Size-effect experiments on concrete in compression

Stefan L. Burtscher, University of Technology, Vienna
Johann Kollegger, University of Technology, Vienna

It is well known from literature that heterogeneous granular materials exhibit a size effect under tensile loading. Thus, the strength determined in experiments is not a material property. Some experiments have been performed regarding the size effect in tension whereas very few experiments have been performed in compression. However, compressive loading of concrete is more important because concrete is applied in structural systems to carry load in compression and not in tension. Furthermore, a compressive failure in a load-carrying member is more brittle, and in most cases more dangerous, than a tensile failure. Experimental investigations on the size effect are therefore needed. Experiments from literature on column-like specimens under compressive loading were performed up to a size range of 1:4. The size range of a series of geometrically equal specimens is given by the amplification factor of a characteristic dimension from the smallest to the largest specimen size. Obviously large size ranges are advantageous for experimental studies on size effect. The largest size range (1:16) of experiments on concrete under compressive loading carried out so far will be presented in this paper. This series was performed in one of the largest testing facilities available. A size effect on nominal strength was detected. The results are compared with the two most common size-effect laws.