LABORATORY INVESTIGATION AND NEURAL NETWORKS MODELING OF DEICER INGRESS INTO PORTLAND CEMENT CONCRETE AND ITS CORROSION IMPLICATIONS

摘要

By exposing reinforced concrete samples to four common chloride-based deicers, the corrosive effect of chloride-based deicers on rebars and dowel bars was systematically investigated. The experiments were designed in such a way that the effect of deicers on reinforced concrete can be characterized in an accelerated manner, by either ponding the concrete samples with deicer solutions at room temperature, or incorporating pressurized ingress, wet-dry cycling and temperature cycling into the test regime. The chloride ingress over time was monitored using a custom-made chloride sensor embedded in each concrete sample. Also periodically measured were the open circuit potentials (OCPs) of the top bar in concrete. Once the chloride sensor detected the arrival of sufficient chlorides near the top bar and the OCP data indicated the possible initiation of top bar corrosion, the corrosion rates of rebars and dowel bars are characterized by macrocell current and corrosion current density derived from electrochemical impedance measurements. From a modeling perspective, artificial neural networks (ANNs) were used to achieve better understanding of the complex cause-and-effect relationships inherent in the deicer/concrete/bar systems and were successful in finding meaningful, logical results from the noisy data associated with the deicer ponding experiments. According to the ANN modeling, corrosion inhibitor (and possibly other additives in the inhibited CaCl_2 and MgCl_2 deicers) did slow down the ingress of chloride into concrete (indicated by more positive chloride sensor potentials), reduce the pitting risk of rebars and dowel bars in concrete (indicated by more positive OCP values) and reduce their corrosion rate in concrete (indicated by reduced macrocell current and corrosion current density of top bar). For both concrete mixes andboth types of deicer ponding, the overall risk of deicers to reinforced concrete was in the order of: non-inhibited NaCl > inhibited NaCl > inhibited CaCl_2 deicer > inhibited MgCl_2 deicer. While the corrosion inhibitors in deicer products, provide some benefits in delaying the corrosion initiation of rebars and dowel bars in concrete, such benefits seem to diminish once the active corrosion of the bars is initiated. In other words, the inhibitors showed little benefits in re-passivating the actively corroding bars in concrete or in stifling the corrosion propagation.