Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Summary uSe of fiber-reinforced PolymerS in HigHway infraStructure This synthesis presents the use of fiber-reinforced polymer (FRP) composites in highway infrastructure. The state-of-the-art review of FRP applications includes material types and characteristics, application guidelines, FRP-reinforced concrete, FRP-prestressed concrete, FRP-strengthened concrete, FRP stay- in-place members and FRP decks, and life-cycle cost analysis. FRP composites consisting of fibers and a polymeric resin provide enhanced engineering properties and performance compared with conventional construction materials; for example, favorable strength-to-density ratio, noncorrosiveness, and reduced maintenance costs. Three types of FRP materials are employed in practice: carbon FRP (CFRP), glass FRP (GFRP), and aramid FRP (AFRP). Basalt FRP (BFRP) is an emerging material. Typical resins used to form FRP composites are epoxy, polyester, and vinylester. To assist practitioners who are interested in FRP applications, several standards organizations or professional societies publish design guidelines, codes, and specifications. FRP-reinforced concrete is an alternative to steel-reinforced concrete. GFRP bars are exclusively utilized to reinforce bridge decks and other elements (e.g., culverts and railings). Unlike steel- reinforced concrete members, FRP-reinforced members allow tension- and compression-controlled failure modes, as a result of FRPâs linear elastic behavior. The potential degradation of FRP bars is addressed by environmental reduction factors. Serviceability often controls the design of FRP- reinforced concrete, because the low modulus of FRP results in more deflection than its steel counter- part. Instead of traditional ductility, deformability is adopted to quantify the flexural behavior of FRP-reinforced concrete members. The in situ use of FRP bars for axial load-carrying members is scarcely reported, although laboratory-scale test results are available. FRP-prestressed concrete is usable for bridge girders and piles. CFRP tendons are employed in preference, because of their stable long-term behavior relative to GFRP tendons that are suscep- tible to creep-rupture. The design approaches for FRP-prestressed concrete are principally identical to those for steel-prestressed concrete. Long-term prestress losses of FRP tendons require more research. Existing structures may be strengthened with FRP sheets or laminates to enhance flexural, shear, and axial capacities. Typically, FRP strengthening can be categorized as two groups: bond-critical (bond failure significantly affects the performance of the strengthening system) and non-bond-critical (local bond failure may not influence the efficacy of the FRP system, such as column confinement). FRP composites are adhesively bonded to the substrate of a concrete member (frequently called externally bonded or EB FRP) or are inserted into the precut groove of the concrete and bonded with an epoxy (near-surface-mounted or NSM FRP). The performance of installed FRP is satisfac- tory with negligible maintenance or repair action. When FRP-strengthened members are subjected to thermal distress, premature failure of the strengthening system can take place owing to a change in the adhesiveâs material properties. FRP composites are also usable for stay-in-place forms (e.g., concrete-filled FRP tubes) or bridge decks with various configurations (e.g., honeycomb and hex- agonal structures). From a financial perspective, the long-term benefits of FRP are measured by life-cycle cost analysis. The relatively high material costs of FRP can be offset by their durable performance, particularly for corrosion-free service (the word corrosion in this report is defined as the deterioration of a metallic
2 material induced by electrochemical reactions with its environment). More case studies are, however, necessary to better quantify life-cycle costs associated with FRP applications. The state of current practice of FRP materials was established through a survey questionnaire and follow-up interviews with 46 responding transportation jurisdictions [44 U.S. departments of transportation (DOTs) and two Canadian agencies: an 88% response rate for the U.S. agencies]. FRP composites for infrastructure projects are generally satisfactory and promising including bridge girders, decks, piers, piles, abutments, buried structures, concrete pavement, drains, and culvert liners. Most agencies have used FRP since 1996 (79% of the participating jurisdictions), although some agencies revealed pioneering endeavors in the early 1990s. The nature of construction projects determines whether FRP applications are experimental or a standard practice. The survey shows that CFRP strengthening for upgrading bridge piers (primarily columns) is the most accepted standard practice, followed by GFRP-reinforced bridge decks. The implementation of FRP is primarily based on technical documents published by AASHTO and American Concrete Institute Committee 440 (Fiber-reinforced Polymer Reinforcement, ACI440). Several agencies have developed in-house specifications to complement the contents of the AASHTO and ACI440 guidelines. Challenges experienced by the responding agencies include a lack of previous experience and specifications, a dearth of skilled designers and contractors, inadequate procurement procedures, and insufficient budget. The responding agencies are interested in the performance of structural members constructed with FRP composites, and conduct various tests to examine the FRPâs behavior at material level (e.g., bond test) and structure level (e.g., visual inspection, nondestructive testing, and load rating). Despite these efforts, the long-term durability of in situ FRP still requires additional research to gen- erate technical data and to convince DOT engineers. Most respondents revealed that more training, either on-site seminars or webinars, is necessary to help understand the use of FRP composites in construction projects.
