Influence of four additional activators on hydrated-lime [Ca(OH)2] activated ground granulated blast-furnace slag

The influences of four supplementary activators were investigated on Ca(OH)2-activated slag system. The additives significantly affected the (1) early strengths, (2) reaction degrees of slag, (3) types of hydration products, and (4) local structures of Si and Al; however, the 28-day strengths were not improved, but the reduction of water content improved the strength more effectively due to a reduction in porosity. In this study, the Na-based additives were less desirable than the Ca-based ones in the Ca(OH)2-activated system because (1) the Na-additives tended to produce lower 28-day strengths; (2) they synthesized U-phases, which may cause expansive failures at later ages and (3) they might suppress the dissolution of Ca(OH)2. Although sulfate ions generally appear to improve 28-day strength in literature, the sulfate-bearing additives in this study did not improve the strengths because the original slag contained a high sulfate content; adding more sulfate may have exceeded the optimal content.