oscillator, vertical pressure distribution

Oscillator system

Fig. 8

With the oscillation principle, which has previously only been developed for and used in special compactors, it is assumed that the oscillatory movement of the drum together with the support of the effective axle load introduces a compaction effective shear stress to the surface of the substrate.

2.1.3 Comparative compaction effect of vibrator and oscillator Figures 9 and 10 show the results of measurements obtained from pressure and acceleration transducers to compare the different performances of vibrator and oscillator with respect to vertical pressures as well as vertical and horizontal accelerations. Figure 9 clearly shows that the maximum vertical pressures achieved by the vibrator are several times higher than with the oscillator and that the oscillator works statically without losing ground contact. The comparison in Fig. 10 reveals that, due to its principle, the oscillator can only introduce minor vertical accelerations compared with the vibrator. From Fig. 10 the conclusion can be made, that the horizontal accelerations of the oscillator are also of minor significance in comparison with the vibrator.

12

Vibrator, vertical pressure distribution

Fig. 9

Fundamental principles of vibratory compaction

2.1.4 BOMAG directed vibration systems The directed vibration systems from BOMAG unify the advantages of rotary and oscillatory vibrators. With the newly developed directed vibration systems VARIO for vibratory rollers a long striven goal of development and an important technological leap was achieved. These new self-controlling systems automatically detect and adjust the energy required for compaction. These systems are based on the analysis of the interaction between the drum and the stiffness of the material to be compacted. The compaction energy is automatically optimised by using the acceleration signals. This adaptation has the effect that the maximum possible compaction energy is transferred at any time, without the drum changing over to a unfavourable jump operation or causing any overcompaction.

Oscillator, vertical acceleration

Oscillator, horizontal acceleration

For the compaction of asphalt a directed vibrator, the VARIOMATIC system (Fig. 11), was developed. This system consists of two counter-rotating eccentric shafts and generates directed vibrations. The direction of the resulting force can be automatically changed between vertical and horizontal (oscillation), depending on the stiffness of the substrate, by simply offsetting one shaft in relation to the other. Both shafts are synchronised by a pair of gears. The control of the force direction is accommodated by a control circuit. The adjustment of the eccentrics is accomplished by a hydraulically controlled adjustment cylinder with integrated way measuring system.

Vibrator, vertical acceleration

Vibrator, horizontal acceleration

Fig. 10

The differences shown in the illustrations, which quantitatively only apply for the examined silty gravel, but qualitatively reveal the different compaction effects of both systems, can be explained by the fact that the vibrator has the effect of a combination of directed vibrator and oscillator. Since the vibrator applies a higher pressure force the vibrator not only introduces a higher vertical compression, but also a higher shear stress than the oscillator. 13

Part 1

VARIOMATIC Control unit

VARIOMATIC 2 Vibratory roller with self-regulating direction of force and effective amplitude Fig. 11

Two acceleration transducers pick up the stiffness data of the substrate and transmit these to a programmable logic control (PLC), which then sends signals to the control unit. The exchange of signals is accomplished by a new, high-speed valve technology. The vertical component of the amplitude (effective amplitude), which is of major importance for the compaction, is automatically reduced before the machine changes to jump operation because of a too high stiffness of the soil or a too high effective amplitude. This not only optimises the energy requirement, but also leads to a material preserving and uniform compaction. Besides the automatic mode, in which the system controls itself, it is also possible to pre-select a certain direction of vibration. In this case he can select from a choice of 6 vibrating directions between horizontal and vertical (Fig. 12). The higher amplitudes needed for the large vibratory rollers used in earthwork led to the development of the VARIOCONTROL system (Fig. 13). This new exciter system with its vibrating mass of 9000 kg 14

Fig. 12

generates vibration amplitudes of up to 2.5 mm and centrifugal forces of up to 500 kN. Two concentrically arranged vibrator shafts carry three eccentric weights, the two smaller weights near the ends and the large eccentric weight in the middle of the exciter shaft (Fig. 14). The middle eccentric weight rotates in the opposite direction of the outer weights. The resulting centrifugal forces add up to a directed vibration. The effective direction of this directed vibration can be adjusted by turning the complete vibrator unit. Any desired angle position between horizontal and vertical direction of vibration is possible. The control technology is based on the same concept as for the VARIOMATIC system. With increasing compaction the directed vibrator changes automatically from the vertical direction of vibration with high vertical acceleration towards the horizontal direction of vibration with a reduced effective amplitude. The amplitude is continually adapted so that areas with low stiffness are compacted with a high effective amplitude and areas with an already high stiffness with an appropriately lower effective amplitude. The offered compaction energy is thereby automatically reduced when the stiffness of the soil becomes too high. This method ensures that high amplitude generated by the vibration system achieves a favourable depth effect already during the first passes and that a premature lid or plate effect can be avoided.

Fundamental principles of vibratory compaction

VARIOCONTROL single drum roller with automatic or selectable amplitude and stiffness control Fig. 13

EVIB FB

S

VARIOCONTROL, design of exciter system

FZ

Processor

m.a

Acceleration measurement and recording of values

FB = Ground contact force s = Vibration path

FB

Rolling track

250 200 150 100 50 0

120

Bodenkontaktkraft [kN] 250 200 150 100 50 0

Bodenkontaktkraft [kN]

[mm]-4 -3 -2 -1 0 1 2 3 4 5

110

250 200 150 100 50 0

100

EVIB [MN/m2]

Dynamic stiffness EVIB determined with the VARIOCONTROL system on silty gravel

Bodenkontaktkraft [kN]

130

Fig. 14

6th pass

[mm]-4 -3 -2 -1 0 1 2 3 4 5

[mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN]

90

250 200 150 100 50 0

80

Bodenkontaktkraft [kN] Bodenkontaktkraft [kN]

250 200 150 100 50 0

250 200 150 100 50 0

[mm]-4 -3 -2 -1 0 1 2 3 4 5

70 60

3th pass

[mm]-4 -3 -2 -1 0 1 2 3 4 5

[mm]-4 -3 -2 -1 0 1 2 3 4 5

50

Bodenkontaktkraft [kN] 250 200 150 100 50 0

40 30

Bodenkontaktkraft [kN] 250 200 150 100 50 0

Bodenkontaktkraft [kN] 250 200 150 100 50 0

[mm]-4 -3 -2 -1 0 1 2 3 4 5

20

[mm]-4 -3 -2 -1 0 1 2 3 4 5

1th pass

[mm]-4 -3 -2 -1 0 1 2 3 4 5

10 0 5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

[m]

Fig. 15 15

Part 1

Total weight

static linear load

The angular position of the directed vibrator of the

vibrating mass

amplitude

frequency

Vibrating mass Centre of gravity of eccentric mass

Movement

Eccentric mass

Eccentricity

Amplitude

Time for revolution of eccentric Vibration path

Axle load, drum (Fstat)

= static weight of drum and drum frame

Static linear load

=

Vibrating mass (M0)

= Drum mass under vibratory motion

Frequency (f)

=

Angular velocity (ω)

= 2πf

Unbalanced mass (me)

= eccentric mass

[kg]

Axle load, drum (kg)

[kg/cm]

Drum width (cm)

Number of revolutions of eccentric Unit of time

[kg] ,

f = 1/T . n

Eccentricity (e) = distance between gravity centre of eccentric and rotation axis Eccentric moment (Me)

= eccentric mass, Me = me . e

Centrifugal force (FC) = Fc = me. e ω2 = me. e (2πf)2 Theoretical amplitude (a) =

Parameters of vibration generation

16

Unbalanced moment(Me) Vibrating mass (M0)

[Hz] [1/sec] [kg] [mm] [kg . mm] [N] [mm]

Fig. 16

Fundamental principles of vibratory compaction

VARIOCONTROL system can be used for a direct and surface covering determination of the dynamic stiffness of the soil (T 1, para. 2.5 and Fig. 15). For this purpose the ground contact force is determined on the basis of the accelerations measured on the vibrating part of the drum and a force-path-diagram is developed by integration of the acceleration. The ratio of the contact force to the related path of compression corresponds with the dynamic stiffness of the soil. The dynamic stiffness provides a physical magnitude as a measure for the compaction status. It can be directly measured and, in comparison with the previously used non-dimensional magnitudes, it is considerably less influenced by machine related parameters (amplitude, frequency, travel speed).

2.2 Parameters of vibration generation On vibratory rollers the generation of vibrations is characterised by the machine related parameters listed in Fig. 16. In T 1, para. 1 these fundamental values are described in more detail (Lit 7, 8, 10).

2.3 Static axle load and vibrating mass The statically effective mass consists of the drum axle load (kg). The static linear load is mathematically determined by the static axle load Fstat, divided by the drum width (kg/cm). The drum diameter influences the static linear load in as far as a high drum axle load requires an appropriately large diameter. When increasing the static axle load while leaving other influential parameters unchanged, the static and dynamic pressure strain applied to the soil by

the drum increase almost proportionally with the axle load. The penetration depth of this stress or the effective compaction depth increases accordingly. The vibrating mass M0 contains all vibrating parts of the machine, such as drum, hydraulics, mass of eccentric and others. The ratio of this vibrating mass to the mass of the suspended and statically effective drum frame influences any compaction effect or the compaction depth. The compaction effect rises with increasing vibrating mass, while other parameters remain comparably constant, because the vibrating mass is dynamically coupled to the sympathetic mass of the soil layers (Lorenz 1934, Lit. 2). The vibrating mass changes with the vibration amplitude generated by the centrifugal force. The increasing vibration amplitude mobilises also less sympathetic mass particles in the soil layers so that the natural frequency of the vibration system drops. 2.4 Centrifugal force, frequency, amplitude Centrifugal force, frequency and amplitude are fundamental machine related magnitudes which control the energy transfer during compaction. However, depending on the type and stiffness of the soil their individual influence has different effects and they must therefore be weighted in a differentiated manner. The centrifugal force FC is generated by the eccentric mass me rotating with a rotary or angular velocity e (revolutions per minute). The gravity centre of the eccentric mass is centred at a distance e from the centre of the rotation axis.

Vertical amplitude

Position of eccentric in connection with the vibration path of the drum

Abb. 17 17

Part 1

The centrifugal force increases quadratic with the angular velocity or the frequency f. The rotation velocity of the eccentric determines the number of revolutions n or the frequency of vibrations f = 1/T . n (frequency in Hz or vibrations per unit of time; see T 1, para. 1.1). The nominal vibration amplitude a (mm) depends on the magnitude of the eccentric moment Me (kg . mm) The drum moves while the eccentric mass is rotating. This movement is 180° out of phase (Fig. 17). The magnitude of the vibration force effecting the substrate is the result of a complicated interaction between drum and substrate. On the one hand, the centrifugal force is a fundamental unit for the calculation of the vibration force, but on the other hand there is no interrelationship between the two magnitudes. The effective vibration force is mainly activated by the vibration amplitude which, however, is not determined by the centrifugal force. However, the centrifugal force controls the vibration intensity (acceleration) of the drum. The centrifugal force can only be used for a direct comparison between various types of rollers if both static mass and frequency are identical, because in this case they reveal the relative differences in amplitudes.

M1-M0 C1

K1 M0 M2 K0

M0

C0

Ko=5.107 C0=2.105 K1=5.106 C1=9.103

= vibrating mass of machine (exciter mass) M1 = machine mass M1-M0 = suspended machine mass M2 = resonant vibrating soil mass

M0=1600 M1- M0=3400 M2=1000 me=1.0

Me K1 K0 C1 C0

= unbalanced moment = resilient value of machine = resilient value of soil = damping of machine = damping of soil

Interrelation between vibration force and frequency (calculation example by Machet 1976) Fig. 18 18

The diagram in Fig. 18, Lit. 3, confirms that the influence of the frequency is limited and that there is no interrelationship between the mathematical vibration force and the centrifugal force. Strong irregular impacts, as occurring during jump operation of the drum, may cause overcompaction or result in a decrease of density. During such jumping of the drum excessive vibrations are generated in the drum frame and the rubber damping elements between drum and fame are highly stressed. The variations in frequency only have a limited effect on the vibration force. The energy transferred into the base rises with a comparably constant vibration force and an increasing frequency. For this case the compaction energy VE per volumetric unit can be calculated by approximation (Yoo and Selig, 1980, Lit. 4). . VE = f1 (FIstat) + f2 (a f) v f1, f2 FIstat a f v

= values of function, = static linear load (kg/cm), = amplitude = frequency = rolling speed

Fundamental principles of vibratory compaction

Raising the vibration force up into the range of resonant frequency has not gained practical significance, since the vibration level of the entire single drum roller increases extremely in such a case, placing extreme stress on roller and operator. Operation with frequencies in a relatively stable frequency range slightly above the resonant frequency is generally of advantage for soil and rockfill compaction, whereby the resonance effect is also utilised to a certain extent.

Influence of the frequency on the compaction amplitude

Fig. 19

The optimal effect of vibratory rollers is normally achieved in the frequency range between 25 and 50 Hz (1.500 - 3.000 vibrations per minute). Throughout this entire frequency range both compaction and depth effect are not achieved to such a great extent by the frequency, but mainly by the size of the amplitude and the axle load of the drum (Fig. 19). This influence is apparent with all types of material, however, in dependence on their composition very coarse particle or stony materials as well as cohesive-plastic materials require a high roller mass for an efficient compaction, as far as this is permitted by the shearing strength of these materials. High amplitudes transfer more compaction energy deep into the layer to be compacted, but achieve only a minor compaction effect in the upper zone of the layer. Low amplitudes produce only a slight compaction deep inside the layer, but transfer more compaction energy into the zone near the surface. The material specific properties of the substrate thereby cause different reactions to the compac-

tion energy introduced by the vibratory roller. From practical experience the following exemplary values can be used: • Compaction of soil layers with a relatively high lift height or a large soil volume as well as stony material: optimal amplitudes ranging from 1.5 to 2.0 mm and optimal frequencies ranging from 25 to 30 Hz (1.500 - 1.800 vibrations / minute). Compare with inherent natural frequencies of soil types acc. to table 1 (Lit. 1, 2).

Soil type

Natural frequency Hz Upm

Fine sand Non-uniform sand Medium sand, uniform Medium sand, uniform Sand, moist Sand, dry Sand/gravel Loam, solid Loam, lose Clay, moist Clay, dry Lime, banked Mottled sandstone

~24 * ~ 1440 ~27 * ~ 1620 ~24 * ~ 1440 ~33 ** ~ 1980 ~24 ** ~ 1440 ~22 ** ~ 1320 ~24-29 ** ~ 1440-1740 ~25-29 ** ~ 1500-1740 ~21-23 ** ~ 1260-1380 ~22 * ~ 1320 ~28 * ~ 1620 ~30 * ~ 1800 ~34 * ~ 2040

*H. Lorenz / **F. Fischer Tabelle 1: Charakteristische Werte für bodenspezifische Eigenfrequenzen (Lorenz, Fischer) • Compaction of unbonded base courses: favourably in the above mentioned frequency and amplitude range, because of the high required degree of compaction. • Compaction of asphalt layers as well as bonded and stabilised base courses, optimal amplitudes ranging from 0.2 - 0.9 mm and favourable frequencies ranging from 35 - 60 Hz (2.100 - 3.600 vibrations / minute).

19

Part 1

The rolling speed of the vibratory roller, the increase of which results in a higher area output, has a significant influence on the compaction effect. The number of vibration impacts decreases with increasing rolling speed, so that more passes are required to achieve the same compaction effect. Within the normal rolling speed range and with a constant lift height the transferred energy is almost proportional to the ratio between the number of passes and the rolling speed. When doubling the rolling speed, the number of roller passes should also be approximately doubled accordingly. Generally recommended rolling speeds are 1 to 2.5 km/h on rockfill material and clayey soils and 2 to 4 km/h on non-cohesive soils. For asphalt compaction rolling speeds of 2 to 4 km/h have proved most favourable for thick layers or stiff mixtures and 2 to 6 km/h for thin layers or soft mixtures.

2.5 Energy transfer Energy transfer in the contact area of the vibrating drum as well as vibration and movement performance of the rollers are substantially influenced by the reaction force and the dynamic stiffness of the layers to be compacted. During the vertical movement of the drums the static weight forces, the spring and damping forces of the rubber buffers, the centrifugal forces, the inertial forces and the contact force are effective, as shown in Fig. 20.

20

Vertically directed equilibrium of forces of the vibrating drum

Fig. 20

The contact force contains the dynamic reaction forces of the base. Entering the contact force over the vibration path results in a force-path-diagram as shown in Fig. 21, in which the movement phases of compaction become apparent (example, Lit. 7, 8).

Fundamental principles of vibratory compaction

compression curve ∆FB / ∆x is used to determine the resilient stiffness of the base.

Compression and expansion phase during the compaction process

Fig. 22 shows measured indicator diagrams for amplitudes of various sizes (Lit. 7, 8). If the roller is used with various amplitudes, the energy transfer changes in accordance with the diagram. As shown in the diagram, the maximum reaction force increases in a degressive way with increasing amplitude. It clearly shows that a most favourable nominal amplitude exists for any drum axle load and that a higher static linear load in combination with a given amplitude also increases the reaction force of the base. The vibrating mass can only fully transfer the vibration intensity to the substrate, if the static axle load is fully applied to the substrate as a pre-load.

Exchange of energy between roller/soil and dynamic resilient stiffness of the soil Presentation of the soil contact force in dependence of the vibration path of the roller drum (vertical component) in the indicator diagram (Kröber 1988) Fig. 21

The indicator diagram shows the ground contact force during compaction. The roller temporarily loses ground contact. During this phase of compaction the amplitude increases from 1.6 mm to almost 2.5 mm and the soil contact force to almost three times the static drum axle load. Due to the low soil stiffness and the low resonance influence of the static drum axle load both ground contact force and amplitude comply with the theoretical values at the beginning of the compaction process. The indicator diagram enables an examination of energy transfer and soil stiffness. The hysteresis area between compression and expansion cycle shows the measurement for the energy transfer into the substrate. The area below the expansion curve reflects reactions to the drum. The inclination of the

Indicator diagram for increasing compaction and different amplitudes (example) Fig. 22 On base layers with a low stiffness the vibratory roller will not lose ground contact when vibrating with a low nominal amplitude and if the maximum contact force does not exceed two times the axle load (Fig. 22). When continuing to increase the amplitude or the stiffness of the substrate, the roller can no longer fully transfer its movement. Its dynamic resting position moves up, so that it jumps up with each revolution of the exciter shaft when certain limit values are exceeded. In this jumping condition a frequency proportion is generated, which is half or an integer 21

Part 1

multiple of the originally shown vibration frequency. This operating condition remains stable and reproducible under steady conditions. With a further increase of the vibration amplitude or the stiffness of the substrate the roller becomes unstable and starts to tumble. Under this operating condition non-periodic vibration movements develop around the longitudinal axis of the drum with frequencies depending on the natural frequency of the vibration system (frame / vibrating mass).

22

Fundamental principles of vibratory compaction

3

Design types and applications for BOMAG compaction technology (Lit. 24 to 28)

3.1 Vibratory tamper Vibratory tampers cause an impact compaction. The engine of the vibratory tamper drives a crank drive with conrod, which is clamped between two pressure springs. The vertical movement of the drive shaft results in a movement against the spring force. After a revolution the tamper plate lifts off the base and hits back after a 180 rotation of the crank drive. (Fig. 23 and 24) Typical weights from 50 to approx. 100 kg. Frequency range approx. between 9 and 11 Hz (540 to 660 blows per minute). An optimal compaction is normally achieved at frequencies around 10 Hz (600 blows per minute) with an amplitude range from 60 to 80 mm. Vibratory tampers are most suitable for applications in confined and difficult to access work areas, where only light compaction equipment can be used or relatively high and non-uniform layer thicknesses are required. Vibratory tampers are used for compaction of cohesive soils, mixed soils and gravely soils. For applications in narrow trenches, e.g. pipeline or cable trenches, vibratory tampers can be fitted with special small tamper plates.

Movement sequence of vibratory tampers

Fig. 23

Design and equipment of the vibratory tamper

Fig. 24

3.2 Vibratory plates/hydraulic plates Vibratory plates normally work with frequencies between 55 and 90 Hz (3300 to 4500 revolutions per minute). The generated centrifugal forces are in the range between 25 and 86 KN (2.5 to 8.6 t). Machines are available up to weight of 700 kg. In comparison with vibratory tampers the compaction performance of the plates widens their applicational versatility. Depending on the soil type the depth effect of a vibratory plate may be as favourable as the depth effect of large vibratory rollers. The dimensions of the plates and especially the working width can be adapted to various applications. Due to the development of quiet machines and a more efficient vibration insulation of the guide handles the latest vibratory plates are much easier to manoeuvre than older types. Vibratory plates are self-propelled or self moving (Fig. 25). A differentiation is made between plates which move only to one direction (Fig. 26) and plates with special controls to reverse the travel direction (Fig. 27). 23

Part 1

Movement sequence of vibratory plates

Fig. 25

One-directional plates are equipped with only one exciter shaft. The amplitude depends on the magnitude of the unbalanced mass, the mass ratio between eccentric and vibrating parts as well as their centre of gravity. The maximum working speed, a design parameter for the development of such a machine, depends on the position of the exciter shaft and the position of the centre of gravity of the entire plate as well as on the ration of weight and centrifugal force. This enables also the working speed in forward direction. This working principle is applied to narrow plates with low weight.

Design and equipment of the vibratory plate (controllable in forward direction) 24

Fig. 26

Design and equipment of the vibratory plate (controllable in forward and reverse)

Fig. 27

BOMAG plates with reversible working direction use two exciter shafts with double directed vibration. The two exciter shafts with their eccentric masses work in opposed position, whereby the direction of the forces generated by the centrifugal force also change. This enables reversing of the travel direction from forward to the opposite direction during compaction. Furthermore, this allows for a controlled change of the working speed and therefore also of the intensity of compaction per pass. Heavy vibratory plates work with an operating weight of more than 120 kg according to this principle. The reversal of the working direction enhances the guidance of the machine and eases work. Heavier plates are equipped with electric starters for easier starting of the diesel engines. Another rationalisation of compaction work is achieved by coupling hand guided BOMAG vibratory plates with a high total weight. This coupling enables forward and backward movement as well as turning on the spot. This application enhances power and mobility during compaction, e.g. in foundation excavations and backfills around buildings as well as adjacent foundation objects. Heavy reversible plates are also used for compaction work in trenches. For these applications the ventilation and filter systems must be specially adapted, the drive system must be well protected and sufficient lateral space for work is required. For this type of work the

Fundamental principles of vibratory compaction

machines are additionally equipped with dirt deflectors and fixed installations for lifting. A new development is the steerable hydraulic plate with a vibrator system similar to the reversible mechanical vibratory plates. Similar to the reversible mechanical plates the steerable hydraulic plates are equipped with two counter rotating exciter shafts which are both fitted with an eccentric weight. The main differences of the steerable hydraulic plate are the hydraulically driven exciter unit and the rear exciter shaft. This shaft is designed in a way that the parts of the split eccentric weight can be offset to each other. This generates a torque that enables the operator to control the machine without a steering handle, i.e. without direct contact to the machine, via a remote control. With this working principle the machine does not only move forward and backward, but can also be steered to right and left.

Working principle of the hydrostatically controlled vibratory plate Fig. 28 Besides their possible use for standard applications, hydrostatic vibratory plates with remote control (Fig. 28) are available for difficult work areas, such as deep trenches. These systems with cable, infrared or radio remote control relieve the machine operator and contribute to safe work in unsupported trenches. 3.3 Hand guided vibratory rollers Hand guided vibratory rollers are available in single drum version or as tandem rollers (Fig. 29 and 30). Both types are self-propelled with reversible travel direction. The operator controls and steers the machines by means of a steering rod. Compared with plates and tampers the mobility of these rollers enhances the compaction work. These rollers are used for soil as well as asphalt compaction and most frequently for small area repair and patch work.

25

Part 1

drum is fitted with its own eccentric shaft. Both drums are driven, are connected by a rigid frame and are mechanically controlled by pulling or pressing the steering handle. Tandem rollers are also available with hydraulic controls, which reduces the controlling effort. Depending on the state of technology hand guided tandem rollers are available with mechanical travel and vibration systems as well as with hydraulic drive and hydrostatic vibration systems. The hydrostatically driven system offers smoother response when changing the travel direction, which is of special advantage when compacting asphalt.

Design and equipment of the hand-guided single drum vibratory roller

Fig. 29

The machines work to their optimum when used on small work areas, for the compaction of soil and, if equipped with a water sprinkler system, on asphalt. The rollers have a very favourable centre of gravity and therefore develop high traction force on uneven ground. Special designs are available for use on trenches and on slopes. 3.4 Tandem rollers Tandem rollers have two drums of identical diameter, each equipped with a exciter shaft. These machines are powered by an air cooled diesel engine. Travel and vibration systems are hydraulically driven. Single lever control and infinite speed regulation enable jerk-free acceleration and deceleration. Tandem rollers are available with hydrostatic articulated steering, heavier versions alternatively with hydrostatic pivot steering. A differentiation is made between light and heavy tandem rollers.

Design and equipment of the hand-guided double drum vibratory roller

Fig. 30

Single drum rollers work with weights of 160 to 460 kg, high frequencies of 70 to 77 Hz (4200 to 4630 revolutions per minute) and amplitudes between 0.4 and 0.5 mm. Hand guided tandem rollers have two drums of identical size with relatively small diameter. Each 26

Light tandem rollers The use of light tandem rollers enhances the area output of the compaction process, because these rollers are have a higher mobility, are faster and more manoeuvrable than hand guided rollers. These roller types were developed for the compaction of asphalt and are therefore equipped with water sprinkler systems. They can, however, also be used for soil compaction.

Fundamental principles of vibratory compaction

Light tandem rollers vary in the range between 1.5 and 4.5 t with working widths from 800 to 1380 mm (Fig. 31).

Heavy tandem rollers Heavy tandem rollers with operating weights between 6 and 12 t are used for the compaction of asphalt surface courses, asphalt binder courses, asphalt base courses and unbound base courses. They normally work with two amplitudes or two frequencies for an optimal compaction of different lift heights. VARIOMATIC tandem rollers with the new directed vibration system described in T 1, para. 2.1.4 allow for an automatic adaptation of the effective amplitude to the material to be compacted. Heavy tandem rollers are equipped with vibration automatic, a system which switches the vibration off when stopping the machine or when changing the travel direction, thereby avoiding transverse depression and unevenness in the asphalt course.

Design and equipment of a light, articulated tandem roller

Fig. 31

The most suitable working width can be chosen to match the site conditions. The static linear loads span from 8 to 15 kg/cm.

Heavy tandem rollers are available with spit and non-split drums. Split drums reduce the risk of shoving and cracking when compacting in tight curves. Depending on the design one must differentiate between tandem rollers with articulated steering and pivot steering, which enable different modes of steering (Fig. 32).

Theses machines are generally designed with double drum vibration and double drum drive and normally work with one frequency. By experience the machines in the range from 3 to 4.5 t have sufficient power to be used behind a paver with an output of 500 to 800 m2 per hour on surface courses or 300 to 400 m2 per hour on base courses, depending on the asphalt mixture. They are therefore specially recommended for this type of application. Apart from this there is another type of application for these small self-propelled tandem rollers, which are available in different designs and successfully used. 222

2

27

Part 1

Heavy, pivot-steered tandem roller with split drums

Fig. 32

Articulated combination roller with smooth drum and four rubber tires Fig. 33

Combination rollers

3.5 Single drum rollers with smooth drum

The combination roller is a combination of pneumatic-tired roller and vibratory roller (Fig. 33).

Single drum rollers are self-propelled compactors with a front drum and rear tires (Fig. 34). These roller types are specially designed for soil compaction, where high tractive power and gradability is required besides excellent compaction work.

The combination combines the advantages of the vibrating drum with the benefits of rubber tires, which have a kneading effect and seal the asphalt surface. One axle of the combination rollers consists of a smooth drum, the other axle carries smooth rubber tires. These rollers are also powered by air cooled diesel engines which drive the hydrostatic travel and vibration systems. The rubber tires are driven in pairs by two hydraulic motors, ensuring adaptation of the left and right hand wheel pairs to the rolling speed differential when driving around curves. Single lever control, hydrostatic power steering as well as vibration automatic ensure simple and safe operation of the large combination rollers.

