Permeable Pavers  - Maintenance
 

After installation of a permeable paver, maintenance is relatively minimal but absolutely necessary to ensure the long lifetime of the system. Grass pavers will require the normal watering and mowing maintenance of any turf system. Porous concrete and interlocking concrete paving blocks require that the surface be kept clean of organic materials (leaves, for example), and periodic vacuuming and low-pressure washing should be used to clear out voids and extend the paver’s functional life. Conventional street sweepers should be used with vacuums, brushes and water ideally four (4) times a year, but the actual required frequency will be determined by local conditions. With the interlocking system, additional aggregate fill material may also need to be added after cleaning.

With all of these systems, snow removal operations should be carefully considered, and the use of sand or ash should be avoided as it may cause clogging of the pavement. Plowing requirements for grass or gravel pavers are similar to those of any other unpaved road; in general, the blade must be lifted to clear the grass or gravel surface. A mall in Connecticut with grass paver parking areas custom fit their plows with rollers so that the blade remained about ½ inch off the turf and was able to keep the lot open for winter use.¹ Most manufacturers of permeable paver systems recommend the use of skids on the corners of snowplow blades. Manufacturers of the interlocking pavement blocks, however, state that the structure of the blocks’ top edges minimizes chipping and allows for normal plowing procedures. In general, as is always the case, the use of salt can create a potential pollution problem (it is not removed by the permeable paver system), and de-icing products adversely affect all concrete and turf materials.

When installed and maintained properly these systems are durable, although there will be some unavoidable loss in water flow through the system over time. Some settling may also occur in portions of the pavement due to poor compaction or construction control. A high failure rate for these systems can usually be attributed to poor design, poor construction techniques, subsoils with low permeability, and/or lack of adequate preventative maintenance.²

There are plenty of successful installations to turn to as examples, however. In Kinston, North Carolina, a parking lot installed with concrete and grass pavers has been monitored since 1999.  Results from this study, along with similar research conducted in other parts of the United States, show that permeable pavement can be very successful at reducing stormwater runoff if proper engineering design, maintenance, and site selection are followed.  The Kinston research group recommends that permeable parking lots be maintained at least once per year to ensure the highest level of permeability in the pavement.³ As a safety measure though, most designs still tend to assume that a reduction in the pavers' infiltration capacity will occur over time due to an accumulation of dirt and debris.

Concerns are often raised with permeable paver systems regarding the potential for groundwater contamination.  This is a threat that will depend on the amount of surface contamination, the length of the filtration passage and the purifying effect of the soil.⁴ Several studies have shown, however, that most metals are retained on the paver's surface, the geotextile layer or in the upper sediments below the paver system, even after several years of operation, with migration depths varying by constituent.^5,6 The soils beneath the pavers should generally be effective in detaining pollutants from infiltrated water, although for areas of special concern, an impermeable barrier and a collection pipe can be used to transport the filtered water for further treatment or disposal.

Example Maintenance Schedule

The primary maintenance requirement for permeable pavers is to clean the surface drainage voids. Fine debris and dirt accumulate in the drainage openings and reduce the pavement’s flow capacity. It is natural for clogging to occur over time, but routine maintenance can reduce this problem. A  maintenance checklist follows:

• Inspection of the site should occur monthly for the first few months after construction. Then inspections can occur on an annual basis, preferably after rain events when clogging will be obvious.
• Conventional street sweepers equipped with vacuums, water, and brushes can be used to restore permeability. Vacuum sweep ideally four (4) times a year, properly disposing of the removed material. Follow the sweeping with high-pressure hosing of the surface pores. If necessary, add additional aggregate fill material made up of clean gravel.
• Potholes and cracks can be filled with patching mixes, and spot clogging of porous concrete may be fixed by drilling approximately 0.5-inch holes every few feet.  Damaged interlocking paving blocks can be replaced.
• An active street sweeping program in the site’s drainage area will also help to prolong the functional life of the pavement.

Even though some irreplaceable loss in permeability should be expected over the paver’s lifetime, you can increase the longevity of the system by following the maintenance schedule for vacuum sweeping and high-pressure washing, restricting the area’s use by heavy vehicles, limiting the use of de-icing chemicals and sand, and implementing a stringent sediment control plan. 

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