Performance vs Prescriptive Concrete 1

[Jabson]

Does anyone have any views or worked with Performance based concrete, and what type of testing during placement was called out for, and what the results were? I am looking at Special Inspection testing of plastic concrete, and the results, including any comparisons to a similar (ingredient type and amounts) prescriptive mix.

 

[henri2]

This is an interesting subject I'd like to learn more about.

I first heard of the term "performance concrete" from ready mixed concrete salesmen back in the 80s. Back then most of it was used on residential projects where strengths were generally between 2,000 psi to 3,000 psi. The mixes were usually classified on the basis of MSA and strength...which meant slumps in excess of 6 inches was not uncommon.

Fast forward to the present. Most concrete mixture proportions in the US are still based on a prescriptive design methodology. Nontheless there are organizations that are strong proponents of performance concrete.

NRMCA have been a powerful advocate for the use of performance concrete. However, to make widespread use of performance concrete for major structural concrete work a reality in the United States, it would be prudent for NRMCA to work with powerful organizations like ACI to develop an ASTM standard that will be referenced by codes like the IBC.

The April 2005 edition of Structure Magazine had an interesting article on it which was consistent with the NRMCA P2P initiative

http://www.structuremag.org/archives/2005/April 2005/Structural-Practices-April-05.pdf

Some related NRMCA links are:

http://www.nrmca.org/P2P/

--discusses the P2P initiative in greater depth

http://www.nrmca.org/P2P/Summary of Performance-based Specification Research.pdf

Check Section 3 of the RMC foundation sponsored report "Preparation of a Performance-based Specification for Cast-in-Place Concrete" by Bickley, Hooten, and Hoover. It delves into tests for fresh and hardened concrete. NRMCA-PRP Initiative committee and RMC cooperated in the development. The link is:

http://www.rmc-foundation.org/newsite/images/Phase I Report Final January 2006.pdf

Clearly ready mix companies which do not have the requisite technical expertise will not be able to deliver performance concrete meeting certain desired properties on a consistent basis. Therefore, NRMCA's desire for qualification criteria is in place.

Apparently the Europeans have decided to embrace performance concrete. BS EN 206: Part 1 - Concrete. Specification, Performance Production & Conformity and BS 8500- Concrete, Complementary British Standard to EN 206-1 deals with this subject. It is also addresed in the RMC Foundation report.

An educative discussion on the new European standard can be found in this thread

http://www.eng-tips.com/viewthread.cfm?qid=98785

To find out some more about the European standard do a search on the website of the British Cement Association

http://www.cementindustry.co.uk/

 

[Jabson]

henri2,
I have recently attended an ACI meeting regarding the documents from NRMCA, with alot of discussion on who is responsible, how it will work, what challenges remain. But City of Seattle Building Code requires a certain amount of cement for a certain strength level. If the suppliers want to use less cement, we then look at the mix performance over a period of time, and if it works, we grant it 'Continuous Approval' where only the engineer needs to approve the mix. So if we were to look at 'performance' mixes, we would be eliminating a system that has provided some of the best concrete construction this side of the Mississippi. Nedless to say, there are some concerns. We are also concerned over the field testing that, from what they say, will be no longer needed. Another is the new tests, the cost, and the time to perform them. Yea, its a whole new ball game.
I think it is something that we will be leading into, and accepting, but I would rather avoid any problems by seeing what other jurisdictions or suppliers or design profesionals have done, and modeling ouprogram after that.
I was not aware there was a concrete forum, so I will be moving any further questions over there.
Thanks for the reply and the web links!