DETERIORATION OF SHOTCRETE IN THE SAFETY GALLERY OF THE GOTTHARD MOTORWAY TUNNEL BY SALT-CONTAINING WATER

The corrosion behavior of shotcrete in the safety gallery of the motor way tunnel Gotthard was investigated. The tunnel was built in 1972/73, sections with water-leading rocks show various signs of concrete degr adation. Samples of corroded concrete were investigated in the laborat ory for their chemical and mineralogical compositions. X-ray diffracti on (XRD), X-ray fluorescence (XRF), and methods to determine acid-solu ble silicon compounds and insoluble contents were used to characterize the samples. Comparisons of original concrete with corroded samples s how the existence or discrete interaction mechanisms. These mechanisms lead either to harmless efflorescence, to detachments of concrete fro m the rock or to more or less complete degradation of the cement paste . Delamination or deterioration of concrete are related to the amount and kind of transformation products formed due to action of specific i onic species of the interacting water. Special attention is drawn to t he formation of thaumasite, which may be formed under special conditio ns, even when sulfate-resistant cements have been used. Physical and c hemical properties of the cement paste as well as the composition of i nteracting water are important for the service life of a concrete stru cture. The potential of concrete degradation due to interaction with a ggressive water may be lowered by preventing its contact or by drainin g the water not to force it to penetrate the concrete structure.