Since its first applications in Europe and Japan in the 1980s, use of bonded repair and retrofit of concrete structures with fiber reinforced polymer (FRP) systems has progressively increased to the extent that today it counts for at least 25 Innovative Bridge Research and Construction (IBRC) projects in the United States, in addition to numerous projects independently undertaken by state departments of transportation (DOTs) and counties. Because of their light weight, ease of installation, minimal labor costs and site constraints, high strength-to-weight and stiffness-to-weight ratios, and durability, FRP repair systems can provide an economically viable alternative to traditional repair systems and materials. It is generally accepted that long-term performance of FRP systems is affected not only by the constituent materials, but also by the processes used during construction. However, the relationships between the long-term performance of FRP systems and the construction processes are not easy to quantify. Hence, there is a lack of generally accepted construction specifications and process control procedures for FRP repair systems, and state DOTs are heavily dependent on FRP manufacturers to provide construction process control. As the FRP technology matures and moves into widespread use, the need has become more urgent than ever to equip state DOTs with the means to specify and control the constituent materials and the adequacy of the construction process.
This study was undertaken to develop recommended construction specifications and a construction process control manual for bonded FRP repair and retrofit of concrete structures that will ensure performance as designed. The three most common types of FRP repair systems were considered: wet lay-up, precured, and near surface mounted.
The study was based on then-current scientific and engineering knowledge, research findings, construction practice, performance data, and other information related to FRP constituent materials and FRP systems. The information was gathered from a literature search, existing databases, a questionnaire survey, telephone interviews, and a clearinghouse website. A number of issues and parameters relevant to FRP repair were identified based on the collected data and were used in developing the recommended construction specifications and the process control manual.
The proposed specifications include eight main sections: General; Submittals; Storage, Handling, and Disposal; Substrate Repair and Surface Preparation; Installation of FRP System; Inspection and Quality Assurance; Repair of Defective Work; and Measurement and Payment. The proposed process control manual covers quality control (QC) and quality assurance (QA) prior to, during, and after completion of the repair project. It consists of planning, record keeping, inspection and QC tests. The manual includes the following main sections: QA Policy and Program Overview; QA Guidelines for Construction Activities; and Implementing and Monitoring of the QA Program.
The manual also consists of a number of QA checklists for the FRP repair projects. Critical review of the FRP research indicates a general consensus on the most relevant issues and parameters for construction specifications and a process control manual.
However, the primary concern throughout this study has been, and remains, to justify the rational basis for the specified tolerances, criteria, and procedures. The novelty of the FRP technology and its subtle differences from the traditional repair systems are reflected in the proposed specifications. Some of the proposed provisions may appear more restrictive than the current practice for traditional materials. Although the industry may find such restrictions counterproductive for further development of new FRP technology, the main objective has been to help protect state DOTs from low-quality applications with major defects. The decision on relaxing or replacing any of the restrictions ultimately lies with the American Association of State Highway and Transportation Officials (AASHTO) and its member states. The states can use the proposed specifications and process control as “model documents” that need to be tailored to their specific needs as well as to the size and intent of each project. At the same time, it should be understood that as the FRP technology matures, and as new research data become available, some of those restrictions may be removed or relaxed. In fact, the report identifies provisions in the two documents that may need further refinement, and recommendations are made for future research to accomplish these refinements. The long-term benefits of this research include lower maintenance costs and longer service life for repaired and retrofitted structures. These benefits will reduce the annual backlog for bridge replacement, resulting in lower costs to maintain or improve the transportation system. It is expected that bridge construction inspectors, general contractors, FRP subcontractors, and FRP and adhesive material suppliers will use the results of this research. Therefore, a four-element implementation plan is suggested for use by highway agencies. The plan includes training and technology transfer, a shakedown period, trial field applications, and an updating process.
Bonded Repair and Retrofit of Concrete Structures Using FRP Composites
AMIR MIRMIRAN, MOHSEN SHAHAWY, ANTONIO NANNI, VISTASP KARBHARI