Synergistic nanomodification of untreated recycled brick aggregate concrete with nanosilica and graphene oxide in OPC–LC3 binders: multi-performance optimization and life cycle assessment

This study investigates the synergistic effects of nanosilica (NS) and graphene oxide (GO) in enhancing the performance of untreated recycled brick aggregate (RBA) concrete, using both 100% ordinary Portland cement (OPC) and a 50:50 OPC–LC 3 (limestone-calcined clay) binder system. The experimental work focuses on multi-performance optimization across mechanical, durability, and environmental parameters. Statistical analysis confirmed significant improvements in compressive strength and durability when NS and GO were used in combination, achieving a 23.8% increase in 180-day compressive strength (44.8 MPa) and a 64% reduction in chloride migration. The optimization process, utilizing Response Surface Methodology (RSM), identified the optimal combination of 3% NS and 0.05% GO for OPC and 2.5% NS with 0.04% GO for LC 3 , balancing mechanical performance and environmental sustainability. Life cycle assessment (LCA) showed that LC 3 -based mixes reduced Global Warming Potential (GWP) by 19%, while maintaining comparable mechanical and durability performance to OPC systems. This study demonstrates the potential of nanomodification combined with low-carbon binders to produce sustainable, high-performance concrete, offering a data-driven framework for optimizing RBA-based concrete for infrastructure applications.