28

Front frame with drum and rear frame are connected by a central oscillating articulated joint. The rear frame carries diesel engine, drive elements and operator’s stand. The infinitely controllable travel systems works hydrostatically via the rear wheels. Single drum rollers are normally equipped with drum drive. The vibration drive also works hydrostatically. Single lever control and hydrostatic power steering enable simple operation. Depending on the tire tread the single drum rollers achieve a gradability of up to 45%. For even higher gradability the single drum rollers can be equipped with a stronger drum drive and an anti-spin-control (ASC). With these features the rollers can be used for gradients of up to 55%. Depending on soil or rock material the single drum rollers are used with smooth drums or with padfoot drum.

Fundamental principles of vibratory compaction

Smooth drums can be used on most soil types, from rockfill to cohesive soils. The single drum rollers are generally equipped with all-weather tires, which ensure favourable traction and gradability under most soil conditions. The operating weights stretch from 2 to 25 t. The heavy single drum rollers are normally available with 2 amplitudes and 2 frequencies for thick and thin layers (Fig. 34).

lic pump on the single drum roller and work with an adjustable frequency of 32 to 50 Hz and a centrifugal force of max. 50 kN.

In order to withstand extreme loads, e.g. during the compaction of rockfill, the drum must be of high strength and durability. A long striven goal of research and development and a remarkable leap in technology was achieved especially with the newly developed VARIO vibrator exciters. These innovative self-controlling systems detect the energy requirement and regulate the system automatically;see T 1, para. 2.1.4.

Single drum vibratory roller with hydrostatically driven vibratory plates attached

Design and equipment of a single drum roller with one vibrating drum Abb. 34 Attachment of vibratory plates:

Fig. 35

Another possible application is the efficient soil compaction in highway and transportation engineering, urban foundation and civil engineering projects or such projects under confined spatial conditions. This work requires compact and extremely manoeuvrable single drum rollers in the 7 t - class, which can be optimally adapted to the permanently changing filling material while considerably reducing the vibration stress for nearby buildings at the same time. The use of the VARIOCONTROL system is therefore also recommended for these compact single drum rollers.

The attachment of hydraulically driven vibratory plates to the single drum vibratory roller extents the range of applications and rationalises compaction work. The depth effect of the single drum roller is thereby combined with the favourable surface effect of the plate, thereby achieving a higher compaction output with less passes. With this combination the single drum roller compacts with the front drum and the vibratory plates attached to the rear at the same time (Fig. 35). The vibratory plates are driven by an additional hydrau29

Part 1

3.6 Single drum rollers with padfoot drum Padfoot drums are designed for the compaction of cohesive soils and mixed particle soils with a relatively high water content. The imprints of the padfeet contribute to a reduction of the water content. They are also used for the compaction of rockfill, in order to reduce the air void content and to crush large particles. As an adaptation to very moist, slippery soil conditions single drum rollers with padfoot drums are equipped with extremely profiled tires, similar to tractors, as a measure to enhance the traction power. These single drum rollers need a highly durable drive system. From the present point of view separate drives of drum and wheels should be standard. BOMAG padfoot rollers are equipped with special teeth (Fig. 36). With their shape and in combination with vibration they should achieve a kneading and impact or crushing effect together with a favourable depth effect: - Pyramid teeth (high studs, small contact areas, extremely steep flanks) for intensive kneading and compaction of cohesive soils, - Triangular teeth for crushing of hard rock by means of high tip pressure and splitting forces, - Triangular teeth with cutters in between for the splitting and crushing of brittle rock, whereby the cutters in between also prevent jamming of parti cles between the teeth (Fig. 37).

BW 225 with 150 standard teeth, H = 100 mm

BW 225 with 100 pyramid teeth, H = 150 mm

BW 225 with 120 triangular teeth and additional wear resistant tips, H = 200 mm

BW 225 with 100 triangular teeth and cutters in between, H = 200 mm

Single drum vibratory rollers with with special teeth

30

Fig. 36

Fundamental principles of vibratory compaction

Crushing of claystone by special padfoot roller drum with triangular teeth and cutters in between Fig. 37

The latest BOMAG class of heavy single drum vibratory rollers (BW 225, 18 t drum axle load, 80 kg / cm static linear load) is a special development for the compaction of rockfill material, extremely stony cohesive soils as well as high lift heights. After compaction the teeth leave a structured surface (Fig. 38). In these impressions water can collect, which increases the water content of the soil when a new layer is placed. On the other hand the structure enlarges the surface of the soil, so that it can dry out more quickly during dry periods or by wind. In most cases it may be necessary to follow the padfoot roller with a smooth drum roller after a short period of time, in order to seal the open texture

Compaction work with a single drum roller equipped with a padfoot drum

Fig. 38

Especially suitable are single drum rollers with an anti-spin-control to achieve the favourable tractive power in a controlled manner. These systems are of highest significance for an economical compaction when a high gradability of the machine is required (Fig. 39). Furthermore, this system enables safe operation on inclined areas.

High gradability during compaction work due to the anti-slip system

Fig. 39

31

Part 1

Fundamental principles of vibratory compaction

3.7 Towed vibratory rollers Towed rollers are characterised by a single drum with a powerful vibrator. The entire operating weight of the drum is used for compaction without any losses, because no tractive power is required. The operating weight may therefore be considerably lower than the operating weight of a self-propelled single drum roller (Fig. 40). However, the costs per hours for the necessary tractor unit are significantly higher than the costs for a self-propelled single drum roller.

Compaction work with a towed vibratory roller

32

Fig. 40

Compaction of soil and rock in earthwork

Part 2

1.

Soil

The properties of the soil types within the corresponding group change due to various parameters, such as water content level of density.

1.1 Soil groups under engineering aspects (DIN 18196/4022) Classification attributes: For the description of engineering properties and their suitability according to DIN 18196 all soil types are classified in groups of almost identical material structure and similar characteristics.

Soils are classified by application of visual and manual testing methods, identical with those described in DIN 4022. Laboratory tests are supplementary used if visual and manual evaluations are not sufficient, and additionally particle size distribution (DIN 18123), consistency limits (DIN 18122), ignition loss and lime content.

The attributes of these groups are purely of material nature: Particle size fractions according to DIN 4022 (Tab. 2), mass proportions of particle size fractions, plastic characteristics, organic and calcareous components. The groups are identified by two identification characters each. The first character identifies the main soil types and the second character the properties of highest importance for engineering purposes. In case of fine particle soil types this is the degree of plasticity, for mixed particle soils the type of fine particle additives (silt, clay) and for coarse particle soil types the curve of the particle size distribution determined by the uniformity coefficient U and the curvature coefficient C. Range/ Designation

Coarse particle range (sieve particles)

Fine particle range (Sediment particles)

Symbol Blocks Stones Gravel particles Coarse gravel Medium grav. Fine gravel Sand particles Coarse sand Medium sand Fine sand Silt particles Coarse silt Medium silt Fine silt Clay part. (finest)

Y X G gG mG fG S gS mS fS U gU mU fU T

Particle size range mm

> >

>

>

<

200 63 to 200 2 to 63 > 20 > 6.3 > 2.0 0.6 to 63 > 0.6 > 0,2 > 0,06 0,0002 to 0,06 > 0,02 > 0,006 > 0,002 0,002

to to to

63 20 6.3

to to to

2,0 0,6 0,2

to to to

0,06 0,02 0,006

Table 2: Particle size ranges acc. to DIN 4022 33

Part 2

Main group coarse particle soils

d in mm < 0,06 > 2,0 < 5% > 40% < 40%

Group

Symbol

Gravel, gravel-sand mixture GE GI GW Sand, sand-gravel mixture SE SI SW Particle 40% Gravel-silt mixture 5-15% GU 15-40% GU mixed particle Gravel-clay mixture 5-15% GT soils 15-40% GT < 40% Sand-silt mixture 5-15% SU 15-40% SU Gravel-clay mixture 5-15% ST 15-40% ST > 40% Silt Ip < 4%1): light plastic WL < 35% UL medium plastic > 35-50% UM distinct plastic > 50% UA fine particle Clay Ip > 7%2): light plastic WL < 35% TL soils medium plastic > 35-50% TM distinct plastic > 50% TA organogenic soils > 40% Silt Ip > 7%3) WL = 35-50% OU soils with Clay Ip > 7%3) WL = 50% OT organic < 40% coarse, mixed particle soils with humus, OH OK admixtures calcarous, siliceous admixtures Peat, not to slightly decomposed Z = 1-54) HN organic soils Peat, decomposed Z = 6-10 HZ Mud F Filling Soil [...] Foreign substances A 1) or below A-line 2) and above A-line 3) and below A-line 4) Z Degree of decomposition Table 3: Engineering soil groups acc. to DIN 18196 (main groups) Coarse particle soils: Coarse particle soils are classified according to their fine particle fraction passing 0.06 mm sieve (less than 5%), the sand or gravel fraction and the particle size distribution (Fig. 41). The particle size distribution is assessed on the basis of the cumulative proportions of the particle fractions and by means of the uniformity coefficient U and the curvature coefficient C. The prerequisites for a wide graded particle size distribution are met if U > 6 und 1 < Cc < 3 In all other cases the particle size distribution is a close or intermittently graded distribution. 34

Compaction of soil and rock in earthwork

Examples of particle size distribution curves

Plasticity diagram (DIN 18196)

Fig. 41

Fig. 42 35

Part 2

Fine particle soils: Fine particle soils are classified by the plastic properties of the fines passing sieve 0.06 mm; the substantial criterion is the plasticity, weighted on the basis of the water content at the liquid limit wL and the plasticity index IP = wL - wP. Basis for the classification is the plasticity chart in Fig. 42. PP

The higher the water content of a fine particle soil, the less dimensionally stable is its mass or the easier it can be deformed. In this respect the soil is differentiated according to various states (of consistency):

Conditions in the plastic range

Liquidity index IL w – wP IL = = 1 - IC IP

liquid pasty soft stiff semi-solid 1) Liquid limit wL

from 1.01) from 0.5 from 0.25 to

to > 0.25 to > 0.25 02) below 0 2) Rolling limit wP

clay with proportions of 5 to 15% passing sieve 0.06 mm and from more than 15 to 40%. In dependence on the proportional composition and plasticity of the fine particle component the properties of mixed particle soils are classified between a cohesive and a non-cohesive soil mechanical performance.

Conditions

Fig. 43

Consistency index IC w –w wL – w IC = L = wL- wP IP below 0 from 01) from 0.5 from 0.75 to > 1.0 (to wS)

to < 0.5 to < 0.75

1.02)

Table 4: Definition and classification of conditions Consistency

Characteristic

solid semi-solid stiff soft pasty liquid

breaks brittle crumbles when rolled kneadable easily kneadable swells out between the fingers not dimensionally stable

The states are by standard defined by means of test specific limiting water contents and classified with the help of identification numbers IC and IL (Fig. 43 and table 4). Mixed particle soils: Mixed particle soils (mixed soils) contain proportions of fine particle material, sand and gravel. The fine particle component is differentiated in silt and 36

The limiting value of 15% approximately marks the transition. Below this value the coarse particle fractions form a supporting granular skeleton, which has a substantial effect on the properties of the soil. This is actually a fluid transition within a range of 10 to 40% particles passing sieve 0.06 mm. The 40%-proportion separates the mixed particle from the fine particle soil types. Organogenic and organic soils: Organogenic soils and soils with organic admixtures are classified according to the plasticity chart, as far as they are silts or clays; according to Fig. 42 they are located below the A-curve. In case of coarse and mixed particle soils a differentiation is made on the basis of the type of admixtures (humus, calcareous, siliceous).

Compaction of soil and rock in earthwork

Characteristics (solely of fractions > 76.2 mm)

Coarse soils more than 50% of soil >0.074 mm

Pure gravels less than 5% Gravels more 4.8 mm gravels more than 12% 50%)

TM

Organic silt Organic clay

OU a. OT

TL

TA

Condition

[°] Silt soils soft stiff 27.5 - 32.5 semi-solid soft stiff 22.5 - 30.0 semi-solid Clay soils soft stiff 22.5 - 30.0 semi-solid soft stiff 17.5 - 27.5 semi-solid soft stiff 18.5 semi-solid Organic soils pasty soft 17.5 - 22.5 stiff

Table 9b: Experience values for the shearing strength (informative) 42

Shearing strength Friction Cohesion φk Clk Cluk [kN/m2]

[kN/m2]

0 2-5 5 - 10 0 5 - 10 10 - 15

5 - 60 20 - 150 50 - 300 5 - 60 20 - 150 50 - 300

0-5 5 - 10 10 - 15 5 - 10 10 - 15 15 - 20 5 - 10 10 - 20 19.5

5 - 60 20 - 150 50 - 300 5 - 60 20 - 150 50 - 300 5 - 60 20 - 150 50 - 300

0 2-5 5 - 10

2 - 20 5 - 40 20 - 150

Compaction of soil and rock in earthwork

1.3.2

from frost and thawing periods, show a particularly critical sensibility and may soften and erode down to a considerable depth.

Geotechnical suitability for earthwork

1.3.2.1 Clays and silts The suitability of fine particle soils for embankments depends on the load applied by the earth moving operations, the stability of the embankment slopes and the applied earth loads as well as the magnitude of the inherent settlement of the embankment. The permissible placement water content resulting from these various conditions, must ensure optimal compaction; otherwise improvement measures including soil exchange or soil redistribution to lower dams and landfills, stabilisation with lime or cement, or a sandwich construction method with coarse particle materials may be necessary (Fig. 45).

Due to their “toughness” (adhesive strength) the distinct plastic soil types are very difficult to process and compact. On the one hand they are less sensitive to water and erosion, but on the other hand they swell when absorbing water or when relieving the load if they contain clay materials with a swelling capacity (e.g. opaline and ornoite clays). During this process these materials develop moderate to high swelling pressures when the free deformability is inhibited. The use of silts and clays with gypsiferous constituents shall be avoided because of the extreme swelling properties of the gypsum. If this cannot be avoided because of economical reasons, the placement shall be performed under the following conditions: - the gypsiferous constituents in the filling material shall not exceed 10% by volume, - the gypsiferous material shall be evenly distributed in the filling material and compacted under dry weather conditions.

Soil stabilising with lime to enhance the compaction properties

Fig. 45

Clays and silts form the main groups of cohesive soils. They differ strongly in particle fineness, mineral constituents and the plasticity resulting from this. Their soil mechanical suitability for earthwork and embankments is decisively limited sensitivity against water and weather during loosening, loading, transport, placement and compaction. The plasticity dependent water absorbing capacity of these soils causes solid to pasty-liquid conditions (consistencies) This results in a extremely sensitively changing deformation and strength performance. Silts and clays of low plasticity (wf < 50%, lP < 15%), the consistency of which drops strongly immediately when absorbing stratum water, percolating water, precipitation water or the accumulated water

Solid clays may destrengthen similar to mudstone, especially as a result of repetitive dry/wet-cycles or frost/thawing-cycles. The resulting cracky or crumbly structures increase the depth of water infiltration and softening. Due to the above mentioned soil mechanical characteristics silts and clays are only suitable for earthwork if they are applied in dry weather with the optimum water content for compaction and without subsequent softening. Because of their general deformation sensitive properties and their potential inelastic deformation under permanent load, especially in case of a distinct plasticity, the placement of these materials shall be restricted to such areas in earth or dam constructions which are less stressed by own weight or external forces.

43

Part 2

In subgrade areas under carriageways down to a depth of 0.6 m these materials shall only be used if the demands for optimum placement water content and plasticity characteristics of w 2

max ρd1

ρd

S r

1+e

wl

1 – min n

=

1,

0

wll

w1 w01 w02 Water content w

1–n

The level of compaction ID is subdivided into D

0.00............................... loosest density 0.00 – 0.35.................... loose 0.35 – 0.50.................... medium dense 0.50 – 0.70.................... dense 0.70 – 1.00.................... very dense 1.00............................... densest density The parameters DPr and ID can be approximately assigned as follows

a) Interrelationship between dry density ρd, water content w and compaction work A ρd

S r

Pr

n

0,8

=

0

0,2

The lower limiting values apply for gravelly, the top limits for sandy mixtures.

1, 0

a

n= a

=

S r=

DPr = 1 ........................... 0.50 < ID < 0.85 DPr = 0.97 ...................... 0.40 < ID < 0.65 DPr = 0.95 ...................... 0.30 < ID < 0.55

48

max ρd2

1

1 + min e

1.4.2.1 Functional interrelationship

A

Pr

Compaction characteristics

A

Besides the degree of compaction D the compressibility of coarse particle soils can also be characterized by the limit values of loosest and the densest level of compaction. Since the bedding orientations illustrated for balls of identical shape can only be applied to natural grain-type material deposits consisting of particles with irregular sizes and shapes in an idealised manner, the limit values for the density must be determined by standard laboratory tests (DIN 18126). The parameters D and ID can be converted to one another using the following equations:

1.4.2

Dry density ρd

With these reference values from international earthwork practice the compaction effect that can be achieved on a certain soil is simulated in a laboratory test; for functional interrelationship and soil physical significance see T 2, para 1.4.2.

b) Interrelationship between dry density ρd, water content w and saturation level Sr air void proportion na

Fig. 50

Compaction of soil and rock in earthwork

With progressing compaction work A2 > A1 the characteristic curve shifts in such a way that ρd increases while w decreases; the increase of ρd thereby drops with progressing compaction work in accordance with a logarithmic function. A certain density ρd < max. ρd is possible within 2 limiting water contents w‘ und w‘‘. With w < w‘ compaction is possible when increasing work A, however, this is no longer possible with w > w‘‘. For certain soil groups the peaks of the compaction curves determined for compaction work of various size are approximately located on a specific saturation line of hyperbolic shape (example see Fig. 52). This line thereby characterises an optimal saturation of the pores opt Sr as a value independent from compaction work A. With saturation below the optimum the compactibility becomes moderate and above the optimum it becomes impossible, if the pores are saturated.

placement, lumpy conglomerates with a high air void content will form. These can then not be sufficiently and evenly compacted. If these soils with their high proportion of air voids are subsequently softened by the infiltration of water, e.g. because of precipitation, their shearing strength will drop. The load bearing capacity drops leading to settlements or subsidence. If the fine particle and mixed particle soils are compacted at a too high water content, a rubbery deformable performance will occur. The soil subsides after compaction. On the other hand, if compaction takes place at a too dry water content, large air voids will remain between the crumbs, so that subsequent wetting will also result in extreme deformations.

r

The compaction of soils in the respective optimum range of water content has an essential soil physical effect on the soil properties relevant for engineering purposes; this applies especially for the fine and mixed particle soil types (T 2, para. 1.4.2.3 and 1.4.2.4) such as - minimum permeability at wPr (+ 1%), increased permeability on the dry side of up to 2 powers of ten, on the wet side up to five times in comparison to the minimum possible, Pr

- minimum compressibility of the soil; on the dry side subsidence (settling collapse) during heavy precipitation possible. Strong com pression for w > wPr due to the low consistency and excessive pore water pressures, - maximum shearing strength of the soils as (wPr – 2%); decrease of shearing strength on the dry side because of the low density, on the wet side because of a too high saturation and excessive pore water pressures.

1.4.2.2 Coarse particle soils Fig. 51 shows characteristic compaction curves from Proctor tests on coarse particle soils. Both the density and the influence of the water content rise with increasing non-uniformity of the mixtures; the curves take an increasingly steeper course and limit the narrowing optimal ranges. In these cases the maximum values and the curve sections w > wPr can no longer be uniquely defined in tests. The optimal saturation index opt Sr can then be used as an auxiliary criterion for the establishment of the maximum dry density ρPr and the related optimal water content wPr. Pr

Pr

PrPr

The intersecting points of the saturation line opt Sr with the compaction curves identify these values with sufficient proximity. According to a statistical evaluation of test results the optimal saturation index for gravel-sand-mixtures opt Sr = 65%; Lit. 15. Fig. 51 also shows very flat curves for uniformly graded sands. From this it can be assumed that their compactibility is low and hardly influenced by the water content.

The properties of the fine and mixed particle soil types are therefore highly influenced by the proportion of air voids na. If these soils are too dry during a

49

Part 2

- the water binding ability of fine particle soils depends on their plasticity. During compaction their sensitivity to changes in the water content increases with decreasing plasticity. s r

=

1,

0

(ρ

Dry density ρd in t/m3

s

=

2, 65

t/m

The optimal water content rises with increasing plasticity and the range widens, in which a certain density can be achieved (limit water contents). Silts therefore have a narrower range of optimal water content and are more sensitive to weather influences than clays. For various degrees of compaction D the air void contents n have approximately the following size:

3

Pr

Proctor curves for various gravels and sands (Compaction work A = 0,6 MNm/m3)

Fig. 51

Depending on the degree of compaction DPr the air void content n has approximately the following size: Pr

Gravel-sand mixtures, silty Gravel-sand mixtures Sands

DPr = 100 %

DPr = 97 %

DPr = 92 %

14 – 20 20 – 28 28 – 36

17 – 22 22 – 30 30 – 38

18 – 24 24 – 32 32 – 39

Silts, sandy, gravely Silts and clays low plastic Clays, medium to distinct plastic

DPr = 100 %

DPr = 97 %

DPr = 92 %

23 – 27

25 – 29

27 – 31

27 – 36

29 – 38

31 – 39

36 – 42

38 – 44

39 – 45

Tab. 11: Estimation of the void proportion n for various degrees of compaction The optimal water content can be estimated with the help of the plastic limit w. For lightly plastic soils it can be specified with 2-4 % and for distinct plastic clays with 3-6 % below the water content at the plastic limit. p

Tab. 10: Estimation of the void proportion n for various degrees of compaction

1.4.2.3 Fine particle soils

The compaction characteristics depend on water content, air content, plasticity and particle size distribution. Fig. 52 shows characteristic compaction curves from Proctor tests: these reveal - the density decreases with increasing plasticity; it is normally lower than for coarse particle soils

50

s r

=

1, 0

(ρ

s

Dry density ρd in t/m3

Compaction of fine particle soils is only possible if a proportion of compressible air voids exists. Due to the incompressibility of water, soils saturated with water cannot be compacted, as long as they are not drained at the same time.

=

2, 70

t/m 3

Proctor curves of various fine and mixed particle soils (Compaction work A = 0,6 MNm/m3)

Fig. 52

Compaction of soil and rock in earthwork

Fig. 52 shows that the air content n is approximately 5 % in the range of the curve maximum.

1.4.3

With increasing water content the fine particle soils change from solid via semi-solid, stiff and soft to the pasty consistency (condition). The strength decreases in the same sequence.

1.4.3.1 Test dependent deformation parameters

a

Tab. 12 shows that, at a degree of compaction of DPr = 100 %, distinct plastic clays have a semisolid to solid consistency (lc > 1), but that soils with medium and low plasticity can already change to a stiff-plastic consistency (0,75 < lc < 1). At compaction degrees of DPr < 100 % the Ic-values corresponding with the top limit water content may already be very low; e.g. at DPr = 97% a soil can already reach the soft-plastic state and at DPr = 92 % it may even reach the transition to the pasty consistency. Pr

Soil type Clays with distinct plasticity Clays with medium plasticity Silts, clays with low plasticity

Consistency index lc DPr = 100 % DPr = 97 % DPr = 92 % 1,3 – 1,0

1,2 – 0,9

1,1 – 0,8

1,9 – 0,9

1,4 – 0,7

1,0 – 0,5

2,1 – 0,9

1,8 – 0,7

1,0 – 0,5

Tab.12: Consistency indices for clay and silt soils with compaction levels DPr < 100 %

1.4.2.4 Mixed particle soils The compaction of mixed particle soils is substantially influenced by the mixing ratio of the fine and coarse particles, the water and air void content of the fine particle constituent as well as by the particle size distribution and the plasticity of the fines. The Proctor density ρPr increases almost directly proportional with the coarse particle fraction and reaches peak values at 5 to 30 % fines. The more uniform the grading of the coarse particles, the higher this optimal fines proportion (fundamentals Lit. 14). Pr

Relations between compaction and deformation parameters

The load bearing and deformation characteristics of soils are described by test, load and stress dependent deformation moduli, modulus of subgrade reaction or strength magnitudes. Besides the actual compaction parameters (DPr, ρ, n, e) these deformation parameters are also used for the identification of the required compaction quality and the achieved level of compaction. Some of these deformation parameters are also most suitable as auxiliary dimensioning values for the design of pavements. This includes quasi-elastic deformation moduli from loading and relieve cycles under static or dynamic load as well as various empirical deformation resistances from penetrometer and punch tests (e.g. California Bearing Ratio CBR). The statistic and dynamic deformation moduli of soils are determined as tension dependent values on the basis of the pressure deflection lines from load tests, the empirical deflection resistances are values depending on special test conditions. Since the deformation parameters are very often correlated with compaction parameters in the practice of soil compaction, here a brief description of the definition of less common values: (1)

Deformation modulus Ev

During plate bearing tests with static loads according to DIN 18134 the deflection of the soil surface under a rigid circular load plate with a diameter of 300 mm is determined. The load plate is centrally and vertically loaded in load stages and normally subsequently relieved step by step; further identical supplementary load and relieve cycles may follow (Fig. 53).

51

Part 2

(2)

Modulus of subgrade reaction ks

For the calculation of the modulus of subgrade reaction ks used for the design of concrete pavements of highways and airports the compression stress σο, which complies with a mean deflection of s = 1.25 mm, is measured with a load plate of 762 mm in diameter. The modulus of subgrade reaction is calculated as follows: #,

ks = σο /s [MN/m²] (3)

v

Settling in mm

In comparison to the static plate bearing test the dynamic plate bearing test is an accelerated test method. The test is applied for an indirect or comparative verification of the load bearing capacity and compaction of test areas in a simple way. The dynamic deflection modulus Evd is determined on the basis of a defined impact load applied to the soil by a light falling weight. Its value is calculated on the basis of the maximum force F measured at the impact of the falling weight on the plate and the settlement amplitude s of the plate using the equation

Principle of a static plate bearing test with pressure-settling curve

max σ

Evd = 0,75 . d . max s

Fig. 53

During this plate bearing test the deformation modulus Ev (resilient modulus) is normatively calculated on the basis of the pressure deflection line for the first and the repetitive load cycles as incline of the secant between points 0.3 σmax und 0.7 σmax according to v

Ev = 1.5 r ∆σ/∆s [MN/m²] This formula is based on the theory of the surface deflection of an elastic isotropic half-space under a centrally and vertically loaded, rigid circular plate.

52

Dynamic deformation modulus Evd (resilient modulus)

Compaction of soil and rock in earthwork

σ = σs =

Test pressure standardised pressure at penetration depth: 0,25 mm σs = 7,03 MN/m² 0,50 mm σs = 10,55 MN/m²

Principle of the dynamic plate bearing test (light falling weight unit) with force-path diagrams Fig. . 54 (4)

California Bearing Ratio CBR

In the CBR-test the pressure generated by a cylindrical pressure punch pressed into the soil with uniform speed down to penetration depths of 0.25 to 0.5 cm is determined: CBR =

σ . 100 in % σs

Principle of the CBR-test with with punch pressure penetration curve

Fig. 55 53

Part 2

1.4.3.2 Soil specific interrelationships Between the compaction parameters (DPr, ρn, e, D, ID) and the deformation parameters described in T 3, para. 1.4.3.1 extremely scattering soil physical interrelationships do exist. These are, on the one hand, caused by load and tension dependent elastoplastic deformation characteristics, and on the other hand, by a series of soil and test specific influence factors. 1) Coarse particle soils (sands, gravel), which are characterized by non-cohesive properties, always show a close dependence Ev = f(DPr) for only one specific particle mixture. The deformation modulus Ev, of a single sized sand, for example, is considerably lower than for a sand-gravel-mixture graded according to the square parabola, at an identical degree of compaction. v

Interrelationship between EV1-or EV2-modulus and air void proportion for sands and gravel sands Fig. 56

If the pore content n is used as a parameter, this interrelationship can be transferred to a general closer form, as shown in Fig. 57; (Lit. 15). Calculating the quotient of the deformation moduli Ev2/Ev1 on the basis of the two compensation curves shown in the illustration, results in the interrelationship presented in Fig. 57. The size of this quotient enables a conclusion on the remaining plastic deformability after compaction; besides others, this value indicates whether or not the Ev2-modulus results substantially from the compaction caused by the initial load.

