Bituminous Mix Design

DESIGN OF BITUMINOUS MIXES FOR BM, DBM, SDBC, BC ETC.

By

B.L.RAWAT B.E.(HONS.), M.E.(HONS.),MBA EXECUTIVE ENGINEER (BUILDING CELL) PWD, CE OFFICE, JAIPUR

TYPES OF BASES AND SURFACE COURSES (BITUMINOUS) Prime Coat  Tack Coat  Bituminous Macadam 

Grade 1  Grade 2  

Bituminous Penetration Macadam  

For 50 mm thick For 75 mm thick

Built-up Spray Grout  Dense Bituminous Macadam  Surface Dressing 

Single Coat  Double Coat  Surface Dressing with Precoated Aggregate 

Open Graded Premix Carpet  Mix Seal Surfacing 

Type A  Type B  

Semi-Dense Bituminous Concrete Grade 1  Grade 2  Grade 3 

Bituminous Concrete  Seal Coat 

Liquid Seal  Premixed Seal 

Bitumen Mastic  Slurry Seal 

3 mm  1.5 mm  

Recycling of Bituminous Pavement

BITUMINOUS MIX DESIGN (JOB MIX FORMULA) 

Marshall Stability Test Marshall Stability Test adopted by US Corps of Engineers is a semi-confined compression test which is comparable to a triaxial test with a cell pressure of about 0.7 kg/sqcm.

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Hveem Stabilometer and Cohesiometer Tests Hveem Stabilometer embodies main characteristics of triaxial test. It requires kneading compactor.

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Types of Bituminous Mixes Dense graded  Open graded 

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Desirable Properties     

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Stability: resistance to deformation Density: degree of compaction Durability: resistance against weathering Flexibility: extent of deformation before failure Resistance to skidding Workability during construction

MARSHALL STABILITY TEST 

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The Marshall Test is made to obtain optimum binder content for the type of aggregate mix and traffic intensity. This stability test is applicable to hot-mix design using bitumen and aggregates with maximum size of 25mm. Stability: The Marshall Stability of the mix is defined as a maximum load carried by a compacted specimen at a standard test temperature at 60°C and at the rate of 5 cm per minute. Flow value: The flow value is the deformation the Marshall test specimen undergoes during the loading, upto the maximum load, in 0.25 mm units.

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Design Steps Select grading to be used.  Select aggregates to be employed in the mix.  Determine the proportion of each aggregate required to produce the design grading.  Determine the specific gravity  Make up the trial specimens with varying bitumen contents.  Determine the specific gravity of each compacted specimen.  Make stability tests on the specimen.  Calculate the percentage of voids, VMA and the percent VFB in each specimen.  Select the optimum bitumen content.  Check the values of Marshall Stability, Flow, Voids in total mix, VFB with optimum bitumen content. 

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Apparatus 

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Marshall Mould: Cylindrical moulds of 10 cm diameter, 7.5 cm height with interchangeable base plate and collar. Sample Extractor: a jack or compression machine Hammer: 8.8 cm diameter, 4.5 kg weight, free fall 45.7 cm. Breaking Head Loading Machine: movement at the rate of 5 cm per minute, proving ring of 5 tonne capacity. Flow Meter: least count of 0.025 mm. Oven, Hot Plate, Mixing Apparatus, Water Bath, Thermometer

MODIFIED MARSHALL TEST Asphalt Institute Manual MS-2 and ASTM D5581.  Used where maximum size of aggregate is more than 26.5 mm.  Mould diameter: 150 mm.  When the modified Marshall test is used, the specified minimum stability values and the specified flow values shall be multiplied by 2.25 and 1.5 respectively. 

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Preparation of Test Specimen Aggregate: 1200 gm, heated to temperature of 175° to 190°C.  Mould Assembly and Rammer: pre-heated: 100° to 145°C.  Bitumen: heated 121° to 138°C.  Mixing temperature 

VG-10 or 80/100 grade: 154°C.  VG-20 or 60/70 grade: 160°C. 

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Compaction 50 blows on either side, for medium traffic roads  75 blows on either side, for heavy traffic roads 

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Compaction temperature VG-10 or 80/100 grade: 138°C.  VG-20 or 60/70 grade: 149°C. 

Compacted thickness: 63.5 ± 3.0 mm.  Bitumen content: 3% to 7.5% with increment of 0.5% 

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Tests 

Specific gravity of Compacted Specimens:

Gt = 100 / (W1/G1 + W2/G2

+ W3/G3 + W4/G4 ) 2

where W1 = percent by weight of coarse aggregates W2 = percent by weight of fine aggregate W3 = percent by weight of filler W4 = percent by weight of bitumen in total mix G1, G2 and G3 are apparent specific gravity values of coarse aggregates, fine aggregates and filler and G4 is the specific gravity of bitumen.

