Concrete is an extremely versatile building material. With the ability to be poured into forms and cure to withstand enormous compressive forces while being composed of some of the most plentiful materials on earth, concrete is a wonderful material. However, the curing process is temperature dependent. Historically, this made it difficult for concrete contractors in extreme temperatures or during poor weather, but today techniques have been developed that allow concrete to be poured in most environments.
Why temperature matters to concrete Curing is the process during which concrete hardens, changing its compressive strength from very little as a liquid to tremendous strength as a solid. The strength of the concrete does not simply come from the process of drying, but hardening over a period of time that allows the material’s strength to build. Wet conditions help the curing process to happen in the desired time frame and to create hardened concrete. The chemical reaction in curing comes from silica reacting with calcium hydroxide in the cement in the presence of water to create mineral hydrates that solidify in interlocking patterns that give concrete its strength. The rate of this reaction depends on the temperature and presence of water, making the temperature important when pouring concrete. Placing concrete in cold weather It is generally recommended that concrete be poured above 40 degrees Fahrenheit. The American Concrete Institute defines cold weather concreting as “a period when for more than three successive days the average daily air temperature drops below 40 degrees Fahrenheit.” The first risk to proper curing in cold weather is ice developing early on. Ice occupies significantly more volume than liquid water, which can expand the concrete itself and diminish its ultimate strength by up to 50 percent. Once concrete reaches a strength of 500 psi, usually within 24 hours, it is capable of repelling the force of ice creation and is protected against freezing. In cold weather, this is accomplished by using heated components, either the aggregate, water or both, as well as heated enclosures. These techniques keep the concrete temperature high enough for the curing process to develop the concrete’s strength. Placing concrete in hot weather When the outside temperature is above 90 degrees Fahrenheit it can also negatively impact the curing process. In these situations, the concrete can dry too quickly. This can remove water from the concrete too early, stopping the curing process before adequate strength is developed. Concrete can also dry unevenly at high temperatures. As concrete dries, it shrinks, and when a slab of concrete dries unevenly, the shrinking top layers can create stress throughout the slab, changing the resulting concrete’s properties. To address these issues, cold components such as water, aggregate or both are used when mixing concrete; placing windbreaks that reduce evaporation; or including additives that decrease the curing time of the concrete. The Conco Companies mission is to be the best supplier of concrete services in the Western United States and to bring expertise, experience, and quality of each project. We continue to upgrade and expand facilities to better serve the growing market for commercial, educational, public works, and parking structure projects as well as other construction development. Please call or email for more information on how Conco can assist your next project with Confoam™, our cost-saving cellular concrete.
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