Quick summary: This methodology covers laying a 30–50 mm single-course Bituminous Concrete (BC) layer on a prepared bituminous bound surface — equipment, materials, mix design (Table 500-17), construction operations, compaction, and quality control (Table 900-3) as per MoRTH.
Quick Reference — BC (MoRTH 507)
- Scope: Lay 30–50 mm BC single course on prepared bituminous bound surface.
- Bitumen: VG-30 / VG-40 or PMB (as per CA / IS 15462 / IS 73).
- Typical gradings: Mix 1 — 19 mm NMAS (50 mm); Mix 2 — 13.2 mm NMAS (30–40 mm).
- Minimum binder: Mix 1 — 5.2%; Mix 2 — 5.4% (by mass of total mix) — see Table 500-17.
- Field density target: ≥ 92% of Gmm (or ≥98% Marshall density where specified).
Scope
Bituminous Concrete Construction Methodology is a systematic process of laying a dense bituminous layer over a prepared base or binder course as per MoRTH Clause 509. This layer provides a smooth, durable, and impermeable surface capable of withstanding heavy traffic loads. The methodology includes proper material selection, surface preparation, mixing, laying, compaction, and quality control tests to ensure long-lasting pavement performance.
Reference
- Contract Agreement
- IRC: SP: 84-2014
- MoRTH Specifications for Road & Bridge Works (5th Revision)
- Relevant Drawings
Equipment
- Crusher of required capacity for aggregates
- Hot Mix Plant & Batching Plant
- Paver with sensor arrangement
- Steel tandem rollers; pneumatic tandem roller
- Bitumen sprayer, dumpers, air compressor
- Pegs for levels, mechanical broom, straight edge
- Thermometers (0–250°C), thickness gauge, survey kit, measuring tape
- Core cutting machine
Materials
The source and test report of all materials shall be submitted to the AE for approval prior to use.
1. Bitumen
Use bitumen grade as specified in Contract Agreement — VG-30 / VG-40 or PMB conforming to IS 15462 / IS 73.
2. Coarse Aggregates — Table 500-16 (Physical requirements)
| Property | Test | Specification | Significance |
|---|
| Cleanliness (dust) | Grain size analysis | Max 5% passing 0.075 mm | Ensures binder adhesion; low dust content. |
| Particle shape | Flakiness & elongation indices (combined) | Max 35% | Controls particle shape for packing & stability. |
| Strength | LA Abrasion / Aggregate Impact Value | Max 30% / Max 24% | Resistance to crushing and wear. |
| Durability | Soundness (Na2SO4 / MgSO4) | Max 12% / Max 18% | Resistance to weathering & disintegration. |
| Polishing | Polished Stone Value | Min 55 | Skid resistance under traffic. |
| Water absorption | Water absorption | Max 2% | Controls porosity & durability. |
| Stripping | Coating & stripping of bitumen-aggregate mix | Min retained coating 95% | Resistance to bitumen stripping in presence of water. |
| Water sensitivity | Retained tensile strength (TSR) | Min 80% | Moisture damage resistance; use anti-stripping agent if below. |
Table 500-16 — Physical requirements for coarse aggregate used in BC.
3. Fine Aggregates
Fine aggregate shall pass 2.36 mm sieve and be retained on 75 μ. Sand equivalent ≥ 50 (IS:2720 Part 37). Plasticity index (fraction passing 0.425 mm) ≤ 4 (IS:2720 Part 5).
4. Filler — Table 500-9
| IS Sieve (mm) | Cumulative % Passing |
|---|
| 0.6 | 100 |
| 0.3 | 95–100 |
| 0.075 | 85–100 |
Table 500-9 — Grading limits for mineral filler (MoRTH).
