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

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.