Graduate Thesis Or Dissertation
 

Evaluation of the Effect of Chloride Ingress and Freeze-Thaw Cycles on Electrical Resistivity of Reinforced Concrete

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  • Performing bridge inspections can be a very daunting task for every department of transportation (DOT) in the country. Because the leading cause of deterioration in reinforced concrete bridge decks is corrosion of the steel reinforcement, the ability to detect the concentration of corrosion-causing chlorides in the concrete, using a non-destructive method, would save DOTs time and resources by allowing reparative action to take place early in the deterioration process. These are the contexts in which the current investigation was carried out, with the primary objective of investigating the potential for surface resistivity to be used as a non-destructive tool to assess the deterioration of concrete due to chloride ingress and freeze-thaw action. In this study, electrical resistivity measurements were taken on concrete cylinders and at various locations on reinforced concrete slabs that were saturated with chlorides from commercially available magnesium chloride de-icing solution, which contained a corrosion inhibitor. The study also provides a deeper understanding of the effect of freeze-thaw cycles on chloride ingress and surface resistivity measurements taken on concrete slabs previously exposed to a de-icing solution. Additionally, chloride profiles were taken congruently with the electrical resistivity measurements to monitor the ingress of chlorides. Surface resistivity values for all concrete increased during the early part of the study, partly due to the hydration of the concrete. However, surface resistivity decreased at the latter half for the chloride-exposed concrete, while water-saturated concrete did not vary. This suggests that SR measurements could identify chloride ingress. As chlorides ingressed in the concrete over time, the amount of bound chlorides increase; however, this increase was dominated by the amount of free chlorides that were retained at a specific depth in the concrete. The increase in free chloride concentrations, which are known to initiate corrosion, may be a cause of the decrease in surface resistivity measurements. This observation was also confirmed by thermodynamic modeling; however, this will need to be studied further. Though the cause of behavior observed on the surface resistivity measurements that underwent freeze-thaw action is not clear, it is evident that freeze-thaw action has a significant negative impact on the rate of chloride ingress on the slabs. The chloride profiles strongly indicated that the penetrability of the OPC mixtures increased compared to the same slab that did not go through freeze-thaw action. An increase in transport of chlorides was not apparent for the HPC mixture and was not seen in the chloride profiles. It is suggested that additional freeze-thaw cycles continue in this study, especially until the concrete starts to fail, in order to evaluate the impact and permanency of deterioration on surface resistivity.
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