Q. What is the rate of expansion and contraction for a concrete slab on grade due to temperature changes, and how much movement can be expected because of temperature change?
A. A general value for concrete's coefficient of thermal expansion is about 5.5 millionths/° F. If an unrestrained, 100-foot-long slab on grade was exposed to a 100° F temperature drop throughout its cross-section, it would contract about .66 inch (100 feet x 12 inches/foot x 100° F x .0000055). Since the slab is restrained by friction between the base and the bottom of the slab, the slab usually cracks instead of contracting the roughly 2/3 inch.
Since aggregate comprises a large percentage of the concrete volume, the coefficient of expansion for concrete varies depending on aggregate type. Typically it ranges from 3.8 millionths/° F for limestone to nearly 7 millionths/° F for quartz.
