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South Dakota Ready Mixed Concrete Association
Pervious, or permeable, concrete lets water from precipitation, storms, and flooding filter through to the soil and groundwater below. This reduces susceptibility to flooding and runoff volume, and can also help filter pollutants that would otherwise run off impervious pavement. After being mixed with less sand and fine particles than conventional asphalt, the concrete is then laid above crushed stone aggregate base to allow for water infiltration. Water is able to permeate the concrete due to void spaces of 18 - 20%, which also reduces the weight of pervious concrete by 20-30% compared to conventional concrete (this can reduce transportation emissions). Rigid pavements like concrete typically do not require aggregate bases for structural stability, though deep aggregate bases are recommended for cold climates like the northeast. Suppliers are easy to find, as pervious concrete can be mixed and applied using the same equipment and methods as impervious concrete, though the lack of fine particles gives pervious concrete a coarser look than conventional concrete. Water flow rates through pervious concrete are usually around 480 in./hr (0.34 cm/s, 5 gal/ft²/ min, or 200 L/m²/min) (National Ready Mixed Concrete Association).
As with other pervious pavements, proper maintenance (primarily vacuum sweeping) is necessary to maintain high rates of infiltration. Infiltration rates are also highly dependent on the subgrade soil. Sandy soils have highest infiltration capacity and increased load bearing capacity, but lower treatment capacity. Potholes and cracks can be fixed with patching mixes unless >10% of the surface needs replacement. The maximum slope of pervious concrete exceeds porous asphalt, allowing for a slope of up to 12% while maintaining infiltration.
Permeable or pervious concrete is often confused with the similar porous asphalt. Regular concrete uses cement as the binding agent, while asphalt uses tar; this is the main difference in their respective porous options, with the result that concrete is generally more expensive but more durable. Learn more about the latter in our Use Porous Asphalt toolkit.
Potential regulatory touchpoints in Boston and Massachusetts include: