Experimental investigation on the performance of engineered spiral fiber: Fiber pull-out and direct tension tests

Recent researches indicate promising characteristics of Engineered Spirally Deformed steel Fiber (SDF) for reinforcing cementitious matrixes. However, the available research includes only limited SDF pull-out tests (mostly vertically aligned fibers) and flexural beam tests on Spirally Deformed Fiber Reinforced Concrete (SDFRC). This paper performed a complete single SDF pull-out and several direct tension tests on dog-bone SDFRC specimens with a proposed fully hinged apparatus to fill the research gaps. Various test parameters were considered in the SDF pull-out study, including matrix strength (20 MPa and 30 MPa) as well as fiber embedment length (10 mm, 15 mm, and 20 mm) and inclination angle (0˚, 15˚, 30˚, 45˚, and 60˚) of the fiber. SDFRC strength (20 MPa and 30 MPa) and fiber volume fraction (0.15 % and 0.25 %) were considered in the direct tension tests of SDFRC. Spiral fibers presented promising energy absorption capacity. Consistent with the outcomes of other fiber pull-out studies, the current study found that the matrix strength positively correlates with peak and post-peak pull-out load, while the fiber embedded length and inclination angle correlated inversely with loads. However, unlike other fully deformed fibers, the inverse correlation between the fiber embedded length and loads is considerably less pronounced. The direct tension tests revealed that such a fiber sustains load bearing even in significant cracks (widths ≥ 15 mm).