In this study, we consider a mathematical model and numerical treatment for the aggregate alkali reaction in fluid leaching processes. This subject is of special interest in analysis of concrete dams in civil engineering and the numerical investigations carried out here are directed towards a better understanding of the model and process in this context. Of particular interest are effects of surface imperfection on the subsequent coupled moisture transport and the reactive formation of gel in the granular porous medium. The numerical experiments also consider the influence of periodic and nonperiodic inhomogeneities in material diffusivity properties. (C) 2003 Elsevier B.V. All rights reserved.