ACHIEVING WORLDWIDE CODE ACCEPTANCE OF FRP MATERIALS THROUGH DURABILITY AND MATERIALS TESTING

Transcription

1 ACHIEVING WORLDWIDE CODE ACCEPTANCE OF FRP MATERIALS THROUGH DURABILITY AND MATERIALS TESTING Amber Wagner 1, Scott Arnold 2, & Elaine Meriwether 3 ABSTRACT: This paper will review the various durability and materials testing requirements that have been developed in order to validate the use of fiber-reinforced polymer (FRP) materials in civil infrastructure repair and retrofit. There are several acceptance criteria, which will be covered in more detail: International Code Council Acceptance Criteria 125 (ICC AC 125), Technical Report (TR) 55/ TR 57: Design Guidance for Strengthening Concrete Structures using Fibre Composite Materials, Canadian Standards Association (CSA) S806-12: Design and Construction of Building Components with Fibre-Reinforced Polymers, the Allgemeine Bauaufsichtliche Zulassung, and the New Zealand CodeMark Certificate of Conformity. The requirements presented in each of these documents have evolved over the years and will continue to change along with the codes and guidelines associated with them. KEYWORDS: FRP; durability testing; acceptance criteria; retrofit 1 INTRODUCTION In 1988, the use of advanced composite materials for infrastructure rehabilitation was initiated by the California Department of Transportation (Caltrans), as an alternative to steel jacketing for the seismic retrofit of bridge columns. Caltrans turned to an independent material testing facility, Aerospace Corporation, to assist in the development of the first prequalification test program, which focused on durability requirements of composite materials under various environmental conditions. After the Northridge earthquake in 1994, the International Code Council (ICC) Evaluation Service developed acceptance criteria for the use of systems to strengthen non-ductile reinforced concrete and masonry structures. This acceptance criteria (ICC AC125 [1]) has been adopted by numerous countries, including New Zealand [2] and Canada [3], as a preferred criteria to evaluate and approve various systems. Other industries (i.e. water and waste water transmission) have developed their own unique requirements for durability testing. While in the European Union (EU), most countries follow the Eurocode 2 [4], which is the European guideline/law for designing concrete structures. However, there are countries within the EU that have their own design and durability requirements. In the United Kingdom, the Concrete Society developed the design guides (TR55 [5] & TR57 [6]) for the design, acceptance, inspection, and monitoring of composite materials, while in Germany the Deutsches Institut für Bautechnik (DIBt) developed a recent general building approval program (Allgemeine Bauaufsichtliche Zulassung) that is similar to ICC, but requires more rigorous testing. The main objective of this paper will be to review several acceptance criteria in order to better understand the various durability and material testing requirements for FRP composite systems. 2 IN SUMMARY: THE ACCEPTANCE CRITERIAS In general, each acceptance criteria was developed to justify the use of FRP materials as an approved building material for construction purposes. Just as any building material needs to have certain standards for general use, the same was required of FRP materials. However, depending on the installation temperature, material substrate, the 1 Amber Wagner, Project Engineer, Fyfe Co., San Diego, CA. amber@fyfeco.com 2 Scott Arnold, Director of Engineering Services, Fyfe Co., San Diego, CA. scott@fyfeco.com 3 Elaine Meriwether, Project Engineer, Fyfe Co., San Diego, CA. elaine@fyfeco.com

2 purpose of the installation (i.e. pipe, building, bridge, see Figure 1 for examples), the location of the installation (i.e. in a seismic zone), and many other factors will all change the design requirements. Figure 1: Completed projects using FRP Technology on a variety of structural applications Some 25 years after the first tests conducted on bridge columns, the use of FRP systems on a variety of structural types continues to evolve. For instance, the use of FRP for underground pipe systems has been growing economically for some time. However, there are several different types of pipe systems, i.e. prestressed concrete cylinder or steel pipes. This has resulted in development of different design/acceptance criteria, which includes the American Water Works Association M45 Fiberglass Pipe Design, Manual of Water Supply Practices [7] and the American Society of Mechanical Engineers PCC-2 Article 4.1 Nonmetallic Composite Repair Systems for Pipelines and Pipework: High Risk Applications [8], just to name a couple. Unfortunately, due to the limited space of the paper only five acceptance criteria created by various countries around the world, and is by no means an exhaustive list, will be discussed. These criteria focus on the general design requirements for applications on general civil infrastructures, i.e. buildings or bridges. The main goal is to provide a comparative look at the different acceptance criteria, in order to better understand their individual approach to the design and installation of systems. 