Dear RG Researchers,
We know that in practice and in the case the estimation of compressive strength of existing RC structures is needed, the reliable manner is drilling cores. However, many diameters are used as 75, 65 and 50 mm or other dimaters, and we know, that the 100 mm core diamter with slenderness 2 is the one equivalent to the normalized standard specimen (150*300) mm. As far as I know, generally the decrease of the core diameter influences negatively the core compressive strength (this fact not for all concrete and depends on the maximum aggregate sizes and other parameters).
In this case, and in order to overcome this issue, we need correction factors and I am wondering if we have standarized correction factors concerning the diameter and not the slenderness ?
Cheers
Slenderness ratio is more important in deciding the failure strength of core and not the diameter correlation. ASTM has also given the correction factor based on slenderness ratio. However, the minimum diameter of core is important in terms of maximum size of the aggregate.
Dear Prof Om Prakash chhangani,
The slenderness is important, yes, and its corrections is known. However, if we consider that always we have double slennderness and we changed the diameter (we use different core diameter) in this case we need correction as function of the core diameter and maximum aggregate sizes which what we need for best estimation
Sincerely
I would recommend the publication "Effect of Core Diameter on Concrete Core Strengths" by "F. Michael Bartlett and James G. Macgregor". You can find it here https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/4160
I have not studied drilled specimens specifically so I am not aware of a more recent publication on this issue
It is important that the failure in the specimen occur in the cement matrix and not in the aggregate, as usually the aggregate is stronger than the concrete.
To achieve failure in the matrix, the specimen diameter should exceed 2 times the nominal size of the aggregate. Therefore, I would not choose a core size of less than 50 mm (2 in) unless the aggregate size is small and the spacing of reinforcement dictates a smaller core. Mr Talaat's answer is also most relevant.
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