Abstract
This study explores the effects of the cations in sulfates, chlorides, and nitrites on calcium-hydroxide activated blast-furnace slag. Using several methods, it was demonstrated that the activators investigated could improve early strength development. Compared with chlorides and nitrites, the type of sulfate has a significant influence on slag hydration. Compared with K2SO4 and Na2SO4, the promotion of slag hydration in MgSO4, at an early age, is limited due to the precipitation of gypsum and brucite which retard the formation of hydrates and limits hydration kinetics during the initial stage. The high concentration of sulfate ions in the pore solution causes some ettringite to remain, promoting strength development. It was observed that the mechanism of pH increase in K2SO4 and Na2SO4 is due to the synergistic reactions between the sulfates and Ca(OH)2, while the low pH of MgSO4 due to the low solubility of brucite inhibits slag dissolution. The critical pH for promoting slag hydration was determined to be 13.1.
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