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Concrete forest: Pervious concrete mimics the way nature drains stormwater - Sound News

Concrete forest: Pervious concrete mimics the way nature drains stormwater

By Sound News reporter Erica Petru

The sample looked like a long rice cake, dipped in cement.  Despite appearing as if it would fall apart at any moment, it felt heavy and sturdy.  It was strange to think that this material could replace the smooth, impenetrable parking lot outside of the Tacoma Mall Plaza Building, or the concrete of Seattle sidewalks and alleys, reducing the severe damage of stormwater runoff to the Puget Sound region.

Pervious concrete – which allows water to filter through to the ground below – is just one piece of the puzzle to improving the environmental health of Puget Sound.  Part of new design techniques and regulations called low impact development (LID), pervious concrete is a revolutionary way to drain surface water, and prevent it from entering creeks, rivers, and eventually, our Sound.

Stormwater runoff is one of the biggest threats to the ecological well-being of Puget Sound.  Chemicals such as PCBs, mercury, and flame retardants travel through creeks and rivers until they concentrate in the sound, threatening the ecosystem and crawling up the food chain.

Low Impact Development

The main purpose of LID is to mimic the way nature drains stormwater.  Low impact developers use components such as rain gardens, alternative paving, and soil that removes pollutants from stormwater runoff to accomplish this task.  The general goal of these eco-friendly methods is to return each site to the way it took care of rain water before modern development. A defining standard for LID design is that residential plans must preserve 65 percent of native vegetation, and commercial plans must preserve 25 percent of existing vegetation.

Dawn Anderson is an engineer who recently shifted her specialty to low impact development.  Prior to her current position as Pierce County’s LID coordinator, she worked for Planning and Land Services.  Once she warmed up to the environmental aspect of her new field, Anderson said she thought, “Ok, this is something I’m passionate about.”  Anderson’s responsibility in Pierce County Public Works and Utilities is to review and regulate LID plans and proposals.

“I’m a cheerleader,” she said, admiring the work of her counterparts in Seattle.  LID design is an interdisciplinary field of planning and development that requires the cooperation of engineers, developers, landscape architects, biologists, and policy makers.  Anderson explained that all of those involved in low impact development have varying interpretations and stakes in each site. She describes it as a collaborative effort that is “really interactive and not streamlined.”

Pervious Concrete

A sample of pervious concrete in Pierce County's Public Works and Utilities department.

A sample of pervious concrete in Pierce County's Public Works and Utilities department.

“Imagine that you have a big glass vase and it’s got a hole in the bottom and you’re gonna fill it with marbles,” said Michael Bledsoe, Vice President of Marketing and Strategic Planning for Pervious Concrete, Inc.  If you pour water through the vase, everything will cascade out the bottom.  So you add some superglue.  But if you add too much superglue, the water will not drain out of the vase.

Bledsoe explained that mixing and installing pervious concrete is a balancing act, and a process that is much more difficult than installing traditional concrete.  If the mixture is too wet, the holes will clog up and the concrete won’t drain surface water.  If the mixture is too dry, it will become like gravel and reduce the structural integrity of the concrete.  Pervious concrete is vulnerable to temperature, humidity, wind, and even how long it takes to deliver the mixture to a site.  Regulators even require developers to have proper certification to install the concrete because it is so easy to do it wrong.

Despite the challenges of installing pervious concrete, Bledsoe saw a business opportunity in the concrete industry due to new development standards of the Environmental Protection Agency.  Becoming prominent in the field of pervious concrete gave his company an advantage in the developing market and a means to address a huge environmental problem of Puget Sound.

Pervious concrete addresses the fundamental problems of stormwater runoff by allowing surface water to drain directly into the soil beneath it, rather than flowing to the nearest storm drain and entering the Sound.  Oil and other pollutants are able to biodegrade as they filter through the concrete.  Anderson explained that another virtue of the concrete is that it reduces the spray from rainfall, which rinses the chemicals from the undercarriage of our cars and empties into storm drains.

Andrew Marks is a self-described “engineer’s engineer.”  As the Managing Director of the Puget Sound Concrete Specification Council, he is the primary source of education on the use of alternative paving materials.  Pervious concrete is just a part of his specialty.

