IRC 74:1979 is the Indian Standard (IRC) for tentative guidelines for hot weather concreting on rural roads and other road works. IRC 74:1979 addresses hot-weather concreting challenges specific to Indian conditions — ambient temperatures > 35°C, relative humidity < 50%, and wind-driven evaporation. Hot weather threats: plastic shrinkage cracking from rapid water loss, accelerated cement hydration (reduced workability, faster setting), reduced 28-day strength, and thermal differential cracking. IRC 74 specifies: cool storage of materials (cement < 30°C, aggregate cooled, water iced if needed), mix design adjustments (higher w/c 0.50-0.55, fly ash/slag partial cement, set retarders), placement timing (avoid 11 AM - 4 PM peak heat), immediate protection (evaporation retarder, plastic cover, water mist), extended curing (14+ days continuous water curing). Amendment No. 1 (2015) added modern chemical admixtures (PCE-based plasticizers, set retarders). Amendment No. 2 (2023) aligned with climate change — Indian summers are getting hotter (> 42°C more common), making hot-weather concreting more frequent. Hot weather concreting is routine on Indian rural roads where most construction happens April-June (pre-monsoon season). IRC 74 compliance is essential for long-term pavement durability.
Specifies methodology, precautions, and material considerations for concrete construction in hot weather (ambient temperature > 35°C) — addressing cement hydration, water loss, crack prevention, and strength development in Indian summer conditions.
Temperature limits, slump-loss, curing and timing controls for concreting above 40 °C.
| Reference | Value | Clause |
|---|---|---|
| Hot weather — defined ambient threshold | > 40 °C ambient air | |
| Concrete temperature at placing — max permissible | 30 °C (desirable); 32 °C (limit) | Cl. 4.1 |
| Mixing water — max temperature | 20-25 °C (use chilled water if needed) | |
| Aggregate temperature — control | Cool with sprinkling / shading | Cl. 5.3 |
| Slump loss in hot weather | Up to 50% within 1 h — increase initial slump | Cl. 3.2 & Cl. 6.1 |
| Initial setting — accelerated by heat | Use retarders if delivery >30 min | Cl. 5.4 |
| Casting time after mixing — max | 30 min (truck mix); 90 min with retarder | Cl. 6.1 |
| Curing — start within | Immediately after final set (within 2 h) | |
| Curing — duration (continuous wet) | Min 14 days (PQC); 7 days (RCC) | |
| Wind speed — bleed rate trigger | Use evaporation chart >1.0 kg/m²/h | Cl. 8.2 & Fig. 1 |
| Plastic shrinkage — mitigation | Fog spray, sun screens, monomolecular film | Cl. 5.3 |
| Casting time of day — preferred | Early morning / night (avoid 11:00-15:00) | Cl. 4.1 |
| Use of ice — % replacement of mix water | Up to 75% (by mass) | Cl. 4.2.2 |
| Form removal — earlier in hot weather | Per strength gain (concrete strength governs) | Cl. 6.3 |
IRC 74 (1979) provides Tentative Guidelines for Hot Weather Concreting on Rural Roads and Other Road Works — the IRC's standard for concrete construction in elevated temperature conditions where rapid setting, water loss, and cracking are concerns.
