Enhanced mechanical properties of fiber reinforced concrete using closed steel fibers

Concrete is weak in tension and fibers are added to it to make it ductile. One of the commonly used methods, for this purpose, is the addition of steel fibers of different geometries. However, failure of fiber reinforced concrete is initiated by pulling out of fibers, failing to utilize their full capacity. In this study, closed steel fibers (CSF) are proposed for addition into concrete. The objective was to avoid the pulling out of fibers in tension for full capacity utilization. When CSF are embedded into concrete, they are expected to reach the breaking point, utilizing their maximum capacity due to the presence of concrete matrix within the closed geometry of fibers. Different volumes of straight steel fibers (SSF) and CSF were used to investigate and compare their performance. Fresh and hardened concrete properties were considered. Results indicated decrease in workability of fiber reinforced concrete with increasing steel fiber content. No significant change in concrete compressive strength and modulus of elasticity was noted. There was a maximum of 46% increase in tensile strength while 36% increase in flexural strength of concrete with the use of CSF compared to that of SSF. The failure of concrete in tension was initiated by pulling out of open fibers and breaking of closed fibers. Thus, use of closed steel fibers is recommended to make full use of steel fiber tensile capacities which may revolutionize the field of fiber reinforced concrete.