51313-02704-Potential-Dependent Chloride Threshold in Reinforced Concrete Damage Prediction

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Product Number: 51313-02704-SG

ISBN: 02704 2013 CP

Author: Andrea Sanchez

Publication Date: 2013

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There is increasing evidence that chloride corrosion threshold increases when steel bar potentials are more cathodic than -200±50 mV (SCE). When corrosion starts at a given location the potential drops and delays corrosion initiation of the passive steel in adjacent regions. Introduction of threshold dependence on potential (TDP) is needed for accurate forecasting as neglecting that phenomenon can lead to erroneously high damage projections. A previous work incorporated TDP in a finite difference deterministic model of a partially submerged reinforced concrete column. Corrosion was assumed to start when the chloride corrosion threshold was reached in an active steel zone of a given size. The model served to demonstrate feasibility of the concept but damage prediction was found to be highly sensitive to the assumed corrosion activation zone size. As the number of nodes used for the model increased resulting in smaller activation zones the total predicted amount of damage at a given age decreased toward a zero limit value. The result was clearly erroneous and constituted a major limitation in further developing the concept. Examination of the model assumptions suggested that the problem stemmed from neglecting the local resistance of the concrete around the steel bars. An improvement is developed by implementing a formulation that accounts for the local resistance polarization associated with the selection of the size of activation zone. The improved damage projections for the terminally small nodes separation converges toward a plausible finite limit value. Criteria for the selection and implementation of activation zone size for practical model applications are developed and discussed.