Use of Seashell and Limestone Fillers in Metakaolin-Based Geopolymers for Masonry Mortars

Abstract

Mortars intended for plastering and masonry works normally comply to EN 413-1 and/or ASTM C91 specifications. This paper seeks to assess the suitability of geopolymers (GPs) composed of metakaolin and seashell wastes for masonry applications. The sodium hydroxide and sodium silicate activators contained air-entraining molecules to secure about 10% ± 2% air content. Just like the cement-based mortars, test results showed that the mechanical properties of GPs including the compressive strength, flexural strength, pull-off adhesion, and water sorptivity decreased when the seashell concentration increased in the mixture. This was mainly related to a dilution effect that reduces the aluminosilicate precursor content and formation of rigid bonds. The replacement of limestone filler by seashell powder slightly increased the mechanical properties, which was attributed to higher seashell hardness that densifies the microstructure and provides additional resistance to support the external stresses. Yet, the grinding of seashells into fine powder required higher energy than what is needed for the comminution of clinker or limestone. The use of GPs is particularly advantageous for masonry applications, as it speeds up the construction operations while eliminating the hassle of moist curing normally required with cement-based plasters.