Bituminous Concrete (BC) specifications viz. Layer thickness, Mix and material requirements, grading , laying trials, Rolling , Construction procedure, transport and joint specifications, surface finish and quality control,measurement and rate etc..as per MORTH and Indian Standard

Bituminous concrete(BC)-

Bituminous concrete( BC) is used for wearing  course and profile corrective courses.BC is generally laid in single layer on a previously prepared bituminous bound  surface.

The thickness of single layer of BC shall be 30mm,40mm and 50mm.

1 -MATERIAL

A- Bitumen -

The bitumen shall be viscosity graded paving bitumin complying with IS 73 or specified in contract aggrement.
The type and grade of bitumen to be used would depend upon the climatic condition and the traffic.

Selection criteria of viscosity graded (VG) paving bitumens based on climatic conditions

B- Coarse Aggregate

It consist of crushed rock,crushed gravel or other hard material retained on 2.36 mm sieve. It shall be clean ,hard,durable and of cubical shape,free from dust,and  soft organic and other deleterious substances.
The aggregates  shall satisfy the physical requirements of table  no. -2 (Table no. 500-16 ,as per MORTH 5th revision) where crushed gravel is proposed  for use as aggregate,not less than 95% by weight of the crushed material retained on 4.75 mm sieve shall have atleast two fractured faces.

                                                      Table no. - 2 Physical requirements for coarse aggregate for Bituminous concrete

* if the min. retained tensile test strength falls below 80% ,use of stripping agent is recommended to meet the requirement.


C- Fine aggregates

 it shall consist of crushed or naturally occurring material, or a combination of the two, passing 2.36 mm sieve and retained on the 75micron sieve. They shall be clean, hard, durable, dry and free from dust and soft or friable matter, organic or other deleterious matter. Natural sand shall not be allowed in binder course. However, natural sand up to 50% of the fine aggregates may be allowed in base courses. The fine aggregate shall have a sand equivalent value of not less than 50 when tested in accordance with the requirement of IS:2720 (Part 37). The plasticity index of the fraction passing the 0.425mm sieve shall not exceed 4, when tested in accordance with IS:2720 (Part 5).

D- Filler

Filler shall consist of finely divide mineral matter such as rock dust, hydrated lime or cement approved by engineer. The filler shall be grade within the limits indicated in table no.-3
                              Table no.- 3

Grading requirement for mineral filler

The filler shall be free from organic impurities and have a plasticity index not greater than 4, The PI requirements shall not apply if filler is cement or lime. Where the aggregates fail to meet the requirements of the water sensitivity test in table no.-2,  then 2% by weight of aggregates, of hydrated lime shall be used and percentage of the fine aggregate reduced accordingly.

E- Aggregates grading and Binder content (Grades of Bituminous concrete (BC))
When tested in accordance with IS 2386 part 1 ( Wet grading method ), the combined grading of coarse and fine aggregate and filler shall fall within the limits shown in table no.- 4(Table no. 500-17 ,as per MORTH 5th revision).
The grading shall be as specified in contract aggrement.
                                        Table no.- 4  Composition of Bituminous Concrete pavement layers

Notes:-
**    The nominal max. particle size is the largest specified sieve size upon which any of the aggregate is retained.


**    Corresponds to specific gravity of aggregate being 2.7. in case aggregate have sp. gravity more than 2.7, the min. bitumen content can be reduced proportionally. Further the region where highest daily air temperature is 30°C or lower and lowest daily air temperature is -10°C or lower, the bitumen content may be increased by 0.5%.

For easy understanding

•Grades of BC

 # GRADING -1

Nominal size of aggregate - 19 mm

Layer thickness= 50 mm

Bitumen content % by mass of total mix should not be less than 5.2%.

# GRADING - 2

Nominal size of aggregate - 13.2 mm

Layer thickness= 30-40 mm

Bitumen content % by mass of total mix should not be less than 5.4%.

