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.