Concrete Puddling

[knightwadda]

Hello all,
The contractor is trying to avoid puddling but the EOR is asking for additional concrete backup data that I am a little confused on. Below is the correspondence between the Contractor and the EOR. All help will be really appreciated.

QUESTION:
SUGGESTION:
Will slab puddling be required at verticals with a greater than 1.4fc to elevated slab
concrete? The specified elevated slab concrete is 5000 PSI, but due to schedule the
shell contractor will be using a mix designed to reach 3000 PSI within 24 hours. The
average elevated slab strength at AC Marriott yielded between 7000 to over 8000
psi.
ANSWER:
Remarks:
In order to use the anticipated slab strength to avoid puddling, as requested in the
RFI, the concrete submittal needs to include the ACI appropriate data confirming
the 1.4f'c threshold will be reached by the slab concrete. ACI requirements have
statistical variability requirements beyond just the historic break values to be rated
for a desired strength.
If the above is not provided, puddling will be required.

Thank you

 

[KootK]

- EOR needs slab concrete in finished state that will not crush between columns.

- early strength concrete probably doesn't help as it's about the finished state.

- EOR needs evidence of concrete on this project getting strong enough at the finished state. Data from past projects and s not sifficient.

Two ways to avoid puddling:

1) Have contractor order a mix that will make it to 1.4 f'c at 56 days as approved by EOR. Based on past experience of the contractor, it should be not be an issue.

2) Add vertical dowels to the joint to reduce the compression demand on the slab between columns.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[knightwadda]

The strength data submitted was 7000 PSI @ 7 Day (7001.7 PSI average of 30 results) and 56 Days (9050 PSI average of 30 results). The STD was also provided, that is why I do not understand why the EOR is requesting more data.

"ACI requirements have statistical variability requirements beyond just the historic break values to be rated for a desired strength."

the above quote is what I don't understand.

Thank you

 

[KootK]

Is that 7000 mix not for s different project called AC Marriott?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[wannabeSE]

Without seeing the mix design submittal, only guesses can be made. It sounds like SEOR doesn't think the required average compressive strength, f'cr, is being calculated correctly from the historical data. Also, does the project specifications have requirements that go beyond what ACI 318 and/or 301 require

You might look at SEAONC's Guidelines for Reviewing Concrete Mix Designs to see if everything looks OK

http://seaonc.org/sites/default/files/attachments/guidelines_for_reviewing_concrete_mix_designs.pdf

 

[Ron]

"ACI requirements have statistical variability requirements beyond just the historic break values to be rated for a desired strength."

This is a correct statement. The ready-mix supplier only has 30 test results for its statistical analysis. Read ACI 214 "Guide to Evaluation of Strength Test Results of Concrete". You'll find that the ready-mix supplier has to provide long term statistical evaluation, including moving averages, of mix designs in order to optimize the design. Otherwise, the R-M supplier has to use an overstrength design.

 

[knightwadda]

I will review ACI 214.

Thanks