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)60/70grade

(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

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 -1RS-1

(ii)Rapid setting – 2RS-2

(iii)Medium settingMS

(iv)Slow setting-1SS-1

(v)Slow setting-2SS-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).

Table 2.1 Requirements for Paving Bitumen

SI.
No / Characteristics / Paving Grades / Methodof Test
Reference To IS No.
VG 10 / VG 20 / VG 30 / VG 40
1. / Penetration at 25ºC, 100g, 5 Sec., 0.1mm, min / 80 / 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, Minimum / 250 / 300 / 350 / 400 / IS 1206 (Part 3)
4. / Flash point, (Cleveland open cup), ºC, Minimum / 220 / 220 / 220 / 220 / IS 1209
5. / Solubility in trichloroethylene, percent, Minimum / 99.0 / 99.0 / 99.0 / 99.0 / IS 1216
6. / Softening Point (R & B),ºC, Minimum / 40 / 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 / 4.0 / IS 1206 (part 2)
ii)Ductility at 25 ºC, cm, Min, / 75 / 50 / 40 / 25 / IS 1208

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
  6. Viscosity - IS: 1206 Part 3 – 1978
  7. Ductility - IS: 1208 –1978
  8. 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
4 / Residue 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 / -
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 ofBitumen Emulsion.

Table 2.3 Requirements for Bitumen Emulsion

S.No /

Characteristics

/ Type of Emulsion
RS -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, Seconds
At 25oC / - / - / - / 20-100 / 30-150
At 50oC / 20-100 / 100-300 / 50-300 / - / -
3 / Coagulation of Emulsion at low temperature temperature. / NIL / NIL / NIL / NIL / NIL
4 / Storage stability after 24 hours, percentage, max. / 2 / 1 / 1 / 2 / 2
5 / Particle Charge / Positive / Positive / Positive / Weak Positive / 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
8 / Miscibility with water / No Coagulation / No Coagulation / No Coagulation / - / No Coagulation
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 / 60-120
c) Ductility 27oC in cm minimum. / 50 / 50 / 50 / 50 / 50
d) Solubility in trichloroethylene. (min) / 98 / 98 / 98 / 98 / 98
10 / Distillation in percent, by volume at
  1. 190°C
/ - / - / - / 20-55 / -
  1. 225°C
/ - / - / - / 30-75 / -
  1. 260°C
/ - / - / - / 40-90 / -
  1. 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.

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. 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 / CombinedFlakiness and Elongation index / Water Absorption /
Stripping
/
Water Sensitivity
(Max). / (Max). / (Max). / (Max). / (Min. retained coating) / Retained Tensile Strength (Min)
Bituminous Macadam / 40% / 30% / 35% / 2% / 95% / 80%
Dense Bituminous Macadam / 35% / 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%

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.

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

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.no / Type 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, 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 andaggregate 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.
  • 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 stabilityto 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 textureandhardness 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.

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

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

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