asphalt

The green alternative to traditional asphalt

Monday, August 26, 2013

New sustainable technologies have been groundbreaking for property owners and developers – literally. Permeable pavement, a ‘green’ alternative to normal asphalt, has been gaining ground around the world due to its porousness and ability to reduce run-off.

Here, Karen Leasa and Michael A. Ormston-Holloway of the Planning Partnership explain what permeable pavement can offer property managers and developers.

How does permeable pavement work?

Permeable pavement, also known as pervious or porous paving, is a type of hard surfacing that allows rainfall to percolate to an underlying base or catchment zone. Rainfall either infiltrates to underlying soil or is removed by subsurface drainage infrastructure.

Typical surfaces such as asphalt and concrete used in most roadway, parking lots and sidewalk applications are ‘impermeable.’ This means that when precipitation occurs, the surface does not allow for percolation or infiltration into soils below and instead creates surface run-off conditions, which carries pollutants into sewers and streambeds.

Permeable pavement is an excellent tool in helping to restore the natural water cycle in urban landscapes. Some examples include unit paving blocks or cobblestones with porous joints, specialty mixes of porous concrete and asphalt, and grid systems filled with sand, gravel or specific vegetation. All of these options either provide a combination of permeable joints and open-graded bedding courses, or the paving components themselves are comprised of a larger matrix of ‘pores,’ or aggregate mixes that allow water and air to migrate quickly through the material.

What are the benefits of permeable pavement versus traditional pavement?

Permeable pavement can substantially reduce the amount of run-off volume on-site, which, in turn, reduces the effect of erosion and sedimentation in local streams and tributaries. It also allows natural groundwater recharge to occur by allowing rainwater to percolate into subsoils and back into the water table. It helps in periods of peak flow to moderate infiltration rates.

Integrating permeable pavement into a site design not only reduces the size and amount of stormwater management infrastructure required but it also lowers the amount of stormwater flow processed through the municipal system.

The naturally occurring microorganisms found in the pores of permeable pavers can help to filter out and break down pollutants suspended in surface run-off such as total suspended solids (TSS), phosphorous, nitrogen, zinc, motor oil and copper.

Why should property owners and developers make the switch from regular pavement? And are there any incentives to do so?

Permeable pavement can be a cost-effective alternative in new development areas where run-off reductions from infiltration can reduce or eliminate the need for expensive drainage infrastructure.

With the reduction or elimination of stormwater management basins and drainage infrastructure, the income potential of the property increases as more space becomes available for other development. Change in paving surfacing can also increase the curb appeal of a property, thus increasing value.

In addition, LEED (Leadership in Energy and Environmental Design) points are available for sustainable sites, water efficiency, materials and resources, and innovative design categories.

Are there any drawbacks to permeable pavement due to maintenance or cost?

The cost of permeable pavement can be approximately two to three times that of traditional asphalt; however, the reduction or complete elimination of a more extensive stormwater management system can offset this cost.

Asphalt requires more regular maintenance than permeable pavement, which has minimal maintenance requirements. This typically involves vacuuming of joints each season (depending on usage) and the occasional cleaning of aggregate and restriping of lines.

The Canadian climate does present special challenges for most building materials, including permeable pavement. In winter months, road salts that are used on these surfaces may contain chlorides that have the potential to migrate through the porous pavement into the groundwater below. Snowplow blades can also cause damage to paver edges and surfaces.

Although proper installation and design of a paving system will mitigate the risk, there is the potential for minor frost heave in applications in northern climates where run-off can freeze below the pavement. However, there are many examples of successful installations of permeable pavement in cold climates. It has shown that the increased surface drainage also allows for higher rates of snowmelt and, in turn, lower snow removal costs, salt application and liability associated with icy surfaces.

Has the use of permeable pavement taken off in Canada? If so, are any groups or sectors leading the charge?

The use of permeable pavement in Canada is slowly taking root within a growing number of municipalities that are focusing on better stormwater management practices. They are finding innovative ways to deal with unique site conditions and environmental regulations to protect the country’s waterways for future generations.

The Toronto and Region Conservation Authority has developed the Sustainable Technologies Evaluation Program (STEP), which helps provide the data and analytical tools necessary to support broader implementation of sustainable technologies and practices within Canada. The program has completed a three-year evaluation on a variety of permeable pavements in cold climates. Its findings highlighted that current products available on the market performed well in these conditions and are ideal for older built-up areas that lack stormwater management as well as newer developed areas where reduced run-off from infiltration can cut down on municipal sewer infrastructure.

Karen Leasa is a landscape designer with the Planning Partnership, and a LEED accredited professional. Michael A. Ormston-Holloway is an associate at the Planning Partnership, where he works in both landscape and urban ecology. He currently lectures at the University of Toronto, University of Waterloo and University of Guelph.

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