Characteristics of concrete cracks and their influence on chloride penetration

摘要

Concrete cracking usually is an unavoidable phenomenon in reinforced concrete (RC) structures and has a significant effect on chloride diffusion and thus the deterioration of the structures. However, actual concrete cracks have complicated characteristics, and the mechanisms in which they influence the chloride penetration have not yet been well clarified. This study presents a careful quantification of the geometrical parameters of actual concrete cracks, including density, orientation, tortuosity and width, and explores their correlation with the chloride diffusion properties of concrete. Uni-axial compression tests were conducted on concrete specimens to create various extents of cracking severity. Afterwards, a non-steady state migration method was employed to evaluate the diffusivity of sound and cracked concretes. The geometry parameters of concrete cracks were quantified by an image analysis technique after the migration tests. The test results suggest a linear relationship between the crack tortuosity and the degree of crack orientation. In addition, chloride diffusion into concrete depends greatly on the crack density and crack tortuosity in addition to the crack width. In particular, the crack tortuosity is a critical factor influencing chloride penetration when the crack width ranges from 150 to 370 μm. Considering the crack tortuosity and orientation, the effective crack width and effective crack density are proposed as correlated with the chloride diffusivity of cracked concrete.