BMPs for Cleaning Pervious Concrete
by Alan Sparkman, CAE, CCPf, LEED AP
AbstractAlan Sparkman is Executive Director of the Tennessee Concrete Association. In the following article, he provides an overview of what his Association has learned about BMPs for keeping pervious concrete roadways and other expanses cleaned and, so, functionally operational.
To the readers of WorldSweeper.com, this is my personal hierarchy of pervious concrete maintenance and cleaning... for whatever that's worth.
First, good maintenance prevents the need for remedial cleaning over the life of the pavement for most situations. And, good maintenance starts with good design! Pervious concrete pavements are part of a system for handling stormwater so they have to function as more than just a pavement.
That means structuring a design that prevents or minimizes flows of sediment-laden water onto the pavement throughout its service life. This is mostly about the relationship of the pavement to the surrounding landscape and intelligent use of curbs or other barriers (for flowing water). Consideration must also be given to the type and sources of traffic that will be using the pavement - if the pavement will routinely receive traffic with muddy tires it is going to require a much more aggressive maintenance plan.
The closing out of the construction process often presents challenges for pervious concrete because contractors aren't used to protecting pavements from sediment and there are often large areas of the site that haven't yet been sodded or seeded. It is fairly common for pervious pavements to get partially clogged with dirt, mulch or other materials as the construction process closes out. In some instances, the offending material can be sprayed off with a power washer and any dirt remaining in the pervious concrete can be washed or flushed through the pavement. This should restore essentially 100% of the pavement's original infiltration capability.
Once past the construction phase and into the operational phase, owners should be encouraged (required) to do routine maintenance – typically this would be sweeping (dry sweeping) the entire parking lot (not just the pervious concrete). The frequency will depend on the individual site, amount of traffic, sedimentation sources, etc. Basically, the parking lot should be swept whenever there is obvious 'junk' on the parking lot (leaves, twigs, dirt, sand, etc.).
I would also point out that asphalt parking lots seem to be especially prone to producing their own sediment from normal wear and tear. This surface raveling is basically sand size particles consisting of asphalt 'chips' and actual sand that is dislodged under normal traffic. This sediment will show up pretty quickly in the leading edge of pervious concrete sections and is pretty easily identified because it is primarily black or dark gray in color, as opposed to the brown or reddish color for dirt sediments. Concrete parking areas most likely produce some of this 'in-service' surface raveling as well, but I suspect there is less volume of this material and it will be harder to distinguish as it will be the same basic color as the pervious concrete.
So, step one in a maintenance plan would be regular sweeping (dry sweeping) with equipment appropriate for the size of the parking lot - walk-behind sweeper, riding sweeper or truck mounted unit. Smaller walk-behind leaf vacuums or leaf blowers could also be used for this routine maintenance function to capture and/or remove sediment particles before they can infiltrate deeply into the pervious concrete matrix.
Step two for regular maintenance would probably be some type of powerwashing. The goal here would be to dislodge particles in the top portion of the pervious and to either flush them off of the pavement or through the pavement. For many cases where routine sweeping has been neglected this may do the trick and restore adequate infiltration to the pavement.
Step three would involve some type of vacuum equipment, probably combined with power-washing to free up the sediment trapped in the pavement so that it can be sucked into the vacuum and permanently removed from the pavement. Again, there is a variety of equipment that could be used for this type of operation ranging from walk-behind or ride-on units up to truck-mounted sweeper/vacuum units. My experience has been that this type of equipment is not well-suited for heavily clogged pavements as the units I have seen don't have enough vacuum power to really provide deep cleaning.
I have seen a couple of other variations on the Ditch Witch machine (shown at the right, above) that provide a little wider swath of cleaning, but they are still basically walk-behind size. The key thing to understand here is that this type of treatment will only be necessary when a pavement is severely clogged from neglect (lack of routine maintenance) or from some unusual event like flooding, etc.
Step four could be classified as remediation for heavily clogged pavements and would most likely involve some variation of the equipment that is being developed with the exclusive purpose of cleaning pervious concrete. We have used a vacuum attachment powered by a trailer-mounted vacuum excavator (about 30 hp) with reasonable success. This unit has a cleaning head with spray bars that pressure wash the pervious concrete surface while also vacuuming at the same time. Other units being developed have rubber lips that actually create some suction onto the pervious concrete and apply a much higher level of vacuum and thus a higher level of cleaning. This unit also provides pressurized water at the same time it is vacuuming and is designed to work off of very large truck-mounted vacuum machines.
I hope this information is helpful to those in the power sweeping industry who will be tasked with keeping pervious concrete 'working' for as long a useful life as possible.
The author, Alan Sparkman, CAE, CCPf, LEED AP, is Executive Director of the Tennessee Concrete Association. You may reach him via email sent to asparkman>@tnconcrete.org or by calling 615-360-7393. To become a TCA Fan on Facebook go to www.facebook.com/tnconcrete.
Thank you to Dr. Heather Brown, professor of Middle Tennessee State University, for providing contact information for this article on pervious concrete. Dr. Brown also provided WorldSweeper with links to studies and other information about pervious concrete, as well as some notes from her own experience of people who have cleaned pervious concrete.
Here are her notes on the topic:
Currently there is no sweeping frequency on any projects I am aware of. There should be but until now no data was available to determine what might work best. It looks as if several dry sweepers should be included in semi-annual sweeping programs and a potential wet vacuum should occur as needed.
Construction mud is a problem. It can be immediately power washed and wet vacuumed but if left unattended will immediately clog the surface.
I have attached a link to a collection of papers that might have more info for you. Click here to download that information as a PDF file. Dr. Brown may be reached via email sent to: Heather.Brown@mtsu.edu.
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