Tensile behavior and microstructural evolution of rubber-modified ECC under thermo-mechanical loadings

Engineered Cementitious Composites (ECC), known for their high ductility and crack control capacity, have been rarely studied under in-situ elevated temperature conditions. Most existing studies evaluate ECC after high-temperature exposure, overlooking its real-time mechanical response and microstructural evolution under thermo-mechanical coupling. In this study, rubber particles were used to replace quartz powder at different ratios (0%, 10%, 20%, and 30%) to produce rubber-modified ECC (R-ECC). Quasi-static uniaxial tensile tests were conducted under various elevated temperatures (25 °C, 70 °C, 100 °C, and 150 °C). The effects of temperature and rubber content on mass loss, pore structure, cracking behavior, and tensile stress–strain response were systematically investigated. Results showed that increasing temperature significantly reduced both the initial cracking strength and tensile strength of R-ECC. However, in the sub-high temperature regime (70−100 °C), R-ECC exhibited enhanced ductility, with the highest ultimate tensile strain observed at 100 °C. This enhancement was attributed to moderate fiber softening, weakened matrix strength, and improved fiber pull-out behavior. In contrast, at 150 °C, fiber melting and interfacial degradation sharply reduced tensile performance. Microstructural analysis demonstrated that internal changes including increased porosity, weakened rubber-matrix interface, and damaged PE fibers collectively contributed to the modified tensile behavior under coupled thermal–mechanical conditions. These findings provide new insights into the practical design and application of rubber-modified ECC in structures exposed to sub-high temperature service environments.