Dependence of the ratio value of the des deformation moduli EV2/EV1 on the air void proportion for Fig. 57 sands and gravel sands The water content has hardly any influence on the deformation resistance of non-cohesive soils. In Fig. 58 this is illustrated for the CBR-index in the function CBR = f(n, Sr) for saturation coefficients 35 0,8 Ic erfassen; näherungsweise > 20 besteht MN/m² folgende > 0,9 Zuordnung > 80 MN/m² > 1,0 > 45 MN/m² > 1,2 Tab. 13: Approximate assignment of Ev-modulus and consistency index IC Tab. 14 contains experimentally evaluated limiting values of different deformation values for various degrees of compaction DPr. These values overlap considerably because of the variable water contents and conditions that plastic soils may have at compaction degrees DPr of identical value. This again demonstrates that the Ev-modulus (or any other deformation parameter) on its own is no quality criterion for the compaction, but that, vice versa, Pr

Pr

Tab. 15 shows a qualitative classification of the deformation performance of compacted mixed particle soils. Here the evaluation depends on the condition of the fine particle fraction and on the proportion of fine particles passing sieve 0.06 mm and coarse particles retained on sieve 2 mm. Group 1 covers all sands and gravel with low pro portions of fines < 0.06 mm. Group 2 includes more or less uniformly graded sands with more than 15% < 0.06 mm, which have deformation moduli similar to sandy clays, at higher water contents. Besides the fine particle silt and clay soils group 5 also includes mixed soils with sand and gravel proportions of up to 40 %, which perform like cohesive soils. Groups 3 and 4 cover the range in between. Their deformation performance depends on the condition of the fines. In dried condition mixed soils of groups 2 to 5 may have very high deformation moduli. 55

Part 2

Group 1 2 3 4 5

Paricle prop. [%] Consistency Ic of the fines (silt, clay) d 2 mm Ic > 1 0,75 < Ic < 1 Ic < 0,75 a < 15 a>³0 ¡ ¡ ¡ 15 < a < 60 a < 30 ¨1) 15 < a < 40 a < 30 ¡1) ¨ 40 < a < 60 a > 30 ¨1) 1) a > 60 a < 40

1) additional requirement: air void content na < 12% Deformation performance: O as with non-cohesive, coarse particle soils (sands, gravel, blocks) as with cohesive, fine particle soils (silt, clay) ¨in appropriately compacted condition between O and MN/m2

Tab. 15: Evaluation criteria for the classification of the deformation performance of mixed particle soils 1.4.3.3 Relationships to international soil classifications Fig. 59 shows relationships between various test empirically evaluated soil parameters in correlation with internationally used soil classifications. Due to the inclusion of the soil classification according to DIN 18196 it is possible to bring the parameters almost to a soil specific compliance with foreign classification system. However, in-situ tests for the direct evaluation of these parameters cannot be replaced by these assignments.

56

Soil classification (USC*/DIN) and load bearing values *Unified Soil Classification

Fig. 59

Compaction of soil and rock in earthwork

2.

Rock (Basic Lit. 12, 16)

2.1 Classification of rock (overview) Rock types are differentiated according to genetic-stratigraphical and petrographical properties. According to their origin they are classified as 2.1.1 Congealed rock (magmatic rock) - Volcanic igneous rock, e.g. trachyte, andesite, basalt, porphyry, dolerite - Dyke rock, e.g. pegmatite - Plutonic rock, e.g. granite, syenite, diorite, gabbro As extrusive igneous rock the volcanic igneous rock originates from the flow of magma that has been forced by gas and tectonic folding pressure to the surface of the earth where it finally solidified. Dyke rock was formed by the flow of rock that solidified under the surface of the earth in open crevices, chimneys and joints. Plutonic rock solidified in very deep depths under high pressure. 2.1.2 Sedimentary rock - Clastic sediments, e.g. sandstone, greywacke, mudstone, slate, tuff - Chemical sediments, e.g. limestone, dolomite, salt, anhydrite, gypsum, chalk - Organogenic sediments, e.g. coal, peat Sedimentary rock originates from weathered rock material that has been displaced by water, wind or glacier and deposited in the sea or at land. Solidification was caused by chemical or organogenic bonding or by pressure. Some sedimentary rock was formed under special formation conditions: Calcareous sinter In the area of the springs emerging from the calcerous terraces and over high raised ground water calcarous crusts are formed by the dissolved lime in the water; these are known as alm, travertine or

tufa. Salt and gypsum Salt and gypsum have formed under hot and dry climatic conditions in sea arms. They are embedded in various types of rock (e.g. Raibler layers, lower triassic). Their presence is identified e.g. by sinkholes and dolines. Limestone and dolomite In the warm sea fine slurries have initially been formed from calcareous spar, algae and plankton. Their alteration to limestone occurred chemically with a distinct stratification and enclosed shell residues from ammonites, snails, oysters and coral stocks. The dolomites are of similar origin. Besides calcium carbonate they also contain magnesium, are mostly more brittle than limestone and change to grush under weathering. Biogenetic or organogenic sediments Absorption of substances dissolved in water by organisms and deposition in their skeleton and shells. After dying they form biogenetic or organogenic sediments. Peat, coal Plant residues in moors and moor forests which are deposited under the absence of air and cannot decompose to water and gas. These form fibrous peat which then changes to limnic peat, lignite, brown coal, bituminous coal and anthracite.

2.1.3

Metamorphic rock

e.g. quartzite, marble, lime silicate, slate, phyllite, mica schist, gneissic rock Metamorphic rock consists of original extrusive igneous or sedimentary rock which were pressed down to deeper depths by tectonic processes, where they were changed to crystalline rock by high overlying strata pressure or by melting.

57

Part 2

2.2 Description of rock During the investigation for engineering or mining purposes in rock the following points must be recorded and uniformly described according to DIN 4022, part 2: the drilling engineering data and properties as well as the results of the drill cuttings (drilling core, sample core, core piece), the drilled rock by type and colour, the divisional planes by number and formation as well as the depth and position of the encountered water conditions. Type and condition of the drilled cores and rock material must be described in detail; this includes type of rock, granularity, space factor (dense, porous, cavernous), strength and grain binding, hardness, variability in water, colour, indications to bonding agents, angularity, condition of surfaces and cutting planes. 2.3 Parting plane structure of rock Apart from its stratigraphical and petrographical characteristic the rock mechanical properties of rock, especially its deformation performance under tension and its permeability, are primarily influenced by its parting plane structure. The parting plane structure comprises the entity of all discontinuity surfaces of a mountain, these are - the cutting planes resulting from sedimentary processes - the secondary foliation planes caused by tectonic effects - the joint planes resulting from tectonic processes as well as stress differences caused by pressure and temperature, whereby dislocations (paraclases offset to each other) are generated. The parting planes are described and evaluated by their distance and spatial orientation (direction of strike and dip). Furthermore, the parting planes must be assessed by their condition and the degree of separation (Tab. 16).

58

Mean distance Designation (in cm) Jointing bedding / foliation Toleranz ± 20% 60 compact massive Tab. 16: Classification of parting plane distances with designation The joints are described and evaluated by the minimum and maximum size of the rock fragments, the joint system (total number of joint planes), the joint width and their extent (direction, length). Shape and size of the rock fragments are determined by the distance of the parting planes: see classification in Fig. 60 (Lit. 12) and Tab. 16 acc. to the code of practice for rock description for road construction (FGSV = German Road And Transportation Research Association).

Classification of rock fragments by L. Müller

Fig. 60

In areas close to the surface the structure of the parting planes may be loosened by weathering or construction related stress effects (Tab. 17). This loosening appears e.g. in form of cracks, crevices, widening, rifting. The attributes of loosening can be characterised by distance, degree of separation and gap width of the parting planes.

Compaction of soil and rock in earthwork

Designation Nonweathered starting of weathering

desolidified

decomposed

Characteristic of rock non-weathered, fresh, no apparent effect of weathering on fresh break plane single mineral particles show signs of weathering (magnifying lense), start of mineral transformation and doiscoloration mineral structure loosened by weathering processes, but still interlocked, mostly in connection with mineral transformation, especially with an on parting planes rock changed by mineral transformation without the properties of a solid rock material, but still in the rock structure e.g. transformation of feldspar materials to clay materials, from clay shale to clay)

Characteristic of mountain range no loosening on separating planes caused by weathering partial loosening at the separating planes

completely loosened at the parting planes

Rock fragments without solid rock properties

Tab. 17: Weathering level of rock acc. to leaflet (FGSV = German Road And Transportation Research Association) 2.4 Strength and deformation properties of rocks Fracture strength, tensile strength, bending tensile strength and shearing strength are some of the most important strength values. Parameters for these strength values and some further properties can be found in the appendix A 3. The single and multi-axis fracture or compressive strength σD increases with the proportion of the particle size and the structural stability of the pressure resistant and non-cleavable minerals. Pore spaces, micro-cracks, weathered mineral aggregates and cleavable minerals reduce the structural stability and the compressive strength accordingly. The tensile strength σZ characterises the adhesive and cohesive bonding strength between the mineral aggregates of the rock. It decreases with the coarseness of grains and the above mentioned discontinuities. σZ is approximately 1/10 to 1/20 of the compressive strength σD. Z

D

The shearing strength τf characterises the frictional and interlocking resistance of the mineral aggregates in the rock under shearing stress. It decreases with the proportion of cleavable materials, clay and water. τf is approximately 1/2 to 1/20 . σD. f

D

The deformation properties of rock depend on its strength and anisotropy: Hard rock with a dense structure behaves like an elastic solid body. A jointed, but massive rock responds mainly plastically under initial loading, but becomes increasingly elastic when repeating the load process several times. Soft rock deforms plastically up to fracture. The sensitivity to weathering and frost can be investigated on the rock aggregates by water immersion, dry-wet cycles and frost-thawing cycles. Heaving and swelling performance can be determined by special mineralogical investigations as well as heaving tests, measurements of the heaving and swelling pressure, investigations of the water absorption capacity and the shrink measurement, the extraction and alteration of minerals by water immersion tests. 59

Part 2

2.5

Suitability of rock (Lit. 11, 23)

2.5.1 Exploitation of rock as filling material

dependence on the borehole depth. The following blasting methods may be used to obtain almost cubic, fragmentary rock as filling material:

Ripping of rock

Method I

The working method (ripping equipment, planning of exploitation, heading direction) depend on the strength and the parting plane structure of the rock to be loosened. As far as possible, the rock shall be ripped fragmentary to a wide graded mixture with favourably shaped stones, to obtain a well compactible filling material; If necessary it must be additionally crushed. Prerequisite for these quality requirements is a narrow parting plane structure with blocky, cubic components.

This method requires the use of highly explosive materials with millisecond igniters or with shortdelay detonators (ignition sequence 0.5 or 1.0 s), to break the rock mainly by the detonation pressure. Big distances or overcharging of the boreholes cause shaking of the surrounding area and disturbance to the slope areas.

Pretests are therefore required to determine the optimal direction of ripping, the depth effect of the ripper tooth as well as other conditions, by which the best graded mixture is achieved. The loosening is accomplished by optional equipment on hydraulic excavators, such as ripper teeth, scarifiers, single and multi-tooth rippers, chisels. The speed of seismic waves is a criterion for the rippability of rock. Fig. 61 shows approximate limits of the rippability.

Method II The same effect, but with less shaking of the surrounding area and less disturbance of the rock formation, can be achieved by multi-row blasting using millisecond or short-delay detonators with a small distance between boreholes and medium to low explosive materials. With this method the small distance between the boreholes results in a good breaking effect despite the buffered detonation waves, because the blasting energy is evenly distributed and the rock is uniformly loosened and broken down. 2.5.2 Rock classes Classification of rock classes 6 and 7 according to DIN 18300 see T 2, para. 1.2 The classification of rock of classes 6 and 7 complies with a simple classification into the following two main groups frequently used in practice:

Ripping ability CAT D 9/D 10N in dependence on the seismic wave speed in soil / rock Fig. 61 Blasting of rock The blasting of rock requires pretests in order to optimise the line of least resistance and the lateral distance of the boreholes as well as the length of the stemming zone and the ignition sequence in 60

- Soft, weather-sensitive rock of low strength, breaking under mechanical load or crumbling to watersensitive soil types under the influence of frost, water, air or other weathering processes. These types of rock include most slates, and also carbonate rock such as marl and limestone as well as clastic rock such as sandstone, siltstone and mudstone. - Hard rock, less or non-sensitive to weather influences, the grain size and grain shape of which remains almost unchanged under mechanical

Compaction of soil and rock in earthwork

loads. This type includes most intrusive and extrusive igneous rock and dyke rock, and also meta morphic rocks such as gneiss and mica schist as well as siliceous rock such as quartzite. Although the soft rock types frequently belong to class 6 and the hard rock types to class 7, the characteristics “hard” and “soft” on their own are not sufficient for a clear classification of rock with respect to its workability. Petrographic, tectonic and weathering dependent characteristics must be additionally used as evaluation criteria. These are - the weathering condition, - the parting plane structure according to type, orientation in space (dip, strike), distance of the parting planes as well as to size and shape of the separated volume parts. 2.5.3 Placement and compaction Solid rock: When classifying rock with respect to its suitability and use as embankment material, loading, haulage, placement and compaction are of importance, besides the loosening which is normally accomplished by blasting, milling or charring (borrow, precut, tunnel). During this process and when estimating the cubatures one must make sure that, after loosening, the rock material is available for placement in a similar condition as the loose soil deposits. Reliable evaluations can, in most cases, only be made during mining in form of an accompanying classification. Solid rocks are rock materials which do not change their properties by weather influences. They are most suitable for rockfill embankments and, with well graded fragmentary components, they may also be used for the filling of higher embankment zones. The conditions are particularly favourable if the rock mixtures consist of well graded fractions with a fines content of less than 15% and a maximum stone size of 150 mm. The stone size of such mixtures shall normally not exceed two third of the lift height that is permitted for compaction (example Fig. 62).

Compacting blasted dolomite using a 19 t single drum roller in layers of 150 cm

Fig. 62

Rock material which is too coarse after loosening can be placed by applying the following methods. - Placement of the rock material in alternating layers with 20 to 30 cm regulating layers consisting of coarse particle material so that the filling is passable and compactible without any problems. - Sorting out of blocks with a volume of more than 0.1 m³ (corresponds with a ball diameter of 60 cm) and placement in the toe areas. If such blocks are placed in the inner zones of a dam, cavities may remain which will later cause settlements resulting from the dislocation of these boulders. If the proportion of rock blocks is so high that sorting out is uneconomical, the material may either be broken down at the source of mining by means of auger drills or in a simple mobile crushing plant. During loading, haulage, unloading and distribution 61

Part 2

of the rock mixture segregation must be avoided or the material must be remixed in special work processes. Rock with variable strength Rock with variable strength includes a variety of facies and are characterised by origination related significant differences with respect to their strength and deformation properties, on the one hand with transition to the clay and on the other hand to solid rocks. Generally valid rules for the placement and compaction of such rock materials are only possible to a limited extent. Their suitability as embankment material must be examined on the basis of either regionally available experiences or the results of material specific trial compaction. In Germany the rocks with variable strength are mainly represented by siltstones and mudstones, slates as well as diverse types of sandstone: Siltstones and mudstones In the structure of rock mass they are normally characterised by distinct stratification and joint planes, by changes from non-weathered to weathered strata with different stratum and bank thicknesses and by partly regular, partly irregular joint plane structures. Depending on the parting plane structure the weathering horizons may locally differ considerably and reach down to various depths. The filling of the joints consists mainly of waterbearing, highly plastic weathered clays, which, in case of the dip of the layers, form prescored sliding planes. The more distinct the parting plane structure, the narrower the parting plane distances and the more sand and silt enriched the mudstones become in the transition to the siltstones, the easier the loosening in ripping operation will become when using appropriately heavy caterpillars and auger drills. If appropriate ripping equipment is used and the working direction is adapted to the changing dip and strike of the stratum and joint planes, a fragmented size of the material can be achieved which 62

is directly suitable for placement. A great difference in the fragment sizes must also be considered because of the substantial differences or changes in parting joint structure, degree of weathering and stratum or bank thickness. In less jointed, nonweathered bedded areas or as a result of loosening up blasting loosened bedrocks of more than 0.1 m³ in volume occur, which require special crushing, whereas in extremely jointed areas well graded and well compactible broken material down to the gravel fraction may be found. During excavation in friable weathered areas extreme decay and abrasion may occur and lead to high proportions of sand and fines. In case of a segregationj of these grain fractions gap graded fractions can be expected. In loosened condition for both the still non-weathered as well as the already weathered siltstone and mudstone it must be considered that a permanent degradation of durability will occur. The strengths of the quarry-stones will extremely drop by the dissolution of the original structure of rock mass and the resulting destressing of the rock as well as by the increase of possible weather influences caused by water, swelling, frost and drying. By experience the highest loss of strength occurs after several drying/ wetting cycles and during frost/thawing cycles, even in rock initially showing only slight changes during immersion in water. Due to the properties described hereunder it must be considered that the placement and compaction of mudstone and siltstone remains very sensitive to weather and frost. The placement should therefore take place under dry weather conditions, whereby the material should be directly transported to the placement location without intermediate stockpiling and that it should be compacted in lifts as thin as possible. In most cases placement and compaction work cannot be continued during frost and longer precipitation periods. If the rock material arrives at the placement location not completely dry no water should be added, since the admission of too much water may considerably impair the compaction properties and the surfaces will become slippery and soaked, so that passing of vehicles may be impossible. After resuming work it may first be necessary to remove the top, softest layer or to reduce the water content by application of special

Compaction of soil and rock in earthwork

measures, in order to achieve a particularly good interlocking effect with the subsequently following lift. On the other hand the dry placement holds the risk of an extremely increasing compaction resistance and that the compacted layer contains too many and large air voids. The drier the mudstone used for filling, the higher the required compaction effort; i.e. heaviest compaction equipment, low lift heights and a high number of compaction passes are required. Due to the highly weather dependent placement and compaction properties and because of the high compaction effort the variably solid siltstone and mudstone materials are only to a limited extent suitable for embankment construction. Normally longterm subsequent settlements must be expected which, however, can be minimised by intensive compaction to remaining pore porportions of less then 10%.

Sandstone and calcareous sandstone These rocks can be found alternately fine or coarse in their structure, but also dense to highly porous. Even though they are solid rocks they still have a relatively low compressive strength, so that excessive particle crushing and accumulation of fines will occur during placement and compaction. As far as these contain argillo-marlaceous components, they possess weather sensitive properties and perform very sensitive to water and weather during placement and compaction in rain periods and also to frost during frost periods. They are generally suitable as embankment material; under consideration of the required lumpiness and gradation they can be used in all embankment areas if they are compacted to a low air void content (example Fig. 63).

Slates In the structure of rock mass the various slates possess a more or less distinct platy foliation with mostly slight, but occasional bigger distances between the foliation planes. They are highly variable solid rocks which can weather, soak and decay. These processes may also continue even in compacted condition. With an optimum water content during placement and with a protection against seepage water slates are mostly suitable for embankment construction, but must be compacted to a very low air void content, i.e. with high energy, which is particularly difficult because of the platy lumpiness.

Compacting and subsequent crushing of sandstone using a 25 t single drum roller with special drum on 60 cm layers Fig. 63 63

Part 2

3.

Application and performance of the BOMAG-compaction technology (Application and performance Lit. 23, 24 to 28, quality assurance Lit. 17 to 23)

3.1 Applications The productive capacity of the vast variety of BOMAG compaction machines ranging from handguided light equipment up to heavy self-propelled single drum rollers and heavy-weight towed rollers covers a wide range of applications with all types of use.

- construction site conditions (confined or spacious working areas, accessibility, obstructions caused by site operations). For the variety of applications table 18 and figures 64 and 65 provide initial decision aids in form of an overview.

When deciding on the suitable compaction machine the following factors must be taken into consideration: - soil and rock specific properties - quality requirements for the execution (degree of compaction, uniformity, evenness), - economical performance, - machine costs

Machine type/ application (soil compaction) Road construction Railway construction Airport construction Hydr. engineering/ landfill site constr. Side and cycle paths Entrances to yards and garages Parking lots and industrial yards Playgrounds and sports facilities Trenches nar. trenches 15m

LR

= 10 D = ramp length (m) (not needed when preparing inside the construction field) = Start and run-out section = Length of compactor (m)

LA LP

= 4a + 3p = Length of trial section (m) D = Thickness of compacted lift (m) a = Distance to and between trial sections (m) p = Length of trial section (m) 69

Part 2

Width Bges

= 3 BG - 2 Ü + 2 b = 2 BG + BP + 2 b = Overall width (m) > 5m

BG

= Width of compactor (m)

Ü

= 0,1 BG = Overlapping of strips (m)

BP

= BG - 2 Ü = Width of trial section (m)

D

= Thickness of compacted lift (m)

b

= D (m) = Safety distance

In order to be able to evaluate the achieved compaction, the degree of compaction DPr or the density pd shall be detected over the entire thickness of the lift. Apart from density tests other suitable tests should also be comparatively be performed to enable a determination and evaluation of the interrelationship between the respective results already at the time of the trial compaction.

The addition of water only makes sense if it is applied in a controlled manner and the soil is uniformly moistened. In case of clayey soils a uniform moistening cannot be achieved without additional milling and mixing processes. Soils with a too high water content must not be placed and layers subsequently soaked to deeper depths must not simply be covered. A too high water content reduces the achievable dry densities and does not allow for an optimal compaction. Under certain soil conditions vibratory compaction has the effect of “pumping” free, excessive water to the surface, thereby soaking the zone close to the surface even more. The water content can be reduced by aeration, drying, milling or adding of water-binding substances (Fig. 70).

Pumpeffekt

3.4 Placement and compaction water content s. information in T 2, para 1.3.2 and 2.5.3 Compaction of the fine, coarse and mixed particle soils shall take place at the optimum water content wPr, approximately within the limits from + 1% to 2%, if this is possible. The lower the water content, the more difficult the processing of soils which are too dry for compaction. In most cases theses soils need to be moistened, although this is time consuming and expensive. The following measures are possible: - artificial sprinkling during loosening at the source, - addition of water in the transport vehicles by means of pressure sprinkler systems, - addition of water at the placement location by means of sprinkler truck, if necessary with water pump. 70

Compaction recommendation for soils with high water content

Fig. 70

Drying of a soil layer by sunshine and wind may take quite a long time (several days up to weeks) until compaction can be continued. Difficulties caused by rainy weather can be minimized by auxiliary construction measures: - Installation of drainage gutters or ring trenches around the placement location to catch water flowing in from outside,

Compaction of soil and rock in earthwork

- Arrangement of the surface slope at the placement location in such a way, that water is dis charged to the outside. - Application of milling machines and graders to aerate the soil layer, to level vehicle tracks and to remove water deposits, - Placement of thin, uniform lifts which are immediately compacted with sufficient results, - Before longer breaks temporary overfilling of the placed layer with extreme slopes to both sides, - Mixing in of quicklime as a measure to reduce the water content in the soil (Fig. 71).

Improving the compaction properties of a fine particle soil by mixing in lime

content is required to achieve a water tightness as high as possible. In such cases a static compaction of a highly reduced lift height with smooth drum rollers without vibration may lead to the best results. When compacting solid rock material an addition of water is normally not required. In most cases water sensitive rock material of variable strength acquires unfavourable placement and compaction properties when water is added or absorbed. With very dry rock material slight wetting of the surface may have a positive effect on the compactibility (e.g. mudstone).

Fig. 71

The placement of thin layers in combination with the use of padfoot rollers for compaction in case of a high water content in the soil layer or under unfavourable weather conditions may be suitable for a continuation of compaction work over a longer period of time. However, this requires that the earthwork operation can be changed to the placement of thin layers and that the soil is suitable for compaction with padfoot rollers. This placement method requires more time, especially since additional passes with heavy smooth drum rollers are required to seal the surface. Another counteracting measure in case of a too high water content is the change to the “sandwich” method, .i.e. placement of alternating layers of gravel, sand or rock. For special placement situations, e.g. sealing layers consisting of plastic clay, a relatively high water 71

Part 2

3.5 General equipment and soil specific recommendations As described in T 1 „Basic principle of vibratory compaction“, certain machine parameters have a substantial influence on the optimisation of compaction. These important parameters of the vibratory

compactors include the static linear load, amplitude, vibrating mass, frequency and rolling speed. The following data can generally be valid as guidelines for commonly used lift heights:

Recommendations for vibratory rollers for average lift heights

Data on output per hour and average compaction depth or compaction lift height can be estimated on the basis of the reference values in tables 20 to 23. By general experience, self-propelled compactors have a higher mobility and are more flexible in 72

Fig. 72

operation than hand-guided machines. They therefore have a higher efficiency and cause less stress for the machine operator.

Compaction of soil and rock in earthwork

Machine

Lift height compacted in (m) Gravel, sand Mixed soil

Silt, clay

-

• 0.30 - 0.40 • 0.30 - 0.40

• 0.20 - 0.25 • 0.25 - 0.30

0.15 - 0.20 0.20 - 0.25

40 - 100 120 - 250 300 - 450 600 - 800

0.30 - 0.50

• 0.10 - 0.20 • 0.20 - 0.30 • 0.30 - 0.40 • 0.50 - 0.70

• 0.10 - 0.20 • 0.20 - 0.30 • 0.25 - 0.35 • 0.40 - 0.50

0.10 - 0.15 0.15 - 0.20 0.20 - 0.25

600 - 800 900 - 1200

-

• 0.20 - 0.25 • 0.20 - 0.30

• 0.20 - 0.25 • 0.20 - 0.25

0.10 - 0.15 0.10 - 0.15

1500 - 1600

-

0,25 - 0,30

• 0,25 - 0,30

• 0,20 - 0,25

Operating weight

Rock

kg

kg

50 - 60 70 - 80

• Machine particularly suitable for this type of soil Tab. 20: Reference values for compactible lift heights

Machine

Operating weight

Rock

t

Lift height compacted in (m) Gravel, sand Mixed soil

Silt, clay

kg

1.5 - 2.5 3.0 - 4.5 7-9 10 - 12

-

• 0.20 - 0.30 • 0.25 - 0.30 • 0.30 - 0.40 • 0.30 - 0.50

• 0.20 - 0.25 • 0.20 - 0.25 • 0.20 - 0.30 • 0.25 - 0.40

0.10 - 0.15 0.15 - 0.20 0.15 - 0.20 0.15 - 0.20

2-3 6-8 9 - 12 13 - 16 19 - 25

0.30 - 0.50 0.50 - 0.80 • 0.80 - 1.20 • 1.00 - 2.00

• 0.20 - 0.35 • 0.30 - 0.50 • 0.50 - 0.60 • 0.50 - 0.80 • 0.80 - 1.50

• 0.20 - 0.35 • 0.25 - 0.35 • 0.30 - 0.45 • 0.40 - 0.60 • 0.60 - 1.00

0.15 - 0.20 • 0.15 - 0.20 • 0.20 - 0.25 • 0.20 - 0.35 • 0.30 - 0.50

6-7

• 0.50 - 0.80

• 0.40 - 0.60

• 0.30 - 0.45

• 0.20 - 0.30

• Machine particularly suitable for this type of soil Tab. 21: Reference values for compactible lift heights 73

Part 2

Machine

Compaction output (m3/h) Gravel, sand Mixed soil

Operating weight

Rock

Silt, clay

kg

kg

50 - 60 70 - 80

-

8 -15 8 - 17

6 - 12 6 - 14

5 - 10 6 - 12

40 - 100 120 - 250 300 - 450 600 - 800

60 - 100

5 - 15 15 - 25 25 - 60 90 - 120

5 - 15 15 - 25 20 - 50 60 - 100

8 - 14 10 - 25 25 - 50

600 - 800 900 - 1200

-

30 - 40 40 - 60

30 - 50 40 - 50

15 - 25 20 - 30

1500 - 1600

-

40 - 60

40 - 60

30 - 50

Tab. 22: Practical output of hand guided compaction equipment in earthwork

Machine

Operating weight

Rock

Compaction output (m3/h) Gravel, sand Mixed soil

t

kg

1,5 - 2,5 3,0 - 4,5 7-9 10 - 12

-

50 - 150 70 - 200 120 - 350 200 - 500

50 - 120 60 - 150 100 - 250 150 - 400

30 - 70 40 - 90 80 - 150 100 - 200

2-3 6-8 9 - 12 13 - 16 19 - 25

200 - 500 400 - 900 500 - 1400 900 - 2200

60 - 180 150 - 400 250 - 600 350 - 1000 600 - 1600

60 - 180 100 - 350 250 - 500 300 - 800 500 - 1200

40 - 100 70 - 200 150 - 300 200 - 500 250 - 800

6-7

300 - 600

200 - 400

150 - 250

100 - 200

Tab. 23: Practical output of compaction equipment in earthwork 74

Silt, clay

Compaction of soil and rock in earthwork

If a high compaction is to be achieved in the shortest possible time, the main object will be to start the work with high compaction energy or maximum amplitude until jumping or beating occurs, then to perform the following passes with a lower energy transfer or low amplitude, finally, if the machine shows a repercussion reaction, followed by an solely static compaction without vibration. With this method the intention is to compact the deep area of the layer first and subsequently the area near the surface with a lower energy. Vice-versa, if a machine works with a low compaction energy and a high number of passes first, it may happen that near the surface the layer is initially compacted very intensively, but is loosened or even damaged when high energy is subsequently applied. In this case the directed vibrator system VARIOCONTROL with controlled amplitude developed by BOMAG is a great help (see T 1, para. 2.1.4), because the single drum rollers with VARIOCONTROL transfer the maximum possible compaction energy at any time, without the drum changing to the unfavourable jump operation or causing overcompaction. The compaction of rockfill material requires heavy machines with a static linear load of at least 30 kg/cm. Oversize lift heights and cohesive soils, especially those with highly plastic properties, also call for heavy machines, as far as this is permitted by the passability and load bearing capacity. With normal soil conditions and lift heights all other soil tasks can be accomplished with less heavy equipment. Overcompaction of a soil layer occurs when a dense bedding is already reached and the introduction of compaction energy is still continued. In this case loosening, segregation, particle destruction and an increase of the fine particle fraction may especially occur in the layer areas near the surface.

