Unsealed concrete drinks water. Along the Front Range, that water freezes overnight, expands, and pries the surface apart, then does it again the next night, most of the winter. 

That's where spalling, scaling, and pop-outs come from, and why a driveway that looked fine in October can look chewed up by March.

Sealed concrete sheds that water before it can freeze inside the surface. Fall is the smart time to do it, but our working window for sealing runs from spring through fall, as long as our Colorado weather allows.