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Density and Void Analysis

Vv, % = 100(Gt – Gb)/ Gt Vb, % = Gb * W4/ G4 VMA, % = Vv + Vb VFB, % = 100 * Vb/ VMA where Gb = bulk density of a specimen Gt = theoretical specific gravity mixture Vv = air voids in the mix, % Vb = volume of bitumen VMA = voids in mineral aggregate, % VFB = voids filled with bitumen, %

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Marshall Stability and Flow Values The specimen is kept immersed under water at 60°C ± 1°C for 30 to 40 mins.  Placed in test head and maximum load before failure is noted.  Flow value at failure is noted.  Correction in thickness if specimen not exactly 63.5 mm.  Correction factor is applied. 

Correction Factors Volume of Specimen in cubcm

Approximate Thickness of Specimen (mm)

Correction Factors

457 – 470

57.1

1.1.9

471 – 482

58.7

1.14

483 – 495

60.3

1.09

496 – 508

61.9

1.04

509 – 522

63.5

1.00

523 – 535

65.1

0.96

536 – 546

66.7

0.93

547 – 549

68.3

0.89

560 – 573

69.9

0.86

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Determination of Optimum Bitumen Content Five graphs are plotted with values of bitumen content against the values of:  Density Gb, g/cubcm  Marshall stability S, kg  Voids in total mix Vv, %  Flow value F, 0.25 mm units  Voids filled with bitumen VFB, %

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Bulk density, Stability and Flow are measured whereas percentage air voids, Vv, VFB and VMA are computed from formula.

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Optimum Bitumen Content

B0 = (B1 + B2 + B3)/ 3 where, B1 = bitumen content corresponding to maximum density. B2 = bitumen content corresponding to maximum stability B3 = bitumen content corresponding to specified voids content, Vv 

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Value of flow and VFB are found from graphs, corresponding to B0. All the design values of Marshall Stability, Flow, Voids and VFB are checked at the B0 with the specific design requirement of the mix. If mix designed does not fulfill any one or more of the design requirements, the gradation of aggregates or filler content or bitumen content or combination of these are altered and the design tests are repeated till all the requirements are simultaneously fulfilled.

JOB MIX FORMULA 

The proportion in which the different aggregates, filler and bitumen are to be mixed are specified by weight or by volume for implementation during the construction, is called Job Mix Formula.

VISCOSITY GRADED (VG) BITUMENS AND THEIR GENERAL APPLICATIONS Viscosity Grade

General Applications

VG-40 (40-60 penetration)

Use in highly stressed areas such as those in intersections, near toll booths, and truck parking lots in lieu of old 30/ 40 penetration grade

VG- 30 (50-70 penetration)

Use for paving in most of India in lieu of old 60/ 70 penetration grade

VG- 20 (60-80 penetration)

Use for paving in cold climate, high altitude regions of North India

VG-10 (80-100 penetration)

Use in spraying applications and for paving in very cold climate in lieu of old 80/ 100 penetration grade

SELECTION CRITERIA FOR GRADE OF MODIFIED BITUMEN

Lowest Daily Mean Highest Daily Mean Air Temperature, °C Air Temperature, Less than 20°C 20 to 30°C More than 30°C °C More than -10°C

PMB/ NRMB 120 CRMB 50

PMB/ NRMB 70 CRMB 55

PMB/ NRMB 40 CRMB 60

-10°C or lower

PMB/ NRMB 120 CBMB 50

PMB/ NRMB 120 CRMB 50

PMB/ NRMB 70 CRMB 55

PHYSICAL PROPERTIES OF COARSE AGGREGATE Property

Test

Requirement

Test method

Cleanliness

Grain size analysis

Max. 5% passing 0.075mm

IS: 2386 Part I

Particle Shape

Flakiness and Elongation Index

Max. 35%

IS: 2386 Part I

Strength

Los Angeles Abrasion Value

BC- Max. 30% Others- Max. 35%

IS: 2386 Part IV

Aggregate Impact Value

BC- Max. 24%

IS: 2386 Part IV

Others- Max. 27% Polishing

Polished Stone Value

Min. 55

IS: 2386 Part IV

Soundness (Either Sodium or Magnesium Sulphate) – 5 cycles Sodium Sulphate

Max. 12%

IS: 2386 Part V

Magnesium Sulphate

Max. 18%

IS: 2386 Part V

Water Absorption

Water Absorption

Max. 2%

IS: 2386 Part III

Stripping

Coating and Stripping of Bitumen Aggregate Mixtures

Min. Retained Coating 95%

IS: 6241

Water Sensitivity

Retained Tensile strength

Min 80%

ASHTO 283

GRADING REQUIREMENT OF MINERAL FILLER IS Sieve (mm)

