Pervious Concrete 4

[Trackfiend]

Has anyone here had any experience with pervious concrete? I'm not asking how to design the section but only any long term issues that may rise from prolonged useage, particularly maintenance issues. There are no known cases in the region that I am in (lower gulf state) where it has been used previously. The pervious concrete in question will be used for a parking lot area. The soil's report has not yet been generated so the water table and soil(s) type is as yet undetermined. Any helpful insight would be much appreciated.

 

[msquared48]

I have no experience with it either,but would be interested in others comments on the subject too, particularly relating to freezing temperature response, cracking and frost heave. I have a civil drainage project coming up where the owner wants to use this and I do have concerns.

Mike McCann
MMC Engineering

 

[sam74]

Here is a good link with lots of information

http://www.perviouspavement.org/

 

[psmart]

The UNH Stormwater Center does a lot of research in this area:

http://www.unh.edu/erg/cstev/

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Trackfiend]

Thanks sam74 and psmart for both of links. I have actually perused thru both of those sites before (and many others) to try and glean as much info as possible. The one problem I have is finding someone who has firsthand experience with the yearly maintenance (actual maintenance) and not what is recommended, such as any particular downfalls or problems experienced with the product several years down the line.

 

[gbam]

Trackfiend;
Have you contacted the any of the contractors that have installed the pc? Maybe they can put you in contact with the correct peeps.

 

[Trackfiend]

gbam,

Yes, we have contacted a large and well known concrete provider and their rep is currently hunting down the "right" people so that they can contact us back with info. I was just curious if anyone on the forums had any experience.

 

[tsgrue]

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1. Cost: The material and installed cost of Pervious Pavers / Permeable Pavements (PP/PP) generally ranges from approximately 3 to 6 times the cost of properly designed and installed asphalt pavement with equal or better performing stormwater structural management measures included.

2. Infiltration: The infiltration capacity/potential of PP/PP decreases with time, even with regular maintenance. This decrease can result in infiltration capacity/potential of mature PP/PP (5 years in place with expected loadings) decreasing to 20%+\- infiltration for an average precipitation event versus 80%+ for newly installed PP/PP. The infiltration capacity/potential of bioretention, in contrast, generally increases over time.

3. Clogging: Greases, oils, and other petrochemicals as well as fine particulates (dust, clays, silts, other) and various non-petro-organics readily clog and/or seal PP/PP installations. Once these are in the PP/PP matrix, it is difficult and expensive to clear the clogging without removing the PP/PP in the clogged/sealed area. PP/PP can be exposed to such clogging agents whenever a vehicle leaks fluids or has fine soils on tires. There is a very high probability of exposure to such at many sites. Wet ponds and bioretention areas - especially, on the other hand, “self-heal” after exposure to such agents, require much more exposure for reduction in performance, and are much more readily fixed if such did become a problem.

4. Maintenance: Regular maintenance - generally weekly or more frequent vacuuming - is required for PP/PP installations. PP/PP installations have one of the highest - if not the highest - maintenance costs of any stormwater structural management measure.

5. Utilities: Even if PP/PP installations work properly, utilities under the PP/PP installations may fail. When this happens, the PP/PP installation is removed for utility repair work. A special fix of the affected area is required to both aesthetically and functionally match the removed area. This must extend beyond the immediate area to “tie-in” to the adjoining PP/PP. It is unlikely this will be done with as much care as the original installation and the patch would almost certainly be more noticeable than a conventional patch (if the PP/PP material is even still available to match the original PP/PP installation - ever tried matching bricks on an old house?).

6. Proof: Studies undertaken to date which show “positive results” have been undertaken in very favorable circumstances - intense maintenance, regular inspection, low traffic loadings, and little to no clogging agent exposure. These are not real world situations and produce misleading results. Studies that take into account real world situations are needed to provide design data on long term performance. There is little monitoring data on the existing installations to determine the performance or conduct a benefit-to-cost assessment relative to alternates in “real-world” situations.

* Also see post, "Rational C Value for Brick Pavers in a Sand Bed" (thread162-200106)

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tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation

http://hhwq.blogspot.com

 

[msquared48]

I don't read any freeze-thaw concerns... ????

Mike McCann
MMC Engineering

 

[bltseattle]

TSGRUE points out potential concerns - but that doesn't mean that all those factors apply to each site, and to each paving system. Many of the clogging issues can be resolved by using appropriate source controls (cover stockpiles and storage areas, provide TESC during grading and earthwork, provide "leaky/dirty" vehicles a separate parking area from the "clean" vehicles, etc).
You should distinguish between permeable asphalt, pavers, and porous concrete. Porous concrete has a permeability of up to like 200 inches/hr, so even if it clogs to 95% it is still going to be able to soak up typical rainfall intensities.
Capacity lost to clogging can be restored with vacuum equipment - a researcher at WSU told us of a section he was monitoring (parking lot at apartment complex) that was clogged by stockpiled landscape materials, went from 200 to less than 10 in/hr, but restored to about 100 in/hr after vacuuming. Clearly, if you have a "dirty" site then this is not going to be the best long-term choice. But for many sites it can work just fine.

Regarding the freeze-thaw issue, a porous concrete has such a high void ratio that there is room for water to expand without heaving overlying materials. If this is a concern in your climate then look for the research, and check whether it is overly-idealized, as Tsgrue suggests.

I've been watching several installations in local City parks and these pavements soak up water more effectively than the adjacent lawns; but the pavement in a park isn't subjected to loaded trucks or excessive sediments like a street or drive might be.

A key to successful implementation is experienced contractors, another key is to require test panels to verify the mix prior to full-scale installation.

Also expect you will need a thicker pavement section when you go with permeable pavements.

I encourage you to go for it! Do your homework but IMO we civils have got to keep pushing the envelope to make this technology work. Being able to soak in water over a large surface is a very valuable practice to incorporate into innovative & effective stormwater management designs, and it does typically not require the higher soil permeability that an end-of-the-pipe facility would need to dispose of the same amount of water.

 

[sam74]

The link I posted earlier has some information on freeze thaw concerns. Here is the paragraph under inspection and maintenance.

"Questions have been raised about the freeze-thaw durability of pervious concrete. Even though most experience with pervious concrete has been in warmer climates, recently there have been several pervious concrete projects in colder climates. Pervious concrete in freeze-thaw environments must not become fully saturated. Saturation of installed pervious concrete pavement can be prevented by placing the concrete on a thick layer of 8-24 inches (200 to 600 mm) of open-graded stone base. Limited laboratory testing has shown that entrained air may improve the freeze-thaw durability even when the pervious concrete is in a fully saturated condition. However, the entrained air content cannot be verified by any standard ASTM test procedure."

 

[cvg]

Permeable paving makes Major League debut

http://www.cenews.com/article.asp?id=2824

 

[tsgrue]

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Try this site for some simplified comparisons of structural stormwater management measures, including Pervious Pavers / Permeable Pavements (PP/PP)...

http://greenvalues.cnt.org/calculator

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tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation

http://hhwq.blogspot.com