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

Lightweight geopolymers (LWGPs) were prepared using fly ash (FA) and pumice aggregate (PA), and their sustainability was enhanced by the addition of recycled waste tire aggregate (WTA). The results show that substituting PA with WTA reduced the density of the LWGP and improved its fluidity. However, this substitution was detrimental to the development of the strengths and durability of LWGP, but was beneficial for improving the thermal insulation performance. The further use of metakaolin (MK) to replace FA enhanced the performance of the WTA-based geopolymer, especially its mechanical properties and durability. When 10% FA was replaced by MK, the compressive strength of the LWGP increased by 5.5–40.4%, and the residual strength after sulfate attack, freeze–thaw cycles, and high-temperature treatment was significantly improved. Using a small amount of MK effectively mitigated the negative impact of WTA on the performance of the LWGP. Utilizing WTA effectively reduces the total cost and carbon dioxide emissions (CDE) of LWGP production. Compared with plain LWGP, the mixtures with 15–45% WTA exhibited a reduction in cost and CDE by 4.5–13.4% and 1.3–4.0%, respectively. Although the inclusion of MK increased both the cost and CDE, its incorporation significantly enhanced the overall performance of the LWGP.