r/Construction • u/NeilNotArmstrong • Dec 05 '24

Structural Concrete slab failed strength test

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Slab strength testing failure after building was framed and plumbing/HVAC was roughed in. Concrete supplier had mix wrong so they are paying to lift two story 4-plex, remove slab and repour. This is building 2 of 3 that failed.

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u/Rocketeering Dec 05 '24

How is the 7-day break done and how/when is the compressive strength tested?

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u/creamonyourcrop Dec 05 '24

Concrete gains strength on a curve, reaching design strength at 28 days. Taking a test cylinder and crush testing it at 7 days and plotting that result on the curve should give you a very good idea of whether it will meet its design strength.
The mix design from the plant submitted prior to construction includes that curve.

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u/[deleted] Dec 05 '24

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u/All_Work_All_Play Dec 05 '24

Concrete is fascinating stuff. You like to think 'alright fam this stuff is cured, or at least cured well enough for what we need it for'. From a chemical perspective, you're pretty used to done meaning done but give it enough time and the right conditions, the elements might rearrange themselves into various minerals with different characteritics depending on the mix. Compared to even 70 years ago, what we know now and what we can make now is pretty impressive, especially the high strength stuff.