Key Reference Standards and Guidelines
| Code/Standard | Title |
|---|---|
| IRC: 120-2015 | Use of Cold Mix Technology in Road Construction |
| IRC SP:100-2014 | Use of Cold Mix Technology in Construction of Bituminous Pavement Layers |
| MoRTH Section 500 | Specifications for Bituminous Works |
| IS: 8887 | Emulsified Bitumen Specifications |
| ASTM D6927, ASTM D6307 | Stability and Bitumen Content Tests |
| IRC SP:16 | Guidelines for Surface Regularity |
🏗️ Overview
Cold Mix Asphalt (CMA) is produced by blending emulsified bitumen, aggregates, and optionally RAP, at ambient temperatures. The use of 20–30% RAP is permitted by IRC:120-2015 in base and surface layers.
🔍 Enhancement: Added reference to surface and base layers where RAP is permissible.
🔧 1. Material Collection and Pre-Mixing Tests
📌 A. Material Requirements
| Material | Specifications |
|---|---|
| RAP | Milled bituminous surface, free from excessive contaminants |
| Aggregates | Conforming to Table 500-17 of MoRTH for DBM/WMM |
| Emulsion | Cationic (CRS-1/CRS-2) per IS:8887 |
| Water | Potable quality for mixing |
🧪 B. Pre-Mixing Tests
| Material | Test | Code | Frequency | Purpose |
|---|---|---|---|---|
| RAP | Bitumen content | ASTM D6307 / IRC SP:100 | 1/100 m³ | Mix proportioning |
| RAP | Gradation analysis | IS:2386 (Part 1) | 1/100 m³ | Suitability check |
| RAP | Stripping test | IS:6241 | 1/lot | Adhesion properties |
| Aggregates | LAA/AIV | IS:2386 Part IV | 1/100 m³ | Strength |
| Emulsion | Residue, viscosity, storage stability | IS:8887 | Every batch | Conformance |
| Water | pH, impurities | IS:3025 | Every source | Suitability |
🔍 Enhancement: Added stripping test, pH test for water, and frequency of testing.
📐 2. Mix Design (Job Mix Formula)
- Follow IRC SP:100-2014, adjusted for RAP inclusion.
- Recommended RAP: 20–30% by weight of total aggregate.
- Optimum emulsion content typically ranges from 3.0% to 5.5% depending on aggregate absorption and RAP binder.
- Moisture content: Pre-wet aggregate (~1.0% by weight) for better coating.
Modified Marshall Test for Cold Mix
| Property | Criteria |
|---|---|
| Stability (air-cured) | ≥ 2.5 kN |
| Flow | 2–4 mm |
| Air Voids | 7–14% |
| Retained Stability (Water-Soaked) | ≥ 70% |
🔍 Enhancement: Added air voids, retained stability targets, and clarified pre-wetting step.
🚧 3. Plant & Site Preparation
A. Mixing Process
- RAP and fresh aggregates are batched and mixed.
- Water is added to pre-moisten aggregates (optional).
- Emulsion is added last, and mixing continued until homogenous.
🔍 Clarified sequence: Water added before emulsion to avoid breaking.
B. Site Preparation
- Base Preparation: Sweep base thoroughly. Remove loose debris.
- Prime Coat (if untreated base): SS-1 @ 0.6–1.0 kg/m²
- Tack Coat (if over bituminous layer): CRS-1/2 @ 0.25–0.5 kg/m²
🔍 Clarified use of tack vs. prime coat depending on base layer.
🛣️ 4. Laying and Compaction
- Lay mix with mechanical paver or manually (for patch works).
- Layer thickness: 25–75 mm (depending on layer type).
