flaking concrete 1

[weswood]

my slab for my shop is 7 days old and is flaking. it was poured in 50-60 degree weather no rain on it for 2-3 days i live in texas so no freezing right now the land was dry before we poured it. the contractor is saying it was a bad mix and the concrete company is saying it was a good mix that its the contractors fault.there were 2 different trucks the first truck looks good the second is where the problem is. where the problem is the slab is a different color than the rest kinda a darker gray color. the concrete company came out today at the 7th day mark and did a hammer test or something to test the psi and said it was 2200 right now we ordered 3000psi any help would be appreciated

 

[JAE]

Most likely the concrete finisher got onto the slab and troweled it before the bleed water came up. Either that or the mix might have had air entrainment in it but being in Texas I'm not sure there would have been air added. A blister/spall like this is most likely poor workmanship.

Hire an engineer to investigate this for you.

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[weswood]

thank you i tried to post a pic idk if you could see it

 

[Ron]

Weswood... your photo shows scaling and blistering. This is a finishing problem caused by trapping bleed water just below the concrete surface during hard troweling. A common cause of this is the finisher adding water to the mix at the site or the aggregates were too wet at the batch plant.

The impact hammer they used on the slab is worthless for any meaningful data. To prove out the issue, you'll need a petrographic examination of the concrete. This is relatively expensive but can clearly show whether it is a mix problem or a construction defect.

 

[weswood]

is there anyway to fix this problem or does the slab have to be redone.

 

[JAE]

Two option that I see:
1. Remove and replace the slab wherever it is blistered. This would require sounding the slab across all surfaces to find the bad areas.
2. By sounding the slab, identifying those areas that are poor - then mill down the top surface of the slab (perhaps 1 1/2" min.) and put back a 1 1/2" thick bonded overlay slab.


Option 2 is probably more expensive than option 1.

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[JAE]

3. Chip down the blistered/scaled areas and patch the surface with a patching mortar.

Option 3 isn't what you paid for and is a diminished quality slab.

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[weswood]

thank you all for the responses

 

[Ron]

Agree with JAE's repair assessment.

 

[TehMightyEngineer]

Here's a good example on sounding concrete with a drag chain:

https://www.youtube.com/watch?v=eQAg9AkQ0qw

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com

 

[dik]

Your 2200 psi @ 7 days will yield roughly 3000 @ 21 days... If an issue, you have to get petrographic testing of a sample, likely a sectioned core. Sample should be taken at an area of delamination; let the tech decide.

If spalling is not an issue then you can 'patch as you go' or check the entire slab for delamination and fix it all. Areas of delamination can be determined by chain drag, or other means.

You likely did not get good value and subject to over wetted aggregate, it is very likely a finisher problem.

Dik

 

[msquared48]

Flaky concrete is placed by flaky contractors.

Mike McCann, PE, SE (WA)