Effects of initial surface treatment timing on chloride concentrations in concrete bridge decks

In consideration of concrete cover thickness and the presence of stay-in-place metal forms (SIPMFs), research was done to determine the latest timing of initial surface treatment applications on concrete bridge decks subjected to external chloride loading before chlorides accumulate in sufficient quantities to initiate corrosion of the reinforcing steel. Chloride concentration data for this research were collected from 12 concrete bridge decks located within the Interstate 215 corridor in Salt Lake City, Utah. Numerical modeling was used to generate a chloride loading function and to determine the diffusion coefficient of each deck.. On the basis of average diffusion coefficients for decks with and without SIPMFs, chloride concentration profiles were computed through time for cover thicknesses of 2.0 in. (50.8 mm), 2.5 in. (63.5 mm), and 3.0 in. (76.2 mm). The results of the work show that the average diffusion coefficient for bridge decks with SIPMFs is approximately twice that of decks without SIPMFs and that, on average, each additional 0.5 in. (12.7 mm) of cover beyond 2.0 in. allows an extra 2 years for decks with SIPMFs and 5 years for decks without SIPMFs before a surface treatment must be placed to prevent excessive accumulation of chlorides. Although the data generated in this research are based on conditions typical of bridge decks in Utah, they clearly illustrate the effect of cover depth and the presence of SIPMFs. This information may be especially valuable to bridge engineers and managers responsible for programming surface treatments on concrete bridge decks.