Cores are cut from structural members in order to establish the quality of in-situ concrete, particularly in terms of uniaxial compressive strength. Although the strength test itself is simple enough, the procedure used has to be carefully established and well understood as numerous factors can affect the measured value and hence the judgement on the quality of concrete. Some of the important factors have been considered in this paper, namely: the diameter of core; its slenderness ratio (R/d), direction in relation to placing of concrete and location in the structure; curing; cube/core strength relationship and soaking of cores prior to testing. The results obtained are discussed and recommendations put forward which could extend the role of core testing, as well as improve the reliability of the test and the interpretation of the results. The existing ASTM and BSI procedures for core testing are examined in the light of the results obtained. A procedure for the determination of in-situ concrete cube strength is described and it is suggested that the estimation from core strength values of the potential strength of concrete as measured by standard cube tests could give very misleading information and should be avoided.
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