There are many reasons for cities to install permeable surfacing. Most importantly, it reduces stormwater runoff. According to the City of Toronto, “The combination of heavy rain and hard surfaces covering the city is resulting in more water making its way into the stormwater system. Too much water in the City’s stormwater system can overwhelm it, leading to flooded basements and poor water quality in local waterways, including Lake Ontario.” However, the permeable surfacing options available in North America do have their drawbacks. Therefore, developers and municipalities are hesitant to install them at scale. Here’s a review of known permeable surfacing options in North America.
Review of Known Permeable Surfacing Options in North America
Permeable Concrete sounds reliable. In fact, concrete has been a staple in the construction of cities since its invention. However, when engineers remove fine aggregates from concrete it becomes structurally flawed by design. Cement, as a binding agent, isn’t designed to hold large aggregates together and support vehicular traffic as usual. Also, it’s incapable of maintaining porosity. Permeable concrete must be thick (8 inch minimum) in order to provide a walkable structure. So, it’s difficult for particles to pass though thicker permeable pavement. Particles accumulate and clog with high speed. Additionally, after installation, permeable concrete is vulnerable to cracking, salt and frost/thaw damage and stone loss from snow removal. Therefore, concrete, our trusted city builder, doesn’t mesh well with porosity.
Permeable Asphalt is thinner than permeable concrete. Though, in terms of structural integrity, the principal issues that apply to permeable concrete are at play here too. Asphalt bitumen is not meant to bind large aggregates. Instead, it’s a mix of mostly fine and small-aggregates heated, blended and compacted. Permeable asphalt does withstand clogging quite well. However, stone loss is present almost immediately upon use in winter climates. Also, winter salt use damages asphalt, making it even more vulnerable as a permeable structure.
Permeable Pavers are regular pavers which are spaced-out further apart from one another than typically designed. The spacing between bricks allows water to pass and drain through a fine-aggregate bed that connects each paver. Though, this leads to rapid clogging since the surface area ratio of permeable to sealed surface is so low. So, there remains a runoff coefficient with this method. Also, the spacing between bricks leads to structural flaws. The bricks pop out of place as they gradually rise over time.
Plastic Grid Paving
Plastic Grid Paving systems are gaining popularity. From Europe to North America these systems are known for their strength in industrial applications. Grid systems hold loose gravel in place within individual cells. Water permeates through the clear-stone sub base. There’s no pavement binder with these systems. They function as loose-finish solutions. Loose aggregate can migrate during snow removal. Therefore, in winter climates, grid systems may require additional gravel to be spread over top.
Decorative Epoxy Permeable Surfacing
Decorative Epoxy systems have introduced the same concept used to produce stunning natural aggregate surfaces indoors to various pedestrian applications outside. The issues with epoxy in winterized climates appear to be its inherent chemical properties. It’s just not designed for winter outdoor applications. The material often fractures within the first winter. Plus, stone loss is prominent with these systems. In winter climates, ground movement and varying temperatures are at play. Therefore, decorative epoxy is not recommended for outdoor paving in winter climates. Though, various European systems have utilized more temperature resistant resin chemistry with a far greater degree of success.
PurePave Permeable Surfacing
PurePave is a revolutionary, eco-friendly and winterized permeable surface solution developed by extensive scientific research and testing via University of Ottawa and the National Research Council of Canada. The combination of a porous base construction and permeable surface allows an incredible amount of water to move freely through the pavement’s porous cavities, while allowing it to expand and contract during frost/thaw cycles. This eliminates the negative heaving effects seen with traditional pavements such as asphalt and interlock. Plus, it’s 6X stronger than asphalt, 1.6X stronger than cement.
The National Research Council of Canada’s Construction Technology division, Conservation Ontario, high-end car dealerships, Low Impact Developers, Universities and the Federal Government of Canada are already working with Pure Pave. Learn more about the benefits of paving with PurePave permeable surfacing.
Click here to read a Toronto Star article about a PurePave, net-zero run-off property in Toronto.