Effect of fiber content and end geometry on the pullout behavior of straight and arc-shaped steel fibers embedded in SIFCON

Understanding the pullout behavior of arc-shaped steel fibers in slurry-infiltrated fiber concrete (SIFCON) materials is crucial to improving their mechanical and deformation properties. This study investigates the impact of various fiber volume contents and end geometries on the pullout behavior of straight (S-type) and arc-shaped (Atype) steel fibers in SIFCON. Specifically, three different end geometries of S- and A-type fibers, i.e., zero plastic hinge (0B), one plastic hinge (1B), and two plastic hinges (2B), and four fiber volume contents of 0 %, 2 %, 4 %, and 6 % were considered. Electron microscopy and X-ray computed tomography techniques were employed to analyze the interfacial bonding mechanism between the steel fiber and SIFCON. The results indicate that, aside from the 2BA fibers, the fiber content in SIFCON had minimal impact on the pullout slip curve shape of the various steel fibers. The peak pullout load, bond strength, and energy absorption capacity of steel fibers were improved by increasing fiber content and plastic hinge numbers. Adding fibers to the matrix boosted the frictional resistance and restraint capacity during the pullout process. A-type fibers demonstrated superior pullout properties than S-type fibers, primarily due to the arc shape, which enhanced frictional resistance and mechanical anchorage within the matrix. Additionally, three distinct mechanisms were identified for the pullout of S- and A-type fibers from SIFCON: mechanical anchorage, snubbing, and confinement effects. The combination of double anchoring at the arc region and end hooks of A-type fibers, along with the snubbing effect, significantly improved the fiber-matrix bonding strength.