Optimal Steel Fiber Strength for Reinforcement of Cementitious Materials

Abstract

Steel fiber is the most common type of fiber reinforcement in cementitious materials. The reinforcement efficiency, in terms of maximum crack bridging force and total energy absorption during fiber pullout, is a function of many parameters including the properties of fiber, matrix, and interface as well as fiber size, volume fraction, geometry, and distribution. This paper focuses on the effect of fiber yield strength on reinforcement efficiency. Fiber pullout specimens are fabricated with fibers of different yield strengths. Because cracks in a concrete member may intersect fibers at different angles, pullout tests are carried out with the fiber inclined at 0 deg (0 rad), 30 deg (0.5 rad), and 60 deg (1 rad). The experimental results indicate the existence of an optimal fiber yield strength for the maximization of pullout load and pullout work. Inspection of the pullout curves as well as microscopic studies show that a higher fiber yield strength will result in more severe matrix spalling around the fiber exit point, thus limiting the further improvement in reinforcement efficiency. The results confirm the qualitative trend predicted by an existing theoretical model and indicate that the fiber yield strength is an important parameter that should not be overlooked in the design of fiber reinforced cementitious composites.