Research on the creep behavior of tunnel lining concrete based on a multi-scale approach

The concrete creep performance of in tunnel lining projects is of great significance because the long-term exposure of concrete structures to geostress loads can lead to a significant increase in the deformation of the lining structures. In this study, a multiscale creep study was conducted on tunnel lining concrete for practical engineering purposes. First, the concrete long-term creep test was implemented with loading time of 180 d. Subsequently, nanoindentation testing was employed to evaluate the microscopic creep behavior of distinct phases. Furthermore, the thickness and creep characteristics of the interfacial transition zone (ITZ) adjacent to the aggregate were determined through a combination of binarized image analysis and micrometer indentation testing. Finally, the creep prediction of concrete was obtained by multiscale homogenization calculation and compared with the measured results. The results show that the creep of tunnel lining concrete progresses rapidly in the early stage. There are large differences in the creep performances of the main phases in the concrete slurry matrix, with the smallest creep modulus in the pore phase and the largest in the unhydrated clinkers. Due to its reduced thickness and lower volumetric proportion, the interfacial transition zone (ITZ) surrounding fine aggregate exhibits a higher creep modulus. By performing creep homogenization calculations across three distinct scales, the long-term creep behavior of tunnel lining concrete can be predicted with improved accuracy, yielding estimation errors below 10%.