The fracture process in concrete-like materials cannot be properly modelled
in an Euclidean framework, due to its complex morphology at the micro- and
meso-level. The inherent flaws interact through a multi-scale process, lea
ding to self-affine fracture surfaces. Moreover, the self-organized network
, of microcracks displays fractal properties prior to the formation of the
final fracture surface. At the same time, due to the presence of pores and
voids, the stress-carrying cross section is a rarefied fractal domain, even
from the beginning of the loading process. A new experimental equipment ha
s been developed which allows the entire fracture surface, or any plane cro
ss section, to be digitised and analysed. This represents an important prog
ress with respect to the study of one-dimensional profiles. In this paper,
the three-dimensional algorithms for evaluating the fractal dimension of in
vasive surfaces and lacunar sections are described. The invasive fractal ch
aracter of the fracture surfaces is confirmed. Moreover, the lacunar fracta
l character of the stress-carrying cross sections, a priori assumed by Carp
interi [A. Carpinteri, Mechanics of Materials 18 (1994) 259-266], is now pr
oven experimentally. (C) 1999 Elsevier Science B.V. All rights reserved.