Thermal Degradation of Polypropylene Fiber-Reinforced Cementitious Composites, Tensile Behavior and Crack Evolution Assessed by Digital Image Correlation

• SEM shows PP fibers degrade above 200°C, causing 48-70% strength reduction of ECC. • Elastic modulus increases 35-100% while energy absorption plummets 93-97%. • 3% fiber composites lose 70% strength versus 43% for plain cement paste. • DIC shows 10∼14 micro microcracks at 0°C versus 1-2 wide cracks at 200°C. • Polynomial models achieve R² =0.85∼0.98 for performance prediction. This study examines the tensile performance and crack evolution of polypropylene (PP) fiber-reinforced cementitious composites after exposure to elevated temperatures up to 400°C. Specimens containing 0–3% PP fibers (by volume) were subjected to controlled thermal regimes and evaluated using direct uniaxial tensile testing combined with digital image correlation (DIC). Results indicate that heating to 100°C caused minimal strength reduction (<5%), while exposure to 200°C reduced ultimate tensile strength by approximately 18–25%, depending on fiber content. At 300°C and 400°C, strength degradation became significant, reaching reductions of 40–65%, accompanied by a marked decline in strain capacity and energy absorption. The tensile strain capacity decreased by up to 70% at 400°C relative to ambient conditions. Despite this overall degradation, elastic modulus increased by 8–15% at intermediate temperatures, suggesting matrix densification prior to severe microstructural damage. Crack patterns transitioned from distributed multiple cracking at ambient temperature to localized single-crack failure beyond 200°C, corresponding to fiber softening and melting observed in microstructural analysis. Composites with higher fiber volume fractions exhibited greater sensitivity to thermal exposure. Regression analysis confirmed a strong nonlinear correlation between temperature and tensile response (R = 0.82–0.93).