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RE: Cylinder Breaks vs. Mix Design

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With regards to review of mix designs, we also require that the concrete supplier provide a unique designation for each mix.  For instance some times there are multiple mix designs that may have the same strength, but one may have “air” and the other may not, etc. You want to be sure which specific “3000 psi” mix was placed in the foundations, etc.

 

We also ask the mix design include a “statement of intended use”. Let’s say you have slabs that are 5000 psi and you have columns that are 6000 psi and let’s say that you get a submittal with only the 5000 psi mix (with no statement of intended use.) The 5000 psi mix looks ok and you approve it (figuring you will be getting the 6000 psi mix in a future submittal.)  You forget all about the 6000 psi submittal until a couple weeks later you get a call from the field asking some question and then mentioning something about “yeah, we poured the first lift of columns this morning…”  DID YOU USE 6000 PSI CONCRETE – I never got a mix design for that concrete?!?!?  To which the contractor’s reply is “Huh??? We used the mix that you approved a couple weeks ago. You approved it – don’t you remember?”  That’s why require a statement of intended use. It’s just an extra precaution to help prevent problems.

 

Also you want to be sure that the compressive strengths you are reviewing are not just a bunch of numbers from tests done 2 years ago.  ACI 318 is specific about what how recent these tests must be.  If you are using some “superduper” mix you also want to be sure that the strength test results provided are for the actual mix design that was submitted.  Sometimes weird things happen when you mix admixtures from different manufacturers, etc.

 

By the way – has anyone read the article in this month’s Concrete International (I think that was the publication) about the 30,000 psi concrete?!?!  Yikes!

 

Cliff Schwinger