2- Mix Design

A- Requirement for the mix

Apart from conformity with the grading and quality requirements for individual ingredients, the rnikre shall meet the requirements set out in Table - 5 (Table 500-11 as per MORTH 5th revision).

                                       Table -5  Requirements for Bituminous Concrete

# % voids in mineral aggregate are given in below table -6.
                                         

B- Binder Content

The binder content shall be optimized to achieve the requirements of the mix set out in Table 5. The binder content shall be selected to obtain 4 percent air voids in the mix design. The Marshall method for determining the optimum binder content shall be adopted as described in the Asphalt Institute Manual MS-2.
Where maximum size of the aggregate is more than 26.5 mm, the modified Marshall method using 150 mm diametre specimen described in MS-2 and ASTM D 5581 shall be used. This method requires modified equipment and procedures. When the modified Marshall test is used, the specified minimum stability values in Table-6 shall be multiplied by 2.25, and the minimum flow shall be 3 mm.
                                                  Table -6 Minimum percentage voids in the mineral aggregate(VMA)

Note - interpolate minimum voids in the mineral aggregate (VMA)  for design percentage air voids value b/w those listed.


C - Job Mix Formula

The Contractor shall submit to the Engineer for approval at least 21 days before the start the work, the job mix formula proposed for use in the works, together with the following details:

i) Source and location of all materials;

 ii) Proportions of all materials expressed as follows:
a) Binder type, and percentage by weight of total mix;
b) Coarse aggregate/Fine aggregate/Mineral filler as percentage by weight of total aggregate including mineral filler;

 iii) A single definite percentage passing each sieve for the mixed aggregate;

 iv) The individual gradings of the individual aggregate fraction, and the proportion of each in the combined grading;

 v) The results of mix design such as maximum specific gravity of loose mix (Gmm), compacted specimen densities, Marshall stability,flow, air voids, VMA, VFB and related graphs and test results of AASHTO T 283 Moisture susceptibility test;

vi) Where the mixer is a batch mixer, the individual weights of each type of aggregate, and binder per batch;

vii) Test results of physical characteristics of aggregates to be used;

viii) Mixing temperature and compacting temperature.

While establishing the job mix formula, the Contractor shall ensure that it is based on a correct and truly representative sample of the materials that will actually be used in the work and that the mix and its different ingredients satisfy the physical and strength requirements of these Specifications.

Approval of the job mix formula shall be based on independent testing by the Engineer for whichsamples of all ingredients of the mix shall be furnished by the Contractor as required by the Engineer.

The approved job mix formula shall remain effective unless and until a revised Job Mix Formula is approved. Should a change in the source of materials be proposed, a new job mix formua shall be forwarded by the Contractor to the Engineer for approval before the placing of thematerial.

D - Plant Trials — PermissiblePlant Trials —Variation in Job Mix Formula 

Once the laboratory job mix formula is approved, the Contractor shall carry out plant trials lo establish that the plant can produce a uniform mix conforming to the approved job nix formula. The permissible variations of the individual percentages of the various ingrecients in the actual mix from the job mix formula to be used shall be within the limits as specifed in table no. -7 (MORTH 5th revision Table 500-18) and shall remain within the gradation band. These variations are intended to apply to individual specimens taken for quality control tests.

                                      Table -7 Permissible Variations in the Actual Mix from the Job Mix Formula

E - Laying Trials

Once the plant trials have been successfully completed and approved, the Contractor shall carry out laying trials, to demonstrate that the proposed mix can be successfully laid and compacted. The laying trial shall be carried out on a suitable area which is not to form part of the works. The area of the laying trials shall be a minimum of 100 sq.m of construction similar to that of the project road, and it shall be in all respects, particularly compaction, the same as the project construction, on which the bituminous material is to be laid.

The Contractor shall previously inform the Engineer of the proposed method for laying and compacting the material. The plant trials shall then establish if the proposed laying plant, compaction plant, and methodology is capable of producing satisfactory results. The density of the finished paving layer shall be determined by taking cores, no sooner than 24 hours after laying, or by other approved method.

