Steel fibre spacing in self-compacting concrete precast walls by X-ray computed tomography

In the paper, a research programme focused on determination of steel fibre dispersion in self-compacting concrete using the X-ray computed tomography method is presented. Large scale specimens were cast (in the form of walls 1.2 m x 1.2 m x 0.15 m), containing different types of steel fibre. The tests were conducted on beam specimens cut from each wall. Both traditional destructive tests (compressive strength, three point bending) and non-destructive tests (X-ray computed tomography imaging followed by image analysis) were performed. The X-ray computed tomography method allowed to precisely determine fibre dispersion in the whole volume of the walls. These results were compared with mechanical properties of cut beams and their original location in the walls. Differences in fibre volume and dispersion between top and bottom parts of the walls were observed. The influence of the fibre type and the casting point location was also significant. Longer fibres became more effectively orientated in parallel to the bending loading direction, resulting in enhancement of the mechanical properties of the concrete. Tests on 16 beams (cut from each wall), through load-deflection relations, provided a thorough picture of mechanical uniformity of the material properties inside the walls. The X-ray computed tomography imaging proved to be intuitive and accurate in the assessment of steel fibre dispersion.