New insights into the early reaction of NaOH-activated slag in the presence of CaSO4

Abstract

This study focused on the reaction and initial setting of NaOH-activated slag with different CaSO4 contents. The macroscopic properties were firstly investigated, and then the reaction process was monitored using a micro-reactor method and a combination of exothermic rate, element concentration and semi-quantification of precipitates. The results prove that there is a proper dosage for CaSO4 as a retarder (specifically, 4 wt% in this study). Below this value, CaSO4 does not retard the reaction; above this value, there is a significant retardation, but also a great loss in compressive strength. The retardation is mainly attributed to the inhibition of high Ca2+ concentration (dissolved from CaSO4) on the slag dissolution, rather than the decreased pH or the effect of SO42−.