5. Aggregate Grading & Binder Content — Table 500-17
Combined grading of coarse, fine aggregate and filler shall follow Table 500-17 when tested as per IS:2386 Part I. Binder content to be determined per Clause 505.3.
| IS Sieve (mm) | Mix 1 — 19 mm (layer 50 mm) | Mix 2 — 13.2 mm (layer 30–40 mm) |
|---|
| 45 | - | - |
| 37.5 | - | - |
| 26.5 | 100 | - |
| 19 | 90–100 | 100 |
| 13.2 | 59–79 | 90–100 |
| 9.5 | 52–72 | 70–88 |
| 4.75 | 35–55 | 53–71 |
| 2.36 | 28–44 | 42–58 |
| 1.18 | 20–34 | 34–48 |
| 0.6 | 15–27 | 26–38 |
| 0.3 | 10–20 | 18–28 |
| 0.15 | 5–13 | 12–20 |
| 0.075 | 2–8 | 4–10 |
| Min Bitumen (% by mass) | 5.2 | 5.4 |
Table 500-17 — Typical gradation & minimum binder content for BC mixes. Minimum binder corresponds to aggregate Gs=2.7; adjust for actual Gs.
Mix Design
- Requirement: Mixture must meet grading and property requirements of Table 500-17. For modified bitumen, use Marshall method (MS-2).
- Binder Optimization: Determine optimum binder via Marshall stability tests (MS-2); Fines/Bitumen ratio should be between 0.6 and 1.2.
- Job Mix Formula (JMF): Prepare JMF per Clause 507.3.3 and submit to AE. Joint testing and approval required.
- Plant Trials: Conduct plant trials to prove production capability; allowable JMF variations per Table 500-18 (permitted variations listed later).
Permissible JMF Variations (Typical)
| Parameter | Permissible variation |
|---|
| Aggregate passing 19 mm or larger | ±7% |
| Aggregate passing 13.2 mm / 9.5 mm | ±6% |
| Aggregate passing 4.75 mm | ±5% |
| Aggregate passing 2.36 / 1.18 / 0.6 mm | ±4% |
| Aggregate passing 0.3 / 0.15 mm | ±3% |
| Aggregate passing 0.075 mm | ±1.5% |
| Binder content | ±0.3% |
| Mixing temperature | ±10°C |
Construction Operation
1. Weather & Seasonal Limitations
Do not lay BC during rain, fog, dust storms, or when base is damp. Avoid work when shade temperature ≤ 10°C as per MoRTH.
2. Preparation of Base
Ensure base is clean, dry and primed/tack coated. Remove dust by sweeping and compressed air.
3. Tack Coat
Apply tack coat per MoRTH Clause 503. Ensure uniform application rate (check trays) and adhesion.
4. Preparation & Transportation of Mix
Produce BC mix in hot mix plant (twin shaft pug mill recommended). Transport in covered tippers to maintain temperature and avoid spillage.
5. Spreading
Discharge mix into paver hopper; use sensor-guided paver to control line & level. Cut transverse/longitudinal joints vertically and apply hot binder on joints before placement.
6. Rolling & Compaction
Rolling should begin immediately behind the paver at speeds ≤ 5 km/h. Sequence established during trial stretch. Complete compaction before temperature falls below minimum rolling temperature.
- Initial / breakdown: 80–100 kN smooth wheeled roller.
- Intermediate: 8–10 ton vibratory roller OR 12–15 ton pneumatic roller (nine wheels, min tire pressure 5.6 kg/cm²).
- Finish: 6–8 ton smooth wheeled tandem roller (number of passes per trial bed).
- Keep roller wheels moist to prevent adhesion; roll longitudinally from edges to center; on superelevation roll from lower to upper edge.
Where rollers cannot reach (kerbs/forms), use mechanical tampers or plate compactors. Rectify any undulations due to reversing or other causes as directed by AE.
7. Field Testing & Acceptance
Field tests per Clause 900: core cutting for compaction, straight edge for surface irregularity, levels for crossfall, thickness gauge checks, temperature measurements, and tack coat spray-rate checks.
Density requirement: Compacted BC should have minimum field density ≥ 92% of theoretical maximum specific gravity (Gmm) on day of compaction (or ≥98% Marshall density where applicable).
8. Opening to Traffic
Allow traffic as per MoRTH Clause 507.5 and project-specific instructions.
