Concrete Strength 2

[Spiteman]

Would like to make a reasonably precise determination of the expected performance variations of a slab with design strength specified as 3000 psi or 4000 psi mix design. Floor to be reinforced concrete, SOG, with 3k versus 4k being the only variable. Floor is approx 30 ksqft and intended for warehouse operations with heavy traffic of hard rubber tired skid and pallet loaders. Design slab thickness is 8 inches. Thanks.

 

[dirtsqueezer]

Spiteman

Good responses already on this thread. I couldn't resist adding more tidbits until we see those 28 day breaks...
I'm ICBO/WABO certified, and I've seen this exact thing before. Same case- 8" slab, incompetent contractor, though yours takes the cake with loading it green. The blame on my site was assigned to a very uneven subgrade, but whatever works. The conctractor paid through the nose for epoxy injection which was finished before they even paved the parking lot, problem mitigated.
One question, did the plans require special inspection? If the project was designed per 97 UBC, special inspection is required whether they said so or not.
You haven't mentioned anything about special inspection. If your plans were designed to the 97 UBC, continuous concrete inspection is required for anything over 2500 psi. Your inspector should have at least reported slump or water added on site, and so given you more clues as to what went wrong. If the inspector was any good, they would have also been able to catch your 3K deficiency from the truck ticket, as well as a host of other issues like proper curing temperature, conditions, batch weights, mixing of the concrete, ect ect ect.
Anyway, just interested. Curing conditions per chapter 19 div. II of said UBC requires a 7 day cure over 50 degrees F. If this just happened recently I would guess cold weather may explain why the slab was still green after 5 days. It's always disappointing to hear nightmare contractor stories like this. Best of luck.