Air and water bubbles are likely to remain on concrete sidewalls in tunnel linings, because the sidewalls are generally constructed with a greater slope than a right angle. The bubbles negatively influence the aesthetic of the concrete lining. In addition, concrete with a lot of large bubbles may decrease durability, such as air permeability. Although most tunnel lining is constructed as plain concrete without reinforcement, the low permeability may affect the maintenance and long-term durability of the tunnel. The study aims to examine the effect of bubble distributions on the permeability of concrete lining. Concrete specimens including various bubble distributions are prepared by using variable angle-forms in a laboratory test. Furthermore, the bubble distribution (area ratio) and the permeability are examined in two actual tunnels. This paper presents a relationship between bubble distribution and air permeability based on these tests. The results show that the relationship is a logarithmic curve of the bubble rate and gas permeability.
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