3D micro-CT driven fibre orientation-confinement correlation model for ultra-high-performance concrete (UHPC)

Accurately characterising steel fibres is paramount for developing a representative confinement model for Ultra-High-Performance Concrete (UHPC). Existing models oversimplify the fibre contributions by assuming a singular orientation, which fails to reflect the material variation resulting from actual fibre distribution. In this study, the authors refined the fibre orientation characteristics to establish a correlation with the confined core capacity at the structural level. To achieve this, multi-scale investigations, from experimental testing to X-ray micro-computed tomography (micro-CT) imaging on steel-confined UHPC specimens, were conducted, by varying internal (fibre types and contents) and external confinement pressures. A novel framework was developed to calibrate effective fibre orientation under varying fibre contents. This led to the introduction, for the first time, of a reliable fibre orientation model for UHPC subjected to varying confinement levels. The proposed model provided accurate predictions of the confined core capacity, aligning well with both scanned and unscanned specimens.