Effects of sustained compressive load on oxygen diffusion in unsaturated concrete: mechanisms and predictive modeling

The oxygen diffusion coefficient is critical for assessing the durability and service life of reinforced concrete. Under sustained compressive loading, concrete undergoes microstructural evolution, which significantly influences oxygen transport, yet cross-scale predictive models remain insufficiently studied. This work quantitatively characterizes concrete damage under different load durations using Digital Image Correlation (DIC), revealing progressive damage evolution. A multiscale model was developed through coupling analysis, incorporating unsaturated diffusion mechanisms, cumulative damage, pore structure parameters, and fractal dimensions to describe oxygen transport in loaded concrete. Results show that in the in-elastic stage, porosity and oxygen diffusivity decrease nonlinearly with increasing load duration and water saturation, while damage accumulates progressively. The proposed model offers a theoretical basis for durability evaluation and optimized design of concrete under coupled long-term load and environmental exposure.