 The compacted layers of bituminous concrete (BC) shall have a minimum field density equal to or more than 92 percent of the average theoretical maximum specific gravity (Gmm) obtained on the day of compaction in accordance with ASTM D2041.

Once the laying trials have been approved, the same plant and methodology shall be applied to the laying of the material on the project, and no variation of either shall be acceptable, unless approved in writing by the Engineer, who may at his discretion require further laying trials.


3 - Construction Operations

A - Weather and Seasonal Limitations 
Laying shall be suspended:
(I) In presence of standing water on the surface

(II) When rain is imminent, and during rain, fog, or dust storm

(III) When the base/binder course is damp

(IV) When the air temperature on the surface
on which it is to be laid is less than 10°C for mixes with conventional bitumen and is less than 15°C for mixes with modified bitumen

(v) When the wind speed at any temperature exceed the 40 km per hour at 2 m height

B-Preparation of Base

This work shall consist of preparing an  black-topped surface for laying bituminous concrete. The work shall be performed on such widths and lengths as shown on the drawings or as instructed by the Engineer or engineer in charge. The existing surface shall be firm and clean, and treated with Tack coat.

C - Geosynthetics

Where Geosynthetics are specified in the Contract, this shall be  laid in accordance with the required specifications and Standards.

D - Stress Absorbing Layer 

Where a stress absorbing layer is specified in the Contract, this shall be applied in accordance with the required  standard and specifications.

E - Tack Coat

Scope: The work shall be consist of the application of a single coat of low viscosity liquid bituminous material to existing bituminous, cement concrete or primed granular surface preparatory to the superimposition of a bituminous mix, when specified in the contract.

Material: The binder used for tack coat shall be either cationic bitumen emulsion (RS 1) complying with IS:8887 or suitable low viscosity paving bitumen of  VG 10 grade conforming to IS:73. The use of cutback bitumen RC:70 as  per IS:217 shall be registered only for sites at sub-zero temperatures or for emergency applications as directed by the engineer.

Weather and seasonal limitations: Bituminous material shall not be applied during a dust storm or when the weather is foggy, rainy or windy or when the temperature in the shade is less than 10°C. Where the tack coat consists of emulsion, the surface shall be slightly damp, but not wet. Where the tack coat is of cutback bitumen, the surface shall be dry.

Application of Tack coat: The application of tack coat shall be at the rate specified in table below. No dilution or heating at the site of RS1 bitumen emulsion shall be permitted. Paving bitumen if used for tack coat shall be heated to appropriate temperature in bitumen boilers to achieve viscosity less than 2 poise. The normal range of spraying temperature for a bituminous emulsion shall be 20°C to70°C and for cutback 50°C to 80°C .

 Curing of Tack coat:Tack coat shall be left to cure until all the volatiles have evaporated before any subsequent construction is started .



F - Mixing and Transportation of the Mix
(α) Mixing
Pre-mixed bituminous materials shall be prepared in a hot mix plant of adequate capacity and capable of yielding a mix of proper and uniform quality with thoroughly coated aggregates.

Appropriate mixing temperatures are given intable-8( Table 500-2 of MORTH 5th revision) of these Specifications. the
difference in temperature between the binder and aggregate shall at no time exceed 14°C. In order to ensure uniform quality of the mix and better coating of aggregates, the hot mix plant shall be calibrated from time to time. The essential features of the hot mix plants are given in
Annex A of IRC:27.
                         Table -8 Mixing, Laying and Rolling Temperatures for Bituminous
Mixes (Degree Celcius)

If a continuous type mixing plant is used, the Contractor must demonstrate by laboratory analysis that the cold feed combined grading is within the grading limits specified for that bituminous bound material. In the case of a designed job mix, the bitumen and filler content shall be derived using this combined grading.

(β) Transporting

Bituninous materials shall be transported in clean insulated and covered vehicles. An asphalt release agent, such as soap or lime water, may be applied to the interior of the vehicle to prevent sticking and to facilitate discharge of the material.

