Assessment of clogging potential of pervious concrete
The Edwards Aquifer is an EPA designated sole source for drinking water supply in south central Texas. It serves San Antonio and surrounding small cities for the last two centuries. But, as the cities are growing augmented land development activities causes hazard to the Edwards Aquifer. Urbanization badly affecting ground water recharge as runoff resulted from rainfall amplifies with imperviousness. Impervious cover needs to be controlled to maintain the natural quality and quantity of recharge. EPA enlisted use of pervious concrete in sidewalks and parking lots as a best management practices (BMP). Pervious concrete can help to keep natural hydrologic infiltration rates on developed properties. But, continuing deposition of fine materials present in runoff water, or the presence of heavy metals, oil and grease, and other contaminants present in the urban stormwater runoff causes clogging problems in pervious concrete. Clogging decreases the porosity, permeability, and hence the infiltration pace of a system.
As the primary advantages of pervious concrete is its ability to rapidly transport water, understanding the clogging issue of pervious concrete is essential before recommending this technology to use as an alternative pavement option. Previous field performance investigation confirmed that properly designed, constructed, and maintained pervious concrete pavements showed negligible amounts of clogging even after many years of service.
The X-ray Computed Tomography (CT) technology and image processing and analysis software have been used to determine the long-term performance of pervious concrete in respect to clogging. To perform these tests, synthetic urban stormwater runoff have been prepared and applied on the pervious concrete samples in the laboratory. Using X-ray CT technology available at Advanced Characterization of Infrastructure Materials (ACIM) laboratory of Texas A&M University, 2D analysis of void structure in pervious concrete specimens has been performed. The image analyses encourage us to neglect clogging potential issue of pervious concrete. Three dimensional images of air voids across the depth shows that the pores inside the pervious concrete specimens remain almost the same even after application of synthetic urban runoff estimated from 20 years average rainfall. Air void distribution graphs across the depth of the specimens before and after applying the runoff gives much interesting result. It shows that there is no significant clogging happened in the concrete portion of the cylinder. But, clogging happened in the subbase portion of the cylinder especially in the interface change portion. At that section, lots of voids have been filled with pollutant and fine materials present in the runoff water. Moreover, synthetic urban stormwater runoff has been applied on pervious concrete specimens and coefficient of permeability has been measured. The result shows that clogging happened with time but runoff water still passes through the specimens in a satisfactory rate.
The pervious concrete minimizes the adverse effects of development by reducing runoff and increasing groundwater recharge. This study suggests that pervious concrete is a sustainable technology and can be used for the parking lot and low volume urban streets construction over Edwards Aquifer recharge zone.