Orientation coefficient in ultra-high performance fiber reinforced concrete and its relationship with casting methods Coeficiente de orientación en el hormigón de muy alto rendimiento reforzado con fibras y su relación con los métodos de hormigonado

Ultra-high-performance fiber-reinforced concrete (UHPFRC) exhibits outstanding mechanical and durability performance, strongly influenced by fiber orientation. This study evaluates the fiber orientation coefficient considering casting methods, element geometry, and thickness effects. Beams (100×100×500 mm³ and 150×150×600 mm³) and slabs (1000×50×1000 mm³) were analyzed. Beams were cast horizontally (with fixed and moving pouring points) and vertically (at different casting speeds). Slabs were cast using fixed and moving pouring points and later cut into longitudinal and transverse specimens. A total of 84 prisms were tested in flexure to determine tensile properties. Results show that casting procedures, structural typology, and thickness significantly affect fiber distribution and tensile behavior. Horizontal beams displayed lower variability, whereas slabs showed marked differences associated with their bidirectional configuration. Fiber orientation was found to influence constitutive law parameters. A good correlation was found between UNE 83519 results and UHPFRCMat app simulations. Reference orientation coefficients are proposed to support structural design.