Efficient use of steel slag in alkali-activated fly ash-steel slag-ground granulated blast furnace slag ternary blends

In order to find an effective way to use steel slag (SS), this study explored the possibility of using SS and ground granulated blast-furnace slag (GGBS) as a composite additive in alkali-activated high calcium fly ash (FA) binder. Through a series of experiments, the setting times, flow, viscosity, compressive and flexural strengths, modulus of elasticity, sorptivity and pH of pore solution of alkali-activated paste (AAP) containing different contents of SS-GGBS were investigated. Moreover, the optimization mechanism of SS-GGBS on the gel products, micro-morphology and pore structure of AAP was discussed based on multi-technical microstructural characterizations. The results showed that the setting time of AAP increased slightly with increasing SS-GGBS content due to the presence of SS. The initial flow of AAP can be improved by adding the appropriate amount of SS-GGBS. The increase in compressive strength of AAP caused by the inclusion of SS-GGBS not only was observed in the early stage but also in the later stage. In addition, the brittleness of AAP can be reduced by the addition of SS-GGBS. The optimum content of SS-GGBS with regard to the flexural strength was found to be 40%. The incorporation of SS-GGBS promoted the formation of amorphous gel products of AAP. The resulting gel products filled the capillary pores and converted them into gel pores with a smaller pore size, which refined the pore structure and resulted in a lower total porosity. The denser microstructure is one of the main reasons for the improvement of strength. This study provides a promising approach to improve the utilization potential of SS. (C) 2020 Elsevier Ltd. All rights reserved.