The reactive forces effecting the machine in case of overcompaction cause damage and expensive repairs. If the overcompaction causes jumping and repercussion of a roller, the vibrator system will experience a hard impact during one revolution of the eccentric mass and lose ground contact during the next revolution. This continuously changing vibration with impact and loss of ground contact is extremely stressful for the machine. Even compactors with impact vibration, such as tampers, may be damaged when working on an overcompacted soil layer, because the normally dimensioned impact vibration changes from a harmonically controlled to a non-uniform operation. If there is a risk that a soil layer may be overcompacted, the compaction energy must be reduced as exemplary shown in Fig. 73:

Avoidance of overcompaction

Fig. 73

3.6 Special machine specific compaction effects 3.6.1 Static smooth drum rollers The compaction effect of these rollers improves with increasing static load. The required number of passes drops with increasing linear load. At a certain linear load the compaction effect and the depth effect rises with the increase of the water content, but only within the optimal range. With a high linear load and a small lift height a good compaction effect can even be achieved with a water content below the optimal level. On mixtures of gravel and sand as well as gravel-sand-silt mixtures the depth effect is higher than on soils consisting of silt and clay. 75

Part 2

3.6.2 Pneumatic-tired rollers The compaction effect of pneumatic-tired rollers improves with increasing wheel load or tire contact pressure. The required number of passes drops with increasing contact pressure, whereby this influence is reduced as the water content increases. The compaction depth also rises with the contact pressure or the wheel load, the contact pressure is mainly effective in the upper zone and the wheel load in the lower zone. The influence of the load has a greater effect on cohesive soils than on noncohesive soils, because the coarse granular soils are loosened at the surface by the shearing stress applied by the rolling tires. 3.6.3 Smooth drum vibratory rollers On all types of soil the compaction effect of vibratory rollers is substantially influenced by the dynamic characteristics of the vibrator system, the linear load of the respective roller type and the soil specific properties. Due to the combined effect of vibration and linear load a considerably lower number of passes is required to achieve a certain compaction effect than with the statically working smooth drum rollers. The influence of the linear load on the compaction depth becomes apparent by the fact that heavy rollers generally have a deeper effect on any soil than light rollers, but that the depth effect achieved with any roller is best within the range of the optimal water content. The depth effect of compaction increases with the number of passes. On gravel-sand-silt-mixtures the compaction normally reaches deeper than on cohesive fine particle soils. Apart from this it is generally found that the light small rollers become ineffective when compacting fine particle soils with an increasing proportion of clay and a distinct plasticity, even with a very high number of passes. An increasing rolling speed requires a higher number of passes, similar to the smooth drum roller without vibration, whereby also here this is influenced by lift height, operating weight of roller and water content 76

The water content of the soil has a tremendous influence on the compaction effect of vibratory rollers, however, with differences depending on the linear load: The light rollers require more water for an optimal compaction, whereas the water requirements drops with increasing linear load when using heavy rollers (over 10 kg / cm). The influence of the linear load reduces with increasing water content of the soil. The size of the vibrator’s centrifugal force has a comparatively minor effect. The vibration frequency influences the compaction effect differently, depending on soil type and initial bedding density. During the compaction of coarse and mixed particle soils favourable compaction effects arise in the frequency range between 25 and 35 Hz, whereby the required number of passes drops with increasing frequency. For fine particle plastic soils no clear statement on the influence of the frequency can be made. 3.6.4 Padfoot rollers with and without vibration Conventional single drum rollers with padfoot drum in the weight range from 6 to 25 t are used for the compaction of cohesive soils, stony mixed soils and solid rock of variable strength. They have proved worthwhile because of their applicational versatility and their compaction performance. The drums are normally fitted with 100 mm trapezoidal padfoot elements (studs) with flat side faces and scrapers for cleaning. In connection with the vibration these studs produce a kneading and pushing effect, which leads to the reduction of the air void volume and to a pulverisation of lumps and rock fragments. Due to the shape of the padfeet the contact surface increases with the penetration depth. The compaction effect adapts to the stiffness of the soil to be compacted via the penetration depth of the studs. The compaction effect depends substantially on the areal pressure of the ground contact area. Foot shape and covering rate of the studs on the drum shell have a tremendous effect. This effect is

Compaction of soil and rock in earthwork

enforced by the increase of padfoot pressure, the increase of the clay proportion and the reduction of the water content in the soil. On clayey soils these padfoot rollers compact most effectively at water contents below the optimum, whereby this influence of the water content diminishes with increasing silt and sand fractions in the soil. The compaction effect increases strongly with the number of passes, but also in this case this influence is reduced by a rising water content. The number of required passes is also influenced by the degree of coverage of the padfoot elements. The more clayey and less moist the soil, the higher the compaction that can be achieved with increasing padfoot pressure. Compaction is even possible at a high water content, as long as the padfoot elements have a kneading effect and do not sink in completely. The surface structure that forms under the roller passes changes strongly with the water content. The thickness of the loose soil ripped up by the profile of the drum is reduced with dropping water content, whereby small or tapered padfeet generally have a higher loosening effect than large area padfeet. Raising the rolling speed results in a sublinear increase in the number of rolled passes. 3.6.5 Single drum rollers with special padfoot drums Extensive investigations of BOMAG about the effect of padfoot rollers aimed at higher compaction performance on cohesive and stony soils as well as high impact and crushing effects when used on rockfill. This resulted in three special padfoot drums which are already successfully used (T 1 para. 3.6 and Fig. 36).

and compaction of the soil. An additional benefit is the better self-cleaning effect between the teeth on cohesive soils. Clogging of the drums, which is disadvantageous for the compaction effect, is avoided.

Improving the compaction output on boulder clay using a 25 t single drum roller with Fig. 74 pyramid teeth (2) Rollers with triangular teeth For the crushing of hard and brittle pieces of rock BOMAG equipped a 25 t single drum vibratory roller with triangular teeth (Fig. 75). When using single drum rollers with vibration on coarse, solid rockfill the tips of the triangles produce such high pressure and splitting forces, that the desired crushing and edge fracturing of the coarse particles and therefore intensive compaction of the packing bed is achieved with a considerable reduction of air voids. In order to withstand the excessive loads acting on the triangular teeth, their tips are made of a wear resistant material.

(1) Rollers with pyramid teeth Compared with conventional padfoot drums, drums with pyramid teeth are characterised by higher teeth, considerably smaller tip areas and steeper tooth flanks (Fig. 74). Due to their high specific pressure pyramid teeth penetrate deeper into the ground and achieve a more intensive kneading

Enhancing the crushing effect of a vibratory roller on quartzite sandstone using a special padfoot drum (triangular teeth) Fig. 75 77

Part 2

(3) Rollers with triangular teeth and cutters in between

a) Low lift heigt in the embankment area

For a further improvement of the crushing effect a 25 t roller was developed with triangular teeth and cutters in between (Fig. 76). Stones and blocks are split by the triangular teeth and subsequently crushed by the cutters. At the same time, the cutters prevent jamming of crushed material between the teeth. With the use of special padfoot rollers the highly expensive crushing, screening and manual sorting of large blocks is no longer necessary. The rollers are able to crush and effectively compact laminated fragments of mudstone and siltstone as well as lumps of quartzitic sandstone of up to 500mm in size.

-+

2m

b) Temporary excessive profile without a change in lift heigt 1

c) Variation to b)

d) Compaction on the slope

Bild: methods Verschiedene Verfahren zur sorgfältigen Various for thorough compaction of slopes Verdichtung von Böschungsbereichen and embankment areas Fig. 77

Improving the crushing effect of a vibratory roller on quartzite sandstone using a special padfoot drum (triangular teeth)

Fig. 76

3.7 Compaction of marginal zones (slopes, embankment shoulder) Thorough compaction of slopes, embankment shoulders and other marginal zones is essential for the avoidance of erosion damage as well as damage to slopes and carriageways; Fig. 77.

78

For compaction of marginal zones of bank fillings light and medium-weight compactors are most suitable. For method d) in Fig. 77 special slope rollers with the engine at the rear should be used. Method b) in Fig. 77 is suitable for embankments if the temporarily existing surplus profile is permissible and the required surplus masses are included in the balanced cut and fill without additional costs.

Compaction of soil and rock in earthwork

3.8 Compaction of layers on an elastic base The compaction of multi-layer systems consisting of relatively thin layers on an elastic base, depends on the stiffness condition of the adjacent layers. Problems of this kind are e.g. bearing, filter and sealing layers. The energy introduced during compaction causes a reaction on the particle skeleton from the base, which increases with the stiffness of the base (bearing effect, rigid fixing). In the opposite case the energy is discharged into the base without any compaction effect. As far as such multi-layer systems are compacted with vibration energy, the resonance range of the entire system as well as the optimal amplitude of the vibratory compactor must be determined by means of trial compactions; general recommendations are: - machines with low amplitude and high frequency, if the base is of sufficient stiffness and shall not be compacted - machines with high amplitude and medium frequency, if the base shall first also be compacted - VARIOCONTROL machine with self controlling amplitude In practice an optimal compaction can very often be achieved by combining static and dynamic passes: the first passes with vibration, the final pass without vibration, if necessary an intermediate pass with a pneumatic-tired roller.

79

80

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1. Asphalt pavements in highway and transportation engineering Asphalt technology is used for pavements of highways and urban roads, for junctions and interchanges, for bus and rail tracks, for multi-purpose traffic lanes, hard shoulders and median strips, cycle paths and footways, for traffic lanes in service areas, etc. Pavements of traffic areas are built in form of asphalt surface courses, binder courses and base courses, to ensure high durability against stresses caused by traffic and weathering. The typical structure of asphalt pavements and their functional properties are shown in Fig.78. The design and execution of highway and transportation areas is based on engineering requirements concerning load bearing capacity, stiffness against permanent deformation, frost resistance and eveness and the required profile of the pavement. Besides the pavement the highway construction also comprises the subgrade and the subbase influenced by static and dynamic traffic loads. This multi-layer system is stressed by load, time and temperature dependent shearing and bending forces and deformed in dependence of the stiffness of effective layers. The carriageway pavement must be designed and built for safe riding traffic under any load condition, whereby its stability shall not be at risk at any time. This design goal demands a constructive interaction of all effective layers and a low and uniform level of deformation. According to this principle the layers must - have load distributing properties complying with the different possible types of loads - be able to mutually compensate overloads. These performance requirements depend on the stiffness of the system, which in turn is depending on the strength and deformation characteristics of the layers as well as the layer thicknesses including the thickness ratio of successive layers. The principle of the constructive interaction is met when the stiffness properties of the individual layers are adpated to each other in a way that the system stiffness increases from the bottom upwards according to the course of stresses.

Compaction of asphalt

The stiffness of the system changes because of the permanent mechanical load applied by traffic in combination with the local conditions or the seasonal climatic cycle. Particularly critical conditions may arise - during winter, when frost related non-uniform heaves occur or the stiffness of the sub-layers drops during thawing intervals. - during summer, when warping stresses develop and the stiffness of the visco-elastoplastic deformable ashalt layers is reduced by high temperatures. The task of design arises primarily as a deformation problem and is based on technical criteria, which can be derived from the rideability of the pavement; these are - the permissible deformation and - the required stability (load bearing capacity) of all layers contributing to the load distribution and influenced by local conditions. Pavements shall therefore be designed and built according to the following two examples: a) Construction in accordance with the required stiffness or the permissible deformation of the layers with the objective, to maintain such deformations at the lowest possible and most uniform level b) Construction of the required load bearing capacity of the layers including the subbase with the goal of maintaining any compression, shearing and bending stresses at such a low level, that deformation caused by tension and shearing will not cause cracking. This design is accomplished by application of theoretical methods of elasticity or plasticity, the applicational limits of which are described in Lit. 30. Some of the soil parameters, which form the foundation of this method, are mentioned in Lit. 23.

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Part 3

even, grip, dense Asphalt surface course wear resistant shear. res. Asphalt binder course

Asphalt base course pavement stable Frost blanket layer subgrade subbase/ subsoil

Structure and functional properties of asphalt pavements In the practice of highway engineering the described principles are simplified to a great extent, by standardising both structure and layer thickness of widely approved construction methods, in dependence on simple assumptions concerning the magnitude of traffic loads (Fig. 79). The German regulations for the standardisation of pavements for traffic areas (RSTO-86/89) differentiate the pavements for the various types of roads and highways according to traffic load dependent classes (Fig. 79). The traffic load index (VB) is mathematically determined on the basis of the average daily heavy vehicle traffic and factors for the forecasted increase in traffic, the number and width of the traffic lanes as well as factors for the gradients and higher axle loads.

Fig. 78 The types of asphalt pavements are designated according to the type of asphalt surfacing and differentiated according to table 24. Asphalt surf. Type of asphalt (normal types) Asphalt concrete (hot mix) Stone mastic asphalt Gussasphalt Asphalt mastic Combined surface-base-course Asphalt concrete (w. cutback bit.) Asphalt veneer coats (special types) Cold thin surface courses Hot thin surface courses Porous asphalt Rolled gussasphalt Tab. 24 Types of asphalt surfacings

Construction class SV Traftic load index (VB) > 3200 Thickn. of frost res. pavement 60 70 80 90 Asphalt base course on frost blanket layer

I 1800 - 3200 50 60 70 80

II 900 - 1800 50 60 70 80

III IV 300 - 900 60 - 300 50 60 70 80 50 60 70 80

V VI 10 - 60 < 10 40 50 60 70 40 50 60 70

-

-

28 38 48 58 32 42 52 62

26 36 46 56

surface course Binder course Asphalt base course Frost blanket layer

Thickn. of frost blanket layer

26 36 46 56

30 40 50

34 44 54

Examples for asphalt pavements in highway engineering acc. to RSTO-86/89

82

30 40 50 60

Fig. 79

Compaction of asphalt

Asphalt surfacings normally consist of an asphalt surface course and an asphalt binder course. Asphalt surface courses require special traffic related properties, such as grip, evenness, resistance against polishing, abrasion, moisture, de-icing salt and it must also provide sufficient sealing for the lower courses against surface water. The binder courses are located between the asphalt surface course and the base course. They enhance the stability and durability of the asphalt surface course and of the complete asphalt pavement. Pavements which are only subjected to low traffic loads do not require a binder course or the asphalt surface course can be replaced by a so-called surface protection layer (T 3, para. 3.4). Asphalt surface courses are normally applied with a thickness of at least 4 cm. The standard thicknesses of binder and base courses vary strongly in dependence on construction class, overall type of construction of the pavement and the composition of the mixture: Standard thicknesses of binder courses at least 4-8 cm, of base courses 8-22 cm. For further information on layer thickness see T 3, para. 3.3. With exception of gussasphalts and the surface treatments, all other types of asphalt are so-called rolled asphalts, the application of which requires compaction by static and/or vibratory compaction energy (see T 3, para.3 to 5). For the air void content in compacted condition minimum values in Vol.% of 6-7 apply for asphalt surface courses, 3-7 for binder courses and 4-14 for base courses. The degree of compaction (see T 3, para. 4.1) is at least 96 and 97% respectively. Traffic load (type and amount of traffic) as well as the climatic and local conditions must be taken into consideration when selecting the components and the cdesigning of the mixture. The mixture must be proportioned in such a way, that it possesses the quality required for the intended use. The substantial values for the execution of the work must be specified by the contractor on the basis of the mix design. The applicaple limit values and tolerances for the execution of the work contain work related deviations as well as tolerances in sampling and testing.

The requirements on the characteristics of the various types and grades of mixtures as well as for the construction of asphalt pavements are specified in German General and Additional Technical Contractual Conditions and Guidelines (ATV / ZTVStb). Important regulations see appendix A4.

2. Bitumen and bituminous binders (Lit. 32) 2.1 Types and manufacturing Bituminous binders as used for highway and transportation engineering mainly origin from the crude oil refining. The materials are classified according to the following groups: (1)bitumens as mixtures of high-molecular hydrocarbons, characterised as dark substances with highly viscous to semi-hard adhesive properties under normal temperatures, (2) the additive modified bitumens, suitable for hot, warm or coliquid processing after adding oil (light, liquid hydrocarbons), (3) bitumen containing binders in form of bitumen solutions, bitumen emulsions and polymer modified bitumes. Further terminological differentiations relate to the different manufacturing methods and areas of application (Fig. 80). Zur Herstellung der Bitumen werden die in den Erdölen enthaltenen Bitumenanteile von den leichteren Bestandteilen getrennt, wofür verschiedene Trennprozeduren zur Verfügung stehen: For the manufacturing of bitumen the bitumen components contained in the crude oil are separated from the lighter components. This is accomplished by one of several possible separating procedures: (1) distillation with the help of steam and vacuum as well as in connection with oxidation, (2) precipitation using special precipitants (e.g. liquified propane), (3)extraction using special extraction agents (e.g. phenolic and propanoic mixtures). 83

Part 3

Bitumen

by fields of application

by manufacturing method

Straight run bitumen

Straight run bitumen

Vacuum bitumen

Hardbitumen

Precipitation bitumen

Bituminous binders

Paving bitumen

Industrial bitumen

Bitumen and bituminous binders (acc. to Lit.4) Besides the type and origin of the crude oils these manufacturing methods have a significant influence on the properties of the bitumen. One very important differentiation characteristic of the bitumen grade is the hardness. During the distillation process the hardness of the bitumen grades can be controlled by the selection of the distillation conditions: The higher the distillation temperature and the lower the throughput rate of crude oil per unit of time, the more heavy oils are separated by distillation and the harder the recovered bitumen. Very hard bitumen (vacuum bitumen) can be recovered using a higher vacuum. Bitumen grades of medium hardness can be produced by intended mixing of hard and soft straight run bitumen. The precipitation and extraction methods produce hard bitumen grades by special temperature dependent airblowing procedures.

2.2 Chemical-physical properties Bitumen grades are clearly distinguished by their chemical-material composition and the molecularphysical structure. They form colloidal systems, in 84

Fluxed bitumen

Bitumen solutions

Bitumen emulsions

Polymer modified bitumen

Cut-back bitumen

Bitumen paint

Bitumen antistripping agent

Fig. 80 which high-molecular hydrocarbons and low-molecular constituents are present fine distributed in form of multiple and complex combined groups of substances. Structurally the groups of substances form a twophase system consisting of a coherent outer phase and an inner phase dispersed therein. The bitumen constituents of the coherent phase mainly consist of low-molecular high-boiling oils, known as malthenes. The dispersed phase is mainly a combination of high-molecular asphaltenes, which are highly polymerised and precipitate if the soluble petroleum resins are diluted when dissolving the bitumen in a solvent. The characteristic physical-chemical properties of the bitumen depend on the chemical-material composition, the quantitative ratio of the participating groups of substances and the temperature dependent stability of the molecular structure. The orientational structure of the molecules is subject to the influences of the intermolecular effective forces and the temperature. The orientational stability decreases with increasing temperature, the asphaltenes become mobile and the bitumen becomes softer. This high dependence on temperature determines the plastic behaviour of the

Compaction of asphalt

bitumen grades. This is why bitumen grades with a low proportion of asphaltenes are highly fluid at high temperatures, but turn brittle and hard at low temperatures. In contrast to this, bitumen with high proportions of asphaltenes and oil as well as a low proportion of petroleum resin reveals a highly plastic behaviour. The more stable the structure of the asphaltenes, the more plastic the behaviour of the bitumen. The characteristic influence of temperature also determines the rheological properties of the bitumen grades, the behaviour of which stretches via the visco-elastic range all the way to a plastic behaviour, similar to a Newton‘s fluid (Lit. 38). The rheological behaviour of elasto and visco-plastic substances is generally characterised by the rudimentary interrelationships (mass laws) between shearing stress, viscosity and of defor-

A= Viscous flow: shearing rate proportional to shearing stress. B= Pseudo-plastic or visco-elastic flow: shearing rate increasing overlinearly with shearing stress. The viscosity decreases with dropping shearing rate and increasing shearing stress. C= Dilatent flow: no proportionality between shearing rate and shearing stress, however, the viscosity

mation rate. For the rheological behaviour of bitumen these mass laws are schematically presented in Fig. 81. Ageing of bitumen is expressed through solidification and a loss of bonding strength. It is caused by chemical and / or physical processes, whereby time, heat, atmospheric oxygen and light with its ultraviolet rays are significant contributing factors. The temporal ageing of bitumen under the condition of rest causes solidification as a result of physical changes in the structure, which may be reversible under the influence of heat and / or mechanical loads. Temporal ageing depends e.g. on the loss of volatile oils, polymerisation of reactive bitumen constituents, oxidation by absorption of atmospheric oxygen and liberation of hydrogen.

may reach a constant value at high shearing rates. D= Plastic flow: characteristic yield value for the shearing rate, at which a flowing process starts. E= Thixotrope flow: yield value as under D, however, additionally a reversible decrese in viscosity after a shearing stress.

Schematic presentation of the flow behaviour of bitumen acc. to E.J.Barth (Lit. 32)

Fig. 81

2.3 Tests Chemical and physical methods are applied to examine the characteristics of bitumen. In accordance with the purpose these are testing methods for the identification and determination of the chemical-material composition, for the reason of safety when handling bitumen and for the determination of material specific

or engineering related behaviour. The material specific tests aim at the evaluation of the time and temperature dependent mechanical and rheological behaviour, including the resistance against ageing. The general principles of the testing methods are based on empirical knowledge, from which practically applicable sim85

Part 3

plified normative methods and requirements based thereon have developed (T 3, para. 2.4 and 3.3). Some important test methods are listed in table 25; regulations on testing technology see appendix A 4. A. Safety Flash point o.T. Water content

°C % by weight

B. Grade designation Penetration 100g/5s/25°C Ring-and-ball softening point Fraass breaking point

°C °C

C. Marking (origin) Density at 25°C Sulphur content Paraffin wax content Asphaltene content

% by weight % by weight % by weight

D. Rheological test method Viscosity 100, 135, 150°C mm2/s Penetration 100g/5s/0°C Penetration 200g/60s/0°C Penetration 50g/5s/46,1, 1°C Ductility 5cm/min, 0-25°C Temperature sensitivity Glass transition temperature

(cSt)

cm °C

E. Chemical-material composition Substance group classification UV analysis Ash content Insoluble by benzene Insoluble by cyclohexane Oliensis spot test Saponifiable proportions Neutralisation index Salinity F. Performance related tests Loss of weight 163°C/5h Properties after the loss of weight test: a) Penetration 100g/5s/25°C b) Softening point ring-and-ball c) Fraass breaking point d) Ductility 5cm/min, 0-25°C Stripping after immersion in water Loss of compressive strength Abrasion loss Foam height

% by weight % by weight % by weight % by weight % by weight mg/g mg/kg %

°C °C cm % % % by weight cm

Tab. 25: Test methods for bitumen (acc. to Lit. 32) Explanations to Tab. 25: The test methods listed under points A, B, D and F do not produce any physical magnitudes, but relative parameters.

To C: These test methods supplement the identification of the chemical-material composition and provide information on the origin of the grades of bitumen.

To A: The flash point identifies the temperature limit at which bitiumen is not yet inflammable. The permissible heating when handling bitumen (storage, pumping) as well as the temperature sensitive foaming reactions of bitumen are strongly influenced by the water content.

To D: The rheological characteristics of the bitumen grades are detected by the empirical test methods listed under point B as well as by viscometer tests. The temperature dependent ductility marks the yield point of the bitumen.

To B: These test methods are used to identify the bitumen grades (Fig. 82 and Tab. 26, 27). The penetration specifies the degree of hardness of the bitumen. The breaking point indicates the temperature at which the bitumen changes to brittle-hard. The softening point (test with ring and ball) is a temperature limit providing information on the deformability of bitumen in case of softening.

To E: These test methods enable conclusions on the chemical-material composition of the bitumen grades and on specific substance groups, whereby simple chemical characteristic tests as well as physical measuring methods (infrared spectral analysis, mass spectrograph, magnetic resonance analysis) are applied.

86

Compaction of asphalt

To F: The so-called performance related tests enable additional conclusions on the behaviour of bitumen during the material specific processing, e.g. mixing processes resting time and changing of properties (strength, drive, antistripping and bonding properties).

2.4 Material specific requirements * 2.4.1 Paving bitumen Paving bitumens are distillation products from the refining of crude oil. For their requirements the regulations DIN EN 12591 (as replacement for the previous regulations DIN 1995) developed in the course of European standardisation with a new ordering of the binder grades is valid; overviews see Tab. 26 and 27. DIN 1995

Determination of needle penetration

Fig. 82a

Penetration in 1/10 mm, by which a standardised needle loaded with 100 g penetrates into bitumen with a temperature of 25°C within 5 seconds.

Grade B 200 B 80 B65 B45 B 25

DIN EN 12591

SP RaB Penetration Grade SP RaB Penetration 37-44 160-210 160/220 35-43 160-220 44-49 70-100 70/100 43-51 70-100 49-54 50-70 50/70 46-54 50-70 54-59 35-50 30/45 52-60 30-45 59-97 20-30 20/30 55-63 20-30

Tab. 26 Binder grades and characterising requirements according to DIN 1995 (old) and DIN EN 12591 (new) * The tables in T 3, para. 2.4 origin from the currently valid technical regulations (appendix A 4)

Determination of the softening point RaB (Ring and Ball)

Fig. 82b

The temperature at which an evenly warmed up bitumen layer inside a brass ring deforms under the weight of a steel ball.

