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03-BITUMINOUS BASE | ESAY EngInfo | Engineering Sources Around You
BITUMINOUS BASE AND SURFACE COURSES
The bituminous base courses included in the MoRTH Specifications for Road and Bridge works (5th revision 2013) and which are normally used in pavement construction are:
The bituminous surface courses include:
Open-graded premix surfacing
Close-graded premix surfacing/Mixed seal surfacing
For more details, Clause 501 of MoRTH Specifications shall be referred.
1. PRIME COAT AND TACK COAT
1.1 Prime coat over granular base
Prime coat is the application of a single coat low viscosity bituminous material over a granular base or subbase to prevent entry of water into the subgrade. The main function of the prime coat in bituminous pavement is to protect the subgrade from moisture and weathering. The specifications and procedure for applying prime coat is giver under Clause 502 of MoRTH Specifications (5th revision).
1.2 Tack coat
A tack coat is a very light spray application of a bitumen emulsion to create a bond between the new bituminous layer and the existing surface.
Table: Rate of application of tack coat
Rate of spray in kg/m2
Primer granular surface
2. BITUMINOUS MACADAM (BM)
Constructing bituminous macadam base shall generally be done as per IRC: 27-1967. The specifications and construction procedure of bituminous macadam is given under Clause 504 of MoRTH Specifications (5th revision).
Table: Physical requirements for coarse aggregates for BM
Max 5% passing 75 micron sieve
Flakiness and elongation indices (Combined)
Soundness – Sodium Sulphate
Soundness – Magnesium Sulphate
Coating and stripping of bitumen aggregate mixtures
Minimum 95% coating retained
Retained tensile strength**
AASHTO 283
Vescosity of binder
IS: 73, IS: 15462
One test for each supply.
IS: 2386 Part 1
Two tests per day.
One test per 350 m3
IS: 2386 Part 4
One test per 200 m3
IS: 2386 Part 3
One test for each source.
IS: 2386 Part 5
IS: 2720 Part 5
ASTM D 2172
Mix grading
One test per 700 m3 area
3. DENSE BITUMINOUS MACADAM (DBM)
The specifications for the design and construction of Dense Bituminous Macadam are giver under Clause 505 of MoRTH Specifications (5th revision 2013).
Table: Physical requirements for coarse aggregates for DBM
Max 5% passing
Flakiness and Elongation Indices
Soundness – Magnesium
Sulphate (5 cycles)
coating retained
*Any one of these shall need to be satisfied.
**Anti-stripping agent shall be added if the value falls below 80%.
Table 2300-12: Quality control test on DBM
Viscosity of binder
One test per 350 m3 .
IS: 2720 Part 37
Aggregate mix grading
Three tests per 400 tonnes.
Max sp. gravity of mix
One test for each mix.
One test per 700 m2 area.
4. SAND BITUMEN MIX
The sand bitumen mix can be used both as subbase and base.
The requirements for sand are prescribed in table 2300-13 (Ref: Table 500-14 of MoRTH Specifications).
Table 2300-13: Grading and physical requirements of sand for sand bitumen mix
Cumulative percentage passing by weight of aggregate
Sand equivalent (IS:2720 part 37)
Los Angeles abrasion (IS: 2386 Part4)
The mix requirements are prescribed in table 2300-14 (Ref: Table 500-15 of MoRTH Specifications).
Table 2300-14: Requirements for sand base course
Minimum stability (kN at 60°C)
Minimum flow (mm)
Compaction level (Blows)
75 on each face
Air voids in the mix (%)
Voids in the mineral aggregate (VMA) %
Percentage voids filled with bitumen (VFB) %
The binder content of the mix shall be determined in the laboratory by Marshall method given in the Asphalt Institute Manual MS-2.
Table 2300-15: Control tests for sand bitumen base / subbase.
QC tests on material and work for surface dressing shall be as indicated in table 2300-16 (Ref: Table 900-4 of MoRTH Specifications).
The QC tests on material and work shall be as given in table 2300-19 (Ref: Table 900-4 of MoRTH Specifications).
