Porous asphalt pavements offer developers and planners a great alternative for managing storm water. This permeable asphalt pavement, used mostly for parking lots, allows water to drain through the pavement surface into a stone recharge bed and infiltrate into the soils below the pavement. Such pavements have been proving their worth since the mid-1970s, and recent changes in storm water regulations have prompted many consulting engineers, property managers and public works officials to see if a porous asphalt surface might be right for their application.
What are the benefits of using porous asphalt?
With proper design and installation, porous asphalt can provide cost-effective, attractive pavements with a life span of more than twenty years, and at the same time provide storm-water management systems that promote infiltration, improve water quality, and many times eliminate the need for a detention basin. The performance of porous asphalt pavements is similar to that of other asphalt pavements. And, like other asphalt pavements, they can be designed for many situations.
How does porous asphalt work?
The technology is really quite simple. The secret to success is to provide water with a place to go, usually in the form of an underlying, open-graded stone bed. As the water drains through the porous asphalt and into the stone bed, it slowly infiltrates into the soil. The stone bed size and depth must be designed so that the water level never rises into the asphalt. This stone bed, often 18 to 36 inches in depth, provides a tremendous sub-base for the asphalt paving.
What kind of costs are involved?
Special features such as the underlying stone bed are more expensive than conventional construction, but these costs are more than offset by the elimination of many elements of standard storm-water management systems. On those jobs where unit costs have been compared, a porous asphalt pavement is generally the less-expensive option. The cost advantage is even more dramatic when the value of land that might have been used for a detention basin or other storm-water management features is considered.
How long do these pavements last, and how long do they remain porous?
Even after twenty years, porous pavements show little, if any, cracking or pothole problems. The surface wears well. Porous asphalt retains its ability to handle rainwater for many years.
Do these pavements look 'different' and are they smooth?
While slightly coarser than standard asphalt, porous asphalt pavements are attractive and acceptable. Most people parking on a porous asphalt parking lot will not notice (or believe) that it is porous. The surface of a porous asphalt pavement is smooth enough to meet requirements of the Americans with Disabilities Act (ADA).
Information provided by NAPA - National Asphalt Pavement Association