Bond-slip response of novel half-hooked steel fibers in ultra-high-performance concrete. (10th November 2019)

• Record Type: Journal Article
• Authors: Yoo, Doo-Yeol; Choi, Hong-Joon; Kim, Soonho
• Is Part Of: Construction & building materials. Volume 224(2019)
• Page Start: 743
• Page End: 761
• Publication Date: 2019-11-10
• Subjects: Ultra-high-performance concrete -- Novel half-hooked steel fiber -- End-hook angle -- Bond-slip behavior, Rate sensitivity; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2019.07.099
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Better pullout resistance of half-hooked fiber in UHPC is obtained by increasing the end-hook angle. Increasing the end-hook length enhances the pullout resistance of half-hooked fiber in general. Using half-hooked fiber and shorter length in the end-hook portion lead to the higher rate sensitivity. Aligned fiber provides higher rate sensitivity on the bond strength than the inclined fiber. The rate sensitivity of half-hooked fiber is not influenced by the end-hook angle. Abstract: In this study, an attempt was made to investigate the effect of end-hook angle on the rate-dependent bond-slip behavior of novel half-hooked steel fibers embedded in ultra-high-performance concrete (UHPC). For evaluating the effects of the number of plastic hinges and length in the end-hook portion, commercially available hooked steel fiber and short half-hooked steel fiber were additionally used. Three different end-hook angles of 30°, 45°, and 60°, two different fiber inclination angles of 0° and 45° to take into account the random orientation of fibers in the composites, and various loading rates ranging from 0.018 mm/s (static) to 1186 mm/s (impact) were considered. Test results indicated that the most influential factor on the static pullout resistance in terms of the bond strengths and pullout energy was the length in the end-hook portion rather than the number of plastic hinges and end-hook angle if the fibers were pulled out without breakage. Increasing the end-hook angle was effective in enhancing the static and dynamic bond strengths and pullout energies of half-hooked fibers in UHPC given the pullout failure mode, and there was no effect of it if they were ruptured. In addition, the increase in length in the end-hook portion significantly improved the static bond strength and pullout energy in the aligned condition, whereas its effectiveness decreased under the impact loads. The use of half-hooked fiber or shorter length in the end-hook portion was effective in terms of the rate sensitivity to the pullout resistance compared with the commercial hooked fiber or the longer-length one, and the bond strength became more sensitive to the loading rate if the fiber was aligned rather than inclined.