Development of Patch Repair Method for Tunnel Concrete Structures of Operating Railroad in Salt-Affected Environment

Abstract

 Urban railroad tunnels located in seaside areas or near rivers at low tide have been affected by leakage of water including chloride ions originating from seawater, resulting in rebar corrosion deterioration. The constraints of repair work for the operating railroad lines in the Tokyo metropolitan area include the problems of short construction time and narrow construction space. Therefore, when the conventional patch repair method using polymer cement mortar with nitrite-based admixture is applied to commercial rail lines, issues such as spraying speed, spraying thickness, and adhesion performance are likely to remain. To solve this problem, we developed a new patch repair method using a two-material shot method in which a rapid hardener of calcium aluminate admixture and a salt fixing material are blended into a fiber reinforced polymer cement mortar, and a liquid plasticizer is added just before the tip nozzle of the spraying equipment. As a result, it was found that, compared with the conventional method, the salt barrier performance was about the same, but the workability and adhesion performance was improved, enabling a 30% reduction in construction costs.