Abstract: Compared with the ground concrete structures, the tunnel lining structures are affected by the carbonated water environment, and its degradation mechanism is significantly different from the carbonization in the atmospheric environment. This study is to reveal the deterioration mechanism of tunnel lining structure under the action of the carbonated water. Experiments were conducted to study the accelerated erosion of cement mortar in the atmospheric and carbonated water environments, respectively. The results show that the carbonization depth of cement mortar in the carbonated water environment is obviously less than that in the atmospheric environment, and its carbonization coefficient is only 0.18 times that in the atmospheric environment. In the atmospheric environment, the volume of pores in cement mortar is reduced due to carbonization, whereas the uniaxial compressive strength and elastic modulus of cement mortar are sharply increased. However, in the carbonated water environment, the loss of Ca element is exacerbated, and the carbonization results in a lower content of Ca in the carbonized layer. As a result, the pore structure of the cement mortar is destroyed, leading to an increase in the pore volume of the cement mortar. Finally, both the uniaxial compressive strength and elastic modulus of the cement mortar are decreased in the carbonated water environment, especially the elastic modulus. The research results reveal that in the carbonated water environment, the loss of Ca is accelerated in the tunnel lining structure, resulting in an increase in the porosity and a decrease in the strength. Ultimately, the deterioration of the tunnel lining structure occurs, which affects the long-term safe operation of the tunnel lining structure.

Key words: carbonated water environment, nitrogen adsorption, erosion, lining structure, experiment study