At The Conco Companies we have years of experience placing concrete in all kinds of weather conditions. We are often asked if it is ever too cold or too hot to safely place concrete. The answer is not necessarily a “yes” or “no” but rather other factors are taken into consideration.
In terms of cold temperature, normal concrete mixes will not properly set or harden when the concrete temperature is below approximately 35° F. However by making some changes to the mix such as adding heated water and aggregates or the addition of accelerating admixtures, concrete can be placed at below freezing temperatures but it is more expensive. Since most of the West Coast (Conco’s primary service areas) does not experience more than occasional episodes of below freezing temperatures, it is generally easier to wait for a warmer day.
In extreme heat of 90° F and above, concrete not only starts to set and harden faster but it can cause a reduction in the ultimate strength of the concrete. Plastic shrinkage and drying shrinkage can also be a problem in very windy or low humidity conditions. To mitigate these problems, the timing of placement along with the addition of retarding admixtures and proper curing are implemented.
On the historic continuous mat pour we did a few years ago for the Wilshire Grand Tower in Los Angeles, we needed to make provisions for the heat generated in mat foundations. In mass concrete structures there are two thermal properties that must be considered: the maximum temperature and the temperature difference between the center of the structure and surface. With help from a team of experts, we developed a thermal control plan specific to the mix design, the geometry of the foundation and the configuration of the rebar.
The fix involved mechanically controlling the temperature by post-chilling the concrete with cooling pipes to remove the heat. We successfully kept the maximum temperature below ACI limits and a temperature difference that was well within the ranges required to avoid thermal cracking.
The Conco Companies are a leading supplier of concrete services for the Western U.S. We got our start in the Bay Area in 1959 by offering clients the best value on a wide range of concrete services and products. Since that time, we have taken a leading role as one of the top concrete contractors in the region. We have four regional offices serving California, Nevada, Washington, Oregon and Colorado.