Pull-Out and Tensile Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Depending on The Replacement Ratio of Macro To Micro Steel Fibers

Abstract

This research was conducted to investigate the pull-out and tensile behavior of ultra-high-performance hybrid-fiber-reinforced concrete. Three types of macro fibers (straight, hooked-end, and twisted) with a length of 30 mm and one type of straight micro fiber with a length 13 mm were incorporated in composites and total volume fraction of steel fibers remained constant at 2%. Macro fibers were gradually replaced with micro fibers by 0.5% from 0 to 2%. Pull-out and tensile tests were conducted and the effect of replacement ratio of the macro fiber with the micro fiber from each experiment and correlation between the two experiments were both analysed. The test results indicated that in macro straight fiber case, the replacement with micro fibers improved the average bond strength and normalized pull-out energy whereas in hooked and twisted fiber cases, they were reduced according to the replacement ratio. On the contrary, tensile test yielded the opposite result. The maximum tensile stress and g-value decreased when macro straight fibers were replaced with micro fibers. And as the replacement ratio of macro deformed, i.e. hooked, and twisted fiber to micro fibers increased, tensile performance of the UHPHFRC was improved. The inverse correlation between fiber pull-out and direct tensile behavior was caused by the unidirectional arrangement of the fibers in pull-out test and the resulting difference in bonding area between the two experiments. Therefore, the correlation between the aligned fiber pull-out test and the tensile behavior of the composites could not be predicted precisely.