Influence of sand on the mechanical properties of metakaolin geopolymers: Fid-Bau Portal

Influence of sand on the mechanical properties of metakaolin geopolymers

Kuenzel, C. / Li, L. / Vandeperre, L. / Boccaccini, A.R. / Cheeseman, C.R.

Highlights • Metakaolin geopolymers need high water content to have appropriate rheology for some applications. • Extensive drying shrinkage and cracking occurs in high water content metakaolin geopolymers. • Geopolymer mortar samples with more than 10vol% sand do not crack on heating to 110°C. • Sand particles limit linear shrinkage by forming a network. • At higher additions micro-cracks form around non-shrinking sand particles.

Abstract Metakaolin geopolymers require a high water content to have appropriate rheology for use in some applications and these mixes exhibit extensive drying shrinkage and cracking. This work aimed to understand the effect of adding sand as inert filler to metakaolin geopolymers. It is found that the viscosity increases with sand addition and mortars become unworkable when more than 40vol% sand is added. Linear drying shrinkage was reduced from about 8% in the absence of sand to less than 1% with 38vol% sand addition. Moreover, geopolymer mortars containing more than 15vol% sand can withstand drying at 110°C without cracking. Because sand addition to metakaolin geopolymer mortars increases viscosity less than a reduction in water content it is possible to formulate mortars that flow but do not crack on drying and these materials have potential for use in a range of architectural and restoration applications.