Residual axial performance of PET/rubber-modified concrete confined with CFRP strips after thermal exposure: Experimental and theoretical analysis

This study investigates the residual axial behavior of concretes with recycled polyethylene terephthalate (PET) and tire rubber after high-temperature exposure and subsequent confinement using carbon-fiber-reinforced polymer (CFRP) strips. Four mixes, including control, PET-modified, rubber-modified, and PET-rubber hybrid, were heated to 400 or 600 °C, cooled, and confined with five or seven CFRP strips before axial compression testing. Parameters examined included compressive strength, peak strain, elastic modulus, lateral/volumetric strains, and toughness indices. Heating reduced strength and stiffness but increased strain capacity and dilation. CFRP confinement markedly improved performance, particularly at 600 °C, with rubberized mixes showing the highest strain capacity under seven-strip confinement. Strength retention ranked as control, rubberized, hybrid, and PET. Volumetric and energy analyses showed that CFRP confinement restrained dilation and enhanced toughness, while rubber modification primarily increased strain capacity and promoted a more ductile, confinement-controlled response. • CFRP strip confinement restores post-heating strength of PET/rubber concrete specimens • Rubber inclusions enhance ductility after heating to 600 °C • PET-modified mixes show greatest strength loss but recover strain with CFRP strips confinement • GEP models predict residual strength, strain, and modulus with high accuracy • Stress–strain model calibrated for heat-damaged CFRP-confined concrete specimens