Effects of Compositional and Physico – Chemical Mix Design Parameters on Properties of Fly Ash Geopolymer Mortars

Abstract

The present experimental study investigated the effects of mix design parameters on workability and compressive strength of fly ash geopolymer (FA – GPC) mortars. Observed effects of the compositional parameters comprising SiO2/FA, Na2O/FA and H2O/FA mass ratios, were inter – linked with those of the physico – chemical mix parameters namely:– the concentration of sodium hydroxide solution, ratio of sodium silicate to sodium hydroxide, and the alkali activator to raw material ratio. In the preparation of mortars, low calcium (Class F) FA was activated using a combined solution of sodium hydroxide and sodium silicate, and mixed with fine aggregate at the aggregate to FA ratio of 2.25. Altogether, seventy – two (72) mortar mixtures were prepared by varying the values of compositional parameters. It was found that the SiO2/FA ratio of 0.08 to 0.11, Na2O/FA ratio of 0.05 to 0.08, and H2O/FA ratio of 0.32 to 0.37, are the optimum ranges that gave the best workability values and compressive strength results, depending on the H2O/FA ratio. In mix design, the various values of compositional parameters are obtained by appropriately combining the aforementioned physico – chemical parameters.