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.
- Status
- Current
- Usage level
- Essential
- Domain
- Transportation — Pavement and Road Materials
- Type
- Guidelines
- Amendments
- Amendment No. 1 (2015) — modern PCE-based plasticizers, chemical set retarders; Amendment No. 2 (2023) — climate change alignment, higher temperature thresholds
Also on InfraLens for IRC 74
Practical Notes
! Hot weather concreting is routine in Indian summers (April-June). Temperatures reach 40-45°C in North India, 35-42°C in coastal areas. IRC 74 compliance is not optional.
! Plastic shrinkage cracking is the #1 hot weather problem. Rapid water evaporation creates tensile stresses exceeding early concrete strength. Mandatory protective measures.
! Early morning or evening placement: avoid 11 AM - 4 PM peak heat. Start at 5-6 AM; complete by 10 AM. Resume 5-6 PM if needed. Saves 40-60% of hot-weather problems.
! Cooling cement: store in shaded area; temperature < 30°C. Hot cement accelerates hydration and reduces working time.
! Cooling aggregate: sprinkle with water; stockpile in shade; use chilled water. Cool aggregate (< 25°C) reduces initial concrete temperature.
! Iced water in mixing: reduces temperature by 10-15°C. Cheap and effective. Standard for hot-weather RMC in India.
! Evaporation retarder: aliphatic alcohol-based liquid sprayed on fresh concrete. Forms monomolecular layer preventing water evaporation for 30-60 minutes until initial set. Cost ₹50-100 per m².
! Fog spray: fine mist of water over concrete. Reduces surface temperature, cools concrete, prevents evaporation. Continuous spray during curing. Requires skilled operator to avoid damaging surface.
! Set retarders (Clause 10): sodium gluconate, lignosulfonate, PCE-based. Extends working time 60-120 minutes. Essential for hot weather placement distance (> 30 km transit).
! Fly ash / slag replacement: up to 35% fly ash or 50% slag. Slower hydration, less heat evolution, reduced thermal cracking. Also cheaper and more durable. Standard for modern concrete.
! Curing criticality: 14 days minimum water curing. First 24-48 hours MOST critical. Continuous water (sprinklers every 30 minutes) or wet burlap/polyethylene.
! Curing compounds (white-pigmented): alternative to water curing for remote sites. Applied immediately after finishing. Cost ₹20-40 per m². Reduces labour but slightly less effective than water curing.
! Temperature monitoring: thermometer in concrete at placement (should be 32°C or below at placement), at 12 hours (peak heat), at 24/48 hours (critical phase). Log in QA records.
! Peak summer concreting (May-June): transit time from batching to placement should be < 20 minutes (not 30). Use admixtures aggressively. Consider overnight concreting.
! Climate change (Amendment No. 2, 2023): Indian summers 2-4°C hotter than 1990s. Previous year-round construction windows compressed. New: night concreting becoming more common in rural areas.
! Quality consequences of non-compliance: plastic shrinkage cracks (visible within 24 hours), reduced 28-day strength (15-25% lower), long-term durability issues (cracking, spalling).
! Economic impact: proper hot-weather concreting adds 5-15% to construction cost (admixtures, cooling, extended curing, timing). Non-compliant concrete may need rework costing 50-150% of original — net cost worse.
! Rural contractor awareness: training critical. Many rural contractors don't understand hot weather implications. PWD site engineer should provide hot-weather checklist.
! Admixture cost: set retarder ₹50-150 per m³ of concrete; fly ash reduces cement cost by 20-30%. Often net cost-neutral or saves money.
! Bridge deck concreting in summer: special challenges. Use large-panel ice blocks, pre-cooling of formwork, nighttime placement. Critical for thermal crack prevention.