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inspektor (Civil/Environmental) (OP)
31 Aug 10 18:54
A guy I work with came back from a seminar with this, and is fixated on this. We have been allowing recycled concrete for use as subgrade, and now this guy thinks our ductile iron pipes will be falling apart.
Anyone every heard of this? Had any experience with it? Know any resources I can consult?
Muchas Gracias.....
cvg (Civil/Environmental)
31 Aug 10 19:52
take a sample in to your favorite geotech and have them analyse it? Not sure why you are placing any pipes on a layer of recycled concrete, doesn't sound like the best practice to me. I would prefer sand or good granular bedding, not crushed concrete.
dgillette (Geotechnical)
31 Aug 10 20:20
We routinely put steel rebar in concrete, and it seems to hold up OK.  Off hand, I'd expect the crushed concrete to either have little effect on the water chemistry, or raise the pH a bit if it contains any soluble carbonates, which might be a good thing for the DI pipe.

De nada.
inspektor (Civil/Environmental) (OP)
1 Sep 10 9:41
Thanks CVG, I guess I was not clear. Water distribution pipe is installed in the usual manner, in Colo. 5 feet down, bedded with Granular material. backfilled and compacted. The compaction is tested. The recycled concrete is used as a roadbase for a composite section with for instance, 8 inches of recycled concrete, and 5 inches of asphalt. I have been a fan of recycled concrete as a roadbase, and we have used it widely, however my coworker is over-reacting in my opinion, and I was curious if anyone else had any information on this.
I think Dgillette had an good observation about water chemistry in case of ground water. This area had a lot of coal mining, and my personal opinion is that the corrosive soils may be caused by groundwater reacting to sulfur gases coming off the coal beds, but my chemistry was never all that good. Thanks for the reply tho.............
dgillette (Geotechnical)
1 Sep 10 10:18
Paonia?

By "it contains any soluble carbonates" I was referring to the recycled concrete containing the carbonates.  In my very limited knowledge of cement, I recall it releasing calcium hydroxide in the curing process.  Upon leaching by rain and exposure to CO2 in the air, that becomes calcium carbonate that appears as efflorescence sometimes (like on the green-colored concrete ret wall and patio I recently put in). Either that or hydroxide might be a good thing to have near your CI pipe to protect it from the acid in some small way.

DRG
cvg (Civil/Environmental)
1 Sep 10 11:09
you might pose this question to the portland cement association. they are generally very willing to help and probably have already researched this. See the following article:

http://www.cement.org/tech/cct_dur_corrosion.asp
TDAA (Geotechnical)
1 Sep 10 13:20
dgillette:

The Paonia are still has active coal mining, but there were also plenty of mines in Bolder/Weld Counties (Denver area) and in the Rockrimmon and "Country Club" areas of Colorado Springs, to name a couple.  Based on the "had", I would guess the Front Range, unless it is another area that I do not know had coal mining.

In addition to the PCA, you might also try calling Recycled Concrete Products.  They sell a bunch of crushed concrete, and I am sure (at least hope) they would be keeping up with issues such as this.
theCorkster (Geotechnical)
1 Sep 10 17:45
Since the issue of concern is corrosion of ductile iron pipe, I'd suggest contacting the pipe association regarding the conditions and materials that may come in contact with the pipe.  

http://www.dipra.org/ductile/

I think that the more important issue is what may come in contact with the pipe resulting from seepage from the surrounding soil that can migrate through the back fill.

Benign back fill is fine but doesn't protect piping subject to seasonal water movement that flushes chloride or sulfate out of the surrounding soil.

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