CHAPTER 1

Introduction

This chapter first describes the current state of practice motivating this synthesis. Then, specific goals for the synthesis are given. Next, scope of the synthesis (including materials considered, how these are defined, and the methods used) is discussed. Last, the organization of this report as a whole is described.

Background

Material degradation affects all components of bridges, often limiting their service lives. For reinforced concrete bridge members, this deterioration is predominantly caused by corrosion of the internal steel reinforcement. In bridges exposed to chlorides (either natural chlorides or chlorides found in deicing agents used for winter roadway maintenance), this corrosion is primarily caused by water or chlorides (or both) permeating through the concrete to the steel. When these compounds and ions reach the surface of the steel, corrosion begins generating iron oxides (i.e., rust), which in turn causes a volumetric expansion of the steel reinforcement. Similarly, diffusion of carbon dioxide from the outside environment into the concrete can cause carbonation, which can also lead to corrosion. These corrosion processes cause internal pressure on the concrete, which can eventually manifest into cracking and spalling of the concrete. This can result in loss of functionality, safety issues, costly repairs, user delays, environmental impacts, and reduced service lives.

In efforts to mitigate these problems, many types of reinforcing bars have been developed and implemented, which are collectively called corrosion-resistant reinforcing bars (CRRBs) in this study. Relative to black steel reinforcing bars, CRRBs provide corrosion resistance through one or both of the following methods: (1) by providing the steel with a protective coating that is intended to prevent water and chlorides from reaching black steel bars, or (2) by replacing traditional black steel with alternative materials that are more resistant to corrosion. The multitude of options has benefits but also complicates efforts to identify which bar type is the optimal solution. This issue is further complicated by the wide range of geographic and site-specific environments, variable costs, service life considerations, construction practicalities, and more. Additionally, some of these options have been in widespread use for many decades, while others are more recent innovations or have been implemented to a lesser extent, making information on their performance more disparate.

Objectives

The objective of this synthesis is to document policies and practices used by state departments of transportation (DOTs) related to the use of CRRBs. Specific types of information of interest include the following:

• Types of CRRBs used, including frequency of use in different member types, use over different time periods, and use in different regions of the United States.

• Decision-making processes for choosing between alternative types of CRRBs, including criteria considered and assumptions made.
• Associated changes to structural and concrete designs that have been implemented.
• Quality control considerations.
• Challenges and benefits of using CRRBs that have been encountered in practice. Benefits considered include but are not limited to corrosion performance. It was also of interest to document how state DOTs have assessed performance. Specific potential challenges that were assessed included material availability, field implementation issues, and problems with dissimilar metals or materials.
• Implementation efforts associated with CRRBs.
• Written policies governing the application of CRRBs.

Scope and Definitions

This section describes the scope of the synthesis with respect to the materials considered and the methods used to synthesize state DOT practices with respect to CRRBs.

Materials Considered

CRRBs are defined herein as any types of bars for concrete reinforcement that provide enhanced corrosion protection relative to the baseline of uncoated plain carbon and low-alloy steel bars, herein referenced as black bars. As stated previously, CRRBs provide improved durability (relative to black bars) by using one or both of the following fundamental approaches: (1) providing the steel with a protective coating that is intended to prevent water and chlorides from reaching black steel bars, or (2) replacing traditional black steel with alternative materials that are more resistant to corrosion. Bar types in the former category are epoxy-coated, galvanized, stainless steel clad, and steel with multilayer coatings, all of which function by providing a barrier between the steel and the water and chlorides that cause corrosion in steel bars. In addition, the zinc-based coating on galvanized bars and on bars with multilayer coatings provides cathodic protection, because zinc will preferentially corrode relative to steel. Existing options in the category of bars that function by using different materials other than black bars are steel bars alloyed with chromium (which can be further divided into low-chromium and stainless steel reinforcing bars) and fiber-reinforced polymer (FRP) reinforcing bars. The specific materials that are considered are defined in the list that follows. Survey respondents also had the ability to enter other bar types specific to their state DOTs; these are discussed in Chapter 3. These include bar types that use both approaches to providing improved durability, which are mentioned elsewhere where relevant but are not common. Materials considered are defined as follows:

