Abstract:

The effect of polypropylene fibers, steel fibers and hybrid polypropylene - steel fibers which consist of (50% polypropylene fiber+50% steel fiber), with various volume fractions 0.25%, 0.75% and 1.25% on the flexural behavior of Reinforced concrete T-beams under static load was investigated in this research. To carry out this research ten concrete mixes were prepared one for reference high strength concrete (without fiber), and the other contain all types and volume fractions of fibers. For eachmix three reinforced concrete T-beams, three cubes (150×150×150mm) and three cylinders (150×300mm) were casted. Water cement ratio was constant 0.38, silica fume with ratio of 10% as a partial replacement by weight of cement and super plasticizer with ratio of 3% by weight of the cementitious material were add to enhance the bond between fiber and cement matrix. 28-day compressive strength and split tensile strength tests were made on hardened concrete specimen. The result showed that polypropylene fiber had little effect on mechanical properties of the high strength concrete. Compressive strength and splitting tensile strength of the steel fiber-reinforced concrete improved with increasing the volume fraction, achieving 24.5%, 43%, respectively, at 1.25% volume fraction. On the other hand, the addition of Hybrid fiber to high strength concrete improved compressive strength and splitting tensile stress with slight decrease as compared with the best improvement. All of the reinforced concrete T-beams were tested in flexure using controlled displacement two point loads applied on simply supported T-beams, during this test the load and deflection at mid span were measured. The result shows that the addition of polypropylene fiber had a little effect on the behavior of reinforced concrete T-beam at first steps of loading until yielding load, while, it was more effective in improving ductility and toughness (energy absorption) where the ultimate load and max deflection were increased with increasing volume fraction. The addition of steel fiber increased the cracking load, yield load and ultimate load capacity with increasing volume fraction, at the same time reduce deflection. The ductility improved by the addition of steel fiber, but this improvement decreased with increasing the volume fraction. The addition of hybrid fiber improved crack load, yield load, ultimate load, ductility and toughness at all steps of loading.

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