Insights into the properties and chloride binding capacity of β-hemihydrate in the presence of slag powder and white calcium aluminate cement

Abstract

Calcium chloride (CaCl2) as a common concomitant in flue-gas desulfurization gypsum has a great negative impact on gypsum-based construction materials. Chloride binding in the form of Friedel's salt in the gypsum-dominating system is of great significance, but the feasibility of this approach has not yet been systematically clarified. In this paper, granulated blast-furnace slag (GBFS) powder and white calcium aluminate cement (CAC) were used as the components to explore their roles on the properties and chloride binding capacity of β-hemihydrate. Experimental results prove that CAC significantly improves compressive strength, water resistance, and chloride binding capacity of hardened paste. The XRD, DTG, SEM-EDS and thermodynamic modeling confirm that Friedel's salt forms in this system even at an early hydration time of 30 min. Mercury intrusion porosimetry and SEM results verify that the use of CAC decreases the volume of the pores in the 0.1–100 μm range. Thermodynamic modeling outcomes are consistent with the experimental data helping to explain the hydration and evolutions of β-hemihydrates in the presence of CaCl2, GBFS, and CAC at early hydration ages.