A lesson in pervious

The art of placing pervious concrete definitely can be learned

By Tom Klemens

When scheduling gets turned upside down, it isn’t always a bad thing. I was trying to get out to cover a one-day pervious concrete placement in August and things worked that way. The date was pushed back several times and finally leapfrogged to the day after I was going to sit in on a pervious training session.

It was great going through the NRMCA class one day and watching a crew the next day as they learned about and got comfortable with this material on what was, for most of them, their first pervious project.

THE PROJECT

This pavement was being placed as a donation on the campus of the Morton Arboretum (www.mortonarb.org) in Lisle, Ill. In addition to being a horticultural reserve, the arboretum serves as an educational showcase for landscape architects and homeowners. The facility repaved its main parking lot in pervious pavers some time ago, and this project provides a second example of pervious paving technology.

The material was provided by Ozinga, based in Mokena, Ill. (www.ozingagreenbuilding.com/filtercrete). Naperville, Ill.-based Builders Concrete (www.builders-concrete.com) provided the workforce. Ozinga’s resident expert on pervious concrete, Brian Lutey, was on hand to help the crew with the new methods they would need. He also brought along the hydraulic roller screed used to flatten and compact the concrete.

Lutey has been working with pervious for more than seven years, first in Indiana with the Indiana Ready-Mixed Concrete Association, and since early 2007 in northern Illinois with concrete producer Ozinga. He says he has put down more experimental pervious than anyone he knows of, which is how he has come up with mix designs that work. As Ozinga’s main man in the field, he has been on every pervious placement they have supplied since his arrival training crews in how to work with the material.

THE MATERIAL

The pervious concrete mix design needs to be adjusted for northern climates, Lutey says, to hold up to freezing and thawing. Primarily this means adding about 100 pounds of sand to a mix that’s otherwise known as “no fines.”

says he has found that a mix that’s stiff but a bit sticky results in better placements than a drier mix

Hydration retarder is one critical component in any pervious concrete mix. The dosage depends on the mixing and transportation schedule, as well as the temperature, but it should be enough to “put the concrete to sleep” until it has been place and compacted. Only then do you want the hydration process to begin.

The amount of water and cement also are critical. Unlike standard concrete, where as a general rule more cement means more strength, pervious concrete doesn’t necessarily get stronger as more cement is added, simply because of the geometry dictated by using gap graded aggregate. For more information, see “Learning to Do Pervious” in the October 2008 issue of Concrete Construction or at www.concreteconstruction.net.

PLACING THE PERVIOUS

Pervious concrete pavement is very much a system. The pavement part can be perfect, but it relies on a well-designed and well-placed base coarse to function properly.

[MA-1]On this project the arboretum staff did the excavation and base work. The Builders Concrete crew set the side forms the day before the concrete placement. Note that the stakes are cut flush with the top of the form so the roller can pass by. The arboretum staff placed and compacted about 6 inches of typical base material for the area atop a non-woven filter fabric.

 

 

 

 

 

[MA-2]Shortly before the concrete arrived, the forms were sprayed with soybean-based oil developed by C2 Products, Cicero, Ind. (www.c2products.com), which is also applied to the concrete as it is placed. It helps in removing and cleaning the forms as well as helping keep the moisture in the concrete while it cures.

 

 

 

 

 

 

[MA-3]The filter fabric is placed with extra at each end of the placement and wrapped up around the end of the base material. This helps keep fines out of the permeable base over the long haul. After the concrete is in place, the remaining filter fabric is simply cut off with a utility knife.

[MA-4]It’s important to have all the equipment and materials that will be needed in place before the placement begins. That includes the plastic to cover it, finishing rollers, sprayers and extra bean oil, materials for fastening and weighting down the plastic, and of course the hydraulic roller screed. The first time you see it you may be surprised how rapidly the steps follow in succession. The idea is to get it placed and covered and as quickly as possible.
 

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[MA-5]The mix should arrive a little dry from the supplier -- it’s easy to add a little water at the site, but if it comes in too wet that can be a real problem. If you make a ball of the concrete in your hand it should hold together; this is referred to as the NRMCA test. However, Lutey says he has found that a mix that’s stiff but a bit sticky results in better placements than a drier mix

[MA-6]At the training session the day before the Morton Arboretum job, he explained how to judge the mix’s consistency by letting it fall from your hand.

