ABSTRACT
Nippon Telegraph and Telephone Corporation has approximately 300km of communication open-cut tunnels. And More than 60% of them have been in existence for 30 years or more after construction. So, there is needed maintenance and repair of exfoliation and flaking of concrete and rebar corrosion due to deterioration. Open-cut communication tunnel is constructed of reinforced concrete and rebar is corroded by neutralization and salt damage of concrete due to aging, and cracks occur in concrete. Then groundwater enter in cracks and accelerate rebar corrosion. Eventually, concrete is exfoliated and rebar is exposed on the outside of concrete and corrosion is progressed in the short term. In the past, we had repaired the part of tunnel where deterioration come to the surface. But, deterioration occurred again near the repaired part of a tunnel and we repaired at every occurrence. As a result, maintenance cost increased. So, we introduced the repair method of preventive maintenance for reducing life cycle cost by reducing repetition of repair. In that method, we per-form detailed inspections and sectionalize a tunnel and predict time of exfoliation and flaking of concrete due to rebar corrosion at each section. Then we repair deterioration section and the section where need to be re-paired in the near future, at the same time. I will introduce this section-repair method.
