Assessment of concrete anisotropy by means of compression and indirect tensile tests

In reinforced concrete structural analysis and design it is normally assumed that the material is globally isotropic and homogeneous. Local departures from this model generally exert a minor influence on observed response and are therefore disregarded. There is overwhelming evidence, however, that in normal concrete there is some degree of meso-scale orthotropic behavior, which results from gravitational effects during concrete casting and hardening. In the present paper, results of compression tests, as well as indirect tensile tests using cylindrical samples, are reported. These tests confirm that both the unconfined compressive strength as well as the indirect tensile strength determined on cylindrical samples are perceptibly influenced by the angle between the sample axis and the vertical orientation during casting. It was determined that the ratio between the unconfined compressive strength of a C50 concrete mix measured in cylindrical samples cast in horizontal position and the strength of samples cast in horizontal position is on average 0.85. Similarly, the tensile strength of concrete in the vertical direction is, on average, also about 15% smaller than the strength determined employing standard laboratory tests.

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