Highway Engineering Design_Pavement Design

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Dr. Wasala Bandara

Pavement is defined as a road or highway with hard, smooth, and leveled surface made using a suitable material such as Portland cement concrete or asphalt concrete

Asphalt co concrete pa pavement

Portland ce cement co concrete pa paveme2 nt

Pavement is defined as a road or highway with hard, smooth, and leveled surface made using a suitable material such as Portland cement concrete or asphalt concrete

Asphalt co concrete pa pavement

Portland ce cement co concrete pa paveme2 nt

In the west; Romans were the pioneer road makers, who use elaborate techniques as far back as 312 B. B.C. C. They construcred the three kinds of roads as follows: 

Levelled earth roads



Compacted gravel road



Stone block-paved roads

The Romens practiced the removal of all soft material under a pavement and building up the road from the hard stratum. Therefore these road had pavement thickness varying from 0.75m to 2.5m.

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The next stage in the development of road making came in the 18 th century when the French engineer Tresaguset (1716-1796) introduced the concept of cross chamber for surface water drainage. This method of construction consisted of preparing a convex road bed or sub grade and laying two layers of hand-packed foundation stones.

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Telford (1757-1834), the founder and first president of the Institution of Civil Engineers proposed a new method of construction in the early 19th century.

He believed in the principle of effecting surface drainage by a cross slope aopte by Tresaguest, but obtained it by laying foundation stone of varying sizes on a flat subgrade.

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In 1827 Jhon Mc Adam, the forerunner of the modern highway introduced a completely different method of road construction based on scientific observations 1.

The earth based or subgrade that the road is built on, ultimately carried the total load

2.

Any well rained compacted good soil could carry such a load. Hence subgrade drainage under a pavement is important

3.

Structure stability of the pavement structure

4.

Stones on the surface layer should be smaller than the width of the wheel or  else loosening of the surface could occur 

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  Defined 

by users (drivers)

Develop methods to relate physical attributes to driver ratings

  Result

is usually a numerical scale

From the AASHO Road Test (1956  – 1961)

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Pavements are classified as “ flexible”  or “ rigid ” or “ composite”  depending on how they distribute surface loads

Pavement

Flexible

Rigid

Composite

Constructed using granular material and bitumen

Constructed of  Portland cement concrete (PCC)

Base layer of PCC and a surface layer of hot-mix asphalt 12

Flexible pavements   are those which are   surfaced (i.e., paved) with bituminous materials such as asphalt concrete  Asphalt

concrete possess a lower stiffness (EI) than Portland cement concrete due to lower modulus of  elasticity of asphalt concrete as compared to Portland cement concrete

 Due

to lower stiffness of asphalt concrete the total structure of a flexible pavement "bends" or "deflects" under traffic loads. This is the logic behind calling such a pavement as "flexible pavement”

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Flexible pavements distribute the wheel load over a coneshaped area under the wheel, reducing the imposed unit stresses as depth increases

Load distribution under a flexible pavement

Stress at lower depth is higher than the stress at higher depth 14

Rigid pavements are those which are  surfaced (i.e., paved) with Portland cement concrete  Portland

cement concrete possess a substantially higher  stiffness (EI) than asphalt concrete due to higher  modulus of elasticity of Portland cement concrete as compared to asphalt concrete

 Due

to high stiffness of Portland cement concrete the total structure of a rigid pavement  "bends" or "deflects" very little   under traffic loads. This is the logic behind calling such a pavement as “rigid pavement”

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Rigid pavements act as flexural members and distribute the wheel load fairly uniformly over the area under the pavement slab

Load distribution under  a rigid pavement

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Structure Surface course  Base course  Subbase course    Subgrade 

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 





Subgrade: Prepared roadbed consisting of natural or  imported soil Subbase course: This is the layer (or layers) under the base layer. A subbase is not always needed and therefore may often be omitted . Base course: This is the layer directly below the Portland cement concrete layer and generally consists of aggregate or stabilized subgrade. Surface course: This is the top layer and the layer that comes in contact with traffic. It consists of the Portland cement concrete slab 18

Jointed Plain Concrete Pavement (JPCP)

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Continuously Reinforced Concrete Pavement (CRCP)

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Slip form

Fixed form

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Structure     

Surface (Wearing) course Base course Road-base course Sub-base course   Subgrade

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 

 



Subgrade: Prepared roadbed consisting of natural or imported soil Sub-base course: A layer between the subgrade and the roadbase course, made from materials superior to that of subgrade. In case of a good quality of subgrade, the subbase course is omitted. Road-base course: A layer between the sub-base and the base course Base course:   This is the layer directly below the asphalt concrete layer and generally consists of aggregate (either  stabilized or unstabilized). Surface course: This is the top layer and the layer that comes in contact with traffic. It may be composed of one or several different asphalt concrete sub layers 23

Dense-graded

Open-graded

Gap-graded 24

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The functions of the different layers of flexible pavement are as follows

1. Wearing course a) b) c) d)

Withstands direct traffic loading. Provides smooth riding Provides skid resistant surface Waterproofs the pavement

2. Base-course (a) Supports wearing course (b) Assists protecting layers below

3. Road-base (a) Main load spreading layer of the pavement structure

4. Sub-base a) Assists load spreading b) Assists subsoil drainage

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

Granular sub-base, called Type 1



Graded Granular sub-base, called Type 2

(Crushed rock; slag; or other hard material such as smaller size material other than what specified in Type 1. Therefore, natural sands and gravels.)

Type 1 is stronger  It h a s g o o d p ar t i c l e d i s t r i b u t i o n an d h e n c e g o o d i n t e rl o c k i n g q u a l it y   28

Sieve size 75 mm 37.5 mm 10 mm 5 mm 600 μm 78 μm

Percentage passing Type 1

Type 2

100 85-100 40-70 25-45 8-22 0-10

100 85-100 45-100 25-85 8-45 0-10

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Lower Sub-base ( Capping layer or Selected Subgrade)

Upper Sub-base Flex ib le

Soil Type Liquid Limit (LL) Plasticity Index (PI) Maximum Dry Density 4-days soaking CBR at 98% MDD Layers thickness Compaction using

Rig id

Type I & II Not to exceed Not to exceed 40% 25% Not to exceed Not to exceed 15% 6%

Type I & II Not to exceed 40% Not to exceed 15%

Not less than 1,750 kg/m 3

Not less than 1,650 kg/m 3

Not less than 30%

Not less than 15%

Not exceed 225 mm 8-10 tonne smooth wheel roller

Optimum moisture content Degree of Compaction

Flex ib le  

2% 98%

95%

Standard Specification for Construction and Maintenance of Roads and Bridges (ICTAD- SCA/5) 30



Wet mix macadam

Crushed rock graded and mixed with 2-6% water. Laid in 200 mm layers and compacted or rolled 

Dry bound macadam

37.5 mm to 50.0 mm single size crushed rock laid in 75-100 mm thick layers and rolled  A 25mm thick 4.7mm down crushed rock layer is laid on top and vibrated into the course layer  Repeat until no more smaller material can be worked in. Excess fines removed and additional course layers are laid to build the required thickness of road-base 

Dense bituminous macadam

Crushed rock (fines