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:
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!
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!
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.
