Effects of nano and micro size of CaO and MgO, nano-clay and expanded perlite aggregate on the autogenous shrinkage of mortar

When the water-to-binder ratio is lower than a critical value, a considerable self-desiccation may occur, leading to autogenous shrinkage (AS). This volume change can induce internal stresses when the shrinkage is restricted, and may cause micro cracks, endangering the durability of the cement based composites. It is essential to find appropriate ways to avoid such a risk of cracking at early ages. Methods based on the concept of internal concrete curing, expansive additives have been suggested in the literature. This paper focuses on the reduction of AS by both methods for the same mix proportions of the mortars to compare their effects. Thus, the effects of different percentages of pre-saturated expanded perlite aggregate (EPA), micro and nano size MgO, CaO and smectite (based) nano clays on AS of the mortars are discussed and compared. The highest reduction was observed for mixes containing 7.5% CaO and nano-MgO and resulting in a reduction of the autogenous shrinkage by 80%, at 28 days. However, reduction obtained by nano-CaO was negligible. EPA replacement of 30% of the fine aggregate reduced AS by 68% at 28 days.