IRC SP 107:2015 is the Indian Standard (IRC) for guidelines for gap graded rubberized bitumen mix surfacing. IRC SP:107 covers rubberized gap-graded bituminous wearing course — using crumb rubber from waste tyres. Promotes waste tyre recycling while providing a durable, crack-resistant wearing course. Government mandates crumb rubber use on certain NH stretches.
Guidelines for use of crumb rubber from waste tyres in gap-graded bituminous wearing course — an eco-friendly pavement solution.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Gap-graded crumb-rubber-modified bituminous surfacing | Scope |
| Crumb rubber | From waste tyres, blended into binder | Material |
| Gradation | Gap-graded wearing course | Mix |
| Benefits | Better fatigue/rutting + waste-tyre reuse | Why |
| Read with | IRC SP 53 (modified bitumen) / IRC 111 | Cross-ref |
IRC SP 107 covers Gap Graded Rubberised Bitumen Mix Surfacing — a wearing-course pavement technology that combines two ideas: a gap-graded aggregate skeleton (heavily skewed toward coarse stone with a deliberate gap in the middle sizes) and a rubber-modified bituminous binder (Crumb Rubber Modified Bitumen, CRMB, made from recycled tyre crumbs).
The result is a wearing course with high stiffness for rutting resistance, high binder content (8-10 %) for durability, and the stone-on-stone contact that distinguishes gap-graded from dense-graded mixes. The rubberized binder adds elastic recovery, raises softening point, and resists thermal cracking.
Use IRC SP 107 when you are: - Specifying a premium wearing course on heavy-traffic NH / expressway (typically AADT > 5,000 commercial vehicles per day) - Re-paving a high-rutting segment where dense-graded mixes have failed - Specifying noise-reducing pavement in urban arterial near hospitals / residential - Doing rehabilitation overlay on heavily-cracked / heavily-rutted existing pavement - Considering value-engineered alternative to Stone Matrix Asphalt (SMA) or Open Graded Friction Course (OGFC) - Specifying environmentally-conscious pavement using recycled tyre rubber
What IRC SP 107 covers: - CRMB (Crumb Rubber Modified Bitumen) production + specification - Gap-graded aggregate gradation envelope - Mix design + volumetric properties (air voids, VMA, VFB) - Construction: mixing, transport, paving, compaction temperature windows - Quality control + acceptance criteria - Performance + design life expectations
It is one of several IRC standards on modified-bitumen wearing courses (alongside SMA per IRC SP 79, Microsurfacing per IRC SP 81-A, and dense-graded BC per IRC SP 53).
Dense-graded vs gap-graded — the fundamental difference:
Why gap-graded works: - Better rutting resistance — load goes through stone-stone contact, not through binder; binder isn't critical for load-bearing - Higher binder content possible — 8-10 % binder (vs 5-6 % in dense BC); binder doesn't compromise structural performance because stones carry the load - High binder = durable, weather-resistant surface - Texture — coarser surface gives better skid resistance especially in wet conditions
Why rubberised binder (CRMB): - Higher softening point (60-75 °C vs ~50 °C for plain bitumen) → less rutting in summer - Lower fragility temperature → less cracking in winter - Elastic recovery typically 30-60 % vs ~5-10 % for plain bitumen - Better adhesion to aggregate → less stripping in monsoon - Environmental benefit — recycles 1,000-3,000 tyres per km of typical pavement
When NOT to use gap-graded rubberised: - Very low traffic — overdesign + cost - Cold climate < 0 °C without precaution — CRMB still cracks at low temp - Long-haul transport — must be laid hot (175-185 °C) so plant must be close - Inexperienced contractor — gap-grading is sensitive; if mixed poorly, performance drops
CRMB binder specification (per IRC SP 53): - Crumb rubber content: 15-22 % by weight of base bitumen - Penetration at 25 °C: 35-50 (0.1 mm) — i.e., harder than plain bitumen - Softening point: 60-75 °C (vs ~50 °C plain VG-30) - Elastic recovery at 25 °C: ≥ 30 % (vs ~5 % plain) - Viscosity at 135 °C: 0.6-1.5 Pa·s - Storage stability (24 hr at 163 °C): difference in softening point < 5 °C - Phase separation at 163 °C: none on storage stability test
Aggregate gradation (IRC SP 107 envelope, 13.2 mm gap-graded mix): - 19 mm sieve: 100 % passing - 13.2 mm: 90-100 % - 9.5 mm: 75-90 % - 4.75 mm: 25-40 % ← significant drop (the 'gap') - 2.36 mm: 18-28 % - 1.18 mm: 12-22 % - 0.6 mm: 9-18 % - 0.3 mm: 7-14 % - 0.15 mm: 5-10 % - 0.075 mm: 4-8 %
Note the gap between 4.75 mm (~30 %) and 2.36 mm (~22 %) is shallow but real; for SMA it's deeper. Indian SP 107 is gentler-gap than European SMA.