Use IRC 74 when you are: - Constructing concrete pavement / structures during summer (ambient ≥ 35-40 °C) - Working in hot arid regions (Rajasthan, Gujarat, parts of MP, Madhya Bharat plains) - Specifying summer concrete operations for PMGSY rural roads - Doing bridge / structure construction in hot weather - Specifying mid-day shutdown schedules for concreting - Designing mix proportions + admixtures for hot weather - Specifying curing methods in hot dry conditions
What IRC 74 covers: - Definition of 'hot weather' conditions - Mix design adjustments for hot weather - Material temperature control - Construction timing + scheduling - Placing + finishing techniques - Curing protocols (water + curing compound) - Worker safety in hot conditions - Quality control + acceptance
Hot weather concrete challenges: - Rapid hydration → reduced workability + difficulty finishing - Water loss to atmosphere → reduced strength + cracking - Higher early-age temperature → thermal cracking - Reduced cure window → reduced final strength - Worker safety → heat stress, fatigue, error
Hot weather threshold: - Ambient ≥ 35 °C triggers hot-weather precautions - Concrete temperature at placement ≥ 32 °C is critical limit - Wind > 25 km/h + low humidity worsens water loss - Solar radiation adds to concrete temperature rise
Mix design adjustments for hot weather:
1. Reduce cement content where possible (within design limits) 2. Use blended cements (PPC, fly-ash, GGBS) — slower hydration + lower heat 3. Increase aggregate-to-cement ratio — lower paste content 4. Add water-reducing admixtures — maintain workability with less water 5. Set-retarding admixtures for very hot conditions 6. Cool the mix water (ice in extreme heat — 50 % of mix water as ice can lower temp by 7-9 °C)
Material temperature targets: - Mix water: < 25 °C (cool source or chilled) - Aggregates: shade + sprinkle stockpiles; < 35 °C surface temperature - Cement: < 50 °C at delivery (typically below 40 °C) - Mix temperature at placement: target < 30 °C; absolute limit 35 °C
Admixtures (commonly used in hot weather): - Set retarder: sucrose-based or lignosulphonate; extends initial set 1-3 hours - Water reducer (plasticizer): maintains slump with less water; cement saving - Superplasticizer (for high-strength): dramatic slump retention - Hydration controller: specialised modern admixtures - Combined admixtures: retarder + water-reducer for slump retention
Construction timing: - Avoid mid-day placement (10 AM - 4 PM) where possible - Best window: early morning (5-8 AM) or late afternoon (4-7 PM) - Night placement for major concrete pours in extreme heat
Material temperature control: - Aggregate shading: sprinkle stockpiles; cover with tarpaulin where possible - Mix water cooling: chiller for large operations; ice for small - Cement bag storage: in shaded area - Transport in covered dumpers (light-colored tarpaulin)
Mix temperature at placement: - Target: < 30 °C - Acceptable: < 32 °C - Absolute limit (reject if exceeded): > 35 °C - For high-strength M40+ mixes: target < 25 °C
Slump targets: - Mass concrete: 50-100 mm - Reinforced concrete: 75-125 mm - Pavement concrete: 25-75 mm (slipform paver) - Plinth + foundation: 50-100 mm
Setting time adjustment: - Initial set: target 45-60 minutes after mixing (with retarder) - Final set: 8-10 hours typically - Workable life: 1.5-2.5 hours at 32 °C with retarder
Placing procedures: - Continuous placement to avoid cold joints - Vibration thorough; vibrator depth-of-vibration tested - Finishing immediately after placement - Burlap covering for fresh surface within 15-30 min
Curing — extended in hot weather: - Initial curing: water spray or wet burlap within 30 min of finishing - Continuous curing: for at least 7 days; 14 days preferred - Curing compound: white-pigmented, applied to fresh concrete; 4-6 m²/L - Polyethylene sheets over fresh surface - Water curing: sprinkler / soaking method - Critical first 48 hours: no drying allowed
Cracking precautions: - Crack-control reinforcement in mass pours - Reduce pour size for large structures to reduce thermal mass - Phased pour with day intervals for cooling - Cooling pipes in very large pours (mass concrete > 1.5 m thick)
Worker safety: - Hydration breaks every 30-45 min - PPE: hat, sun protection, light clothing - Shade availability for rest periods - Medical kit + heat-stroke awareness training - No work during heat-warning conditions (heat index > 40-45 °C)
