Effect of fly ash on compressive strength and chloride binding of seawater-mixed mortars

Abstract

This paper presents the effect of seawater as mixing water of fly ash mortars on compressive strength and chloride binding ability of fly ash matrix. Results show increase in compressive strength at all ages with increase in fly ash contents in seawater mixed fly ash mortars, which is not usually observed in fresh water mixed fly ash mortars. However, the seawater mixed mortar containing 20% fly ash exhibited lower compressive strength at early age (4 days) than its counterpart fresh water mixed mortar. At higher fly ash contents of 30% and 40% an opposite phenomenon is observed. Free chlorides and pH values of seawater mixed fly ash mortars also decreased and increased, respectively with increase in fly ash contents. Existence of Friedel’s salt peak and reduction in intensity of calcium hydroxide peaks in the seawater mixed fly ash mortars show the evidence of binding of chlorides with hydration products of fly ash-cement matrix in X-ray diffraction (XRD) analysis.