Effect of Concrete Class, Maximum Aggregate Size and Specimen Size on the Compressive Strength of Cores and Cast Specimens

Core sampling is the most accurate method of evaluating the compressive strength of concrete structures. However, it is preferable to take only small cores to avoid damaging the structures. It turns out that various elements influence the strength of compressed cores. This study examines the influence of specimen size, aggregate size, concrete class, and curing method on compressive strength. Three aggregates measuring 3/8, 8/15, and 15/25 mm are used to make six sets of concrete compositions with strengths of 25 MPa and 30 MPa. Nine specimens are made, one for each variety of aggregate and concrete. Cores of 100 mm, 75 mm, and 50 mm sizes are made. These cores are extracted from concrete blocks curing in the outside air to simulate the real concrete curing environment. Cast specimens cured in water and air with diameters of 50 mm, 100 mm, and 150 mm are also made. The objective is to compare the average compressive strength of all cast or extracted specimens with that of cylindrical standard specimens of diameter 150/300 mm and the cores and cast specimens. The obtained findings showed that the compressive strength is overestimated when we compare f_p100 cores and standard air-cured specimens (f_c), with a conversion factor varying from 0.69 to 0.96. However, a decrease is observed in comparison with water-cured specimens. The use of f_p75 cores reduced the conversion factors, which are between 0.83 and 0.87 for B25 concrete. The highest f_p/f_c ratios are obtained for f_c50 cores, which can reach 1.24. It turns out that the size of the core and the class of concrete have a much greater influence on the f_p/f_c ratios.