Bending performance of ECC-RC composite beams under extreme temperature differences

To study the influence of engineered cementitious composites (ECC)- Reinforced concrete (RC) composite beams on the bending bearing capacity under extreme temperature differences, four groups of ECC-RC composite beams were tested in this study. The test beams were subjected to heating and cooling treatment at external temperatures (approximately -20°C), 200°C, 400°C, and 600°C, respectively, and then loaded to failure. The experimental and theoretical results showed that the characteristic load, ductility, and toughness of ECC-RC composite beams were reduced under extreme temperature differences. The ultimate load and toughness of ECC-RC composite beams after fire at 200°C, 400°C, and 600°C were reduced by 9.68%/20.71%/30.38%, and 12.86%/32.79%/43.58%, respectively, compared with -20°C, indicating that the comprehensive mechanical properties of ECC-RC composite beams under extreme temperature differences exhibit significant degradation behavior. Based on the thermodynamic properties of materials in different sections, a segmented cross-sections calculation method was established. In addition, the characteristic load calculation formula of ECC-RC composite beams under extreme temperature differences was proposed. This study enriches the fire simulation test and theoretical research methods of ECC-RC composite structures in cold regions and provides important reference value for similar research in this field in the future.