2.1 ICC ACCEPTANCE CRITERIA (AC) 125 In 1994, the International Code Council (ICC) was established as a non-profit organization in the United States by three main founding organizations: the Building Officials and Code Administrators International, Inc., the International Conference of Building Officials, and the Southern Building Code Congress International, Inc. For a number of years prior to the creation of the ICC, these code organizations saw the rising popularity of regional code development. However, they also realized the time had come to bring together these codes into a single set or body of codes. In order to make this possible, they first had to decide upon their vision, which (still remains to this day) is to protect the health, safety, and welfare of people by creating safe buildings and communities [1]. Then concurrently their primary objective became to develop a single body of International Codes (I- Codes), which is both comprehensive and coordinated. Their vision and primary objective was put into action by creating a plethora of Acceptance Criteria (AC) for different structural products, which are not part of the current international building codes. By completing all the necessary testing, a manufacturer could obtain approval through the ICC and be issued an Evaluation Service Report (ESR) number. This number ultimately says the structural system complies with the minimum requirements and can now be justified as an approved building material per the current building code. Now specifically looking at systems, the ICC AC document is entitled Acceptance Criteria for Concrete and Reinforced and Unreinforced Masonry Strengthening Using Externally Bonded Fiber-Reinforced Polymer (FRP) Composite Systems, dated June 2012 [1]. By receiving an ESR, the system meets the minimum requirements established in the acceptance criteria and thus complies with the current International Building Code (IBC) and the Uniform Building Code (UBC). In the end, the purpose for the development of this acceptance criterion was to serve as a guideline to evaluate alternatives to the current structural rehabilitation systems for concrete and masonry structures. Currently, both the IBC and UBC do not provide adequate testing requirements to determine the structural capacity, reliability, and serviceability for systems. The need for minimum requirements was ultimately

3 established by the ICC and now systems can be used to strengthen structural elements within the civil infrastructure. However, the acceptance criterion does have its limitations. The only approvable systems are passive systems used to strengthen concrete and masonry structural elements. Also, there are limited properties evaluated, i.e. the flexure and shear capacities; performance under environmental exposures and exposure to fire conditions; and structural design procedures. However, it is important to note, even with the limitations mentioned above, there is still a significant amount of testing required for approval, approximately 8 full-scale structural tests and 11 composite qualification tests [1]. 2.2 TECHNICAL REPORT (TR) 55/ TR 57 By 2000, the Concrete Society (based out of the United Kingdom) saw a need to develop a design guideline for FRP strengthening. A technical group was formed, consisting of members from both the industry and academia, who were commissioned to create a document, later called Technical Report 55: Design Guidance for Strengthening Concrete Structures using Fibre Composite Material (TR 55) [5]. However, there have been some concerns over the content in the TR 55. Even though there was extensive guidance on the design of the FRP composite systems for a variety of applications, including strengthening structural members for flexure, shear, and axial loading conditions, there was still no clear guidance on the required workmanship and long-term performance of the FRP system. By February 2003, this led to the publication of Technical Report 57: Strengthening Concrete Structures using Fibre Composite Materials: Acceptance, Inspection and Monitoring [6]. This new document was and is intended to be used in conjunction with the TR 55 and not as a stand-alone document, which is why the TR 55 does not include sections on inspection or maintenance. Then by 2011, later editions of the TR 55 were published to improve/update the current design procedures by incorporating state-of-the-art testing and analysis, which included techniques such as near-surface-mounted reinforcement and revisions to the shear strengthening sections [5]. There are also additional references to strengthening approaches for other structural types, such as masonry and metallic structures. There had also been a growing consensus that the TR 55 should become more aligned with the Eurocodes. With this inclusion, the document now reaches a broader audience (i.e. engineers in other countries) and with the hope of increasing the uses of systems in other European countries. Currently, the TR 55 has become the industry standard on FRP strengthening in the United Kingdom and some European countries. 