Service life prediction of reinforced concrete exposed to marine water

© 2016 Australasian Corrosion Association. All rights reserved. Exposure of reinforced concrete to sea water allows chloride ions (Cl-) to initiate corrosion of steel reinforcement. Service life of concrete cover is calculated from the time Cl-penetrates cover to specific depth to a defined Cl-concentration. Although there are many models for predicting Cl-concentration at depth, a recent working group concluded that most failed to predict reality. We have previously used a semi-empirical method to do this prediction based on time dependence of diffusion and surface concentration of Cl-. However because of the semi-empirical nature of the fitting equations we suggested that the method should be used with caution. Since then we have found some evidence to suggest that the fitting method has some scientific validity. We now suggest that it should be possible to predict service life (which is defined to be the time to corrosion initiation) from the diffusion of Cl-measured at 28 days provided that time dependant estimates of (a) diffusion in cement paste & (b) surface chloride concentrations on pastes exist. We suggest that if the time dependant properties in the cementitious pastes measured on samples cured for up to a year are combined with 28 days results from concrete then meaningful service life predications can be made. The postulated method enables a more realistic prediction of service life of reinforced concrete exposed to sea water than is presently available.