The multi-scale damage evolution of nano-modified concrete under the cold region tunnel environment based on micromechanical model

In cold region tunnel construction environments, concrete performance often deteriorates due to consistently low temperatures. Nanomaterials, as efficient admixtures, can significantly improve the pore structure of concrete. Given the significant impact of pore structure characteristics on concrete performance in cold regions, this study investigates the effects of nanomaterial modification on concrete using a micromechanical model. In-situ CT tests on nano-modified concrete provided digital volume images of the pore structure. The region-growing algorithm (RGA) and digital volume correlation (DVC) method were used to reveal pore structure evolution. The microscopic damage during the phase transition of pore water was analyzed based on the pre-melting dynamic theory and the micromechanical model. The fatigue damage mechanism and generalized self-consistent model were employed to study the macroscopic performance. The results indicate that while nanomaterials do not significantly inhibit the formation of small pores/defects in concrete, they can effectively prevent the interconnection between pores. This suppression leads to fewer larger pores forming. However, the thinner matrix concrete around these large pores results in more severe damage.