Mechanical Behavior of Hybrid Fiber Reinforced High Strength Concrete with Graded Fibers

Brittleness, which was the inherent weakness in High Strength Concrete (HSC), can be avoided by reinforcing the concrete with discontinuous fibers. Reinforcing HSC with more than one fiber is advantageous in an overall improvement of the mechanical performance of the composite. In this experimental study, Hybrid Fiber Reinforced High Strength Concrete (HyFR-HSC) mixes were formed by blending single length glass fiber and single length steel fiber with a total volume fraction of 1.65% into the concrete and Hybrid Graded Fiber Reinforced High Strength Concrete (HyGrFR-HSC) mixes were obtained by mixing different lengths of glass fiber with different length of steel fibers at a total volume fraction of 1.65% into the concrete. A comparative study was made between HyFR-HSC and HyGrFR-HSC specimens to investigate the effect of fiber grading on strength properties and the uniaxial compressive behaviour of HSC with hybrid fibers. In both HyFRC and HyGrFRC mixes, glass fibers improved the pre-peak behaviour, and steel fibers improved the post-peak behaviour of concrete, thereby exhibiting a positive synergy in combining glass and steel fiber into the concrete. Among the two-hybrid FRC’s, HyGrFRC outperformed HyFRC with substantial improvement in both strength and ductility. Among all the HyGrFRC mixes, HyGr9 mix, which contain a higher amount of long-length fibers exhibited better improvement in peak strain, ductility factor, total energy and toughness index. The replacement of single length of fibers with graded length fibers at higher volume fraction in HyFRC is useful in improving workability, thereby providing better fiber dispersion and thus enhances both the pre-peak and post-peak performance of the concrete. From this investigation, it can be inferred that grading of fibers improved the mechanical behaviour of HyFRC by exhibiting positive synergy from both fiber geometry and fiber type.