Effects of activator content on properties, mineralogy, hydration and microstructure of alkali-activated materials synthesized from calcium silicate slag and ground granulated blast furnace slag

Calcium silicate slag (CSS) is the solid waste of the alumina recovery from high-alumina fly ash project based on combined pre-desilication and lime-soda sintering process. Alkali-activated materials (AAMs) were synthesized from calcium silicate slag (CSS), ground granulated blast furnace slag (GGBFS) in this study. The properties, mineralogy, hydration and microstructure of AAMs with various content of activator (sodium silicate) were investigated. The results show that the AAMs synthesized from 70 wt% CSS, 30 wt% GGBFS and sodium silicate solution with a Na2O/H2O mass ratio of 0.15 reached an optimal compressive strength over 65.0 MPa at 28 d. The reaction products of AAMs synthesized from CSS, GGBFS and sodium silicate are C(N)-(A)-S-H gels. The properties of CSS-based AAMs varied with the activator content - The increasing sodium silicate content is favorable to the hydration, microstructure and strength development. However, as the Na2O/H2O ratio of alkaline solution exceeded 0.15, the significant increase of the viscosity inhibited the hydration and the removing of air bubbles during preparation. This consequently decreased the compactness and compressive strength of CSS-based AAMs.