Precise evaluation of fiber orientation coefficients and the impact of magnetic flux density on the mechanical properties of <scp>UHPC</scp> via <scp>CT</scp> scanning

Abstract Steel fibers have been demonstrated to play a crucial role in enhancing the mechanical performance of ultra‐high‐performance concrete (UHPC). However, the precise quantitative relationship between fiber inclination angles and UHPC's mechanical behaviors remains underexplored. This study utilizes computed tomography (CT) scanning to obtain the fiber orientation coefficients in UHPC specimens prepared under varying magnetic flux densities. The compressive and flexural strengths of standard specimens were tested, and a strength prediction model for UHPC, based on composite material theory, was proposed. The results reveal that fibers within UHPC, cast using standard molds, are not uniformly distributed but exhibit a droplet‐shaped annular distribution due to the flow of the cementitious matrix. Furthermore, UHPC samples with distinct fiber orientation efficiencies can be accurately produced by varying magnetic flux densities. The relationship between strength indices and fiber orientation coefficients follows a power‐law function. Overall, when fibers are oriented parallel to the tensile stress direction, the mechanical properties of UHPC are significantly enhanced. Notably, a slight strength improvement was observed when the orientation coefficient approached approximately 0.2, which can be attributed to fiber pull‐out behavior.