- Compaction sequence:
- 8–10T Vibratory or Tandem Roller
- 3–4 passes or until no movement observed
- Avoid over-compaction which squeezes binder
🧪 5. Tests During Laying
| Test | Standard | Frequency | Criteria |
|---|---|---|---|
| Mix Temperature | Thermometer | Every 50 m | Ambient (15–40°C) |
| Loose Thickness | Measurement | Every 50 m | As per JMF |
| Compactness | Core Density | Every 250 m² | ≥ 95% of lab |
| Surface Regularity | 3 m straight edge (IRC SP:16) | Every 30 m | ≤ 10 mm |
| Aggregate Coating | Visual + IS:6241 | Continuous | ≥ 95% coated |
| Field Moisture | Oven dry method | 1/lot | Near optimal |
| Emulsion Break Check | Visual | Periodic | Uniform dark coat |
🔍 Added emulsion break check and clarified acceptable tolerances.
🌤️ 6. Post-Laying Curing and Opening to Traffic
- Minimum curing period: 24–72 hours depending on weather.
- Accelerated curing may be done using fog seal (optional).
- Opening to traffic: Only after full binder setting (visually dry, no bleeding).
🧪 7. Post-Laying Tests
| Test | Frequency | Specification |
|---|---|---|
| Core Density | Every 250 m² | ≥ 95% of lab density |
| Stability of cores (cured) | Random | ≥ 2.5 kN |
| Water Sensitivity | 1/lot | TSR ≥ 70% |
| Skid Resistance | Random | SRV ≥ 40 (optional) |
🔍 Added TSR (Tensile Strength Ratio) and skid resistance value.
📑 8. Documentation Checklist
- Job Mix Formula with approval
- Source and batch test reports
- Daily mixing logs
- Site preparation photos
- Rolling pattern and density reports
- Emulsion delivery certificates
- Curing and opening timeline
✅ Summary
| Stage | Key Activities |
|---|---|
| Pre-Mix | Material testing, JMF design, emulsion QA |
| Mixing | Pre-wet, uniform mixing, ambient operation |
| Laying | Surface prep, laying, compaction (3–4 passes) |
| Post-Laying | Curing, field testing, documentation, traffic opening |
🧾 Optional Additions for Reporting
- Use QCR format (as per MoRTH)
- Attach Emulsion MSDS for safety
- Include calibration certificates for rollers/mixers
- Provide 7-day and 28-day stability test (optional, long-term strength)
Check list
| Stage | Activity | Reference Code | Frequency/Remarks |
| Material Collection | Collect and stockpile RAP separately | IRC:120-2015 | Once per site |
| Material Collection | Collect fresh aggregates and emulsion | MoRTH Section 500 | Every batch |
| Material Testing | Conduct tests on RAP, emulsion, aggregates (bitumen content, gradation, LAA, viscosity) | IS:2386, IS:8887, ASTM D6307 | 1 per 100 m³ or batch |
| Mix Design | Determine optimal RAP %, emulsion %, and moisture content | IRC SP:100-2014 | As per design requirement |
| Mix Design | Perform modified Marshall Test and finalize JMF | ASTM D6927 (modified) | 3 samples minimum |
| Mixing | Weigh and blend RAP and aggregates | IRC SP:100 | Every batch |
| Mixing | Add water and emulsion in correct sequence | IRC SP:100 | Each mix cycle |
| Site Preparation | Clean surface, apply tack/prime coat | MoRTH 502/503 | Each layer/section |
| Laying | Lay cold mix using paver or manually | MoRTH 507 | Continuous |
| Laying | Check loose thickness and temperature | IRC SP:100 | Every 50 m |
| Compaction | Perform rolling (3–4 passes) and monitor compaction | MoRTH 508 | Every 100 m² |
| Post-Laying | Allow proper curing (24–72 hours) | IRC SP:100 | Visual + 24–72 hr |
| Post-Laying | Check for uniform binder break and surface finish | IRC SP:100 | Field visual check |
| Final Testing | Core cutting for density check | IS:2720 | Every 250 m² |
| Final Testing | Conduct Marshall stability test and TSR (if required) | ASTM D6927 | Random cores |
| Documentation | Submit test reports, JMF, density logs, photographs | MoRTH QCR Format | Before handover |