[MA-7]Of the two open-handed tests shown here, the upper shows too little paste left on the hand, which is an indication that it is too dry. [MA-8]The lower has left a good coating of paste on the hand, even though the ball itself stuck together.

 

[MA-8]We also saw an example of a wet mix. One rule of thumb: When you can see bubbles in the mix, you know it’s too wet. Spinning it in the drum sometimes can drive off enough of the excess moisture to proceed.

 

When a crew first works with pervious concrete, there’s a need to learn a few new techniques. First, you want to keep a head or one to two inches in front of the roller screed. If it were standard concrete, that would be too much, and [MA-9]first-timers instinctively rake it away.

 

 

 

 

 

[MA-10][MA-11]But when they find themselves constantly shoveling to fill in behind the roller, and then making another pass, they learn pretty quickly. By the time the seocnd truck came for this project, they had a good feel for what they were doing.

    

Using a heavy roller screed is an effective way to flatten and compact the fresh pervious concrete in a single operation. Developed by Bunyan Industries (www.bunyanusa.com) and consisting of a steel pipe weighted with pea gravel, this two-person screed’s rotation comes from a hydraulic motor[MA-12], while the personnel on each end provide the forward movement.

 

 

 

 

 

 

 

 

[MA-13]Overcharge the material along the edge forms and press down with your foot ahead of the roller screed. This densifies the edges, making them more durable.

[MA-14]To control hydration and limit evaporation in fresh pervious concrete, “The Bean” is sprayed on as soon as the concrete has been placed, leveled and compacted. Jim Miller of C2 Products developed the soybean-based, biodegradable liquid specifically for use with pervious concrete.

 

 

 

[MA-15]Cross rolling further flattens the surface. It can begin before, and continue after, the plastic covering is put in place.

 

 

[MA-16]It’s very important to completely cover the concrete with plastic. The concrete’s open structure allows both water and air to pass freely through it, which is good once it has hardened but makes it very susceptible to drying out before the cement has hydrated. If that happens, the concrete has no strength.

 

 

    
[MA-17][MA-18]On this project, the Builders Concrete crew used cap nails to fasten the plastic directly to forms. The large plastic washer allows it to hold the plastic without tearing through.

 

 

[MA-19]Any holes that are made in the plastic must be patched with tape. Seams should be overlapped 6-12 inches and sealed -- a good spray adhesive can do this effectively.

 

 

[MA-20][MA-21]Because the mix also includes some polypropylene fibers, balls sometimes form. They cause no problems for the concrete structure, but should be pushed down into the mat to avoid anything strange on the surface.

    

[MA-22][MA-23]The project included placing a 4-foot-diameter expanded polystyrene plug which will later be removed and replaced by a stone compass to match several others within the arboretum.

 

[MA-24]This 168-foot long, 12-foot wide, 5-inch-thick project took about 32 cubic yards and was finished in about three hours. Leaving the forms and plastic in place -- secured on all edges and held down on the concrete surface -- throughout the seven-day curing period ensures that the mix water remains available for hydration. 

 

 

Elastic man

The pedestrian mall on Pearl Street Boulder, Colorado, boasts a full complement of street performers. Joe Nasvik, Bill Palmer, Bill's daughter and I spent a little time there this evening before we met Bill's wife for dinner.

Bill had told us about this guy who curled up and put himself into a little box, so it was easy to identify him when we reached the corner of Pearl and 13th Street, where he says he has been performing for nearly 17 years. Besides being exceedingly flexible, this fellow is also a pretty good showman and knows how to engage the crowd. Check him out the next time you're in Boulder.



By the way, that plexiglass box is 20 inches on a side.

Some frank talk about concrete contracting

The annual industy roundtable convened each fall by the editors of Concrete Construction magazine always yields some interesting glimpses of what's going on in the industry. Editors Bill Palmer, Joe Nasvik and Tom Klemens met this afternoon in Denver with several concrete contractors, material producers, a testing agency representative and a business consultant specializing in construction.

A summary of the discussion will appear in the November issue of Concrete Construction, but here are a couple of main themes that came out of the discussion.

