*Article* **Bond Behaviors of Steel Fiber in Mortar Affected by Inclination Angle and Fiber Spacing**

**Xinxin Ding 1, Mingshuang Zhao 1, Hang Li 1, Yuying Zhang 1, Yuanyuan Liu <sup>1</sup> and Shunbo Zhao 2,\***


**Abstract:** Considering the random orientation and distribution of steel fibers in concrete, the synergistic reinforcement of steel fibers on concrete is much complex than the bond of single fiber. It is meaningful to study the bond behavior of steel fiber during many actions. With the inclination angle of steel fiber to pullout direction and the fiber spacing as main factors, this paper carried out fifteen groups of pullout tests for hook-end steel fiber embedded in manufactured sand mortar. The inclination angle ranged from 0 to 60◦, and the fiber spacing ranged from 3.5 mm to 21.2 mm. The characteristic pullout load-slip (*PL-S*) curve of steel fibers are given out after treating the original complete curves of each group test. The values of key points featured the debonding, peak and residual pullout loads and slips are determined from the characteristic *PL-S* curves. Based on a multi-index synthetical evaluation method, the nominal debonding strength, bond strength, residual bond strength and the debonding work, slipping work, and pullout work, as well as the debonding energy ratio, slipping energy ratio, and pullout energy ratio are analyzed. Results indicate that the bond performance represented by above indexes changes with the inclination angle and spacing of steel fibers. Except for the bond mechanism performing the same as aligned steel fibers by pullout test, the bond is dominated by the resistance of mortar to peeling off near pullout surface and scraping along pullout direction. When the inclination angle is over 15◦ or 30◦, the bond performance is generally decreased, due to the peeling off of mortar on surface of transversal section with a certain depth. When the fiber spacing is over than 5 mm, the bond performance becomes worst due to the scraping out of mortar along with the slip of steel fibers.

**Keywords:** hook-end steel fiber; bond performance; pullout test; inclination angle; fiber spacing; pullout load-slip curve
