Abstract

Chloride-induced deterioration of concrete bridge decks can be described in terms of three phases: 1) initiation of rebar corrosion, 2) rust formation and development of deck damage, and 3) accelerated deck damage towards structural failure. The first objective of this research was to investigate relationships among chloride concentration at the top mat of reinforcing steel, deck age, cover depth, and occurrence of delamination for concrete bridge decks with selected surface treatments and rebar types. Relating these factors can help establish greater understanding about the duration of each phase of the deterioration process. A second objective of this research was to investigate the relationship between chloride concentrations that develop between the bars and those that develop directly above the bars in the top mat of reinforcing steel to better understand the effects of the presence of reinforcing steel on diffusion of chloride ions through the concrete matrix.Data collected from 48 concrete bridge decks in Utah were used to address both of the objectives stated for this research. Surface treatment types included bare concrete, thin-bonded polymer overlays, and asphalt overlays, and rebar types included uncoated and epoxy-coated rebar. Regarding the first objective, baseline relationships between chloride concentration, deck age, and cover depth were developed for all three deck types. The results show that, as deck age increases, chloride concentration also increases and that chloride concentrations are much higher for shallower concrete depths than for deeper concrete depths. Based on these relationships, the duration of the first phase of the deterioration process was estimated using the critical chloride threshold of 2.0 lb Cl-/yd3 of concrete. For decks with asphalt or polymer overlays, development of clear relationships between chloride concentration, deck age, and cover depth required consideration of treatment time. The data show that chloride concentrations for decks that had an overlay applied 10 or more years after construction are higher than those for decks that had an asphalt overlay applied immediately after construction. Relevant to determining the duration of the second phase of the deterioration process, the relationship between delamination occurrence and chloride concentration for bare concrete bridge decks was developed. In general, the results show that the occurrence of delamination increases with increasing chloride concentration. Estimated durations of the second phase of the deterioration process were then determined using a chloride concentration threshold of 4.0 lb Cl-/yd3 of concrete for each of the same combinations of surface treatment and cover depth used for determining durations of the first phase of the deterioration process. Regarding the performance of epoxy-coated bar, the data clearly demonstrate the benefit of epoxy coatings on reinforcing steel for the purpose of significantly delaying the onset of chloride-induced delamination in concrete bridge decks. The relationship between the ratio of chloride concentrations directly above and between steel reinforcing bars and deck age was then developed. The results show that, as deck age increases, the average ratio of chloride concentrations directly above and between the bars asymptotically decreases from above 1.5 toward 1.0, which is reached at a deck age of approximately 30 years. Given that increasing deck age generally corresponds to increasing chloride concentration, which would in turn eventually lead to similar chloride concentrations directly above and between bars as the concrete pore water within the cover depth approached chloride saturation, this observed relationship is consistent with theory.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering