IRC SP 92 : 2015Manual on Use of Cold Mix Technology in Construction and Maintenance of Roads

IRC SP 92 (2015) provides Guidelines on Use of Cold Mix Technology in Construction and Maintenance of Roads — the IRC's standard for ambient-temperature bituminous mixing + paving, an alternative to traditional hot-mix asphalt. Cold-mix technology has gained traction in hill states, remote PMGSY projects, and routine maintenance work where centralised hot-mix plants are impractical.

Use IRC SP 92 when you are: - Doing pavement maintenance in hill states / remote areas (no nearby hot-mix plant) - Specifying cold-mix asphalt for PMGSY rural roads in hilly / forested areas - Doing routine pot-hole + patch repair - Specifying low-traffic surface where structural performance is secondary - Considering environmentally-conscious paving (cold mix has lower carbon footprint) - Doing bituminous overlay on existing roads where night/winter laying is needed

Cold mix vs hot mix: - Hot mix: mixed at 155-175 °C; laid at 140-160 °C; cures in hours - Cold mix: mixed at ambient (10-40 °C); laid at ambient; cures over weeks (slower with cooler weather)

Advantages of cold mix: - No centralised plant needed; portable mixer + truck - Lower energy cost; lower emissions - Can be laid in cool / wet weather where hot mix fails - Reduces transport-distance constraint

Disadvantages: - Slower cure (weeks vs hours) - Lower early strength - Higher cement / additive cost - Performance variability higher than hot mix - Inappropriate for high-traffic NH

Cold-mix systems: 1. Bitumen emulsion-based: most common; uses anionic / cationic emulsion mixed with aggregate at ambient 2. Cutback-based: older; uses cutback bitumen (RC-2, MC-2) + aggregate 3. Foam-asphalt-based: foamed bitumen (modern); short curing time 4. Polymer-modified emulsion: higher performance for moderate traffic

Bitumen emulsion (most common, IS 8887): - Cationic Slow Setting (SS-1): aggregate-bond, slower set; typical cold mix - Cationic Quick Setting (RS-1): faster but more critical timing - Polymer-modified emulsion: improved performance - Residue: 60-65 % bitumen, 35-40 % water

Cold-mix design philosophy: - Lower binder content than hot mix (4-6 % residue vs 5-6 % in hot) - Specific aggregate gradation to optimise emulsion coating - Curing additives sometimes added (cement, lime, fly ash) - Compaction immediately while emulsion is wet - Cure period of 1-4 weeks before traffic

Process: 1. Aggregate preparation (clean, gradation per spec) 2. Add cement / lime if specified (typically 1-3 %) 3. Add emulsion (typically 6-9 % by weight of dry aggregate) 4. Mix at ambient in mobile mixer or pugmill 5. Transport in standard truck 6. Lay by paver or hand-spread + roll 7. Initial compaction (when emulsion is wet) 8. Allow water to evaporate (cure period 7-21 days) 9. Open to traffic carefully

Performance: - Service life: 5-8 years for routine maintenance - Strength gain over 3-6 months as emulsion fully cures - Final strength approaches that of hot mix

Aggregate gradation (dense cold mix, 13 mm max): - 19 mm: 100 % - 13.2 mm: 95-100 % - 9.5 mm: 70-90 % - 4.75 mm: 45-65 % - 2.36 mm: 30-50 % - 0.6 mm: 15-30 % - 0.075 mm: 4-10 %

Cement / lime additive: - 1-3 % cement OR - 1-2 % hydrated lime OR - 5-10 % fly ash - Improves early strength + reduces cure time + waterproofs

Emulsion specification: - Residue: 60-65 % - Storage stability: 1 day minimum - Settling: < 5 % in 24 hr - Cement test: < 2 % cement mixing causes coagulation (negative test) - Stripping coating test: ≥ 90 % retained

Mix design: - Marshall (modified for cold mix): residual binder 4-6 % - Air voids: 5-15 % (higher than hot mix; emulsion water leaves voids) - Stability (after 7-day cure): ≥ 5 kN - Stability (after 28-day cure): ≥ 9 kN - Moisture sensitivity: ≥ 70 % retained

Construction: - Mixing time: 30-90 seconds - Transport: within 1-2 hours - Laying: by paver or hand-spread; 25-50 mm typical thickness - Rolling: 4-6 passes static + vibratory while emulsion is wet - Cure: 1-4 weeks depending on weather + thickness

Curing acceleration: - Cement / lime additive (above) - Active mixing (allows water to evaporate faster) - Sun exposure - Initial light traffic helps compact mix during cure

Acceptance criteria: - Layer thickness: ± 6 mm of design - Surface evenness: 5 mm under 3-m straight-edge (less strict than hot mix) - Density after 28-day cure: ≥ 95 % of Marshall density - Skid resistance: ≥ 50 BPN after 28-day cure - Stripping resistance: ≥ 70 % retained

Application limits: - Best for: low-volume rural roads, maintenance patches, surface restoration - Acceptable for: medium-volume district roads, hill roads - Not recommended for: NH/SH high-traffic, expressway wearing course - Avoid: highly-loaded industrial pavements, heavy-truck routes

• IRC:29:2019 — DBM/DBC Specifications. Hot-mix alternative.
• IRC:27:2009 — Bituminous Macadam. Hot-mix BM.
• IRC:107:2013 — BC Wearing Course.
• IRC:14:2004 — Surface Dressing.
• IRC:17:1965 — Single Coat Surface Dressing.
• IRC:37:2018 — Pavement Design.
• IRC:SP-89:2018 — Soil + Granular Stabilisation. Cement-based binders.
• IRC:SP-79:2008 — Stone Matrix Asphalt.
• IS 8887 — Bitumen Emulsion.
• IS 8887-2 — Modified Bitumen Emulsion.
• IS 73 + IS 15462 — Bitumen Specification.
• IS 1206 — Methods of Test for Bitumen.
• IS 2386 — Methods of Test for Aggregates.
• IS 8887 — Emulsion Bitumen.
• ASTM D 977 — Standard Specification for Emulsified Asphalt.
• ASTM D 2397 — Standard Specification for Cationic Emulsified Asphalt.
• ARRA (Asphalt Recycling + Reclaiming Association) Cold Mix Best Practices Manual.
• MoRTH Specifications for Road and Bridge Works — Section 500 (Bituminous Pavement Layers).
• PMGSY Rural Road Manual.

1. Insufficient cure time before traffic. Traffic opened in 1-2 days; mix not cured; rutting + scour. Wait 7-21 days minimum depending on conditions. 2. Cold weather curing. Below 10 °C; water doesn't evaporate; cure stalls; mix remains workable. Avoid cold weather laying. 3. Wet weather application. Surface wet; emulsion-aggregate bond fails. Avoid laying in rain. 4. Wrong emulsion type. Quick-setting emulsion used for slow application; emulsion sets before mix; mix fails. Match emulsion to application + conditions. 5. No cement/lime additive on critical projects. Slow cure; weak surface; rutting. Add 1-3 % cement for critical applications. 6. Emulsion-aggregate incompatibility. Aggregate type causes immediate coagulation; mix unworkable. Test compatibility before bulk production. 7. Insufficient binder. Marshall design omitted; mix dry + brittle. Verify binder content per batch. 8. Layer thickness too thick. > 50 mm cold mix; inner portion doesn't cure; weak inner layer. Limit to 25-40 mm per layer; multiple layers if needed. 9. No compaction. Mix laid without rolling; voids excessive; cure poor. Roll immediately while emulsion wet. 10. Cold mix on high-traffic road. Specification mismatch; mix fails within months. Use cold mix only for appropriate applications. 11. Storage degradation. Emulsion stored too long; phase separation; quality lost. Use fresh emulsion; storage ≤ 6 months. 12. No acceptance test after cure. Cure complete but performance not validated; structural inadequacy hidden. Marshall test after 28-day cure. 13. Storage tank contamination. Old residue in tank; mixed with new emulsion; phase incompatibility. Clean tank between batches. 14. Construction temperature too low. Below 10 °C ambient; ambient mixing not feasible. Schedule for warmer weather. 15. No documentation. Mix design + application records not maintained; troubleshooting future failures impossible. Maintain comprehensive records.

Cold-mix project — IRC SP 92 touchpoints:

1. Application selection: - Identify low-volume / remote location appropriate for cold mix - Compare cost / quality / time vs hot mix - Decide on emulsion-based vs foam vs cement-stabilised

2. Mix design (laboratory): - Aggregate gradation - Emulsion compatibility test - Additive optimisation (cement / lime / fly ash) - Modified Marshall test - Moisture sensitivity check

3. Plant setup: - Mobile pugmill or batch mixer - Emulsion supply tank - Additive feeding mechanism - Quality control on-site

4. Trial section: - 50-100 m at site - Validate plant + paver + roller - Verify mix consistency - Cure observation over 7-21 days

5. Mass production: - Mix at ambient - Transport in trucks (no insulation needed) - Laying by paver (preferred) or hand-spread - Initial compaction while wet - Cure period before traffic

6. Quality control + acceptance: - Aggregate gradation + emulsion content per batch - Layer thickness + density (post-cure) - Surface evenness - Moisture-sensitivity test

7. Operations: - Phased traffic opening - First-year monitoring (cold mix takes time to fully cure) - Mid-life dressing or overlay schedule

8. Maintenance: - Annual visual inspection - Patch repair as needed - Periodic surface refresh

IRC SP 92 is the enabling specification for cold-mix asphalt in India — increasingly applied on PMGSY in hill states + remote regions, on routine maintenance contracts, and on environmentally-conscious projects. The 2015 specification remains current.