Setting Time and Carbonation Resistance of Alkali-Activated GGBS-Fly Ash Mortar

Abstract

In this study, the setting time and carbonation resistance under normal laboratory conditions are evaluated for alkali-activated GGBS-fly ash blends. Three binder combinations including GGBS as sole binder, GGBS:fly ash ratio of 3:1, and GGBS:fly ash ratio of 3:1, were activated using sodium hydroxide and sodium silicates solutions with various solution alkalinities. Initial setting time (IST) of 100%GGBS mortar samples increased as the molarity of sodium hydroxide is increased from 10M to 16M, with the longest initial time being only 20.3 minutes. Mortars that use 75%GGBS + 25% fly ash exhibited a maximum IST of 31 minutes, very similar to typical ordinary Portland cement (OPC), as the 25% fly ash helped extend the IST. The longest IST for mortars using 50%GGBS + 50% fly ash was 45 minutes, offering ample time for placement of concrete. Under normal laboratory conditions, none of the samples exhibited in signs of carbonation after 90 days of curing.

Keywords: Alkali activated mortar; Carbonation; Fly ash; GGBS; Setting time