2.3 CANADIAN STANDARDS ASSOCIATION (CSA) S The Canadian Standards Association (CSA) is a private not-for-profit company that develops standard approved by the Standards Council of Canada. Since their establishment in 1919, the need for standards in Canada has continued to grow. By 2002, the first edition of the CSA S806-02: Design and Construction of Building Structures with Fibre-Reinforced Polymers [3] was published to directly address the requirements for the design and evaluation of systems to reinforce building components per the National Building Code of Canada. This standard primarily covers three types of systems: aramid, carbon and glass, and can be broken down into two major sections. The first section covers the general design requirements, including: Limit state design; Mechanical properties of FRP components and the reinforcing substrates; Design of both wet lay-up, near-surface mounted and pre-stressed FRP systems on concrete substrates; Design of fiber-reinforced concrete composite cladding; Added provisions for seismic design; And construction techniques and requirements. The second section includes a vast number of appendices (19 to be exact), which give specific guidelines on a variety of quality control testing procedures. Some of the testing procedures include criteria to determine the cross-sectional area and tensile properties, and the bond-to-concrete strength of the system. In addition,

4 there are other criteria for specific cases such as a test method for FRP bent bars and stirrups and a test method for tensile fatigue of FRP rods. In general, the latest second edition CSA S covers the widest range of FRP topics compared to the other codes/criteria presented in this paper [3]. The CSA group has spent a considerable amount of time and energy to develop this standard, which not only focuses on the basic uses of systems, but also on the specialty cases that are not frequently used by structural engineers. 2.4 ALLGEMEINE BAUAUFSICHTLICHE ZULASSUNG (ABZ) The Allgemeine Bauaufsichtliche Zulassung (abz), or translated into english means General Building Approval, was developed by the German Institute for Building Technology (DIBt) to provide manufacturing companies the opportunity to obtain non-regulated construction product building code approval. However, this approval is usually only granted for two to five years, at which point the company must request an expiry extension if they want to continue installing their building material in Germany. The DIBt also provides European Technical Approval for companies wanting to not only receive German approval, but also approval throughout Europe. Typically, the extent of testing, validation and many other requirements is quite extensive, which means the cost to receive approval could be high (ranging between 500 to 30,000 euros, excluding the cost of product testing). In the end, a committee of experts will review your data and determine if abz approval notification can be granted. For FRP systems in particular, there are several different tests that need to be performed and the results certified by an approved laboratory. Once all the testing is completed the approval notification will include several items: Description of the system; Scope of the intended application; Specification of the system, i.e. material properties, manufacturing, packaging, labelling, compliance/conformity declaration; Design and dimensions; Quality control procedures for installation; And finally, quality assurance procedures for care and maintenance. It is widely known, that the regulations and restrictions in Germany are far more stringent than any other country in the European Union. This implies that if a manufacturer spends the time and money to obtain German approval, then it can be assumed that most European nations will not require any additional approvals for the building material to be installed in their country. 2.5 CODEMARK CERTIFICATE OF CONFORMITY (CM) In 2010, New Zealand s Ministry of Business, Innovation, and Employment and the Austrailian Building Codes Board decided to create a joint certification program called CodeMark (CM) Certificate of Conformity [2]. As with the other criteria mentioned above, the CodeMark was designed to improve building quality and performance. Thus allowing non-building code approved materials find acceptance through this program and comply with the current building codes of Australia and New Zealand. As of today, the certification is still a voluntary program, but there are significant benefits if one chooses to apply for certification. Primarily, the CodeMark certification provides confidence and certainty to governing authorities and the building market. Specifically looking at FRP Systems, New Zealand and Australia have adopted the ICC AC125 criteria as part of the CodeMark certification requirements. Furthermore, a third-party inspection agency verifies the testing and manufacturing of the FRP composite system meets the New Zealand Building Code and the requirements per the ICC AC125. The third-party inspector will also be responsible for evaluating the system as part of a required annual audit, which keeps all certificates valid and current. 3 COMPARISON OF THE ACCEPTANCE CRITERIA Now that a variety of acceptance criteria have been described in detail, it is important to identify the different qualification testing, composite testing, quality control/assurance requirements and design guidelines required to meet each. Given there is overlap and differences between them, a description of the testing requirements will be provided. Then after all the tests have been described, Table 1 is presented to compare the

