Chloride Penetration Resistance of Ultra-High Performance Fibre Reinforced Concrete - How to Test the Performance Using the Rapid Chloride Migration Test

Currently, fibre-reinforced composite materials such as Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) are increasingly being used to protect structures exposed to chlorides. Due to the almost capillary pore-free binder matrix, UHPFRC ensures the durability of the building members concerned. The chloride penetration resistance of cementitious building materials is frequently determined by accelerated laboratory tests such as the rapid chloride migration test (RCM test). For this purpose, the penetration of chlorides into a test specimen is accelerated under the influence of an electric field. However, this established method is problematic with regard to the use of electrically conductive components such as steel fibres. On the one hand, there are fundamental doubts about the applicability, on the other hand there is no consensus about the effects of steel fibres on the chloride penetration itself. This paper describes the influence of the steel fibres as well as the effect of fibre orientation on the chloride penetration resistance of different UHPFRCs. The test methods used were the determination of the electrical resistivity, the RCM test and a modified chloride migration test (MCM test). The penetration fronts of the steel fibre reinforced concretes were additionally analysed by means of Laser Induced Breakdown Spectroscopy (LIBS). Furthermore, the results were validated by diffusion tests and the fibre orientation was determined by means of a 3D X-ray microscope. The results suggest that the UHPFRCs investigated have lower chloride penetration resistance than the fibre-free reference concretes. Furthermore, the chloride penetration resistance of the UHPFRCs was reduced more when the steel fibres were oriented in the direction of the chloride flow. The investigations indicate that RCM and MCM tests can also be used for steel fibre reinforced concretes under certain restrictions.