Repair and strengthening of sulfate damaged self-consolidating concrete with high performance fiber reinforced concretes

This study investigates the bond performance of engineered cementitious composites (ECC), ultra-high-performance concrete (UHPC), and self-consolidating concrete (SO) overlays for repairing and strengthening sulfate-damaged normal-strength concrete substrates. Specimens with as-cast and grooved surface conditions were subjected to two exposure regimes: strengthening with overlays prior to 180-day wet-dry sulfate exposure in a 10 % sodium sulfate solution; and repair after substrate damage. Bond strength was evaluated through slant shear and splitting tensile tests, with degradation mechanisms analyzed through scanning electron microscopy. Results demonstrated that fiber-reinforced overlays (ECC/UHPC) significantly outperformed SO in both shear and tensile bond strength, particularly on grooved substrates, with the composite performance depending primarily on overlay mechanical properties and substrate surface preparation. Notably, this study presents a novel quantitative assessment of interfacial phase assemblages, enabling the identification and distribution of hydrates and degradation products at the substrate–overlay interface. This advancement provides a new basis for evaluating long-term durability of repair materials in chemically aggressive environments. Furthermore, mathematical models were developed to predict the mechanical behavior of each composite and testing method based on the experimental outcomes.