IRC 27:2009 is the Indian Standard (IRC) for specifications for bituminous macadam. IRC 27:2009 specifies Bituminous Macadam (BM) — a hot-mix asphalt base course widely used in Indian flexible pavement construction for state highways, district roads, and urban roads. BM consists of graded aggregate + bitumen (3.5-4.5% by weight) hot-mixed, laid, and compacted. Three grades: Grade I (40 mm max size) for heavy base, Grade II (25 mm) intermediate, Grade III (20 mm) for light traffic. Mix design via Marshall method (75 blows, stability > 7.5 kN, flow 2.5-4.5 mm). Typical 50-80 mm compacted thickness per layer. BM serves as the base course between granular sub-base (GSB or WBM) and surface wearing course (DBM, BC, or SDBC). Amendment No. 1 (2018) updated bitumen grade references (VG-30 default replacing 80/100) and raised aggregate quality standards. Amendment No. 2 (2022) added provisions for recycled asphalt pavement (RAP) up to 25% in BM mix. BM is less costly than DBM (dense bituminous macadam) but provides less structural capacity — choose by traffic and design requirements.
Specifies the materials, mix design, production, construction, and acceptance criteria for Bituminous Macadam (BM) used as base course in Indian flexible pavements — a hot-mix asphalt bound aggregate layer.
- Status
- Current
- Usage level
- Essential
- Domain
- Transportation — Pavement and Road Materials
- Type
- Specification
- Amendments
- Amendment No. 1 (2018) — VG-30 default, aggregate quality upgrades; Amendment No. 2 (2022) — RAP (recycled asphalt pavement) up to 25% in mix
Also on InfraLens for IRC 27
Practical Notes
! BM vs DBM (Dense Bituminous Macadam per IRC 29): BM has coarser gradation (40 mm max), lower bitumen content, higher voids. DBM has denser gradation (26.5 mm max), higher bitumen, lower voids. DBM for heavier traffic; BM for moderate.
! Typical pavement section: WBM/WMM (granular base) + prime coat + BM (bituminous base) + tack coat + DBM or SDBC (wearing course). Each layer specific function.
! Aggregate quality is the leading cause of BM failure — use rejection criteria strictly. Weathered or soft aggregate fails within 5 years of traffic.
! Marshall mix design is standard for BM. Typical 75 blows per face, samples tested for stability, flow, density, VMA, VIM. Mix design done at start of project by certified lab.
! Bitumen content 3.5-4.5%: below 3.5% causes brittle mix, poor fatigue resistance; above 4.5% causes instability, rutting in hot weather. Site verification daily via extraction test.
! VG-30 bitumen (Amendment No. 1, 2018): replaces old 80/100 grade. VG-30 has specific viscosity range suitable for Indian climate range 0-50°C. VG-40 for hotter conditions.
! Mixing temperature: 150-170°C aggregate + 135-155°C bitumen. Too-cold = under-mixing, poor bitumen distribution. Too-hot = bitumen oxidation, premature hardening.
! Transport: insulated trucks ideal; tarpaulin minimum. BM at < 135°C is unusable — aggregate separation, poor compaction. Short haul (< 30 km) preferred.
! Laying with paver: critical for uniform layer. Hand-laid BM has poor profile, density variation. Pavers cost ₹50 lakh-2 crore but indispensable.
! Compaction pattern: breakdown (steel wheel) immediately after laying → intermediate (pneumatic) for density → finish (steel wheel) for smoothness. Proper roller pattern essential.
! Compaction density 97% Marshall: verification by nuclear gauge (fast, 5 minutes per spot) or core sampling (slow, 2-day lab result). Nuclear gauge for real-time QC; cores for dispute resolution.
! Joint construction: longitudinal joints (between two lanes) and transverse joints (at end-of-day) must be straight, vertical, tack-coated, and compacted. Poorly-made joints are initiation sites for cracking.
! Weather: air temperature > 10°C minimum. Below this, bitumen cools too quickly for proper compaction. Monsoon: avoid — wet surface prevents laying; bitumen emulsion in rain becomes unusable.
! Opening to traffic: after cooling below 40°C. 2-3 hours post-compaction typical. Earlier traffic causes rutting in soft, hot mix.
! Recycled Asphalt Pavement (RAP, Amendment No. 2): up to 25% recycled asphalt allowed in BM mix. Reduces virgin material demand, lowers cost 10-20%. Strong environmental benefit.
! Surface irregularity: ± 3 mm under 3 m straight edge is ideal; < 6 mm acceptable. Greater irregularities indicate laying/compaction issues.
! Compaction in cold-joints: layers placed next to cold (previously laid) areas must be tack-coated and rolled into the joint. Failure causes delamination.
! Economics: BM per m² = ₹800-1200 (depending on thickness). DBM per m² = ₹1200-1600. SDBC wearing = ₹600-1000. Total flexible pavement wearing + base: ₹2500-4000 per m² typical.
! Life expectations: BM base course 12-15 years under design traffic; wearing course 7-10 years; pavement re-surfacing cycle 8-12 years.
! Quality control documentation: daily mix temperature log, aggregate gradation log, bitumen content log, density log, surface regularity log. Audit-ready file per project.