5 similarities and differences of each criterion or design guidelines in order to better understand their respective requirements. 3.1 QUALIFICATION TEST PLAN Typically, qualification tests over the years have been used to verify the design assumptions used by structural engineers for any structural system used, i.e. reinforced concretee or steel. For systems in particular, the ICC AC 125 and the New Zealand/Australia CodeMark Certification programs require this type of testing, see Figure 2 for examples of full scale testing set-ups. information is given and meets the required design assumptions, then the test can obtain the passing approval required COMPOSITE TESTING Now the term composite testing refers to a plethora of different tests. However it is important to note, that each criteria requires some similar but sometimes different tests. For the purposes of this section, only some of the more popular testing procedures willl be covered Physical and Mechanical Properties The most common tests, and is required by all, are ones which determine the physical and mechanical properties. Some of these properties include the Young s modulus, Poisson s ratio, in-plane shear modulus, coefficient of thermal expansion, and the glass transitionn temperature. For instance, Figure 3 shows a flat specimen going to be tested in tension. Once the specimen is cut to the correct size, it will be mounted by grips within a self-aligning testing machine. A constant load is then applied to the specimen until failure. Based on the load- deformation curve obtained, the Young s modulus for the system can be obtained. Even though there are other testing methods available, this still remains the most common testing procedure to determine the system s design properties, which are vital for any future design scenarios [3]. Figure 2: Examples of Large-Scale FRP System Testing Within both criteria, they specify 8 full-scale tests to be completed with a detailed description for each test set-up. These testss include: For columns - flexure and shear tests; Beam to column joints; For beams flexure and shear tests; For walls out-of-plane and in-plane shear testing; Wall to floor joints; And for slabs flexural testing. For each of the tests presented above, there is necessary results data, which includes, 1) providing the material property data of the system, 2) the final orce/deformation limit states, and 3) the ultimate failure modes [1]. Once this Exteriorr Exposure In general, FRP composite systems will be installed either inside or outside of a building. This test will focus on the systems exposed to exteriorr surfaces. This means the system will need to withstand any pertinent weather conditions; here exposure to moisture is the testing parameter. Testing per the ICC AC 125 requires five specimens to be subjected to two cycles: first being exposed to the light and then being exposed to both the light and a water spray within a weatherometer chamber. The duration of the test should be at least 2,,000 hours. At the end of the required number of cycles, a tensile test is performed on each specimen. In order to pass, each specimen is required to retain 90 percent of its strength when compared to the control specimens [1].

6 of Ca(OH) 2, NaOH and KOH in deionized water [3]). Once the specimens have been in the solution for a given period of time (usually 1,000 hours), then each is tested to determine the percent retention compared to the control specimens, which is typically 90 percent Fire Resistance Construction Figure 3: Direct Tension Pull-Off Test Freezing and Thawing Now another exposure condition is if the FRP composite system is installed in an environment where the temperature will fluctuate between freezing and thawing. For this test method, the FRP composite system is required to cycle between the temperature fluctuations. Typically the criterion will require a minimum of 4 cycles. Then, as before, a tensile test is performed and a 90 percent retentionn compared to the control specimen is required to pass this test [1] Aging In order to determinee the design life of the FRP composite it is important to perform aging tests. However, there has been increasing debate over the method of compliance. Currently, samples are immersed in water, saltwater, alkali and dry heat environments for three different time periods, i.e. 1,000; 3,000; and 10,000 hours. After each time period is complete, then tensile tests are performed on both the control and aged specimens. Depending on the duration in each environment the required percent retention will vary. There has been growing concerns with this method because from the test results it is hard to justify a 50-year design life. Furthermore, there have been discussions to possibly change