Designers of slabs on grade have an obligation to their clients to ensure that the concrete mix with the lowest practical shrinkage is used and that shrinkage testing is specified to be done before and on a regular basis during installation. Instead of expecting slump to control shrinkage, designers should bring about real shrinkage reduction by specifying low-shrinkage, stony concrete mixes with large maximum-size coarse aggregate.
Drying shrinkage and curling can be reduced by using less water. However, high-range water reducers do not necessarily reduce shrinkage in proportion to their ability to reduce water content.
When reinforcement is used to permit greater joint spacing, use the subgrade drag formula to compute distributed reinforcing steel, but specify at least 0.15% reinforcement in the upper half of the slab. Shrinkage-compensating and post-tensioned concretes offer alternative methods of minimizing joints and reducing shrinkage and curling.
Designers and their clients must be aware that some drying shrinkage cracking and some upward curling at slab edges may still take place. By following the guidelines presented here, however, designers can reduce the problems caused by shrinkage and curling.