Recycled Aggregate Green Concrete with Graphene Oxide-Coated PVA Fibers: Performance Improvement and Life Cycle Evaluation.

Recycled aggregate concrete provides a sustainable route to reduce natural aggregate consumption and promote the recycling of construction and demolition waste. However, recycled aggregates generally contain residual old mortar, initial microcracks, and weak interfacial transition zones, which disturb the pore structure and increase cracking susceptibility under mechanical loading. Fiber reinforcement can improve crack resistance and toughness, but the reinforcing efficiency of polyvinyl alcohol (PVA) fibers is still limited by interfacial defects around the fiber-matrix transition zone. To address this issue, graphene oxide (GO)-coated PVA fibers were developed and incorporated into fiber-reinforced recycled aggregate concrete. Two coating methods, physical stirring and three-step dip coating, were compared. The coating morphology, elemental distribution, and chemical characteristics of the modified fibers were characterized using SEM-EDS, FTIR, and Raman spectroscopy. The results show that the three-step dip-coating method produced a more uniform and effective GO-based coating on the PVA fiber surface. Compared with the reference specimen, the compressive and flexural strengths of recycled aggregate concrete reinforced with three-step dip-coated GO-PVA fibers increased by 53.5% and 56.3%, respectively. Fractal dimension analysis and deep learning-assisted image analysis further indicate that GO-coated PVA fibers improved microstructural compactness, promoted tortuous crack propagation, and enhanced crack-bridging performance. Molecular dynamics simulations confirmed that GO nanosheets promoted interfacial stress transfer and energy dissipation, which supported the experimentally observed mechanical improvement. Life cycle assessment showed that although the GO coating process increased the production-stage environmental burden, the three-step dip-coating method exhibited better economic and environmental benefits after normalization by unit compressive strength. These findings demonstrate that GO-coated PVA fibers can simultaneously improve the mechanical performance and unit-strength environmental competitiveness of recycled aggregate concrete, providing a feasible strategy for developing high-performance and low-carbon cementitious composites.