Effects of metakaolin and waste tire aggregate on the properties of pumice-based lightweight geopolymer

The lightweight geopolymers (LWGPs) were prepared using fly ash (FA) and pumice aggregates, and their sustainability was enhanced by recycling waste tire aggregates (WTAs). The results show that substituting pumice aggregate with WTA reduces the density of LWGP and improves its fluidity. However, this substitution is detrimental to the development of the strengths and durability of LWGP, but it is beneficial to the improvement of thermal insulation performance. The further use of metakaolin to replace FA enhances the performance of WTA-based geopolymer, especially improving its mechanical properties and durability. When 10% of FA is replaced by metakaolin, the compressive strength of LWGP increases by 5.5%-40.4%, and the residual strength after sulfate attack, freeze-thaw cycle and high temperature treatment is significantly improved. Using a small amount of metakaolin effectively mitigates the negative impact of WTA on the performance of LWGP. Utilizing WTA effectively reduces the total cost and carbon emission of LWGP production. Compared to plain LWGP, the mixtures with 15%-45% WTA exhibit a relative reduction in cost and carbon emission by 4.5%-13.4% and 1.3%-4.0%, respectively. Although the inclusion of metakaolin escalates both the cost and carbon emissions, its incorporation significantly enhances the overall performance of LWGP.