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In the present paper the mechanical compressive behaviour of quasi-brittle materials is analyzed by means of an ad hoc boundary element
algorithm. The analysis is carried out by taking into account the initial crack distribution, which cannot be neglected if the experimental reality
(developing over three scale levels, micro-, meso- and macro-scale) is to be modelled.
The algorithm permits to follow the evolution of the crack geometry during the loading process, which is characterized, at each step, by the
propagation of the most critical meso- or macro-crack. Moreover, in order to take into account the micro-crack effect causing the progressive decay
of the material, a decreasing variation of the elastic modulus is assumed, depending on the strain energy density absorbed during the loading
process.
Different geometries, with different slenderness and size-scale, are considered by the proposed model, with and without friction between specimen
and loading platens. The numerical simulations represent the experimental results consistently.