Differences in Distribution and Orientation of Industrial and Recycled Steel Fibers on Fiber-Reinforced Self-Compacting Concrete Using Computed Tomography

Fiber properties significantly influence the behavior of steel fiber-reinforced self-compacting concrete (SFRSCC), mainly through their effect on fiber distribution and orientation. This study investigated two main aspects of SFRSCC: (1) the influence of fiber type (industrial and recycled steel fibers), fiber dosage, and specimen depth on fiber distribution and orientation, and (2) the structural performance of SFRSCC and its relationship with fiber type, distribution, and orientation. Four SFRSCC slabs containing different types and dosages of steel fibers were cast from the center outward. Cylindrical specimens were extracted and notched either parallel (θ = 0°) or perpendicular (θ = 90°) to the concrete flow direction to evaluate the influence of fiber orientation on tensile behavior. Splitting tensile tests were performed to assess post-cracking performance. Fiber distribution and orientation were analyzed using digital image analysis (DIA) and micro-computed tomography (CT) on cut sections of the specimens. The results indicated that the use of recycled steel fibers leads to a reduction in tensile performance compared with industrial fibers; however, their structural use remains feasible and offers environmental benefits by valorizing waste materials and reducing the carbon footprint of fiber-reinforced concrete. CT analysis provided accurate three-dimensional characterization of fiber orientation and distribution, revealing clustering effects in recycled fiber mixes not detectable by DIA.