Abstract:

:Based on the corrosion polarization theories of metal, two theoretical models of the corrosion rate of steel bars embedded in concrete are derived, one is for the corrosion controlled by the electrochemical polarization and another is for the corrosion controlled by the concentration polarization of oxygen. The model for the electrochemical polarization indicates that in a stable corrosion state, the corrosion rate is affected by the concentrations of Fe ^2＋ and OH^- in the pore liquid beyond the Nemst diffusion layer in a negative exponential relation, and the effect becomes more visible with the decrease of the concentrations;  temperature greatly affects the corrosion rate in a approximately positive exponential relation;  in general, the corrosion rate approximately doubles when the temperature increases by 10K; and  stress affects the corrosion rate approximately in a positive linear relation, and the effect on ordinary steel bars under low stress is relatively small but proves remarkable on the prestressed rein- forcement under high stress. Moreover, the model in the concentration polarization condition indicates that the co- rrosion rate is proportional to the equivalent diffusion coefficient of oxygen in concrete cover but inversely propor- tional to the depth of concrete cover and to the temperature of steel bars.

Key words: concrete structure, durability, corrosion rate, electrochemical polarization, concentration polarization