3D cohesive fracture of heterogeneous CA-UHPC: A mesoscale investigation

Abstract

Ultra high performance concrete with coarse aggregates (CA-UHPC) exhibits complicated damage and failure mechanisms due to intricate interactions of irregular mesoscale phases, including random aggregates, fibres, mortar, and interfaces. This work proposes a 3D numerical framework to investigate the complex cohesive fracture of CA-UHPC at mesoscale for the first time. Automatic algorithms are proposed to model realistic aggregates, mortar, aggregate-mortar interfaces and steel fibres in large quantities. Zero-thickness cohesive interface elements are automatically inserted in the mortar and on the aggregate surfaces to capture potential cracks, and an efficient non-conforming methodology is developed to model the fibre-mortar bond-slip behaviour using orientation-dependant pullout force-slip relations. The proposed models are validated using typical uniaxial tension tests, and elucidate that the progressive interactions of aggregate barrier, interfacial cracking and fibre bridging govern the early cracking, strain-hardening behaviour, fibre activation and final crack networks. Quantitative analyses are performed to optimize the mechanical properties of CA-UHPC: as the aggregate content increases, there are more torturous crack surfaces and fewer activated fibres with lower load-carrying capacities, but the downside of coarse aggregates can be alleviated by increasing fibre content, especially when needing aggregates to reduce carbon footprints and improve anti-shrinkage performance.