Durability degradation and life prediction of economical ECC-concrete interfaces for tunnel repair under sulfate attack

ABSTRACT The failure at the interface between repair materials and existing concrete is a predominant cause for the durability degradation of tunnel linings in sulfate-rich environments. This study proposes a cost-effective reinforcement strategy using an Engineered Cementitious Composite (ECC), incorporating polypropylene-basalt hybrid fibers and artificial sand. Composite specimens of ECC-strengthened ordinary concrete were exposed to 150 cycles of accelerated sulfate attack. The effects of interface roughness (Ra=0.5, 1.9, and 4.0 mm) and the use of an epoxy resin coupling agent on the interfacial deterioration were investigated. An integrated approach, combining apparent morphology, mass variation, ultrasonic pulse velocity, and splitting tensile tests, was employed to elucidate the progressive interfacial failure mechanism. An durability evaluation system was established using the CRITIC method, and a Gray-Markov model was developed for life prediction. Results demonstrate that interfaces with low roughness are highly susceptible to debonding and failure, while high-roughness interfaces combined with the epoxy agent significantly enhance resistance to sulfate attack, maintaining a durability coefficient above 0.98. The Gray-Markov model, accounting for data fluctuation, showed superior predictive accuracy over the traditional GM(1,1) model. This work provides a practical solution and a reliable life-prediction tool for preventing interfacial failure in tunnel repair and reinforcement projects.