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Loads on mat foundation

Loads on mat foundation

Loads on mat foundation

I have a 18 story building being constructed on a 4'deep mat foundation. The contractor has started constructing reinforcement and placing concrete for the sheared walls on day 7. I received the 7 day breaks yesterday for the 6000 psi foundation and the breaks were all around 3200-3500 psi. Does ACI state anywhere what the % must be prior to placing the load? The first placement of the shear wall was 6"thick by 15' tall half the width of the building. The contractor is now proceeding with the next placement 15'-25' seams like a lot of weight not to have any breaks higher than maybe 55%. I am not sure how much strength the concrete will gain over the next 21 days but I will be surprised if it gets over 5000. The contractor did use some admixtures to raise the slump to 7" however I don't think this would effect the strength beyond 7 days. Any thoughts? The engineer gets copied on all reports and has not commented or expressed any concerns.

RE: Loads on mat foundation

1) The resulting pressure from the wall is very small, compared to the available compressive strength at the time of placement.
2) 4' thick mat foundation is border on the mass concrete category, the concrete might have used cement with low heat of hydration, or additives to minimize the heat during placement, bot can lead to slower pace in earlier strength gain, but speed up later. You should talk to the person/lab who did the mix design, and ask for anticipated strength in each stage.
3) If the contractor used admixture permitted by standard, and with correct dosage, it should not affect the concrete strength.

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