Influence of expansive calcium sulfoaluminate agent dosage on properties and microstructure of expansive self-compacting concretes

Expansive concretes based on the formation of ettringite from calcium sulfoaluminate agents are presented as an effective alternative to minimize the problems derived from shrinkage and low tensile strength at the early ages of the concrete. However, determining the mechanism responsible for the expansion is still a controversial issue today. In this study, the influence of three doses of expansive agent on fresh state and on compressive strength and magnitude of free expansion under two curing environments was evaluated on a reference mixture of self-compacting concrete (SCC). The microstructural evolution of the hydrates and anhydrous related with the expansive phenomena was also studied. From our observations it seems that an eminently amorphous ettringite is formed and that this ettringite would be strongly related to expansion. As a result, the influence of the ratio w/cementitious material and curing environment on the magnitude of the expansion as well as the influence of this on the mechanical properties of the SCCs was identified.