Comparison of the condition of steel fiber-reinforced shotcrete with water-glass and alkali-free activators after more than 20 years of service in a subsea road tunnel

The in-service condition of steel fiber-reinforced shotcrete installed more than 20 years ago as single-shell rock support lining in the Nordkapp subsea road tunnel was investigated. The novelty of this study is the comparison of shotcrete with water-glass and alkali-free activators in a saline groundwater environment. The lowest shotcrete density was obtained at joints between two adjacent shotcrete layers. In the case of alkali-free accelerator, ettringite enrichment was observed in these joints. Leaching appeared to be the main degradation mechanism in the outermost 10-15 cm towards the traffic room.

Automated summary

The in-service condition of steel fiber-reinforced shotcrete installed more than 20 years ago in the Nordkapp subsea road tunnel was investigated. This study compared shotcrete with water-glass and alkali-free activators in a saline groundwater environment. It was found that the lowest shotcrete density was obtained at joints between two adjacent layers, and ettringite enrichment was observed in these joints when alkali-free accelerator was used. Leaching was identified as the main degradation mechanism in the outermost 10-15 cm towards the traffic room.