BITUMEN AND AGGREGATE(By Er.A.Venkatachalam, Deputy Director/Bitumen Lab, HRS)

BITUMEN & TAR

Bitumen is a binder obtained from fractional distillation of crude Petroleum oil. But tar is a

binder obtained from destructive distillation of coal during manufacturing of coke. Tar has excellent

binding capacity rather than bitumen. But tar becomes brittle within 4 or 5 years. Hence, life of tar is

comparatively lesser than bitumen.

TYPES OF BITUMEN

1) Conventional Bitumen

a) Penetration Grade

Based on hardness (penetration values), this is classified as many types. But most important

types used for road construction are

(i) 30/40 grade

(ii) 60/70 grade

(iii) 80/100 grade

b) Viscosity Grade

The variability in performance at high temperatures can be addressed by adopting a viscosity

– graded specification (based on viscosity at 60 deg C). The viscosity grade bitumen shall be

classified into four types

(i) VG-10

(ii) VG - 20

(iii) VG-30

(iv) VG-40

2) Cut Back Bitumen

1

This is a homogeneous mix of bitumen and anyone of the solvent like Petrol, Diesel, Heavy

engine oil etc. This mixture remains in liquid stage and hence it need not be heated when put into

use. Depending on the type of solvent used, it can be classified as

(i) Slow curing (SC) cut back bitumen.(eg: Heavy engine oil as solvent),

(ii) Medium curing (MC) cut back bitumen (eg: Diesel as solvent) and

(iii) Rapid curing (RC) cut back bitumen. (eg: Naptha as solvent.)

3) Bitumen emulsion

This is similar to cut back Bitumen, but the solvent is water. Bitumen particles are kept

suspended in water by means of stabilizing agents. Since this is in liquid form, it can be directly used

for work without heating. But before using, the drum containing bitumen emulsion should be rolled

on ground to and fro four or five times for about 15 m distance to prevent the settlement of bitumen

particles. Based on the setting time it can he classified as

(i) Rapid setting -1 RS-1

(ii) Rapid setting – 2 RS-2

(iii) Medium setting MS

(iv) Slow setting-1 SS-1

(v) Slow setting-2 SS-2

TESTS FOR ASSESSING THE PROPERTIES OF CONVENTIONAL BITUMEN

IS 1201 to IS 1220 specifies the different test to assess the quality of bitumen. The

important tests to be conducted are:

1. Penetration test - IS: 1203 - 1978.

2. Softening Point test - IS: 1205 - 1978.

3. Ductility test - IS: 1208 - 1978.

4. Viscosity test - IS: 1206-1978 -Part 2 & 3

5. Flash point test - IS: 1209 - 1978.

6. Solubility in Trichloroethylene - IS: 1216 - 1978.

I.S. REQUIREMENTS OF CONVENTIONAL BITUMEN:

IS 73 –2013 specifies the requirements of conventional Bitumen (Viscosity Grade).

2

Table 2.1 Requirements for Paving Bitumen

SI.

No Characteristics

Paving Grades Method of

Test

Reference To

IS No.

VG 10 VG 20 VG 30 VG 40

1.Penetration at 25ºC, 100g, 5

Sec., 0.1mm, min80 60 45 35 IS 1203

2.Absolute Viscosity at 60ºC,

Poises

800-

1200

1600 -

2400

2400 -

3600

3200 -

4800

IS 1206 (Part

2)

3.Kinematic Viscosity at 135ºC,

cSt, Minimum250 300 350 400

IS 1206 (Part

3)

4.Flash point, (Cleveland open

cup), ºC, Minimum220 220 220 220 IS 1209

5.Solubility in trichloroethylene,

percent, Minimum99.0 99.0 99.0 99.0 IS 1216

6.Softening Point (R & B),ºC,

Minimum40 45 47 50 IS 1205

7. Tests on residue from thin – film oven tests/RTFOT

i) Viscosity ratio at 60 ºC, Max 4.0 4.0 4.0 4.0IS 1206 (part

2)

ii) Ductility at 25 ºC, cm, Min, 75 50 40 25 IS 1208

3

TESTS FOR ASSESSSING THE PROPERTIES OF CUT BACK BITUMEN:

