Effects of recycled concrete powder on shrinkage, mechanical, and thermal behaviours of multi-walled carbon nanotubes-reinforced engineered geopolymer composites

Although multi-walled carbon nanotubes (MWCNTs) can enhance the performance of engineered geopolymer composite (EGC), the related high costs and carbon emissions remain significant challenges. This study explored the feasibility of incorporating construction waste-derived recycled concrete powders (RCPs) as fine aggregates in EGC reinforced by polyethylene (PE) fibres or hybrid MWCNTs and PE fibres. The investigated properties included drying and autogenous shrinkage, compressive and tensile performance, and thermal resistance up to 600 °C, together with cost-benefit and carbon footprint analyses. The results demonstrate that replacing natural aggregates with 75 % RCPs in MWCNT-EGC contributes to improved shrinkage, mechanical, thermal, economic, and environmental performance, while only 25 % RCPs in EGC is favourable for the compressive strength. After thermal exposure to 140 °C, MWCNT-EGC with 75 % RCPs exhibits improved tensile strength (9.49 MPa) and comparable strain capacity (9.98 %) to those at ambient temperature. After thermal exposure to 600 °C, the residual compressive strength of MWCNT-EGC with 75 % RCPs maintains 80.4 MPa, 58.2 % higher than the control group. The cost-benefit analysis and carbon footprint assessment indicate that introducing 75 % RCPs reduces costs and associated carbon emissions to achieve a unit strength than the conventional EGC with varying proportions of RCPs but without MWCNTs. These findings suggest that incorporating 75 % RCPs as fine aggregates is a financially viable and environmentally sustainable solution for MWCNT-EGC production. • Incorporating RCPs in MWCNT-EGC is favourable for shrinkage mitigation. • Replacing 75 % QS with RCPs increases the compressive strength by 20.3 % (120.8 MPa). • Tensile strength and strain capacity are increased by 11.7 % and 8.4 % with 75 % RCPs. • Incorporation of RCPs in MWCNT-EGC is beneficial for the thermal resistance. • Introduction of RCPs in MWCNT-EGC increases sustainability and cost-effectiveness.