Effect of sodium sulfate activation on the early age behaviour and microstructure development of hybrid cementitious systems containing Portland cement, and blast furnace slag

Alkali activation may help to increase the early strength and reduce the setting time of mixtures with high contents of supplementary cementitious materials (SCMs). In this research, the effect of sodium sulfate activator on reaction kinetics, compressive strength and pore structure of hybrid systems produced with 70 wt% ground granulated blast furnace slag (GGBFS) and 30 wt% Portland cement (PC) was determined. The setting time was shortened by adding sodium sulfate, but increasing the dose above 3 wt% did not influence it drastically. In-situ XRD measurements revealed an increasing ettringite formation within the first 2 days of hydration. A greater reaction of the GGBFS resulted in a pore refinement of the mortars studied and consequently raised the early age compressive strength. The assessment of a convenient dosage of activator was based on both technological and environmental parameters. The contribution of PC and GGBFS to compressive strength was "decoupled".