Experimental study on the fracture behavior of a novel multi-scale fiber reinforced ultra-high performance concrete with hollow microspheres after high temperatures

Abstract

In this paper, a novel multi-scale fiber reinforced ultra-high performance concrete (MSFUHPC) reinforced with polyethylene (PE) fibers, steel fibers, and carbon fibers mixed with lightweight aggregates is developed to obtain high strength and high toughness. The fracture behavior of MSFUHPC after exposure to elevated temperatures is critical to understanding the structural behavior of engineering structures in a fire accident. Therefore, the effects of multi-scale fibers, fly ash cenospheres (FAC), and hollow alumina microspheres (HAM) on the fracture properties of MSFUHPC are investigated. Results reveal that multi-scale fibers can significantly enhance the fracture toughness of UHPC by restraining crack propagation. Incorporating hollow microspheres increases the number of microcracks around the main crack, which prolongs the unstable crack propagation stage and improve the deformation capacity, as a result of which the unstable fracture toughness and the total fracture energy can be strengthened. Moreover, the fracture toughness and fracture energy of the specimen gradually decrease as the temperature increases from 25 °C to 600 °C due to the weakened bonding effect of the fibers with the matrix and the deteriorated microsphere-matrix ITZ. After 400 °C, the specimens mixed with FAC can maintain a relatively high ductility index because of the good bonding between FAC and the matrix. After 600 °C, the fracture energy of MSFUHPC decreases by about 82.3 %-92.1 %, mainly thanks to the thermo-damaged bridging capability of the steel and carbon fibers.