Coring Sample
Coring Sample
(OP)
Coring of hardened concrete at 12 days ( at 67% maturity ) for cylinder compression test. Is the result reliable as a depiction of concrete strength. Please let me have your suggestions.
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RE: Coring Sample
Be sure to keep the cores wet. Some specifications allow dry testing of cores if the service environment will be dry. In my opinion, if you are coring at early times or for low strength confirmation, you don't need the potential drying shrinkage effects, so test them wet.
Ron
RE: Coring Sample
If you use ACI...check out ACI 318, Section 5.6.5 for their take on field cores.
RE: Coring Sample
Compressive strenght result of the core is 10 N/mm2. Cube strength thus would be 1.25 x 10 = 12.5 N/mm2.
This is lower than anticipated value of 0.67 x 25N/mm2 = 16.7 N/mm2 at 7 days.
RE: Coring Sample
As an example, you cored at 12 days with, I am assuming, a measured maturity of 67 percent. If your cores achieved 85 percent of that value (0.67 x 25 N/m^2 X (0.85)=14.2 N/m^2)then you would consider that acceptable. However, early strength gain is affected by lots of "stuff". The fineness of the cement, the type and quantity of admixtures, whether the cement was modified ( using fly ash, ground blast furnace slag cement, or materials), curing conditions, aggregate influence, w/c ratio, air content, temperature, and probably a few I have left out. This is a danger of coring/evaluating too early. The time between placement and about 15 to 18 days is the steepest part of the strength gain curve, so minor mix issue can significantly affect strength gain. These tend to moderate with time (20 to 60 days.
Your next step might be to get a petrographic examination of a core to evaluate a few of the hardened concrete characteristics that might lead you to a conclusion.
Good luck.
Ron
RE: Coring Sample
Carl Bauer CEng MICE
Bauer Consult
PO BOX 2224
Gaborone
Botswana