Q: We've been told that the coefficient of thermal expansion of concrete is about 5.5 millionths per degree F but that it can be higher or lower. There wasn't any explanation of what changes it. What's the story?
The main factor that affects the thermal coefficient is the kind of aggregate. Below are some typical coefficients for concrete made with various aggregates. For any particular local source the coefficient may vary somewhat from the value listed, particularly if it is a gravel, granite or limestone.
Type of
Aggregate
Coefficient of thermal
expansion, millionths inch per inch per º F
Quartz6.6
Sandstone6.5
Gravel6.0
Granite5.3
Basalt4.8
Limestone3.8