Prediction equations for corrosion rate of reinforcing steel in cement-fly ash concrete

This study is to incorporate the time-dependent development of microstructures of cement-fly ash concrete into the evaluation of corrosion severity for newly constructed structures and existing structures. The electrical resistivity, corrosion potential, and corrosion rate were determined for twelve series of concrete mixtures prepared with various water-to-binder ratios, fly ash contents, and chloride contents. The time-dependent developments of cement-fly ash paste, including hydration degree, pozzolanic reaction degree, and capillary porosity, are adopted based on previous models. The correlation between the corrosion rate and the time-dependent developments was considered for the proposed equations. The experimental results indicate that low water-to-binder ratio concrete and fly ash concrete show a low corrosion rate of reinforcement. Because the microstructure of concrete became denser, represented by a high degree of hydration and low porosity. This phenomenon increases the corrosion resistance of concrete. Besides, the chloride ions can accelerate the corrosion rate of reinforcement. Its effects of corrosion acceleration are found to be different in fly ash concrete because the fly ash can capture free chloride ions.