As shown in the last term of equation 3.7, thermal strain is the product of the coefficient of thermal expansion and temperature change, which is usually within the range of -22 to 65 C. Since cement paste and aggregate have dissimilar thermal coefficients, the coefficient for concrete depends upon its composition and also the moisture condition at the time of temperature change. The role of aggregate is similar to that in shrinkage and creep, namely, the aggregate restrains the thermal movement of the cement paste since the latter has a higher thermal coefficient. The coefficient of thermal expansion for concrete is related to thermal coefficients of cement paste and aggregate as follows (Hobbs, 1971):