Environmental Control
- Dispose excess material without polluting streams or water courses.
- Keep vehicle tracks moist to reduce dust generation.
- Control plant smoke & dust by adequate measures (bag filters, water sprays, etc.).
Joints
Transverse Joints
When the laying of the mixture is to be suspended long enough to permit the mixture to become chilled, a transverse joint shall be constructed.
All transverse joints shall be cut vertically to the full thickness of the previously laid mix using an asphalt cutter or pavement breaker, and the surface shall be painted with hot bitumen before placing fresh material.
The joint shall be constructed square to the lane alignment, and all excess materials shall be removed and cut back into the previously constructed pavement to the point of full pavement depth.
The exposed edge of the previously constructed pavement shall then be lightly coated with tack coat.
Longitudinal Joints
The paver used covers the required width, so typically there will be no longitudinal joints. However, if longitudinal joints are necessary, the edges shall be constructed true to the delineating line parallel to the centerline of the road.
All joints shall be cut vertically to the full thickness of the previously laid mix and the surface painted with hot bitumen before placing fresh material.
Longitudinal joints shall preferably be hot joints. Cold longitudinal joints shall be properly heated with a joint heater to attain a suitable temperature of about 90°C before laying the adjacent material.
Surface Finish & Quality of Work
Surface finish shall conform to MoRTH Clause 902. Quality control shall follow Section 900 of MoRTH.
Table 900-3 — Quality Control during Production of Mix (Key Tests & Frequency)
| Test | Purpose | Minimum Frequency |
|---|
| Aggregate Impact Value / LA Abrasion | Strength / resistance to wear | 1 test per 350 m³ per source or on quality change |
| Flakiness & Elongation Indices | Particle shape | 1 test per 350 m³ per source or on quality change |
| Soundness (Na₂SO₄ / MgSO₄) | Weathering resistance | 1 test per source or on quality change |
| Water absorption | Porosity | 1 test per source or on quality change |
| Sand Equivalent | Fines/cleanliness | 1 test per source or on quality change |
| Plasticity Index | Plasticity of fines | 1 test per source or on quality change |
| Polished Stone Value | Skid resistance | 1 test per source or on quality change |
| % Fractured Face | Aggregate angularity | 1 test per 350 m³ when crushed gravel used |
| Mix grading | Gradation of constituents & blended mix | 1 set per 400 t of mix; min 2/day/plant |
| Stability & Voids Analysis (Marshall) | Strength, flow, air voids, VMA, VFB | 3 tests per 400 t of mix; min 2/day/plant |
| Moisture Susceptibility (AASHTO T283) | Resistance to moisture damage | 1 test per mix type or when aggregate source changes |
| Binder content | Correct binder proportion | 1 set per 400 t of mix; min 2/day/plant |
| Temperature checks (binder/agg/mix) | Proper coating, mixing & compaction | At regular intervals during production & laying |
| Rate of spread (laying) | Correct application rate/thickness | After every 5th truck load |
| Density of compacted layer | Final in-situ density | 1 test per 700 m² |
Table 900-3 — Key QC tests during mix production & laying (MoRTH Section 900).
Top FAQs — Bituminous Concrete (BC)
- What is BC? BC is the wearing course: a dense-graded hot mix providing smooth, skid-resistant surface over binder courses.
- Difference between BC & DBM? DBM is binder/base course (structural); BC is the wearing surface (smooth & skid-resistant).
- Minimum binder? Mix 1 (19 mm) — min 5.2%; Mix 2 (13.2 mm) — min 5.4% (adjust for aggregate Gs).
- Can BC be laid on WMM? Typically BC is placed over DBM/binder; if placing over WMM, ensure appropriate tack/primer and design checks.
- What density should be achieved? Minimum field density ≥ 92% Gmm (or ≥98% Marshall density where specified).
