By: Joe Marin Quality Control Director
When placing concrete in hot weather concrete temperature must be kept below 95°F according to NPCA and TXDOT standards. Concrete sets as the cement hydrates causing a reaction that generates heat, and that reaction accelerates when the concrete is hot. When cement hydrates it absorbs water and concrete crystals grow around the aggregate particles. When it’s hot and that reaction is rapid, the crystals grow quickly but don’t have time to grow strong. The main concern with the concrete’s strength and set time isn’t really the air temperature but the concrete temperature.
One of the many practices used all around the country to maintain the concrete temperature under 95°F is the use of chilled water, ice and/or liquid nitrogen. Another tool that is also used is keeping the coarse aggregate wet by using sprinklers to maintain a uniform moisture content and allow concrete to last a bit longer for the production crew to perform the proper finish. Having the aggregates on SSD (Surface Saturated Dry) condition not only helps the concrete temperature but also helps the concrete use less water/admixtures to obtain the desired slump and also helps the concrete strength. This will help the concrete hydrate at desired rate that will not affect the structural integrity of the concrete member.