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2.4.2 Special bitumens and bituminous binders Requirements acc. to DIN 1995 (s. appendix A 4 and Lit. 39) Fluxed bitumen Flux bitumen is manufactured by adding heavy-liquid flux oils to paving bitumen. These oils reduce the viscosity, enabling warm laying of fluxed bitumen. Bitumen emulsions Bitumen emulsions consist of colloidal solutions of medium hard straight-run bitumen in water, whereby the fine distribution (emulsification) of the binding agent is achieved by adding emulsifying agents and lyes. The alkaline or acidy emulsification reduces the interfacial tension between the bitumen particles and water. Addition of stabilising agents (fine particle clays, betonites) causes the formation of film-like protective sheaths around the bitumen particles, which reduces the interfacial tension even further.

Bitumen grades Penetration at25°C DIN EN 1426 Softening point DIN EN 1427 Resistance to hardening at 163°C (DIN EN 12607-1/3) -Change of mass maximum + -Remained penetration, minimum -Softening point after hardening, minimum Flash point minimum (DIN EN 22592) Solubility, minimum (DIN EN 12592) Wax paraffin content (DIN EN 12606-1) Fraaß breaking point maximum (DIN EN 12593) Increase in softening point after hardening, maximum

Emulsions are graded according to their viscosity and breaking time (stability up to the desintegration into bitumen and aqueous phase). Bitumen emulsions are processed in cold liquid condition. Cold bitumen Cold bitumen (petroleum cut-back bitumen) is manufactured as bitumen solutions using soft to medium hard paving bitumen and adding volatile solvents. Since this reduces the viscosity of the bitumen, these materials can be processed in cold liquid condition. Polymer modified bitumen The properties of bitumen can be modified by adding synthetic polymeric materials (elastomeres, thermosetting plastics and thermoplasts acc. to DIN 7724) or by polymeric waste or side products. These materials must be used according to special technical delivery conditions for the hot laying of asphalt layers and for surface treatments; see appendix A 4.

0,1mm

20/30 20-30

30/45 30-45

50/70 50-70

70/100 70-100

160/220 160-220

°C

55-63

52-60

46-54

43-51

35-43

0,8

1,0

%

0,5

%

55

53

50

45

37

°C

57

54

48

45

37

°C

240

230

% (m/m) %

99,0

°C

-5

°C

2,2

8

Tab. 27: Requirements for paving bitumen acc. to DIN EN 12591 88

220

-6

-10 9

-15 11

Compaction of asphalt

3.

Asphalt*

3.1 Mineral aggregates

specified in technical product specifications (s. appendix A 4).

The asphalt consists of mineral aggregates and bitumen or bituminous binders as described in T 3, para. 2. The general requirements for mineral aggregates used in highway and transportation engineering are

Important aggregate product sizes: a) non-crushed aggregates: gravel and natural sand, b) crushed aggregates: crushed rock, chippings, crushed sand, high-grade chippings, high-grade crushed sands, stone dust, filler (Tab. 28).

Natural sand Gravel

Crushed sands/chippings Crushed rock

Natural sand 0/2 mm Gravel 2/4 mm Gravel 4/8 mm Gravel 8/16 mm Gravel 16/32 mm Gravel 32/63 mm -

Crushed sand/chippings0/5 mm Chippings 5/11 mm Chippings 11/22 mm Chippings 22/32 mm Crushed rock 32/45 mm Crushed rock 45/56 mm

Stone dust High-grade crushed sand High-grade chippings Stone dust 0/0,09 mm High-grade crushed sand 0/2 mm High-grade chippings 2/5 mm High-grade chippings 5/8 mm High-grade chippings 8/11 mm High-grade chippings 11/16 mm High-grade chippings 16/22 mm -

Tab. 28: Product sizes for mineral aggregates The technical regulations, which apply particularly for asphalt pavements in highway and transportation engineering, differentiate between natural aggregates (crushed rock, crushed and non-crushed gravel, sand) and artificial ggregates (slags from blast furnaces and steel plants as well as metal slags). Industrial side products and recycling materials are alternative highway construction materials. Requirements concerning maximum density, compressive strength and impact resistance see Tab. 29 The aggregates used in surface courses and gritting must have an additional polishing resistance. On the single-size aggregate 8/10 mm the polishing resistance is evaluated with the PSV-test (Polished Stone Value), representative for all high-grade coarse fractions (see T 3, para. 3.3.1); polishing tests acc. to TPMin-StB (appendix A 4).

The tables in T 3, para. 3 are taken from the currently effective regulations (appendix A 4) in connection with Lit. 39 and 40. *

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Rock/ rock group

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

1 Granite, granodiorite, syenite Diorite, gabbro Rhyolite, rhyodacite, trachyte, phonolite, micro-diorite, andesite Basalt, melaphyre Basaltic lava Lava slag Diabase Lime rock, dolomite rock Graywacke, quartzite, vein quarz, quartz, sandstone Gneiss, granulite, amphibolite, serpentinite Gravel, crushed Gravel, round Metal slag MHS-1 Metal slag MHS-2 Blast furnace slag HOS-A Blast furnace slag HOS-B Blast furnace slag HOS-C Steel plant slag Ash from incineration of domestic waste Recycling materials

Max. density Crushed rock ρR g/cm³ 2 2,60 – 2,80 2,70 – 3,00 2,50 – 2,85 2,85 – 3,05 2,40 – 2,85 2,75 – 2,95 2,65 – 2,85

Compress. strength

Resistance against impact Crush. rock Chipp./gravel SD10 SZ 8/12 M.-% 1) M.-% 2) 4 5

βD N/mm² 3 160 – 240 170 – 300 180 - 300 250 – 400 80 – 150 Requirements acc. to MLS 3) 180 – 250 80 – 180

10 – 22 8 – 18

12 – 27 10 – 20

9 – 22 7 – 17 13 – 20

11 – 23 9 – 20 16 – 22

7 – 17 16 – 30

9 – 20 17 – 28

2,60 – 2,75

120 – 300

10 – 22

12 – 27

2,65 – 3,10 2,60 – 275 2,55 – 2,75

160 – 280 -

10 – 22 -

12 – 27 14 – 24 17 – 34

3,40 – 4,00

> 150

15 – 24

18 – 25

2,60 – 3,50

> 80

20 – 33

22 – 34

2,40 – 2,80

-

15 – 24

18 – 25

2,10 – 2,60

-

20 – 33

22 – 34

2,10 – 2,60 3,20 – 3,60

-

No tests and parameters 12 – 29

10 – 26

-

-

≤ 33

≤ 40 ≤ 28

Explanations to Tab 29: 1) SD 10 Resistance of crushed rock against crushing during the impact test (DIN 521156-2) 2) SZ 8/12 Resistance of chipping or gravel ageinst crushing during the impact test (DIN EN 1097-2) 3) MLS Information leaflet on lava slag in highway and transportation engineering Tab. 29: Requirements for mineral aggregates acc. to German TL Min 2000

90

Compaction of asphalt

3.2 Asphalt for base courses In their function of main load bearing elements in highway pavements the asphalt base courses protected by surface course and binder course have load distributing functions. The mixture consists of aggregates and paving bitumen as binder (T 3, para. 3.1 and 2.4.1). Mixture types are classified under specific aspects of the intended use: for components and properties refer to Tab. 30. Requirements for the asphalt base course: The thickness of each course or layer must be at least 8 cm, 6 cm for regulating courses and at least 2.5 times the diameter of the largest particle.

Asphalt base courses are laid down and compacted hot (Fig. 83). Experience values for lowest and highest mixture temperatures according to technical regulations: Binder grades: Temperature °C1) B 80 120 – 180 B 65 120 – 180 B 45 130 – 190 Upper temperature when receiving the mixture at the mixing plant or silo, lower temperature for the time of laying. 1)

Degree of compaction for mix type CS, C, B: > 97% for mixture type A, AO: > 96% Deviation from specified thickness: < + 1,0 cm Unevenness under a 4 m straight edge: < 1,0 cm Laying thickn./weight mean value, undercut: < 10% Laying thickn. single value, undercut: < 2,5 cm

Compaction of the asphalt base course with using a 8 t VARIOMATIC roller Type of mixture

Particle size

Particles > 2 mm

Particles < 0,09 mm

Coarsest particle minimum

Oversize particle maximum

Minimum binder content

1 AO A B C CS

mm 2 0/2 bis 0/32 0/2 bis 0/32 0/22; 0/32 0/22; 0/32 0/22; 0/32

weight % 3 0 bis 80 0 bis 35 über 35 bis 60 über 60 bis 80 über 60 bis 80

weight % 4 2 bis 20 4 bis 20 3 bis 12 3 bis 10 3 bis 10

weight % 5 10 10 10 10 10

weight % 6 20 20 10 10 10

weight % 7 3,3 4,3 3,9 3,6 3,6

Marshall stability at 60°C minimum kN 8 2,0 3,0 4,0 5,0 8,0

Fig. 83

Marshall flow

Air void content

mm 9 1,5 bis 4,0 1,5 bis 4,0 1,5 bis 4,0 1,5 bis 4,0 1,5 bis 5,0

Vol.-% 10 4,0 bis 20,0 4,0 bis 14,0 4,0 bis 12,0 4,0 bis 10,0 5,0 bis 10,0

Explanations to Tab. 30: 1) Mixture type AO only for full depth asphalt pavements 2) Mixture type A only for lower layer of base course 3) Mixture type CS for construction class SV and traffic areas subject to special loads: minimum 60% crushed particles bigger than 2 mm, ratio of crushed sand to natural sand at least 1:1 4) Mixture types B, C, CS for all other pavements or construction classes (B limited) 5) For the use of paving bitumen 6) Determination on Marshall samples (see T 3, para. 4.1) Tab. 30: Components and properties of bearing course mixtures 91

Part 3

3.3

Asphalt for surfacing

designed binder course and base course, are recommendet for the use for construction classes SV, I, II, III and St SLW.

3.3.1 General requirements The required composition of the asphalt for surface courses and binder courses depends substantially on the type of traffic load and the construction class. The overview in Tab. 31 specifies nominal aggregate sizes for asphalt binder courses and surfaces courses, as well as for various types of mixtures, depending on the traffic load. The mixtures marked S, which are characterised by a higher stability and require a sufficiently Traffic load normal or special special normal

Constr. class/ traffic area SV + 1

Asphalt binder 0/22 S

Asphalt concrete -

Stone mastic asphalt 0/11 S

II III + St SLW III + IV V +VI St LLW, cycle and sidewalks

0/16 S 0/16 s 0/16 -

0/11 S 0/11 S 0/11 0/11, 0/8 0/11, 08, 0/5

0/8 S 0/11 S, 0/8 S 0/8 0/8, 05 0/8, 0/5

Gussasphalt 0/11 S 0/11 S 1) 1) 1)

Explanations to Tab. 31: Figure1) Use only in exceptional cases for gussasphalt with aggregate sizes of 0/8 or 0/11 mm, for cycle paths and sidewalks 0/5 or 0/8 mm. Tab. 31: Rock particle fractions for asphalt binders and surface courses in dependence on loads

The permissible laying thickness for the relatively thin surface courses depends mainly on the particle size of the mixture (Tab. 32), independently from the standardised thickness specified in T 3, para. 1. mm cm 0/5 1,5 – 3,0 0,8 2,5 – 4,5 0/11 3,0 – 6,0 0/11 S 4,0 – 5,0 0/16 S 4,0 – 7,5 Stone mastic asphalt 0/5 1,0 – 3,5 0/8 S 2,0 – 5,5 0/11 S 2,5 – 7,0 Tab. 32: Experience values of mat thicknesses for surface courses Asphalt concrete

92

The stability of asphalt surfacings (asphalt binder courses and surface courses) made of rolled asphalt can be improved by a favourable adjustment of the proportions of chippings and crushed sand as well as the use of high-grade aggregates with a higher proportion of crushed surfaces, whereas the durability can be enhanced by a perfect adaptation of the binder content to the air void content (Lit. 35). Hard binders or low binder contents, as may be considered for high traffic loads, contribute to the potential of crakking. The stability and durability of gussasphalt depends to a great extent on the interaction between binder and filler and their homogeneous distribution in the chippings/sand particle skeleton. For the polishing resistance of high-grade chippings in surface courses and for the spreading of chippings certain PSV-values are demanded:

Compaction of asphalt

-

Construction class III – VI with normal traffic load PSV > 43 Construction class SV, I, II as well as for highways of construction class III subject to special loads PSV > 50

The deformation resistance of asphalt surface courses is substantially influenced by the temperature of the mixture and, during laying, by its cooling and reheating (Lit. 36). During mixing and laying certain maximum and minimum temperatures must therefore be complied with, in dependence of binder grade and type of mixture (Tab. 33) Type of binder

B 25 B 45 B 65 B 80 B 200 FB 500

Asphalt binder

Asphalt concrete (hot laying)

130-190 120-180 120-180

140-190 130-180 130-180 120-170

Stone mastic asphalt

150-180 150-180 120-170

Gussasphalt

200-250 200-250 200-250

Asphalt mastic

180-220 180-220 180-220 170-210

Combined surface base course

120-180 100-170

Asphalt concrete (warm laying)

60-130

Explanations to Tab. 33: 1. The top temperature when receiving the mixture at the mixing plant or silo, the lower temperature for the time of laying. 2. When exceeding the top temperature bitumen may harden and lose its bonding strength. When cooling down below the lower temperature the viscosity of bitumen increases. This may considerably impair the workability and rolling may become in-effective.

Tab. 33: Reference values for permissable mixture temperatures for asphalt binder and asphalt surface courses Further information on the effect of temperature see T 3, para. 4.2.2.

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Part 3

3.3.2 Binder course asphalt Components and properties as well as course requirements see Tab. 34. 0,22 S 0/16 S High-grade chip., high grade sand, stone dust mm 0/22 4 to 8 4 to 8 70 to 80 70 to 75 > 25 > 25 < 10 < 10 1:0 1:0

Mineral aggregates

Particle size fraction Part. prop. < 0,09 mm % by weight Part. prop. > 2 mm % by weight Part. prop. > 8 mm % by weight Part. prop. > 11,2 mm % by weight Part. prop. > 16 mm % by weight Part. prop. > 22,4 mm % by weight Crushed sand/natural sand ratio Binder Grade B 45, PmB 45 Binder content % by weight 4,0 to 5,0 Mixture Air void content of the Marshall specimen Vol.-% 5,0 to 7,0 Course Course thickness cm 7,0 to 10,0 or laying weight kg/m2 170 to 250

Degree of compaction

%

> 97

0/16 0/11 High-grade chip., high-grade crushed sand, natural sand, stone dust 0/16 0/16 0/11 3 to 9 3 to 9 60 to 75 50 to 70 > 20 > 20 < 10 < 10 > 1:1 > 1:1

B 45, PmB 45 4,2 to 5,5

B 65, B 80 4,0 to 6,0

B 65, B 80 4,5 to 6,5

5,0 to 7,0

3,0 to 7,0

3,0 to 7,0

5,0 to 8,5

4,0 to 8,5

125 to 210

95 to 210

> 97

> 97

only for profil regulating, not for classes SV. I to III and highways with special loads > 97 for thickn. up to 3 cm

Tab. 34: Binder course asphalt

The mixture for asphalt binder courses is hot manufactured and laid by pavers and compacted with rollers (Fig. 84). Experience values for lowest and highest mixture temperatures acc. to the technical regulations: Binder grade B 80 B 65 B 45

Temperature °C 1) 120 – 180 120 – 180 130 – 190

The top temperature when receiving the mixture at the mixing plant or silo, the lower temperature for the time of laying. 1)

94

Compaction of an ashalt binder course using a 2.5 t vibratory roller

Fig. 84

Compaction of asphalt

3.3.3 Asphalt concrete Components and properties as well as course requirements see Tab. 35. Mineral aggregates Paricle size fraction mm Part. prop. < 0,09 mm % by weight Part. prop. > 2 mm % by weight Part. prop. > 5 mm % by weight Part. prop. > 8 mm % by weight Part. prop. > 11,2 mm % by weight Part. prop. > 16 mm % by weight Crushed sand/natural sand ratio Binder Grade B 65 Binder content Gew.-% Mixture Air void content of the Marshall specimen Vol.-% a class SV, I, II, III S, IV S, u. St SLW b class II u. IV c. class V, VI, rural roads Course Course thickness cm or laying weight kg/m2 Degree of compaction % Air void content Vol.-%

0,16 S 0/16 6 to 10 55 to 65 25 to 40 > 25 < 10 > 1:1

0/11 S 0/11 0/8 High-grade chipping, high grade crushed sand, natural sand, stone dust 0/11 0/11 0/0 6 to 10 7 to 13 7 to 13 50 to 60 40 to 60 35 to 60 > 15 15 to 30 > 15 < 10 < 10 < 10 > 1:1 > 1:11) > 1:11)

B 65 5,2 - 6,5

B 80 5,9 - 7,2

3,0 to 5,0

3,0 to 5,0

0/5 0/5 30 to 50 > 10 -

B 80 6,2 - 7,5

B 80 6,4 - 7,7

6,8 - 8,0

2,0 to 4,0 1,0 to 3,0

2,0 to 4,0 1,0 to 3,0

1,0 to 3,0

5,0 - 6,0

4,0 - 5,0

3,5 - 4,5

3,0 - 4,0

2,0 - 3,0

120 - 150 > 97 < 7,0

95 - 125 > 97 < 7,0

85 - 115 > 97 < 6,0

75 - 100 > 97 < 6,0

45 - 75 > 96 < 6,0

Tab. 35: Asphalt concrete 1)

Construction class III

The mixture is hot manufactured, laid by pavers and compacted with rollers (Fig. 85). Spreading of crushed sand or fine chippings onto the hot surface before or during rolling enhances the initial grip of the surface course. Asphalt concrete can be laid warm in exceptional cases, e.g. as surface courses for low volume highways and agricultural roads.

Compaction of ashalt concrete using a 12 t VARIOMATIC roller

Fig. 85 95

Part 3

3.3.4 Stone mastic asphalt Components and properties as well as course requirements see Tab. 36. Mineral aggregates Particle size fraction mm Part. prop. < 0,09 mm % by weight Part. prop. > 2 mm % by weight Part. prop. > 5 mm % by weight Part. prop. > 8 mm % by weight Part. prop. > 11,2 mm % by weight Crushed sand/natural sand ratio Binder Grade Binder content % by weight Stabilising additives Content in mixture % by weight Mixture Marshall specimen: Compaction temperature °C Air void content Vol-% Course Course thickness cm Laying weight kg/m2 Course thickness cm Laying weight kg/m2 Degree of compaction % Air void content Vol.-%

0,11 S 0/8 S High-grade chip., high grade sand, stone dust 0/11 0/8 9 to 13 10 to 13 75 to 80 75 to 80 60 to 70 > 55 > 40 < 10 < 10 1:0 1:0 B 65 > 6,5

0/8 0/5 High-grade chip., high-grade crushed sand, natural sand, stone dust 0/8 0/5 8 to 13 8 to 13 70 to 80 60 to 70 45 to 70 < 10 < 10 > 1:1 > 1:1

B 65 > 7,0

B 80 > 7,0

B 80 > 7,2

0,3 bis 1,5 135 + 5 3,0 to 4,0

135 + 5 3,0 to 4,0

135 + 5 2,0 to 4,0

135 + 5 2,0 to 4,0

3,5 to 4,0 85 to 100 2,5 to 5,0 60 to 125

3,0 to 4,0 70 to 100 2,0 to 4,0 45 to 100 > 97 < 6,0

2,0 to 4,0 45 to 100 -

1,5 to 3,0 35 to 75 -

Tab. 36: Stone mastic asphalt High binder contents with stabilising additives are characteristics for this mixture. The hot mixture is laid down by pavers and, due to its composition of high stiffness, it must be intensively compacted with heavy rollers. Crushed sand or chippings spread over the hot surface and rolled in enhances the initial skid resistance (Fig. 86).

Compaction and gritting of stone mastic asphalt

96

Fig. 86

Compaction of asphalt

3.3.5

Gussasphalt

Components and properties as well as course requirements see Tab. 37. Mineral aggregates

0,11 S

0/11 0/8 0/5 high-grade chip., high-grade crushed sand, natural sand, stone dust 0/8 0/5 22 to 32 8 to 13 40 to 50 60 to 70 > 15 > 10 < 10 -

Particle size fraction mm 0/11 Part. prop. < 0,09 mm % by weight 20 to 30 Part. prop. > 2 mm % by weight 45 to 55 Part. prop. > 5 mm % by weight Part. prop. > 8 mm % by weight > 15 Part. prop. > 11,2 mm % by weight < 10 Crushed sand/natural sand ratio > 1:2 Binder Grade B 45 B 45 Binder content % by weight 6,5 to 8,0 6,8 to 8,0 Softening point RaB after extraktion °C < 70 < 70 < 70 Mixture Indentation test 5 cm2 at 40°C on sample cube after 30 min. mm 1,0 to 3,5 1,0 to 5,0 1,0 to 5,0 Increase after another 30 min. mm < 0,4 < 0,6 < 0,6 Course Course thickness (incl. gritting material) cm 3,5 to 4,0 2,5 to 3,5 or laying weight (incl. gritting material kg/m2 80 to 100 65 to 85 Gritting material/quantity High-grade chippings 2/5 mm High-grade chippings 2/5 and/or 5/8 mm High-grade crushed sand or natural sand

7,0 to 8,5 < 70

1,0 to 5,0 < 0,6 2,0 to 3,0 45 to 75 5 to 8 kg/m2 15 to 18 kg/m2 2 to 3 kg/m2

Tab. 37: Gussasphalt The mixture is hot manufactured, transported to the site in heated transportation tanks with stirring equipment and laid down by means of a machine driven screed. In the areas of the traffic lanes the hot surface is gritted with chippings, in other areas the grip is enhanced with sand.

97

Part 3

3.3.6 Asphalt mastic

3.3.8 Natural asphalt and modified asphalt

Components and properties as well as course requirements see Tab. 38.

(1) Natural asphalt

0/2 Natural sand or natural sand and high-grade crushed sand, stone dust Particle size fraction mm 0/2 Part. prop. < 0,09 mm % by weight 30 to 60 Part. prop. > 2 mm % by weight < 15 Binder Grade B 65, B 80 Binder content % by weight 13,0 to 18,0 Mixture Softening point Wilhelmi °C suitability test Course Laying weight of asphalt mastic kg/m2 15 to 25 Mineral aggregates

Tab. 38: Asphalt mastic The mixture is hot manufactured, transported in motorised boilers with permanent stirring and distributed after pouring. Binder coated high-grade chippings are spread over the hot surface and immediately rolled into the mastic down to the substrate. 3.3.7 Combined surface-base-courses Components and properties as well as layer requirements see Tab. 39 Mineral aggregate Particle size fraction Part. prop. < 0,09 mm Part. prop. > 2 mm Part. prop. >11,2 mm Part. prop. >16 mm Binder Grade Binder content Mixture Air void content of Marshall specimen Marshall stability Marshall flow Course Coursethickness or laying weight Degree of compaction Air void content

mm % by weight % by weight % by weight % by weight % by weight

0/2 Natural sand or natural sand and high-grade crushed sand, stone dust 0/16 7 to 12 50 to 70 10 to 20 < 10 B 80, B 200 > 5,2

Vol.-% kN mm

1,0 to 3,0 > 4,0 2,0 to 5,0

cm kg/m2 % Vol.-%

5,0 to 10,0 120 to 250 > 96 < 7,0

Tab. 39: Combined surface-base-courses Combined surface-base-courses are used as single layer pavements on low volume roads as well as for cycle paths and sidewalks. The mixture is manufactured, placed and compacted hot. 98

Natural asphalt is added to gussasphalt, stone mastic asphalt and mortar enriched asphalt concrete among others, e.g. as natural Trinidad-asphalt (épuré, flour). These additives can enhance the stability of the surface course or binder course and have a positive effect on processing and compaction. (2) Elastomere modified asphalt The mechanical and elastic properties of rolled asphalts can be modified by adding caoutchouc or rubber. This improvement is particularly related to elasticity, adhesion strength, ageing resistance against water and weather influences as well as fatigue resistance. (3) Polymer modified asphalt The use of polymer modified bitumen or the addition of polymeres enhance the adhesive properties, the stability and elasticity and, when increasing the binder content, even the ageing resistance and durability against the influence of water and weather.

3.3.9 Asphalts for special construction methods (1) Vibro asphalt (rolled poured mastic asphalt) The mixture consists of approx. 60% chipping, 10% filler, equal proportions of crushed and natural sand as well as approx. 6.4% binder B 45. It is mixed at a temperature of approx. 230°C and transported with insulated special trucks. During laying with a paver the mixture is liquified and compacted by vibration and chippings are subsequently spread over this poured mastic asphalt like surface and rolled in. (2) Drainage asphalt (porous asphalt) The mixture for drainage asphalt surface courses is combined of a high quantity of chippings with a highly resistant binder and mortar. It is then applied as a surface course on a dense substrate or an additional

Compaction of asphalt

waterproofing layer. This type of asphalt is characterised by a higher content of air voids which enhances the drainage between the surface of the carriageway and the vehicle tires. It also changes the thermal conductivity and the low temperature performance. (3) Cold laying in thin layers Cold mixed asphalt consisting of mineral aggregates 0/3 to 0/8 mm, water, polymer modified cationic bitumen emulsion and additives is mixed and placed with a laying weight of 10 to 30 kg/m² (dry mass), using special self-propelled mixing and paving equipment. The necessary bonding between the layers requires an absolutely clean substrate. (4) Hot laying in thin layers Hot placed thin layers consist of asphalt concrete, stone mastic asphalt or gussasphalt and are applied with a laying weight of 30 to 50 kg/m², depending on load and condition of the substrate.

3.4 Asphalt veneer coats Asphalt veneer coats are placed on surface courses in order to seal these surfaces or to enhance their grip. They are applied as so-called surface treatment or in form of thin layers by cold laying. This treatment is applied as protection against the influence of weather and traffic loads and against moisture, mainly on low volume traffic areas (construction classes IV to VI), as well as for sidewalks and yards, but not as an independent surface course. For surface treatment the substrate or the previously spread chippings are sprayed with a bituminous binder agent and subsequently gritted once or twice with raw or coated chippings. Cold placed thin layers are mixtures consisting of mineral aggregates (high-grade chippings, high-grade crushed sand and reclaimed filler), polymer modified cationic bitumen emulsions, additives and water; see T 3, para. 3.3.9.

99

Part 3

4. Compaction characteristics of asphalt 4.1 Fundamentals After laying asphalt layers must be compacted to achieve stability and reduce air voids to a minimum, in order to avoid subsequent compaction or deformation under the influence of traffic loads and climatic conditions, which could impair the suitability of traffic areas or reduce their durability. Purpose of the compaction of asphalt layers is therefore the production of a load related high density and a reduction of the air void content in the asphalt mixture that is adapted to the required binder content. Compaction requirements see tables in T 3, para. 3.2 and 3.3 as well as para. 4.4. The required compaction work depends on the properties and workability of the asphalt mixture, as well as the thickness of the asphalt layer to be compacted. The compaction effect is influenced by the laying conditions as well as by the effectiveness of compaction machine and compaction technique. The compaction characteristics differ considerably in dependence on the composition and the temperature dependent deformation resistance of the asphalt mixture. The term compactibility describes the temperature dependent characteristic of increasing the density of an asphalt under the influence of defined compaction work. In dependence on the deformation resistance a differentiation between easy and difficult to compact mixtures can generally be made: a) Easily compactible mixtures show a high increase in density right at the beginning of the compaction process, followed by an early end of this increase. b) Relatively low density increase rates from the beginning right to the end of the compaction process are characteristic for difficult to compact mixtures, whereby a considerably higher number or more powerful compaction passes and a longer work process is required. In both cases the increase in density decreases over the course of the compaction process. When considering that the bulk density ρA = f (Z, A, T) is a function of mixture composition Z, compaction work A and temperature T, the interrelations can be combined in a formula. According to Lit. 31, 34 and the 100

leaflet on the compaction of rolled asphalt mixtures is described by an exponential formulation, derived from the bulk densities ρA of Marshall specimen (T 3, para. 4.2) produced by compaction work S of various extent according to DIN 1996, T. 4. This exponential regularity has the following form -S C

ρA(S) = ρA∞-(ρA∞-ρAO) . e

[g/cm3].

