Why does concrete buckling occur in the heat?
The reason is simple physics: Heat causes materials to expand.
When concrete slabs expand beyond the space in the joints they press against each other, causing the surface to buckle at the joint or in a weak spot within the slab, rocks also can get in the joints and prevent them from being able to expand into the joint. Moisture can also become trapped below the surface. When it gets hotter and hotter, it can work like a tea kettle creating steam that expands and pushes the concrete up enough to heave and eventually can break and flake. The age and type of the concrete can also be a factor, as is temperature. When it gets to around 90 degrees outside, the pavement can get as hot or hotter than 135 degrees. Parking lots and roads that have asphalt over the concrete will heave as it is more elastic than concrete, but eventually can give way and break apart.