the abovementioned method to one that uses the Arrhenius relationship, which will be describedd in more detail in a later section Alkali Resistance For alkali resistance testing, a number of specimens are immersed in an alkaline solution (combination Generally the design of the system involves situations where a certain level of fire resistance is required by the complete structural system, i.e. strengthening for gravity loads. Each building code has their own set of fire resistance requirements, such as fire resistance rating, flame- or spread rating, smoke development classifications non-combustibility requirements. In most cases, the system itself cannot meet the fire resistance requirements, in which case the manufacturer is now required to develop systems (which will be applied over the system) that can meet the code specifications. In the United States, for instance, the ICC AC 125 requires the complete system (including any additional assemblies) to be evaluated per Section 703 of the IBC or UBC. Ultimately, this willl require additional testing and a certification from the Underwriters Laboratories (UL) [1]. A similar requirement is seen in the CSA code, where each system must meet the requirements set forth in the National Building Code of Canada, which includes a fire endurance test described in more detail in the UL Canada S101 [3] Interiorr Finish The testing of the system as an interior finish is only seen in the ICC AC 125 criterion. In order for the system to have an interior finish classification, is determined according to Section 803 of the IBC and Section 802 of the UBC [1] Fuel Resistance As with the interior finish requirement, the fuel resistance requirement is also only mentioned in the ICC AC 125. Each specimen is to be tested according to American Standards Testing Method (ASTM) C 581, where they are exposed to diesel fuel for at least 4 hours [1]. Then each specimen is ested to determine the percent retention of its tensile strength, tensile modulus, elongation, glass transition temperature, and interlaminar shear

7 strength and must be above a certain threshold to pass the test Adhesive Lap Strength Typically, determining the adhesivee lap strength is only required for prefabricated systems; see Figure 4 for the test set-up. When prefabricated systems are created, the length is usually limited based on the facility manufacturing the system. This results in overlap splices during field installations. The adhesive lap strength test determines the splice tensile properties for both the unidirectional and bidirectional FRP materials, see Figure 4. These results will, in short, determine the appropriate overlap length required during installation. Figure 5: Direct Tension Pull-Off Test Drinking Water Exposure The final composite test that will be mentioned is the drinking water exposure test, which looks at the effects of drinking water on the system. As with the fuel resistance and the interior finish tests, this one is also only required by the ICC AC 125. In the end, each system is evaluated based on a testing procedure specified in accordance with NSF 61 [1] QUALITY CONTROL/ASSURANCE Figure 4: Overlap Tension Specimen Bond Durability The purpose of the bond durability test is to determine the bond strength between the FRP composite system and the applied substrate, in order to ascertain if it meets the design requirements. Normally, this test is conducted in the field using a portable pull-off test machine, which is bonded to the FRP substrate similar to Figure 5..Once everything has fully cured, then the test apparatus is attached and aligned so that the tension force is applied perpendicular to the surface. Then a constant load is applied to the fixture until it detaches from the surface, where the final value is recorded. Typicallyy the minimum required values are 200 psi for concrete and 1.5 x (f m) 0.5 for masonry, where f m is the compressive strength of the masonry. When examining the quality control/assurance of a system, it is important to look at three different areas: the manufacturing, installation, and long-term inspection. Within all the criteria, there is a specific section which mentions how the material is created, i.e. manufactured. Typically, documentation is required to assure the materials are being manufactured to the standards set forth in the different criteria. In addition, some of the criteria require extra inspections be performed by independent agencies in order to monitor the production facilities. While the installation of the system is typically required to be completed by trained and approved applicators. Considering the FRP composite system is a specialty system, it is important to have trained professionals applying the material. In addition, each manufacturer is usually required to develop an installation procedural and applicator training manuals that will then be used by the applicators. Furthermore, a majority of the criteria also require the presence of a special inspector during the installation of the system. This inspector is required to provide a report showing compliance of the FRP composite system to the installation manual created by the manufacturer.

