A quantitative analysis of toughening mechanisms in steel fibre reinforced ultra-high-performance concrete through multimodal nondestructive evaluation

For the joint purposes of better informed meso-scale models and for more rational for “materials by design” concepts, we seek to isolate and measure the different mechanisms that lead to high strength and high ductility of steel fiber reinforced ultra-high-performance concrete (UHPC). The work described here jointly applies quantitative x-ray computed tomography(CT) and acoustic emission (AE) techniques to monitor and measure damage progression in split cylinder tests of UHPC. 50-mm diameter specimens of two different fiber types were CT scanned both before and after load testing. From the resulting images, fiber alignment was evaluated to quantify its effect on specimen performance. Results demonstrate the significance of fiber alignment, with best case being between 20 and 30% higher than the worst case. Cumulative AE energy was also affected commensurately. Post-test CT scans of the specimen were used to measure internal energy dissipation due to both matrix cracking and fiber pullout using calibration measurements for each. AE data, processed using an artificial neural network, was also used to classify energy dissipation. CT analysis showed that fiber pullout was the dominant energy dissipation mechanism, however, the sum of internal energy dissipation measured amounted to only 60% of the total energy dissipated by the specimens as measured by the net work of load. AE analysis showed a more balanced distribution of energy dissipation. AE data additionally showed how the dissipation mechanisms shift as damage accumulates.