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Civil Engineering/concrete test cylinders and their expression for the real compressive strength


Dear Mr. Babak
our project is in KSA and under the american specification. The compressive strength for RCC concrete is specified to be 35 MPA. It's required to take 3 specimen for each 100 cum(each specimen is of 4 cylinders i.e 12 cylinders for each 100 cum), 6 cylinders to be crushed after 7 days and the rest 6 after 28 days. However, the consultant instructed us to keep 50% of the cubes in the Lab and the rest 50% to be kept on site beside the member poured and be subject to all site conditions of curing. My question is if the cylinders that would be kept in the Lab under the standard conditions are required to attain at least the 35 MPA so how much required for the cylinders that would be kept on site? and is the concrete which has been poured on site and cured with water and burlap for 7 days well expressing the fc' specified which is 35 MPA in our case (same as the concrete which has been taken from the truck mixers into cylinders and kept under standard conditions of curing at the Lap??)

Dear Khaled

The tests on concrete specimens are accelerated type of test. So the meaning of a 28 days test in laboratory is very typical and symbolic and related to probabilistic nature of engineering design. Then I will never accept in situ test as criteria for specific strength. BUT always consulting engineers may have their vision about to investigate the real situation via tests. I suppose the 28 days laboratory test may have correlation in some extent (say 85%) with in situ maintained tested results of physically infinite time ( say 90 days). Then try to get the permission to test the 90 days aged in situ maintained specimen to be considered as an idea of 28 days well kept laboratory test and don't be confused with not more than 95% (85 to 95% ) of matching with respect to ideally kept specimen results.


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Babak Esmailzadeh Hakimi


I can answer questions in Structural Engineering, Earthquake Engineering, Project Management and Project Control topics!


I am experienced in the area of earthquake engineering in electrical power industry, i.e. Lifeline Earthquake Engineering. My focus has been on structural seismic design of power installations. Recently I have got involved in project management in the category of constructional engineering.

Sinam Consulting Engineers Co.

Bs degree in Civil Engineering from Ferdowsi University ,1988, Mashhad Iran, Ms degree in Earthquake Engineering, Sharif University of Technology, 1993, Tehran, Iran

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