Test Methods for Steel Fiber Segregation in Ultrahigh-Performance Concrete

Fiber reinforcement segregation can affect the mechanical properties of ultrahigh-performance concrete (UHPC), posing a critical challenge in structural component fabrication using UHPC-class materials. Despite the importance of this topic, a readily available, widely accepted method for real-time evaluation of fiber segregation does not exist. This study examined the applicability of existing standards for conventional concrete, including a static segregation column test and a static segregation resistance test using a penetration device. The research team investigated modifications to the testing procedures and apparatus to make the tests more applicable to UHPC-class materials. Results of the fresh material testing were correlated with the visual assessment of hardened samples that were sectioned and analyzed using image processing techniques. The modified static segregation resistance test method is recommended as a practical approach to assess the suspension of steel fibers in fresh UHPC materials; a penetration depth limit of 10 mm (0.4 in.) at 30 s may be used as a threshold value for UHPC resistance against steel fiber segregation.