Cumulative % passing by weight of total aggregate

0.6

100

0.3

95 – 100

0.075

85 – 100

AGGREGATE GRADING AND BITUMEN CONTENT Specification

DBM

Grading

1

2

1

2

1

2

Normal maximum aggregate size

37.5 mm

26.5 mm

13.2 mm

9.5 mm

19 mm

13.2 mm

Layer thickness

75–100 mm

50 – 75 mm

40 mm

25 mm

50 mm

25/ 40 mm

IS Sieve size (mm)

SDBC

BC

Cumulative percent by weight of total aggregate passing

45

100

37.5

95 – 100

100

26.5

63 – 93

90 – 100

19

-

71 – 95

100

13.2

55 – 75

56 – 80

90 – 100

9.5

-

-

4.75

38 – 54

2.36

100 90 – 100

100

100

59 – 79

90 – 100

70 – 90

90 – 100

52 – 72

70 – 88

38 – 54

35 – 51

35 – 51

35 – 55

53 – 71

28 – 42

28 – 42

24 – 39

24 – 39

28 – 44

42 – 58

1.18

-

-

15 – 30

20 – 34

34 – 48

0.6

-

-

15 – 27

26 – 38

0.3

7 – 21

7 – 21

10 – 20

18 – 28

0.15

-

-

5 – 13

12 – 20

0.075

2–8

2–8

3–8

3–8

2–8

4 – 10

Bitumen content (Min)

4%

4.5%

4.5%

5%

5.2%

5.4%

9 – 19

TRRL METHOD, HER MAJESTY’S LONDON

PERMISSIBLE VARIATION FROM THE JOB MIX FORMULA Description

Permissible Variation DBM

SDBC/ BC

Aggregate passing 19 mm or larger

± 8%

± 7%

13.2 mm/ 9.5 mm

± 7%

± 6%

4.75 mm

± 6%

± 5%

2.36 mm, 1.18 mm, 0.6 mm

± 5%

± 4%

0.3 mm, 0.15 mm

± 4%

± 3%

0.075 mm

± 2%

± 1.5%

Binder Course

± 0.3%

± 0.3%

Mixing Temperature

± 10°C

± 10°C

MIXING, LAYING AND ROLLING TEMPERATURES FOR DENSE MIXTURES (°C)

Bitumen Viscosity Grade

Bitumen Aggregate

Aggregate Temperature

Mixed Material Temperature

Laying Temperature

Rolling Temperature

VG – 40

160 – 170

160 – 175

160 – 170

150 Min.

100 Min.

VG – 30

150 – 165

150 – 170

150 – 165

140 Min.

90 Min.

VG – 20

145 – 165

145 – 170

145 – 165

135 Min.

85 Min.

VG – 10

140 – 160

140 – 165

140 – 160

130 Min.

80 Min.

REQUIREMENT OF THE DENSE GRADED BITUMINOUS MIX USING VISCOSITY-GRADED (VG) PAVING/ MODIFIED BITUMEN Properties

Viscosity Grade Paving Bitumen

Modified Bitumen Hot climate

Test Method

Cold climate

Compaction level (Number of blows)

75 blows on each face of the specimen

Minimum stability (kN at 60°C)

9.0

12

10

AASHTO T245

Marshall flow (mm)

2–4

2.5 – 4

3.5 – 5

AASHTO T245

Marshall Quotient (stability/ flow)

2–5

2.5 – 5

% Air Voids

3–5 65 – 75

% Voids filled with bitumen (VFB) Tensile Strength Ratio Coating of Aggregate Particles with bitumen

MS-2, ASTM D2041

80% (Minimum)

MS – 2 AASHTO T283

95% (Minimum)

IS: 6241

% VOIDS IN MINERAL AGGREGATE, VMA Nominal Maximum Particle Size (mm)

Min. % VMA related to designed % air voids 3

4

5

9.5

14

15

16

13.2

13

14

15

19.0

12

13

14

26.5

11

12

13

37.5

10

11

12

RECOMMENDED TYPE AND THICKNESS OF BITUMINOUS WEARING COURSES UNDER DIFFERENT SITUATIONS

(IRC:37:2001) Sl. No.

Type of Base/Binder course

Type of Bituminous Wearing Course

Annual Rainfall L: 3000 mm

Design traffic (msa)

1.

WBM,WMM, Crushed Macadam, Built up Spray Grout

20 mm PMC with sand seal coat

L and M