Effect of fiber type and content on the flexural behavior of high strength concrete beams with low reinforcement ratios

The effect of fiber types and fractions on the flexural behaviors of High Strength Concrete (HSC) beams with minimum reinforcement ratios were investigated experimentally. The main parameters in the conducted study were fiber type, the volume fraction of fiber and axial reinforcement ratio. Therefore, totally eighteen beam specimens containing both fiber reinforced concrete (RC) and conventional concrete were tested to examine pure bending regions of beams using four-point loading method. Three aspects were analyzed: (i) cracking, yielding and ultimate flexural loads, (ii) variation of the neutral axis depth and (iii) minimum reinforcement ratio required to sufficient ductility. Test results indicate that increase in the volume fraction of the steel fiber significantly improves the yielding load level of HSC beams, while addition of carbon fiber has a trivial effect on that load. Increasing the volume fraction of steel and carbon fiber causes the decline of the flexural ductility of HSC beams with low reinforcement ratio and makes the behavior of the beams more brittle in an interesting manner. Therefore, an optimum ductility number based on fracture mechanics principles was evaluated experimentally to determine the minimum reinforcement ratio supplying sufficient ductility for HSC with steel fibers.