Nov 01, 2010

Keeping Porous Pavement Porous

The key to a successful porous pavement application is making sure the basics—engineering, installation and maintenance—are covered. If any of these three aspects is slighted, the surface will fail to perform as expected. Engineering and installation are well understood, and trade organizations provide classes and workshops to ensure that jobs are successful. However, until very recently, the maintenance aspect has not been understood or properly executed.

Elgin Sweeper has actively participated in various research programs across the U.S. to develop a better understanding of the maintenance requirements of porous pavement. This research has helped clarify the role sweepers play in maintaining and cleaning porous pavement surfaces.

Clogged in California

The importance of proper maintenance was recently demonstrated at a school in Monterrey, Calif. Several parking lots on the grounds of the school were covered with interlocking concrete pavers to serve as a storm water pollutant mitigation aid. The engineering and installation met the local requirements, but the site manager was unaware of any maintenance requirements for the surface of the pavement. As a result, the parking lots quickly became plugged with vegetation from eucalyptus and cedar trees and were no longer pervious.

This undesirable outcome served as the impetus for a training course conducted by Dr. William Hunt of the Department of Urban Stormwater Management at the University of Northern Carolina. Sponsors of the course included Elgin Sweeper, the Interlocking Concrete Pavement Institute and Advanced Pavement Technology Co.

Material Considerations

Research conducted over the last few years has determined that a porous surface regularly maintained by moderate vacuum sweeper will continue to function as designed for more than 20 years. An improperly maintained porous surface, such as the scenario involving the parking lots at the school in Monterrey, will eventually require total restoration with a high-powered vacuum sweeper.

Preliminary research on porous pavement plugging focused on deposits of silt and dirt, but more recent evidence suggests that vegetation can be more difficult to deal with. Traffic will shred vegetation and embed it into the pores of the road surface.

In the case of the school parking lots, the gaps between the blocks were jammed with shredded eucalyptus leaves, cedar needles and mashed acorns. The resultant mix was “glued” in place with the pitch from the vegetation.

While surfaces clogged with silt have been restored successfully after one or two passes with a high-powered vacuum sweeper, the debris from the school parking lots was compressive and sticky. This situation required a minimum of three passes with a high-powered vacuum sweeper operating at maximum power to successfully restore the surfaces to optimal condition. Once the gaps between the blocks were refilled with crushed stone filler, the parking lots functioned as well as when they had when first installed.

The Need for Routine

This case study highlights the need for routine maintenance cleaning of porous pavement . If the school parking lots had been regularly cleared of leaves, needles and other debris, the vegetation mashed into the pores would have been easily removed by a low-power vacuum sweeper.