When I was at the Green Summit a couple weeks ago I saw some vendors demonstrating pervious concrete which is porous concrete that water can flow through to the ground. Turns out this is quite a useful characteristic for some applications where traditional non-pervious concrete is usually used such as parking lots, drive ways, and paths. It reduces the heat island effect, helps recharge aquifers, saves space, and reduces toxic runoff.
Probably one of the greatest benefits of this is that it reduces the heat island effect. Concrete already reflects more heat than asphalt because of its light color, but pervious concrete goes a step further. Since it is porous it allows moisture from below to evaporate which acts to cool the concrete. One of the vendors also said that since it has less thermal mass it doesn’t absorb as much heat.
Another benefit is that pervious concrete can help recharge aquifers. Instead of rainwater being diverted into storm drains or water retention basins the water goes straight down to the ground. This helps recharge aquifers and water trees and plants around the area of the lots. Trees around lots with pervious concrete have been shown to live longer and grow wider.
Effective use of land is an issue in cities and since water flows through pervious concrete in many cases the need for retention basins to collect rainwater is reduced or completely eliminated. This is a huge benefit in places where space is at a premium.
Permeable concreate produces no toxic runoff. Most asphalt lots are sealed with coal-tar based sealants, which is the black coating you often see and smell used on streets and parking lots. Run off from coal-tar sealed parking lots have been found to have 65% more polycyclic aromatic hydrocarbons (PAHs) than unsealed lots. PAHs are one of the most widespread organic pollutants and have been found to be probable human carcinogens. PAHs have been long associated with causing lung cancer in roofers and asphalt workers according to the National Institute of Environmental Health Science. Large concentrations of PAHs can also kill aquatic life. I’m not sure how true this is, but the vendors claim that when automobile fluids are washed down under parking lots that they are filtered out and transformed by microorganisims into inert materials before they reach aquifers.
If you are looking to build a pathway, drive way, or parking lots pervious concrete might just be the perfect alternative to traditional concrete. Vendors are popping up all over the country and here in Phoenix Progressive Concrete Works is probably one of the best known. They’ve done some large installations such as ASU’s Art Museum parking lot.
James Towner | Posted in 
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September 21st, 2008 at 9:18 pm
This stuff is so cool! I loved seeing the demonstrations at the Green Summit, I had heard of this type of material before but seeing just how permeable it is was shocking. I hope it will become more widely used as it seems like a winner of a product.
September 30th, 2008 at 7:09 am
I wonder if this can be used in regions where the ground would be subject to freezing ….
… or in areas with a possibly high level of run-off soil sediments (which could settle inside the concrete pores)
September 30th, 2008 at 7:41 am
it sounds good in theory, but the first thing I thought of was the ice also. I don’t think this would work well in colder regions.
September 30th, 2008 at 8:01 am
What about weeds? They’ll love this surface in they they will very effectively grow through it.
September 30th, 2008 at 8:08 am
Found this info about ice and pervious concrete:
http://articles.directorym.net/Benefits_Of_Pervious_Concrete-a934316.html
“Recent studies at the National Concrete Pavement Technology Center (CP Tech Center) at Iowa State University in Ames, Iowa ? where tests under freeze-thaw conditions have been applied to pervious concrete mixes ? have shown that this pavement system can withstand the powerful expansion forces of freezing water in colder climates. Research at Iowa State has identified pervious concrete mixes that will meet freeze-thaw durability requirements. The traditional ASTM test for freeze-thaw is 300 cycles of freezing and thawing with less than 85-percent mass loss. One of the mixes developed at Iowa Sate will provide that with 95-percent retention of mass.
There are also steps that can be taken when placing pervious concrete in colder climates with longer and greater number of freeze-thaw cycles. The following precautions are recommended to enhance the freeze-thaw resistance of pervious concrete:
* Use an 8-inch- to 24-inch-thick layer of clean aggregate base below the pervious concrete.
* Attempt to protect the paste by incorporating air-entraining admixture in the pervious mixture.
* Place a perforated polyvinyl chloride (PVC) pipe in the aggregate base to capture all of the water and let it drain.”
September 30th, 2008 at 9:20 am
Another concern I’d have is oil. Presently, the worst a car leaking oil is likely to do is stain the concrete. With pervious concrete, the oil ends up in the water supply instead; not the best outcome.
Weeds are a concern too, but not a huge one… except in the case of weeds that can grow big enough to damae the concrete.
September 30th, 2008 at 1:30 pm
Weeds. This material lets water through, this does not necessarily mean that it lets light through nor does it necessarily mean that the paths through the material that the water takes would be large enough for weeds to pass: there are membranes widely available that allow water to pass but supress weeds so I see no reason why this material would not have that property, especially considering its depth when laid.
September 30th, 2008 at 7:44 pm
My father invented/perfected this back in the 80s in Florida at the Florida Concrete and Productions Association. He got the idea from some previous work in the 1920s, although his Portland mixture worked the best. AASHTO yielded his calculations for the optimum mix, as my memory recalls.
September 30th, 2008 at 7:47 pm
@Adam Bard: Oil draining off normal concrete ends up in the water supply at the same concentration as previous concrete. It might take a rain or two more to make it happen, but in the mid-term, it is the same.
October 1st, 2008 at 7:38 am
Would a friend of mine have appreciated this! A school was built uphill from his property with traditional materials. The runoff drained onto his property, which caused flooding, making his property just about worthless. Of course the school and city which permitted it weren’t responsible. ~ Daryl
October 1st, 2008 at 9:22 am
What a smart idea! It could make a miracle in the big City as London…
October 1st, 2008 at 5:59 pm
it sounds good in theory, but the first thing I thought of was the ice also. I don’t think this would work well in colder regions.
There’s a brand spanking new parking lot in downtown Ann Arbor, MI with pervious concrete. I guess we Michiganders (I walked across the lot earlier today) will find out about that soon.
October 9th, 2008 at 10:08 am
The city of Glendale just installed over 15,000 square feet of pervious concrete at their new park and ride. That equates to around 2.5 NFL football fields. It is really neat and I use this park and ride every day. It even feels cooler walking through the parking lot at the end of the day then a regular asphalt parking lot.