Service life of RC structures: chloride induced corrosion: prescriptive versus performance-based methodologies

Reinforced concrete (RC) structures subjected to aggressive environmental exposure conditions are traditionally designed to satisfy safety, serviceability, durability and aesthetics requirements throughout their operational design service life. This is usually established using time-dependent mathematical models, developed through performance-based methodologies in guidelines and European and national standards. However, at present, in most cases, prescriptive methodologies are used. The objective of this paper is to compare, as regards chloride induced corrosion, defined target periods of service life according to a prescriptive methodology with service life results of a performance-based methodology. In the laboratory concrete specimens were manufactured having compositions according to a prescriptive specification. These specimens were tested in order to determine their performance properties (strength, chloride diffusion and capillary absorption). Test results were included in the mathematical models of the performance-based specifications. The classic safety factor and recent probabilistic approaches have been used to estimate the service life of each composition being compared to the target periods defined in the prescriptive specification. Numerical calculations show that the results of the Partial Safety Factor and a full probabilistic approach are distinctly different and consequently their convergence still needs to be improved, due to the complexity of the process of chloride penetration into the concrete, not only the model but also the input values. When compared to performance-based approaches it would be expected that the prescriptive methodology would be more conservative due to its less quantified information on concrete and environment properties, though in this study this was not always true.