COMPLEX FRACTURE ENERGY-DISSIPATION IN CONCRETE UNDER DIFFERENT LOADING CONDITIONS

Two different investigations on the scaling properties of damage in co ncrete have been carried out. In the case of uniaxial tensile tests, a laser profilometer was adopted to scan the post-mortem fracture surfa ces. 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 dete ct the stress-induced crack patterns. The highly localized energy diss ipation in uniaxial tension evolves from a narrow damage band to a fra cture surface with fractal dimension comprised between 2.0 and 2.5. Th e microcracks networks induced by compression present fractal dimensio n even larger than 2.5 in the bulk. Fractality permits to explain some aspects of the fracture behavior, like the stable crack growth encoun tered in the tests and the smoothing of the dynamic stress-intensify f actor which causes the cracks to propagate slower than at the theoreti cal Raleigh speed. (C) 1997 Elsevier Science Ltd.