Effects of activator dosage and silica fume on the properties of Na2SO4-activated high-volume fly ash

Abstract

The Na2SO4-activated high-volume fly ash (Ns-activated HVFA) is a promising alternative to ordinary portland cement (OPC) due to its ecological and technical benefits. In this work, the effects of alkali dosage and silica fume incorporation on the flowability, setting time, compressive strength, porosity, composition and phase assemblage, and sulfate and acid resistance of Ns-activated HVFA are studied. The results show that an intermediate alkali dose at 2.5% by binder mass largely accelerates and enhances the strength development of HVFA. The synergic effect of Ns and silica fume further improves the strength of HVFA by about 20%. Exposure to the sodium sulfate solution can potentially promote the later activation of HVFA; while being exposed to the sulfuric acid solution, HVFA exhibits better resistance and less strength loss than the OPC-counterparts. The incorporation of silica fume negatively affects the acid resistance of Ns-activated HVFA.