ABSTRACT
Cracks, which grow on concrete linings in tunnel, have been recognized to be one of serious problems for tunnel maintenance because it is part of potential greater failure. Development of convenient methods is requested to detect cracks on the concrete lining, precisely in early stages. Electric conductible paint contains carbon particles to achieve high electric conductivity. We employed this paint as a sensor for detecting cracks on the tunnel concrete lining. In this system, the paint is given a coat on the surface of concrete linings to be a line of 2–3cm width, and the electric conductivity of the paintshould be monitored due to measuring electric resistance of it. When a concrete lining cracks, the line of paint will be cut off at that place, and then the electric resistance will becomes infinity immediately. Therefore, occurrence of cracks can be detected precisely by monitoring the electric conductivity in control offices distant from the tunnel. We have made some experiments with the concrete samples tostudy : 1.Durability of the paint under various conditions. 2. Relationship between the size of concrete cracks and cutting of the paint. The experiment made it clear that the paint shows the good performances in the durability. It has been also made clear that the sensibility of the change in electric conductivity depends on the thickness of the paint. It means that various size of the cracks can be detected
