Effect of curing age on pullout behavior of aligned and inclined steel fibers embedded in UHPFRC

Abstract

Ultra High-Performance Fiber Reinforced Concrete (UHPFRC) is a promising material for applications in precast industry characterized by fast construction. However, there is a gap in investigations on the pullout behavior of inclined fibers at different ages. Therefore, pullout tests were performed in UHPFRC at 1d, 3d, 7d, and 28d, with fibers having embedment angles of 0°, 30°, and 45° for each age. An exponential function described well the growth of bond strength. It was found an increase in average bond strength of 2.98, 4.50, and 3.89 for fiber inclinations of 0°, 30°, and 45°, from 1d to 28d. For equivalent bond strength, the increase was 3.68, 4.37, and 2.82, respectively, from 1d to 28d. The smaller growth for 45° than 30° is attributed to greater matrix spalling for higher inclinations. In contrast, the more significant increase for fiber inclined 30° is mainly attributed to the increased friction at the interface due to the snubbing effect. Furthermore, maximum fiber stresses reached ratios to the tensile strength of 0.54, 0.65, and 0.59 for fiber inclinations of 0°, 30°, and 45°.