Study on fracture mechanical properties and mechanism of engineered cementitious composites (ECC) after high temperature

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The low melting point characteristics of organic fibers restrict the utilization of ECC in engineering applications. In this paper, the fracture mechanical properties of ECC were studied considering temperature and polyethylene fiber content, and the crack propagation rule and potential mechanism of ECC were clarified by using digital image correlation (DIC) technology and microscopic testing technology. The following conclusions are mainly obtained through the study. When the fiber content is 0 %, with the increase of temperature, the unstable fracture load, initial fracture toughness and unstable fracture toughness of the specimen are all reduced, while the fracture energy increases first and then decreases. When the fiber content is 0.5 %, 1 % and 1.5 %, the fracture parameters (unstable fracture load, fracture energy, initial fracture toughness and unstable fracture toughness) of the specimens decrease with the increase of temperature, and the decrease of the fracture parameters of the specimens is more obvious especially at 400℃ and later. The higher the PE fiber content, the more the fracture parameter is reduced by the temperature effect. The fracture parameters of the specimens increased significantly with the increase of PE fiber content at both room temperature/20℃ and 200℃, while the fracture parameters of the specimens decreased with the increase of fiber content when the temperature was not lower than 400°C, but the decrease was not significant. The results of the DIC technique showed that, with the increase of temperature, the crack initiation stage is advanced, the rapid crack development period is delayed. The development trend of crack length of the specimen is slowed down. At the same time, the mechanism of high temperature on the deterioration of ECC fracture mechanical properties under different PE fiber content was revealed. The results of this paper provide a theoretical basis for the safety assessment and analysis of ECC in engineering structural applications after fire.