The authors revealed a deterioration mechanism of concrete for tunnel lining, which originated the concrete contained diatomaceous earth. The concrete lining constructed in 1928 became brittle on the surface of the carbonated zone. Investigation by using concrete specimens suggested that compressive strength of concrete mixed with diatomaceous earth declined with carbonation. The study results are conclusive that the tunnel lining concrete deteriorated by carbonation of diatomaceous earth contained as cement substitutes.

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