Structural performance of corroded RC beams with recycled aggregate a parametric FEM study and UHPC strengthening approach

Abstract As sustainable construction and infrastructure durability become critical priorities, understanding the coupled influence of reinforcement corrosion and recycled concrete aggregate (RCA) is essential. This study develops three-dimensional finite element models in ABAQUS to simulate the flexural response of reinforced concrete (RC) beams with RCA replacement ratios ranging from 0 to 100% and reinforcement corrosion mass-loss levels of 0–20%. Corrosion effects were represented through corrosion-dependent degradation of steel mechanical properties and bond behavior, together with strength reduction in the corrosion-cracked concrete cover. The numerical framework was validated against published experimental beam tests, showing good agreement in load–deflection response and damage distribution within the tension zone corresponding to the observed cracking regions, with ultimate-load differences generally within 7%. A parametric investigation was conducted to quantify the reduction in ultimate capacity under combined deterioration mechanisms. For natural-aggregate beams, peak-load reduction increased from approximately 8–12% at 5–7% corrosion to about 18–22% at 10% corrosion, reaching nearly 30–35% at 20% corrosion. Increasing RCA content reduced the baseline capacity and amplified corrosion sensitivity, with higher replacement ratios showing larger peak-load losses at moderate-to-severe corrosion levels. Ultra-high performance concrete (UHPC) bottom-layer strengthening was also evaluated as a mitigation strategy. In this approach, UHPC was used only as a thin localized layer at the tension zone, resulting in a limited material volume while extending the service life of RCA-based RC beams. A 20 mm UHPC layer typically restored the ultimate load to within ± 5% of the corresponding un-corroded control beam (for corrosion levels up to about 10%), while 40 mm and 60 mm layers increased the ultimate load to approximately 8–18% and 15–25% above the corresponding control response, respectively. Finally, a modified cracking moment equation based on the American Concrete Institute (ACI) formulation was proposed to account for the combined influence of reinforcement corrosion and recycled aggregate content for the investigated beam configuration.