Concrete curling
Slab edges and corners lift off the base, most obvious at joints where two panels no longer meet flush. Under wheel traffic a curled joint edge breaks down quickly, and the lifted section may rock underfoot.
VerdictCosmetic — does not compromise the slab
What causes it
Curling is differential drying shrinkage. A slab dries from the top, so the top shrinks more than the bottom, and the resulting stress lifts the edges. Anything that increases the differential makes it worse: high water content, a slab placed directly on a vapour retarder with no way to dry downward, thin sections, and long joint spacings. It is a dominant concern on commercial floors, which is why ACI 302.1R treats it at length.
How it is repaired
Curled edges can be ground flush, which is the usual remedy on a floor in service, though it removes the wear surface at exactly the point that takes most abuse. Severe curling with rocking panels may need underslab stabilisation by grouting or foam injection. Neither reverses the shrinkage; they manage the consequence.
How to prevent it
Lower water content, adequate slab thickness, closer joint spacing, and a sand layer over the vapour retarder where the design allows it so the slab can dry from both faces. Proper curing reduces the differential rather than eliminating it.