Concrete doesn't explode in the summer. There are cases were the entire assembly can heave in the summer due to excessive heat though. It's as simple as this: 200 feet of highway is cut into 10-20' squares. In the joints crud/debris/dirt collects, and when the concrete returns to it's maximum plastic size, it heaves as the dirt filled joints allow for no expansion. Even this is a rarity considering there's millions of yards of concrete roads out there.