Pull-out behavior of steel fiber embedded in flowable RPC and ordinary mortar

•Embedment length is more important for the smooth fiber than the hooked-end fiber.•The fiber bond was improved as the W/C ratio decreased in all curing conditions.•Congestion of hydration products in fiber–matrix interface improves bond characteristics. The aim of this research is to investigate some of the factors which affect the steel fiber–matrix bond characteristics by means of pull-out test. Ordinary mortar (OM) and reactive powder concrete (RPC) were used as main matrices. The effect of parameters such as end condition of fiber (smooth or hooked-end), embedment length, water/binder ratio, paste phase of RPC, steel-micro fiber, and curing conditions on fiber–matrix pull-out behavior were determined. The fiber–matrix bond characteristics improved as the embedment length of fiber increased, especially for smooth fiber. Low W/C ratio, which enhances the bond strength, reduces the importance of embedment length of the hooked-end fiber. Furthermore, the pull-out peak load and debonding toughness increased as the W/C ratio decreased in the all curing conditions. Microstructural investigation revealed that the congestion of hydration products in fiber–matrix interface improves pull-out behavior remarkably.