Development of a sustainable engineered geopolymer composite with mitigated autogenous shrinkage, enhanced mechanical performance, and improved thermal behaviour by recycled concrete powder

The application of recycled concrete powder (RCP) into engineered geopolymer composites (EGC) could be a sustainable alternative to decreasing the carbon footprint and improving the mechanical properties of EGC. This paper evaluated the mechanical properties, autogenous shrinkage, thermal resistance, and microstructures of RCP-EGC. The results indicated that the replacement of natural sand (NS) with RCP decreased the autogenous shrinkage of RCP-EGC by up to 19.1 %. With partial replacement of NS with RCP (75 %), the compressive strength was increased from 66.6 to 77.7 MPa and slightly decreased to 76.8 MPa with complete replacement. The 100 % replacement of NS with RCP increased the tensile strength and strain capacity from 4.93 to 6.25 MPa, and 9.26 % to 11.14 %, respectively. The improvement in the mechanical behaviour was attributed to the enhanced gel formation, as can be verified by the microstructural results. After thermal exposure to 60 and 120 °C, RCP-EGC with 100 % RCP exhibited enhanced compressive strength (87.4 MPa), tensile strength (7.18 MPa), and strain capacity of (10.44 %), higher than those without RCP (73.3 MPa, 5.45 MPa, and 8.15 %). For the samples exposed to 180 °C, the strain-hardening behaviour could not be determined. The RCP-EGC exhibited higher compressive strength after the higher thermal exposure of 180, 300 and 400 °C. The results from carbon footprint calculation and cost-effectiveness analysis suggested replacing NS with RCP can be an environmentally friendly and economically affordable alternative to improving the behaviour of EGC at ambient and elevated temperatures.