Quality control: - Mix temperature measured at delivery (every batch) - Cube samples taken; cured at site under specified conditions - Workability test: slump per batch - Visual inspection for honeycombing, plastic-shrinkage cracking - 28-day strength verification
Documentation: - Daily temperature log - Mix temperature per batch - Pour sequence + timing - Curing record - Visual + strength quality observations
1. Mix temperature exceeds 32 °C. Cement hydration rapid; finishing impossible; cracking. Cool materials + use admixtures. 2. No retarder used. Workable life short; cold joints in extended pours. Mandatory retarder in hot weather. 3. Curing inadequate. Surface dries within 24 hours; shrinkage cracks; durability compromised. Mandatory water curing or curing compound. 4. Mid-day pour during peak heat. Mix arrives at site at 40 °C; cooling insufficient. Schedule for cooler hours. 5. Stockpiles in direct sunlight. Aggregate at 50-60 °C; mix temperature exceeds limits. Shade stockpiles + sprinkle. 6. Workforce fatigue / errors. Inadequate hydration breaks; mistakes in placement, finishing, vibration. Mandatory breaks + supervision. 7. No mix-temperature monitoring. Operator pours without measurement; over-temperature mix accepted. Mandatory temperature log per batch. 8. Cement bag storage exposed. Cement at 45-50 °C at use; rapid set. Shaded storage. 9. Plastic shrinkage cracks. Fresh concrete dries before initial set; shallow surface cracks. Apply burlap or curing compound within 15 min. 10. Mass-concrete heat of hydration. Internal temperature 70-80 °C; thermal cracking. Use blended cements (PPC); reduce pour size; cooling pipes for very large pours. 11. Ice for mix water mishandled. Ice not fully melted; sets in mixer; mix unworkable. Pre-melt ice in mix water. 12. Admixture dosing error. Over-retarder; concrete not setting in time. Verify admixture dosage per batch. 13. Curing compound poorly applied. Streaks + missed areas; partial drying. Spray application + verify coverage. 14. No documentation. Pours done; conditions + procedures not recorded; troubleshooting impossible. Daily logs + procedures. 15. Strength loss in summer cubes. Cube samples cured at site conditions; strength below design. Cure cubes at standard 27 °C ± 2 °C; isolate from heat.
Hot-weather concrete project — IRC 74 touchpoints:
1. DPR + design: - Identify hot-weather periods + likely construction schedule - Mix design with hot-weather adjustments (blended cement, admixtures, reduced cement) - Construction sequence + timing strategy
2. Material procurement: - Order chilled mix water capacity - Set-retarder + water-reducer admixtures (per IS 9103) - PPC / blended cement for slower hydration - Sufficient aggregate + shading provisions
3. Trial mix: - Test mix at simulated hot conditions - Verify setting time, workability, finishing - Adjust admixture dosage if needed - 7 + 28-day strength check
4. Construction setup: - Stockpile shading + sprinklers - Mix water chilling system - Covered transport trucks - Curing facilities (compound spray, sheets, water)
5. Pre-pour preparation: - Weather check (temp, wind, humidity, forecast) - Schedule pour for cooler hours (early morning / evening / night) - Equipment + worker readiness - Curing materials staged
6. Concreting: - Mix water cooled - Aggregate temperature controlled - Mix temperature monitored per batch (target < 30 °C) - Continuous pour without delays - Immediate finishing - Curing within 15-30 minutes of finishing
7. Quality control: - Mix temperature per batch (log) - Slump test per batch - Cube samples taken; cured at standard temperature - Visual inspection for cracking + workability issues
8. Curing: - Water curing 7-14 days minimum - Curing compound applied to all surfaces - No drying allowed in first 48 hours
9. Post-cure: - 28-day cube strength verification - Visual inspection of cured surface - Crack documentation if any
10. Worker safety: - Heat-stress monitoring - Hydration + rest breaks - Medical kit + first-aid trained personnel - No work during heat-warnings
IRC 74 is the practical guide for hot-weather concrete operations in India's many high-temperature regions — applied annually on summer concrete pours across Rajasthan, Gujarat, MP, southern states, and any project encountering temperatures > 35 °C.