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Calcium Chloride in concrete for perimeter foundation??

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nirias

Civil/Environmental
May 16, 2011
9
Hi,

I hired a contractor to replace the brick foundation on my two story house with an inverted "T" concrete foundation. The footing is 18" wide by 18" deep with an 8" stem wall. Reinforcing is #4 bars with 3" cover.

Only after the concrete was in the forms did he explain he had ordered the concrete with 2% CaCl2 in order to save some time. But I have read that CaCl2 should never be used with reinforced concrete because it will lead to rapid corrosion of rebars, with corrosion failures occurring as quickly as 10 years.

What is the typical experience with CaCl2, when there are no other sources of chlorides (The house is in San Francisco well above the groundwater so there are no salts from winter ice control or ground water table to contribute to the problem).

Is there any chance this foundation will survive for 50 or more years? Is there any mitigation, such as sealing the surface to minimize availability of oxygen, that is practical at this point?

thanks for any info you can provide
 
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Chlorides should not be introduced into reinforced concrete. I am surprised that you can still order concrete with calcium chloride as an additive. It should be illegal. There is no way of predicting the long term behaviour of your footings, but what has been done is not good.
 
I'm assuming a permit was required for this type of work. If so, that means someone put together a set of permit drawings. If so, there are probably notes on the drawings that specifically prohibit the use of chlorides in concrete, and that all admixtures shall be subject to the owner's approval. These are pretty standard notes and are usually on any set of recently prepared drawings. If so, you may have ammunition to seek more drastic recourse: i.e., make the contractor take it out and redo it at his own expense.

However, if the contractor did the permit drawings for you, those notes are probably not there!

I'm not sure of any mitigating action you can take, as I've never been involved in this sort of thing before...but you definitely need to do something.

Good luck.
 
nirias...to put it bluntly, you're screwed. As hokie66 noted, this should never be allowed. The contractor probably gave you a 1 year warranty. It will last more than a year, but who knows how much longer. It won't last 50 years or anywhere near it, particularly if you have moist ground conditions at your foundation level.

Have the contractor remove the concrete and start over. Not acceptable.
 
any chance the foundation checks out as plain concrete?
 
Thanks for the replies.

The contractor said calcium chloride but I just got a look at the concrete delivery tag and it says:
"6 sack 1/2" PM PL NC 2 dosage"

Any chance the "NC 2 dosage" refers to a non-chloride accelerator of some sort? I plan to call the concrete plant tomorrow to ask them exactly what they mixed.
 
Stop work until you know - you have a chance now to recover, but not after the rest goes up over the foundation.

Follow up. Be sure to check with that specific batch plant - a different one may use a different term.

Lots of dollars/lawyers involved here to recover the damages damages and rebuild - or to have the contractor to pay for the ripout, disposal, and replacement. Make a copy of the batch tag, use it. Don't lose the original.
 
There are lots of non-chloride accelerators available. Get a tech bulletin on what was used, get confirmation from the ready-mix supplier, and get a material safety data sheet for the admixture.

If chlorides show up anywhere, have them remove the concrete. If it clearly is a non-chloride accelerator, just inspect the concrete for any indication of problems from the faster set (most common will be plastic shrinkage cracks that do not heal and interconnect to become long cracks).
 
Good news. I talked to the concrete plant today and the accelerator used in the mix is Pozzolith NC534, which is chloride free. They placed the footing in cool weather and there are no visible cracks thus far (2 weeks), so I hope no ill effects from the accelerator.

The contractor said calcium chloride several times so that must be what he asked for. Fortunately the ready mix plant didnt fill his order exactly as he specified.

Thanks everyone for your feedback.
 
Yes, good news, if you can trust the concrete supplier. Did you ask them if they EVER use chloride additives? How old is the contractor? Probably an old guy who has been asking for the same thing for 40 years.
 
I would not not rely on what the concrete supplier told you verbally. You should get a copy of the delivery ticket from them. But best to have it tested for chloride concentration. The chloride corrosion concentration threshold above which corrosion of rebar will occur in the presence of oxygen and moisture is not exact, but is usually taken as between 0.025% to 0.035% of water soluble chloride by weight of the concrete. The usual test is to drill some cores in not critcial areas, and take slices out of the core to be tested by a concrete lab. A concrete testing lab can arrange for the drilling and for the testing. Here in Toronto Canada it is a very common test. Contrary to what some have said on this site, it is not against Code to use calcium chloride in the concrete - in fact there was a paper in ACI Concrete International about a year ago, by a trade organization, promoting its use in concrete that is in permanently dry envionment. I strongly disagreed with the paper because it is risky trying to assess a dry environment. I would not classify a foundation as a dry environment. The problem will be that the bars corrode and the corrosion product is 4 time the volume of the original metal and splits the concrete apart. So even if the foundation might have worked without the rebar, it won't likely work after the concrete has been split apart. Better to get it tested and have it removed now if it was made with chloride; if the test shows it was not, well then at least you can sleep at night. The whole coring and testing procedure should be under $1,000.
 
ajk1,

I have used core drilling and taking slices for chloride testing before and it is great for determining chloride levels at various horizons/depths, which is very valuable for determining whether the chlorides have penetrated to the level of the reinforcement. However, if calcium chloride has been added to the mix, it should be more or less evenly distributed throughout the concrete. Therefore would it not be cheaper and less intrusive in this case to use a concrete drill bit, rather than core drilling, and collect a powdered sample directly from the drill hole? I have encountered labs in the Ontario area using this procedure before.
 
The following article was originally written in 1974 and modified in 2005. There were lots of buildings where the Contractor used 1% or 2% CaCl in the '60s and '70s. Many of those buildings are still around today and I haven't heard reports of many problems arising from its use. Have others had a different experience?


BA
 
To Skis and Bikes: yes you can do it by drill bit dust and save the core driller's cost, but the labs I work with around here have never wanted to do it that way because the bit can be easily contaminated. If things went to litigation, may be harder to justify the finding from drill dust. But if you just want to satisfy yourself that it was not made with chlorides, perhaps the drill bit dust procedure can be used if you use a clean bit not contaminated from other projects. I have never done it though.
 
BA,

I have worked on upwards of twenty multistorey projects over the years (and have knowledge of many more) where concrete repairs were required on vertical, exterior elements and balcony slabs located above grade (i.e. away from deicing salts). Exposed slab edges, columns, shear walls and balcony slabs all showed signs of concrete delamination due to corrosion of the rebar. Testing, in the majority of cases showed elevated chlorides. However, I will add that the majority of problems occurred at locations where there were chlorides AND low concrete cover. Where concrete cover was significant, there were much fewer problems.
 
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