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ssiguy (Geotechnical) (OP)
3 Mar 07 15:43
I recently came across an unusual case while reviewing the log of break strengths. For a 5000 psi concrete, that strength was reached in less than 3 days with very little strength gain afterwards. Literature says concrete should be at about 0.7 of its long-term strength at 7 days. I realize the time to reach this can be made much shorter for high-early strength concrete. However, there should some strength gain afterwards. Does anyone have experience that can explain this situation?

http://www.soil-structure.com

civilperson (Structural)
3 Mar 07 19:00
Texas DOT has done research and developed a "maturity " meter.  Time and temperature are the two parameters which effect the maturity of the concrete.  A concrete that experiences elevated temperatures has a maturity equal to longer existence at 70 degrees F.  Thus, a 28 day strength may be achieved at 48 or 72 hours at high temperatures. This could explain the leveling off of the strength gain curve for your specimen.
henri2 (Materials)
4 Mar 07 12:45
The rate of strength gain, ratio of 3 day and 7 day, to 28 day strength, depends on a host of factors. These include amongst other things the following: physico-chemical properties of ingredients, mix proportions, batching operations,fabrication and curing of specimens, testing procedure, reliability of testing machine, human error, etc

A few questions for you:

1. Could you post the mix design? Batch weights per cubic yard, type of cement, W/C ratio, including admix used will suffice.

2. How were specimens cured...standard curing per C31 or steam cured?

3. Is the current strength gain behaviour typical with this particular mix? Hopefully the QC dept of the ready mix company will have back-up data.



Bill888 (Materials)
26 Mar 07 23:38
Concrete strength gain can and does flat line frequently the previous post is correct.  Generally the faster the concrete gains its strength the sooner it will flat line.
BigH (Geotechnical)
27 Mar 07 11:48
henri2 - also add the fineness of the grind of the cement to your fine post.  In many countries they use OPC 33, OPC43 and OPC53 where the number indicates the requisite cement strength at 28 days. (British background).

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