• Nailing down expectations early in the game -- essentially settling disagreements before they come up -- is becoming more important.
• Use of "referee panels" is often proving to be an effective way to adjudicate the acceptability of architectural and decorative concrete work.
• The importance of establishing good relationships among the team members on construction projects has clearly risen in concrete contracting as margins remain slim and even small claims can turn an otherwise profitable job into a money loser.
• Two keys to succeeding in this business are carefully selecting who you want to work with and differentiating your work from that of your competitors.
• A shrinking workforce and material availability and pricing are going to continue to add to the uncertainty of concrete contracting.
• Training and education are important. But because the offerings run from short demonstration to intensive hands-on sessions, it's hard to compare and select which might be most beneficial.

While you're waiting for this year's rundown, you can check out the roundtable reports from 2004 and 2003. Meanwhile, tomorrow the ASCC seminars and demonstrations are on tap. Should be very interesting.

A little surprise in Denver

I don't know why I was surprised, but driving in from the Denver airport I just didn't expect to see prairie dogs. It's like they live there, in the wild! Which, of course, they do.

At first I thought they were in a preserve area or something -- silly me! Look at that barbed wire fence ... the spacing's a little wide for prairie dog containment. Back in Illinois we have a few trees and squirrels running around all the time. So out here in Denver it makes sense that, with few trees, there would be prairie dogs, fashioning their own retreats underground. A pleasant little diversion for the observant visitor.

Time for the next step

So it seems like we've tinkered around enough to get this blogging thing figured out, at least enough to be dangerous. And with that, it's time to take it to the next level, namely to link into it from the MIP Web page (www.mip2006.com) and start putting up some information on MIP entries. That we'll get to shortly.

However, in the true spirit of blogging, the thought occurs to me that someone out there might be interested in the development process we've gone through -- short though it has been -- and our continuing thought process, too (which may also be on the short side). So I'm going to link to the this developmental, prototypical blog from the MIP page, and we'll keep it going as long as we need to for experimenting with before we go live with new features.

For example, Ted was at a decorative concrete demonstration last Friday. I know he took some photos and got some good information. How does it fit in with MIP? Don't know for sure -- maybe the sponsoring company will enter something -- but in the mean time we'll probably post a little something here and see how it works. Let us know how it strikes you. You can comment on this post, or, if you don't want to register as a blogger, just send an email to tklemens@hanleywood.com.

Oh, and another thing. I'm working with Susan Clancy, who has been putting together the World of Concrete seminar program for a good long while now -- she really knows her stuff -- on developing a blog that would give up-to-the-minute updates on what's new to the 2006 seminar program. Any thoughts? Anything you'd like to know along those lines? Let us know. And thanks for your interest.

So far, so good

It's the end of day one and we now have an MIP blog (and I think we know how to use it!) The process could be the poster child for user-friendliness. For those of you who are reading this and wondering whether it's worth the effort of signing up, be not afraid.

We've chosen to require that you register, for free, with the idea being that will discourage non-construction professionals from bothering with this blog. But if you're interested in what's new and exciting in concrete and masonry, and especially if you're planning to attend the World of Concrete in January, do register and visit the site often. Registering is simple (and free) and it gives you the opportunity to comment on the various news items and products that will be appearing here in the coming months.

So, if you haven't already done so, sign up at www.blogger.com, then let us know what you're thinking.

Thanks for your interest, and come again soon.

Off and running

Well, we took the first step. It was all Ted's idea, but if it works, maybe he'll share some of the credit. And as they say, World of Concrete is almost here. And so is the MIP Blog.

Oh, you may be wondering who we are and what we're up to. (So do we ...!) Ted Worthington is the editor of Concrete & Masonry Construction Products (CMCP) magazine and I am Tom Klemens, contest coordinator for the 2006 Most Innovative Products contest. MIP, as it's affectionately known, is sponsored by CMCP (as it's affectionately known) and happens at World of Concrete every year.

Scheduled for Las Vegas from January 16-20, WOC (as it's affectionately known) is really much more exciting than it first sounds. Really. Check out the photos from last year's show and see if something doesn't catch your fancy. And if it doesn't, then maybe you don't really have any interest in the rest of what we're going to be posting here, either ...

So, what do you think of that, Ted?