G - Spreading
 prior to spreading the mix, the base shall be well prepared. Except the area where paver cannot get access, bituminous materials shall be spread, levelled and tamped by an approved self-propelled paving machine equipped with an electronic sensing device.

When laying binder course or wearing course approaching an expansion joint of a structure, machine laying shall stop 300 mm short of the joint. The remainder of the pavement up to the joint, and corresponding area beyond, it shall be laid by hand, and the joint or joint cavity shall be kept clear of surfacing material.

H - Rolling

(α)Compaction
Bituminous material shall be laid and compacted in layers, Which enable the specified thickness, surface level, regularity requirements and compaction to be achieved. Compaction of bituminous materials shall commence as soon as possible after laying and completed before the temperature falls below min. Rolling temperature. Rolling shall commence at the edges and progress towards center longitudinally except that on super elevation and unidirectionally cambered portions, it shall progress from lower to the upper edge parallel to the C.L. of the pavement. Rolling shall be continued until all roller marks have been removed from the surface. The initiator breakdown rolling shall be done with 8-10 tonne static weight smooth- wheel rollers. The intermediate rolling shall be done with 8-10 tonne static weight or vibratory roller or with a pneumatic tyre roller (PTR) of 12 to 15 tonne weight, with a tyre pressure of at least 0.56 MPa. The finish rolling shall be done with 6 to 8 tonne smooth wheel tandem rollers.

    The roller shall first compact material adjacent to joints and then work from the lower to the upper side of the layer, overlapping on successive passes by at least one-third of the width of the rear roll or, in the case of pneumatic tyres roller at least the nominal width of 300 mm.

In portions with super- elevated and unidirectional camber, after the edge has been rolled, the roller shall progress from the lower to the upper edge.

Roller should move at least at a speed of not more than 5 Km per hour.

The roller shall not be permitted to stand on pavement which has not been fully compacted, and necessary precautions shall be taken to prevent dropping of oil, grease, petrol/ diesel or other foreign matter on the pavement either when the rollers are operating or standing. The wheels of roller machine shall be in good working order, to prevent the mix from adhering to the wheels. Only sufficient moisture to prevent adhesion between the wheels of rollers and the mix should be used. Surplus water shall not be allowed to stand on the partially compacted pavement. 

(β)Joints 

Where joints are made, the material shall be fully compacted and the joint made flush in one of the following ways: 

a) All joints shall be cut vertical to the full thickness of the previously laid mix. All loosened material shall be discarded and the vertical face coated with a suitable viscosity grade hot bitumen, or cold applied emulsified bitumen. While spreading the material along the joint the material spread shall overlap 25 mm to 50 mm on the previously laid mix beyond the vertical face of the joint. The thickness of the loose overlap material should be approximately a quarter more than the final compacted thickness. The overlapped mix shall be dragged back to the hot lane so that the roller can press the small excess into the hot side of the joint to obtain a high joint density.

 b) By using two or more pavers operating in echelon, where this is practicable and in sufficient proximity for adjacent widths. to be fully compacted by continuous rolling. 

(1) All longitudinal joints shall be offset at least 300 mm from parallel joints in the layer beneath or as directed, and in a layout approved by the Engineer. Joints in the wearing course shall coincide with either the lane edge or the lane marking, whichever is appropriate. Longitudinal joints shall not be situated in wheel track zones. 

(2) For transverse joints method 

a) above shall apply. Transverse joints in the successive and adjoining layers shall have a minimum offset of 2 m. 

I - Opening to Traffic 

As directed by the engineer

 J - Surface Finish and Quality Control 

A- Horizontally alignments

Horizontally alignments shall be reckoned w.r.t. the center line of the carriageway as shown on the drawings. The edge of the carriage way as constructed shall be correct within a tolerance of ±10 mm there from.

B- Surface Level 

The levels of the Bituminous Concrete layer shall not vary from those calculated with reference to the longitudinal and cross-profile of the road shown on the drawing or as directed by the engineer beyond the tolerance mentioned in table below(table 900-1).