• Black bars. Uncoated plain carbon and low-alloy steel bars for concrete reinforcement that meet the requirements of AASHTO M 31/ASTM A615.
• Chromium-alloyed steel bars. Bars with chromium content of less than 16%, such as those meeting the requirements of ASTM A 1035 (including proprietary products such as ChromX, formerly marketed as MMFX). Although bars with 16% or greater chromium are also alloyed with chromium, these are defined as stainless steel bars.
• Epoxy-coated steel bars. Steel bars that meet the requirements of AASHTO M 31 with epoxy coatings that meet the requirements of ASTM A775 or similar.
• Fiber-reinforced polymer (FRP) bars. Bars made up of fibers (such as carbon, glass, basalt, and others) in a polymer matrix, including but not limited to those meeting the specifications of ASTM D8505, Standard Specification for Basalt and Glass Fiber Reinforced Polymer Bars for Concrete Reinforcement (ASTM 2023b).
• Galvanized steel bars. Steel reinforcing bars with protective zinc coatings that are applied by immersing the bars into a molten bath of zinc [e.g., hot-dip galvanizing that meets the

• requirements of ASTM A767, Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement (2019)]; through the process of uninterrupted passage of long lengths of bars through a molten bath of zinc or zinc alloy [e.g., continuous hot-dip galvanizing that meets the requirements of ASTM A1094 (ASTM 2020a)]; or similar.
• Stainless steel bars. Uncoated stainless steel bars that meet the requirements of ASTM A955 or AASHTO M 334 (which have a minimum chromium content of 16%) and other products with equivalent chromium content.
• Stainless steel clad bars. Steel bar with stainless steel cladding that meets the requirements of AASHTO M 329 or similar.
• Steel bars with multilayer coatings. Steel reinforcing bars with multilayer coatings, such as galvanized steel with epoxy coatings.

Additional Definitions

The survey also defined the following terms:

• Metallic bars. This refers to all forms of corrosion-resistant reinforcing bars composed of any type of steel; it represents all forms of CRRBs identified herein (with the exception of FRP bars).
• Qualitative information. In the context of this survey, this term refers to performance data that cannot be readily quantified. Examples of this include but are not limited to visual observations, photographic evidence, and experiences of personnel (e.g., state maintenance engineers or inspectors). For findings resulting from the experiences of personnel to have the appropriate value, it is imperative that such qualitative information be based on collective experience within the state DOT that is informed by factual information and is free from bias and opinions.
• Quantitative information. In the context of this survey, this term refers to performance data that can be quantified. Examples include (but are not limited to) condition ratings, measurements of defects (e.g., crack lengths), service lives, or monetary values.
• Splash zone. The portion of a structure that is intermittently directly exposed to water that has high concentrations of chlorides. These include natural sources of saltwater as well as water containing dissolved deicing agents. Bridge members that can be exposed to water with dissolved deicing agents include bridge decks, superstructure and substructure elements of highway overpasses that are in proximity to the underpassing roadway, and superstructure or substructure elements that may be exposed to chlorides because they are located beneath leaking expansion joints.

Methodology

The methodology for this synthesis consisted of a literature review, survey, and interviews (to develop case examples). The literature review focused on domestic sources published within the last 20 years and research that was supported by state DOTs, although other sources were included when especially relevant. A survey was designed and refined based on feedback from the panel; it was then distributed to one voting member of the AASHTO Committee on Bridges and Structures from each state as well as the District of Columbia and Puerto Rico.

Survey responses were analyzed and preestablished criteria were used to identify a group of state DOTs that could serve as case example participants. These criteria made parallel considerations of (1) which of the state DOTs could provide the greatest volume of relevant information and (2) which group of state DOTs could provide the greatest breadth of information. State DOTs that indicated in the survey that they had information on topics of interest that was not conducive to being queried through a multiple-choice format were also prioritized as potential case example participants. Interview questions were then developed and used during interviews with the case example participants. The verbal comments made during these interviews, combined with the information contained in written documentation (e.g., state specifications or internal

reports provided by the participants), were used to compare and contrast different approaches and to elaborate on specific policies, practices, and experiences to form the case examples.

Report Organization

Chapter 1 serves to establish the motivation, objectives, scope, and organization of this report. Chapter 2 summarizes the literature review. Chapter 3 presents an analysis of the survey results. Chapter 4 contains case examples detailing the use of CRRBs in six state DOTs. Chapter 5 provides a summary of the findings of chapters 2, 3, and 4.

Appendices A, B, and C provide additional information on the survey, including the survey questions, a list of survey respondents, and the responses given by each state DOT, including links to state DOT information on CRRBs that were provided during the survey, respectively. The questions that were asked during interviews of the case example participants are provided in Appendix D.