Because of the problems that hot weather can create in both plastic and hardened concrete, cooling is encouraged by American Concrete Institute Committee 305 for concrete that is mixed, transported, or placed under hot weather conditions. A limiting temperature would probably be between 75 and 100 degrees F according to the committee.
Placing concrete at too high a temperature can adversely affect setting time, slump and water demand; and when the plastic concrete has hardened it may have decreased strength and durability and show a lack of uniformity of appearance. Also, concrete placed at an elevated temperature may have a tendency to develop drying shrinkage cracking and differential thermal cracking. Cooling the concrete can help eliminate these undesirable characteristics. In recognition of this, a ready-mix firm in North Carolina now uses liquid nitrogen at a temperature of -320 degrees F to form an ice/water slush for cooling concrete mixes that must be placed during very hot weather. The system enabled the company to meet strict concrete temperature specifications required in a 1979 contract for the construction of an electric generating plant. The company finds the system a vast improvement over the ice cooling method it used in 1973 during construction of a concrete dam.
From an onsite cryogenic storage tank, liquid nitrogen is introduced into the flowing water just prior to its exit from a pipe into the mixer. The amount of icy slush produced by the process can readily be adjusted to meet various concrete requirements. The system easily reduced concrete temperature as much as 20 degrees F, the decrease required to meet the 80-degree-F temperature limitation of the contract. Even when ambient temperatures went above 100 degrees F, tests showed the cooling system capable of reducing the concrete temperature to below 70 degrees F.