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.