Companies having concrete work done may have heard the term ‘concrete cooling’ used before. For some people who are unfamiliar with the concrete industry this term may have seemed confusing or surprising. Many people may have been left wondering why concrete cooling was necessary at all. Below is a discussion of why concrete cooling is important, what problems can arise from concrete that is too hot, which projects may be most in need of cooled concrete, and what factors can influence concrete temperature.
The Chemistry of Concrete
Though in casual conversation some people may use the terms “concrete” and “cement” interchangeably, it is important to understand the distinction. Cement is the mixture that, when combined with water, forms the material known as concrete. Concrete formation itself is accomplished through a process known as cement hydration. This essentially refers to the chemical bonding of cement aggregates with water. Concrete cannot harden and strengthen without hydration.
All chemical processes can be classified as either endothermic, meaning they absorb heat and thus lower the temperature of their surroundings, or exothermic, meaning they release heat and thus raise the temperature of their surroundings. The process of cement hydration involves mostly exothermic chemical reactions. Thus as hydration occurs the concrete gets hotter. In some applications concrete temperatures may exceed 200°F.
Problems Associated with Hot Concrete
As concrete hardens the process is known as curing. Unfortunately high curing temperatures for concrete can result in reduced tensile strength and performance. It is well documented that concrete that cures at temperatures of 95°F or higher will have significantly less strength than concrete that is cured at around 70°F.
Part of the problem is that concrete that is curing will expand at higher temperatures. This results in a less dense setting, thereby reducing the strength of the concrete. This is especially a problem in large-pour settings where the inner concrete may be significantly warmer than the outer concrete, sometimes by as much as 10-20°F, resulting in non-uniform density and weak spots.
Another problem associated with hot concrete is related to water evaporation. As most people are well aware, water evaporation occurs much more quickly at higher temperatures than at lower temperatures. Thus as the temperature of the concrete rises, more and more water is evaporated. Unfortunately since the process of cement hydration relies on water this can create serious problems and may prevent some of the cement from ever fully hydrating.
Industrial Applications Are Particularly Vulnerable to High Concrete Temperatures
Industrial settings are among the most vulnerable to problems associated with high concrete temperatures. This is because industrial settings often require large-pour applications, which as discussed above often results in higher concrete temperatures and potentially non-uniform density and reduced tensile strength and performance. Another reason that industrial settings are particularly vulnerable to strength problems associated with high concrete temperatures is because industrial settings require very strong concrete to begin with. Thus any weakness could prove catastrophic in an industrial setting, whereas in lower-demand settings it may not prove problematic. In industrial settings often the safety and integrity of the entire facility is dependent on the performance and strength of its concrete.
Factors That Affect Concrete Temperature
The temperature of concrete is most significantly affected by the water used in the hydration process. Thus concrete cooling methods often involve cooling the mixing water prior to hydration. However, the temperature of the cement aggregates is also important and by pre-cooling the aggregates lower hydration temperatures can also be achieved. Another method of concrete cooling is drum cooling, which involves cooling the concrete mixtures as it hydrates. Naturally many concrete cooling systems involve using these techniques in conjunction with each other for maximum performance.
Semco is an industry leader in providing industrial cooling systems, including for the purpose of cooling concrete. Our systems can be fully customized based on the particular needs and preferences of each of our clients. Please contact us for more information about concrete cooling.