Stormwater: What’s the Big Deal?

Sometimes we get so caught up in our own world that we lose sight of other's perspective. I was reminded of this last week while meeting with the Upper Chattahoochee Riverkeeper along with Jimmy Cotty, Executive Director of the Georgia Concrete & Products Association. Jimmy suggested that we refer to pervious concrete formally as a stormwater system instead of a pavement system and instead of having a specification for Pervious Concrete Pavement, we should have a specification for a Pervious Concrete Stormwater System. I thought this was an interesting proposal because it really focuses on the perspective of those concerned with stormwater. Then I began to wonder if we really understand the perspective of the stormwater professional?

To illustrate this, let me relate an experience I had in 2009. I was invited to Seattle, WA to help write a pervious concrete guide document for Puget Sound in association with the Puget Sound Partnership and Washington State University. This was my first time to the Pacific Northwest and I was looking forward to spending a few extra days as a "turista" and seeing the natural beauty of the Puget Sound. So, after my release from the committee work in Tacoma, I headed north through Seattle and took the ferry across Puget Sound and made my way to Kingston. I was awestruck at the beauty of it all. Yes, I was on a boat and that contributed to my positive experience, but the fact is the Puget Sound is truly a treasure.

Of course, as a proud tourist, I grabbed as many brochures of the area as possible and I also took note of any newspaper articles concerning the Sound, especially anything concerning water quality. Now keep in mind that I am from Atlanta so I had a pretty good excuse for my ignorance of the issues facing the Puget Sound, although it didn't take me long to discover the issues. Each morning, on the front page of local newspapers, there were reports concerning the Sound and its precarious condition. There were stories about oysters not reproducing, a story about toxic chemicals, even one about the "Tacoma Aroma". There was also a story about the $50 million budgeted yearly to stop pollution from entering the Sound, mainly from stormwater, and how more was needed. It was evident to me that the locals had a pretty good assessment as to where the Sound was and where it needed to be as it relates to its wellbeing.

That's why I was surprised by the responses I received from locals when I asked their opinion as to the health of the Sound. Most seemed to be unaware of any threat to Puget Sound.

Consider this...every year, roughly 52 million pounds of toxic chemicals are washed into the Puget Sound from such things as cars and boats leaking oil. To put this into perspective, the equivalent of a Exxon Valdez size oil spill is taking place every eighteen months in the Puget Sound. Congress has created a special Puget Sound office within the EPA with its main emphasis on trying to get a handle on controlling stormwater runoff into the Sound.

So what about you. Are you aware of the stormwater issues in your area? If you are involved with pervious concrete in any way, I encourage you to reach out to stormwater professionals in your area and support their initiatives. It's an ideal way to gain their perspective.

New Ways to Cure Pervious

Curing pervious concrete is no doubt one of the most critical aspects of a successful placement. Historically, the curing has been done with plastic sheeting covering the pavement for 7-10 days. For lack of a better alternative, this method is the standard even though it comes with many disadvantages. One of the main downside to using plastic sheeting is the amount of plastic that goes into landfills. For every SF of pervious concrete cured this way, 1.2 SF of plastic will be used. Yes, recycling is an option but we have to admit that hardly no one (if anyone) recycles their plastic. Every once in a while, if the plastic is not damaged, it will be reused but eventually it gets thrown away.

Then we consider the placement restrictions that plastic sheeting puts on the installer. Use of the plastic forces the installer to pour in strips and produces all those construction joints, by far the hardest joints to keep from raveling. Some feel these joints have poor compaction and some feel they have insufficient curing, but whatever the cause, I say minimize the joint and you'll have less problems. And of course we need to consider the labor costs and impact that plastic curing has on the project schedule. At least one week after placement, someone has to remove the plastic, and this phase of the project is stalled for the curing week. Although no traffic should be allowed on the pavement, sawing and/or stripping could take place during the curing phase if not for the plastic sheeting. Again, many disadvantages.

Thankfully, there are other ways to cure pervious that I expect will soon be available if not already. Here are some that I am aware of:

One manufacturer is developing a biodegradable plastic curing sheet for pervious concrete. One manufacturer has developed a sprayed on curing compound combined with a densifier for improved surface durability. Many are aware of the internal curing admixture that I have been using for years but also saturated lightweight sand is being used in pervious concrete for internal curing (expect ACI report on internal curing soon).

Using these curing techniques individually or combined should prove to be an advantage to pervious concrete, providing the benefits of curing without the disadvantages of traditional plastic sheeting.

Pervious Concrete Needs _______?


What is the number 1 need for pervious concrete right now? Training for installers? Training for producers? Better tools? Better standards? Better Design? More testing? More environmental laws? Better economy?

What do you think? Give your thoughts on this at the NPCPA LinkedIn site. linkedin