Exploring microscopic and mechanical tools to uncover the anisotropic damage evolution of prestressed concrete sleepers affected by internal swelling reactions

This work examined the anisotropic behaviour of internal swelling reactions (ISRs), specifically alkali–silica reaction (ASR) and delayed ettringite formation, in prestressed concrete sleepers retrieved from a northern Brazilian railroad. The research highlights the role of restraint, driven by prestress forces and the sleeper’s geometry, in ISR-induced damage progression. Visual inspection, damage rating index analysis, stiffness damage tests and scanning electron microscopy with energy dispersive spectroscopy were used to evaluate cracking patterns, damage extent, mechanical properties loss and the chemical composition of ISR products. The results indicate that restraint influences crack propagation, the interplay of mechanisms and damage anisotropy, with the shoulders of the sleepers exhibiting greater deterioration than the restrained centres. Chemical analyses revealed variations in ASR gel and ettringite composition, which were related to swelling potential and damage severity. These findings emphasise the influence of anisotropy in ISR-affected members and underscore its importance in guiding maintenance strategies for ISR-affected sleepers.