Impacts of anisotropy and exposure conditions on ASR-induced deterioration in columns from the Robert-Bourassa/Charest overpass after nearly 50 years of service

The anisotropic behaviour of 50-year-old reinforced concrete bridge columns affected by alkali–silica reaction (ASR) was investigated, focusing on the Y-shaped columns of the Robert-Bourassa/Charest overpass in Québec, Canada under different exposure conditions. A multi-level assessment approach, incorporating microscopic and mechanical evaluations, was employed to evaluate ASR-induced damage, with an emphasis on anisotropic expansion, stress redistribution, mechanical property degradation and cracking orientations. Diagnostic tools such as the stiffness damage test and damage rating index provided insights into internal microcracking and reduction of the modulus of elasticity, accounting for the influence of environmental exposure conditions. Measurements of strain and residual tensile strength from reinforcement stirrups further revealed the structural implications of ASR anisotropic progression, including reinforcement embrittlement and loss of confinement. The findings highlight the critical role of exposure conditions, reinforcement configuration, and geometric constraints in shaping the deterioration patterns of ASR-affected concrete.