Complex fracture energy dissipation in concrete under different loading conditions

Two different investigations on the scaling properties of damage in concrete have been carried out. In the case of uniaxial tensile tests, a laser profilometer was adopted to scan the post-mortem fracture surfaces. In the case of compression tests, a fusible alloy (Wood's metal) was injected inside the specimen under load (ante-mortem). Afterwards, scanning electron microscope was used on the sliced specimens to detect the stress-induced crack patterns. The highly localized energy dissipation in uniaxial tension evolves from a narrow damage band to a fracture surface with fractal dimension comprised between 2.0 and 2.5. The microcracks networks induced by compression present fractal dimension even larger than 2.5 in the bulk. Fractality permits to explain some aspects of the fracture behavior, like the stable crack growth encountered in the tests and the smoothing of the dynamic stress-intensify factor which causes the cracks to propagate slower than at the theoretical Raleigh speed. (C) 1997 Elsevier Science Ltd.