Porous Asphalt

Usage: Pilot

Asphaltic concrete with open-graded aggregate, in which the amount of fine particles is kept to a minimum, and in which the binder content is lower, allowing water to pass through into an open-graded reservoir.

Craig Road N, Governors Island
Porous asphalt

Benefits

See benefits of Asphaltic Concrete

  • Reduces impermeable surface, thereby increasing water infiltration
  • Exhibits structural properties similar to conventional asphalt
  • Reduces peak sewer discharge during storm events
  • Reduces likelihood of ponding and slick or icy road conditions
  • Helps reduce urban heat island effect

Considerations

See considerations for Asphaltic Concrete

  • Extra care must be taken where there is water-sensitive sub-surface infrastructure
  • Only certain soil types are appropriate as sub-bases for infiltration
  • Porosity of pavement can convey harmful materials into the soil
  • Sand and certain chemical de-icers should not be applied to surface

Application

  • Porous asphalt is a pilot material that the city is testing at select locations
  • Use of this material beyond the city-led pilots will require a maintenance agreement
  • Can be proposed for use in parking lanes, parking lots, and recreational paths
  • Most effective on slopes less than 5%
  • Must have adequate sub-surface conditions to detain stormwater and level bottom to allow for stormwater infiltration
  • Avoid sites where there is high potential for soil and groundwater contamination
  • Not recommended for implementation over significant underground utility corridors

Design

  • No specification source
  • Minimum 3-inch-thick wearing course, typically
  • Roadway should be crowned to drain stormwater from the road surface
  • Aggregate gradation should be engineered to provide open gradation and an adequate stone matrix
  • Bitumen content should be lower than in standard Asphaltic Concrete, as necessary for the provided gradation
  • Do not seal coat
  • Typically, a 12 – 30-inch open graded stone infiltration bed is recommended.
  • Bottom of infiltration bed should be at least 2 feet above high water table and 2 feet above bedrock
  • Consider use in gutter area near pedestrian ramps to reduce ponding

Maintenance

  • Requires vacuuming of surface with regenerative air sweepers to maintain permeability and prevent clogging
  • Difficult and more expensive to replace or patch in sections where utility cuts or defects occur

 

Parking lot paved with porous asphalt

Porous asphalt in parking lot at the Bronx Zoo: Bronx

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