When is it "hot weather"?
Concrete is sensitive to all four of these — temperature alone isn't enough. A 25°C morning in Pune with low humidity and a 25 km/h dry wind can dry fresh concrete faster than a 40°C still afternoon. Treat each as a separate trigger.
ACI 305R — evaporation thresholds
The American Concrete Institute's ACI 305R chart tells you whether you have a plastic-shrinkage-crack risk on your hands, based on air temperature, concrete temperature, RH and wind speed.
| Evaporation (kg/m²/hr) | Concrete temp | What to do |
|---|---|---|
| < 0.5 | ≤ 40°C | Normal precautions |
| 0.5 – 1.0 | 40 – 45°C | Cooling / windbreaks required |
| > 1.0 | > 45°C | Special precautions — fog mist, ice, postpone |
Time-of-day placement
The cheapest hot-weather concreting strategy is to pour when it isn't hot. For most of India, that means the night-early morning window. Here's a practical schedule for summer pours:
Ambient still moderate. Concrete temperatures manageable. Recommended slot.
Peak heat. Concrete temp may exceed 40°C. Avoid major pours.
Heat breaking. Cool aggregates / chilled water still needed.
Best thermal conditions. Plan illumination & logistics for night pours.
Mix & material modifications
- · Shade stockpiles, sprinkle with cool water
- · Use chilled washed aggregate when feasible
- · Saturated surface-dry (SSD) condition — not oven-dry
- · Chill to 5°C or use ice (part of the mix water)
- · Below-grade tanks keep water cooler than overhead tanks
- · Pumping chilled water is often the most effective single step
- · PPC / PSC generate less heat of hydration than OPC
- · Fly ash / slag reduce peak temperature rise
- · Use lower-heat cement in mass pours
- · Retarders — extend workability in transit
- · Plasticizers — reduce water demand
- · Avoid accelerators (raise heat of hydration)
Curing — IS 456 minimums
Hot weather doesn't change the chemistry — it accelerates water loss. Cure longer, not shorter.
| Exposure / Cement | Minimum curing |
|---|---|
| Mild exposure · OPC | 7 days |
| Severe exposure · OPC | 10 days |
| Extreme exposure · OPC | 14 days |
| PPC / PSC (any exposure) | 14 days |
Reference: IS 456:2000 Table 5
Run the ACI 305R Evaporation Calculator
Plug in your ambient temperature, concrete temperature, relative humidity, and wind speed. The calculator applies the modified Menzel/Uno equation and returns the evaporation rate in kg/m²/hr — with the same 1.0 kg/m²/hr danger threshold ACI 305R uses.
Open Evaporation Rate CalculatorRelated articles
Amit Haridas
Founder & Proprietor, ConcreteInfo. 25+ years of experience in construction QA/QC and concrete technology. NRMCA Certified Trainer and ISO Lead Auditor.