Curing and Low Curling/Crack Resistance

Concrete will crack. The key is to get it to crack in the right place. Shrinkage is a main cause of cracking. As concrete hardens and dries, it shrinks due to the evaporation of excess mixing water. The wetter the concrete mix, the greater the shrinkage will be. Also, rapid drying of the slab will increase the possibility of cracking. Avoid pouring concrete on windy days and use a "liquid membrane" product to keep moisture in the slab.

Proper curing of the slab is essential. Do not pour on frozen ground. The expanded sub-grade will shrink when it thaws causing the concrete to cave in to fill the void. Tooled control joints or sawed joints are necessary to make the slab crack in the correct location. Proper joints are those that are at least one-quarter of the thickness of the slab.  If joints are created at that depth at the correct time, the liklihood of cracking outside the joints is greatly reduced. 

There are many more issues to consider when preveting cracks.  Please reference Concrete in Practice numbers 4, 5, 6, and 7 for more detailed information.