Assessment of impact resistance recovery in Ultra High-Performance Concrete through stimulated autogenous self-healing in various healing environments

Ultra High-Performance Concrete (UHPC) is widely acknowledged for its remarkable mechanical properties, owing to its compact microstructure. The response of UHPC to impact forces plays a vital role in ensuring the safety and longevity of structures, specifically in protective buildings, high-performance pavements and offshore concrete structures. In this context, this paper reports on an experimental investigation aimed at assessing the effects of stimulated autogenous self-healing of UHPC on the recovery of its performance under impact loadings. Drop weight tests were performed on UHPC slabs, with a 10 kg heavy impactor dropped from the height of 1 m on the centre of the specimens. Specimens were pre-cracked by repeated impacts up to 40% of their predetermined capacity. Pre-cracked specimens were exposed to different healing conditions, water submersion, 95% ± 5% RH, and wet/dry cycling (12/12 h) either in water or in a NaCl solution. Self-healing was evaluated through rebound height, elastic stiffness recovery, natural frequency, and laser displacement measurements. High-speed cameras and Digital Image Correlation were used to capture rebound height and crack formation. Performance was assessed at time 0, pre-damaging, 1, 2, and 4 months. After the healing period, all specimens were tested to failure. Specimens exhibited an increasing healing efficiency when moving from 95% ± 5% RH, over wet/dry cycling, to submerged conditions. Specimens healed continuously under submerged conditions exhibited a complete closure of surface cracks (50–150 μm) and an 80% recovery in natural frequency. Furthermore, they showed a more than 10% increase in stiffness and energy dissipation capacity after four months of healing.