The various tests which are conducted to assess the quality of cut back bitumen are

1. Kinematic Viscosity at 60oC - IS:1206 part 3-1978

2. Flash Point Test - IS: 1209 –1978

3. Distillation Test - IS: 1213 – 1978

4. Water content Test - IS: 1211 - 1978

5. Test on residue from distillation

a. Viscosity - IS: 1206 Part 3 – 1978

b. Ductility - IS: 1208 –1978

c. Solubility in trichloroethylene - IS: 1216 – 1978

I.S. REQUIREMENTS OF CUT BACK BITUMEN:

I.S: 217 - 1988 specifies the requirements of cut back bitumen. Even though many grades are

available in cut back bitumen, MC 30 grade alone is commonly used in practice. Hence, the

requirement of MC 30 grade cut back bitumen alone is furnished below.

Table 2.2 Requirements for MC Cut back Bitumen (MC 30)

S.No Characteristics

Requirement

(MC30)

Min. Maxi.

1 Kinematic viscosity at 60° c in centistokes. 30 60

2 Flash point Pensky martens closed cup, o c. 38 -

3 Distillate volume, percent of total distillate upto 360oc.

a) Up to 225° c. - 25

b) Up to 260° c. 40 70

c) Up to 315° c. 75 93

4Residue from distillation upto 360o C, Percent volume by

difference.50 -

5 Tests on residue from distillation upto 360o C

a) Viscosity at 60o C, poises 300 1200

b) Ductility at 27oC, cm 100 -

4

c) Solubility in trichloroethylene percent. 99 -

6 Water content, percent by mass - 0.2

TESTS FOR ASSESSING THE PROPERTIES OF BITUMEN EMULSION:

Various tests, which are generally conducted to assess the quality of Bitumen Emulsion are:

1. Viscosity Test - IS: 3117 - 1965

2. Coagulation Test - IS: 8887 - 2004

3. Storage Stability Test - IS: 8887 - 2004

4. Coating Ability Test - IS: 8887 - 2004

5. Miscibility Test - IS: 8887 - 2004

6. Tests on residue - IS: 8887 – 2004

I.S. REQUIREMENTS OF BITUMEN EMULSION

IS: 8887 - 2004 specifies the physical and Chemical Requirements of Bitumen Emulsion.

Table 2.3 Requirements for Bitumen Emulsion

S.No Characteristics Type of EmulsionRS -1 RS -2 MS SS-1 SS-2

1 Residue on 600 micron IS sieve (percent By mass. max)

0.05 0.05 0.05 0.05 0.05

2 Viscosity by say bolt Furol Viscometer, SecondsAt 25oC - - - 20-

100

30-150At 50oC 20-100 100-

300

50-300 - -

3 Coagulation of Emulsion at low temperature temperature.

NIL NIL NIL NIL NIL4 Storage stability after 24 hours, percentage,

max.2 1 1 2 2

5 Particle ChargePositiv

e

Positiv

e

Positiv

e

Weak

Positiv

e

Positive

6 Coating ability and water resistance.1) Coating, dry aggregate. - - Good - -2) Coating, after spraying. - - Fair - -3) Coating, wet aggregate. - - Fair - -4) Coating, after spraying - - Fair - -

7 Stability to mixing with cement (Percentage Coagulation), Max

- - - 2 2

5

8 Miscibility with water

No

Coagul

ation

No

Coagul

ation

No

Coagul

ation

-

No

Coagul

ation

9 Tests on Residue

a) Residue by evaporation. Percent, Minimum. 60 67 65 50 60

b) Penetration 25°C / 100g / 5 sec. 80-150 80-150 60-150 60-

350

60-120c) Ductility 27oC in cm minimum. 50 50 50 50 50d) Solubility in trichloroethylene. (min) 98 98 98 98 98

10 Distillation in percent, by volume at1. 190°C - - - 20-55 -2. 225°C - - - 30-75 -3. 260°C - - - 40-90 -4. 315°C - - - 60-

100

-11 Water content, percent by mass, Max - - - 20 -

Table 2.4 Suitability of Different Types / Grades of Bitumen (Viscosity Grade)

Viscosity Grade (VG) General Applications

VG-40 (40-60 Penetration)

Used 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 of paving in most of India in lieu of old

60/70 penetration grade

VG-20 (60-80 Penetration)Use of 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.

