Natural Pozzolan-based geopolymers for sustainable construction

Abstract

The study presented herein evaluates effects of alkaline activator (sodium hydroxide) concentration, solution (sodium hydroxide solution)-to-binder ratio (S/B), and curing condition on properties of alkali-activated natural Pozzolan mortars (geopolymers). To this end, several mixtures were made having natural Pozzolan as their binder with different concentrations of alkaline activator solution including 2.5, 5, 7.5, 10, and 12.5 molar (M) at various S/B of 0.50, 0.54, and 0.58. The produced mortars were cured at 80 °C under three different conditions of exposed (dry), sealed (wrapped), and moist until testing at ages of 1, 3, and 7 days. Multiple tests were conducted on the alkali-activated natural Pozzolan mortars including flow spread, compressive strength, flexural strength, PH measurement, absorption, and rapid chloride migration. Test results showed the sealed curing condition to be most conducive to strength gain, whereas the exposed curing condition caused dehydration and/or carbonation within the samples and the moist curing condition did not allow for full removal of excess water resulting in reduced bond formations. The moist oven-cured mortars produced higher strength than the exposed cured mortars when alkaline activator with lower molarities was used. The opposite trend was observed for the higher molarities mortars. The compressive and flexural strengths, absorption, and depth of penetrated chloride improved when NaOH concentration increased and S/B decreased.