TEKKEN CORPORATION (President: Shiyoshi Kanda; hereafter "TEKKEN") and Kuraray Co., Ltd. (President: Yasuaki Wakui; hereafter "Kuraray"), in collaboration with the Public Works Research Institute, an incorporated administrative agency, announce the development of a new "high-strength, thin concrete tunnel reinforcement method" for the interiors of previously constructed tunnels that utilizes high-strength fiber reinforcing mortar. The new method employs mortar that contains staple fiber with high compressive strength and exceptional pliability that acts as an inner concrete reinforcing agent, combined with a fiber mesh that acts as a tension-reinforcing agent. The method utilizing a combination of these agents was developed in order to renovate and reinforce concrete lining that has deteriorated as a result of aging or geostatic pressures. The Public Works Research Institute conducted load testing on its full-size test rig, examined whether or not sufficient reinforcing effects could be obtained and established a new design and construction method.
The method employs a reinforcing layer made thinner than conventional thickness through the use of high-strength, pliable materials, enabling the reinforcement of concrete within previously constructed tunnels where limited space prevents additional layering. Construction may also be carried out in stages so that the tunnel can remain in operation while construction is in progress, which helps to lower costs and shortens the time needed to complete the process. Leveraging these characteristics, TEKKEN, Kuraray will work toward the widespread utilization of the method, primarily for reinforcing road tunnels where falling concrete and significant deterioration are concerns.
Carrying out systematic and efficient maintenance and renovation work is necessary on safety grounds and to ensure that aging infrastructure can remain usable. In light of these needs, TEKKEN and Kuraray are engaged in joint research aimed at developing maintenance technologies to prolong the service lives of existing structures. The development of this new reinforcement method is the result of collaborative efforts between TEKKEN, Kuraray and the Public Works Research Institute to create an effective new method of restoring and reinforcing concrete of diminishing quality.
The new reinforcement method uses a high-strength mortar containing PVA staple fiber and a PVA filament as agents to buttress the concrete linings within tunnels. The thinness of the reinforcing layer is attributable to the use of the high-strength reinforcing mortar, which has a compressive strength of 40–60 MPa. A PVA-fiber mesh is also utilized as a tension-reinforcing agent to enhance pliability and prevent warping. Despite its thinness the reinforcing layer exhibits significant reinforcing properties, enabling its use within existing tunnels where limited space prevents additional layering.
Applying the new method offers the following advantages.