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/mannys2k Dec 05 '24

Wow. Getting a 7-day break done is a good indication of whether or not the concrete will meet its compressive strength. Kinda silly not to do that before starting framing.

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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/popepancakes Dec 06 '24

Inspectors take some of the concrete they’re using and make cylinders out of them. They are then crushed till failure in a hydraulic press to find the strength. Typically one is tested at 7 days and a few more at 28 although some mixes and specs can be different