Mechanical Properties of Mortar with Alkali-Activated Fly Ash and GGBS Binders

The purpose of this study is to evaluate the compressive strength and splitting tensile strength of mortar samples that use alkali-activate ground granulated blast furnace slag (GGBS) or GGBS+ fly ash as binder. The binder was activated using alkaline solution consisting of combination of Na2SiO3 and NaOH. One set of mortar samples was cured by exposure to normal air at a temperature of 22±2 0C and 70% RH, and another set was cured under 10% sulfuric acid solution, in order to quantity its effect on compressive strength development. Water-cured mortar samples exhibited higher compressive strength at the age of 28-days in contrast with air-cured samples. The highest compressive strength at the age of 28-day was developed by mortar samples with binders consisting of GGBS: fly ash ratio of 3:1, compared to binders with equal amounts of fly ash and GGBS, as well GGBS as sole binder. This was consistent for NaOH concentration of 10M, 12M, and 14M. A 2nd degree polynomial was found to strongly correlate splitting tensile strength to 28-day compressive strength of air-cured mortar samples. The correlation weakens with the addition of 25% fly ash, and diminishes when fly ash is 50% of the binder content.