Thermal and mechanical properties of sustainable lightweight strain hardening geopolymer composites

The thermal and mechanical properties of sustainable lightweight engineered geopolymer composites (EGCs), exhibiting strain-hardening behavior under uniaxial tension, are reported in this study. Fly ash-based geopolymer was used as complete replacement of cement binder to significantly increase the environmental sustainability of the composite compared to the engineered cementitious composite (ECC). Additionally, three types of lightweight aggregates including expanded perlite, microscopic hollow ceramic spheres and expanded recycled glass were used as complete replacement of micro-silica sand to reduce density and thermal conductivity of the composite. The influences of the type of aggregates on the fresh and hardened properties of the composite including matrix workability, density, compressive strength, thermal conductivity and uniaxial tensile performance were experimentally evaluated. The results indicated that the density and compressive strength of all EGCs developed in this study, even the EGC containing normal weight micro-silica sand, were less than 1833 kg/m³ and more than 43.4 MPa, respectively, meeting the density and compressive strength requirements for structural lightweight concrete. Replacing normal weight micro-silica sand with lightweight aggregates reduced the compressive and tensile strengths of the EGCs by a maximum of 24% and 32%, respectively. However, the tensile ductility of the EGCs containing lightweight aggregates was comparable to that of the EGC containing micro-silica sand. In addition, the thermal conductivity of the EGCs containing lightweight aggregates were significantly (38–49%) lower than that of the EGC containing normal weight micro-silica sand, resulting in an end-product that is greener, lighter, and provides better thermal insulation than ECC.