Severe exposure to unknown substances 1

[JMorrison]

Got a bit of a fun one here - it's a single-story concrete moment frame, supported on caissons, with about half of the building extending out over the Anacostia river here in DC - so half of the building columns are going to be exposed to running water from one of the most polluted waterways in the nation. Basically, there could be pretty much ANYTHING in this water. The other half of the project is sitting on a recovered brownfield, and we're not sure what's buried there either.

My main concern is the concrete itself - we're planning on using 40-50% GGBS both to help resist sulfide attack and for the LEED points (project is shooting for platinum certification). I'm figuring we'll need a Class V cement, and gut is saying a significant level of air entrainment for crack control since freeze/thaw is a definite consideration, although I'm concerned about the pockets that would create.

I'm also quite concerned about cover and jointing - I wouldn't consider using less than the 3" cover from ACI, but in this case I'm wondering if even that's too low - and can't seem to find a specific reference for exposure to indeterminate deleterous substances. Similar issue with the cold joint between caisson and column - definitely don't want it underwater, but don't particularly want it right below my slab either.

Anyone have any specific experience or recommendations for research on this type of condition?

 

[csd72]

Have you considered epoxy coated rebar? It may be worth it even with the 3" cover.

Any way you can get a membrane on the outside of the concrete?

Just throwing a couple of ideas at you, I dont have any answers, sorry.

 

[JAE]

I'm not sure, but would adding silica fume help? It would densify the concrete and reduce permeability.

 

[csd72]

Check out the PCA website, they have some pretty good reference materials on this type of stuff (Some of it is free).

http://www.cement.org

 

[JMorrison]

The epoxy coated bar would probably help out a bit, and I'll look into the local availability of silica fume. Membranes and other exterior-based protection - we may be able to use 'em for the above-water portions to protect against splash / tides - and that may be a good solution for protecting the cold joint. I'll see what PCA's got and post any solutions.

 

[cvg]

I would recommend testing the water first before recommending anything. Unless you have sea water, you may not need some of this. Standard procedures like requiring air entrainment, low water cement ratio, higher strength concrete, and perhaps fly ash along with insisting on tight QA/QC especially on the minimum cover thickness over the rebar will go a long way in preventing corrosion.

 

[JedClampett]

I agree with cvg. We design a lot of wastewater treatment plants and with a couple of common sense adjustments (low w/c, 4000 psi concrete, etc), just use batched concrete.

 

[DarthSoilsGuy]

nothing to add.

your post just reminded me of when i worked at the DCWASA wastewater treatment plant serving DC, North VA, and South MD on that river in Anacostia. ~400 MGD typical and ~700MGD after storms i think it was. The effluent from that plant is the best thing going for that nasty river.