Any experience with excessive retardation of concrete?

[Bernie]

I am trying to help a client who has had a problem with excessive retardation of concrete in drilled shafts (piles).
When tested by sonic logging at 7 days some of the concrete had low UPV. When retested at 14 days UPV had increased by 50 percent. The mix was self-consolidating (9 inch slump) with double the recommended dose of Master Builders Pozzolith 300R. I am looking for any conference papers or journal articles describing similar experiences. Can anyone point me in the right direction?

 

[Ron]

Be careful drawing too many conclusions from variable UPV in early curing stages. Unless you have correlation to maturity, the data could be meaningless, as void structure has not finalized(void faces change during curing process, and as water migrates interstitially).

 

[Bernie]

Thanks for the response Ron, but that is exactly my point. The engineer on the project rejected the shafts based on the early UPV data. My contention is that retesting showed improvement, and the likelihood is that the material would have ended up with more than adequate strength. I have experienced the same thing on a couple of previous projects. My problem is that I can find very little written material to support my point in a dispute review. There is plenty of anecdotal information about delayed maturity, but not much is written.

 

[dik]

Right on the button about not much stuff... just checked my library and 'nada'... I've seen many articles in both ACI and PCI journals about the slow strength gain but higher strengths attainable using pozzolans/flyash, but can't put my finger on anything.

I'm not sure, but the following site may have information that is useful to your purpose:

http://www.ndt.net/article/v05n02/castro/castro.htm

The material and lack of fineness can have a big impact on the retardation. Doubling the recommended dose would likely have an even bigger impact (ie., greater than 2X, because there is less cement to hydrate). I assume that you've already checked with Masterbuilders regarding their product. They should have tekkies that have a really good handle on their product as well as info on using it in greater quantities.

Only other case I've heard of regarding severe retardation was a railroad tanker car that was transporting cement powder that had previously been used for transporting sugar. I guess that sugar really messes with the gel!

 

[dik]

That should read PCA (Portland Cement Assn) and not PCI (Prestressed Conc Institute).

 

[TA]

I am an analytical chemist and frequently been asked to detect sugar/retarder in hardened concrete. If anyone knows of a method please send it to me. Identify lignin and amine in concrete is fairly easy. But corn syrup, molasses, or sucrose is very difficult.

Thank you.

 

[ThuyAi]

If anyone knows of any method to detect sugar in concrete, please let me know.
Thanks
Thuy Ai Nguyen
Senior Analytical Chemist
Essroc Cement