Discussion on:

Pervious concrete drains water, filters pollutants

So what are the long term issues in relation to mould and fungus growth under the slab and a haven for tree roots to feed and undermine the slab. I didn't notice any reinforcement rods in that slab either. Nice idea but I owuld want to see how it resolves a few practical issues. A cracked slab will let water through without all the nice filtration benefits. Meanwhile the slab acts as a pollutant concentrator. It doesn't answer the issue of run off either.

Nice idea, needs more work.

As you of course know mold and fungus need a steady cool, dark, moist environment to grow, quite the opposite from happens with in the pervious concrete system. Because water is allowed to pass through the system and infiltrate into the ground, where it should go, the interior portions dry out quickly once the rain stops; no moisture, no mold.

In traditional concrete the base is highly compacted and impermeable, when it rains water is wicked into the space in between the bottom of the concrete slab and the base and because it has no place to go this area tends to stay wet for long periods of time: a perfect source of moisture for tree roots where they then grow and force the concrete up. Remember, roots only go where there is water. In a pervious concrete system ALL the water is allowed to soak deep into the ground, not only feeding the deep tree roots but replenishing the local aquifer.

Right now your local water way that receives the municipal storm water runoff IS a pollutant concentrator. Non-point source loads of pollutants (hydrocarbons, phosphates, nitrates, etc, etc) from local run-off is collected in a central drain system and dumped untreated in the local marine environment. All the major lakes, rivers and bays in the US are polluted due to contaminated storm water run-off. Pervious concrete systems as well as bio-swales and rain gardens have highly efficient and well documented bio-filtration/remediation functions.

Bottom line is that not only can a well designed and installed pervious concrete system satisfy municipal regulations to reduce or eliminate run-off, but we can also reverse a significant amount of environmental damage caused by our built environment. I like to say pervious concrete allows us to have our cake (hard surfaces) and eat it too.

David Liguori - Bay area pervious concrete

....and in a couple of years, the top layer started spalling off and it became rougher than a cob. Maybe the guys who did it didn't use the right stuff, but we ended up replacing that section this year because it had become almost unusable to pull/push anything with wheels over it.

Although it technically is concrete, pervious concrete has unique properties that cause it to behave very differently. As such it requires a completely different set skills and knowledge that can only be acquired through completion of the certification program and hands on experience with the product. The NRMCA is the certifying body for pervious concrete, be sure your installer is certified AND has several successful installations you can go see.

David Liguori - Bay area pervious concrete

Is this an option for cold weather climes? What happens in freeze-thaw climates? I doubt that it would hold up under such circumstances...

It takes advanced knowledge to do properly but pervious concrete is being used successfully as far north as Canada. Feel free to contact me for referrals.

David Liguori - Bay area pervious concrete

The need for this product was overestimated by some investors. One company from Brazil is being investigated for fraud.

Brazil? Investors?

I personally know most of the top pervious concrete installers in north America (it's a small group) and I can assure you we are all independent local small business owners.

Besides, I've never even been to Brazil

David Liguori - Bay area pervious concrete

It could be used to line underground sumps for occasional flows, where temperature extremes and traffic are not encountered. This would have no advantage over layers of sand and clay, though. It might have some use in slowing down a flow to make it flow less swiftly but for a longer time, providing a seep for gardens or orchards, for example.

It appears to be made from medium sized pebbles with an increased ratio of stone to concrete. The concrete acts like a glue to join the pebbles together, but there is not enough concrete to block the space between the pebbles

There is a bit more to it than that, but you've got the general idea right.

David Liguori - Bay area pervious concrete

How does it compare to "traditional" concrete??

Here is how our costs compare

http://bayareaperviousconcrete.com/faq/pricing/pricing.html

David Liguori - Bay area pervious concrete

This sounds like an ecological nightmare waiting to happen. If it filters the pollutants as water flows through it, where is that gunk supposed to eventually go? Right now, any pollutants that fall on pavement goes into the storm drains, or the ground, and natural reactions break it down. With this stuff it sounds like it sits there like a dirty sponge collecting gunk until it overflows.

You make the statement that pollution going into the storm drains breaks down naturally. In the storm drain, really? Evey piece of research I've ever comes across says the opposite; contaminates picked up by storm water go, completely untreated, directly into the nearest waterway where they destroy the marine environment.

If you would like to learn how bio-filtration and remediation actually work in pervious concrete, and how much we can improve our environment by using it, please read this article

Storm water solutions: http://bayareaperviousconcrete.com/faq/downloads-2/

Here is a brief excerpt:
As the breakdown of oil by aerobic processes generates carbon dioxide, this can be measured to give a good idea of the rate of biodegradation. Simultaneously, the consumption of oxygen can be measured also gives an idea of the rate of treatment. The background concentration of CO2 is 0.03 %, the levels in the PPS atmosphere reached 0.47 %.
This was conclusive proof that the oil was being progressively removed from the system and the Pervious pavement system was not just a trapping mechanism for pollution, but an aerobic bio-reactor capable of significantly improving discharged water quality.

David Liguori - Bay area pervious concrete

Even if this material does not stop the migration of pollutants to storm drains, et al it still provides the benefit of slowing the movement of water to the street and drainage systems, which in some ways makes up for the loss of trees (watershed), which would have that affect. Loss of trees and open expanses of earth through real-estate development have contributed to the increased speed of water making its way to drainage systems, which are being overwhelmed by the ever increasing volume of water in places like Pennsylvania, where this contributes to flooding. Pervious concrete and green roofs serve a similar goal in slowing the movement of rain water to drainage systems. This is why both technologies have been exhibited at the Philadelphia Flower Show for many years now.