A comparative study on the pullout behavior of hooked-end straight and arc-shaped steel fibers from brittle SIFCON matrices under the influence of adjacent fibers

Since the interaction between fibers in SIFCON exhibits a considerable effect on the bond properties, this study investigates the bond properties of steel fibers in brittle SIFCON matrices under the influence of adjacent fibers. Two different geometries of steel fibers were used, i.e., hooked-end straight (2BS) and arc-shaped (1BA). Two brittle SIFCON matrices with different W/B ratios were considered. This study evaluated the bond properties by examining the "fiber interlock" effect of 2BS and 1BA fibers and the "fiber cross-lock" effect of 1BA fibers. The results showed that the pullout curves of 1BA fibers exhibited an interesting double-peak characteristic due to the mutual cross-locking of fibers. The peak pullout load, average bond strength, pullout energy, and equivalent bond strength of 2BS and 1BA fibers were enhanced by the interlocking effect between adjacent fibers. The enhancement effect of 1BA fibers was higher than that of 2BS fibers under the same conditions. Regarding improving pullout load and pullout energy, the cross-locking effect between 1BA fibers is more effective than the interlocking effect. 1BA fibers showed superior pullout energy ratios under the fiber cross-locking effect, attributed to the additional pullout resistance provided by the mutual cross-locking between fibers after extensive matrix spalling. Furthermore, the contribution to the total pullout energy of 1BA fibers was primarily dominated by the cross-locking effect between fibers, especially at lower matrix strengths.