Reducing drying shrinkage of concrete by treatment of aggregate

Abstract

Drying shrinkage of concrete has been found to cause cracking, water leakage and other serviceability problems and is thus an important research topic. In early studies, it has been found that the shrinkage of concrete varies with the rock aggregate used. This is partly because the aggregate also shrinks and the shrinkage of aggregate is dependent on the type of rock from which the aggregate is derived. However, there have been few studies on the shrinkage of rock and how the shrinkage of aggregate would affect the shrinkage of concrete. In this study, the shrinkage of the granite rock in Hong Kong was measured. It has been found that the rock shrinks quite substantially upon drying and that its shrinkage is dependent on the initial moisture condition. Based on such observation, two alternative methods of treating the aggregate before use so as to reduce the shrinkage of concrete are proposed. Long-term shrinkage measurement of concrete made with untreated and treated aggregates revealed that the proposed methods of aggregate treatment, which are still rudimentary, can significantly reduce the shrinkage of concrete.