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<ul><li><p>7/29/2019 018 civil engineering structures</p><p> 1/33</p><p>Construction and Building Materials 17 (2003) 405437</p><p>0950-0618/03/$ - see front matter 2003 Elsevier Ltd. All rights reserved.doi:10.1016/S0950-0618(03)00041-2</p><p>A model specification for FRP composites for civil engineering structures</p><p>Lawrence C. Bank *, T. Russell Gentry , Benjamin P. Thompson , Jeffrey S. Russella, b a a</p><p>Department of Civil and Environmental Engineering, Room 2206, University of Wisconsin, Madison, WI 53706, USAa</p><p>College of Architecture, Georgia Institute of Technology, Atlanta, GA 30332, USAb</p><p>Abstract</p><p>A proposed model specification for FRP composite materials for use in civil engineering structural systems is described in thisarticle. The model specification provides a classification systems for FRP materials, describes admissible constituent materials</p><p>and limits on selected constituent volumes, describes tests for specified mechanical and physical properties, specifies limitingvalues of selected properties in the as-received condition and in a saturated state, and provides a protocol for predicting long-termproperty values subjected to accelerated aging based on the Arrhenius model. The model specification is included as an appendixto the article. 2003 Elsevier Ltd. All rights reserved.</p><p>Keywords: Accelerated aging; Acceptance criteria; Arrhenius model; Classifications; Mechanical properties; Minimum properties; Physicalproperties; Specifications; Test methods</p><p>1. Introduction</p><p>It is widely recognized that in order for fiber rein-</p><p>forced polymer (FRP) composite materials to be usedin the construction of civil engineering structures suchas buildings and bridges a uniform procedure for speci-fying these materials is required. Standard specificationsexist for all commonly used materials in the civilengineering construction. These specifications ensurethat materials used in civil engineering projects aredefined in specific classes, are tested using standardprocedures, are certified in a uniform format and providespecific properties for their intended use. A consensus-based general material specification for FRP materialsfor use in civil engineering structural applications does</p><p>not exist at this time. A model specification has beendeveloped by the authors, under sponsorship of the USFederal Highway Administration (FHWA) and in coor-dination with the American Association of State Trans-portation and Highway Officials (AASHTO). Thespecification has not yet been approved by either AASH-TO or the America Society for Testing and Materials(ASTM). This article describes the development of themodel FRP material specification and the key elements</p><p>*Corresponding author. Tel.: q1-608-262-1604; fax: q1-608-262-5199.</p><p>E-mail address: bank@engr.wisc.edu (L.C. Bank).</p><p>that the specification contains. The Appendix to this</p><p>article contains the model specification itself. The spec-</p><p>ification is titled Standard Specification for Fiber Rein-</p><p>forced Polymer (FRP) Composite Materials for</p><p>Highway Bridge Applications as per the requirements</p><p>of the contract under which it was developed.</p><p>The model specification was developed by a team of</p><p>researchers who have extensive experience and expertise</p><p>in the use of FRP materials for civil engineering struc-</p><p>tures and extensive prior expertise in the development</p><p>of material specifications. The model specification was</p><p>developed in the following steps: (a) technical literature</p><p>on the subject of characterization of the mechanical and</p><p>physical properties of FRP composite materials for both</p><p>short-term and long-term properties was studied fromthe perspective of writing a specification; (b) existing</p><p>material and design codes and specifications for com-</p><p>posite materials were reviewed and evaluated; (c) exist-</p><p>ing design codes for conventional materials were</p><p>reviewed to determine their relationship to material</p><p>specifications; (d) key elements for a FRP material</p><p>specification for civil engineering structures were iden-</p><p>tified in consultation with design professionals and end-</p><p>users, state and federal officials; and (e) draft</p><p>specifications and commentaries were developed at 30,</p><p>60 and 90% completion targets for review.