Mix volumetrics: - Air voids (Va): 3-5 % at Marshall design point - VMA (Voids in Mineral Aggregate): ≥ 17 % - VFB (Voids Filled with Binder): 70-80 % - Binder content (by mass): 6.5-8.5 % (higher than dense-graded BC at 5-6 %) - Stability (Marshall): ≥ 10 kN - Flow: 2-4 mm - Tensile strength ratio (TSR, moisture susceptibility): ≥ 0.80 (good adhesion)
Construction temperatures: - Mixing: 170-185 °C at plant - Loading + transport: minimum 165 °C at start - Laying: 160-175 °C at paver - Compaction completion: must complete before 130 °C (mix stiffens rapidly below) - Tack coat: spray within 5 m of paver position; 0.20-0.30 kg/m² of bitumen emulsion
Rolling pattern: - 1-2 passes static (immediately after paving) - 4-6 passes vibratory tandem roller - 1-2 passes finishing - Pneumatic roller acceptable but rare with rubberised mix (rubber binder sticks to rubber tyres)
Layer thickness: - Wearing course: 35-50 mm typical - Maximum aggregate size = 1/3 to 1/2 of layer thickness - 13.2 mm mix → layer ≥ 40 mm - 19 mm mix → layer ≥ 60 mm
Acceptance: - Density: 96-98 % of Marshall density (95 % absolute minimum) - Layer thickness: ± 5 mm of design - Surface evenness: 3 mm max under 3-m straight-edge - Texture (mean profile depth, MPD): 0.6-1.0 mm (high-texture surface)
Performance + design life: - Design life: 8-12 years as wearing course - Rutting at end of life: < 5 mm - Performance window: AADT > 5,000 commercial vehicles preferred (low-volume = overdesign)
1. CRMB quality variable batch-to-batch. Crumb rubber size / content / origin varies; softening point + elastic recovery readings vary. Verify each tanker / batch against IRC SP 53 specification before acceptance. 2. Storage temperature too high or too long. CRMB stored > 8 hours at 175 °C degrades (rubber phase separates). Storage temp 160-170 °C; use within 4-6 hours of arrival. 3. Mix temperature too low at paver. Below 160 °C, CRMB stiffens rapidly; compaction insufficient; density < 95 %. Reject any mix arriving below 160 °C. 4. Aggregate gradation deviates from envelope. Stockpile contamination / segregation; produced mix outside SP 107 envelope. Pre-paving acceptance test every 200-500 tonnes. 5. Tack coat omitted or insufficient. Bond between layers fails; delamination + scuffing within 6-12 months. Tack coat 0.20-0.30 kg/m² mandatory. 6. Rolling pattern wrong. Pneumatic roller used (rubber sticks to rubber tyres) → surface texture damaged. Use tandem vibratory + static finish; avoid pneumatic. 7. Layer thickness inadequate. 35 mm laid for 13.2 mm mix; aggregate-thickness ratio < 1/3; stones break under roller, surface rough. Minimum 40 mm for 13.2 mm mix. 8. No moisture sensitivity test. TSR not done; first monsoon causes stripping. Mandatory TSR ≥ 0.80; reject mix < 0.75. 9. Mix laid in cold weather (< 10 °C ambient). Temperature loss too fast during compaction; under-compacted patch develops; ravelling starts. Avoid laying below 10 °C ambient. 10. Plant calibration outdated. Bitumen + aggregate dosing drift; mix composition off-design; performance below expectations. Plant calibration before every major contract. 11. No control of crumb rubber size. Spec calls for 30-mesh crumb but supplier delivers mixed sizes; mix workability + viscosity wrong. Specify mesh size in BOQ + verify on receipt. 12. Marking material incompatible with surface. Conventional paint chips off CRMB textured surface; markings fail in 6 months. Specify cold-applied plastic or thermoplastic compatible with CRMB. 13. Cost-cutting: rubber content reduced. Producer skimps on rubber to save cost; softening point + elastic recovery deteriorate; performance approaches plain bitumen. Spot-check binder properties + audit production records. 14. Mix design done with one aggregate then plant uses another. Different gradation, different optimum binder content; mix performs differently. Mix design must use site aggregate.
Pavement project — IRC SP 107 touchpoints:
1. Concept / design selection: premium wearing course identified for high-traffic NH / expressway / urban arterial; SMA vs CRMB vs OGFC trade-off considered. 2. DPR + design: - Wearing course thickness from IRC:37:2018 - Mix selection: gap-graded CRMB per IRC SP 107 - CRMB grade selection: typically CRMB-60 for plains, CRMB-55 / 75 for hot climates - Layer system specification (binder course + wearing course) 3. Mix design (laboratory): - Aggregate gradation within SP 107 envelope - CRMB content optimisation at Marshall test (Va = 3-5 %) - Volumetric verification (VMA ≥ 17 %) - TSR ≥ 0.80 - Storage stability validation 4. Plant setup: - Batch mixer or drum mixer capable of 175-185 °C operation - Cement-bound silos / stockpiles for aggregates - CRMB storage tank with agitation + temperature control - Calibrate dosing every 6 months + before major contract 5. Trial section: - 100-200 m on representative subgrade + base - Validate plant + paver + roller pattern - Adjust rolling sequence + mix temperature for site conditions - Take cores for density + mix-design conformance 6. Mass production: - Plant mixing under quality control - Transport in covered insulated dumpers within 1.5-2 hrs of mixing - Tack coat 0.20-0.30 kg/m² ahead of paver - Paver-laid at 160-175 °C - Rolling: static + vibratory + finish; complete before 130 °C 7. Quality control + acceptance: - Plant: aggregate gradation + binder content + temperature per batch - Site: laying temperature + roller pass count + density (nuclear gauge) - Cores: 1 per 1000-2000 m²; thickness + density + extracted binder content - Surface: texture + evenness + skid resistance 8. Tender + payment: premium wearing course paid per tonne or per m²; quality deductions for density, gradation, surface tolerance. 9. Opening + first-year monitoring: - Surface inspection for ravelling, segregation, flushing - Joint inspection (where adjacent layers meet) - Skid resistance check after first dry season 10. Operations + maintenance: - Annual visual inspection - 5-year cycle: surface texture + skid resistance check - 8-12 year design life; resurfacing when rutting > 5 mm or polishing reduces skid below limit
IRC SP 107 represents the modern wearing-course standard for premium Indian highways — gradually replacing dense-graded BC on NH 4/6-lane and expressway projects, with strong environmental story (recycled tyre rubber) and proven performance in tropical climates.
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