SUMMARY

State DOT Policies and Practices on the Use of Corrosion-Resistant Reinforcing Bars

This synthesis was motivated by the widespread material degradation that affects all components of bridges, often limiting their service lives. For reinforced concrete bridge members, that deterioration is predominantly caused by corrosion of the internal steel reinforcement. In efforts to mitigate these problems as well as the associated costs, user delays associated with repair, and environmental impacts, a wide range of types of reinforcing bars have been developed and implemented. These are collectively referred to as corrosion-resistant reinforcing bars (CRRBs) in this study. The policies and practices of different state departments of transportation (DOTs) differ with respect to CRRBs.

It was the goal of this study to collect information on, summarize, and synthesize these CRRB practices. This goal was accomplished through a literature review, surveys of state DOTs, and interviews with state DOTs in order to develop case examples. The survey was sent to 52 DOTs representing each state, the District of Columbia, and Puerto Rico (state DOTs) and was completed by 45 state DOTs (87% of possible participants). Six state DOTs participated in the case examples. Through these efforts, information on eight different aspects of CRRB use was synthesized and is summarized as follows:

• The most commonly used bar types are traditional black and epoxy-coated steel bars. At present, 67% (30 of 45) and 73% (33 of 45) of respondents, respectively, consider use of these bar types to be part of their DOT’s typical practices. The relative use of these two materials varies in specific situations depending on member type and region of the country. Most other types of CRRBs have been used by increasing numbers of state DOTs since 2010.
• The approaches that state DOTs use for deciding between types of CRRBs vary in terms of their scope with respect to bar types, philosophical approach, and factors considered. A common consideration is exposure to chlorides, either at the bridge site in general or for specific member types and locations within the bridge. Service life considerations are also typically (directly or indirectly) considered, to various degrees of formality. Life-cycle cost analyses (LCCA) have been used in limited situations. These analyses typically justify the initial cost premium of more durable options.
• The use of metallic CRRBs does not require changes to existing design practices. Some metallic CRRBs can provide an additional benefit due to their yield strengths of 100 ksi or more, although there are uncertainties regarding the ideal stress capacity to be assumed for both service and strength-limit states. The use of fiber-reinforced polymer (FRP) reinforcing bars requires additional considerations for design. The AASHTO Load and Resistance Factor Design Bridge Design Guide Specifications for GFRP-Reinforced Concrete (AASHTO 2018) and other guidelines are available to provide direction for these designs. The use of CRRBs was reported as rarely affecting any of the aspects of concrete mix design that were queried in the survey. However, permeability was the most commonly modified parameter (as reported by 9% of respondents, or 4 of 45).

• Quality control specifications for CRRB are widely available [e.g., AASHTO Load and Resistance Factor Design (LRFD) Bridge Construction Specifications (AASHTO 2020c) and ASTM specifications for specific bar types]. Several (4 of 6) case example participants have additional and alternative specifications on damage tolerances for the coatings and cut ends of coated steel bars.
• The most common factors that limit the use of CRRBs were reported to be uncertainties regarding corrosion performance, cost, and material availability as well as uncertainties regarding the potential changes to design practice. However, there is variability in the most common concerns for different bar types.
• Of the survey respondents, 76% (34 of 45) reported that their state DOTs had observed benefits from using CRRBs. All of these respondents reported improved durability of decks. Other benefits reported include the durability of other components, less need for maintenance (resulting in fewer road closures and, consequently, reduced life-cycle cost), and reduced environmental impacts.
• The survey indicated that 96% of the respondents (43 of 45) had engaged in some form of implementation activities regarding CRRBs. Demonstration or pilot projects were by far the most common example of this. Other common implementation efforts include research and liaising with fabricators and suppliers.
• Most survey respondents (60%, or 27 of 45) indicated that their DOTs have written policies governing the application of CRRB. The scope and structure of the approaches contained in—and practices resulting from—these policies vary widely.

This synthesis also identified the following knowledge gaps and potential complementary research:

• The need for better information on the long-term performance and service life of alternative CRRBs was a common theme among the types of information desirable to the case example participants. Although some data on this topic presently exists, there is variability in laboratory data and even more so in field data, where the effects of different environmental conditions, design practices, and maintenance practices lead to a wide range of observed performance. The causes of these differences are not quantified with respect to the numerous variables involved in real-world scenarios. Therefore, there is a need for additional laboratory and field studies and to consider linking the results of these two types of research for findings that can ultimately be both scientifically explained and realistic.
• The need for information on the long-term performance of repairs to damaged coating areas.
• The need for additional data to perform reliable LCCA of CRRBs.
• A need to identify best practices for concrete mix design, to be used in conjunction with various types of CRRBs.
• A need for additional guidelines on the use of FRP bars—because the fundamental behavior of structural components using these bars differs from the behavior of concrete members reinforced with metallic bars. Ideal practices for performing demolition and repairs of members with FRP reinforcing bars are an additional knowledge gap for this bar type.
• The need to identify the ideal stress capacity that should be assumed for high-strength metallic CRRB types that lack a clearly defined yield point—for both service and strength-limit states.