CUTBACK BITUMEN

Generally suitable for patch works and emergency works.

6

Used for priming coat and tack coat also.

BITUMEN EMULSION

Bitumen Emulsion or cut back bitumen alone should be used for priming coat and tack coat.

Conventional Bitumen should not be used.

Suitable for making mix for premix carpet Layer and laying surface dressing.

Suitable for repairing patches potholes and emergency works.

AGGREGATE

Types of Rocks

i) Igneous rocks (e.g.) Granite, Basalt.

ii) Sedimentary rocks (e.g.) Lime stone.

iii) Metamorphic rocks (e.g.) Slate, Marble.

Generally igneous rocks are suitable for road works.

Requirements of Good Aggregate

Angular in shape.

Free from foreign matters.

Capable of withstanding high stresses due to traffic.

Capable of resisting abrasion due to traffic.

Capable of withstanding the impact due to moving wheel loads.

Sound enough for weathering action.

Tests for Assessing the Properties of Aggregate

The various tests, which are generally conducted to assess the quality of aggregates, are

1. Flakiness index test

2. Impact test

3. Los Angeles abrasion test

4. Stripping test

5. Soundness test

6. Aggregate crushing Value

7

7. Unit weight of aggregates

8. Specific gravity of aggregates

Table 2.5 Physical Requirement of Aggregate for Various Works MORT&H – 2013 Vth Revision

Type of pavement

Los

Angeles

Abrasion

Value

Impact

Value

Combined

Flakiness

and

Elongation

index

Water

Absorption StrippingWater

Sensitivity

(Max). (Max). (Max). (Max).

(Min.

retained

coating)

Retained

Tensile

Strength (Min)

Bituminous Macadam 40% 30% 35% 2% 95% 80%

Dense Bituminous

Macadam35% 27% 35% 2% 95% 80%

Bituminous Concrete 30% 24% 35% 2% 95% 80%

Close Graded Premix

Surfacing / Mix Seal

Surfacing

35% 27% 35% 1% 95% 80%

Stone Matrix Asphalt 25% 18% 30% 2% - -

Mastic Asphalt 40% 30% 35% 2% 95% 80%

Surface Dressing 35% 27% 35% 1% 95% 80%

8

BITUMINOUS MIXES

Preparation of Mix

Bituminous mix is generally prepared in central mix plants where high degree of quality

control is possible. In central mix plants (CMP), generally mixes are prepared in a large scale at a

convenient location with the help of sophisticated and automatically controlled machines. The mixes

from such plants are conveyed by tippers or dumpers to the work site. If mix is to be prepared for

small works, then site plants (Mini hot mix plant) may be used where the mix is prepared at the site

itself.

Temperature Control

While preparing the mix, aggregates shall be heated to a temperature as specified to remove

the moisture and inorganic matters so as to enable proper coating of bitumen. Bitumen shall be

heated in a separate tank to obtain the required fluidity and the added to the aggregates in the mix

chamber. Then mixing is carried out. Bitumen has not been heated beyond the range, because at

higher temperature, bitumen will loose its desirable properties for road work and it will be charred.

Excess heating of aggregate is also not preferable, as it may be increase the temperature of bitumen,

which in turn affect the quality of mix.

Table 2.6 Mixing, Laying and Rolling Temperatures for Dense Mixtures ( Degree Celcius)

Bitumen

Viscosity

Grade

Bitumen

Temperature

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.

* Rolling must be completed before the mat cools to these minimum temperatures.

9

Rolling operation shall be completed in every respect before the temperature of mix falls below

100°C. Effective compaction may not be possible below 100°C.

Rolling

This shall be done by 8 to 10 tonnes rollers. Rolling shall start as soon as possible after the

material has been spread deploying a set of rollers as the rolling is to be completed in limited time

frame. The roller shall move at a speed not more than 5 kmph.

Initial rolling shall be done with 8-10 tonnes dead weight smooth-wheeled rollers.

