Multiscale analysis of carbon microfiber reinforcement on fracture behavior of ultra-high-performance concrete

• Carbon microfibers significantly enhance UHPFRC’s fracture resistance. • Multiscale analysis reveals impact of microfiber reinforcement on pore structure. • Optimized carbon microfiber content improves fracture energy and tensile strength. • Advanced X-ray CT and SEM techniques link fiber distribution to mechanical behavior. This study delves into the intricate world of ultra-high-performance concrete, specifically how its mechanical integrity and fracture resistance are influenced by the incorporation of carbon microfibers of varying lengths. Employing a suite of multiscale analytical techniques, we link the mechanical attributes of concrete to its microstructural composition, with a keen focus on porosity distribution as revealed by advanced X-ray computed tomography and porosimetry assessments. We uncover how the selection of microfiber type affects the concrete’s internal pore landscape, which in turn dictates the material’s fracture behavior. An innovative use of inverse analysis, based on established fracture mechanics, allows us to formulate cohesive laws for the fracture process zone. Our results uncover a direct correlation between the variability in fracture properties and the specific types and amounts of fibers used, providing mix designers with critical insights for customizing concrete formulations to meet precise performance criteria.