Permeable pavements: Specifications

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Specifications for pervious concrete, porous asphalt, and permeable pavers
Material Specification Quantity
Pervious concrete
  • NO4-RG-S7 mix with air entrainment proven to have the best freeze-thaw durability after 300 freeze-thaw cycles.
  • 28 day compressive strength = 5.5 to 20 MPa.
  • Porosity between 14% to 31%.
  • Permeability = 900 to 21,500 mm/hr.
  • Proprietary pre-cast slabs meeting required specifications are also available.
Thickness will range from 100 mm - 150 mm depending on the expected loads.
Porous asphalt
  • Open-graded asphalt mix with a minimum porosity of 16%.
  • Polymers can be added to provide additional strength to heavy loads.
  • The University of New Hampshire Stormwater Center has detailed design specifications for porous asphalt.
Thickness will range from 50 mm - 100 mm depending on the expected loads.
Permeable Interlocking Pavements
  • Pavers shall meet the minimum material and standard specifications for precast concrete pavers (CSA A231.2 in Canada; ASTM C936 in United States).
  • Open space between pavers (i.e. joint space) typically ranges between 5 and 15% of the total surface area.
  • ASTM No. 8 (5 mm dia.) crushed aggregate is recommended for fill material in the paver joints (typically HPB).
  • For narrow joint pavers, a smaller sized aggregate may be used. Narrow joints are required where pavement must be AODA compliant.
  • For vehicle applications the minimum paver thickness is 80 mm
  • For pedestrian applications the minimum paver thickness is 60 mm and joint widths should be no greater than 15 mm.
Stone Resevoir
  • All aggregates should meet the following criteria: (i) maximum wash loss of 0.5%, (ii) minimum durability index of 35, (iii) maximum abrasion of 10% for

100 revolutions and maximum of 50% for 500 revolutions

  • Most OPSS aggregates are not recommended for PP, with the exception of ‘granular O’.
  • The granular subbase material shall consist of granular material graded in accordance with ASTM D 2940. Material should be clear crushed 50 mm diameter stone with void space ratio of 0.4.
  • The granular base material shall be crushed stone conforming to ASTM C 33 No 57. Material should be clear crushed 20 mm diameter stone.
  • The granular bedding material shall be graded in accordance with ASTM C 33 No 8. Typical bedding thickness is 40 to 75 mm. Material should be 5 mm diameter stone or as determined by the Design Engineer. In Ontario, high performance bedding (1 to 9 mm diameter) or equivalent is often used.
  • See LID Planning and Design Wiki (Permeable pavements: Sizing) to size aggregate bed depth and multiply by application area to get total volume.
  • Should be woven monofilament or non-woven needle punched fabrics. Woven slit film and non-woven heat bonded fabrics should not be used as they are prone to clogging.
  • Primary considerations for Geotextile are:
    • suitable apparent opening size (AOS) for non-woven fabrics, or percent open area (POA) for woven fabrics, to maintain water flow even with sediment and microbial film build-up
    • maximum forces to be exerted on the fabric (i.e tensile, tear and puncture strengths required)
    • load bearing ratio of the underlying native soil (i.e. is geotextile needed to prevent downward migration of aggregate into the native soil?),
    • grain size distribution of the overlying aggregate material, and
    • permeability of the native soil.
  • Geotextiles are not always necessary and may be prone to eventual clogging. Consider using sand or fine aggregates instead. Where they are necessary (typically on low strength soils of CBR <4) between stone reservoir and native soil, material specifications should conform to Ontario Provincial Standard Specification (OPSS) 1860 for Class II geotextile fabrics. Geotextile socks on pipes should conform to ASTM D6707 with a min. water flow rate conforming to ASTM D4491 (12,263 L/min/m2 at 5 cm head).
Underdrain (optional)
  • PVC or HDPE, continuously perforated with smooth interior and a minimum inside diameter of 200 mm.
  • Perforations in pipes should be 10 mm in diameter.
  • A standpipe from the underdrain to the pavement surface can be used for monitoring and maintenance of the underdrain. The top of the standpipe should be covered with a screw cap and a vandal-proof lock.

Pipes should terminate 0.3 m short from the sides of the base.