Utilization of hybrid sisal and steel fibers to improve elevated temperature resistance of ultra-high performance concrete

This paper investigated the mechanical properties and elevated temperature resistance of sisal fibers and steel fibers hybridization reinforced ultra-high performance concrete (UHPC). The compressive strength, flexural strength, and toughness of UHPC before and after exposure to elevated temperature were measured. Moreover, the spalling behavior, gas permeability, and sorptivity of hybrid fiber reinforced UHPC after the elevated temperature exposure was also studied. The spalling resistance mechanism was elucidated by thermal analysis and microstructure observation. The result shows that hybridization of sisal fibers and steel fibers exhibits an excellent synergy effect on improving the mechanical properties of UHPC before and after elevated temperature exposure. The addition of sisal fibers significantly increases the gas permeability of UHPC, hence the spalling of UHPC at elevated temperatures was prevented efficiently. A sisal fiber content of 0.6 vol% was most favorable in terms of improving the residual mechanical properties. Sisal fibers can increase the porosity of UHPC after elevated temperature exposure as indicated by sorptivity results, therefore excessive sisal fibers impaired the residual mechanical properties. This study provides new insights into the utilization of natural sisal fibers to produce sustainable and cost-effective UHPC with high spalling resistance characteristics at elevated temperatures.