Concrete in Hot Weathers (

Concrete specifications contain a maximum temperature for the freshly mixed concrete as delivered. Typical values are between 27° and 35° C (Max) as measured by ASTM C 1064-86 (Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete).

ACI 305R section 3.2.1 states that “Concrete can be produced in hot weather without maximum limits on placing temperature and will perform satisfactorily if proper precautions are observed in proportioning, production, delivery, placing, and curing. As part of these precautions, an effort should be made to keep the concrete temperature as low as practical.”

As per observations and tests, Concrete placed and cured at a moderate temperature (16° to 32° C) outperforms in strength and durability. If looking for superior concrete, control the temperature of fresh concrete.

The other problem with warmer concrete is Cracking. These maximum specified temperatures are necessary to help control early cracking in concrete. Concrete is usually poured during the day when it is warm. Early cracking in slabs and other large concrete structures is often caused by a steep temperature gradient through the concrete caused by the cooling of the surface by the night air when the concrete has very low strength. After hydration starts, concrete will gain in temperature reaching a maximum, which will depend on member thickness, type, and quantity of cement, and so forth. As soon as the concrete begins to cool, the gradient, which depends strongly upon external temperature, will determine the cracking risk of that concrete. During this phase (from 24 to 72 hours after pouring), if the concrete is able to generate tensile stresses higher than the tensile strength, a crack will appear. Any measure to reduce temperature differences, such as using special low hydration cements, lower cement content, cooling down the compounds before mixing, cooling down concrete during the first hours, or avoiding extreme temperature drops after 1 day, will help. One way is to pour during the night, first to reduce the maximum temperature because, during the night, external temperature helps cool the concrete, and second, when the day starts, the temperature increase helps decrease temperature differences and gives the concrete more time to generate tensile strength.