Potential use of small-diameter concrete cores for in situ compressive strength assessment

This paper examines the potential use of small-diameter cores (D< 100 mm), for estimating the in situ cube strength of concrete. The assessment is based on systematic analysis and evaluation of data sourced from published work since 1961, by 243 researchers working at 128 institutions in 32 countries, that yielded a matrix of 32 953 data points. The effects of core diameter (D), length to diameter ratio (L/D) and core diameter to maximum aggregate size (A) ratio (D/A) formed the main basis of the analysis. It is shown that there appears to be no technical justification for having requirements that limit D to 100 mm and/or D/A >= 3. Conversion factors are proposed for estimating, from the test results of small cores, the strength of cores having D = 100 mm and L/D between 1.0 and 1.2, which is currently the required size of cores to estimate the in situ compressive cube strength of concrete in the UK. It is shown that, in complying with the test data variability requirement, damage to structural elements through the coring can be reduced by adopting the use of small-diameter cores, down to 25 mm, where the damage is 10% that of 100 mm dia. cores.