New concrete crumbling on surface

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  #1  
Old 03-02-15, 07:22 PM
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New concrete crumbling on surface

I just had a contractor pour new steps and after a few months, this crumbling just occurred (please see the photos). If the photos are not visible, the concrete is crumbling on the top of the steps landing but it looks only to be a small top layer and not the structure itself (although the structure itself could be next).

Could someone knowledgeable about concrete tell me what the probable cause of this is?

* Too much sand in the mix?
* Too much water in the mix?
* Something else?

I don't think it could be the 0-15 degree (F) temps we have been having because no one else's concrete is doing this. Thanks!

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Old 03-02-15, 07:30 PM
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Water is getting in the concrete, freezing, and popping the top off. Usually air is added to the mix in cold climates to give a bit of cushion for this expansion.

Was this ready mix, or mixed on site? I am also assuming this was a new pour, and not a top coat over something that was existing.

Here is some more information on the subject http://joneakes.com/jons-fixit-datab...ained-Concrete
 
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Old 03-02-15, 07:48 PM
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This is a new pour and was poured in September from a concrete delivery truck and done by a concrete contractor.

But why isn't water getting in everyone's concrete and popping off the top? SOMETHING had to be done incorrectly for this to happen, right?
 
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Old 03-02-15, 07:54 PM
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It is possible the concrete didn't have air added to the mix to begin with. Even here in Canada, we have to ask for it to be added based on the intended use of the mix. If a vibrator was used to settle the concrete you can over do it, and remove too much air that way as well. Pooling of water on the surface or a poor finishing job can also let more water into the concrete and create problems.
 
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Old 03-03-15, 04:36 PM
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Thanks a lot for the reply. I notified the contractor and suggested it could be the lack of air in the mixture.

One other question - in order to know what to accept as a solution from the contractor: Will the whole thing eventually crumble, or is this something that just happens to the top layer?

Thanks again for all the help!

-Tony
 
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Old 03-03-15, 06:00 PM
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Generally this only happens to the top layer and does not lead to structural issues, but it does need to be patched.

Also, this does not mean the whole pour is bad, it is possible the defect is just in that one area. I personally would not expect A complete replacement.
 
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Old 03-03-15, 07:15 PM
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probably ' worked ' too much by the finisher which can cause bleedwater troubles as you're seeing now,,, than again, note we only have a picture to look at.
 
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Old 03-03-15, 07:39 PM
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If you scrape off all of the loose stuff in a small area, then sweep the surface relatively clean of all dust and fines, and then lightly tap on the exposed surface with a steel hammer, you can generally tell if a surface repair will suffice, or a deeper, full-depth replacement will be needed. Soft, pulpy concrete giving off a dull thud is bad, while concrete having a nice solid ring to it is good.

Pouring a thin lift of new concrete on junk, underlying concrete will be what less scrupulous contractors like to do, as it's a relatively easy out for them, and inexpensive. And you won't find out about its poor performance until at least a year down the road.
 
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Old 03-04-15, 12:10 PM
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Well, I finally emailed the contractor about the problem and his reply email was "It looks like someone put salt or de-icer on it."

What does he mean; is it common knowledge or something that salt will cause concrete to break apart? If it does, why isn't everyone's concrete all crumbled like mine?

Any thoughts? Thanks again.
 
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Old 03-04-15, 01:32 PM
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Heres an article that may be of interest. Deicing Salts And Concrete | Ask the Builder
 
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Old 03-04-15, 01:40 PM
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Great article ray, that sums thing up perfectly.
 
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Old 03-04-15, 09:12 PM
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Except a few details in the article are either misleading, or not particularly accurate. Concrete does not gain strength by "drying," as the article implies. Rather, it gains strength by cement particles locking onto molecules of water in the mix, causing a process known as hydration. Allowing newly-placed concrete to actually dry, without enough free moisture being available for adequate cement particle hydration, is a recipe for disaster, and will result in concrete that is neither strong nor durable.

The article also refers to siloxanes and silanes as being some kind of magic elixir, enhancing the performance of in-service concrete. The DOT I devoted 25 years of my life to, conducted many years (and dollars) studying the advantages of silane and siloxane as concrete bridge deck preservatives. The conclusion of that study resulted in a "Do Not Use" memo going out to all of the Districts, stating that the net benefits of applying these products did not justify their use. I remember one of our chemists summing it up rather nicely, calling them glorified (meaning expensive) rubbing alcohols.
 
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Old 03-05-15, 08:34 AM
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The answers to my original posting was all about not enough air in the mixture. How can an article about using salt "sum up perferctly" the lack of air I've been told which was the problem?

Anyway, BridgeMan: Do you recommend I seal it and if so, with what? I'd think that sealing concrete would help protect against salts melting ice causing the water to soak in.

Something doesn't make sense: If people here agree that salt caused the popping off of the surface:

(1.) Why isn't everyone else's concrete going bad too? I just went to 3 places today (restaurants & retails stores) and saw tons of salt on their concrete ...but none of it is doing what mine is.

(2.) Why would the salt break up the surface in just one small area (where salt wasn't applied) but not the rest of the surface which had a LOT more salt?

Thanks for all the input! -Tony
 
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Old 03-05-15, 09:58 AM
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The article sums up the conditions that lead to the issue you are having. Salt itself will not cause this but it lets more water in the concrete. The water is what causes the problem.

Bottom line, if the pour was done with the right mix and the right installation procedure, you should not be having an issue. Something was not done right here. Maybe it was overworked in that one area and that is why it's the only one causing problems. Or maybe water lays in that one area more than the rest.
 
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Old 03-05-15, 10:14 AM
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Everyone else's concrete isn't crumbling when salt is applied because of many variables involved. No doubt, the examples you mentioned are a lot older and closer to being at full strength than yours was, making them more resistant to damage caused by freezing water. They also could have been cast using air-entrained, higher-strength concrete, along with being more effectively cured to begin with, using curing compounds or other methods, instead of being allowed to "air dry" (as yours probably was). Edges and corners of concrete placements are often more vulnerable to freeze-thaw damage, both from being exposed to freezing air and water on two surfaces, and from being overworked by finishers during initial placement. Overworking tends to bring up too many fines, which will also weaken the surface; if edging was done after initial set took place, water was probably added to aid the re-working process, which also lowers the surface's strength and durability.

Sealing concrete that has experienced the extent of deterioration that yours has, will do nothing to restore it--the damage has already been done.
 
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Old 03-05-15, 11:00 AM
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BridgeMan has hit on the head in his detailed description regarding finishing, edges, corners and curing. Anytime you are placing concrete for a horizontal surface or where runoff can contain salt, it should be air entrained and a higher strength for durability.

Here, it is routine to use 3500-4000 psi air entrained concrete for those applications since it is a minimal extra cost compared to repairs and disputes. For some uses, that mix is almost automatically delivered unless the contractor specifically wants something different.

Dick
 
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Old 03-10-15, 05:11 PM
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Thanks again everyone for your time and knowledge (Bridgeman especially for that good info).

The mason is not offering to fix it, so I'm just out of luck. He is hell bent on blaming it on the one time I used salt on it. I see TONS of salt on perfectly good concrete everywhere I go on commercial retail concrete work. It's hard to believe one salt treatment destroyed the surface of mine, but I guess it's possible.
 
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