GUEST BLOG: A Better Concrete
Guest Author
By Dave Frentress, Glacier Northwest, Inc.
In today’s climate of environmental sensitivity, owners and developers have real challenges in dealing with stormwater regulations. Glacier Northwest has developed a pervious concrete that allows an owner or developer to provide parking, sidewalks, low speed roadways, and other hard surfaces without sacrificing valuable land areas for ponds, bioswales and other stormwater mitigation and management issues. Based on life cycle costs and the elimination of impact fees for impervious surfaces, maintenance, and other issues with stormwater, pervious concrete can save owners and taxpayers thousands of dollars per year.
Pervious concrete is a unique cement-based concrete product that has a porous structure that allows rainwater to pass directly through the pavement and into the soil naturally. It consists of Portland cement, course aggregates, fibers, water, and admixtures.
Because pervious concrete allows rainwater to seep directly into the ground, ground water is recharged, water resources are preserved, stormwater runoff is reduced or eliminated, and water quality is improved. Because of the light color and the ability of the pavement to “breathe” by evapotranspiration, urban heat is also vastly reduced.
Durability Means Longer Lasting, More Efficient Infrastructure
A significant sustainable attribute of concrete is it durability. In most applications, over time, concrete requires less energy and resources to repair or replace. Concrete builds durable, long-lasting structures including sidewalks, building foundations and envelopes, as well as roadways and bridges. As the most widely used building material in the world, concrete structures have withstood the test of time for more than 2,000 years. Because of its longevity, concrete is a viable solution for environmentally responsible design.
Pervious Concrete Carries A Proven Track Record
In the 1970s, a civil engineer and several other members of the Florida Concrete & Products Association created a domestic formula called "Portland Cement Pervious Pavement". This formula has since proven itself highly successful in the U.S. and most particularly in Florida and the Southeast where water management has been a critical and costly concern. The strength and durability of
pervious concrete appears to be superior to regular asphalt. There are several examples of parking lots built more than 20 years ago with pervious concrete that are still structurally sound and in use. Due to large void spaces, pervious concrete is also less susceptible to freeze-thaw cracking. Safeway has installed a pervious concrete parking lot at a store in Denver, Colorado.
Here in the Northwest, notable pervious concrete parking lots have been installed at Fort Lewis, Clean Water Services, and at the Drano Lake Boat Launch in Skamania County. In addition, various city sidewalks and bike trails, walkways at the Portland Zoo, and many other private installations have been done.
Concerns about clogging can be "designed out" by reducing erosion and sediment runoff through strategic design and water retaining ground cover. Studies indicate that through high volume washing, a "clogged" pervious concrete pavement can restore 80-90 percent of the permeability. Pervious concrete requires a sub-grade of soil or gravel with good infiltration rates. Impervious sub-grades, such as clay, must have a permeable layer at least six inches thick installed between it and the pavement.
Pervious Concrete for a More Livable Environment:
Light-colored concrete absorbs less heat and reflects more light than dark-colored materials––thereby reducing heat gain. This means reduced storm water temperatures. The open void structure of pervious concrete allows cooler earth temperatures from below to cool the pavement. These factors allow pervious concrete to approach natural ground cover in heat absorbing and storage capacity.
Light colored pavements also require less site lighting to provide safe night-time illumination levels, whether on parking lots, driveways, or sidewalks.
The void content of 15-25 percent offers an enormous amount of surface area to catch oils and chemical pollutants. Research studies have led many experts to conclude that the bacteria living in these spaces break down pollutants, thus making this design an effective water filtration system. This prevents much of the polluted runoff that normally occurs with traditional pavements. Parking lots, in particular, hold a tremendous potential for this material because of the amount of oil and other hydrocarbons from parked cars.
Green Design-Sustainability from the Start
A new mindset is needed when designing stormwater management systems. Rather than designing a system to pass huge storm events (that may occur only twice a century) rapidly from an area, water management planners should consider the benefits of capturing and recharging water from the smaller, more frequent rain intervals. In the Pacific Northwest, most of the annual rainfall comes in the form of precipitation events of less than an inch. A stormwater system incorporating pervious concrete will be much more effective in reducing total runoff and increasing the amount of filtered groundwater.
Pervious concrete’s ability to manage stormwater while providing the infrastructure needed for development makes it a very exciting example of green and sustainable building practice that is an economical solution to a costly problem.
Posted by Guest Author on August 26, 2005
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Very good blog. Everything you stated is true. Our company has been installing pervious concrete for 18 years.
dlm
Posted by: david m | May 17, 2006 4:02:45 PM