Porous Paving consists of a pervious surface overlaying a crushed stone base that stores rainwater before it infiltrates into the underlying soil. Permeable pavements rely on the ability of open-graded aggregate in their surfaces and base to receive, store, and infiltrate runoff.
With high surface infiltration rates, permeable pavements can immediately infiltrate and store rainfall from most storm events. In many cases, stormwater runoff from the pavement is completely eliminated - along with the pollutants that come with it (Samantha Search Inc.).
In theory, porous paving is an excellent concept and may help with the reduction of stormwater runoff and pollutant loading in local watersheds during rainstorms. Porous paving is a short-term solution to a growing long-term problem.
Major Disadvantages of Porous Paving
Pollutant loadings
There are many locations where pollutant loadings will exceed those typically found in stormwater, these areas can include parking lots, gas stations, commercial facilities, marinas, etc. The use of porous paving in these areas is not recommended due to the increased introduction of pollutants to the subgrade below the paving.
Weight & Traffic Loads
Porous Paving does not include rebar reinforcement, which is one of the most common ways of increasing the strength of different paving types. Also, porous paving is "porous" due to the lack of sand/fines in the concrete mix. This allows for water to pass through, but also creates air pockets due to the lack of a concrete mortar paste that serves as the glue in the concrete mixture. Due to these reasons, porous paving cannot handle heavy vehicular traffic and is unsuitable for most driving lanes.
Longevity and maintenance
The longevity of porous paving is strictly dependent on the particular use. Porous paving in parking stalls that is susceptible to frequent turning of wheels and vehicle traffic can easily unravel and dislodge aggregates. Once a large number of aggregates has been dislodged, it is recommended by most installers that the fix is to remove and replace.
Porous paving silts up, which will clog the void space that gives porous paving its draining capability. Therefore, porous paving requires at least quarterly maintenance that includes washing and vacuuming of the entire porous paving surface. This maintenance can become quite expansive over time.