Redefining the cement substitution potential of recycled concrete powder using graphene oxide coating

Reutilizing recycled concrete powder (RCP) offers substantial benefits in the construction industry. However, increasing RCP's substitution rate in cementitious composites often leads to significant deterioration in properties. In this study, we propose an innovative approach to enable high substitution rates of RCP by uniformly coating its particles with graphene oxide (GO) nanosheets. In this way, the modification effect is concentrated at the interfacial transition zone (ITZ), thereby maximizing the reinforcing benefits of GO. Our results show that GO-coated RCP can be used to replace up to 40 wt% of cement, while still achieving improvements of 4.1 % in compressive strength and 10.2 % in flexural strength compared to pure cement slurry. Microstructural characterization reveals that the coated GO enhances the composite structure through nucleation and pore-infilling effects, leading to a reduction in porosity by 9.4–20.3 %. Molecular dynamics simulations further reveal the crack-bridging mechanism of GO, showing that the failure mode of the RCP-cement composite shifts from the ITZ to the C-S-H matrix. Our approach also has significant economic and environmental potential. At a 40 % RCP substitution rate, greenhouse gas emissions and primary energy demand per unit compressive strength are reduced by approximately 39.7 % and 40.2 %, respectively, compared to plain cement slurry. The findings of this study not only deepen the understanding of GO reinforcement mechanisms but also promote the broader application of RCP in developing cost-effective and environmentally friendly cementitious composites for future construction.