Mechanical properties and microscopic damage mechanism of PVA-ECC after high-temperature cooling

To investigate the mechanical performance and microscopic characteristics of Engineered Cementitious Composite (ECC) after high temperatures, material mechanical tests and microscopic observations of ECC after high temperatures were conducted. The compressive tests and the bending tests of ECC specimens were carried out after natural cooling and spray cooling methods at room temperature (25 ℃), 200 ℃, 300 ℃, 400 ℃, and 500 ℃ and analyzed the failure characteristics of ECC microstructure by scanning electron microscope, and investigated the damage mechanism of ECC after high temperatures. The results show that the concrete on the surface of ECC does not peel off after high temperatures, and there is no burst phenomenon within 500 ℃. As the temperature increases, the fiber gradually melts from the surface of the concrete to the inside, the water loss increases and the maximum burning loss rate is 13. 9% . In terms of mechanical properties, the compressive strength of ECC after natural cooling decreases first then increases, and then decreases with the increase in temperature. After water spray cooling, the compressive strength decreases monotonously with the increase in temperature, and the strength decreases significantly. The flexural strength after high temperature decreases gradually with the increase in temperature, and the decrease of natural cooling is more significant than that of water cooling. Combined with the change of microstructure, when ECC undergoes high temperature, the partial melting of the fiber leads to the weakening of the bonding performance between the fiber and the matrix. With the increase in temperature, the hydration products gradually show independent dispersion. However, the secondary hydration of unhydrated particles after water spray cooling is evident, which makes the flexural strength of ECC increase by 17% compared with natural cooling. ECC has excellent thermal stability, and cooling methods influence the apparent characteristics, mechanical properties, and microscopic characteristics of ECC. © 2024 Harbin Institute of Technology. All rights reserved.