Pullout Test of Bio-inspired Steel Fiber from Cementitious Matrix

In this study, tapered steel fibers with various angles (0°, 2°, 5°, and 7°) were designed in the point view of biomimetic. The surfaces of the fibers were classified into chemical bonding and no chemical bonding based on whether their surfaces were treated or not. The fibers were pulled out from cementitious matrix under various loading speeds (2.5 mm/min, 25 mm/min, and 250 mm/min) using a MTS load frame. Pullout force and displacement of the fiber were recorded for further calculation of maximum pullout force and work of pullout. The experimental results show that the maximum pullout force increases significantly when the taper angle increases from 0° to 5°, but decreases slightly when the angle is 7°. The maximum pullout force increases by 20.2% and 13.4% with the pullout speed increasing from 2.5mm/min to 250mm/min for 5° and 7° fibers, respectively. The maximum pullout force decreases by 25.9% and 8.2% for 0° and 2° fiber when pullout speed increases from 25 mm/min to 250 mm/min, respectively. The maximum pullout force for untreated fibers are 64.1%, 22.2% and 6.7% higher than that for treated fiber when the taper angles are 0°, 2° and 5°, respectively. However, for the fibers with 7° taper angle, the maximum pullout force of untreated fiber is 6.2% lower than the treated ones. The work of pullout for 2° fiber is the largest under three various speeds. There is no obvious effect on the work of pullout whether the fiber is treated or not. The tapered fibers designed in this work can effectively enhance equivalent adhesive strength between the fiber and cement mortar matrix. © 2018, Editorial Department of Journal of Hunan University. All right reserved.