Correlation Analysis between Different Core Diameters and Standard Cylinder Strength in Concrete Assessment

One of the most important things to do before the assessment of the compressive strength of concrete in its original place in existing structures is the selection of the most appropriate diamond core diameter, because the use of undersized cores can lead to underestimated strength values. Thus, the focus of this paper is to investigate the influence of 2-inch, 3-inch, and 4-inch nominal diameter core diamonds on the measured compressive strength of concrete slabs prepared in the district of El Tambo, Huancayo. In order to perform an adequate analysis, a concrete slab with a target design strength (f'c) of 210 kg/cm² was cast, and different cores were extracted from it. It was also necessary to prepare standard 4"x8" cylindrical specimens from the same mix, so a reference could be obtained. After waiting for 28 days, different compressive strength tests were performed. The Results obtained from these tests showed that the smaller diamond cores, which means the ones of 2-inch and 3-inch, yielded average strengths that were significantly lower than the design strength (158.09 kg/cm² and 187.73 kg/cm², respectively). In contrast, the 4-inch cores, which are the biggest one, exhibited a higher average strength (350.27 kg/cm ²), and this exceeds both the design strength and the average reference cylinder strength. After adequate analyses, strong correlations were found between core strengths and reference cylinder strengths for all the diameters studied. In addition, quadratic regression models consistently gave the best fit (highest R²), particularly for 2-inch (R²≈0.96) and 3-inch (R²≈0.94) cores. Later, the derived quadratic models, such as y = -0.0024x² + 2.4811x - 282.62, were employed for predicting equivalent cylinder strength ('y') from the 4-inch core strength ('x'); these models offer a robust method for strength correction. To conclude, it can be argued that the core diameter has a significant impact when measuring strength, with smaller diameters giving lower results. Also, the developed quadratic models are recommended for accurately estimating concrete strength, especially when utilizing 2-inch and 3-inch cores.