ρA(S) = Bulk density in dependence on the performed compaction work in g/cm3, S = Compaction work [42 Nm], number of compaction blows per side of specimen, ρA∞ = max. mathematically achievable bulk density in g/cm3 (ρA(S = ∞ )). ρAO = math. initial bulk density at the beginning of the compaction process in g/cm3 (ρA(S = 0 )). C = Compaction resistance determined by change in density.

Compaction resistance C and bulk density ρA in dependence on compaction work for two mixture variants with Fig. 87 identical initial and final density

Compaction of asphalt

According to Fig. 87 the compaction resistance C characterises the permanent change in bulk density ρA during the compaction process or the interrelation between density and compaction work S. The so-called relative compaction potential is defined as a derived magnitude: P = (ρA ∞ - ρA o ) / ρA∞ By definition the density is mathematically determined as quotient from mass and volume V. ρA (S) =

m = F = d(S) =

m V (S)

=

m F · d (S)

4.2

Mass of specimen, Base of form cylinder (Marshall) Thickness of specimen depending on the applied compaction work.

Since m and F are of constant size, the change in density in dependence on the compaction work is only characterised by the thickness of the specimen or its reciprocal value 1/d. The above mentioned exponential approach for ρA can also be applied to the reciprocal value of the specimen thickness 1/d: 1 d(S)

=

1 d∞

–

[

1 d∞

Similar regularities as for the simulation of compaction in a laboratory apply analogue for asphalt compaction with rollers after the laying of asphalt. For a practical application of laboratory results the number of compaction blows must be converted to the number of rolling passes of the compaction machine using so-called equivalent rolling work. This equivalent rolling work specifies the required double-blows performed with a Marshall hammer to achieve an identical change in density on the specimen under identical conditions as by a rolling pass with the compaction machine.

–

1 do

]

e

–S D

[mm-1]

d (S) = Specimen thickness in dependence on the applied compaction work in mm, S = Compaction work [21 Nm], number of compaction blows, d∞ = mathematically determined achievable minimum specimen thickness in mm (d(S = ∞)), do = mathematically determined initial thickness at the beginning of the compaction process in mm (d(S=0)), D = Compaction resistance determined by the change in thickness

Test methods

4.2.1 Marshall stability and flow Marshall stability and Marshall flow are used as parameters for the resistance of hot placeable rolled asphalt mixtures against mechanical loads. The corresponding test methods (DIN 1996, T. 11) are most suitable for hot placed mixtures graded in accordance with the asphalt concrete principle, containing not more than 15% particles bigger than 22.4 mm. These methods are therefore not suitable for gussasphalts and mastic asphalt. The Marshall stability is the maximum force related to specimen height of 63.5 mm, which is measured during a compression test on a cylindrical specimen with partly restricted lateral expansion. During the compression test the specimen is positioned between pressure shells (Fig. 88). From the force-deformation diagram the max. recorded force can be determined as Marshall stability on 0.1 kN (Fig. 88).

Test specific dimensions for the sizes C, D, see T 3, para. 4.2

101

Part 3

mm, normal height 63.5 mm). The hot mixture is compacted inside a cylindical mould from each side of the specimen with 50 blows of a 4.5 kg drop hammer falling from a height of 46 cm. Layer thickness, bulk density and air void content of the specimen are thereby evaluated as a measure for the achieved compaction. The maximum bulk density achieved by this test serves also as reference value for the determination of the degree of compaction of the laid and compacted asphalt (DIN 1996, T. 7). This parameter specifies the percentage of the bulk density ρA which must be achieved or is required as standard after laying and compacting the asphalt. For the determination of the achieved degree of compaction cores or other geometric samples must be taken.

4,5 kg Falling weight 460 mm Falling height Standard: 50 Impacts per side Modified: 75 Impacts per side

Schematic example for the compression device Fig. 88 by Marshall (DIN 1996) The Marshall flow is the deformation in direction of load application measured when the maximum force is reached. From the diagram the flow can be determined as a distance in 0.1 mm, situated between the distinct deviation of the curve from the neutral axis and the point of the maximum force (Fig. 88). 4.2.2 Compactibility The standard compaction work required for the preparation of specimens in accordance with the Marshall test method (DIN 1996, part 4 and Lit. 33) is used as comparison and reference magnitude for the compactibility of asphalt mixtures (Fig. 86). Marshall specimens are prepared using a standard method (diameter 101.6 102

Specimen Bulk densitiy Bulk densitiy drill core

ρA ρA‘

ρ Degree of compact. k = ρA‘ A

Marshall method for the determination of the compactilitiy of asphalt mixtures

Fig. 89

On the basis of the theoretical regularities described in T 3, para. 4.1 the compaction resistances C and D of rolled asphalt mixtures can be examined by using the interrelation between change in density or the change in thickness of Marshall specimen in dependence on the compaction work (Lit. 31, 33, 34 and leaflet on the compaction of asphalt).

Compaction of asphalt

During the test procedure for the determination of the change in thickness, the thickness of the specimen is continuously measured after each compaction blow. The reciprocal values for these thicknesses are approximised with the help of the function specified in T 3, para. 4.1, in dependence on the compaction work. Magnitude D is determined as measure for the compactibility. In test method for the detection of the change in density, Marshall specimen are prepared with a different number of compaction blows from each side, in order to determine the bulk densities. The bulk densities are approximised in dependence on the number of blows, using the exponential function in T 3, para. 4.1. The interrelation is then quantified with the help of magnitude C. The dimension of magnitude C complies with the test specific compaction work and, for 2 blows per specimen side with a dropping mass of 45.4 N dropping from a height of 0.46 m, results in: 2 x 45,5 x 0,46 = 42 Nm. 4.3 Influencing factors In laboratory simulation as well as during the laying of asphalt the compaction process is influenced by a number of factors, which interact integrally in a very complicated manner and can only be examined separately in the analysis. Both the mixture components as well as the compaction temperatures belong to the factors with highest influence (Lit. 33, 34, 36 and leaflet on the compaction of asphalt).

4.3.1 Composition of mixture By experience, mixture components and mineral aggregates in particular have the most significant influence on the compaction resistance (Fig. 90). The mechanical properties of the mineral aggregates influence the compactibility in such a way, that, due to their lower inherent friction and interlocking resistance, round particle mixtures are easier to compact than mixtures consiting of crushed particles. Sand particle and chipping fractions thereby have the strongest effect, whereby the compaction resistance mainly rises with the increasing proportion of crushed sand or a high content of chippings. With a decreasing coarse particle fraction bigger than 2 mm the so-called mortar components (binder, sand, filler) gain a higher influence with mixture types composed according to the asphalt concrete principle, whereas the compaction resistance does not increase to such an extent when increasing the coarse particle content. Mixtures with a very high proportion of chippings (stone mastic asphalt and drainage asphalt) are also mainly influenced by the high mortar content. The influence of the filler with its stabilising effect on the compactibility of the mixture is only of minor significance, but is effective in the entirety of the mortar components, whereby the compaction resistance of the mixture decreases with increasing mortar content. The compaction resistance is highly influenced by the binder content, however, the grade of binder is only of minor significance. The sliding resistance on the contact faces decreases with increasing thickness of the binder film on the particle surfaces, which enhances the compaction of the mixture.

Easy to compact: Natural sand

Low chip. cont.

Small max. part. size

High filler content

Crushed sand

High chip. cont.

Big max. part size

Low filler content

Difficult to compact: Pictorial representation of the influence of mineral aggregates on the compaction resistance

Fig. 90 103

Part 3

The highly temperature dependent properties of the bituminous binders in turn result in a significant influence of the temperature on the compaction characteristics of the mixture. The temperature of the mixture is a very sensitive influential factor, which has an effect in combination with the mixture composition and the temperature dependent variable viscosity of the binder: With increasing compaction resistance the mixture specific critical compaction temperature rises to a level, where an effective compaction of the mixture is no longer possible. For a difficult to compact mixture type the compaction temperature must therefore not drop below a critical limiting value. The required minimum temperature is considerably higher than for easily compactible material. The critical temperature limits must be carefully evaluated by suitability tests and monitored during the laying and compaction of the asphalt by measurements. Under aspects of compaction practice the temperature shall be as high as permissible at the beginning of compaction work, since this is of advantage for the compaction effect. The top temperature limit is specified because of the fact that the mixture must remain stable under the influence of the roller and that an effective particle redistribution and reduction of air voids occurs during compaction must be accomplished without any shoving or lateral displacement of the mixture. Depending on the grade of binder the normal temperature when tipping the mixture into the paver is 150 – 180°C, the compaction temperature range approx. 130 – 170°C. In the temperature range between 90 - 100°C compaction must be finished, because a further drop in temperature will result in an excessive increase of the binder viscosity, making compaction work almost ineffective (Fig. 91).

104

Compaction effort

4.3.2 Influence of the temperature

End of Compaction most favourable compaction temperature Start of compaction

Mixture temperature Compaction effort and temperature limits for mixtures with bitumen B 65 bis B 200

Fig. 91

The temperature influence has an effect on the layer thickness of the asphalt mixture. The thicker the layer, the slower it cools down, the longer the mixture remains compactible and the less weather sensitive are laying and compaction.

Compaction of asphalt

5. Application and performance of BOMAG compaction technology in asphalt construction 5.1 Planning and fields of application The laying and compaction of asphalt layers requires thorough planning and preparations. Focal points of this planning are the arrangement of temporal and area related sequences of laying and compaction work as well as the decisions concerning the use of appropriate equipment for laying and compaction. The performances rendered for the delivery and processing of the asphalt must be carefully adjusted under due consideration of the laying and compaction progress as well as the necessary quality assurance activities, so that these processes progress almost continuously without any exceptional downtimes. The optimization of these complex arrangements require exact knowledge about the material properties of the asphalt mixture, the asphalt engineering interrelationships during laying and compaction as well as the required level of quality. The quality requirements aim at the production of an asphalt pavement of appropriate load bearing capacity and wear resistance for the traffic area with the required profile and with a permanent evenness and with a homogeneous surface structure with maximum grip.

The load bearing capacity of the asphalt pavement requires a high resistance (stability) against deformation under traffic loads. The demands for stability, wear resistance and durable evenness of the asphalt pavement require a high density of the compacted mixture with an inherent interlocking of the particles. The longterm stability of asphalt pavements is assured by an air void content, that is as low as possible, and an effective adhesion between layers. A low content of air voids is also a very important criterion for the weathering resistance and the wear resistance of the asphalt pavement. The position according to the required profile, the long-term evenness and grip of the surface structure are quality features which comply with the demands of traffic safety and driving comfort. The strived for excellent evenness of the surface course can only be achieved when the stringend evenness requirements for the lower layers are also met. The asphalt mixture must be composed, processed and compacted with technical and economical efforts to such an extent, that the above mentioned characteristics can be assured. The suitability of the machines used for laying and compaction is of highest significance in this complex task. Due to the high requirements placed on the compaction quality of asphalt pavements a careful decision must be made of which compaction machines and compaction technologies are most suitable for the respective construction task (Fig. 92).

Construction task

Type of material

Compactibility

Compaction requirem.

Site conditions

Productive capacity

Selection criteria for compaction equipment for a certain construction task

Economy

Availability

Experience

Fig. 92 105

Part 3

When planning the use of equipment it is necessary to take complex influential factors into consideration. These arise from the mixture composition in question, the laying conditions and the machine related requirements; overview Tab. 40. Asphalt

Machine

Placement conditions

Mineral aggregates • max. particle size • chippings content • crushed/natural sand • type/content of filler

Type of roller • static roller • rubber tire roller • vibratory roller • combination roller

Bituminous binder • type • quantity

Design characteristics • weight • weight distribution • vibrating mass • geometry and number of drums or tires

Compactibility Compaction temperature

Condition of substrate • stiffness • roughness

Application values • frequency • amplitude • tire pressure • rolling speed

Weather conditions • ambient temperature • insolation • wind Layer thickness Precompaction by paver Number of passes Rolling technique

Table 40: Factors influencing compaction The focal points of the BOMAG compaction technology concentrate on the use of vibratory rollers, as described already in part 1 and part 2. For the compaction of asphalt the tables 41, 42 and 43 first of all provide general recommendation for a preselection of machines.

Type of machine/ field of application

Vibratory tamper

Asphalt compaction Highway construction Airport construction Hydraulic engineering/waterproofing Sidewalks and cycle paths, Yard and garage driveways Parking lots and industrial yards Minor maintenance and repair work Maintenance and repair work

Vibratory plates

+++ highly suitable ++ well suitable

Tab. 42: Recommendations for the use of BOMAG light equipment for asphalt compaction

Single wheel vibratory rollers

Double vibratory rollers

Tandem vibratory rollers

Combination rollers

O

O X

X X X

X X

X

X O

O

X

X X

X X

X X

X O

X O

X X

O X

O X

x = well suitable, 0 = suitable

Tab. 41: Suitability of compaction machines for various types of application 106

+ conditionally suitable - not suitable

Compaction of asphalt

+++ highly suitable ++ well suitable

+ conditionaly suitable - not suitable

Tab. 43: Recommendations for the use of BOMAG heavy equipment for asphalt compaction 5.2 Influences caused by ambient laying and compaction conditions Stability and evenness of the substrate layers, laying thickness in connection with the available time for compaction, temperature of compaction and weather conditions belong to the most important influential factors contributing to compaction effect, compaction quality and compaction output when placing and compacting asphalt layers. (1) Stability and evenness of the subbase The stability and evenness of the substrate influences the compaction quality of the asphalt layer. The problem arises mainly on non-uniformly compacted unbound base and subbase courses, in case of effects caused by the subgrate and also on extremely stiff or rigid base courses.

Prerequisite for a proper and optimal compaction of asphalt layers is an even subbase with a uniform load bearing capacity and which is neither soft and yielding, nor rigid in reaction and which does not inhibit any considerably stiffness differences. Critical areas, which do not comply with such conditions, must be subsequently compacted before the laying of mixture or should be enhanced by a replacement of material. Significant unevenness require reworking of the profile before laying. For minor unevenness it may be appropriate to accept certain thickness deviations in the asphalt layer to applied, if this is permitted by the type of mixture and the biggest particle size of the aggregate mixture. Too high stiffness values of thin layers may cause crushing of particles.

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Part 3

(2) Laying thickness The laying thickness has a considerable effect on the required time for an effective compaction of the asphalt layer. It normally is a magnitude determined by the dimensioning or the quantitative output of the paver. It is, however, mandatory to adapt the laying thickness or paver output to the time required for compaction or the compaction work; see also point (3) and T 3, para 5.3 Compared with a thick layer, a thin layer cools down very quickly, i.e. in such a case compaction must progress very quickly and the laying temperature of the mixture must be as high as possible. Since cold weather even accelerates this cooling process, laying of thin layers should be avoided under such conditions; see also T 3, para. 4.3.2 and Fig. 90. Another influence of the laying thickness arises from its relation to the biggest particle size of the mineral aggregate mix of the asphalt, meaning that laying, thickness and biggest particle size must be perfectly

adapted to each other. If this ratio is too small, crushing of particles and segregation may occur and the obstructed redistribution of particles may increase the compaction resistance. If, in contrast, the ratio between laying thickness and biggest particle increases significantly, the stability of the asphalt layer will be impaired or reduced. As a general recommendation the laying thickness shall be 3 to 4 times the diamter of the biggest particle in the aggregate mix of the asphalt. (3) Influences by weathering and temperature Apart from the laying temperature and the laying thickness of the asphalt, the weather conditions have a substantial influence on the cooling of the mixture and thereby on the available compaction time. Speed of wind, air temperature, insolation and temperature of the substrate are contributing factors (Fig. 93).

Direct and indirect effects of the weather conditions on the available time for compaction Under hot weather conditions the cooling process of the asphalt will slow down tremendously, so that thick layers in particular or mixtures with low compaction resistance may not be subjected immediately to the weight of a heavy roller. If heavy rubber tire or vibratory rollers are 108

Fig. 93

used too early, the mortar will accumulate at the surface, whereby the structural grip will be reduced. In such cases it is important to stabilise the asphalt layer initially by pressing it with a light and statically working roller.

Compaction of asphalt

Cold weather promotes the quick cooling of the mixture and decisively shortens the time period down to the critical mixture specific minimum temperature, at which further compaction is impossible. This influence increases with the composition related compaction resistance of the asphalt mixture. Under cold weather conditions rolling work must therefore be performed especially quickly and immediately behind the paver and intensified by the use of especially effective compaction equipment. Low temperatures also impair or prevent the required adhesion between the layers. Under such conditions prewarming of the substrate or spraying of a bituminous tack coat may be of help. The compaction and adhesion between layers is also adversely effected if the hot mixture is placed on a wet base, whereby the heat is extracted. If the developing steam has no possibility to escape, blisters and cracks will develop in the asphalt layer. If deposits of water remain on the placed asphalt layer, the layer will cool down more rapidly from the top resulting in an insufficient sealing of pores at the surface and the development of cracks during the rolling process. The laying temperature of the mixture and the weather dependent cooling speed have a significant effect on the compaction or the required compaction effort. These interrelations have already been described in T 3, para. 4.3.2. Further information can be found in T 3, para. 5.3. The more difficult to compact the the asphalt because of its composition, the higher the required laying temperature. The temperature losses during the transport of the mixture must be maintained at a low level, similar to the temperature losses caused by a heat exchange with the substrate and the outside air or the temperature losses caused by the evaporation of water. The asphalt cools quicker in the upper and lower zones than inside the layer. The required compaction by roller should therefore be finished before the temperature in the in the centre of the layer has dropped below 90 to 100°C (surface temperature approx. 80 to 90°C). For mixture types with a relatively hard bitumen, a high filler proportion and stabilising additives the critical temperature limit is higher. In critical cases it is even more important to utilise the comparably high temperature of the mixture in the paver by intensive compaction close

behind the paver. Regular measurements of the temperature of the mixture inside the paver and in the freshly laid mat are therefore absolutely necessary. 5.3 Area output and volumetric output of the machines Both area output and volumetric output of the paving and compaction equipment are interdependently related with each other. During the planning process these two types of output must be exactly adjusted to each other and evaluated (Fig. 94). The area output of paving depends on the paving width, the working speed and the utilisation rate of the paver. The volumetric output of paving is based on the mixture laying quantity and the area output of the paver. The area output and volumetric output of compaction machines are influenced by the available rolling time as well as by the number of machines, their mode of operation, the rolling speed and the rolling width. The combination of compaction machines to be used must be selected by due consideration of a number of influencing factors and various quality criteria, such as sufficient compaction, even surface with closed pores, (see T 3, para. 5.1 and Tab. 40).

Laying and compaction of an asphalt binder using 2 pavers and five 10 t vibratory rollers, paving width 11m, daily output 5000t Fig. 94 109

Part 3

Theoretical area output F and volumetric output M of a paver can be mathematically determined in accordance with the leaflet on compaction of asphalt: F = B . v . fn (m2/h) F B v fn fn fn fn

= area output of paver (m2/h) = paving width (m) = paving speed (m/min) = efficiency factor = 0,8 to 1,0 for volumetric output to 100 t/h = 0,7 to 0,9 for volumetric output 100 t/h to 200 t/h = 0,6 to 0,8 for volumetric output > 200 t/h

M =

F.g 1000

(t/h) (t/h) (m2/h) (kg/m2).

The following formulas are recommended for the estimation of output data: a) for the area output of a paver when assuming an efficiency factor of fn = 0,83 F = B . v . 50 (m²/h) b) for the paving speed of a paver F B

. 0,02 (m/min)

c) for the area output Fw of a roller: Fw =

beff . v . 50 n

(m²/h)

v = mean rolling speed (m/min) n = number of rolling passes b = effective rolling width (m) d) for the number N of parallel rolled tracks, depending on the paving width B:

110

B b

e) for the effective rolling width beff =

B

(m)

N

f) for the rolling time t, comprising of pre-rolling, breakdown compaction and finish rolling: t=

M = volumetric output F = area output g = laying weight

v=

N = 0,9 .

L.n.N v

(min)

L = length of rolling track (m), N = number of rolling tracks, n = number of rolling passes The practical application of the output formulas mentioned above requires the consideration of certain fundamental rules and values of experience: - The area output of the roller must be evaluated separately for each compaction machine. The total output of all machines used for compaction must be higher than the area output of the paver. - The area output of the roller decreases when compacting smaller paving widths and when performing special tasks such as the compaction of joints or along edges. - From practical experience it is recommended to use at least two rollers per paver, if necessary even with different output capacities, in order to be able to per form the required tasks (e.g. breakdown compaction, bonding of layers, closing of pores, connection of joints) in an optimal way and to be able to compensate a possible failure of a machine. Type and number of machines must be chosen in such a way, that the machines will obstruct each other. - The time required for compaction must be less than the time period during which the mixture will cool down from laying temperature to the critical temperature, at which the mixture can no longer be compacted.

Compaction of asphalt

The compaction conditions can be improved by precompaction, intensifying the main compaction process and by using a higher mixture temperature. In this regard it must, however, be noted, that a higher rolling speed can reduce the compaction effect and may, in many cases, cause evenness deficiencies. In accordance with Lit. 13 the following speeds are recommended: 70 to 90 m/min (4.2 to 5.4 km/h) for pressing (static) 60 to 90 m/min (3.6 to 5.4 km/h) for breakdown compaction (static) 50 to 80 m/min (3.0 to 4.8 km/h) for breakdown compaction (vibration) 60 to 100 m/min (3.6 to 6.0 km/h) for breakdown compaction (rubber tire roller) 70 to 100 m/min (4.2 to 6.0 km/h) for finish compaction (static) 80 to 120 m/min (4.8 to 7.2 km/h) for finish compaction

(rubber tire roller)

Tab. 44: Recommended rolling speeds in accordance with the leaflet on compaction of asphalt The number of required roller passes can only be estimated on the basis of previous experience or must be determined by trial compaction passes. In each individual case the number of passes depends on the compaction resistance and the temperature of the asphalt mixture, the mat thickness, the rolling speed, the roller type and the operating mode of the machine. Lit. 13 recommends the values in Tab. 44 for an estimation.

For BOMAG compaction equipment experience values for areal output (m²/h) and volumetric output (t/h) are available. These are listed in Tab. 45 - 48. Machine type Operat. weight kg

Areal output Compaction capacity (m2/h) with a mat thickness 2 - 4 cm 6 - 8 cm 10 - 14 cm

50 - 60 70 - 80 40 - 100 120 - 250

50 - 100 80 - 130

20 - 35 30 - 40 50 - 80 70 - 100

20 - 30 30 - 35 50 - 80

300 - 450 600 - 800

-

90 - 140 -

80 - 120 -

150 - 500

80 - 160

70 - 120

60 - 100

600 - 800

200 - 270

130 - 190

120 - 170

Tab. 45: Practical output ranges of compaction equipment in asphalt engineering Machine type Operat. weight t

Areal output Compaction capacity (m2/h) with a mat thickness 2 - 4 cm 6 - 8 cm 10 - 14 cm

1,5 - 2,5

250 - 450

200 - 350

150 - 300

3,0 - 4,5

400 - 800

250 - 600

250 - 450

7-9

600 - 1500

500 - 900

400 - 700

1000 - 2200 800 - 1200

600 - 900

10 - 12 1,5 - 2,5

250 - 450

200 - 300

150 - 250

3,0 - 4,5

400 - 800

250 - 500

250 - 400

7 - 10

600 - 1500

500 - 800

400 - 650

Tab. 46: Practical output ranges of compaction equipment in asphalt engineering

111

Part 3

Machine type Operat. weight kg

Volumetric output Compaction capacity (t/h) with a mat thickness 2 - 4 cm 6 - 8 cm 10 - 14 cm

50 - 60 70 - 80 40 - 100 120 - 250

5 - 10 7 - 15

3-5 4-6 9 - 15 12 - 18

6 - 10 8 - 10 20 - 28

300 - 450 600 - 800

-

16 - 25 -

25 - 35 -

150 - 500

6 - 15

10 - 20

20 - 35

600 - 800 900 - 1200

8 - 20 10 - 25

20 - 30 20 - 35

40 - 55 40 - 65

Tab. 47: Practical output ranges of compaction equipment in asphalt engineering Machine type Operat. weight t

Volumetric output Operation capacity (t/h) with a mat thickness 2 - 4 cm 6 - 8 cm 10 - 14 cm

1,5 - 2,5

10 - 40

25 - 60

40 - 100

3,0 - 4,5

20 - 60

40 - 90

70 - 160

7-9

40 - 100

70 - 160

120 - 220

10 - 12

70 - 120

100 - 200

180 - 280

1,5 - 2,5

10 - 35

20 - 55

35 - 90

3,0 - 4,5

20 - 55

35 - 80

65 - 140

7 - 10

35 - 100

60 - 170

90 - 200

Tab. 48: Practical output ranges of compaction equipment in asphalt engineering

Arithmetic example for the planning of rollers (from leaflet on compaction of asphalt) For the laying of 96 kg/m² asphalt concrete 0/11 with a thickness of 4 cm and a paving width of 3,75 m. Volumetric capacity of paver: 80 t/h. Procedure: • Areal output M . 1000 80 3 . 1000 F= = = 833 m²/h g 96 • Paver speed F . 0,02 833 . 0,02 V= = = 4,5 m/min B 3,75 • Use of a tandem vibratory roller with a drum width b = 1.42 m Required number of rolling passes (by experience) n = 2 static + 4 with vibration mean rolling speed v = 70 m/min • Rolling width B 3,75 N= = = 2,9 rounded to 3 = N b . 0,9 1,42 . 0,9 beff =

B

=

3,75

= 1,25 m N 3 • Arreal output of roller beff . v . 50 1,25 . 70 . 50 F= = = 729 m²/h n 6 Since the areal output of the roller (729 m²/h) is lower than the areal output of the paver (833 m²/h), a second roller is required. This roller should also be used to compact joints and edges. • Rolling time t=

L.n.N v

=

50 . 6 . 3 70

= 12,9 min

Here it must be checked whether the available time for an effective compaction in dependence on weather and mat thickness is longer than the calculated rolling time.

112

Compaction of asphalt

5.4 Compaction equipment (Lit. 25, 27, 28, 37) 5.4.1 Pre-compaction during paving Pre-compaction of the asphalt mixture with the compaction screed of the paver (normal screed or high performance screed) generally improves the stability of the fresh and hot asphalt mixture, enables the use of vibratory rollers immediately behind the paver and reduces the compaction effort during rolling. A high pre-compaction with the paver screed also has a positive effect on the achievable evenness of the asphalt course. However, during the subsequent compaction with rollers it must be taken into consideration that the pre-compaction with the paver screed is mostly quite irregular, with lower values in the middle and at the edges of the respective paving width. The compaction effect depends on the adjustment of the paver screed, the mat thickness and the laying speed, on the stability and evenness of the substrate as well as on the composition and temperature of the asphalt mixture. Under normal conditions up to 82 to 90% of the Marshall density is achieved by pre-compaction with normal paver screeds whereas high performance screeds achieve slightly higher values. The compaction elements of the screed should be adjustable, so that the compaction effect can be adapted to the influncing factors specified before and an uniform surface structure is produced over the entire paving area. The uniformity of pre-compaction and the surface structure is favourably supported by the constant laying speed of the paver.

- pre-compaction, particularly required in case of insufficient pre-compaction by the paver screed, laying of thick courses and a high temperature of the asphalt mixture, mostly performed with a light roller, - breakdown compaction with rollers, whereby, in dependence on the properties of the asphalt mixture, the first one or two rolling passes are performed statically and may also be used as pre-rolling, - finish rolling, as a measure to achieve the required transverse evenness and to close the pores in the surface courses, - joint rolling, normally separately performed by the roller used for main compaction (T 3, para. 5.5.1, point 8), Fig. 96.

