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The finishing part of it comes to mind, if done in hot weather, wet concrete hydrates too quickly, have you ever seen what contractors do on bridge decks, burlap and a sprinkler system, after the it sets up and the finish surface is done. This keeps the concrete from hydrating too quickly (drying). This helps it to cure slowly Was the concrete placed in hot weather, contractors daily report for the job should provide that information. You could have a bad mix, or they added too much water on site, weakening it, were any test cylinders taken and what were the results ? Could be a compressive strength issue, which could be determined from those test cylinder breaks, or existing with a windsor probe. Concrete has a capillaries, and using salt in the winter will absorb into the concrete, when it contacts any unprotected steel like typical woven wire mesh it will expand the steel and cause it to spall, this used to happen a lot on NYS bridges, with reinforced decks, not enough cover over the rebar, it expands rapidly and fractures the concrete. For some reason it is spalling and the cementitious material in the mix has not created the bond between the aggregates as intended by the mix design, there are a lot of variables to consider when trying to determine a material failure like this.
If this work is less than 1 year old, the building owner may very well have a claim for defective work or materials, this is one reason that retainage is witheld from a contractors monthly payment requisition, and may not be released for 1 year if stated so in the contract, a lot of times there is a 1 year warranty and it is stipulated that the retainage will not be released until that time period has expired.
If it was a state job, at least here in NY, there may be some recourse and retainage withheld, someone needs to investigate the problem and will end up dealing with the contractor that did the work, daily reports, concrete mix design that was submitted and approved, any test reports from test cylinder breaks, you could also contact an independent materials testing lab for investigative work. I have discovered defective materials intentionally placed by contractors, had a paving contractor do that once in Brooklyn, yeah watch your car he told me, try it buddy, you just try it I said, then I fried his @ss over it, because I kept good records everyday on site, over 60,000 S.F. + all the ponding low areas, rejected, cause was a clear violation of the specifications for both situations, he did not know how to set up grades either, could not use an optical level, complete idiot, they're out there and they end up on state jobs all the time. I had a testing lab take samples and the aggregate was recycled, clear violation of the spec's, + the bituminous material in it was below what the design called for, he made a deal with the plant to cut costs and I caught him red handed. These people think you're stupid I swear.
The concrete could have sat too long on the trucks, or it could have been a weak mix. I followed the specifications for 1000 psi mix design and ordered 20 something yards for an elevator machine room roof deck, interior deck and some infill areas including stairs. We did it after hours and cash deal to the regular shift guys who wanted to do it, the darned mix sat in the trucks longer because it was hoisted by crane in a hopper, and had to be placed, that and the light weight 1000 psi as specified by the architect/engineer was ordered, it was crap, it failed, the finish was spalling, so we chipped that off and when the contractor came in to level the concrete plank floors we had him coat those surfaces too, it bonded nicely and would suffice, but not for an outdoor exposure, never forgot that pour, what a disaster, it happens, instinct told me to order 3000 psi, but you have to follow the designers plans and specs, not sure if the extra weight for a regular mix would have been a structural issue, if it was, I'd have been liable for changing it unless signed off by the A/E.
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