Cementitious Permeable Pavement as an LID Practice for Hydrologic and Particle In-Situ Control

The development and application of multifunctional engineered permeable pavement, for example cementitious permeable pavement (CPP), can fulfill requirements for relatively smooth load-transmitting surfaces while serving as a more environmentally-conscious infrastructure material that functions to restore the in-situ hydrology and as a passive unit operation and process for treatment. This construction material technology reduces runoff, filters and treats infiltrating runoff pollution and reduces thermal pollution and temperature; while providing the load carrying capacity of conventional pavement. Cementitious permeable pavement (CPP) for rainfall-runoff has the potential to provide in-situ quantity and quality control. Two specific aspects of this control that have been the subject of significant interest and discussion are filtration and clogging. This study investigated filtration and clogging of CPP subject to stormwater particle loadings for a sandy-silt particle size gradation. The CPP was one component of an LID partial exfiltration reactor (PER) system that was designed as a pre-treatment and primary treatment interface for down-gradient secondary adsorptive-filtration in the PER. The CPP was installed and utilized at a source area loading site in urban Cincinnati, OH site subject to direct runoff loadings. Each CPP specimens had similar pore size distributions, with an effective porosity of greater than 20%, and total porosity that exceeded 25%. Results indicated total removal efficiencies exceeded 80%, and ranged from nearly complete removal for sediment-size particles to a 50% removal for suspended particles. Turbidity reductions were significant and effluent turbidity was generally reduced to below 10 NTU, with the reduction following a first-order exponential decline. Filtration by CPP included surficial straining and deep-bed filtration with the associated reduction of initial hydraulic conductivity for a fixed hydraulic gradient. For all loading conditions the initial hydraulic conductivity was reduced from that of clean coarse sand to fine silt. The hydraulic conductivity profiles illustrated a first-order exponential decline. Any unit operation or BMP that is effective requires regular maintenance; and CPP is no different. The high degree of effectiveness exhibited by CPP is a clear indication that the filtration capacity of CPP must be maintained. In-situ CPP cleaning methods illustrate that greater than 90% of the initial hydraulic conductivity can be restored after CPP clogging, respectively. Results provide a quantitative assessment of filtration, clogging and hydraulic restoration of CPP loaded by rainfall-runoff. CPP particle removal efficiency illustrated a dependence on loading concentration on a mass basis, as would be expected since higher mass concentrations were generally a result of more mass towards the coarser particle fractions.