Provided, however, that the negative tolerance for wearing course shall not be permitted in conjunction with the positive tolerance for base course, if the thickness of the former is thereby reduced by more than the following limits-

4mm for bituminous wearing course of thickness 40 mm or more

3mm for bituminous wearing course of thickness less than 40 mm

Measurements of the surface levels shall be taken on a grid of points placed at 6.25 m longitudinally and 3.5 m transversely. For any 10 consecutive measurements taken longitudinally or transversely, not more than one measurement shall be permitted to exceed the tolerance as above, this one measurements being not excess of 5mm above the permitted tolerance.

For checking the compliance with the above requirements for bituminous wearing course, Measurements of the surface levels shall be taken on a grid of points spaced at 6.25 m along the length and at 0.5 m from the edge and at the centre of the pavement. In any length of the pavement, compliance shall be deemed to be met for the final road surface, only if the tolerance given above is satisfied for any point on the surface.

C - Surface Regularity of pavement courses

The longitudinal profile shall be checked with a 3 metre long straight edge/moving straight- edge as directed by the engineer at the middle of each traffic lane along a line parallel to the centre line of the road.

The max. allowable difference b/w the road surface and underside of a 3 met.

Straight-edge when placed parallel with or right angles to the centre line of the road at points decided by the engineer shall be:-

For bituminous pavements surface               3mm

D - Rectification
Where the surface regularity of subgrade and the various pavements course fall outside the specified tolerance. The contractor shall be liable to rectify these in manner described below -

For wearing course, where the surface is high or low, the full depth of layer shall be removed and replaced with fresh material and compacted. In all cases where the removal and replacement of a bituminous layer is involved, the area treated shall not be less than 5m in length and not less than 3.5 m in width.


E -Riding Quality:

The riding quality of bituminous concrete wearing surface, as measured  by a standard towed fifth wheel bump integrator(TFWBI- It is also known as Roughometer or Automatic Road Unevenness Recorder gives quantitative integrated evaluation of surface irregularities on an digital counter I LCD screen. It comprises of a single wheeled trailer, with a pneumatic tyre mounted on a chassis, on which an integrating device is fitted ), shall not more than 2000mm per Km.

K - Arrangements for Traffic 

Dung the period of construction, arrangements for traffic shall be made in accordance with the required specifications and standards.

L -  Measurement for Payment
Bituminous concrete  material shall be measured as finished work either in cubic metres, tonnes or by the square metre at a specified thickness as  indicated in the contract drawing, or documents, or as otherwise directed by the engineer.

M - Rate

The contract unit rate for premixed bituminous material shall be payment in full for carrying
out the required operations including full compensation for, but not necessarily limited to:
i) Making arrangements for traffic as by the engineer
ii) Cleaning of the surface;
iii) Providing all materials to be incorporated in the work including arrangement for stock yards, all royalties, fees, rents where necessary and all leads and lifts;
iv) Mixing, transporting, laying and compacting the mix, as specified including all wastage in cutting joints;
v) All labour, tools, equipment, plant including installation of hot mix plant, power supply units and all machinery, incidental to complete the work
to these Specifications;
vi) Carrying out the work in part widths of the road where directed;
vii) Carrying out all tests for control of quality;
viii) The rate shall cover the provision of bitumen at the application rate
specified in the contract, with the provision that the variation in actual percentage of bitumen used shall be assessed and the payment adjusted accordingly as per Contract;
ix) The rates include for all testing, mix design, transporting and testing of
samples, and cores and tests as directed by the Engineer; and
x) The cost of all plant and laying trials as specified to prove the mixing and laying methods shall be deemed to be included in the Contractor's
rates.

All above apply except that the rate shall include the provision of bitumen at 5.2 percent & 5.4 percent for grading 1 and grading 2 by weght of total mix respectively. The variation in actual percentage of bitumen used will be assessed and the payment adjusted plus and minus accordingly.



Source of content - Ministry of Road transport and highway specifications  and other relevant standards


Thank you
Mukesh Kumar
Gyan of engineering