Effect of calcium sulfate type and dosage on early strength and porosity of self-leveling underlayments

Abstract

In recent years, self-leveling underlayments (SLUs) are often used due to high flow ability and self-smoothing properties. Besides the strength, other characteristics of SLUs such as workability, rapid drying, rapid hardening, shrinkage compensation, etc… are required. This paper presents the effect of calcium sulfate type and dosage on early-age strength and porosity of SLUs based on ettringite binders. The raw materials used for making SLUs binders are calcium aluminate cement (CAC), Portland cement (PC) and calcium sulfate (C$Hx). Two types of calcium sulfates (hemihydrate and anhydrite) were used in this research. The ettringite formation is the reaction that controls the mechanical properties at early age of SLUs such as rapid hardening, early strength gain, etc. It was found that using hemihydrate in SLUs gives higher compressive strength than using anhydrite at the same content of calcium sulfate. On the other hand, the pore size of SLUs will decrease with increasing the amount of calcium sulfate in SLUs thanks to the higher amount of ettringite.