The CRACKES IN CEMENT (ETC) cracked side walks‚ were taught that it's caused by little mini Earthquakes but there are also other natural phenomenons like weathering but when heat is constantly hitting concrete it reacts as always it expands and separates causing cracks in cement.
This is a more engineering answer, but, an example of thermal expansion is Railroad Tracks. When it gets cold, they will shrink, when they get hot, they expand. Does that help?
