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Thermal movement depends on daily temperature cycle and the thermal coefficient of the concrete. A considerable variation in the value of the coefficient of linear thermal expansion has been found for South African conditions. Several factors influence this coefficient but it is generally accepted that thermal volume change is strongly influenced by the coefficient of expansion of aggregate. The values of concrete made with different types of aggregate vary from a high of 0,012 % to a low of 0,007%(4). Other factors that influence the thermal coefficient include type of cement and water content of the concrete but practical values between 0,008 % and 0,012 % seem appropriate.

 

Although the thermal coefficient does not vary much, temperature cycles (day/night and winter/summer) will have an effect on both crack width and curling. The daily temperature cycle is the more pessimistic value and is referred to in the section on the weather and environment.