Similarity properties of demineralization and degradation of cracked porous materials

The paper analyze the similarity properties of demineralization processes i n cracked porous materials, coupled with diffusive and advective mass trans fer through fractures. The aim is to find out, whether, when and how fractu res accelerate or magnify the overall chemical degradation process. A dimen sional analysis of a simplified dissolution process around a fracture chann el reveals different self-similar properties for diffusion and advection do minated mass transport in the fracture. For a pure diffusive transport, the fracture degradation length develops with the quadratic root of time; whil e it evolves with the square root of time when advection dominates. These a symptotic behaviors are confirmed by model-based simulations of 'real' calc ium leaching in cracked cement-based materials. It is shown, that a diffusi on dominated mass transport in a fracture does not significantly accelerate the overall chemical degradation, since the one-dimensional-degradation th rough the porous material catches up with the initially faster diffusion th rough the fracture. In turn, advection dominated mass transfer in fractures can significantly accelerate the overall calcium depletion for 'high' flui d velocities in the fracture. Finally, diffusive dominated mass transport i n a crack network may also accelerate the calcium leaching process for smal l values of crack spacing factors. A rough analytical solution for estimati ng this effect of a crack network is derived and validated through model-ba sed simulations. (C) 2001 Elsevier Science Ltd. All rights reserved.