Hydro-mechanical coupling characteristics and mechanism of salt intrusion freeze-thaw concrete under complex stress paths

Abstract

This study explores the hydro-mechanical coupling characteristics and mechanisms of salt intrusion freeze-thaw concrete subjected to complex stress paths. The dimensionless permeability, dimensionless permeability difference, volume strain, and the evolution of permeability are introduced to analyze the hydro-mechanical coupling characteristics of concrete, and the seepage evolution mechanism under the stress state is elucidated through an examination of the internal pore structure. The findings reveal that permeability exhibits a nonlinear development under axial pressure loading and unloading. In comparison to 10 cycles, the dimensionless permeability of concrete after 40 cycles of salt intrusion freeze-thaw decreased by 35.17 % and 34.32 %, respectively, while the dimensionless permeability difference increased by 21.36 % and 35.79 %, respectively. Under continuous loading, the minimum permeability occurs approximately 95 % before the point of maximum volumetric compaction, and permeability shows an exponential relationship with volume strain. Nuclear magnetic resonance results indicated that salt intrusion freeze-thaw cycling led to an expansion of the concrete pore structure, with the number of pores after 40 cycles increasing by 87.82 % compared to 10 cycles. Specimens with higher cycle counts exhibited significant deterioration from the combined effects of salt intrusion freeze-thaw, leading to considerable pore development, enhanced hydraulic coupling, increased permeability channels, and a rise in initial permeability.