Porous asphalt and pervious concrete compared to FilterPave

The Urban Drainage and Flood Control District (UDFCD) works with local governments to address multi-jurisdictional drainage and flood control challenges in order to protect people, property, and the environment. In January of 2013 they issued a formal position on porous asphalt and pervious concrete.

Pervious concrete was removed from the Urban Storm Drainage Criteria Manual Volume 3: Best management Practices (USDCMV3), and porous asphalt was not added to the manual. Both porous pavements were reported to clog and require great effort to unclog, making the pavements ineffective. Pervious concrete was also noted for deteriorating.

FilterPave has a much larger void space than both pervious concrete and porous asphalt. This prevents sediment from clogging the pavement. The University of Central Florida (.pdf) conducted independent tests of FilterPave, pervious concrete, and porous asphalt. The tests concluded that if clogged, FilterPave can be easily rejuvenated while porous asphalt and pervious concrete remain mostly clogged.

Take a look at these videos of a 5 gallon bucket of water poured onto FilterPave and porous asphalt. Notice how much quicker the water from the bucket disappears into the FilterPave and how much longer the asphalt video is.

FilterPave 5 Gallon Bucket Test

Porous Asphalt 5 Gallon Bucket Test

The National Renewable Energy Laboratory (NREL) also discusses FilterPave compared to pervious concrete in their 2013 Site Sustainability Plan (.pdf).

NREL’s monitoring activities evaluated two other existing systems, filterpave and pervious concrete which was installed in the STM surface lot in 2010. The filterpave system has performed very well. In late spring of 2012, a maintenance top coat was reapplied per the manufacturer’s recommendation. Unfortunately the pervious concrete underperformed with large expanses decomposing. As part of the collaborative pervious pavement research and pilot project efforts, Urban Drainage and Flood Control District (UDFCD), who monitors these types of installation, visited late summer and agreed the product was an inferior performer.

pervious concrete
Less than 2 years old this pervious concrete is deteriorating rapidly.

Memorandum excerpts from Urban Drainage and Flood Control District

Pervious Concrete

In June 2008 UDFCD called for a moratorium on pervious concrete pavement due to widespread surface raveling problems with this best management practice (BMP). Since that time we collaborated with the Colorado Ready Mixed Concrete Association (CRMCA) and others to develop a guidance document titled The Specifier’s Guide for Pervious Concrete Pavement Design, which we believed would minimize, and hopefully prevent future failures. In 2010, The National Renewable Energy Laboratory (NREL) constructed a pervious concrete demonstration pad at its research laboratory in Golden, Colorado, to the new specifications and under the supervision of CRMCA. After only two years in service, the surface of this pervious concrete has heavily deteriorated. This, combined with several other premature failures and very few successes in Colorado, indicates to us that, until significant advances are made in pervious concrete composition, mixing and placing, successful implementation of this BMP is highly unlikely even under tight controls and ideal conditions.

For this reason, UDFCD does not at this time recommend the use of pervious concrete pavement as a sustainable stormwater quality best management practice in Colorado and we have removed it from the Urban Storm Drainage Criteria Manual Volume 3: Best Management Practices (USDCMV3).

Full Memorandum on pervious concrete (.pdf)

Porous Asphalt

In April 2008, UDFCD worked with the Colorado Asphalt Pavement Association (CAPA) and several pavement contractors to install a porous asphalt demonstration pad in front of the City and County of Denver’s Wastewater Management building. This site has been monitored regularly to determine if porous asphalt can maintain the minimally acceptable infiltration rate for any permeable pavement in the UDFCD region. For the UDFCD-recommended impervious tributary area/pavement area ratio of 2:1, this minimally acceptable infiltration rate is equal to 20 inches per hour. Over a few years, the infiltration rate at this site and several other porous asphalt installations in the UDFCD region fell below this minimum standard and that cleaning with reasonably available methods and equipment were generally not successful in restoring infiltration rates to the minimum acceptable level. To properly clean porous asphalt on a commercial scale, regenerative air or vacuum sweepers are recommended. More intensive cleaning with power washers and higher efficiency vacuums was performed at some of these sites by CAPA and they were generally able to restore infiltration rates via these more extreme methods.

UDFCD considers porous asphalt an adequate BMP for use in locations where clogging sources are minimal, traffic volume is low, and maintenance is regular and intensive, but our experience indicates that such locations are rare. The intent of the USDCMV3 has always been to include only stormwater BMPs can be widely used throughout the UDFCD region and that have a good chance of success in capturing and treating the full design volume of stormwater over the life of the BMP with only reasonable maintenance practices and readily accessible equipment.

For this reason we will not at this time include porous asphalt pavement in the USDCMV3 and we further recommend both caution and realistic expectations in regard to performance and maintenance costs when implementing this particular permeable pavement.

Full memorandum on porous asphalt (.pdf)

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