Chloride binding capacity of hydrotalcite and the competition with carbonates in ground granulated blast furnace slag concrete

This paper further investigates the hypothesis and recent preliminary findings that hydrotalcite is responsible for the remarkable improvement of chloride binding in concretes containing ground granulated blast furnace slag (GGBFS). In this paper, the chloride binding capacity of hydrotalcite has been examined in a wide range of GGBFS and GGBFS-OPC (ordinary Portland cement) blends. X-ray diffraction (XRD) was conducted to identify hydrotalcite in GGBFS pastes and to distinguish it from Friedel's salt. Using Rietica software for quantifying crystalline minerals, this paper presents quantified XRD analysis of the relative proportion of hydrotalcite formed in GGBFS and binary blend pastes. XRD revealed that hydrotalcite was formed in all pastes containing GGBFS. The results clearly demonstrated that hydrotalcite made up a significant proportion of the crystalline phase in GGBFS pastes. The results further showed that the ability of hydrotalcite to bind chlorides was not significantly impaired by the competitive adsorption of carbonates.