Stamping a concrete mix design

[Rinehart]

I'm working as a consultant to a contractor for a large WWTP upgrade. The design engineers are requiring an engineers stamp on all concrete mix designs. I have been asked to stamp some existing mix designs from the local concrete supplier. Some have historical test results, others do not. My question is what should I look for to responsibly stamp these designs and what is my liability in doing so? I don't see a problem with stamping a design but does that mean I'm certifying it will meet the required strength? What is the accepted design guide for concrete mixes? I'd appreciate any input you all might have.

Bret Rinehart, PE
Rinehart Engineering & Construction

 

[JAE]

Stamping a mix design is a new one for me. I've never seen it, nor have I ever done it in 28+ years.

That said, if the engineer of record is requiring it on the construction documents/specs, I'd be forthright about it and call him/her up to ask what exactly they are looking for in an "engineered" mix.

What you could do, is write a letter, stating that in your engineering opinion:

1. You have reviewed the mix and found it to meet x, y, and z of the specifications and,
2. That it appears to meet the intent of the specifications and design documents and,
3. You qualify it to state the truth, that past performance of a certain mix does not necessarily mean a guarantee of future performance and,
4. You also refer them to chapter 5 of the ACI code as to acceptance of concrete and that it is typically the engineer of records responsibility to respond to concrete test results with respect to their design.

I'm not sure I'd agree that developing a mix design is truly engineering and requires a stamp. But you can always express an opinion and qualify it in an engineering letter.

 

[shin25]

I agree with JAE. Developing a correct mix design is more like an art than engineering. The mix design is developed based on history of certain mix, personal experience, engineering knowledge and trial & error.

As you have mentioned, the mix design will be for a large project. Therefore, this project will have a good specification to go along. The mix design should be developed to satisfy all the requirements specified in the specification. Do not think that the mix that you are going to stamp may meet all these requirements. In fact, it may take revising the mix few times before getting the correct one. More over, the results of the trial mix is going to tell the truth, there is very little to no requirement of a engineer's stamp to certify this.

 

[JKStruct]

This is also a strange concept to me... From your post, it seems to indicate that you are not actually preparing the designs, but reviewing the design of the supplier and stamping it prior to submission. What is ironic about the situation is the EOR is requiring this of you, and I would expect you'd simply review his concrete spec and ensure the mix is designed in accordance with the specification (concrete strengths, w/c ratios, air entrainment, admixtures, etc), which I believe should be his responsibility during the shop drawing review.

JAE gave very good advice. Such a letter limits your liability to a review that the design meets x, y, and z provisions of the spec but does not guarantee performance.

 

[BigH]

I have to throw my hat in with the others - I've never heard of stamping a mix design. And, I would never consider stamping, if pushed, a mix design that I didn't personally develop and oversee - the use of the engineering stamp means that the work was done under your direction - historic designs/results were not - therefore you can't do it. JAE gave good advice.

 

[archeng59]

I agree with the others, I've never been asked to seal and sign mix designs and I've not seen it done before. Seems like a very odd request. If you were not directly involved in formulating the mix designs, you should not provide a seal and sign in my opinion. If you are reviewing the mix designs for compliance with the project requirements, just put a shop drawing review stamp on the mix design submittal.

 

[bridgebuster]

I've seen sealed concrete mix designs BUT these were sealed by engineers employed by concrete plants.

I agree with JAE. I've reviewed mix designs but never sealed them; I've treated them like shop drawings as someone above mentioned. What I do is compare the mix with NYSDOT specifications.

 

[Lion06]

I have to agree with everyone above. We simply review mix designs. I have never seen one stamped and I can't imagine a reason to have one stamped. We always have a note in a memo that goes back to the contractor that says something along the lines of "....final acceptance of this mix design is dependent upon the in-place concrete". That is to make sure we don't say, "yes, this is fine", and then the truck takes too long to get to the site so they dump a bunch of water in the truck.

 

[BigH]

On my highway projects, the contractors always prepared their mix designs (we don't have ready mix plants where I am located for the last 12 years) - we will approve - or better, offer no adverse comments to the mix design but as StructuralEIT says, it all depends on the concrete placed and tested. Any approvals/no objections by the engineer in no way relieves the contractor for meeting the specifications. He's on the hook.

 

[Rinehart]

Thanks for all the input and good advice. I think I'll take the approach recommended by JAE above. I've never heard of this requirement on any other projects. I'll leave names out but the engineering firm requiring this is one of the big boys of wastewater engineering in the US. The requirement is on Plan Sheet S1 - General Structural Notes and says "Mix designs submitted for review shall bear the seal of a professional engineer registered in the state of California." If I find out more about their intent here, I'll let you all know. Thanks again.

Bret Rinehart, PE
Rinehart Engineering & Construction