CaCO3 dissolution-driven enhancement of strength and microstructure in clinker-free CaCO3-blended GGBFS binder via hydrated Al2(SO4)3

Abstract

This study highlights the beneficial impact of hydrated aluminum sulfate (Al-2(SO4)(3)center dot 14-18 H2O) on strength development and microstructural changes in a CaO-activated ground granulated blast furnace slag (GGBFS) binder containing CaCO3. The incorporation of hydrated Al-2(SO4)(3) promoted (1) ettringite formation, (2) GGBFS dissolution, and (3) enhanced CaCO3 dissolution, thereby leading to greater participation in forming hydration products, as well as (4) hemicarboaluminate precipitation and pore-size refinement at the optimal hydrated Al-2(SO4)(3) content (1 wt%). In this study, the formation of ettringite and hemicarboaluminate was driven by the aluminum and sulfate provided byAl(2)(SO4)(3), along with calcium released from the dissolution of GGBFS and CaCO3. However, when more than 3 wt% of hydrated Al-2(SO4)(3) was added, the hemicarboaluminate content decreased, possibly due to anion (SO42-) exchange, and large pores (similar to 1 mu m) were formed. These changes were closely linked to excessive gas generation from increased CaCO(3)dissolution, ultimately leading to strength degradation.