Reducing drying shrinkage cracks

Drying shrinkage occurs within the cement paste fraction of the concrete. Therefore the occurrence of drying shrinkage cracking can be reduced by using a concrete with a lower water content or by increasing the aggregate volume where possible to minimise the cement paste volume. Good curing will also help, particularly on slabs, as it will enable the concrete to gain greater tensile capacity before drying out occurs. The extent of shrinkage cracking can be reduced at the design stage by providing movement joints and sufficient crack control reinforcement. The aim is to produce a large number of fine cracks rather than a few wide ones.

Additional information on shrinkage movements and the control of cracking may be found in Concrete Society Technical Report 67, Movement, restraint and cracking in concrete structures.

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