Skeptics of alternative paving, including some developers and regulators, criticize the concrete for requiring more maintenance than conventional concrete, and being confined to sidewalks, alleys, side roads, and flat ground.  Marks proclaimed that the limitations of pervious concrete lie more in how water drains on a particular site than the concrete itself.  He said that pervious concrete demands a different method of installation, but accompanied with proper training, it is just as durable and long-lasting as conventional pavement.  Furthermore, the pavement will effectively give back buildable resources to the developer with decreased need for conventional drainage systems such as costly ponds.

Why, then, is it uncommon to see pervious pavement?  According to Marks, the idea of pervious concrete was extremely controversial at first because historically the purpose of concrete was to contain water, preventing the ground below from weakening.  As with any new technique, increased use and trust is a matter of education.

Education: the means to acceptance

Anderson and Marks both stress that through exposure to low impact development, politicians, contractors, and the public will support the expansion of pervious concrete and the like. Both hope that LID will be mainstreamed in the future.

It is Teresa Lewis’ job to expedite this acceptance.  As an Education and Outreach coordinator for the Public Works and Utilities Department of Pierce County, she spends her time explaining the environmental effect of stormwater runoff to the public and introducing solutions such as LID.

She said that people need to realize that their actions and lifestyles have a direct effect on the Sound, and through environmental education they can make the changes necessary to become better stewards of the environment.

In the meantime, environmental development practices, standards, and techniques such as LID and pervious concrete can address these problems on a structural level.

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  1. One thing I didn’t see mentioned was that this new pervious concrete will have a downside as well. Seeds will get into it and start growing. I like the idea, but do you want to mow your sidewalk? We all know grass seeds will find their way into this stuff. Then you have to ask yourself, how do you deal with it? With chemicals? There goes the whole environmental benefit. We’re here in the Puget Sound. We have strange weather. We have moss everywhere. How does this stuff handle moss growth? How does it handle tree growth? Birds will drop seeds anywhere and everywhere. How will this stuff hold up to ice forming on the 1.5 weeks we have snow and ice every year? Water could remain inside this stuff, freeze, expand, and next you have a pile of rubble.

    Those are just some things I pulled off the top of my head. I’m sure there are other things we ought to test first before using this stuff. It sounds like something I’d like to see used, but only if we know as taxpayers that we won’t have to replace it every few years.

  2. Great article. I like the concept. How do the building codes treat this product? What are the load bearing characteristics? Building codes consider gravelled areas as impervious, how would this be different?

  3. Pervious concrete is used in a lake in North queensland as see from the vedio clip. It is performaing well without any moss formation. Water is free to flow in and out, drys out quickly due to large pores and small capillariy pore, no vegetation growth, it looks brand new all the time. It is mazing hoow well it is performing. In Syydney, pervious concrete also finding use as a materials around the trees in impervious sidewalks along the main roads.
    http://www.youtube.com/watch?v=u4aLKbkUOmM&feature=channel_page

  4. One thing I didn’t see mentioned was that this new pervious concrete will have a downside as well. Seeds will get into it and start growing. I like the idea, but do you want to mow your sidewalk? We all know grass seeds will find their way into this stuff. sikiş izle Then you have to ask yourself, how do you deal with it? With chemicals? There goes the whole environmental benefit. We’re here in the Puget Sound. We have strange weather. We have moss everywhere. How does this stuff handle moss growth? How does it handle tree growth? Birds will drop seeds anywhere and everywhere. How will this stuff hold up to ice forming on the 1.5 weeks we have snow and ice every year? Water could remain inside this stuff, freeze, expand, and next you have a pile of rubble.

    Those are just some things I pulled off the top of my head. I’m sure there are other things we ought to test first before using this stuff. It sounds like something I’d like to see used, but only if we know as taxpayers that we won’t have to replace it every few years.

  5. The concrete is alternately wet and dry as the water drains away. That means there isn’t water to allow the seeds to germinate and the roots to reach soil. The pervious concrete installations in the Seattle area are surprisingly clean and free of moss or weed growth, even when covered by leaves or needles. Both scientific and anecdotal studies show that pervious concrete is not damaged by freeze thaw cycles. There are literally thousands of square yards of pervious concrete pavements in place from Olympia to Arlington in the Puget Sound area, and there have been no reported failures.