Recursive reuse of recycled concrete powder with second-cycle performance retention through graphene oxide modification

Nanomodification technology opens a prospective pathway to transform construction solid waste into higher-value cementitious resources. However, whether recycled cementitious materials can be repeatedly reintroduced into new composites, rather than reused only once, remains insufficiently understood. This study investigates the role of graphene oxide (GO) modification in enabling the recursive reuse of secondary recycled concrete powder (SRCP) in cementitious composites. The results indicate that GO significantly influences the high-value recycling of SRCP, but the effect strongly depends on the substitution pathway. When used as cement substitutes, GO-bearing SRCP shows a less favorable strength response, particularly at higher replacement levels. In contrast, when SRCP serves as aggregate substitutes, GO not only enhances the filling effect of the recycled powder but also optimizes the microstructure of the cement matrix through nucleation and crack bridging. Consequently, at a 40% substitution rate, the compressive strength of the GO/SRCP composite increases by 27.3%. Molecular dynamics simulations suggest that GO facilitates interfacial load transfer and crack bridging in the modeled C-S-H/GO/SRCP system, where external tensile work increases by 27.7% relative to the GO-free model. More importantly, life cycle assessment shows that GO-modified SRCP substitution achieves synergistic optimization of cost and environmental impact, reducing strength-normalized cost, GHG emissions, and primary energy demand by 34.65%, 21.91%, and 20.68%, respectively. These findings not only promote the transition of construction waste from reuse to circular recycling but also support the transformation of the cement industry toward a low-carbon model based on closed-loop recycling.