Initial results of local strength analysis of a fiber concrete plate by 4-point bending tests

The analysis of the post-cracking behavior of a large plate cast of fiber concrete shows a large variability due to the fiber alignment and dispersion. Therefore, one can expect, that the bending strength and other material parameters depend on the position in the plate. This means that the position the samples for testing are taken from may play a significant role in assessing the mechanical properties and strength of composite materials. Often, the investigation of fiber concrete properties have been performed by testing small size beams. The results can be influenced by the boundary restrictions, such as wall-effect, which influences the fiber distribution. In this study the four-point bending strength of beams cut out of a large plate was investigated, the results represent the local strength of the plate in this particular place. The fiber orientation and distribution have been evaluated by X-ray Computed Tomography and Image Analysis Method. The results of the experiments have shown that the position of the beam inside of a large-size plate has a strong influence on the mechanical properties and post-cracking behavior. The analysis of the obtained outcomes proposes the following conclusions: the beams that were located near the edges of the formwork have shown a strong, strain-hardening behavior, and the beams that were located on the way of the casting bucket (a zone of the high turbulence/perturbation/disturbance) have shown a weak, strain-softening behavior.