8 Finally, there has been some mention to include long-term inspections on the installed systems to further advance the quality control/assurance requirements. However, this is currently only a part of the TR 55 [5]. 3.4 DESIGN GUIDELINES Design guidelines are essential to determine the allowable strength of the system. Depending on the type of application will usually determine which design equations are required. Each criteria mentioned in section 2, has specific design equations presented within their documents and for the purposes of this paper each design guideline will not be mentioned in further detail. Table 1: Comparison of Acceptance Criteria/Codes Qualification Tests Composite Tests 1. Physical and Mechanical Properties 2. Exterior Exp. 3. Freezing and Thawing 4. Aging 5. Alkali Soil Resistance 6. Fire-Resistant Construction 7. Interior Finish 8. Fuel Resistance 9. Adhesive Lap Strength 10. Bond Durability 11. Drinking Water Exp. Quality Control 1. Manufacturing 2. Installation 3. Long-term Inspection Design Guidelines AC 125 TRs CSA S806 abz CM 3.5 FUTURE ADVANCEMENTS IN CODE/CRITERIA DEVELOPMENT Even with years of development, each code/criteria still has areas to which it can improve upon. One of those areas is the understanding of the long-term properties for each of the systems. Many engineers and owners ask similar questions such as: How long will it last? What is average lifespan of the material? Can you assume a 50-year design life? However, not one of the codes/criteria specifically answers any of these questions. They will have sections that include accelerated testing, but the results read more like a pass or fail and don t provide the answers people are truly searching for. In recent years, there has been a push by manufacturer s to explore these questions. Not only to answer the questions above, but to better understand the durability of the materials they are selling. One such way to determine this is through the Arrhenius relationship, which is defined as a chemical process that is accelerated and then presented as an exponential function of temperature [9]. In short, the systems can be conditioned and tested at a variety of different temperatures (at least 4 based on the glass transition temperature), and through the resulting mechanical behavior, i.e. the time rate of degradation at an average service temperature, can be predicted. Ultimately, the mechanical tests are performed both in tension and in short beam shear after roughly 28, 56, 112, and 224 days of conditioning in deionized water. With these results the Arrhenius relationship can be concluded and the long-term properties can be determined. As with each type of prediction model, there are several advantages and disadvantages to using the Arrhenius model to determine the long-term properties. Some advantages include: The long-term properties can be determined without having to wait 50 years; Purchasers and manufacturers are able to identify reliable materials with the most profitable long-term properties; Purchasers can select the most resilient material based on a variety of options; And finally, FRP design committees will now be able to derive the most efficient safety factors depending on how the material changes as a function of time. While the disadvantages are: The property retentions need to be reasonably linear to apply the Arrhenius relationship. The lack of linearity doesn t

9 mean the material is of poor quality, just means this relationship can t be applied; The conditioning of the material at elevated temperatures, i.e. near the glass transition temperature, is deemed too high and will skew the results; And the system must be conditioned in an aqueous environment and not dry, in order to see any noticeable change in the properties. Furthermore, the only other major crossroad is the lack of long-term data. Ultimately, once this information becomes more readily available, then the use of the Arrhenius relationship can be justified and possibly used in later revisions of the acceptance criteria mentioned in section 2. 4 CONCLUSIONS Throughout the past 30 years, there have been a variety of different criteria developed, which are all aimed at a specific purpose: to justify the use of systems as a building material. Nevertheless, to fulfill this purpose requires several factors to be investigated. With each criterion mentioned, it was important to understand the purpose and location of the installation. Through a discussion of each, it became clear that each country, i.e. United States, United Kingdom, Canada, Germany, and New Zealand, has their own building qualifications and there was no way that one criterion could ever cover all the necessary aspects. [1] ICC Evaluation Service: Acceptance Criteria for Concrete and Reinforced and Unreinforced Masonry Strengthening using Externally Bonded Fiber-Reinforced Polymer (FRP) Composite Systems: AC 125. June [2] CodeMark: Certificate of Conformity: Tyfo Fibrwrap System. October 5, [3] Canadian Standards Association: S Design and Construction of Building Structures with Fibre-Reinforced Polymers. March [4] Eurocode: Design of Concrete Structures General Rules and Rules for Buildings, December [5] The Concrete Society: Design Guidance for Strengthening Concrete Structures using Fibre Composite Materials Technical Report (TR) 55, October [6] The Concrete Society: Strengthening Concrete Structures using Fibre Composite Materials: Acceptance, Inspection and Monitoring Technical Report (TR) 57, February [7] American Water Works Association: M45: Fiberglass Pipe Design, Manual of Water Supply Practices [8] American Society of Mechanical Engineers: PCC-2: Part 4- Nonmetallic and Bonded Repairs; Article 4.1: Nonmetallic Composite Repair Systems for Pipelines and Pipework: High-Risk Applications [9] L.C. Bank et. al.: A model specification for s for civil engineering structures. Construction and Building Materials, 17: , However, considering their purpose there is overlap in regards to the durability and material testing between the countries. This includes the requirements on the material properties testing and the emphasis on quality control, i.e. the installation and manufacturing of the system. However, there is still some research to be done on the design life of the systems. Nevertheless, through the extensive testing requirements encompassed in each criterion has provided engineers with the confidence to design and install systems; knowing they are approved not only by councils or committees, but also the associated building code. REFERENCES