testing of concrete

[pardal1]

I have used concrete hand made.it was silly ,but now is done.
After testing cylinders( 28 days) got average strength 12 MPa.not satisfied I used Schmidt Hammer after 28 days, and got average 16 MPa.what a discrepancy.
Is there any correlation between cylinders and rebound numbers results.I was told the hammer gives always 2.5 MPa more than cylinders.
Hard to believe, both generated doubt in my mind, and I will have to accept the concrete without doing anything.
My fate.

 

[JAE]

I'm not an expert, but I thought that the Schmidt Hammer had to be calibrated by popping concrete nearby in which you already knew the compressive strength. Otherwise, the Hammer results are even more inaccurate than they naturally already are.

 

[pardal1]

Maybe need to clearify this.
I have done previously compressive tests, it was a period of turbulence in the company who did the test, and I actually didn´t see how they have done.posteriorly I hired another company to run the hammer test, this last result came showing strenght( based on the Rebound values) far above the cylinders at 28 days.The test was done in the columns( 26 columns) of concrete.
each point taken 12 points and find the average .
Globally their statistics show fc28 of 10 MPa(1430psi) versus fck of 16MPa(2286psi) ,respectively for concrete cylinders, and hammer.
Now I am more in doubt than initially,but suspect the tests were not well done.samples were not appropriately prepared,my guess.
I thank any one who can show me any correlation between these two averages.

 

[BigH]

I can't remember exactly the post, but check out one of the concrete forums - the Schmidt hammer was thoroughy discussed in one of the threads. In my view, it is only a tool for confirming the consistency of the concrete from place to place and mix to mix. It is not - nor should not - be used to determine strength. There is oh so much that can affect the results and besides, unless you have a specific correlation developed for your particular mix, you are using some formula that was developed in the 1960s in Germany on some concrete mix or another. Not what I would suggest to give me a warm fuzzy feeling. Do search for the previous thread.