Flexural behavior of precast reinforced concrete composite members reinforced with structural nano-synthetic and steel fibers

In this study, structural nano-synthetic and steel fibers were used to reduce the amount of steel rebar distributed in precast reinforced concrete composite members. The flexural performance of the members was evaluated using longitudinal steel ratios of 1.65 and 1.20 and a transverse steel ratio of 0.20. Hybrid fiber mixtures consisting of various amounts of structural nano-synthetic and hooked-end steel fibers were used as reinforcing materials along with the steel rebar. The nano-synthetic fiber volume fractions were 0.4, 0.5, and 0.6 vol.%, and the steel fiber contents were 5, 10, and 20 kg/m3. Flexural performance tests were carried out for the resulting hybrid fiber-reinforced cement composites. The test results demonstrated that the hybrid fiber-reinforced cement composites satisfied the necessary conditions to replace the general reinforcing bars according to the RILEM standard when the mixture contained 0.4 vol.% of nano-synthetic fiber and 20 kg/m3 of steel fiber. The flexural behavior of a 350 × 180 × 1500-mm precast composite member reinforced by such a hybrid fiber mixture and steel rebar was evaluated; its maximum load was 30% greater than the designed ultimate load and 3.5% greater than that of a steel fiber-reinforced composite member.