Revealing the role of multi-scale fibers in the compressive behavior of a novel ultra-high performance concrete subjected to elevated temperatures

Abstract

Ultra-high performance concrete has received widespread attention due to its excellent performance. However, the mechanical properties can seriously degrade at high temperatures. To improve the thermal resistance, cenospheres and multi-scale fibers such as polyethylene fiber, steel fiber, calcium sulfate whisker, carbon fiber, and carbon nanotubes, are added to develop a type of ultra-high performance (MSFUHPC) in this work. The effects of cenospheres and multi-scale fibers on peak strain, compressive strength, Young's modulus, specific toughness and stress-strain curve are studied at various temperatures (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C) through uniaxial compression tests. Additionally, mercury intrusion porosimetry tests and scanning electron microscope tests are used to discuss the effect of cenospheres and multi-scale fibers on the microstructure. The results demonstrate that both CE and multi-scale fiber can reduce the thermal damage of MSFUHPC. The multi-scale fiber can significantly improve the mechanical strength of the material, while CE has the opposite effect. It is found that microscale and nanoscale fibers have negligible effect on the specific toughness, while the effect of CE on specific toughness depends on the temperature and its content. Results show that the incorporation of multi-scale fibers effectively decreases the fraction of large pores while simultaneously refining the pore structure and enhancing the proportion of gel pores. Furthermore, the stress-strain relationship of MSFUHPC is established by considering the influence of multi-scale fiber content and high temperature.