Flexural toughness and characterization method of hybrid fibers reinforced ultra-high performance concrete

In order to research the toughness characteristics of hybrid fiber on ultra-high performance concrete(UHPC), 161 specimens of three-point bending beam fracture testing of UHPC reinforced with four type fibers and various contents have been conducted. The load-crack mouth open displacement (CMOD) curves and load-deflection curves were measured. We took the peak-load CMOD of plain UHPC as the reference initial CMOD value of hybrid fibers reinforced UHPC. Based on the load-CMOD curves, a characterization method of equivalent fracture toughness was proposed. This new method has clear physical meaning, and unveils the influence rule of hybrid fibers type and contents to fracture toughness of UHPC. The research shows that the toughness of UHPC depends on the content of steel fiber in small deformation stage (less than the 50 times CMOD value of plain UHPC at peak load) and macro-synthetic fiber plays toughening effect in middle deformation and large deformation stage (larger than the 50 times CMOD value of plain UHPC at peak load).