On the accuracy of diffusion models for life-cycle assessment of concrete structures

In durability analysis and life-cycle assessment of concrete structures transport of chlorides and other aggressive agents is generally described by using Fick's laws of diffusion. This model is frequently applied in a simplified one-dimensional (1D) form. However, in practical applications the diffusion process is more properly described by two-or three-dimensional patterns of concentration gradients. In this paper, the accuracy of the 1D modelling of diffusion and its impact on the life-cycle assessment of concrete structures under corrosion is evaluated in deterministic and probabilistic terms with respect to more accurate two-dimensional (2D) formulations. The influence of the diffusion modelling on the time-variant corrosion damage of concrete cross-sections is studied with reference to the local damage of the reinforcing steel bars and the global deterioration of bending moment-curvature capacity curves. The results show that 2D diffusion models may be necessary for a realistic life-cycle assessment of concrete structures under corrosion, since 1D models can lead to significant inaccuracies depending on the geometrical aspect ratio of the cross-section, location of reinforcing steel bars and exposure conditions.