Table: Quality Control tests for open / close graded premix surfacing
5. CLOSE-GRADED PREMIX SURFACING/MIX SEAL SURFACING
The specifications and construction procedure for close-graded premix surfacing are given under Clause 508 of MoRTH Specifications. Close-graded premix surfacing/mix seal surfacing shall be either Type A or Type B and is laid to a thickness of 20 mm. Type A surfacing is recommended for areas where average annual rainfall is more than 1500 mm.
The binder shall be viscosity grade bitumen of the grade specified in the contract conforming to the requirements of IS: 73. For the selection of the grade of binder, table 2300-17 shall be referred.
The coarse aggregates shall satisfy all the physical requirements set for BM except that the water absorption shall be 1% maximum. The polished stone value (PSV) shall not be less than 55% when tested in accordance with BS: 812-114.
Fine aggregates shall be crushed rock, natural sand or a mixture of both which shall be clean, hard, durable, dry and free from soft, friable, flaky particles and organic and deleterious substances.
The coarse and fine aggregates shall be combined to get a grading as stipulated in table 2300-20 (Ref: Table 500-19 of MoRTH Specifications).
Clause 511 of MoRTH Specifications provides the details for the application of a seal coat for sealing the voids in the bituminous surface laid to the specified levels, grade and cross fall (Camber). The seal coat shall be either type A (Liquid seal coat) or type B (Premixed seal coat).
Table 2300-21: Physical requirements for stone chips for Type A seal coat.
Soundness – Sodium Sulphate (5 cycles)
Soundness – Magnesium Sulphate (5 cycles)
7. SLURRY SEAL
Slurry seal is a mixture of mineral aggregate, slow setting cationic bitumen emulsion, water, additives if required, proportioned, mixed and uniformly spread over a previously prepared surface. The detailed specification and construction procedure for slurry seal is given under Clause 512 of MoRTH Specifications. The three different types of slurry seal and their applications are given in table 2300-22 (Ref: Table 500-25 of MoRTH Specifications).
7.1 Filler
Ordinary Portland Cement (OPC) in the range of 0.5% to 2% by weight of total aggregates shall be incorporated as filler.
a) The mix design criteria for slurry seal mix is given in IRC: SP-81.
b) The requirements for the slurry seal mix is given in table 2300-26 (Ref: Table 500-29 of MoRTH Specifications).
Table 2300-26: Mix Design criteria for sluryy seal
IRC:SP-81, Appendix 1
180 sec (Min)
IRC:SP-81, Appendix 3
3 cm (Max)
IRC:SP-81, Appendix 4
20 kgcm (Min)
IRC:SP-81, Appendix 5
Wet track abrasion loss (1 hour soak)
IRC:SP-81, Appendix 6
800 gm/m2 (Max)
c) The design report shall indicate the proportion of aggregate, filler, water and residual bitumen content based on dry weight of aggregate, additives to be used.
a) The surface finish of construction shall meet the requirements of Clause 2202 (Clause 902 of MoRTH Specifications).
b) Control on the materials and paving shall be done as given in table 2300-28 (Ref: Table 900-4 of MoRTH Specifications).
Table 2300-28: Quality control tests
Quality of emulsion
IS: 8887
One test per lot of 20 tonnes.
Two tests at site per day.
One test for each source/site.
Two tests per lane/km.
Calibration of machine
Once per project.
(By weight of aggregate)
Daily (Travel time of machine).
9. MICRO-SURFACING
Micro-surfacing is provided for surface treatment of pavements in accordance with the procedure given in Clause 514 of MoRTH Specifications.
The micro-surfacing is applied to an existing pavement surface which is structurally sound but the surface showing signs of premature ageing, aggregate loss, cracking, higher degree of polishing. The types of micro-surfacing and rates of application are given in table 2300-29 (Ref: Table 500-31 of MoRTH Specification).
9.1.1 Bitumen
The bitumen emulsion shall be a modified bitumen emulsion conforming to requirements specified in table 2300-30 (Ref: Table 500-32 of MoRTH Specifications).
