Pervious Concrete: The Road Less Raveled

Pervious Concrete - Asphalt Transition

In the NRMCA training for both stormwater designers and contractors, we teach the use of header curbs between the pervious concrete and adjacent asphalt to prevent water from migrating from under the pervious concrete to under the conventional pavement.  Such flows often cause subgrade failure under the plain pavement due to differential subgrade support as the area near the pervious concrete tends to be saturated while the soils farther away tend to be drier.  

Here are the slides from the contractor training class:

ACI SP-282 The Leading Edge of Pervious Concrete

ACI has released the first compilation of peer-reviewed technical papers specifically focused on pervious concrete, "ACI SP-282 The Leading Edge of Pervious Concrete".  This compilation includes papers presented at the full-day technical session held in New Orleans.  

Edited by Charles Weiss, tHe authors include some of the big names in the world of pervious concrete: Norb Delatte, Heather Brown, Narayanan Neithalath, John Kevern, Liv Haselbach, Zhifu Yang, and Matt Offenberg.  A full listing of papers can be found here. 

Top 3 Pervious Concrete Firsts at WOC 2012

It's always fun and exciting to see new technology for pervious concrete.  This year at World of Concrete, I experienced a few exciting "firsts" -- here are my top three:

1) First time vacuuming pervious concrete with Ditch Witch's attachment for pervious concrete: Ditch Witch developed a head specifically for cleaning pervious concrete.  By combining pressurized water with a strong vaccum they created a tool that was able to remove sand from the surface of five day-old pervious concrete without causing raveling.  I don't have the technical specifics, but I can safely say this vacuum really sucks!

 

2) First time for Dave Mitchell to pan float pervious concrete with his homemade, hydraulically powered machine:  In the quest to reduce raveling, experienced pervious concrete crews have been using trowels and fresnos to create a tight, dense, pervious surface.  Some contractors have taken it as far as using pan floats.  The PervMaster himself, David Mitchell, cooked up a machine to do just that, then demonstrated it to a crowd of skeptical onlookers at Pervious Concrete Live!

 

While the tool and technique did create a beautiful, dense, pervious concrete surface, this was done on a cool, cloudy Las Vegas day.  To pull this off on a large paving job in July would be much tougher.  So, for now, maybe we can leave this to the guys doing small, decorative pervious concrete work.

3) First time to see Alan Sparkman's cool hardhat:  I mean, look at this thing -- awesome!

 

Pervious Concrete Educational Opportunities at WOC 2012

If you're looking to learn more about pervious concrete, there is no better opportunity that this year's WOC!

The educational program starts Monday afternoon with the "Contractor's Introduction to Placing Pervious Concrete Pavements"   This session will present four of the six chapters from the text for the NRMCA pervious concrete contractor certification program. Attendees will learn about the basics of pervious concrete, how it is different from plain concrete, and the tools and techniques for placing, consolidation, finishing, edging, jointing and curing of pervious concrete. After completing this session and reading the accompanying text, the student will be ready to take the NRMCA certification exam which will be offered later in the week.

Tuesday kicks off the second annual "Pervious Concrete LIVE!" featuring live demonstrations of placement equipment and techniques, design details, testing, decorative pervious concrete and more.  The full schedule of events can be found here.  

Hands-on training and certification are also being offered at WOC. If you are new to pervious concrete and want to learn the art or a technician needing to upgrade to installer, the staff on hand will be there to help.

What I really look forward to, however, is the opportunity to speak directly with the experts and innovators in the pervious concrete world -- they'll all be there!  

ASTM C 1747-11 for Pervious Concrete

Saw in an email that the new Standard Test Method for Determining Potential Resistance to Degradation of Pervious Concrete by Impact and Abrasion will be numbered C 1747-11.  It hasn't been published yet, but will be soon!

Pervious Concrete at the Fitzgerald, GA Wal-Mart

If you ever find yourself in south Georgia, at the crossroads of cotton and peanut country, near the home of the "Wild Chicken Festival" you'll be in Fitzgerald.  Recently, I had a chance to visit the Wal-Mart there.  If you don't know where Fitzgerald is, it's right here:

Hard to believe they have a Wal-Mart there, but you can find it at 120 Benjamin H Hill Drive West, Fitzgerald, GA.  The store and associated pervious concrete parking lot, were built in 2003.  The pervious section is the rarely used overflow lot on the north side of the property.  It's roughly 300' by 200' and in generally good condition for a pavement that's approaching 9 years old.  

Here are a few photos to give you a feel for how it's holding up.

The Store

Condition of the pavement and joints.  Not bad for its age.

 

Some joints are performing well...

...and some aren't.

The ribbon curb is doing a good job of protecting the pavement edge.  It's interesting to see that the asphalt next to the curb is shoved up.  I'm not sure if this is from the concrete expanding or the asphalt expanding, but I've seen this on other, older pervious concrete projects.

 

As we've seen with other pervious concrete installations where asphalt drains onto the pervious, there is a bit of clogging near the inlet to which the asphalt run-off is directed.  I didn't run the 1701, but water did still drain through the clogged panels.  In the future, this may become a maintenance issue for the owner.

This shot will give you a feel for how much asphalt area drains onto the pervious concrete.


For me, this was the highlight of the whole trip -- a beautifully patched core hole!  These were scattered all over the lot.  I've been looking for years for a photo that shows how to patch the core holes, and this is a great example.

