Axial tensile softening characteristics of PVA fiber concrete cured in super absorbent polymer under temperature effects

To study the axial tensile softening characteristics and the intrinsic fracture mechanism of Polyvinyl Alcohol (PVA) fiber-reinforced concrete specimens cured in Super Absorbent Polymer (SAP) at different temperatures, the study was carried out by uniaxial tensile test using MTS universal testing machine, and the variation rules of the axial tensile mechanical properties, damage morphology, stress-displacement curves, fracture energies, critical cracks, and characteristic lengths of the concrete were analyzed. Based on the test curves, the softening model proposed by Hordijk and Li was used for fitting, and the relevant parameter laws and concrete softening characteristics were analyzed. The test results show that: the concrete specimen is tensile fracture at the weak point, and the fracture location is randomly distributed along the axial direction; with the increase of temperature, the softening section after the peak of the stress-displacement curve is more gentle, and the stress decreases slower; the synergistic effect of SAP and PVA fibers at room temperature can improve the toughness of the concrete better, and too much mixing amount of PVA fibers will accelerate the damage of the concrete at high temperatures; The fracture energy of the concrete generally decreases with the increase of temperature, and the characteristic length ranges from 970.6 mm to 2110.2 mm. With the increase of PVA fiber content, the characteristic length generally increases first and then decreases, while the critical crack length generally increases with the increase of temperature. The research results show that the temperature effect has a significant influence on the strength, fracture properties, and synergistic effect of SAP and PVA fibers in concrete, leading to changes in the failure mode and inherent fracture mechanism of concrete. Adding an appropriate amount of SAP and PVA fibers can improve the crack resistance and toughness of concrete specimens, while an excessive amount of PVA fibers can accelerate the damage of concrete at high temperatures. By comparison, it is found that the Hordijk model can better simulate the softening curve of internally cured fiber-reinforced concrete axial tensile tests at different temperatures.