Impact of sodium silicate solution chemistry on product formation and jelly hardening of alkali-activated GGBS mortars

This study investigated the effect of silicate modulus (M = silicon dioxide (SiO2)/sodium oxide (Na2O) by mass) and activator content S (mass proportion of sodium oxide and silicon dioxide to ground granulated blast-furnace slag (GGBS)) of sodium silicate (SS) solution on the compressive strength of alkali-activated GGBS (AAS) mortars. At a given solid content, the specimens activated by SS with modulus of 1.0 and 1.5 had the highest compressive strength. In the case of the same modulus of SS, the compressive strength of the AAS mortars rose linearly and then remained unchanged or declined slightly with the increase in S. The mechanism of the action of SS on AAS was studied using backscattered electron (BSE) and energy-dispersive spectroscopy (EDS). The BSE image of AAS shows that GGBS particles are tightly bonded to the surrounding hardened, jelly-like slurry, and that the structure of the GGBS particles in the AAS slurry is intact without an apparent hydrating layer around it. EDS analysis revealed that only active materials in the GGBS, mainly calcium, are dissolved to participate in reaction, and that dissolving these materials does not damage the GGBS structure. S is solidified by these active materials, which embed the GGBS particles therein to form a whole.