Pre-rolling with a light roller on material sensitiv shoving

Fig. 95

Finish rolling of a surface sourse with a 12 t roller with pivot steering

Fig. 96

5.4.2 Selection criteria Compaction equipment with jerk-free steering, control, acceleration and deceleration is most suitable for the compaction of asphalt mixtures. Further general demands aim at a completion of the compaction work with the required quality before the critical cooling temperature of the asphalt mixture is reached (see T 3, para. 5.2). All compaction machines and combinations capable of meeting these general demands are available. Another differentiation must be made with respect to the application, the areal size and the laying thickness. Normally one must differentiate between the following applications:

113

Part 3

According to Lit. 13 rollers are recommended for various fields of application and applicational conditions (Tab. 49). Further requirements especially for for light and heavy compaction equipment from BOMAG see Tab. 42 and 43. The use of small compaction machines is most suitable for small areas, in trenches and as additional equipment for special duties. The ratio between static linear load and drum diameter is an important machine related influencing parameter, which must be observed when compacting asphalt layers. Rollers with identical drum load, but different drum diameters produce different compaction results. Drums with smaller diameters sink deeper into the mixture and cause transverse cracking. In comparison, large drum diameters produce lower horizontal shearing forces, thereby achieving a better evenness and reducing the displacement (shoving) of material (formation of bow waves) and rolling cracks. This influences is accounted for by Application

High breakdown compaction Low pre-compaction Thick layers Thin layers on a rigid substrate Thin layers on a flexible substrate Depth effect Evenness Closing of pores Compaction in the lower critical temperature range Compaction in the upper critical temperature range Finish rolling

means of the so-called Nijboer-factor Nf (Fig. 97 and Lit. 29). For this reason BOMAG compaction rollers are designed with a drum diameter as large as possible and a low Nijboer-factor, to enable perfect compaction even of highly sensitive asphalt mixtures.

Nf =

Static linear load Drum diameter

Influence of the drum diameter on the compaction

Tandem roller Three-wheel roller Vibratory roller

Fig. 97

Rubber tire roller

Combi-roller

-

X

X

X -

X

X

X -

X -

(x) (x)

X X (heavy) (x) X

(x) X

-

X

-

(x)

X

X X

X

(x) (x)

X -

X -

(x) X X (pre-rolling)

X (x)

X X X

X

(x)

X -

(x) X X (heavy)

(x) X (x)

X = suitable, (x) = conditionally suitable, - = not suitable

Tab. 50: Applications and applicational conditions for the compaction of asphalt by rollers 5.4.3 Static smooth drum rollers Static smooth drum rollers compact by the effect of their own weight. In asphalt engineering these rollers are used for pre-compaction, breakdown compaction and finish compaction tasks. By design and weight one differentiates between: (1) Tandem rollers with two drums of identical size and one or two driven axles, weight up to12 t 114

Compaction of asphalt

(2) Three-wheel rollers with two driven rear drums of identical size and a smaller non-driven front drum, weight 4 to 16 t. Drive axle with differential as a measure to avoid shoving, or with floating axle, which has a positive effect when compacting areas with roof profile. Large drum diameters enable rolling of smooth surfaces. However, when used on asphalt mixtures with a high chipping content, pores cannot be completely closed. The depth effect of static smooth drum rollers is relatively low and reaches down to max. 8 cm. With only one driven axle the gradability is limited. Working speed up to 4 km/h. 5.4.4 Pneumatic tired rollers Pneumatic tired rollers are available with 5 to 11 wheels and smooth tires in the weight range from 5 to 25 t (Fig. 99). They compact the mixture by the dead weight of the machine and by the kneading effect resulting from the deformation of the rolling tires (Fig. 98). The wheels are suspended by a floating axle, ensuring compaction even of small dents or uneven laying thicknesses. The depth effect increases with the wheel load and the tire inflation pressure; it decreases with increasing drive speed. The inflation pressure must be identical in all tires, but should be variable to enable an adaptation of the compaction to varying conditions of paving and substrate: a tire inflation pressure of 5 to 6 bar is commonly used for asphalt compaction.

Areal pressure under the tires (30-80 Mpa) and overlapping of front and rear wheels for uniform compaction and ironing of tire marks Fig. 98 The main applications are pre-profiling, breakdown compaction of easily compactable asphalt mixtures

and for the sealing of surface courses and base courses. Drive speeds of up to 20 km/h, working speeds of 3 to 4 km/h, or even higher when used for the sealing of surface courses. The grip between rubber tires and asphalt mixture has a positive effect on the gradability of these machines, enabling these rollers to compact effectively even on very ascending gradients. The hot mixture does not stick to the tires when they are warm (at least 60°C), but at very high temperatures (higher than 160°C) it is harmful for the rubber. Under such conditions the roller must not be left standing on the asphalt layer. During deployment the pneumatic tired roller normally works in combination with a smooth drum roller or a vibratory roller. The tire inflation pressure depends on the type of mixture under consideration of the required compaction effect, the sealing of pores and the required evenness. With a continuous paving output of the paver best results are achieved by pre-rolling with a smooth drum roller, followed by the compaction with a slow driving pneumatic tired roller with warmed up tires and without sprinkling of water („hot and dry“). The kneading effect results in a favourable closing of pores, closing even rolling cracks originating from pre-rolling (Fig. 99). For the rolling pattern sufficent overlapping for „ironing out“ tire marks must be taken into consideration. An excessive number of rolling passes at high temperature of the mixture cause a fatting up of the surface with mortar, leaving the surface very slippery.

Use of pneumatic tired rollers for main compaction and for intensive closing of pores by the kneading effect of warm, dry tires Fig. 99 115

Part 3

5.4.5

Vibratory rollers

5.4.5.1 Effectiveness in asphalt compaction For asphalt compaction vibratory rollers are used in form of hand-guided single drum and double drum vibratory rollers as well as tandem rollers and combination rollers. Due to the interaction of basic machine weight and vibration these machines produce very intensive compaction and depth effects in contrast to dead weight compaction machines. Fundamentals see T 1, para. 1 to 3. Contrary to other types of rollers, vibratory rollers are able to achieve high compaction effects already after a few passes, whereby the optimal vibration amplitude and the vibration frequency mainly depend on the type of asphalt mixture and the laying thickness. According to general experience surface courses are compacted with low amplitudes and relatively high frequencies, whereas low frequency vibrations and high amplitudes are recommended for thick layers. In order to achieve a smooth surface the finish rolling pass is best performed without vibration.

5.4.5.2 Hand-guided vibratory rollers A differentiation is made between the following machine types: (1) Vibratory rollers with only one drum are small compactors steered via a steering rod, which is adjustable in height. The drum is connected to the upper part of the machine via vibration isolating rubber buffers. (2) Steering rod guided vibratory rollers (Fig. 100 and 101) with two drums of identical size arranged close to each other in line are equipped with exciter shafts and with mechanical or hydrostatic travel and vibration drives; machines with all-drum drive, low centre of gravity, hydrostatic steering and parted frame with articulated joint in particular are characterised by favourable traction and manoeuvrability .

Large drum diameters are particularly favourable for the high level of evenness that can be achieved with vibratory rollers. At standstill the vibration must be switched off, in order to avoid the formation of transverse depressions. The recommended working speeds for practical applications are 2.5 to 4 km/h for thin layers and 1.5 to 2.5 km/h for thick layers. A too high number of rolling passes or the use of too heavy rollers must be avoided, especially on thin layers, since this may cause structural disturbances with longitudinal cracks and a poor bond of layers. At high temperatures of the asphalt mixture this effect may even cause the mortar to move up, leaving a slippery surface. On thin surface courses or layers on a rigid substrate there is a risk of crushing particles, loosening of layer bond and structural disturbances with cracking. These disadvantages can be avoided by compaction without vibration or by using the directed vibration system BOMAG VARIOMATIC or oscillating vibration systems; see T 3, para. 5.4.6 and. T 1, para. 2.1.4. 116

Steering rod guided vibratory rollers with two drums

Fig. 100

Usw of a steering rod guided single drum roller for secondary asphalt work Fig. 101

Compaction of asphalt

5.4.5.3 Tandem vibratory rollers See T 1, para. 3.4 with illustrations as well as Fig. 102 and 104

Two different types of steering are normally available, steering via an articulated joint or pivot steering. Both variants have advantages for certain compaction and movement operation (Fig. 103a and103b).

This type of roller is equipped with two drums of identical size, each fitted with an exciter shaft (Fig. 102 and 104), and is characterised by the following technological advantages for asphalt compaction: hydrostatic drives for travel and vibration system powered by an air cooled diesel engine, single lever operation and infinite travel speed control for jerk-free starting, acceleration and deceleration, hydrostatically controlled articulated steering for highest manoeuvrability. An automatic vibration feature shuts the vibration down when stopping the roller or when reversing the travel direction, so that the vibration will only continue for a short moment, whereby the formation of surface depressions and shoving of material is avoided.

Tandem vibratory roller

Fig. 102

Heavy tandem rollers are designed for medium to large scale sites: Working widths between 1.5 and 1.8 m or even 2.13 m for the biggest machines. The static linear loads range from 20 to 30 kg/cm.

Crabwalk and articulated steering

Fig. 103a

Single and double pivot steering with and without crabwalk

Fig. 103b

If rollers with a large drum width are used in tight curves, the rigid drum can cause cracking and deformation in the asphalt layer. This is caused by the fact, that the track length of the outer side is longer than the track length for the inner radius. This problem is by-passed by using so-called split drums. However, the design of such a split drum is quite complicated, because for an uniform vibration and highest possible drive power two drive motors and two eccentrics are required (Fig. 105).

These rollers generally have two vibrating drums with the possibility to choose from two amplitudes and two frequencies, to enable an adaptation of the machine power to various types of material and paving thicknesses. 117

Part 3

5.4.5.4 Combination rollers The combination roller is a combination of a pneumatic tired roller and a vibratory roller in the weight range between 2 and 18 t. One axle of the combination roller carries a smooth drum, whereas the other axle is fitted with smooth tires (Fig. 106). These machines also use air cooled diesel engines as power source for the hydrostatic travel and vibration drives. The rubber tires are driven in pairs by two hydraulic motors, ensuring perfect adaptation of the left and right hand wheel pairs to the different rolling speeds when driving around curves. Single lever operation, hydrostatic power steering as well as automatic vibration enable simple and safe operation of the large combination rollers. Tandem roller with split drum

Fig. 104

Combination roller with split drum and four smooth tires Influence of the split drum on the distribution of strain on an articulated roller

118

Fig. 105

Fig. 106

Similar to the pneumatic tired rollers, these machines can also be beneficially used for the „hot and dry“method. It must, however, been taken into consideration, that the combination rollers have a lower wheel load. No attempt should be made to compensate this lower wheel load by a higher tire inflation pressure, because the tires may then pick up material. The tires should be arranged in such a way, that the gaps between the tires are smaller than the width of the tires, so that any remaining tire marks can be „ironed“ by offsetting the machine laterally for the following pass.

Compaction of asphalt

Combination rollers are mainly used for compaction work on small areas and on steep gradients, whereby an effective compaction is only possible with warmed up tires. When compacting thin layers and under cold weather conditions it is necessary to use an oil emulsion as a separating agent for the tires. The steel drum must be sprayed with water to prevent material from sticking to the drum. 5.4.5.5 Plates and tampers Vibratory plates and tampers are used for the compaction of asphalt mixtures in areas which cannot be accessed with rollers, as well as for minor repair work. These plates and tampers are available in different designs and various weights; see also T 1, para. 3.1 and 3.2 as well as Fig. 107 and 108. Machines that can be adjusted to a low amplitude and a high frequency are particularly suitable.

5.4.6 Applicational advantages of the directed vibration system BOMAG VARIOMATIC The latest development of the directed vibration system BOMAG VARIOMATIC with all its applicational advantages has already been described in T 1, para. 2.1.4; see also Lit. 24 to 28. The VARIOMATIC system helps the user to improve output and quality to a remarkable extent and releases the roller operator from critical application related decisions. The applicational advantages for asphalt compaction can be summarised as follows: - universal use on surface, binder and base courses with intensive and uniform compaction - no particle size reduction during compaction of thin layers as a result of the automatic change-over to horizontal vibration (comparable with oscillating compaction machines) - laying and compaction of thin layers without loosening or subsequent compaction of the underlaying strata by using horizontal vibration (of advantage when laying hot on warm)

Use of vibratory tampers

Fig. 107

- when complying with the fundamental requirements for asphalt compaction, as mentioned in para. T 3, 5.5, the formation of bow-waves, shoving of the asphalt and cracking is almost completely avoided, because the asphalt is not pressed forward, but pulled under the drum - particularly favourable smootheness of the surface, because the directed vibrations are automatically adapted to the working direction of the roller - excellent performance when rolling joints (beneficial when rolling hot on cold).

Use of vibratory plates for small work areas

Fig. 108

Another applicational advantage of the VARIOMATIC system is the use in urban areas and on bridges, where excessive vibrations of the environment must be avoided. Measurements reveal that the vibration load on nearby buildings can be substantially reduced by preselecting the vibration; see Fig. 5 in T 1, para. 1.4.

119

Part 3

5.4.7 List of recommendations for the use of BOMAG vibratory rollers Figures 109, 110 and Tab. 50 contain lists of recommendations for the use of vibratory rollers in asphalt compaction, for the selection of rollers in dependence on mat thickness and laying conditions as well as for the required number of rolling passes for tandem rollers in asphalt compaction.

Recommendations for the use of vibratory rollers for asphalt compaction

120

Fig. 109

Compaction of asphalt

Selection of BOMAG vibratory rollers depending on mat thickness of asphalt courses and laying conditions

Fig. 110 121

Part 3

Thickn. of asphalt

Number of vibration passes for various

course d (cm)

Laying direction

tandem vibratory rollers 3t

6t

9t

2

2–4

1 – 2 (L)

1 – 2 (L)

4

4–6

2 – 4 (L)

2 – 4 (L)

6

4–8

4 – 6 (L)

2 – 4 (L)

10

6–8

4 – 8 (L, H)

4 – 6 (L, H)

14

-

6 – 8 (H)

4 – 6 (H)

18

-

6 – 8 (H)

4 – 8 (H)

Stone mastic d = 2

1-2 (L) + stat. pass

1-2 (L) + stat. pass

d=4

4-6 (L) + stat. pass

4-6 (L) + stat. pass

Drain.asphalt d = 4

1-2 (L) + stat. pass

1-2 (L) + stat. pass

L = low amplitude; H = high amplitude; Assumption: compaction temperature > 100°C 3 t = Machines with one amplitude only

Tab. 50: Recommendations for the number of rolling passes for BOMAG tandem vibratory rollers used in asphalt compaction 5.5

Basic rules of rolling technique (Lit. 27, 37 and leaflet on compaction of asphalt)

Wrong: Non-driven wheel at front

Correct: Driven wheel at front

Influence of the position of the driven drum to the laying direction and shoving of asphalt mixture

Fig. 111

(2) Overlapping of rolling tracks Parallel rolling tracks must neither have any uncompacted nor any overcompacted strips. The overlapping must be determined with greatest care; normally this overlap should be approx. 10 cm.

5.5.1 Rolling pattern

(3) Reversing the travel direction

Intensive and uniform compaction requires an uniform distribution of rolling tracks and rolling passes over the entire paving area. With a large paving width the parallel tracks must be compacted with the same types of rollers. The following basic rules are based on practical experience:

Once work on a compaction track is finished the roller must return on the same track all the way back to the already cooled down area. There the machine can be laterally displaced for the next track. The machine must not perform a U-turn on a soft or hot asphalt mixture, since this will cause shovingor loosening of material. The machine must also not be stopped on a hot mixture. When reversing the travel direction the machine must roll out moothely before it is reversed without any jerks. Here machines with torque converter and hydraulic travel hydraulics are of advantage. On vibratory rollers the vibration must be switched off in due time before reaching the reversing point, so that it comes to a halt before reversing the machine.

(1) Position of the roller to the paver The driven drums or driven wheels (e.g. combination rollers) should be positioned towards the paver, so that the non-driven drums and wheels transfer the shearing forces into the asphalt mixture, that they do not shove the material and create cracks (Fig. 111). Rolling must generally be performed smooth and without any jerks. Fig. 112 shows the rolling technique behind the paver. For compaction on steep gradients see point (7).

122

(4) Crossfalls For the stability of a pavement with crossfall it is important to start rolling at the lowest edge and move across to the highest edge in the middle.

Compaction of asphalt

(5) Unsupported edges, curbstones Solid curbstones avoid that mixture is pressed out at the sides. On unsupported edges special attachments on the paver screed or on the roller can prevent pressing out of material. They also have a positive effect on the compaction of such edges.

Rolling pattern with curbstone

Fig. 112a

If no curbstones or other means are available it is good practice to roll the first pass approx. 30 cm away from the edge. The outer strip should then be subsequently compacted after the mixture has stabilised by cooling (Fig. 112b). (6) Rolling in curves

Rolling pattern without curbstone: Outer strip to be compacted last after stabilisation by cooling Fig. 112b

When rolling in curves compaction shall be started on the inner side (Fig. 113). The rolling pattern in curves depends on the curve radius, the sensitivity of the asphalt mixture against displacement and shoving as well as on the type of compaction machine. The tighter the curve, the more critical the compaction procedure, because in a curve the roller will introduce transverse shearing forces into the asphalt layer, whereby the mixture is dilatantly deformed along the outer radius of the roller track and contracted along the inner radius. This effect is most significant when using rollers with non-split steel drum and a large distance between the drums. However, the use of vibratory rollers with split drums considerably reduces the risk of shoving and crakking. As an alternative solution the rolling pattern may be changed. Compaction should then be started with a two tangetial pre-compaction passes instead of rolling curves.

Rolling pattern behind two pavers with curbstone

Fig. 112c

Presentation of rolling patterns behind a paver

123

Part 3

Position of the driven drum or the wheels on ascending gradients Rolling pattern for the compaction in curves

(8) Longitudinal, transverse and connecting joints

Fig. 113

(7) Compaction on ascending gradients On ascending gradients the working direction of the roller is of utmost importance, because the required higher tractive power of the machine introduces shearing forces into the asphalt layers. For this reason, on rollers with a non-driven drum or on combination rollers the driven drum or driven rubber wheels shall always follow the non-driven drum, even if the first passes have to be performed downhill (Fig. 114).

124

Fig. 114

For the rolling of longitudinal and transverse joints as well as connecting joints between freshly laid and existing mixture certain preparations are required: cleaning, treatment with sealing asphalt sprays or heating of these areas during laying. Longitudinal joints can be rolled using various methods, whereby the VARIOMATIC rollers with their automatic vibration mode are of particular advantage. a) Start from the cold side (Fig. 115a): first pass statically without the machine jumping and with only 10 to 20 cm overlap to the fresh mix. Then continue rolling of the fresh asphalt mixture, starting from the outside.

Compaction of asphalt

Rolling of joints, starting from the cold side

Fig. 115a Compaction of transverse joints

b) Start from the side of the freshly laid asphalt mixture (Fig. 115b): Rolling, for instance, with vibration starting from outside towards inside with an approx. 10 to 20 cm overlap on the inside track. Also in this case the roller must not jump.

Fig. 115c

5.5.2 Monitoring of quality influences Thorough monitoring of the laying and rolling process as well as the compliance with the compaction rules described in para. 5.5.1 is an essential element of selfmonitoring and quality control. This will help to detect and rectify quality deficiencies in due time: (1) Rolling cracks

Rolling of joints starting from outside on the freshly laid asphalt mixture

Fig. 115b

Transverse joints between an old and a new asphalt course must be rolled under a right angle to the laying direction (Fig. 115c). At the beginning the roller shall only cover 10 to 20 cm of the new hot layer. For the next pass the overlap is then increased, before changing to rolling in laying direction. Alternatively it may be of advantage to use an additional small roller for this special job or to start rolling under an oblique angle to the transverse joint.

Transverse cracking may be caused by a number of reasons, such as incorrect position of the roller to the paver, the use of too heavy rollers or insufficient precompaction, the too late start of compaction when laying of thick layers, sudden cooling (weather, cold drums, too much sprinkling water), shoving of asphalt mixture on the substrate, on ascending gradients especially on thick courses or sandy mixtures with insufficient binder. These cracks mostly reach to a depth of only a few millimetres. They will be bonded when rolling the next hot layer, during subsequent compaction with a pneumatic tired roller or when sealing with a tack coat.

125

Part 3

Longitudinal cracking is caused by inhomogeneities or deficiencies in the substrate or even by shearing forces in the asphalt mixture caused by the effect of heavy rollers. In these cases it may be necessary to roll the first compacting pass with reduced compaction energy (low amplitude or statically) in order to gain stability, so that the roller can roll without crushing the material. (2) Transverse unevenness Transverse unevenness occurs, for example, when the roller shoves the asphalt mixture, if it is stopped on hot material and sinks in, if it is too heavy or has a too small drum diameter, if rolling tracks remain because of non-compliance with the rolling pattern or if the travel direction was reversed on hot asphalt. If the machine shoves the asphalt mixture like a bow wave or if it sinks in, the machine or operating mode is unsuitable for the job, the mixture is too hot or the layer has not been sufficiently pre-compacted. Another reason may be an insufficient bond between layers or an insufficient adhesion between asphalt layer and the bituminous substrate, e.g. caused by wetness, dirt or excessive spraying, e.g. of a tack coat. (3) Surface structure Smoothness and gloss on the surface are indicators for a fattening up of mortar, caused e.g. by vibration, suction by rubber tires. The grip of the surface can be enhanced by interrupting the rolling process until a slightly lower temperature is reached, by changing from vibratory to static rolling or by reducing the number of passes. (4) Excessive number of rolling passes The number of passes required for a certain compaction work may vary strongly. They depend on a vast variety of factors, such as the compactibility of the asphalt mixture, laying thickness, stability of the substrate, pre-compaction by the paver, temperature of the asphalt mixture, type and weight of rollers, rolling speed, weather. 126

Even though no standard values are available and own experiences with the machines in dependence on mixture and laying conditions must be used or trial compactions with density measurements must be performed, empirical reference values, as specified in paragraphs T 3, 5.3 and 5.4.7 as well as in Tab 50, do exist. By experience, 8 to 12 passes with static rollers and pneumatic tired rollers and 4 to 8 passes with tandem vibratory rollers are required to achieve an intensive or required compaction. Combination rollers have a similar effect as tandem vibratory rollers. With pneumatic tired rollers there is a risk that mortar will fat up to the surface and reduce the grip when rolling too many passes at high temperature, especially on mortar enriched and dense asphalt mixtures. When using vibratory rollers, a too high number of passes with vibration can cause loosening of material and disturbances in the structure. This applies mainly for thin and already cooled down courses. In order to avoid loosening and fattening up of mortar to the surface, thin asphalt courses (thinner than 10 cm) shall only be rolled with low amplitude. Pneumatic tired rollers should not be used on open graded asphalts with a high chipping content (e.g. stone mastic asphalt, porous asphalt), because the pores in the surface would then be sealed and the proportion of air voids in the surface zone reduced. For vibratory rollers the number of passes with vibration must remain restricted to two, because the topical friction and transfer of forces may cause crushing of particles. For asphalts with a high chipping content and for open graded asphalts heavy static rollers are most suitable.

Compaction of asphalt

(5) Picking up of hot asphalt mixture During the compaction of asphalt mixtures in practice the picking up of hot asphalt mixture is counteracted by spraying the steel drums with water and the rubber tires with a bituminous emulsion as separating agent. When the water contacts the hot mixture it is evaporised and extracts heat from the mixture. In extreme cases the surface of the asphalt course will become porous and susceptible for wear. The steel drums must therefore not be sprayed with too much water (rubber scrapers, relaxation agents will help). Modern machines are therefore equipped with interval sprinkler systems with a reduced water consumption and a longer water capacity. On pneumatic tired rollers the hot mixture will not stick if the tires are hot and dry. Spraying of the tires with an emulsion consisting of a separating oil and water is therefore only necessary, until the tires have reached a temperature of at least 60°C. However, this is also necessary after the machine has been stopped. The tires can also be warmed up by initial slow driving or by using an infrared radiator.