</p></li><li><p>7/29/2019 018 civil engineering structures</p><p> 2/33</p><p>406 L.C. Bank et al. / Construction and Building Materials 17 (2003) 405437</p><p>From a detailed review of codes and specificationsfor composite materials a number of key sources wereidentified as a basis for the development of the modelFRP material specification for civil engineering appli-cations. These documents, detailed below, provide pro-cedures for material characterization, methods for</p><p>prediction of long-term properties and performance, andacceptance criteria. The American National Standard forLadders w1x, the specification for reinforced plasticladders, provides detailed procedures for testing andminimum properties for acceptance of FRP materials foruse in ladders. Tests for physical properties (e.g. density,maximum water absorption and cure) and mechanicalproperties subjected to dry, wet, elevated temperatureand weathered conditions are stipulated. The Internation-al Conference of Building Officials (ICBO) AcceptanceCriteria AC-125 w2x specifies selected physical andmechanical properties to be measured and reported for</p><p>composite materials used for repair and retrofit ofconcrete structures. While no minimum properties arespecified for use, limits on minimum property retentionvalues following conditioning for 1000 and 3000 h arestipulated. The US Department of Defense MilitaryHandbook 17 w3x provides procedures for obtainingproperties for design for FRP composites for aerospaceapplications, as well as property data for specific com-posite material systems. Finally, specifications of theAmerican Society of Testing and Materials (ASTM)related to fiberglass tanks, pipes and poles (e.g. ASTMD2997, D3754, D4021 and D4923) provide guidanceon test methods, acceptance criteria and methods for</p><p>prediction of long-term properties of FRP compositesw4x.</p><p>Key sections of the specification are discussed in thetext that follows. The order of the discussion followsthat of the specification, which is organized and pre-sented in the generally-accepted format provided byASTM w5x: scope, classification, materials, manufactur-ing, qualification testing, acceptance testing, reportingand quality assurance. Sections on terminology, orderinginformation, keywords and product marking are con-tained in the specification but are not discussed in thearticle. References to tables, figures and text sections</p><p>that are numbered with the decimal point (e.g. Section9.5.2) refer to elements of the specification and not tothe article itself.</p><p>2. Scope</p><p>According to ASTM, a specification is an explicit setof requirements to be satisfied by a material, product orsystem. A material specification serves three main pur-poses: (1) to aid in the completion of purchasingagreements between materials suppliers and purchasers,so that all batches and lots of a material conform to therequirements; (2) to define standard classes and forms</p><p>of the material; and (3) to identify performance datathat must be disclosed as part of the material purchasew5x.</p><p>In addition, the FRP materials specification was devel-oped to apply to a wide range of FRP compositematerials for numerous different uses, while still ensur-</p><p>ing quality and promoting durability. The specificationfocuses on materials most likely to meet AASHTOsstated goals of providing a 75-year life in its structures.It was determined that the specification should, at aminimum: (1) classify FRP materials into groups sothat similar materials will be tested in an identicalmanner and will meet the same minimum performancerequirements; (2) require that material manufacturersprovide sufficient property data for structural designusing the FRP materials; (3) ensure that high qualityconstituent materials and well-controlled manufacturingprocesses are used to produce the FRP materials; (4)</p><p>provide long-term data on mechanical property retentionand a method for service life prediction; and (5) providequality assurance procedures so that agencies procuringthe material can verify that FRP materials meet thespecification.</p><p>FRP composite parts covered by the specification aremade of one or more qualified laminates. The quali-fying procedure includes a number of mechanical andphysical screening tests. In the specification itself andin this article, the term qualification implies a set oftests that are completed on trial laminates or on lami-nates cut from production parts. The qualification testsare Procedure A, which provides a wide range of test</p><p>data and screens for key properties, and Procedure B,which provides long-term property retention data on thematerial. The parts themselves are accepted if thetesting completed on coupons cut from production partsshows that the material properties are essentially equiv-alent to those of the qualified laminates. The testingregime for part acceptance is a small subset of the testsrequired for laminate qualification. The acceptance testsare Procedure C, which provides a comparison test toshow that the material being accepted is substantiallythe same as the qualified (Procedure A) material, andProcedure D, which requires that the material retain key</p><p>mechanical and physical properties in a hotwet envi-ronment. The step-by-step procedure for qualificationtesting and subsequent acceptance testing is describedin Fig. 1.</p><p>It is important to note that the materials specificationonly covers coupon-level properties. In some applica-tions a materials specification alone will be sufficient tospecify an FRP structural element. In many cases addi-tional element-level specifications that consider full-sectional mechanical behavior, bond and anchorageproperties, andyor connections may be necessary. Forcomplex FRP parts, full-section behavior will be evenmore difficult to predict from coupon data. The effect</p></li><li><p>7/29/2019 018 civil engineering structures</p><p> 3/33</p><p>407L.C. Bank et al. / Construction and Building Materials 17 (2003) 405437</p><p>Fig. 1. Flowchart of required qualification and acceptance testing.