Optimizing gypsum content in Portland limestone cement with ground granulated blast furnace slag

Abstract

This study aimed to identify the optimum gypsum content and elucidate its effects on the physicochemical properties of Portland limestone cement (PLC) incorporating ground-granulated blast-furnace slag (GGBFS). As the gypsum content increased, the C3A reaction was retarded during the first 72 h, producing a clear separation of C3S hydration peaks. Partial replacement with limestone at 15 wt% and GGBFS at 20, 40 wt% reduced the clinker fraction of the binder, and consequently, the cumulative heat release. Higher compressive strengths were observed for OPC and PLC pastes with 5 wt% gypsum, which reflected these early-age hydration differences, whereas slag-bearing pastes with 20% and 40% GGBFS (S20, S40) peaked at 3 wt%. Therefore, gypsum dosage acts as an important control variable for hydration reactions and the resultant physicochemical properties of PLC–slag cement systems.