Ground granulated blast-furnace slag/fly ash blends activated by sodium carbonate at ambient temperature

Abstract

Alkali-activated materials (AAMs) with low carbon emission acted as a potential alternative for Portland cement. To further reduce the CO2 emission, FA and weak base were proposed. However, the strength development of slag/FA blends activated by sodium carbonate (NC) seemed unacceptable for actual engineering application. In this study, the strength of slag-FA blends activated by NC at ambient temperature was systematically studied, and the various fineness slag and activators dosage were used; hydration flow and chemical shrinkage was used to analyze the hydration process; the hydrates were characterized by XRD, TGA, SEM and 29Si NMR; the pore structure was characterized by MIP; the pH value and sodium ions were tested. Results showed that lower slag fineness and higher dosage of NC significantly shortened the induction period of slag hydration and promoted the formation of C-(N)-S-A-H and calcite. Moreover, due to the higher hydration degree of slag, FA was continuously activated over time. It seemed that NC-activated slag/FA activated blends showed an excellent mechanical property, and the compressive strength was up to 55.5 MPa and 63.8 MPa at 28 d and 90 d. The research suggested the experience for the design of weak base-activated slag/FA.