Permeability Reduction in Pervious Concretes due to Clogging: Experiments and Modeling

The ability of in-place pervious concretes to effectively drain storm water runoff gradually reduces as it becomes clogged due to the ingress of fine particles into its pore structure. This study systematically investigates several pervious concrete mixtures proportioned using different size aggregates and their blends on their propensity to clogging so as to bring out the influence of pore structure features on particle retention and the consequent permeability reduction. A finer and a coarser sand are used as clogging materials and the experimental study on permeability reduction (as a result of particle retention) is carried out using a falling head permeability cell. Significant permeability reductions are observed when finer sand is used as the clogging material. A certain effective pore size to clogging particle size ratio is found in this study, that is most conducive to particle retention. Thus pervious concrete specimens of similar porosity, having very large $\left(\sim 5–6\text{mm}\right)$ or very small $\left(\sim 1–2\text{mm}\right)$ pore sizes are found to be less susceptible to clogging under the conditions of this study. An idealized three-dimensional geometry obtained from two-dimensional planar images of pervious concrete sections is used, along with a probablistic particle capture model to predict particle retention associated with clogging material addition and simulated runoff. The trends in the predicted particle retention and the experimentally determined permeability reduction agree well. A “clogging potential” is defined in this paper, either as a ratio of the porosity reduction because of clogging to the initial porosity, or as a ratio of the permeability reduction to the permability in the unclogged state.