Scaling phenomena due to fractal contact in concrete and rock fractures

Concrete-to-concrete friction contributes in many cases to the stability of a structure. At different scales, the slope stability of rock joints is deeply influenced by the surface morphology and shows a marked size-dependence. In this paper, the closure and sliding-dilatant behaviour of cracks in concrete and rocks is investigated by means of a coupled numerical/experimental approach. These natural interfaces show self-affine properties in the relevant scale range. Attention has been focused on the stress transfer mechanism across the interfaces, showing that the sets of contact points possess the self-similar character of lacunar fractal sets. Scaling laws come into play and the size-effects on the shear strength of rough interfaces, and on their closure deformability, can be explained.