Development of a sealing component for corrosion protection of rock bolts

Rock bolts are used as rock support in tunnels, caverns, and slope stabilities to strengthen the rock fragments in the periphery of the excavation. Since the designed service life of the main structure of infrastructure facilities in Sweden is 120 years, it is essential to sufficiently protect the bolts against corrosion in the rough underground environment. To fulfill that, bolts with corrosive-protected cover are often used. In addition, the cement grouts used to fill around the bolts for anchoring to the rock mass act as corrosion protector due to their high pH value. To prevent the exposed part of the bolts and the fixing components, i.e. the domed plate, the dome washer, and the hex nut, from corrosion they should be covered with cementitious products as well. This is achieved by completely filling the gap between the rock and the domed plate with cement paste and a shotcrete cover after the installation of the anchor. It is essential to perfectly fill all the cavities, not leaving any void behind potentially resulting in water ingress and consequently local corrosion. However, inspections of the rock bolts in several projects in Sweden have shown that defective installations occur frequently. The defects though are mainly detected under the dome plate and in the boreholes close to the rock surface reducing the durability and load bearing capacity. Hence, this project aims to develop a new technique/component to fill under the dome plate safer, faster, and more efficient. The idea is to develop a paper packet filled with premixed cementitious grout to simply put it under the dome plate during the installation. The paper packet is immersed in water before the installation to sufficiently wet the grout and start the hydration of the cement.