Pervious Concrete: The Road Less Raveled

A Pervious Concrete Thank You!

To my 353 loyal readers, THANK YOU! 

And, to the thousands of casual tourists, you're always welcome to pop by.

To put it in perspective, I know that 353 isn't pea rock compared to Newsweek, TV Guide, or even Coonhound magazine, but it's more than I expected would ever read this thing, and the number keeps growing every week.  Now that I'm 2 years and 112 posts in on this little blog project, it's humbling that so many of you keep coming back to read more.  And, you're in good company -- this website has reached 90 countries, 48/50 US states, and has even been ripped off in Korean.  As you may notice, there are times when I get too busy with my day job to put up some good content, and often think about giving up on it, but I'd hate to disappoint you, so I'll keep on writing!

 

 

Surface Texture Variability in Pervious Concrete

Two guarantees with pervious concrete pavements:

1) There will always be some raveling.

2) There will always be some variation in surface texture, especially on larger projects.

The combination of the contractor's skill at finishing and the concrete producer's ability to produce a consistent mix will determine the variability in the pavement's surface texture.  As the rare exception, I've seen craftsmen take some rough looking concrete, and work their magic to make it look beautiful.  However, more than likely, a consistent concrete mix will help the installer make a good looking pavement, especially for the unskilled contractor.  I don't often show my bias in this blog, but a good pervious concrete admixture, like Grace's V-MAR VSC500, can do a lot to make the concrete more consistent.

How much variation in surface appearance is acceptable?  Within the ACI 522.1 specification, there is no way to quantify variations in surface texture, thus, there is no limit on variability in surface appearance.  

What is the Architect/Engineer/Owner to do about accepting the surface appearance of pervious concrete pavements?  For reference, below are photos of projects demonstrating the range of acceptable variation in serviceable pavements.  Some have suggested using an image analysis technique as described in this previous post; however that has not yet been evaluated for standardization, so the validity of the method is not known. The testing that is in the current specifications includes density tests by ASTM C140 -- this should cover wide variations in surface texture that would also show up as wide variations in core density.  Wide variations, beyond the specification limit make the acceptance/rejection decision easier for the specifier.

ACI 522 Spring 2011 Committee Meeting Update

How to describe today's ACI 522 committee meeting? Exciting. Exhausting.  Productive.
A few highlights of the meeting include:
1) 522R -- John Kevern presented a progress report from his task group to rewrite 522R.  The task group is targeting 2014 for publication of the revised document.  Interested in helping?  Contact Dr. Kevern directly and let him know on which chapter you'd like to help.
2) Concrete Knowledge Center -- The committee resolved the negative votes on the CKC Pervious Concrete sustainability document.  A revised version will be posted shortly.  522 is working on a second document for the CKC.  The standard details for pervious concrete pavements are still under development.   The committee expects to ballot this for inclusion in the CKC within the next 4 weeks.
3) 522.1 -- The specification passed the committee ballot that closed last night.  At the meeting, the committee resolved all of the negative ballots.  A cleaned up version will be submitted to TAC (targeting by 4.13.11) for formal review at their summer meeting.