Effect of recycled fine aggregates on performance of geopolymer masonry mortars

Abstract

Masonry mortar are normally produced using masonry cement complying to EN 413-1 and/or ASTM C91 specifications. The main objective of this paper is to assess the suitability of metakaolin-based geopolymers (GPs) containing recycled fine aggregate (RFA) for masonry applications, including their compliance to relevant standards. Three GP classes proportioned with different metakaolin-to-limestone ratios are tested; the sodium hydroxide and sodium silicate activators contained air entraining molecules to secure about 10% ±2% air content. Test results showed that GP mortars prepared with or without RFA additions exhibited excellent water retentivity, which was related to the viscosity of alkaline solution that increases overall cohesiveness. The bond strengths to existing substrates slightly improved at 20% RFA replacement rates, but then dropped at 40% and 60% rates due to higher liquid demand as well as reduced RFA-modified mortar density. The sorptivity of GP mortars was about 1.5- to 2-times lower than equivalent masonry cement (MC) mixtures, reflecting reduced water permeation that enhances the durability of plaster. The use of GP mortars was found particularly advantageous for masonry applications to speed-up construction operations while, at the same time, eliminate the hassle of moist curing normally required with cement-based plasters.