Dynamic mechanical behaviour and life cycle assessment of rubberised solid waste-based geopolymer concrete

Abstract

Waste rubbers, which account for a large amount of solid waste worldwide, are needed for green reutilisation to protect the environment. Owing to their good ability to dissipate energy, pretreated waste rubbers are suitable for use as aggregates in geopolymer concrete to reduce solid waste and improve the dynamic mechanical properties of concrete. Therefore, the suitable replacement ratio of RS by CR should be considered based on the balance of dynamic strength and static properties. For this purpose, ground granulated blast furnace slag (GGBS) and fly ash (FA) were used to prepare geopolymer paste, and crumb rubber (CR) from waste rubber was used as a partial fine aggregate in this study. The impact resistance of rubberised geopolymer concrete was tested via a 100-mm split Hopkinson pressure bar apparatus. Life cycle assessment (LCA) analysis was carried out to evaluate the environmental impacts of the concrete. The study revealed that replacing ordinary Portland cement (OPC) with FA/GGBS had a minimal effect on the mechanical properties of rubberised geopolymer concrete (RGC), despite the different chemical compositions of the cement paste and geopolymer. Moreover, the dynamic compressive strength (∼90 s^-1) increased with increasing CR replacement ratio by 18.43% from 0 to 10%. When the CR replacement rate was further increased to 20%, the dynamic compressive strength gradually decreased by 1.96% because of a deteriorated pore structure. Although the X-ray diffraction results revealed no significant difference in mineral composition, the better absorption ability of CR and lower porosity of RGC, as characterised by the mercury intrusion porosimetry test, favoured its dynamic compressive strength at a suitable CR content. Considering the effect of the CR and its substitution rate ratio, a recalibrated model is proposed for predicting the dynamic increase factor of the RGC under impact loads. The LCA revealed that geopolymers have lower environmental impacts associated with the construction industry than OPC does. However, measures must be taken to further reduce the environmental burden of RGC. Based on the dynamic mechanical properties, environmental impact, and production cost, the geopolymer concrete containing 10% CR exhibited the best performance among all the RGCs.