Nondestructive experimental characterization and numerical simulation on self-healing and chloride ion transport in cracked ultra-high performance concrete

Ultra-high performance concrete (UHPC) contains a large number of unhydrated particles which are prone for self-healing in the presence of water. In this work, three-dimensional X-ray microscope was employed to investigate the self-healing degree. To aid in understanding the evolution of self-healing, a hydration model CEMHYD3D was utilized to simulate the distribution of solids and pores phase in a cracked microstructure. Based on the random walk model, the influence of crack self-healing degree on chloride ion transport process was analysed. The results show that the smaller crack width and the longer healing time reflect a lager self-healing degree. According to the rehydration products, it was found that portlandite crystallizes in the middle of the crack while C-S-H gel accumulates only on the crack surface. Moreover, the ions transport depths in cracked UHPC was simulated by finite difference method. As time increases, chloride ions not only transport vertically along the crack, but also propagate in the horizontal direction of the crack. Mixture proportions have little influence on the diffusion coefficient of chloride ion.