Suitability of metakaolin-based geopolymers for masonry plastering

Abstract

The development and use of geopolymers (GP) considerably increased in the construction industry. This paper assesses the suitability of metakaolin-based GP mortars for masonry plastering works, including their comparison to masonry cement (MC) mortars and compliance to relevant EN 413-1 and ASTM C91 specifications. Three classes of GP mortars prepared with different metakaolin-to-limestone ratios are tested; the sodium hydroxide and sodium silicate activators contained air-entraining molecules to secure approximately 10% ±2% air content. Test results showed that GP mortars exhibited excellent water retention and increased rheological properties, which was related to higher viscosity of alkaline solution that increases stickiness and overall cohesiveness. For given limestone concentration, the mechanical properties of GP mortars including the pulloff bond strength and sorptivity were remarkably better than MC mixtures. Almost 90% of ultimate compressive strength was achieved after 7 days for GP mortars cured at ambient temperature, while this varied from 55 to 80% for MC mixtures cured in moist conditions. This can be particularly advantageous in masonry applications to speed up construction operations while, at the same time, eliminate the hassle of moist curing normally required with cement-based plasters.