Specimen size effect on compressive and flexural strength of high-strength fibre-reinforced concrete containing coarse aggregate

It is a well-known fact that the size of the sample influences values of mechanical properties of concrete measured during the tests. However, the comparison of results of various researchers clearly shows that the importance of this effect varies for different types of concrete. The paper presents outcomes of extensive experimental study focused on determination of relations between the size of the specimen and results of mechanical tests of high-strength fibre-reinforced concrete (HSFRC) with coarse aggregate (maximum aggregate size 16 mm). The main observed parameter was compressive strength. Six different HSFRC mixes having the expected compressive strength between 100 and 175 MPa were investigated. Cube samples of four sizes - 40, 100, 150 and 200 mm - were examined. The results proved that the size dependence of compressive strength diminishes with increasing strength of concrete. For very high strength materials (more than 130 MPa), the results were almost size independent. Additionally, flexural strength of two high-strength concrete mixes was measured on prismatic specimens of two different sizes. The results indicated that flexural strength of HSFRC with coarse aggregate is size dependent without regard to expected compressive strength. Conversion factors for the tested type of material were proposed for both compressive and flexural strength measurements.