Pervious Concrete Retaining Walls

I was introduced to pervious concrete at a GreenBuild Conference last winter. Cool stuff for flat work. I’m wondering if I could use it on retaining walls up to about 4′ tall. The advantage in my mind would be that there would be no need (?) for drainage behind the wall, and that the water that perked through would feed an interesting assortment of moss and lichen that one could grow on the face for additional texture.
The concern I have is that the concrete would have less compressive strength, and that the rebar would be exposed to corrosion. These two factored together might lead to structural issues in subsequent years.
Anybody out there have any thoughts or experience on this one? Thanks in advance.
Replies
Interesting question. The batch plant here has just started to push pervious concrete. I wonder if you could use epoxy coated rebar in a wall like that?
SaturdayNight.... please take a moment and fill out your profile. It helps us better assess your question once we know where you are coming from (pun intended).
To answer what I can, if you are in a location that has any freeze/thaw cycles, don't even think about it. You would only be asking for the concrete wall to crumble in a couple of years since the moss and lichen keep the concrete moist and in deeper locations, keep the concrete saturated. And when concrete with water in it's voids is frozen, it is a Bad Thing©.
And eventually the moss and lichen would eventually breakdown the aggregate bonds in the concrete causing spawl.
You don't stop laughing because you grow old. You grow old because you stop laughing -- Michael Pritchard
I updated my profile, but it asked for no "pertinant info" about where I was coming from. Is there another page I am not seeing?
I am a remodelor (GC) in the Puget Sound region of Washington State, where we don't have freeze/thaw cycles like elsewhere, just a lot of rain. But we do have cold snaps that might last a couple of weeks, where the temperature might drop to the teens on the worst overnight low, and remain below freezing during the day. Probably enough to cause problems like you describe. And if the water in the wall did freeze, and the groundwater continued to move behind the wall, the stresses on the wall would potentially compound when the wall was in its weakest condition. A scenario I did not think of.
"Thank you Engineer Guy, you saved the day!"
If you specifically want the moss/lichen growth, Pour a rich mix, 5 sack to 6.5 sack, air entrained, with fibermesh and an additive that improves flexion. (I'm meeting a mental speed bump and can't retrieve the correct nomenclature here. Fly ash would work well.)
Use good drainage behind it.
Parge with Zypex, then apply about 1/2" of a rich mix with perlite added.
Do both Zypex and Perlite within 24 hours of the previous and consider the perlite coat to be a maintenance item, like paint or stain.
Be sure to use an impervious wall cap.
SamT
Edited 8/7/2007 11:29 am by SamT