Twin-twist effect of fibers on the pullout resistance in cementitious materials

As a part of ongoing research to develop a new type of a twin-twisted steel fiber and characterize its tensile performance in cementitious materials, an initial experimental study was performed to evaluate the pullout behavior of the fiber. Comparative analyses were carried out with straight and hooked-end fibers to examine the twin-twist effect on the pullout resistance of fibers. The maximum and residual pullout capacity, bond strength, and energy absorption capacity were evaluated. The twin-twisted fiber showed higher maximum and residual pullout load compared to the straight and hooked-end fibers. In particular, the new type of the twin-twisted fiber retained the residual pullout resistance until the final failure of the fiber, which could significantly improve the toughness and resistance of cement-based materials.