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Bridge engineers and managers in coastal areas and cold regions frequently specify the application of surface treatments on concrete bridge decks as barriers against chloride ingress. In consideration of concrete cover thickness and the presence of stay-in-place metal forms (SIPMFs), the objective of this research was 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 during the service life of the deck. Chloride concentration data for this research were collected from 12 concrete bridge decks located within the I-215 corridor in Salt Lake City, Utah. Numerical modeling was utilized to generate a chloride loading function and to determine the diffusion coefficient of each deck. Based on average diffusion coefficients for decks with and without SIPMFs, chloride concentration profiles were computed through time for cover thicknesses of 2.0 in., 2.5 in., and 3.0 in. 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. 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. Given these research findings, engineers should carefully determine the appropriate timing for initial applications of surface treatments to concrete bridge decks in consideration of cover depth and the presence of SIPMFs. For maintenance of concrete bridge decks with properties similar to those tested in this study, engineers should follow the guidelines developed in this research to minimize the ingress of chlorides into the decks over time and therefore retard the onset of reinforcement corrosion; altogether separate guidelines may be needed for decks having substantially different properties. Surface treatments should be replaced as needed to ensure continuing protection of the concrete bridge deck against chloride ingress.

The objectives of this research were to investigate the effect of stay-in-place metal forms (SIPMFs) on the performance of concrete bridge decks in Utah. The research program included six bridge decks with SIPMFs and six decks without SIPMFs, which were all located within the Interstate 215 corridor in the vicinity of Salt Lake City, Utah, and therefore subject to similar traffic loading, climatic conditions, and maintenance treatments, including applications of deicing salts during winter months. All of the tested decks were constructed between 1984 and 1989 using epoxy-coated rebar. Several tests were performed at each of six locations on each deck, including visual inspection, chain dragging, hammer sounding, Schmidt hammer testing, half-cell potential testing, and chloride concentration testing. Because differences in deck age and average cover for the two deck types were found to be statistically significant, the collected data were subjected to analysis of covariance (ANOCOVA) testing, with age and cover as covariates. All calculated p-values were compared to the standard value of 0.05. The distress survey results indicate that the average crack width and crack density for decks without SIPMFs were greater by 41 and 25 percent, respectively, than the corresponding values for decks with SIPMFs and that decks without SIPMFs had more potholes than decks with SIPMFs. However, the delamination density for bridge decks with SIPMFs was 71 percent higher than that of decks without SIPMFs. The average Schmidt rebound number for decks with SIPMFs was higher than that for decks without SIPMFs by an equivalent of 1,400 psi. The half-cell potential for decks with SIPMFs was 0.123 lower than that of decks without SIPMFs, indicating that a more active state of corrosion exists on decks with SIPMFs. On average, the chloride concentration in the bridge decks with SIPMFs was 205 percent greater than the concentration in the decks without SIPMFs. Among all of the distress measurements evaluated in the ANOCOVA, crack width was the only parameter that was determined to be significantly different between the two types of decks at the time of testing. In addition, Schmidt rebound number, half-cell potential, and chloride concentration at 2-in. depth all yielded p-values less than 0.05, indicating that significant differences in these properties exist between decks with and without SIPMFs. Specifically, the decks with SIPMFs have a higher compressive strength, a more active state of corrosion, and a higher chloride concentration, which may all be attributable to elevated moisture contents in decks with SIPMFs arising from the reduction in deck surface area from which moisture may evaporate. These data indicate that decks with SIPMFs are clearly more susceptible to reinforcement corrosion compared to decks without SIPMFs and may therefore exhibit greater magnitudes of damage with time. Given these research findings, engineers should carefully compare the short-term advantages against the potential long-term disadvantages associated with the use of SIPMFs for concrete bridge deck construction. If SIPMFs are approved for use, engineers may consider applying surface treatments to the affected decks early in the deck life to minimize the ingress of chlorides into the concrete over time and therefore retard the onset of reinforcement corrosion.

Concrete bridge decks in Utah are experiencing observable deterioration due primarily to freeze-thaw cycles and the routine application of deicing salts during winter maintenance activities. Given the need for increasingly cost-effective strategies for bridge deck maintenance, rehabilitation, and replacement (MR&R), the Utah Department of Transportation (UDOT) initiated this research to ultimately develop a protocol offering guidance as to whether deteriorated bridge decks should be rehabilitated or replaced. While threshold values for various non-destructive condition assessment methods were proposed in earlier UDOT research, this work focused on implementing the recommended test criteria. Twelve bridges were identified by UDOT engineers for inclusion in the study, and data were collected from each deck to determine whether the bridge decks warranted rehabilitation or replacement based on the proposed threshold values. Several evaluation techniques were employed to assess concrete bridge deck condition, including visual inspection, hammer sounding and chaining, dielectric measurements, ground-penetrating radar imaging, resistivity testing, half-cell potential testing, and chloride concentration testing. The condition assessment testing confirmed that chloride-induced corrosion of reinforcing steel is the primary mechanism of deck deterioration and that inadequate cover over the upper steel mat facilitated accelerated corrosion damage in many instances. The bridge deck condition analyses produced from the results of non-destructive testing were compared to the visual inspection ratings assigned to each deck by UDOT. Concrete bridge deck condition data should be collected regularly through inspection and monitoring programs to facilitate prioritization of MR&R strategies for individual bridges and to evaluate the impact of such strategies on the overall condition of the network. Performance indices based on selected condition assessment parameters should be developed for use in bridge management activities, and mathematical deterioration models should be calibrated in order to forecast both network-level and project-level conditions and predict funding requirements for various possible MR&R strategies. Further research, including statistical analyses of the data presented in this report, should be completed to develop relevant mathematical deterioration models for predicting the service lives of concrete bridge decks in Utah.

