Curling
Curling is the distortion (rising up) of a slab's corners and edges due to differences in moisture content or temperature between the top and bottom of the slab. The top dries out or cools and shrinks more than the wetter or warmer bottom. If the curled section of a slab is loaded beyond the flexural strength of the concrete, cracks may develop to relieve the stress.

Steps to reduce curling:

1. Use a low-shrinkage concrete mix
2. Using proper control-joint spacing
3. Create uniform moisture content and temperature of the slab from top to bottom
4. Use large amounts of steel 2 inches down from the surface
   

Concrete Links

National Ready Mixed Concrete Association

Tilt-Up Concrete Association

The Portland Cement Association

American Concrete Institute

American Society of Testing Materials

Concrete.com

Effingham Area Home Builders Association