The construction of some civil and mining structures requires the installation of rock bolt to strengthen, consolidate and stabilize the rock-rock, rock-concrete or concrete-concrete interfaces. In this paper, an experimental study was put on to validate non-destructive methods aiming at detecting the state of corrosion in these rock bolts in real condition. The acoustic techniques were applied on rock bolts that were embedded in concrete blocks and submitted to accelerated corrosion using the impressed current corrosion method. In fact, ultrasonic pulse echo measurements were taken every 24 hours. In addition, an acoustic emission system was attached to the corroded blocks as well as a reference block, in order to monitor the corrosion activity during the corrosion process. Half-cell potential was also performed at the beginning and in the end of the corrosion process. For ultrasonic pulse echo measurements, a quantitative assessment of the energy of the echo from the walls and the end of rock bolts shows a decrease of the energy in the rock bolts when they suffer from corrosion. While the energy of the echoes stays unchanged in the absence of corrosion.
Corrosion of metallic materials in concrete and in rock is a major problem in the construction and repair industry. Visual inspection of metallic systems once installed does not provide proper indications of the current problem. Non-destructive methods are then very useful.
Hadjigeorgiou et al. studied corrosion that affects the rock bolts in mining in Canada, and they recommended monitoring of the effectiveness of the rock bolts in order to evaluate their current state .
Baxter et al  observed that rock bolts will inevitably be affected by corrosion, and some explanations were provided:
• Injecting the bolts with cement grout or resin is often not well-performed, as several voids could be observed.
• Bolts injected with resin usually show more signs of corrosion.
• Corrosion is higher near the bolt head, mainly due / to poor sealing with grout. And impact of external environment.