The use of supplementary cementitious materials (SCMs), including ground granulated blast furnace slag (GGBS), is an effective approach in reducing the CO2 emissions of construction.However, both clinker and slag hydrate at different rates and vary in composition, changing hydrate composition and amounts;these changes consequently determine how slag cements perform under field conditions upon sulphate exposure.This study probed at these differences to better understand the implications of slags upon sulphate resistance.