Interfacial bond characteristics of polypropylene fiber in steel/polypropylene blended fiber reinforced cementitious composite

•The interfacial bond characteristics between polypropylene fiber and concrete matrix was investigated.•The factors of hybrid fiber content within matrix, matrix strength and fiber embedded length were considered.•The frictional bond strength of polypropylene fiber was analyzed. This paper investigates for the first time the interfacial bond characteristics of polypropylene fiber in blended hybrid steel-polypropylene fiber reinforced concrete, which contributes to improving the polypropylene fiber utilization efficiency and then promoting the overall performance of the composite. Single-sided fiber pullout tests were performed on 21 groups of macro polypropylene fiber pullout specimens. The complete fiber pullout load-slip responses were captured, and the fiber interfacial properties were analyzed for different hybrid fiber dosage, fiber embedded length and matrix length. Results show that partial fiber rupture with a non-zero residual pullout load is the dominant failure mode. Increasingly severe abrasion at the PF surface is observed during the pullout process, resulting in a strain hardening behavior after a bent-over point is reached in a typical pullout load-slip curve. An appropriate polypropylene fiber addition in the concrete matrix can effectively improve the maximum pullout load, residual pullout load, the pullout energy, and the contribution of polypropylene fibers is more critical than that of steel fibers. Besides, the reinforcement of polypropylene fibers on the toughness and cracks resistance is proven to be more pronounced in plain concrete than that in high-strength concrete. Finally, theoretical analyses were performed on the polypropylene fiber direct pullout problem and the frictional bond stress vs. slippage relation is obtained with hybrid fiber content taken into account. The research provides a base for an optimized hybrid fiber reinforced concrete with high fiber efficiency and less cement consumption.