The American Concrete Institute (ACI) recently released ACI 562-19: Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures and Commentary, the third version of the concrete repair code developed by ACI to be a performance-based document for the assessment and repair of existing concrete structures. Since the publication of the first edition in 2013, ACI Committee 562 (the committee responsible for creating and updating the code, of which I am a member) has focused on improving the code provisions and increasing the technical depth of the document. While changes to the code are of direct interest to the engineers and designers who will be referencing them, these improvements will also initiate some process changes that may be seen on the jobsite.
History of ACI 562
In 2004, an initiative known as Vision 2020, which sought to improve the efficiency, safety, and quality of concrete repair and protection, was created at the request of the concrete repair and protection industry. The concepts of a concrete repair code and concrete repair specifications were proposed as a part of Vision 2020 as a way to improve the performance of repaired concrete structures. Combined with the publication of ACI 563-18: Specifications for Repair of Concrete in Buildings, ACI 562-19 represents the continued development of standardized documents that were called for in the third and fourth stated goals of the Vision 2020 program. These documents will significantly improve the safety and durability of repaired concrete structures. Below, we will discuss how standards potentially improve the performance of repaired structures, describe changes in ACI 562-19, and briefly discuss future directions for the ACI 562 standard.
How ACI Standards Improve Concrete Repair Performance
The intent of the concrete repair code was to establish evaluation, design, and inspection practices that raise the performance level of repair and protection systems. A dedicated code document was needed since existing codes and standards address new construction and are not directly applicable to existing structures.
ACI 562-19 was developed to work with the International Existing Building Code (IEBC). The IEBC provides some minimum requirements for repair of existing structures that are largely limited to delineating when a structure might need to be upgraded to satisfy current code requirements. The IEBC provides no insight on assessment of existing structures, unique considerations associated with repair of existing structures, or durability.
A key goal of ACI 562-19 was to provide the repair community with a code that established minimum practices for assessment of existing structures and the design of repairs that ensure life safety, but which is also durable within the desired service life of the repaired structure.
Changes in ACI 562-19
Some of the changes in ACI 562-19 include improvements in the code requirements for external reinforcement and clarification in how unsafe conditions are defined.
External Reinforcement: Installation of external reinforcement, in the form of fiber-reinforced polymers, external post-tensioning, or external steel plates, are common strengthening methods. However, in contrast to internal reinforcement, external reinforcement could be exposed to fire or an elevated temperature in service. ACI 562 includes additional load combinations and code requirements that must be satisfied to ensure external reinforcement systems perform as intended. These provisions were updated in ACI 526-19 for consistency with other ACI standards and to improve the clarity of the provisions.
Unsafe and Potentially Dangerous Conditions: A key part of the assessment of any structure is the identification of unsafe and dangerous conditions. The first version of ACI 562 used definitions of “dangerous” and “unsafe” that were directly adopted from the International Existing Building Code (IEBC). Its definition of “dangerous” was “any concrete building, structure, or portion thereof that meets any of the conditions described below shall be deemed dangerous: 1. The building or structure has collapsed, has partially collapsed, has moved off its foundation, or lacks the necessary support of the ground. 2. There exists a significant risk of collapse, detachment or dislodgement of any portion, member, appurtenance, or ornamentation of the concrete building or structure under service loads.”
A crucial question arose from this definition: When does an existing member or structure have a “significant risk of collapse under service loads?” To address this question, a reliability approach was used to develop a demand-to-capacity ratio which provides the design professional with a mechanism to determine when a structure may be unsafe and in need of shoring or other intervention. This demand-to-capacity ratio is also used to delineate when a structure will need to be strengthened to meet current code requirements.
Future Directions for ACI 562
All standards are regularly updated to reflect the latest technology, practice issues, and research results. This process allows the code committee to introduce new provisions and to improve the language of existing provisions. ACI 562 is a relatively “young” standard, having been first published in 2013, and has room to grow; improvements will continue to be developed. Future changes are likely in the areas of precast-prestressed and post-tensioned structures. The presence of either bonded prestressing steel or unbonded post-tensioning needs to be considered both in the design of structural repairs, and in the development of durable repair solutions. New subcommittees are currently examining if additional code provisions and commentary are needed for these types of structures.
A critical part of any successful repair program is quality assurance, including construction inspections, conformance testing of repair materials, and construction observations. The quality assurance requirements in ACI 562 are largely based on new construction. The committee will be reviewing these requirements to attempt to improve the construction inspection and oversight process.
ACI 562-19 was developed for repair of existing concrete structures beyond just buildings. Accordingly, the committee is also reviewing the code to determine mechanisms to expand use of the code for nontraditional building structures.
The long-term success of a concrete repair project is the result of identification and quantification of the damage present, development of repair plans and specifications that address the structural and durability needs, and implementation of the repairs consistent with the project specifications. The development and use of codes and standards will improve repair performance by establishing minimum levels of practice, which will have the effect of raising the performance of the entire repair industry.
In his companion piece to this article, Concrete Construction editor-at-large Bill Palmer covered the new version of the International Concrete Repair Institute's Technical Guideline No. 320.1R-2019, Guide for Selecting Application Methods for the Repair of Concrete Surfaces, to which seeks to “help illustrate the methods commonly used for the repair of deteriorated concrete surfaces using cement-based repair materials and to highlight the applications for which each method is considered to be most suitable.” Click here to read that article.