Intermediate rolling shall be done with 8-10 tonnes dead weight vibratory roller or with a pneumatic

tyred roller of 12 to 15 tonnes weight having nine wheels, with a tyre pressure of at least 5.6

kg/sqcm. The finish rolling shall be done with 6-8 tonnes smooth wheeled tandem rollers. Rolling

shall be continued till the entire surface has been rolled to 100% of the average laboratory density

mentioned in the mix design. Final rolling is done by tandem roller to remove the roller marks.

Overlapping on successive passes by at least one-third of the width of the rear roll or in the case of a

pneumatic-tyred roller, at least the nominal width of 300mm.

The distance between the CMP site and work site shall be so fixed that the temperature of the

mix in all the stages shall be strictly maintained as per Specifications.

Curing

Generally overnight curing is sufficient. But it is desirable to cure the surface for about

24 hours.

PRIMING COAT & TACK COAT

The bitumen coat which is applied on the Granular surface before laying the bituminous mix is

called prime coat. It serves the following purposes.

It fills the capillary voids in the Granular surface.

It binds the dust particles on the Granular surface.

The bitumen coat applied in between two bituminous surfaces to bind the over lay with the

existing bituminous layer is called tack coat.

The requirements as per MORTH – Vth Revision is as follows

10

Table 2.7 Quantity of Bitumen Emulsion (SS-I) as Primer for various Surface Types

Type of Surface Rate to Spray (Kg/m2)

WMM/WBM 0.7-1.0

Stabilized soil bases/ Crusher Run Macadam 0.9-1.2

Table 2.8 Type and Quantity of Cutback Bitumen Primer

Type of Surface Type of Cutback Rate to Spray (Kg/m2)

WMM/WBM MC 30 0.6-0.9

Stabilized soil bases/ Crusher Run Macadam MC 70 0.9-1.2

Table 2.9 Rate of application of Tack coat

Sl.

noType of Surface Rate of Spray (Kg/m2)

1 Bituminous Surface 0.20 to 0.30

2 Granular Surface treated with primer 0.25 to 0.30

3 Cement Concrete Pavement 0.30 to 0.35

Further quality control shall be undertaken for Prime coat and Tack coat works are as

tabulated below

Table 2.10 Control tests for Prime Coat / Tack coat

TEST FREQUENCY OF TESTS

Quality of Binder Number of samples per lot and tests as per IS: 73, IS: 217,

11

and IS:8887 is applicable

Binder Temperature for application At regular close intervals

Rate of Spread of binder Three tests per day

IMPORTANT TYPES OF BITUMINOUS LAYERS & CONSTRUCTION PROCEDURE:

1. Bituminous Macadam (BM).

2. Dense Bituminous Macadam (DBM).

3. Bituminous Concrete (BC).

4. Surface Dressing (SD).

5. Mix Seal Surfacing / Close Graded Premix Surfacing.

6. Stone Matrix Asphalt.

7. Mastic Asphalt.

The construction procedures for the first three types above are same. It involves

Collection and stacking required quantity of materials at the CMP site

Obtaining job mix formula for the materials collected

Preparing mix of bitumen and aggregate at CMP

Transporting to the road site

Preparation of the surface to receive the bituminous mix

Spreading and rolling

But the strength of these layers varies with each other because of the difference in gradation of

aggregate and binder content in each type. Bituminous Macadam and Dense Bituminous Macadam

are used for Base courses and it requires surface course (BC) over it to provide smooth riding

surface.

The construction of Surface dressing involves

Spraying of bitumen

Spreading the aggregates over it

Rolling.

Mix seal Surfacing Consists of laying and compacting mix seal surfacing in a single course

composed of suitable aggregates premixed with binder.

12

Stone Matrix Asphalt is a gap-graded mixture with about 70-80 percent stone content,

minimum 5.8 percent of binder, 8-12 percent of filler and about 0.3 percent fibres or similar

modifier. The high stone content of the mixture forms a skeleton-type structure offering high

resistance to deformation. The fibres or modifier prevent drainage during manufacture,

transportation and laying. The mixture is laid at a thickness of 40 to 75 mm.

Bitumen mastic, alternatively known as Mastic Asphalt, is an intimate homogenous mixture

of selected well graded aggregates, filler and bitumen in such proportions as to yield a plastic

and void less mass, which when applied hot can be trowelled and floated to form a very

dense impermeable surfacing. The material derives its mechanical strength from the

resistance to strain of the continuous matrix of fine aggregate, filler and bitumen. The final

product is very hard, durable fully impermeable, resistance to deformation and self-healing.

