Effects of high temperature and substitution rates of fly ash on the mechanical properties and microstructures of steel-basalt hybrid fibers reinforced cementitious composites

•Increasing fly ash properly can reduce the rate of strength degradation, but will reduce the compressive strength and increase the explosive spalling rates.•Hybrid fibers can significantly improve the explosive spalling behavior, flexural and splitting tensile strength.•The microstructures become loose and the porosities increase after exposure to high temperatures.