Influence of Recycled Glass on Strength Development of Alkali-Activated High-Calcium Fly Ash Mortar

Abstract

This article presents the development of green and sustainable mortars using alkali-activated high-calcium fly ash (AAFA) and recycled glass (RG) as part of the fine aggregate. RG was used to replace river sand at dosages of 0%, 25%, 50%, 75%, and 100% by weight. Sodium hydroxide (SH) and sodium silicate (SS) solutions were used as liquid alkaline activators in all mixtures. The AAFA samples were prepared with different liquid-to-binder ratios of 0.6 and 0.7, and the ratio of SS-to-SH was fixed at 2.0. Compressive and flexural strengths were determined at the ages of 7, 28, and 60 days. Test results showed that the compressive and flexural strengths of AAFA mortars declined as RG replacement increased; nevertheless, they increased with curing time. The high Na2O concentration derived from RG and the weak interfacial transition zone of RG are reasons for the decrease in strength development. The optimum percentage replacement of fine aggregates with RG was found at 25%. The 28-day compressive strength of AAFA with 25% RG was 32.5 MPa for L/B ratios of 0.6 and 29.5 MPa for L/B ratios of 0.7, which resulted in a strength index higher than 75% while releasing low CO2.