Performance Enhancement of Reinforcing Bars in Concrete with Hooked-End Steel Fibers: A Pull-Out Study

This experimental study provides a comprehensive assessment of the bond performance of two deformed steel reinforcing bars with diameters of 8mm, 10mm, and 12mm in two concrete mixes incorporating hooked-end steel fibers. A total of 36 cylindrical pullout specimens were prepared and subjected to rigorous pullout tests. The study meticulously examined the impact of four critical parameters: bar diameter, embedment length (5, 10, and 15 times the bar diameter), concrete strength, and spacing between deformed bars (25mm and 50mm). The influence of these parameters on bond strength was thoroughly evaluated, and failure mechanisms were analyzed. Results indicated that pullout failure was the dominant failure mode for specimens with shorter embedment lengths, while splitting failure prevailed in specimens with the longest embedment lengths. Increasing the embedment length significantly enhanced the ultimate load, toughness, and slip values of the tested specimens. Additionally, specimens with closer bar spacing exhibited superior bonding performance compared to those with wider spacing. Thus, reducing the spacing between reinforcing steel bars in concrete has been proven to improve load transfer efficiency and minimize stress concentrations, leading to higher structural integrity. This practice enhances the bond strength between steel and fiber concrete, resulting in improved resistance to cracking and deformation under applied loads.