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[[Properties of permeable pavement]]
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Revision as of 20:47, 5 December 2012

illustration of pervious concrete

Pervious concrete is a special type of concrete with a high porosity that allows water from precipitation and other sources to pass directly through.

The most commonly used permeable pavement surfaces are pervious concrete, porous asphalt and permeable interlocking pavers. Lesser utilized options include plastic grids and amended soils (artificial media added to soil to maintain soil structure and prevent compaction) (MPCA 2008). For the purpose of this document, the focus will be on pervious concrete, porous asphalt and permeable interlocking pavers.

Pervious concrete is a special type of concrete with a high porosity used for concrete flatwork applications that allows water from precipitation and other sources to pass directly through, thereby reducing the runoff from a site and allowing groundwater recharge. The high porosity is attained by a highly interconnected void content. Typically pervious concrete has little or no fine aggregate and has just enough cementitious paste to coat the coarse aggregate particles while preserving the interconnectivity of the voids. Pervious concrete is traditionally used in parking areas, areas with light traffic, residential streets, pedestrian walkways, and greenhouses.

Porous asphalt is standard hot-mix asphalt with reduced sand or fines and allows water to drain through it. Porous asphalt over an aggregate storage bed will reduce stormwater runoff volume, rate, and pollutants. The reduced fines leave stable air pockets in the asphalt. The interconnected void space allows stormwater to flow through the asphalt as shown in Figure 1, and enter a crushed stone aggregate bedding layer and base that supports the asphalt while providing storage and runoff treatment. When properly constructed, porous asphalt is a durable and cost competitive alternative to conventional asphalt.

illustration of porous asphalt

Porous asphalt is standard hot-mix asphalt that allows water to drain through it.

illustration of permeable interlocking pavement

Permeable interlocking pavers consist of concrete or stone units with open, permeable spaces between the units.

Permeable interlocking concrete pavement (PICP) consists of concrete (or stone) paver units with open, permeable spaces between the units. They give an architectural appearance, and can bear both light and heavy traffic, particularly interlocking concrete pavers, excepting high-volume or high-speed roads. Some products are polymer-coated and entirely porous face. Other variants not discussed in the articles on permeable pavement include single-sized aggregate, porous turf, permeable clay brick pavements, resin bound paving, and bound recycled glass porous pavement.

For each of the pavement surfaces presented above, there are many design variants depending on the design goals. For instance, permeable pavement can be installed with a deep underlying reservoir consisting of well graded, crushed rock. This design provides both water quality and quantity control by storing runoff and infiltrating it into the subgrade soils over an extended period of time. A second design variation may include only a thin layer of sand and crushed stone under the permeable pavement for structural support only. This type of system would be less expensive; however, it will only provide minor water quality and quantity control due to its minimal storage capacity. A thirddesign variation includes a deep underlying reservoir consisting of well graded, crushed rock above an impermeable layer of soil or a liner and an underdrain. The underdrain will typically discharge to a stormwater pond or storm sewer system. This design provides some runoff attenuation, filtering, and volume reduction. All three variations do not provide the same treatment.

To assist with selection of the type of surface, a general comparison of the properties of the three major permeable pavement types is provided below. Designers should check with product vendors and the local review authority to determine specific requirements and capabilities of each system. Schematic cross sections of each system are illustrated in the design section for permeable pavement.

Summary of properties of permeable pavements.
Link to this table

Properties Pervious concrete Porous asphalt PICP
Typical pavement surface thicknessa 5 to 8 inches 3 to 4 inches (thicker for high wheel load applications) 3 inchesa
Bedding layera,f None 1 in. AASHTO No. 57 stone 2 inches of AASHTO No. 8 stone (MnDOT 3127 FA-3)
Reservoir layerb,f AASHTO No. 57 stone or per hydraulic design AASHTO No. 2, 3, or 5 stone 4 inches of AASHTO No. 57 stone over No. 2, 3 or 4 stone
Construction properties
  • Cast in place
  • Seven day cure
  • Must be continuously covered
  • Cast in place
  • 24 hour cure
  • No cure period
  • Manual or mechanical installation of pre-manufactured units
Installed surfacing costc 3 to $4/square foot $2/square foot 3 to $4/square foot
Minimum batch size
20 to 30 years
Catch basin, overflow edge, elevated underdrain
Runoff temperature reduction
Cooling at the reservoir layer
Surface colors/texture Range of light colors and textures Black or dark grey colors Wide range of colors, textures and patterns
Load bearing capacitye
Handles all vehicle loads with appropriate surface and base/subbase layer material and thickness design
Surface cleaningg
Periodic vacuuming; replace if completely clogged and uncleanable
Periodic vacuuming; replace jointing stones if completely clogged and uncleanable
Other issues
  • Avoid concentrated deicers
  • Avoid winter sanding
  • Avoid seal coating
  • Avoid winter sanding
Avoid winter sanding
Design reference Report 522-2010 Hansen 2008NAPA Smith 2011 ICPI

aThickness may vary depending on site and traffic conditions
bReservoir storage may be augmented by corrugated metal pipes, plastic arch pipe or plastic lattice crates
cSupply and install minimum surface thickness only; minimum 30,000 sf with Minnesota 2012 prevailing labor wages. Does not include base reservoir, drainage appurtenances, engineering, or inspection
dBased on pavement being properly maintained. Resurfacing or rehabilitation may be needed after the indicated period
eDepends primarily on on-site geotechnical considerations and structural design computations
f ASTM D448 Standard Classification for Sizes of Aggregate for Road and Bridge Construction or ASASHTO M-43
gPeriodic vacuuming frequency determined from inspection, intensity of use, and other potential sediment sources

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