Effects of Presoaked Lightweight Aggregate on Deformation Properties of Ordinary Portland Cement-Calcium Sulfoaluminate Cement Blends

Calcium sulfoaluminate (CSA) cements were developed for shrinkage compensation of concrete. The expansive nature of CSA-based cements can be used to enhance the resistance against shrinkage cracking by inducing compressive stress in concrete. Because of the higher water demand of CSA cement for achieving full hydration, as compared with ordinary portland cement (OPC), elevated water-cement ratios (w/c) for OPC-CSA cement blends are required for a successful mitigation of shrinkage. This study examines the effects of presoaked lightweight aggregate (LWA) addition on deformation properties of OPC-CSA mortar and concrete as an alternative to increasing the w/c. The motivation behind this work is to promote CSA hydration and increase the early-age expansion of OPC-CSA blends by curing concrete internally while avoiding the undesirable impacts of increased w/c on the microstructure of the mixture. The influence of LWA addition on autogenous and drying shrinkage of OPC-CSA blend was studied. It is shown that the early-age expansion of OPC-CSA blends can be dramatically increased when internal curing is implemented using LWA. Based on thermogravimetric (TG) results, it is indicated that the increase in expansion is partially due to the enhanced hydration of CSA cement in the mixture, which results in an increased rate of ettringite formation. Furthermore, the effects of LWA on total capillary porosity and compressive strength of OPC-CSA blends was also examined to verify the benefits of using LWA to promote CSA hydration as compared to increased w/c. Keywords: calcium sulfoaluminate cement; internal curing; lightweight aggregate; shrinkage.