MIX DESIGN

Objectives of Bitumen Mix Design

To determine a cost-effective blend and gradation of aggregates and bitumen that yields a mix

having

1. Sufficient Bitumen and proper gradation of aggregates to ensure a durable pavement by

bonding the aggregates

2. Sufficient mix stability to satisfy the demands of traffic without distortion or displacement

3. Sufficient voids in the total compacted mix to allow for a slight amount of additional

compaction under traffic loading and a slight amount of bitumen expansion due to

temperature increase without flushing, bleeding and loss of stability

4. A maximum void content to limit the permeability of harmful air and moisture into the mix

5. Sufficient workability to permit efficient placement of the mix without segregation and

without sacrificing stability and performance

6. For surface mixes, proper aggregate texture and hardness to provide sufficient skid

resistance in unfavorable weather conditions.

Procedure:

Generally Marshall Method is universally adopted for bituminous mix design. The design

involves the following steps.

13

1) The suitable proportion of each size of aggregate is arrived so that the combination of all sizes

would satisfy the MORTH-V grading requirements.

2) Then Marshall mould is prepared with different binder contents and the following values are

arrived for each percentage of binder.

i) Marshall stability value.

ii) Flow value.

iii) Unit weight.

iv) Percentage voids in total mix.

v) Percent voids filled with bitumen.

Then Graphs are plotted with the bitumen content on X-axis and the above values on Y-axis. The

optimum binder content is found for Binder content corresponding to 4% percent air voids in total

mix.

Then the Marshall Stability value, Flow value and percent voids filled with Bitumen at the optimum

binder content are checked with the design requirements given in MORTH-V specification.

IMPORTANT QUALITY CONTROL TESTS ON BITUMINOUS LAYER

Bitumen Extraction test

Determines the bitumen content in the bituminous mixture

Conformity test as bitumen content is already controlled by computer panel

Gradation on aggregates

Determines the combined gradation of aggregates in the bituminous mixture by sieve

analysis

Conformity test as aggregate percentage is already controlled by computer panel

Field density test

Compaction of constructed bitumen surface is evaluated

Relative compaction achieved as per MORTH-V specifications

Conforms proper rolling done during construction at the specified temperature of mix

Evaluated through core cut samples

FAILURES AND DEFECTS OF SURFACE

14

Surface Defects

Fatty surface Smooth surface Streaking Hungry surface

Cracks

Hairline cracks

Alligator cracks

Longitudinal cracks

Edge cracks

Reflection cracks

Shrinkage cracks

Deformation

Slippage

Rutting

Corrugation

Shoving

Shallow depression

Settlement and Upheaval

Disintegration

Stripping

Ravelling

Pothole

Edge breaking

Modified Bitumen:

Rubber and Polymer Modified Bitumen

15

Addition of certain percentage of rubber in the form of rubber milk or rubber powder or

crumb rubber powder from discarded truck tyres or polymer with the bitumen improves the property

of bitumen and such modified bitumen possesses many advantages including increase in life and

satisfying serviceability requirements. It also minimizes the maintenance cost “IRC – special

publication 53, 2010 – guidelines on use of polymer and rubber modified bitumen in road

construction, specifies the advantages and general requirements of modifiers. Type of modifiers;

their dosage, choice of particular modifier, design procedure, handling procedure and precaution to

be adopted while using rubber/polymer modified bitumen for road works.

Specification Requirements for Modified Bitumen

The requirements of modified bitumen are given in table below

For snow bound area, Fraass breaking point values of modified bitumen will be taken in to account.

The value of Fraass breaking point shall be less than 7 days minimum atmospheric temperature of

the area or as indicated in Table below.

For checking the elastic recovery of modified binder, Field Engineer shall test for Torsion Recovery

at 25 oC using Torsion Recovery method as per Annexure -4. The Torsion recovery value shall not

be less than half of the elastic recovery value at 15oC as indicated in the laboratory testing.

Table 2.11 Properties of Modified Bitumen

Highest Mean Air Temp<20oC 20oC to 35oC above

35oC

Lowest Mean Air Temp. >-10 <-10 >-10 <-10 >-10

Sl.

