Multi-factor patterns and predictive modeling of corrosion-induced cracking in recycled aggregate concrete with endogenous chlorides

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The corrosion mechanisms of recycled aggregate concrete (RAC) containing endogenous chloride ions differ from those of ordinary concrete when used in engineering structures. Existing durability assessments still primarily rely on external chloride ion attack models, neglecting the influence of endogenous chloride ions. This study systematically investigates the influence of endogenous chloride ions on corrosion-induced cracking behavior in reinforced RAC, focusing on water-to-binder ratio, recycled coarse aggregate (RCA) quality and replacement rate, fly ash content, and cover thickness. The research employed accelerated electrochemical corrosion tests combined with guided ultrasonic wave monitoring technology to track the damage progression. The results indicate that a higher water-to-binder ratio enhances pore connectivity and promotes the release of endogenous chloride ions, thereby accelerating cracking. The deterioration of RCA quality exacerbates chloride ion migration and weakens interfacial performance. Increasing the RCA content simultaneously raises the initial chloride ion concentration and the number of interfacial transition zones, significantly shortening the time to cracking. Fly ash exhibits a dose-dependent threshold: when the admixture content is ≤ 20%, it densifies the matrix and delays cracking, whereas excessive admixture accelerates cracking due to reduced strength and the potential re-release of bound chloride ions. A larger cover thickness extends the diffusion path and improves confinement, effectively delaying cracking. Based on experimental results, a prediction model for corrosion‑induced cracking time was established, yielding errors within −6.55–6.51% and a coefficient of variation of 3.51%, which may provide a basis for evaluating the durability of reinforced recycled aggregate concrete members.