Abstract: Most of the concrete structure in entity engineering is always in the unsaturated state with alternating wet and dry seasons.It is of great importance to do the research chloride salt erosion in unsaturated concrete for concrete durability.According to the chloride ion transmission mechanism,the chloride convection-diffusion control equation in unsaturated concrete was derived by considering the difference of moisture transmission the dry-wet alternate process.Crank-Nicolson method was engaged to develop the finite difference format of equation above.The results of proving experiment reveal that the results of model calculation have a good correlation with the measured results.The parameter sensitivity analysis result shows:chloride ion concentration increases decreases with the increase of dry and wet ratio surface and pore saturation.The chloride ion concentration gets its highest with the concrete initial saturation is 0.3.

Key words: unsaturated concrete;chloride;diffusion;convection;convection zone depth