No

(1)

Characteristics

(2)

Specified values for the

bitumen

(3) (4) (5)

Method of Test

IS No. (6)

Ref to

Annexur

e (7)

IPenetration at 25 oC, 0.1mm,

100g, 5 Sec60 to 120 50 to 80 30 to 50 1203 -

II Softening point (R&B) oC Min 50 55 60* 1205 -

III FRAASS breaking point oC -20 -16 -12 9381 -

16

Max

IV Flash Point COC oC Min 220 220 220 1209

V

Elastic recovery of half thread

in ductilometer at 15 oC

percent, Min

50 60 60 2

VI

Complex Modulus (G*/sin) as

min 1.0 KPa at 10 rad/s at a

temperature oC

58 70 76 1

VIISeparation, difference in

softening point (R&B) oC Max3 3 3 3

VIII Viscosity at 150 oC Poise 1-3 3-6 5-9 1206(Part 2) -

IX

Thin film oven test and tests

on residue

a) Loss in Mass, percent, Max

b) Increase in softening point oC, Max

c) Reduction in penetration of

residue at 25 oC percent

Max

d) Elastic Recovery of Half

thread in ductilometer at 25 oC percent, Min Or

Complex Modulus as

(G*/sin ) as Min 2.2 KPa at

10 rad/s at temperature C

1.0

7

35

35

58

1.0

6

35

50

70

1.0

5

35

50

76

9382

1205

1203

-

-

-

-

-

4

1

Where max temperature exceeds 40oC, softening point should be 65 oC

17

Fraass breaking point requirement will be applicable for areas of subzero temperatures.

Design of Mixes

The mix design for dense graded bituminous mixes using modified bitumen shall be done in the

same manner as used for conventional bitumen by Marshall Method of mix design (MS 2). The

requirements of mixes with modified bitumen are indicated in table below.

Table 2.12 Requirements of Mix Prepared with Modified Bitumen

Sl.No

Properties

RequirementMethod of

TestHot Climate

Cold Climate High Rainfall

1Marshall Stability (75 blows) at 60 oC Kg , Minimum

12 KN 10KN 12KN MS:2

2 Marshall Flow at 60 oC mm 2.5-4.0 3.5-5.0 3.0-4.5 MS:2

3 Marshall Quotient, Kg/mm 250-500 Stability-flow

4 Voids in Compacted mix % 3.0-5.0

5

Modified binder content by weight of Mix minimum**

BC Grading 1* -5.4%

Grading 2* -5.6%

SDBC Grading 1* - 4.7%

Grading 2* - 5.2%

DBM Grading 1* - 4.3%

Grading 2* - 4.7%

6Requirement of Retained stability after 24 hours in water at 60 oC % Minimum

90 95 100 MS:2

7 Coating with aggregate, % 95 95 100 AASHTOT

18

182

Grading 1 & 2 corresponds to IRC 111

Corresponds to specific gravity of the aggregate being 2.7. In case aggregate have specific

gravity more than 2.7, bitumen content can be reduced proportionately. Further for regions

where highest daily mean air temperature is 30 oC or lower and lowest daily mean air

temperature is - 10 oC or lower, the bitumen content may be increased by as much as 0.5 %.

Temperature Requirements for Modified Binders

The temperature of mixing and rolling shall be higher than conventional bituminous mixes.

The broad range of temperature at different stages is given in Table below. The exact temperatures

depend upon the type and amount of modifier used and shall be adopted as per advice of supplier.

Table 2.13 Broad Range of Temperature Requirements for Modified Binders

Stage of Work Indicated Temperature (oC)

Binder at mixing 165-185

Aggregates temperature 165-185

Mix at mixing plant 150-170

Mix at laying site 130-160

Rolling at laying site 115-155

Coloured Bitumen:

Bitumen in desired colours may also be prepared for any specific purpose or ornamental

purpose.

Antistripping Agents:

When the coated aggregates are in contact with water, bitumen from aggregates may be

removed which is called as stripping. To prevent this stripping, some chemicals are added to the

19

bitumen during the preparation of mix which are called as Anti stripping agents. Many anti stripping

agents are available in the market with different brand names.

20