Table 2300-30: Requirement for modified bitumen emulsion for micro-surfacing
Residue on 600 mic sieve (% by mass)
Saybolt Furol viscosity at 250C
Storage stability after 24 hrs (168 hrs)
2 (4) % (Max)
a) Paving bitumen complying with IS: 73 shall be used for designing BC mix.
b) Coarse aggregates shall be crushed rock retained on 2.36 mm sieve. The source of aggregate shall be approved only after testing for stripping. The physical requirements for coarse aggregates specified in table 2300-33 (Ref: Table 500-16 of MoRTH Specifications) shall be achieved.
Table 2300-33: Physical requirements for coarse aggregate for BC
Or Aggregate Impact value
BS: 812-114
recommended to meet the requirement.
a) The control of alignment, level and surface regularity shall be as given in Clause 2202 (Clause 902 of MoRTH Specifications).
b) The control tests and their minimum frequencies for BC work shall be as given in table 2300-37 (Ref: Table 900-4 of MoRTH Specifications).
Table 2300-37: Quality Control tests for bituminous concrete (BC)
Table 2300-38: Physical requirements of aggregates for SMA
<2% passing
0.075 mm sieve
Either sodium or magnesium ( 5 Cycles)
12.1. Mix requirements
The SMA mix shall be designed using AASHTO MP8 - Standard Specification for designing Stone Matrix Asphalt and AASHTO PP41 - Standard Practice for designing SMA.
Compaction of the mix shall be carried with 50 blows on each side using Marshall Method given in Asphalt Institute Manual MS-2.
Table: 2300-43: Quality Control tests for SMA
13. SEMI-DENSE BITUMINOUS CONCRETE
The specifications for SDBC are more or less similar to dense bituminous macadam (DBM). This item is not included in the 5th revision published in 2013. Hence for the detailed specifications and construction procedures of Semi-dense Bituminous Concrete (SDBC) wearing and profile corrective courses (PCC) Clause 508 of MoRTH Specifications for Road and Bridge works (4th revision 2001) shall be referred.
a) Paving bitumen complying with IS: 73 shall be used for designing SDBC mix.
b) Coarse aggregates shall be crushed rock retained on 2.36 mm sieve. The source of aggregate shall be approved only after testing for stripping. The physical requirements for coarse aggregates are specified in table 2300-44 (Ref: Table 500-14 of MoRTH Specifications - 4th revision).
Table: 2300-44: Physical requirements for coarse aggregate for SDBC
Coating and stripping of bitumen aggregate mix*
Retained Coating
The aggregate may satisfy one of the requirements.
If the minimum coating retained is ≥95%, the water sensitivity test need not be carried ou
If the minimum retained tensile strength falls below 80%, use of anti-stripping agent is recommended to meet the requirement.
The variations in quantities of the ingredients from the approved job mix formula shall not exceed the prescribed limits (Ref: Table 500-13 of MoRTH Specifications-4th revision).
The temperature requirement for bituminous mixes shall be as given in table 2300-36 (Ref: Table 500-2 of MoRTH Specifications – 5th revision).
The difference in temperature between the binder and the aggregate should at no time exceed 14 0C.
The control of alignment, level and surface regularity shall be as given in Clause 2202 (Clause 902 of MoRTH Specifications).
The QC tests and their minimum frequencies for SDBC work shall be as given in table 2300-49.
Table: 2300-49: Control tests for SDBC
1. MoRTH Specifications for Road and Bridge Works, 5th Edition 2013 -Published by IRC, New Delhi.
2. MoRTH Specifications for Road and Bridge Works, 4th Edition 2001 -Published by IRC, New Delhi.
3. MoRTH Manual for construction and supervision of bituminous works, Edition 2001 – Published by IRC, New Delhi.
4. IRC SP: 11 Quality Control for the Construction of Roads and Runways -Published by IRC, New Delhi.
5. MS-2 Marshall method of mix design for asphalt concrete and other hot mix types – Asphalt Institute Manual Series No. 2 (MS-2) - Published by Asphalt Institute (USA).