Existing studies on spiral steel fiber pullout behavior confirm their superior interfacial bond performance, while previous studies were limited to low or medium-strength ordinary concrete and focused on either large coil-diameter spiral fibers or small coil-diameter spiral fibers with low pitch-to-coil-diameter ratios. This study examines the pullout behaviors of short-cut small coil-diameter spiral steel fibers with high pitch-to-coil-diameter ratios in slurry-infiltrated fiber concrete matrix (compressive strength of about 60 MPa). The experimental design comprised five distinct fiber geometries (S, C2-P10, C2-P15, C3-P10, and C3-P15), two embedment lengths (12 mm, 18 mm), and three inclination angles (0°, 23°, and 45°). Comparative analyses focused on failure modes, pullout load-slip curves, and pullout parameters. C2-P10 and C3-P10 fibers exhibited fiber fracture failure at the embedment length of 18 mm, while all other cases exhibited fiber pullout failure. Excluding fiber fracture cases, all four types of spiral steel fibers showed superior pullout performance to straight fibers. Relative to the straight fibers, the average bond strength ( τ av ) of these spiral steel fibers increased by 32.6–540.3%, and the equivalent bond strength ( τ eq ) increased by 28.0–313.4%, under the same embedment length and inclination angle.
Li et al. (Fri,) studied this question.