Effect of NaCl solution wet-dry cycles on pore structure and oxygen diffusivity of axial tensile fatigue damaged concrete

Oxygen diffusion plays an important role in the corrosion process of reinforced concrete structures exposed to marine environment. The diffusion properties of concrete subject to fatigue loads and the performance recovery after periodic drying-wetting cycles have not been studied. In this study, the pore structures and the oxygen diffusivity of concrete with different damage degrees before and after the NaCl solution drying-wetting cycles were measured by nuclear magnetic resonance (NMR). After 28 days of drying-wetting cycle, the concrete porosity decreased and the pore structures became finer. After the drying-wetting cycle, the increase in the fractal dimension of pores between 100 and 1000 nm was the most obvious. After the drying-wetting cycles, the oxygen diffusivity of damaged concrete decreased by 3.3-7.7 times, while the diffusivity of undamaged concrete decreased by nearly 10 times. This reduction effect on the diffusivity was generally smaller as the concrete damage degree increased. The result showed that the oxygen diffusivity was most relevant to the fractal dimension of pores between 100 and 1000 nm.