Mechanical behaviors of concrete combined with steel and synthetic macro-fibers

In this paper, hybrid fibers including high elastic modulus steel fiber and low elastic modulus synthetic macro-fiber (HPP) as two elements were used as reinforcement materials in concrete. The flexural toughness, flexural impact and fracture performance of the composites were investigated systematically. Flexural impact strength was analyzed with statistic analyses method; based on ASTM and JSCE method, an improved flexural toughness evaluating method suitable for concrete with synthetic macro-fiber was proposed herein. The experimental results showed that when the total fiber volume fractions ($V_f^a$) were kept as a constant ($V_f^a=1.5%$), compared with single type of steel or HPP fibers, hybrid fibers can significantly improve the toughness, flexural impact life and fracture properties of concrete. Relative residual strength RSI', impact ductile index ${\lambda}$ and fracture energy $G_F$ of concrete combined with hybrid fibers were respectively 66-80%, 5-12 and 121-137 N/m, which indicated that the synergistic effects (or combined effects) between steel fiber and synthetic macro-fiber were good.