Structural Performance and Damage Evaluation of Corroded Infill Slabs from the Champlain Bridge After 60 years in Service

Abstract

The rapid deterioration of aging civil infrastructure represents a critical challenge for global transportation networks. While extensive research has focused on the performance of reinforced and prestressed concrete (PC) members subjected to laboratory-accelerated corrosion, there remains a fundamental disconnect between these controlled simulations and the complex, long-term degradation observed in field-aged structures. This doctoral research bridges this gap through a comprehensive multi-scale forensic and structural evaluation of roadway infill slabs extracted from the former Champlain Bridge in Montreal, Canada, after 57 years of aggressive environmental exposure. The research program integrates high-resolution non-destructive testing (NDT), forensic material characterization of 975 individual prestressing wires, and destructive testing of 15 full-scale slab panels under realistic boundary conditions. Material-scale analysis identifies a robust ductility transition threshold at approximately 3% mass loss, beyond which the ultimate strain capacity of parallel-wire tendons significantly deteriorates, independent of gauge length or prior loading history. At the structural scale, the research reveals a fundamental divergence in performance that is independent of average material degradation. Experimental results demonstrate a significant "capacity spread" at low corrosion levels. Specifically, specimens with nearly identical average mass-loss values exhibited ultimate load capacities varying by over 140% (160.1 kN to 384.3 kN). This disparity is identified as a consequence of localized interface conditions rather than distributed section loss. The forensic investigation confirms that grout integrity is a governing factor influencing the ultimate limit state. While solid grout coverage ensures ductile flexural behavior, crumbled or powdery grout leads to a more variable structural response. Such deterioration can trigger a premature transition to brittle shear failure. However, it can also facilitate bond-slip mechanisms that redistribute stresses and activate arching action. As demonstrated in the numerical investigation, this shift in the load-carrying mechanism can result in higher ultimate load capacities.

The experimental findings are further validated through nonlinear finite element (FE) modelling, which successfully isolates the "ductility gap" caused by bond-slip mechanisms. The results prove that simplified evaluation metrics relying on average section loss, which is the current industry standard for large-scale bridge inventories, can lead to unconservative safety estimates. This thesis contributes a performance-based framework for the assessment of aging PC infrastructure, advocating for the prioritization of grout integrity and localized bond-penalty factors in national design codes. By integrating the assessment of volumetric steel loss with the governing physics of the tendon-concrete interface, this work provides bridge owners with a data-driven methodology to ensure the continued safety and reliability of aging transportation networks.