The influence on the bond between the steel fiber and the matrix of the anticorrosive treatments of steel used for concrete reinforcement is not yet fully understood. The topic of steel fiber treatment was not also studied clearly in terms of brass removal before. This paper deals with how the brass on the surface of steel fibers behaves in the UHPC matrix and how it affects its properties. The steel fibers were firstly modified with a number of surface treatments to remove brass on their surface. Some of the treatments have never been tried before for this purpose. Secondly, the surface of the fibers was analyzed by SEM, EDS, XRF, and stereomicroscopy. Lastly, the properties of the composites were analyzed. It was found out that the majority of brass on the surface of the fibers could be removed by mixture of NH3 and H2O2 with a ratio of 3:1 (v/v). It was also found out that the surface treatment slightly affects the mechanical properties, but it does that only by mechanical interlocking between the fiber and the matrix. No dissolution of the surface treatment was observed under the given conditions. According to the results, steel fibers without surface treatment should be used in UHPC if available.
Keywords: brass; compressive strength; flexural strength; reactive powder concrete; ultra-high-performance concrete.