Considering the pervasive presence of chlorides in concrete bridge decks, bridge engineers have a critical responsibility to perform proper and effective preventive maintenance and rehabilitation operations. Bridge engineers often perform scarification and overlay (SO) procedures on concrete bridge decks to minimize the corrosion of reinforcing steel due to chloride ingress. Given the need to develop guidelines for the initial timing of SO treatments, the specific objectives of this research were to collect information from several department of transportation (DOT) personnel about their SO procedures and, subsequently, to determine the recommended timing of initial SO procedures on concrete bridge decks for preventing the accumulation of corrosion-inducing levels of chlorides and extending deck service life. A questionnaire survey of state DOTs was conducted, and numerical modeling of SO treatments was performed. Simulations involving both decks with and without stay-in-place metal forms (SIPMFs) were performed. Numerical modeling was performed for each unique combination of variables through a service life of 50 years to determine the recommended initial timing of SO treatment in each case. The research results show that, overall, bridge decks without SIPMFs can endure longer delays in SO treatment timing than those with SIPMFs; in all cases, the absence of SIPMFs extended the amount of time before an SO treatment was needed. For decks with SIPMFs, the allowable delay in SO timing ranged from 2 to 6 years, while on decks without SIPMFs the allowable delay in SO timing ranged from 6 to 18 years. These delays are only 1 to 3 years longer than allowable delays associated with placement of surface treatments investigated in previous research. On average, the period of additional delay allowed before an SO treatment is required in decks with SIPMFs was 2 years with each additional 0.5 in. of OCD. In decks without SIPMFs, the presence of a greater OCD had a more pronounced effect on the latest recommended timing of treatment than in the decks with SIPMFs; an average additional delay period of 5 years was obtained with each additional 0.5 in. of OCD in decks without SIPMFs. Together with the findings of this research and the specific properties of the bridge deck under scrutiny, engineers can determine the appropriate timing of rehabilitation procedures to prevent or mitigate corrosion of the steel reinforcement of a bridge deck and ensure the usability of the deck for its intended service life. Although the conditions studied in this research were consistent with bridges located in the state of Utah, bridge decks that exist in similar environments and that are subjected to similar treatments of deicing salts as part of winter maintenance could exhibit similar properties to the decks simulated in this research. Engineers should carefully consider the results of this research and implement proper timing of SO treatments on their respective bridge decks to protect against and minimize the effects of corrosion due to chloride ingress.

Half-cell potential testing has been recommended as a non-destructive method for assessing the corrosion potential of reinforcing steel in concrete bridge decks. The technique is particularly useful because it can be utilized to evaluate the probability of corrosion before damage is evident at the surface of a bridge deck. The specific objective of this research was to quantify the effects of age, chloride concentration, concrete cover thickness, spatial position, temperature, and presence or condition of epoxy coating on half-cell potential measurements of concrete bridge decks typical of those in Utah. The laboratory testing associated with this research followed a full-factorial experimental design. Nine rectangular concrete slab specimens were prepared, each containing three black reinforcing steel bars at three different concrete cover depths and four epoxy-coated bars each having different coating conditions. Three replicate slabs were created at each of three different chloride concentrations. Three repeated measurements were made at each of three locations along each of the seven bars in all nine of the slabs at three ages, with testing performed at three temperatures per age. In addition, compressive strengths of the concrete cylinders were measured at 7 and 28 days. Statistical analyses of the half-cell potentials were performed using analysis of variation and Tukey's method for multiple comparisons. Although American Society for Testing and Materials C 876 only specifies the measuring of half-cell potentials of uncoated reinforcing steel, credible half-cell potentials were also obtained for epoxy-coated rebar in this research. The results of the testing indicated that all of the factors except for cover thickness and spatial position have important impacts on half-cell potentials over the ranges of levels investigated in this research. Half-cell potential measurements became consistently less negative with increasing age and consistently more negative with increasing chloride concentrations and increasing temperature. With regard to the factor of treatment, the uncoated rebar had the most negative half-cell potential, followed by epoxy-coated rebar with rib scrapes, pliers strikes, end cuts, and full epoxy coatings, in that order. While these data indicate that a coating, even damaged, reduces the probability of corrosion when compared to uncoated rebar, the data also suggest that both the amount and distribution of the coating damage over the affected rebar influence corrosion. Given these research findings, bridge engineers and managers should have confidence in using half-cell potential testing for assessing the corrosion probability of reinforcing steel in concrete bridge decks. In decks with properties similar to those investigated in this research, variations in age, chloride concentration, temperature, and presence or condition of epoxy coating cause variation in half-cell potential readings consistent with the effects of these factors on corrosion. Therefore, the half-cell potential technique is recommended for assessing the probability of corrosion of reinforcing steel on bridge decks. Although the use of epoxy-coated reinforcement, even when damaged, reduces the probability of corrosion, care should still be taken to minimize any damage to the coating during shipping and field handling. Owners and contractors alike should establish appropriate inspection protocols and repair methods for epoxy-coated reinforcing steel used on bridge decks to ensure maximum service life.