Fracture behavior of nano‐silica‐modified recycled aggregate concrete: Experimental evaluation and predictive modeling using work of fracture and size effect methods

Abstract This study investigates the fracture behavior of recycled aggregate concrete (RAC) modified with nano‐silica (NS), aiming to enhance the performance of sustainable concrete made with recycled materials. While recycled aggregates reduce environmental impacts, they compromise concrete's mechanical properties and fracture resistance due to weak interfacial transition zones (ITZ) and increased porosity. This research explores the influence of NS (0%–6% by binder weight) on the fracture parameters of RAC through three‐point bending tests on 90 notched beams. Fracture energy and toughness were evaluated using both the work of fracture method (WFM) and the size effect method (SEM). The addition of 4.5% NS yielded the highest improvements in fracture energy (21% by WFM, 34% by SEM) and fracture toughness (25%), while decreasing characteristic length and process zone length by 14% and 24%, respectively. Scanning electron microscopy images confirm that NS densifies the ITZ and enhances bonding. Despite increased brittleness, the RAC behavsior increasingly aligns with linear elastic fracture mechanics at higher NS contents and beam depths. Predictive models for fracture parameters were developed and validated against existing datasets, showing high accuracy. These findings support the structural application of NS‐modified RAC in sustainable infrastructure.