The chloride diffusivity of ultra-high performance concrete (UHPC) is the key parameter that determines the service life of UHPC structures in chloride environments. In this study, a multi-scale model, which considered the structural information at micro and meso-scale, was proposed to predict macro property, i.e. chloride diffusivity, of UHPC. At micro-scale, the chloride diffusivity of UHPC paste was predicted based on an extended HYMOSTRUC3D model and a finite element method. At meso-scale, Anm model and finite element method were applied to calculate the chloride diffusivity of UHPC mortar. At macro-scale, the chloride diffusivity of UHPC was determined with a two phase model. The chloride diffusivity at a lower scale was used as input to predict the chloride diffusivity at the higher scale. Non-steady chloride diffusion tests were performed to validate the proposed model. The results showed that the proposed multi-scale model gave a little higher chloride diffusivity of UHPC than experiment results. However, the proposed model is still helpful for the durability design of UHPC structure in chloride environments.@en

The flexural response of ultrahigh performance fiber-reinforced concrete (UHPFRC) was simulated based on the lattice fracture model. Fiber was modelled as separated beam that was connected to the matrix with interface beams. The simulated results were compared with the experimental results. Deviations occurred at the late stage of the strain-softening period. But both the strain-hardening behavior and multicracking phenomenon were observed in the simulation. The effects of fiber orientation and fiber content were studied with the lattice fracture model. The flexural strength and toughness of UHPFRC improved as the fibers were aligned distributed or the fiber content increased. The proposed model has the potential to help with the materials design of UHPFRC, and the limitations of the model were also discussed in the paper.@en