Influence of Core with Different Dimensions and Conditions on Compressive Strength of Concrete

Abstract

The core test is essential in the concrete industry for estimating concrete strength and sometimes serves as the sole method for evaluating the safety of existing concrete structures. An extensive experimental study was conducted to assess the factors that influence the interpretation of core test results.

The study included five different concrete mixes and five concrete strength classes (20, 30, 40, 50, and 60 MPa), two core diameters (150 and 100 mm), four core aspect ratios (ranging from 1 to 2), two sizes of coarse aggregates (maximum sizes of 10 and 20 mm), and two coring directions (vertical and horizontal). Concrete prototypes were constructed, and more than 225 cores were prepared and tested to produce a substantial number of concrete cylinders (nine cylindrical specimens for each concrete mix design), with sizes of 150x300 mm and 100x200 mm used.

The results indicated that core strength decreases with an increase in aspect ratio, a decrease in core diameter, drilling perpendicular to the casting direction, and a decrease in concrete strength. Statistical analysis was performed to identify reliable strength correction factors that account for the variables studied. A simple weighted regression analysis model was developed using the "Data Fit" software. The new model for interpreting core test results incorporates all the identified factors affecting core strength. When calibrated against a large set of test data, the model demonstrated good agreement. The proposed model can effectively estimate the in-situ concrete cylinder strength based on core test results.