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46 corrosion rates, and corresponding probability and reliabil- Update Experience with Different ity analyses. These issues are related to reliability of metal Reinforced Fills loss modeling, quantification of the effect of construction An example of the experience gained from collecting and practice on performance, and understanding the cost bene- analyzing data relates to the use of reinforced fills that may or fits of using different materials. All of these are important may not meet AASHTO specifications for electrochemical components of asset management. For example, the data- properties. The database was divided into two primary groups base can be used to including data from reinforced fill conforming to AASHTO criteria and from reinforced fill not conforming to AASHTO Study the mean and variance of corrosion rates for data criteria. The AASHTO corrosion model was applied to esti- sets grouped according to different climate, site conditions, mate reinforcement corrosion rates and to compare them to and reinforced fill conditions; measured corrosion rates. The observations below were made Quantify performance for marginal reinforced fills; and from the existing database. These observations may be updated Evaluate the performance of different materials (e.g., steel as more data become available. vs. zinc, other forms of metallization, and the use of poly- meric coatings). For reinforced fills conforming to AASHTO criteria, the AASHTO corrosion model overestimates steel corrosion These applications will lead to better estimates of service life rates for 98% of the data. It should be noted that most of and can help to quantity the benefits of selecting higher quality the data in this group are associated with reinforced fills backfill for construction or the costs associated with using mar- that meet AASHTO requirements by a wide margin. ginal quality fill. Performance data can also facilitate evaluation For reinforced fills conforming to AASHTO criteria, marine of alternative materials, including use of galvanized versus plain environments have minor to no effect on measured cor- steel, or other corrosion protection measures that may include rosion rates of galvanized reinforcements, but marine epoxy or polymer coatings. Practices that may lead to poor per- environments accelerate corrosion rates of plain steel formance may also be identified and quantified, including the reinforcements. impact that poorly maintained drainage inlets may have on For reinforced fills that do not satisfy AASHTO criteria, service life, or the effect of fill contamination during service. The marine environments are associated with relatively high database needs to be continuously updated and should include corrosion rates. performance data from sites where good practice has been Reinforced fills that do not meet AASHTO criteria (i.e., soil followed as well as from sites with questionable conditions. resistivity values < 3,000 -cm and pH values < 5) can significantly affect steel corrosion rates, which tend to dra- Maintenance, Rehabilitation, matically increase beyond rates estimated by the AASHTO and Replacement corrosion model. Based on available data, organics content, chlorides, sul- Issues that can address future needs for maintenance, reha- fates, and relatively high values of pH have much less effect bilitation, retrofit, or replacement include on measured corrosion than do relatively low resistivity and low pH. Spatial variations of element condition and corrosion rate Review of the latest research information confirms the safety (e.g., top vs. bottom of wall), of the electrochemical requirements for fill and associated Special areas that may deserve increased maintenance (e.g., metal loss rates in the current AASHTO standards. in proximity to drainage inlets), and Effects of different climates, use of deicing agents, and so forth. Recommendations for Future Research Improved knowledge of spatial variations and special prob- NCHRP Project 24-28 assessed and improved the predictive lems can lead to improved allocation of resources. For exam- capabilities of existing computational models for corrosion ple, in some cases, extended service life may be best achieved potential, metal loss, and service life of metal-reinforced systems by retrofitting areas surrounding drainage inlets, or the ben- used in retaining walls and highway cuts and fills. Methodology efits of improved maintenance of drainage inlets may be real- was developed that incorporates the improved predictive mod- ized in terms of increased service life. In areas where deicing els into an LRFD approach for the design of metal-reinforced salts are used, corrosion monitoring can demonstrate the need systems. Recommended additions and revisions were prepared to maintain pavements, improve drainage, or install and to incorporate the improved models and methodology in the maintain impervious barriers. AASHTO (2009) LRFD Bridge Design Specifications.