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Flexural response of hybrid fiber reinforced cementitious composites Soleimani, Sayed Mohamad


In spite of the brittleness of concrete, it is a widely used material in construction. In Fiber Reinforced Concrete (FRC), short and randomly distributed fibers abate the nucleation and growth of matrix cracks and bridge them after their creation. This reduces brittleness, and provides sources of strength gain, toughness and ductility. Fibers as reinforcement can be effective in arresting cracks at both macro and micro levels. Most of the FRC used today involves use of a single fiber type. This implies that a given fiber can provide reinforcement only at one level and within a limited range of strain. For an optimal response, therefore, different types of fibers must be combined to make Hybrid Fiber Reinforced Concrete (HyFRC). The scope of this research was to investigate the flexural response of HyFRC. Up to three different types of fibers were combined in each mix. Hybridization was amongst steel/polypropylene macro fibers and carbon/polypropylene/steel micro fibers. Compressive strength of the matrix was around 55-60 MPa. The main purpose of this research was to investigate the influence of various hybrid fiber combinations on fresh properties of concrete (i.e. workability) and on mechanical properties including compressive strength and toughness in bending. In this study, 14 different mixes containing only one type of fiber, 12 different mixes containing two kinds of fibers and 5 different mixes containing three kinds of fibers were made as well as plain concrete for reference (32 different mixes in total). For each mixture, six 100x100x350 mm prismatic specimens and six 100x200 mm cylinders were made and tested. Measuring the VeBe time for each and every mix assessed the workability of FRC/HyFRC. Cylindrical specimens were used to determine the compressive strengths. Beam specimens were used to obtain the load versus deflection curves in third point loading to calculate their flexural toughness and first-crack strengths. Finally, synergistic effects between fibers were observed in the hybrids with enhanced performance of the material over a wider range of deflections.

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