</p><p>of T and L junctions, thickened regions and ply dropssimply cannot be predicted at the coupon level. Further-more, with the exception of laminate thickness, thegeometric tolerances of the FRP part, such as straight-ness and twist, are not considered, as these cannot be</p><p>ascertained at a coupon scale. Finally, the materialsspecification requires that a wide range of mechanicalproperty data be collected and published, but it does notprovide design allowable stresses or strength-reductionfactors for design. These design specifications are stillbeing developed for FRP composites, and design speci-fications for FRP composite concrete reinforcements andfor FRP composite highway sign supports have recentlybeen published w6,7x.</p><p>3. Classification</p><p>Laminates supplied according to this specification areclassified according to fiber volume fraction, percentage</p><p>of fiber oriented in the longitudinal direction, fiber typeand resin type. The purpose of the classification systemis to provide broad categories of FRP materials, so thatminimum properties for each of the broad categoriescan be specified. The classification of materials takes</p><p>place on the laminate level. In the general case, it is notpossible to classify a complex FRP part itself, becausesuch a part could be constructed of multiple differentlaminates. Annex B2 of the specification presents suchan example. Therefore, each laminate within the part isclassified and tested.</p><p>A laminate is considered to be a relatively thin plate,which has two dimensions that are considerably largerthan the third (thickness) dimension. A laminated com-posite is generally envisioned as being made of discreetplies or laminae with identifiable fiber orientation andproperties in each ply. This draft specification does notdeal with composites on the ply level, and in fact</p></li><li><p>7/29/2019 018 civil engineering structures</p><p> 4/33</p><p>408 L.C. Bank et al. / Construction and Building Materials 17 (2003) 405437</p><p>anticipates that many of the composites that meet thespecification will not be laminated per se. In manyplates that are reinforced primarily with rovings or tows,no laminated structure is identifiable. However, sincethree-dimensional reinforcements are rarely used, thelaminated assumptions apply. A laminated structure is</p><p>much more evident in plates constructed with wovenrovings, non-woven fabrics or stitchmat, for example.According to this specification, small regular shapessuch as round rods, square bars and narrow strips canalso be considered to be laminates. Therefore, as it isused in this specification, a laminate is the basic buildingblock of a composite part.</p><p>The primary resin systems currently in use in struc-tural FRPs are included in the specification. The speci-fication does not include thermoplastic polymers orphenolics at this time, because these resin systems arenot in widespread use in structural applications, and</p><p>because the mechanical properties and durability of FRPcomposites made with these resins has not been providedin or demonstrated by documented laboratory researchand field application.</p><p>The specification allows for the use of glass andcarbon fibers. The sub-type of glass or carbon fiber isnot limited. Both E-glass and S-glass and both PAN-based and pitch-based carbon fibers are permitted.Aramid fibers are not included at this time due to thesmall number of aramid-fiber FRPs used in infrastructureapplications and due to the lack of laboratory and fielddata on these FRPs. Hybrid FRP composites using amixture of glass and carbon fibers are permitted as long</p><p>as the secondary fiber volume is less than 20%. Thisallows for the specification to use the same mechanicalproperty requirements for a given class of FRP and forhybrids based on that class. So, for example, the sameminimum property requirements hold for a carbon fibertype 1 laminate and any hybrid based on that class.</p><p>The primary indicator of mechanical performance inan FRP composite is the volume or weight fraction offiber reinforcement in the composite. It is the fiber inan FRP composite that primarily provides the desiredstrength and stiffness of the composite material. Thefiber content should, therefore, be as high as reasonably</p><p>possible within the FRP composite. This fiber contentcan be expressed as a volume fraction or as a weightfraction. In this specification, volume fractions for fibersare always used, because weight fractions cannot becompared when dealing with fibers of different densities(glass and carbon, for example). The specification usesthis primary characteristic of an FRP compositethevolume fraction of fiberas a means of classifying thecomposite. The theoretical limit of fibers in a unidirec-tional composite approaches 90% w8x. Practical limitsfor unidirectional composites are approximately 60%,with limits for composites with transverse reinforce-ments dropping to 50% and below depending on th...</p></li></ul>