A micro-macro description of the engineering properties of randomly inhomogeneous cement-based composites

Cement-based composites, reinforced with randomly distributed short fibers exhibit a nonlinear behavior, called damage, which could be described in terms of microcrack initiation, growth and coalescence leading to the creation of macrocracks. A Micromechanics-based continuum damage mechanics MBCDM model is proposed for the prediction of the effect of initial microcrack configuration on the macroscopic young's modulus and thermodynamic force associated with the chosen damage variable. Parametric studies for a number of periodic crack distributions in a two-dimensional case have been carried out. Both brittle (un-reinforced) and fiber reinforced cementitious materials have been considered. It is shown that low-order damage measures cannot capture the difference between crack distributions that yield markedly different global behaviors. Simulation results reveal that, whereas the evolution of the normalized stiffness is practically the same for all configurations over the entire range of damage variation, the damage thermodynamic force is different for each case. The results predicted by the proposed approach, agree rather well with experimental observations.