News

Background

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.

Overview

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.

1. Construction can be conducted in stages

The method can be implemented in stages. For example, one lane of a two-lane tunnel may be utilized while the other lane is under construction, enabling traffic to flow with a minimum of disruption.

2. Thin reinforcing layer

The reinforcing layer can be made thin due to the use of a fiber reinforcing mortar of exceptional strength (compressive strength: 40–60 MPa). Results of research conducted in collaboration with the Public Works Research Institute showed that a 75mm reinforcing layer had the same load-bearing performance as existing 300mm liners.

3. Reduction of construction costs

The high-strength, fiber reinforcing mortar used when applying the method can be manufactured at ready-mixed concrete plants, eliminating the need for special mixing machinery at the construction site. Costs may be even further reduced, as the new method does not require the center forms that are needed with conventional reinforcing techniques.

4. Shorter construction times

Construction times may be significantly shortened in comparison with previous methods for reinforcing tunnel linings because center forms are not required and because construction may be carried out in stages.

5. Shaping potential

With the new method, cement board made of staple-fiber reinforcing mortar can act as embedding forms as needed. This board has exceptional impact resistance and can be readily shaped, enabling processing matched to the curved surfaces of specific tunnels. It can also be shaped easily using a sander, enabling conformity with the tunnel to which it is being applied.

6. Flexibility in design

The strength of the fiber reinforcing mortar, as well as the reinforcing capacity and thickness of the fiber-mesh tension-reinforcing agent may be selected according to preferences, allowing the building of optimal reinforcing layers.

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