Shrinkage Compensating Concrete

There are significant developments in concrete technology for a number of different and unique applications. Shrinkage compensating concrete is a concrete made with an expansive cement which, when properly restrained by reinforcement or other means, will expand by an amount equal to or slightly greater than the anticipated drying shrinkage.

Ideally a residual compression will remain in the concrete reducing the risk of shrinkage cracking. In the USA and Russia, expansive cements are produced as an enity, whereas in Japan they are produced by adding expansive admixtures to ordinary porland cement (OPC). A number of types of expansive cements have been used in USA namely Types K, M and S but type K is most prevalent. These cements which either contain or are blended with combinations of calcium sulphate,* calcium aluminates and calcium aluminate sulphates. In Japan another type of expansive cement. not based on sulphate and owing it s expansive properties to hydration of free lime, is used.

Care must be taken to ensure that continuous wet curing is provided for at least 7 days after placing to ensure that the expansion develops. Care also needs to be taken to prevent plastic shrinkage cracking. Expansive cements have been used to produce both shrinkage compensating concrete and self-stressing concrete for use in slabs, pavements, prestressed beams and roofs.