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"Rusting" Concrete

 
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Old 01-12-2012, 04:26 PM   #1
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"Rusting" Concrete


I was called by a home owner that had a couple of pads poured the day before Thanksgiving by another contractor and said that the concrete looks like its rusting and has holes appearing in it. So i met with her yeaterday to check it out and for the life of me cannot figure out what is causing this reaction. As you can see in the pics it looks like it is rusting and it slowly eats away at it until it creates a hole in it, does not come out in chunks just slowly eats away. Anybody ever see this before? In @0 yrs of concrete and construction, this is a first for me. Any ideas would be appreciated. She wants a price to tear it out and repour it but also wants an opinion of what caused it. There are several of these holes and new ones appearing.
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Old 01-12-2012, 04:41 PM   #2
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Re: "Rusting" Concrete


I've seen similar results when the sand/aggregate that was used in the mix was contaminated. Mostly with beach sand.

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Old 01-12-2012, 05:20 PM   #3
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Re: "Rusting" Concrete


What you have there in techical term called Concrete Popouts. Popout is a conical fragment that breaks out the surface of concrete. Usually a fractured aggregate particle can be found at the base of the hole.

There is a few causes for that... one of them is when porous aggregate pieces used which have a higher rate of absorption and they fail in freezing conditions. Another cause is when deleterious aggregates being used like chert, coal, soft limestone, hard burned dolomit, pyrite etc... or aggregates that swell with moisture, not to mention Chemical reaction between reactive aggregates and alkalis in the cement can also be the cause of that.

To prevent this is hard to do because you don't know what aggregate will be used in the mix. Some smaller companies will use cheaper aggregates to be able compete with the bigger guys, etc.

Another few methods can be used to prevent this is using proper curing methods, have the proper pitch so you have good dranage.

To repair a popout can be done by drilling out the spalled particle and patching the hole.

If a bad batch of mix is noticed on bigger jobs like bridges, wearhouses, or any other big job, the engineers will request the company to replace the concrete and reduce alkali aggregate reaction with proper mix design, aggregates or mineral additives like type F fly ash or slag.
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Old 01-12-2012, 05:29 PM   #4
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Re: "Rusting" Concrete


Possible greg but dont think its an aggregate issue, my thinking is a chemical issue as it isnt popping out but eating out.
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Old 01-12-2012, 06:11 PM   #5
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Re: "Rusting" Concrete


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Possible greg but dont think its an aggregate issue, my thinking is a chemical issue as it isnt popping out but eating out.
Daniel,
Popout is a technical term... and is one of the 8 issues specified on the chart which is used by most professionals in the Concrete industry today... When I took my certification course 22 years ago I got this chart, which is being used by building inspectors, architects, engineering inspectors,etc and they use this chart to identify the problems on big or any job for that matter. I haven't been taking any courses since then, so unless there is something new out there, I'm all ears.
The following is the 8 most known concrete issues which use to identify the problem, the cause and the remedy for repair. I specified everything it said for your particular issue, and today is not your lucky day for me to type everything out for the rest of the issues Sorry.

So here it is, the 8th causes to identify the problem with concrete.

1.Cracks
2. Scaling
3. Blistering
4. Discoloration
5. Crazing
6. Plastic Shrinkage
7. Dusting
and 8. Popout

I hope you find this helpful... Good luck
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Old 01-12-2012, 07:59 PM   #6
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Re: "Rusting" Concrete


Lol, dont expect you type it all out. I am familiar with the 8 most known issues, but still think it is a chemical issue that is connected to the mix. You mention something about aggregates freezing and possibly causing this but im in SC and we havent had a whole lot of freezing temps yet, so i have ruled that out. Thanks for the info and input.
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Old 01-13-2012, 04:51 AM   #7
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Re: "Rusting" Concrete


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Lol, dont expect you type it all out. I am familiar with the 8 most known issues, but still think it is a chemical issue that is connected to the mix. You mention something about aggregates freezing and possibly causing this but im in SC and we havent had a whole lot of freezing temps yet, so i have ruled that out. Thanks for the info and input.
No problem, any time, and if you read it again " There is a few causes for that... one of them is when porous aggregate pieces used which have a higher rate of absorption and they fail in freezing conditions. Another cause is when deleterious aggregates being used like chert, coal, soft limestone, hard burned dolomit, pyrite etc... or aggregates that swell with moisture, not to mention Chemical reaction between reactive aggregates and alkalis in the cement can also be the cause of that.
So don't rule that out just yet
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Old 01-13-2012, 05:23 AM   #8
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Re: "Rusting" Concrete


I have to say that I agree Greg on this one but if it is actual rust some times you get what we call fin fish. When a pice of the fins in the the truck break off and comes out in the mix. Looking at the finish on that slab (for out side) I would say start all over.
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Old 01-14-2012, 08:52 AM   #9
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Re: "Rusting" Concrete


I highly doubt that it's aggregate of any kind. Could be part of the drum/fin, but looks more like a mud that either found it's way up from the bottom, or got kicked in from the edge.......
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Old 01-16-2012, 11:18 AM   #10
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Re: "Rusting" Concrete


Quote:
Originally Posted by daniel8675 View Post
I was called by a home owner that had a couple of pads poured the day before Thanksgiving by another contractor and said that the concrete looks like its rusting and has holes appearing in it. So i met with her yeaterday to check it out and for the life of me cannot figure out what is causing this reaction. As you can see in the pics it looks like it is rusting and it slowly eats away at it until it creates a hole in it, does not come out in chunks just slowly eats away. Anybody ever see this before? In @0 yrs of concrete and construction, this is a first for me. Any ideas would be appreciated. She wants a price to tear it out and repour it but also wants an opinion of what caused it. There are several of these holes and new ones appearing.
I have seen the same thing happen in the past. Leaves poured over with concrete will give that effect that you are having or mud. Sometimes calcium chloride chunks will cause somthing similar as well.

Last edited by CONCRETE MIKE; 01-16-2012 at 11:26 AM.
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Old 01-16-2012, 02:36 PM   #11
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Re: "Rusting" Concrete


Concrete Mike, u hit the nail on the head. The owner had the salesman from the concrete plant come and take a look at it and he said the contractor had asked for the calcium to be added on site instead of at the plant and probably didnt get it mixed in good. First time ive seen this as ive always had the calcium mixed in at the plant and have never had an issue with it myself. Thanks to everyone for the input!
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Old 01-16-2012, 03:17 PM   #12
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Re: "Rusting" Concrete


Quote:
Originally Posted by daniel8675 View Post
Concrete Mike, u hit the nail on the head. The owner had the salesman from the concrete plant come and take a look at it and he said the contractor had asked for the calcium to be added on site instead of at the plant and probably didnt get it mixed in good. First time ive seen this as ive always had the calcium mixed in at the plant and have never had an issue with it myself. Thanks to everyone for the input!
No problem, try to help a fellow concrete finisher anytime!

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