ASTM Pervious Concrete Winter Meeting 2011 Update

To say the body of knowledge in pervious concrete is growing is an understatement -- it is exploding!  This week the ASTM meeting added to that explosion with the first ASTM Symposium on Pervious Concrete.

The symposium featured eight speakers covering some of the latest research and updates on test methods for pervious concrete.  Some of the more interesting presentations included:

 

• "Validation of the Performance of Pervious Concrete in a Field Application with Finite Element Analysis (FEA)" Md. Ashraful Alam, Liv Haselbach, William F. Cofer, Washington State University, Pullman, WA USA 
• "Pervious Concretes Pore Structure Characterisation by 3D image analysis - Impact on their Permeability" Samuel Meulenyzer, Eric Stora, Fabien Perez Lafarge Centre de Recherche, Saint-Quentin Fallavier, Franc
• "More Information on ASTM C 1688 Variability" L. K. Crouch, Ph.D., P.E. Tennessee Technological University,  Cookeville, Tennessee, USA; John Hendrix, P.E. Tennessee Technological University,  Cookeville, Tennessee, USA; Alan Sparkman, CAE, CCPf, LEED AP Tennessee Concrete Association, Nashville, Tennessee, USA; Daniel Badoe, Ph.D. Tennessee Technological University,  Cookeville, Tennessee, USA 
• "The Development, Implementation and Use of ASTM C1701 Field Infiltration of In Place Pervious Concrete" Heather J. Brown, MTSU, Murfreesboro, TN, USA; Alan Sparkman, Tennessee Concrete Association, Nashville, TN, USA 
• ...and, of course:"Development of a Test Method to Determine the Raveling Potential of Pervious Concrete" Matthew Offenberg, W.R. Grace, Canton, GA, USA 

The papers and presentations are not available, yet.  But I'll post an update as soon as they are, or you can sign up to get an alert from ASTM here. 

ASTM's subcommittee on pervious concrete also met on Monday.  The raveling test has moved a step closer as it passed the main committee ballot, so is headed off for staff review.  The hardened density and voids test likewise is advancing, but had a few negative votes to resolve by the close of the meeting.  The compressive strength task group has a draft standard, but will also be testing out a new compaction technique using a hammer drill.  They expect to open their first ballot this coming spring.

BREAKING NEWS: New UFGS Pervious Concrete Specification

BREAKING NEWS:

The United States Federal Government's new pervious concrete specification has finally been published!

The new section, numbered 32 13 43, replaces the old section 32 13 13.06 which was the plain concrete pavement spec that had pervious language scattered throughout.  Likewise, an updated 32 13 13.06 has also been published to remove the old pervious concrete references.  A copy of the new pervious concrete specification can be downloaded for free from the National Institute of Building Sciences. 

Many thanks to the project team that made this happen.  Specifically, Chuck Weiss from the Army Corps of Engineers, Toy Poole, and the NRMCA staff who participated along the way.

 

Pervious Concrete Contractor Training for Union Workers

In a unique partnership with the National Ready Mix Concrete Association (NRMCA), the Operative Plasterers' and Cement Masons' International Association (OPCMIA) has begun training contractors in the art of pervious concrete.  Under this agreement, the OPCMIA will offer an intensive, hands-on training program to its members and provide the NRMCA pervious concrete contractor certification exam.  The exam will be administered through the NRMCA Local Sponsoring Group in coordination with the local union hall.

Individuals completing the class and passing the exam will be certified technicians. When they complete three projects with at least 10,000 square feet of pervious concrete pavement they will be able to upgrade their certificaiton to the installer level.  

Overall, this partnership will provide union-heavy markets with a pool of trained individuals, while still mainting a uniform level of quality, across the country, in the certification process.  

Interested individuals can find information on their local union hall through http://www.opcmia.org/.   

Grouted Edges for Pervious Concrete

The goal of any pervious concrete installation is to make a strong, durable pavement that will drain water.  Seems easy enough, but 'strong and durable' are the opposite of 'drain water'.  So, the skilled pervious concrete contractor has to maintain a delicate balance between these two opposite targets to buld a pavement that will last for years while maintaining permeability.

Unlike conventional concrete pavements, when pervious concrete fails, it fails in raveling (the wearing away of the pavement surface caused by the dislodging of aggregate particles).  Raveling is usually most pronounced at the edges and joints where compaction didn't happen in a smooth operation like with the rest of the pavement.  Some strategies to prevent this distress include over-compacting the edges, and paying special attention to tightening up the joints.

Raveled edge along a construction joint

Our friend Dave "The PervMaster" Mitchell has come up with a unique way to prevent raveling along the construction joints -- he calls them 'grouted edges'.  He uses a bagged grout mix that, when mixed to a stiff consistency, the finisher works into the edge of the pavement adjacent to the form.  The result is a strong, decorative edge to the pervious concrete that shouldn't ravel.

 

Grouted edge along a formed joint

 

The advantages of this technique are obvious, the disadvantages might include: extra labor needed to mix and place the grout, reduced freeze thaw durability of the grout (if not selected properly), and difficulty in matching color for decorative work.  I like the way Dave's edges are wavy and irregular; however, every building owner might not appreciate the look which would require more labor to keep the lines straight.

Decorative grouted edge border

 

This previous post shows a driveway with grouted edges along the outside border (and The Pervmaster himself showing off his work).