Alkali-activated natural pozzolan/slag mortars: A parametric study

This study was devoted to assess the influence of binder' aluminosilicate precursor combination (natural pozzolan/slag combinations), activator combination (sodium silicate/sodium hydroxide combinations), sodium hydroxide concentration, and alkaline activator solution-to-binder ratio (S/B) on properties of alkali-activated natural pozzolan/slag mortars. The evaluated properties included flow, setting time, hydration heat, compressive strength, absorption, rapid chloride permeability, and drying shrinkage. The performance of alkali-activated natural pozzolan/slag mortars were also compared with the performance of Portland cement mortars. The results of this study revealed that in comparison with the Portland cement mortars, alkali-activated natural pozzolan/slag mortars generated significantly lower heat, thus offering a great benefit to mass concreting. Their hydration activity accelerated and setting time shortened with increases in sodium hydroxide concentration and dosage within the studied ranges, increases in slag portion of binder, and decreases in S/B. The compressive strengths of alkali-activated mortars were lower than those of the Portland cement mortars. It was shown, however, doable to produce alkali-activated natural pozzolan/slag mortars reaching the strength of portland cement mortars. The compressive strength improved with increases in sodium silicate dosage and reduction in S/B. Regarding compressive strength, the optimum binder combination and sodium hydroxide concentration were found to be interdependent of one another. While absorption of alkali-activated mortars was slightly higher than that of the portland cement mortars, their chloride penetration depths were significantly lower than those of the portland cement mortars. The chloride penetration depth reduced with decreases in natural pozzolan portion of binder, sodium silicate dosage, NaOH concentration, and solution-to-binder ratio. A similar trend was seen for the drying shrinkage as reduction of these variables also decreased the drying shrinkage. The drying shrinkage of the studied alkali-activated natural pozzolan/slag mortars was considerably higher than those of the portland cement mortars.