Hello,
I need your help for calculating correction factor. Please can you read the the below answer I found it in internet, but when I go to ASTM C42, I find the correction factors, but I don't know how to calculate them when I have the experimental results? I think, is it a statistical method??
The correction factor should have come from Section 5.7 of ASTM C 42, "Standard Method of Obtaining and Testing Drilled Cores and Sawed Beams of Concrete." The reason for applying a correction factor is that tall specimens tend to give lower test values than short specimens of the same cross-sectional area. In order to convert all core specimens to approximately the same strength basis as the standard 6x12-inch test cylinder, a correction factor is applied to the calculated strength. This factor, based on the ratio of length to diameter (l/d), has been given as 0.98 for l/d = 1.75, 0.96 for l/d = 1.50, 0.93 for l/d = 1.25 and 0.87 for l/d = 1.00.
Regards
According to North American standards, compressive strength is measured on cylinders with the length to the diameter (L/D) ratio of 2/1. With this ratio, the end conditions (friction and shear stresses at the contact surface with the testing machine) don't have a significant effect on the test results. However, for lower L/D ratios the strength will be higher. The lower L/D ratio the higher is the effect of end conditions and the higher is the compressive strength obtained in the test. For drilled cores the ratio of length to diameter may vary. Since the experimental value of compressive strength of a cylinder depends on the ratio between the cylinder length and diameter, a correction factor is needed to compare the results of drilled core tests and standard compressive cylinder strength. The correction factor is given in section 7.9.1 of ASTM C42-13 (the same as in the paragraph you cited). Let say you tested a core that has the length 1.5 times the diameter of the core. Then you have to multiply your measured strength by a factor of 0.96. You can interpolate the factor according to your actual L/D ratio. Multiply you drilled core test results by the correction factor to get the values that you can compare to the standard cylinder compressive strength. Note that, in practice, the diameter of the core also has an effect of measured strength.
Hi Najia, the interpretaion of in-situ core drilling is a topic that is well approche at the ACI 214.4-10, also the NBRT 7680-15 (a brazilian standard) and also at the eurpeen standards EN 13791-09. There are more correction factor than those established at the ASTM C-42, they take acount of diference in diameter, mositure condition at the time of testing, and drilling damage among other. I recommend the ACI standard for a full understanding of the problem, because after you apllied the factors to each core test result you have to use statistical methods to determine a characteristic value of the compressive srtegth for checking the structure safety. I hope you solve your problem, best Alejandro
Thank you for your answers, if I have experimental data, how can I calculate or develop correction factor.? for example, correction factor=0.96 for L/D=1.5, what is the method used to develop correction factor=0.96?
The correction factors listed in ASTM C42 are empirical. See for example the paper of Bartlett and MacGregor:
Bartlett, F. M., and MacGregor, J. G, “Effect of Core Length-to-Diameter Ratio Concrete Core Strengths,” ACI Materials Journal, 91(4), 1994, pp. 339–348.
They tested 758 core specimens of 4" diameter and set the correction factors based on the experimental results.
By the way, if you find the answers helpful, please upvote them.
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