Of course they don't add rebar to asphalt roads, that would be ridiculous. The sealant process is done manually, with some poor sod pushing a machine along each crack and injecting hot sealant which prevents further water incursion and the associated frost heave. That's partly why I'm so fascinated with it: some sections of highway are cracked everywhere, with hardly a square metre that doesn't have a crack running through it, and yet they're extremely smooth.