Prediction of service life of concrete structures using corrosion rate model Available to Purchase

The uncertainties that exist in the chloride diffusion model may lead to considerable error in the prediction of the time to initiation of corrosion in the service life estimation of concrete structures. An alternative approach based on polarisation resistance (R_p value) has been proposed. Enhancement of the service life of concrete made using blended cements was measured experimentally using the electrochemical impedance technique (EIS) in the presence of 0, 0·5 and 1% of added chloride. The time to initiation of corrosion (T_i) predicted from the R_p value agreed well with the value from the weight loss measurement, whereas it was overestimated by the chloride diffusion model. Using the Maaddawy mathematical model, the time to propagation (T_p) was obtained. From the results it was concluded that in the presence of 1% of added chloride, the time to failure T_f = (T_i + T_p) of Portland pozzolana cement (PPC) and Portland slag cement (PSC) concrete was four and ten times higher than that of ordinary Portland cement concrete, respectively, even in low-strength concrete of 20 MPa. Parameter T_f increased as the strength of the concrete increased. The T_f value predicted by the corrosion rate model agreed very well with the T_f from the weight loss measurement and cracks on the concrete surface. The reduced rate of diffusion of chloride due to pore constriction and the higher chloride binding ability of blended cements lead to the enhancement of the service life of concretes when exposed to marine atmospheric conditions. The estimation revealed that a rebar embedded at 25 mm cover in 40 MPa PPC and PSC concrete (0% Cl⁻ added) could have a service life of more than 100 years.