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 Na
2
SiO
3
and NaOH. One set of mortar samples was cured by exposure to normal air at a temperature of 22±2
⁰
C 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 2
^nd
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.