Investigation of the fracture energy of concrete strengthened by hybrid fibers

Two different approaches are actively representing the behavior of the concrete under loading, that is the strength approach and the fracture mechanic approach. In the current work, fibrous concrete was investigated, the effect of the fiber types (Steel fiber, Glass Fiber, Polyvinyl alcohol Fiber, Polypropylene Fiber, and Nylon Monofilament Fiber) and its volume fraction (0.5, 1.0, and 2%) on the strength and fracture energy. Thirty-six prisms and its corresponding standard cylinders were constructed and used in the comparisons. The results showed that, among the different types of fibers the highest improvement in mechanical properties was obtained by adding 1% of Steel fiber, where the compressive and tensile strength were improved 24 and 107%. Moreover, among the hybrid fibers, the highest improvement in compressive and tensile strength compared to the plain concrete was 33% and 137%, respectively, this was obtained from including 1% of Steel fiber and 1% of Polyvinyl alcohol Fiber. The highest improvement in fracture energy was produced from using 1% of Steel fiber and 1% of Nylon Monofilament Fiber, the improvement percentages were 80 times the plain concrete. Comparing to the using of single fibers, using the Steel fiber alone was improved the fracture energy by 36 times of the plain concrete, and using the Monofilament Fiber alone were improved the plain concrete just 19 times. Using 1% of Glass Fiber wasn't shown any effect on the fracture energy and compressive strength in spite of its improvement in tensile strength (16%). Key words; Fracture energy, Fibrous concrete, hybrid fiber, compressive strength