Abstract
A protocol is described whereby time-to-corrosion, Ti, of reinforcing steel in concrete exposed to chlorides is calculated as a distributed, rather than discrete, parameter. The method consists of inputting distribution functions for 1) surface Cl- concentration (Cs), 2) the effective diffusion coefficient (D), 3) concrete cover over the reinforcement (x), and 4) the critical Cl- concentration threshold to initiate active corrosion (CT) into a governing, first principles equation from which the fraction of identically exposed, electrochemically independent elements that has initiated corrosion is calculated at a specific time. By doing this for multiple times, a cumulative distribution function (CDF) plot of Ti is developed. Example analyses were performed based upon either literature or assumed distributed Cs, D, x, and CT data. The results indicate that reinforced concrete durability should be characterized not simply in terms of the time at which reinforcement corrosion occurs initially, as is normally the case, but also by the rate at which active corrosion subsequently commences for the remaining passive elements. Further, an important but often overlooked aspect of how Cs is determined or chosen for diffusion analyses in concrete is emphasized. Advantageous attributes of this methodology in which influential variables are distributed are discussed and comparisons made to the more traditional discrete parameter approach.
