Chloride ingress into reinforced concrete sustaining in-service loads

The service life of a reinforced concrete (RC) bridge deck in cold climates is often limited by chloride-induced corrosion of the reinforcement due to exposure to de-icing salts routinely applied in the winter. Although there has been an extensive research effort on chloride ingress into concrete in the last three decades, research conducted on structural concrete members carrying in-service loads is limited. The objectives of this study were to investigate the effect of sustained load on chloride ingress into concrete and to examine the reliability of spraying a AgNO3 solution onto concrete as a quick method to determine chloride penetration. To achieve these objectives, an experimental program was carried out, in which a small-scale RC slab was subjected to wet and dry cycles with a saturated chloride solution while sustaining static service loads. The concrete slab was cast with three strips of different water-to-cement ratios to represent different field conditions. Supports were located to create both positive and negative moment regions in the top mat reinforcement of the slab. Concrete cores were taken at several sections along the RC deck, which were stressed to different levels, and at three time intervals, each of them after a wet/dry cycle of 90 days. Concrete cores were sprayed with a AgNO3 solution to determine an average chloride penetration front, and chloride profiles along the concrete cover for each core were measured by potentiometric titration. Chloride diffusion coefficients were obtained from the data obtained from spraying AgNO3 and titration, the latter by curve-fitting to Fick's 2nd law. The comparison between both sets of data reveals that the differences diminish as the time of exposure increases. The chloride diffusivity along the span of the slab, relative to that of an unstressed section, was related to the applied bending moment. The experimental results also indicate that there is a dependence of chloride ingress properties on the type and level of sustained load. An analysis of the data to study the effect of exposure time and water-to-cement ratio using colourimetric and potentiometric titration methods was also carried out