4291 - SIZE EFFECT EXPERIMENTS ON CONCRETE UNDER MULTIAXIAL COMPRESSION

In this paper, we present the results of an experimental/numerical investigation on the influence of specimen and aggregate size on concrete fracture under multiaxial compressive loading conditions. Scaled thick-walled cylindrical specimens in a size range 1:4 have been tested under an external hydrostatic pressure. The stressinduced deformations at the inner opening were monitored and the fractures around it were preserved. Two concrete mixtures of high similitude were utilized in the investigation with the main variable being their maximum aggregate size, viz. 2 and 4 mm. Complementary, numerical simulations using the discrete particle code PFC have been employed for analyzing the experimental findings. Observed experimental results indicate a decrease of stress with an increase in specimen size for the two tested materials. The linear sizestress relationship in a bi-logarithmic scale suggested a size effect in the form of a power relation for both materials. In terms of fracture behaviour, observations suggest a splitting mode as the initial failure mechanism for the tested materials regardless to specimen size. Both interand intra-granular crack types are observed that are aligned all around the inner-wall mostly parallel to it. Preliminary outcome of the simulations using PFC have revealed its ability in simulating macroscopic material behaviour observed in the laboratory experiments in terms of realistic fracture patterns and reproducing observed damage zone.