Shimizu : Another Application for Toughness Coat: Tunnel Maintenance and Preservation

In collaboration with the Railway Technical Research Institute (President: Norimichi Kumagai) and Mitsui Kagaku Sanshi Co., Ltd. (President: Shu Saito), Shimizu Corporation (President: Yoichi Miyamoto) verified the effectiveness of Toughness Coat in preventing the flaking of tunnel lining concrete. The technology has been proven to dramatically improve the performance of concrete structures while meeting the requirements of renovations under traffic operation.

Toughness Coat, a revolutionary technology jointly developed by Shimizu Corporation and Mitsui Kagaku Sanshi, involves spraying several millimeters of a resin known as polyurea (strength 25 N/mm², stretching performance 200%) onto the surface of a concrete structure. This treatment improves various aspects of structural performance, including impact resistance and durability. To date, we have performed demonstration experiments targeting the maintenance and preservation of concrete protective walls on highways and concrete embankments and gathered a wide range of data to establish its application methods.

Shimizu Corporation and Mitsui Kagaku Sanshi have long noted that Toughness Coat may prevent flaking from concrete structures. The Railway Technical Research Institute, for its part, observed that flaking of the concrete lining in a railway tunnel, whether caused by aging or other factors, may lead to major accidents and therefore set about developing relevant maintenance and preservation methods. The joint development in question was launched in August 2014, based on the common interests of all three parties.

For the use of Toughness Coat as a method for preventing flaking of concrete tunnel lining, concrete surface is cleaned prior to the application of primer. Nextly, the polyurea resin is sprayed as coat measuring at least 1.5 mm thick. Despite the simplicity of this procedure, it ensures a polyurea adhesion strength of at least 1.5 N/mm², the reference threshold value needed to prevent flaking. Unlike conventional methods for preventing flaking, this process combats flaking attributable to deformation or cracking of the concrete, as well as that attributable to concrete deterioration. The effect of the treatment is highly durable over time.

To verify effective flaking prevention, laboratory experiments and test construction were implemented in September 2014. The laboratory experiments involved test equipment for loading a large tunnel lining owned by the Railway Technical Research Institute. The1:5 scale tunnel lining concrete specimen is built.(inner diameter 1.85 m, length 300 mm, thickness 150 mm). After coating the surface of the specimen with Toughness Coat, the specimen was placed on the equipment and subjected to load. The results confirmed that Toughness Coat prevents concrete flaking even when the specimen develops cracks or experiences significant deformation.

In collaboration with Hokkaido Railway Company, in-site application test of Toughness Coat was performed in July 2015 in a tunnel for an unused railway line. The tasks in question proved quite feasible, and the work produced the specified coating thickness (at least 1.5 mm) and adhesion strength (at least 1.5 N/mm²) on the concrete surfaces with and without water leaks and after different surface preparations. The effectiveness for the flaking prevention by Toughness Coat has been confirmed as the practical method.

Shimizu Corporation will evaluate the durability of the Toughness Flaking Prevention Coat and pursue further improvements in workability, as well as applications to tunnel lining materials other than concrete.

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