Materials — Material Requirement Table
| Material | Requirement / Specification |
|---|
| Bitumen | VG-30 or VG-40 (or PMB as per CA / IS 73 / IS 15462). Grade as per contract / climatic requirements. |
| Coarse Aggregates | Crushed rock / gravel retained on 4.75 mm; clean, durable, cubical; satisfy LA abrasion / AIV, flakiness & elongation limits. |
| Fine Aggregates | Passing 4.75 mm, retained on 75 µ; sand equivalent ≥ 50; PI ≤ 4. |
| Filler | Rock dust / hydrated lime / cement approved by AE; grading per Table 509-2. |
| Quality Tests | IS:2386, IS:6241, AASHTO T283, IS:2720, Marshall stability (MS-2 / ASTM) |
Note: Submit material source & test reports for AE approval prior to use.
Highway Construction Quality Control Tests
A. Binder Tests
| S. No. | Characteristic | Purpose | Test Method | Typical Requirement | Test Frequency |
|---|
| i | Absolute Viscosity @ 60°C | Measures resistance to flow at high pavement temperatures | IS 1206 (Part 2) | 2400 – 3600 Poises | Per lot / consignment |
| ii | Kinematic Viscosity @ 135°C | Ensures proper coating during mixing and compaction | IS 1206 (Part 3) | 350 cSt (min.) | Per lot / consignment |
| iii | Penetration @ 25°C | Measures hardness under standard load | IS 1203 | 45 mm (min.) | Per lot / consignment |
| iv | Flash Point (COC) | Safe heating limit to prevent fire | IS 1209 | 220°C (min.) | Per lot / consignment |
| v | Solubility in Trichloroethylene | Checks purity of bitumen | IS 1216 | 99.0% (min.) | Per lot / consignment |
| vi | RTFO Residue Tests | Measures short-term aging resistance | IS 9382 | Viscosity Ratio ≤ 4; Ductility ≥ 40 cm | Per lot / consignment |
| vii | Elastic Recovery | Fatigue resistance | IS 15462 | 50–75% (min.) | Per lot / consignment |
| viii | Separation Test | Storage stability of modifier | IS 15462, App. A | Softening Point difference ≤ 2.5°C | Per lot / consignment |
| ix | Softening Point | Temperature susceptibility & rutting resistance | IS 1205 | 50–75°C (depending on grade) | Per lot / consignment |
B. Aggregate Tests
| S. No. | Test | Purpose | Minimum Frequency |
|---|
| ii | Aggregate Impact Value / Los Angeles Abrasion | Aggregate strength | 1 test per 350 m³ per source or on quality change |
| iii | Flakiness & Elongation Indices | Shape of aggregate | 1 test per 350 m³ per source or on quality change |
| iv | Soundness (Na₂SO₄ / MgSO₄) | Weathering resistance | 1 test per source or on quality change |
| v | Water Absorption | Checks porosity | 1 test per source or on quality change |
| vi | Sand Equivalent | Fines content / cleanliness | 1 test per source or on quality change |
| vii | Plasticity Index | Soil plasticity | 1 test per source or on quality change |
| viii | Polished Stone Value | Skid resistance | 1 test per source or on quality change |
| ix | % Fractured Face | Aggregate angularity | 1 test per 350 m³ when crushed gravel is used |
C. Bituminous Mix Tests
| S. No. | Test | Purpose | Minimum Frequency |
|---|
| x | Mix Grading | Gradation of mix | 1 set per 400 t of mix, minimum 2/day/plant |
| xi | Stability & Voids Analysis | Strength, flow, density, void content | 3 tests per 400 t of mix, minimum 2/day/plant |
| xii | Moisture Susceptibility (MSHTO T283) | Resistance to moisture damage | 1 test per mix type or on aggregate/source change |
| xiv | Binder Content | Correct proportion in mix | 1 set per 400 t of mix, minimum 2/day/plant |
D. Process Control & Field Tests
| S. No. | Test | Purpose | Frequency |
|---|
| xiii | Temperature (Binder, Aggregate, Mix) | Ensure proper mixing and compaction | At regular intervals |
| xv | Rate of Spread | Proper layer thickness in field | After every 5th truck load |
| xvi | Density of Compacted Layer | Ensures compaction meets specification | 1 test per 700 m² |
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