127

128

Appendix A 1 Conversion Tables

Length Millimeter Centimeter Meter Kilometre Inch Foot Yard Mile english 1 mm 1 cm

1m

1 km

1 in

1 ft

1 yd

1 mile

[mm] [cm] [m] [km] [in] [ft] [yd] [mile] = = = = = = = = = = = = = = = = = = = = = = = = = = = =

1 sqin 1 sqft

1 sqyd 0,03937 in 10 mm 0,3937 in 0,03281 ft 0,01094 yd 100 cm 39,37 in 3,281 ft 1,094 yd 1000 m 39370 in 3281 ft 1094 yd 0,6214 mile 25,4 mm 254 cm 0,08333 ft 0,02778 yd 30,48 cm 0,3048 m 12 in 0,3333 yd 91,44 cm 0,9144 m 36 in 3 ft 1609 m 1,609 km

Area Square centimeter Square meter Square inches Square feet Square yards 1 cm² 1 m²

1555 sqin 10,76 sqft 1,196 sqyd 6,452 cm² 929 cm² 0,0929 m² 144 sqin 0,1111 sqyd 8361 cm² 0,8361 m² 1296 sqin 9 sqft

Volumes Cubic centimeter Cubic meter Cubic inches Cubic feet Cubic yards

[cm³] [m³] [cuin] [cuft] [cuyd]

1 cm³ 1 m³

= = = = = = = = = = = = [l] [gal] [pint]

0,06102 cuin 1 . 106 cm³ 61023 cuin 35,32 cuft 1,307 cuyd 16,39 cm³ 28316 cm³ 0,0283 m³ 1728 cuin 0,037 cuyd 0,7646 m³ 27 cuft

= = = = = = = =

100 cm³ 1,7605 pint 0,2642 gal 47,3 cm³ 0,473 m³ 0,125 gal 378,5 cm³ 8 pint

1 cuin 1 cuft

1 cuyd Liter Gallons (US) Pints (US) 1l 1 pint

[cm²] [m²] [sqin] [sqft] [sqyd] = =

= = = = = = = = = = = =

1 gal

0,155 sqin 1 . 104 cm² 129

Appendix A 1 Conversion Tables

Mass Gram Kilogram Ton Ounce Pound Ton short Ton long 1g 1 kg 1t 1 oz 1 lb 1 tshort 1 tlong

[g] [kg] [t] [oz] [lb] [tshort] [tlong] = = = = = = = = = = = = = = =

1 bar 1 lb/sqft 1 lb/sqin

0,357 oz 1000 g 35,27 oz 2,205 lb 1000 kg 2205 lb 28,35 g 0,0625 lb 453,6 g 0,4536 kg 16 oz 907,2 kg 0,9072 t 1016 kg 1,016 t

Force Newton Kilonewton Weight

[N] [kN] [kgf], [kp], [lbf]

1 kgf

= = = = = = = =

1N 1 kN

1 kp 9,81 N 2,205 lbf 0,102 kp 0,225 lbf 1000 N 101,9 kp 224,8 lbf

Pressure 1 N/m² 1 N/mm² 130

= = = =

1 Pa 1 . 10-5 bar 1,02 . 10-5 kp/cm² 1 . 106 Pa

= = = = = = = =

10 bar 10,2 kp/cm² 1 . 105 Pa 14,399 lb/sqin 47,892 Pa 143,989 lb/sqin 1 psi 6894,76 Pa

[J] [W] [kW] [BTU] [kcal] = = = = = =

1 Ws 0,7376 ftlb 3,6 . 106 J 860 kcal 1,054 kJ 4187 J

[hp] = = = = = = = =

1 J/s 1000 W 1,341 hp 0,239 kcal/s 5,614 hp 4,187 kW 7457 W 0,1782 kcal/s

Energy Joule Watt Kilowatt Brit. Ther. Unit Kilocalories 1J 1 kWh 1 BTU 1 kcal Power Horsepower 1W 1 kW 1 kcal/s 1 hp

Temperature Celsius Fahrenheit

[°C] [°F]

from [°C] to [°F] from [°F] to [°C]

ð ð

(°C x 9/5) + 32 (°F - 32) x 5/9

Appendix A 2 Compaction Parameters (Soil)

e

Void index

min e

Void index at densest beddiing Void index at loosest bedding Void proportion

max e n

min n

na

Void proportion at densest bedding Void proportion at loosest bedding Air proportion

D

Bedding density

ID

Related bedding density

γ

Volume weight of moist soil

max n

γl

γd

γr

Volume weight of soil under buoyancy Dry volume weight

Volume weight of water saturated soil

γs ρ ρl ρd ρPr

Particle volume weight Density of moist soil Density of soil under buoyancy Dry density Proctor density

Dpr

Degree of compaction

ρr

Density of water saturated soil Particle density Water content optimal water content Saturation index

ρs wA wPr Sr

Void volume, relating to the solids volume n γs (1+w) γs - γd e= = -1 = 1-n γ γd

Void volume relating to the total volume e γ n = nw + na = = 1+e (1+w) . γs

-1 =

nw - Proportion of water filled voids nw = w . γs na - Proportion of air filled voids

γs - γd γs

Volume proportion of air filled voids on the total volume γd na = 1 – w • γd – γs max n - n D= max n - min n ID =

max e - e max e - min e

γ = γd (1+w) = (1-n) • (1+w) • γs =

1 1+e

1+e

• γs

γs - γw

γ l = (1-n) • (γs - γw) = γd = (1-n) • γs =

1+w

1+e • γs

γr = (1-n) • γs + n • γw =

γs + e • γw 1+e

Solid mass, relating to the solids volume analogue γ analogue γ l analogue γd maximum dry density in Proctor test ρd Dpr = ρPr analogue γr analogue γs Mass ratio of water to the dry solid matter Water content, assigned to the maximum dry density in the Proctor test Volume index for water filled voids on the total proportion of voids n nw w • γs Sr = = n n 131

132

ρw

ρs

s

w

ρw - w (ρr + ρw)

ρr . ρw

1

ρs . ρw

w . ρs + ρw

-

(1 + w) . ρs . ρw w.ρ +ρ

w.

w

a

w

s

.

w

(1 - n) . ρs + n . ρw

1-n

n

n

ρ . w 1-n ρs

nw

ρ . w n-1 ρs

nw

n (nw)

Sr . ρ . ρw

1-n

ρ - nw . ρw

n

wges

(1+w) . ρs - w . ρ

nw

(1 - n) ρs

w

Sr . ρs . ρw

Sr . ρs . ρw (1 - n) . ρs + nw . ρw . w ρs + Sr . ρw

w . ρs + Sr . ρw

(1+w)

r

ρw

ρs

(Sr + w) . ρs . ρw w. ρ +S. ρ

Sr

w

w . ρs . w ρs + Sr . ρw

w

Sr

w

wi Sr < 1

**ρr ; ρd or ρ must be known instead of ρs

ρ . ρw (1+w).(1-na)-ρw-w.ρ

(1 - na) . w . ρs w . ρs + na . ρw

(1 - na) . ρs . ρw w . ρs + ρw

(1-na).ρs.ρw (1+w) w . ρs + ρw

na . ρw

s

(w + w) . (1 + na) . ρs . ρw + w.ρ +ρ

w

w . ρs + na . ρw ρ . (1 - n )

s

w . ρs + na . ρw w.ρ +ρ

w . ρs . w ρs + ρw

(1-na) . ρs

na . (w . ρs + ρw)

w

w+

wi na = n-nw

-

w

w = wges Sr = 1;na = 0

Specified Magnitudes ρs and ρw*

*In general ρw can be set to 1,0 g/cm3

Particle density ρs**

Saturation index Sr

Dry density of the soil ρd

Density ρ (partly saturated soil)

(saturated soil)

ρr

Density

Void index e

Void content n

Water content W (partly saturated soil)

Water content w (saturated soil)

Required Magnitudes

ρs - ρw

(1 + e) . ρ - ew . ρw

e

. ρs

ρd + ρw - ρr)

ρd . ρw

1

ρs - ρw ew

ρr - ρw

-

ρs

ρr

-

1+e

1+e

ρs + ew . ρw

1+e

ρs + e . ρw

ρs - ρw

ρs - ρr

ρs - ρr

e

e

ρr ρs - ρr ρw . ρr - ρw ρs

1+e

ρs

ρw

ρs

ρw

ew .

e.

e (ew)

ρ

1-

-1

ρw

ρs

( )

1+w

ρ

ρ

1+w

ρ

ρs

ρ . ρw

ρ - (1 + w).(ρr - ρw)

w . ρ . ρs ρw [(1 + w) . ρs - ρ]

ρw +

ρ (1 + w) . ρs

(1+w).

1-

Sr . (ρs - ρ) ρw . ρ - ρr . ρw ρs

ρw ρw ρ ρs

ρ (w)

(1+w).

Specified Magnitudes ρs and ρw*

ρs

ρd

ρw

-1

)

w

s

d

ρd . ρw

ρw - w . ρd

w . ρd + ρs ρ . (ρ - ρ )

ρd

(1 + w) ρd

ρs

( )

ρd

ρs

ρw ρw ρd ρs

ρw + ρd 1-

1-

( Sr .

ρw ρw ρd ρs

ρd (w)

Appendix A 2 Conversion of Compaction Parameters

133

134

t/m3

Bulk density DIN 52102

2,70 - 2,74 2,69 - 2,72

1,70 - 2,60 2,40 - 2,50

1,80 - 2,00

2,65 - 3,00 2,70 - 2,80 2,65 - 2,75

Volcanic tuff

Metamorphic rock Gneiss, granulite table slate marble 2,67 - 3,05 2,82 - 2,90

2,62 - 2,75

2,70 - 2,90

2,65 - 2,85

2,64 - 2,72

2,00 - 2,65

Limestone: Dense lime, dolomite other limestone lime conglomerate travertine

2,64 - 2,68

2,58 - 2,83 3,00 - 3,15 3,00 - 3,15 2,85 - 2,95

2,62 - 2,85 2,85 - 3,05

t/m3

0,4 - 2,0 1,6 - 2,5

20 - 30

0,5 - 30 5 - 12

0,5 - 0,6

0,5 - 25

0,4 - 0,2

0,4 - 1,8 0,2 - 0,9 20 - 25 0,3 - 1,1

0,4 - 1,5 0,5 - 1,2

%

Theor. density Porosity DIN 52102 DIN 52102

2,60 - 2,65

2,50 - 2,80 2,85 - 3,05 2,20 - 2,35 2,75 - 2,95

2,60 - 2,80 2,70 - 3,00

Quartziferous rock: vein quartz, quartzite ) Grauwacke ) quartziferous sand) stone other quartziferous sandstone

Sedimentary rock

Volcanic rock Quartz porphyry. porphyrite, andesite basalt basaltic lava diabase

Plutonic rock Granite, syenite diorite, gabbro

Rock

0,1 - 0,6 0,5 - 0,6 0,1 - 0,5

6 - 15

0,2 - 10 2-5

0,2 - 0,6

0,2 - 9

0,2 - 0,5

0,2 - 0,7 0,1 - 0,3 4 - 10 0,1 - 0,4

0,2 - 0,5 0,2 - 0,4

Mass-%

0,3 - 1,8 1,4 - 1,8

12 - 30

0,5 - 25 4 - 10

0,4 - 1,8

0,5 - 25

0,4 - 1,3

0,4 - 1,8 0,2 - 0,8 9 - 24 0,3 - 1,0

0,4 - 1,4 0,5 - 1,2

Vol.-%

Water absorption DIN 52102

3-7 4-8

5-8

1-4

2-5

3-7

5 - 12 5 - 13 6 - 10

5-8 4 -8

N/mm2

Shearing strength

4-7

1-5

2-5

3-6

5 - 11 6 - 12 6 - 10

4-7 5-8

N/mm2

Tensile strength

160 - 280

20 - 30

20 - 90 20 - 60

80 - 180

30 - 180

150 - 300 120 - 200

180 - 300 250 - 400 80 - 150 180 - 250

160 - 240 170 - 300

Compression strength dry condition DIN 52102 N/mm2

Appendix A 3 Properties of Rock

Anhang A 4 Normen, Vorschriften, Richtlinien

Part 1: DIN 1311

Vibrations Sheet 1: Kinematic terms Sheet 2: Simple oscillators Sheet 3: Vibration systems with a finite number of degrees of freedom

DIN 4150

Vibrations in building Part 1: Prediction of vibration parameters Part 2: Effects on persons in buildings Part 3: Effects on structures

DIN 45669-1

Measurement of vibration immission Part 1: Vibration meters; requirements, verification Part 2: Measuring method

Recommendation of committee 9, subgrade dynamics, of the „Deutschen Gesellschaft für Erd- und Grundbau e.V.“, July 1992, Bautechnik 1992, Heft 9 Part 2: Safety verification and design loads DIN 1054

Subsoil - verification of the safety of earthworks and foundations

DIN 1055

Design loads for buildings: Part 1: Stored materials, building materials and structural members, dead load and angle of friction Part 2: Soil characteristics Part 3: Live loads

DIN 1072

Road and foot bridges; design loads

Contract procedure for construction quantities VOB DIN 1960

Part A: General directions of contract letting for building works

DIN 1961

Part B: General conditions of contract for the execution of building work

DIN 18299

Part C: General technical specifications for building works; general rules for all kinds of building work

DIN 18300

Part C: General technical specifications for building works; earthworks

DIN 18301

Part C: General technical specifications for building works; drilling works

135

Appendix A 4 Standards, Regulations, Guidelines

Metrology DIN 1319

Fundamentals of metrology Part 1: Basic terminology Part 2: Terminology relating to the use of measuring instruments Part 3: Evaluation of measurements of a single measurement, measurement uncertainty

Soil examinations DIN 1080-6

Terms, symbols and units used in Civil Engineering; soil mechanics and foundation engineering

DIN 4020

Geotechnical investigations for civil engineering purposes

DIN 4021

Soil; exporation by excavation and borings; sampling

DIN 4022

Subsoil and groundwater Part 1: Classification and description of soil and rock; borehole logging of soil and rock not involving continuous core sample recovery Part 2: Designation and description of soil types and rock; stratigraphic representation of borings in rock Part 3: Designation and description of soil types and rock; borehole log for boring in soil (loose rock) by continuous extraction of cores

DIN 4023

Borehole logging; graphical representation of the results

DIN 4094

Soil; exploration by penetration tests

DIN 4096

Subsoil; vane testing; dimensions of apparatus, mode of operation, evaluation

DIN 18121

Soil; investigation and testing - water content Part 1: Water content, determination by drying in oven Part 2: Determination of water content of soil by rapid methods

DIN 18122

Soil; investigation and testing - consistency limits Part 1: Consistency limits; determination of liquid limit and plastic limit Part 2: Consistency limits; determination of the shrinkage limit

DIN 18123

Soil; investigation and testing; determination of grain-size distribution

DIN 18124

Soil; investigation and testing; determination of density of solid particles; capillary pycnometer; wide mouth pycnometer

136

Appendix A 4 Standards, Regulations, Guidelines

DIN 18125

Soil; investigation and testing Part 1: Determination of density of soil; laboratory tests Part 2: Determination of density of soil; field tests

DIN 18126

Soil; investigation and testing; Determination of density of non-cohesive soils for maximum and minimum compactness

DIN 18127

Soil; investigations and testing; Proctor-test

DIN 18128

Soil; testing procedures and testing equipment; determination of ignition loss

DIN 18129

Soil; investigation and testing; determination of lime content

DIN 18130

Soil; investigation and testing; determination of the coefficient of water permeability; laboratory tests

DIN 18132

Soil; testing procedures and testing equipment; determination of water absorption

DIN 18134

Soil; testing procedures and testing equipment; plate load test

DIN 18136

Soil; investigation and testing; unconfined compression test

DIN 18137

Soil; testing procedures and testing equipment Part 1: Determination of shear strength; concepts and general testing conditions Part 2: Determination of shear strength; triaxial test

DIN 18196

Earth construction; soil classification for civil engineering purposes Technical testing specifications for soil and rock in highway engineering (TP BF-StB)

Soil exploration in highway engineering, FGSV * Part 1: Part 2:

Guidelines for the description and evaluation of soil conditions Guidelines for contract awards for tze evaluation of soil conditions

Leaflet on surface covering dynamic methods for compaction testing in earthwork, FGSV* Leaflet on the description of rock groups for civil engineering purposes in highway engineering, FGSV* Leaflet on description of rock for highway engineering, FGSV* Leaflet on compaction of subsoil and subgrade in highway engineering, FGSV* Recommendations, DGGT **: No. 1 Monoaxial compression tests on rock specimen. Die Bautechnik 56 (1979), Heft 7 2 Triaxial compression tests on rock specimen. Die Bautechnik 56 (Heft 1979), Heft 7 11 Swelling tests on rock specimen. Die Bautechnik 63 (1986), Heft 3 *Forschungsgesellschaft für Straßen- und Verkehrswesen

** Deutsche Gesellschaft für Geotechnik e.V. 137

Appendix A 4 Standards, Regulations, Guidelines

Part 3: Contract procedure for construction quantities VOB DIN 18317

Part C: General technical specifications for building works; construction works for traffic lines, top layers of asphalt

DIN 1996

P. 1 to20: Testing of bituminous materials for road building and related purposes

DIN EN 12591

Bitumen and bituminous binders; specifications for paving grade bitumen (replaces DIN 1995)

Bitumen and bituminous binders: DIN EN 1425

Characterization of perceptible properties

DIN EN 1426

Determination of needle penetration

DIN EN 1427

Determination of the softening point – ring and ball method

DIN EN 1431

Determination of recovered binder and oil distillate from bitumen emulsions by distillation

DIN EN 12593

Determination of Fraaß breaking point

DIN EN 12595

Determination of kinematic viscosity

DIN EN 12596

Determination of dynamic viscosity by vacuum capilary

DIN EN 12697

Bituminous mixtures – Test methods for hot mix asphalt Teil 11: Determination of the compatibility between aggregate and bitumen

DIN EN 12697

Bituminous mixtures – Test methods for hot mix asphalt Teil 34: Indention using cube or Marshall specimens

Additional technical contractual conditions and guidelines for base courses in highway engineering (ZTVT-StB 95/98) (German regulation) Additional technical contractual conditions and guidelines for the construction of asphalt pavements (ZTV Asphalt-StB 2000) (German regulation) Guidelines for the standardization of pavements in highway and transportation engineering (RstO-StB 86/89) (German regulation) Additional technical contractual conditions and guidelines for the maintenance of traffic areas - asphalt construction meathods (ZTV BEA-StB 98) (German regulation) Guidelines for quality assurance of mineral aggregates in highway engineering (RG Min-StB 93), edition1993, FGSV* 138

Appendix A 4 Standards, Regulations, Guidelines

Technical delivery conditions for mineral aggregates in highway engineering (rock particle fractions and work stones) (TL Min-StB 2000) (German regulation) Technical delivery conditions for asphalt in highway engineering. Part: Quality assurance (TLG Asphalt-StB 89) (German regulation) Technical delivery conditions for polymer modified bitumen, Part 1: Ready to use polymer modified bitumen (TL PmB, Part 1) (German regulation) Technical test instructions for mineral aggregates in highway engineering (TP Min-StB 99) (German regulation) Leaflet for suitability tests on asphalt, FGSV* Leaflet for the use of natural asphalt in asphalt applications for highway engineering, FGSV* Leaflet on compaction of asphalt, FGSV* Part 1: Practice of compaction Part 2: Theory of compaction Leaflet for indention measurements with the Benkelman-beam, FGSV* Leaflet on evenness tests, FGSV*

*Forschungsgesellschaft für Straßen- und Verkehrswesen e.V. 139

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[3]

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[4]

YOO, T.S.; SELIG, E.T. (1980): New concepts for vibratory compaction of soil. International Conference on Compaction, Paris

[5]

HAUPT, W. (1986): Bodendynamik, Grundlagen und Anwendung. F. Viehweg u. Sohn-Verlag

[6]

STUDER, J.; ZIEGLER, A. (1986): Bodendynamik. Springer-Verlag, Berlin – Heidelberg – New York – Tokyo

[7]

KRÖBER, W. (1988): Untersuchung der dynamischen Vorgänge bei der Vibrationsverdichtung von Böden. Diss. Lehrstuhl und Prüfamt für Grundbau, Bodenmechanik und Felsmechanik der Technischen Universität München, Schriftenreihe Heft 11

[8]

KRÖBER, W. (1995): Numerische Simulation der Vorgänge bei der Vibrationsverdichtung. Festschrift: Beiträge aus der Geotechnik. Lehrstuhl und Prüfamt für Grundbau, Bodenmechanik und Felsmechanik der TU München, Schriftenreihe Heft 21

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HUBER, H. (1996): Untersuchungen zur Materialdämpfung in der Bodendynamik. Diss. Lehrstuhl und Prüfamt für Grundbau, Bodenmechanik und Felsmechanik, Technische Universität München, Schriftenreihe Heft 23

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ANDEREGG, R. (1997): Nichtlineare Schwingungen bei dynamischen Bodenverdichtern. Diss. ETH Nr. 12419, Eidgenössische Technische Hochschule Zürich

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MÜLLER, L. (1963): Der Felsbau, 1. Band: Grundlagen, Ferdinand Enke Verlag, Stuttgart

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(1976): Handbuch des Straßenbaus. Band 2. Springer Verlag, Berlin – Heidelberg – New York

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FLOSS, R.; SIEDECK, P.; VOSS, R. (1968): Verdichtungs- und Verformungseigenschaften grobkörniger, bindiger Mischböden. Bundesanstalt für Straßenwesen, Wissenschaftliche Berichte H. 6. Verlag W. Ernst & Sohn, Berlin – München – Düsseldorf

[15]

FLOSS, R. (1970): Vergleich der Verdichtungs- und Verformungseigenschaften unstetiger und stetiger Kiessande hinsichtlich ihrer Eignung als ungebundenes Schüttmaterial im Straßenbau. Bundesanstalt für Straßenwesen, Wissenschaftliche Berichte H. 9. Verlag W. Ernst & Sohn, Berlin – München – Düsseldorf

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WITTKE, W. (1984): Felsmechanik, Grundlagen für wissenschaftliches Bauen in Fels. Springer Verlag, Berlin – Heidelberg – New York

[17]

FLOSS, R. (1985): Dynamische Verdichtungsprüfung bei Erdbauten. Straße und Autobahn 36, Heft 2

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FLOSS, R.; REUTHER, A. (1990): Vergleichsuntersuchungen über die Wirkung von vibrierend und oszillierend arbeitender Verdichtungswalze. Lehrstuhl und Prüfamt für Grundbau, Bodenmechanik und Felsmechanik der Technischen Universität München, Schriftenreihe H. 17

[19]

Lehrstuhl und Prüfamt für Grundbau, Boden- und Felsmechanik der Technischen Universität München (1991): Dynamische Verdichtungsprüfung bei Erd- und Straßenbauten; Forschungsberichte aus dem Forschungsprogramm des Bundesministers für Verkehr und der Forschungsgesellschaft für Straßenund Verkehrswesen e.V., Heft 612

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FLOSS, R. (1992): Flächendeckende Qualitätskontrolle bei Verdichtungsarbeiten im Erd- und Straßenbau. Proc. 1. Internationales Symposium „Technik und Technologie des Straßenbaus“, BAUMA 1992

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FLOSS, R. (1996): Qualitätssicherung im Erdbau – Anwendung der neuen Prüfmethoden gemäß ZTVE-StB 94, Forschungsgesellschaft für Straßen- und Verkehrswesen, Köln, Schriftenreihe der Arbeitsgruppe „Erd- und Grundbau“, Heft 7

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FLOSS, R.; HENNING, J. (1998): VARIOMATIC. Ein entscheidender Schritt zur Qualitätssicherung im modernen Erd- und Verkehrswegebau. BOMAG Heft BA 049, Boppard; Vortrag Floss, R. 3. Internationales Symposium „Technik und Technologie des Straßenbaus“, BAUMA 1998

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FLOSS, R.; KLOUBERT, H.-J. (2000): Newest Innovations into Soil and Asphalt Compaction Technology. International Workshop on Compaction of Soil, Granulates and Powders, Innsbruck, Febr. 2000, A.A. Balkema-Verlag, Rotterdam

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FORSCHUNGSGESLLSCHAFT FÜR STRASSEN- UND VERKEHRSWESEN (1987): Arbeitsanleitung für die Bestimmung der Verdichtbarkeit von Walzasphalt mit Hilfe des Marshall-Verfahrens

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HÜNING, P. (1994): Grundsätze für die Zusammensetzung von Asphalten zur Erzielung bestimmter Eigenschaften, Asphalt 5/1994

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144

und

Verkehrswesen,

145

146

Glossary

*Definition, description

A AASHO – American Association of State Highway Officials ...........................................................38 Air void content Asphalt ......................83, 91, 94, 95, 96, 98, 100 Air voids (soil) .....................................46, 48, 50, 55 Amplitude ....................... 8*, 16*, 17, 18, 21, 79, 120 Anti-sticking agent .......................................119, 127 Areal output, compactor ..................................66, 67 Articulated steering .......................................26, 117 ASC Anti-Spin-Control system .......................28, 31 Asphalt base course ........................................82, 91 Asphalt binder ............................................... 93, 94* Asphalt binder course .....................................82, 83 Asphalt concrete................................ 82, 92, 93, 95* Asphalt mastic ................................................93, 98 Asphalt surface course ....................................82, 83 Asphalt temperature Laying .............................................................93 Rolling................................................... 104, 109 Attachment plates ...........................................29, 45

B Bedding modulus...................................................52 Bitumen ...........................................................83-88 Bitumen emulsion .................................................88 Blasting of rock ......................................................60 Bulk density (asphalt) .................................100, 102

C Calcareous sandstone ..........................................63 Calculation of output........................................66, 67 CBR California Bearing Ratio ................. 52*, 55, 56 Centrifugal force ....................................16*, 17*, 18* Circular exciter (circular vibrator) ..........................11 Combination roller .........................................28, 118 Compaction depth ...........................................72, 73 Compaction energy .........................................13, 19 Compaction of joints ....................................124, 125 Compaction output Soil..................................................... 66, 67, 74 Asphalt................................................... 109-112 Compaction resistance (asphalt) .................100-104 Compaction temperature (asphalt) see asphalt temperature

Compaction water content.........................43, 44, 70 Compaction work Soil..................................................... 47, 48, 49 Asphalt ..................................................100, 101 Compactness...................................................46, 48 Consistency index .........................36, 39, 51, 55, 56 Curvature index ...............................................33, 34

D Deformation modulus .......................................51-56 Static ............................................................. 52* Dynamic ........................................................ 53* Degree of compaction Soil..................................40, 46, 48*, 50, 51, 55 Asphalt ..................................... 83, 94-96, 102*, Depth effect .................19, 29, 76, 76, 115, 117, 118 Directed vibrator ..................................11, 13, 14, 75 Dolomite ...............................................................57 Double vibratory roller ....................................26, 64 Drum .......................................................27, 28, 118 Drum acceleration .......................................... 13,16* Drum diameter.............................................114, 116 Dry density ............................................................46 Dynamic stiffness ...........................9, 10, 15, 17, 21

E Energy transfer .....................................................75 Exciter shaft...........................................................11

F Frequency .......................... 16*, 17*, 19, 72, 76, 120 Fundamental vibration .............................................7

G Gradability of roller ..........................................28, 31 Gussasphalt ................................ 82, 83, 92, 93, 97* H Hand-guided vibratory roller ...................25, 26, 116 Harmonic vibration ..................................................9 147

Glossary

Hot and dry .................................................115, 118 Hydraulic plate ......................................................25

I Igneous rock .........................................................57 Indicator diagram ..................................................21 Inflation pressure, pneumatic tired roller ............115

J Jump operation......................................13, 9, 22, 75

L Layer thickness (lift height) .......................66, 67, 73 Limestone ..............................................................57 Liquid limit .............................................................36 Loosening of surface ......................................45, 75

M Marshall-method..................................................102 Metamorphic rock ..................................................57 Mudstone...............................................................62

N Natural frequency ..............................................8, 22 Natural vibration ......................................................8 Nijboer factor .......................................................114

O Optimal water content.................. 47*, 43, 49, 50, 70 Oscillator .........................................................11, 12 Output of compactor ..............................................74 Soil..................................................... 66, 67, 74 Asphalt ...................................................109-112 Overcompaction ..............................................75, 13

148

P Padfoot roller ............................30, 31, 63, 70, 76-78 Particle size fraction ..............................................33 Penetration (Bitumen) .....................................87, 88 Pivot steering.................................................26, 117 Plastic limit.............................................................36 Plasticity diagram ..................................................35 Plasticity index ................................................36, 39 Pneumatic tired roller ............................76, 114, 115 Polymer modified asphalt .....................................98 Polymer modified bitumen ..............................83, 88 Pre-compaction ...................................................113 Pressure distribution Vibrator ...........................................................12 Oscillator .........................................................12 Proctor curves ...........................................47, 48, 50 Proctor test ......................................................47, 49 Propagation of vibrations.....................9, 10, 29, 119 PSV – Polished Stone Value ...........................89, 92

R Resilient stiffness ........................................8, 10, 21 Resonance vibrations .............................................8 Ripping of rock.......................................................60 Rock classes .........................................................60 Rock of variable strength ......................................62 Rolled asphalt................................................83, 101 Rolling cracks ..............................................122, 125 Rolling passes Soil...........................................20, 66, 67, 77, 79 Asphalt.....................................20, 101, 122, 126 Rolling pattern Soil........................................................... 67, 68 Asphalt .................................................122 - 125 Rolling speed ..............20, 66, 67, 72, 111, 116, 120

S Sandstone ............................................................63 Saturation index.........................................44, 46, 48 Sedimentary rock ................................................ 57* Seismic wave speed .............................................60 Self-regulating system ...............................13, 14, 29 Shearing strength (soil) ..................................41, 42 Siltstone.................................................................62 Single drum roller ..................... 28-31, 45, 61, 63-67

Glossary

*Definition, description

Single wheel vibratory roller ...........................26, 64 Slates.....................................................................63 Softening point RaB (bitumen) .......................87, 88 Soil............................................................................. Engineering properties ....................................40 Compaction properties ...............................48-51 Soil classes............................................................39 Soil classification ..............................................33-37 Soil contact force ..................................10,15, 20, 21 Soil parameters ...............................................41, 42 Soil stabilisation (treatment) ...........................43, 71 Solid rock ..............................................................61 Sprinkler system..................................................127 Static axle load ................................................16, 17 Static compaction ..........................................75, 126 Static linear load .............................. 16*, 72, 76, 120 Stiffness of substrate..................10, 11, 17, 21, 45, 79, 116, 117 Stone mastic asphalt .............................. 92, 93, 96* Subharmonic vibration.............................................9 Surface course ......................................................82 Surface protection courses.............................83, 99, Surface treatment ............................................88, 99 Surface waves .........................................................9

Vibration generation ............................................ 17* Vibrating mass.................... 14, 16*, 17*, 21, 72, 120 Vibration path ...................................................... 16* Vibration speed..................................................8, 10 Vibratory plate ........................................23, 119, 24 Vibratory rollers ......... 25-32, 76-79, 94-96, 116-121 Vibratory tamper ...........................................23, 119 Viscosity (bitumen) ...............................................85 Void proportion ...........................................46-51, 54 Volcanic rock ....................................................... 57*

T Tandem roller..............................26-28, 94, 113, 109 Towed roller ..........................................................32 Traffic load .......................................................82, 92 Trial compaction ..............................................68, 69

U Unbalanced mass.......................................... 11, 16* Uniformity index...............................................33, 34 Uniform sands .................................................45, 49 USC Unified Soil Classification System................ 37

V VARIOCONTROL ................. 14, 15*, 16, 29, 75, 79 VARIOMATIC .................. 13, 14*, 91, 116, 119, 124 Vibration acceleration ..................................9, 10, 29 Vibration exciter.....................................................11 Vibration force .......................................................18 149