Mechanical performance and self-sensing capability of an amorphous fiber-reinforced concrete for radioactive waste storage facilities

Abstract

This study results from a research project initiated by the French National Radioactive Waste Management Agency (Andra) as a part of the Cigéo (Industrial Center for Geological Disposal) project. This project addresses many challenges related to sustainability, and health monitoring of confinement structures planned by Andra. In order to reduce issues related to corrosion in the tunnels, fiber reinforcement can be used to reduce the amount of steel reinforcement while maintaining high mechanical performance and durability. The fibers used in this study are named Fibraflex, metallic fibers provided by Saint Gobain SEVA. Various aspect ratios (82 and 123) and volume ratios (0.27% and 0.41%) of fibers were tested. These fibers feature high specific surface area (around 70 m²/m³), corrosion resistance, and high electrical conductivity. To characterize the contribution of fibers to concrete mechanical performances, European standard EN 14651 flexural tensile tests were conducted. Results show that fibers bring better performances, especially concerning the post-peak behavior. In fact, fibers effectively transfer stresses across cracks, resulting in better residual tensile strengths. Since these fibers are electrically conductive, tests were also conducted to design self-sensing concrete based on electrical measurements. Firstly, resistivity was monitored on saturated specimens with different mix design throughout the curing time. Results show that when fibers were added, concrete resistivity was reduced due to the ability of the fibers to transmit electrons. A relationship between reinforcement index and resistivity was thus revealed. The self-sensing capacity was investigated on specimens subjected to cyclic bending loading, with electrical properties measured by using a Wheatstone bridge. Results show a good agreement between the level of cracking in concrete and its electrical response.