Investigation of shear behaviour of self-compacting concrete containing hybrid steel fiber

Self compacting concrete (SCC) is a special type of concrete with high deformability without segregation and good cohesiveness. In this paper, micro and macro steel fibers having different lengths were used to understand the influences of fiber addition on the fresh and hardened properties of SCC as well as shear strength of full-scale beams subjected to four point bending. All ingredients in each mixture were constant to study the effect of macro and micro fibers except for high-range water reducing admixture (HRWRA). Five mixtures containing micro and macro steel fibers in different combinations were prepared and in each mixtures the sum of the steel fiber content was kept constant as 1%. To measure the workability, slump flow diameter, T50 and J-ring tests were conducted. To determine the hardened properties of SCC mixtures, compressive strength, flexural tensile strentgth and shear strength tests using full-scale beams for 28 and 56 curing days were conducted. The results indicated that when the micro steel fiber ratio became more than 0.25%, although the fresh properties of SCC were affected negatively, the slump-flow values of all mixtures were acceptable as per the limit values of EFNARC. The micro steel fiber inclusion had positive effect on compressive strength while it caused a reduction in flexural tensile strength. In the tests of full-scale beams produced from SCC with hybrid steel fiber, all mixtures containing steel fiber had more bearing capacity than control mixtures as well as more ductility behavior. Moreover, it was observed that in beam specimens with hybrid steel fiber, the cracks occured after failure turned to perpendicular bending cracks from inclined shear cracks when the use of micro steel fiber instead of macro steel fiber increased.