ISIS EC Module 6 - Notes (Student)

ISIS Educational Module 6:

Application and Handling of FRP Reinforcements for Concrete Prepared by ISIS Canada A Canadian Network of Centres of Excellence www.isiscanada.com Principal Contributor: L.A. Bisby, Ph.D., P.Eng. Department of Civil Engineering, Queens University Contributor: Garth Fallis, P.Eng. March 2006 ISIS Education Committee: N. Banthia, University of British Columbia L. Bisby, Queens University R. Cheng, University of Alberta R. El-Hacha, University of Calgary G. Fallis, Vector Construction Group R. Hutchinson, Red River College A. Mufti, University of Manitoba K.W. Neale, Universit de Sherbrooke J. Newhook, Dalhousie University K. Soudki, University of Waterloo L. Wegner, University of Saskatchewan

ISIS Canada Educational Module No. 6: Application and Handling of FRP Reinforcements for Concrete

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Objectives of This Module The overall objective of this module is to provide engineering and technical college students with an overall awareness of the significant issues to keep in mind when applying fibre reinforced polymer (FRP) materials in applications involving reinforcement or strengthening of concrete structures. The module is targeted toward the user sector, and covers information specific to the handling, storage, and application of FRP reinforcing and strengthening systems for concrete. It is one of a series of educational modules on innovative FRP and structural health monitoring (SHM) technologies that are available from ISIS Canada. Further information on the use of FRPs and SHM in a variety of innovative applications can be obtained by visiting the Educational Modules link at www.isiscanada.com.

The primary objectives of this module can be summarized as follows: 1. to provide engineering and technical college students

with a general awareness of significant issues in the application and handling of FRPs in reinforcement or

strengthening applications with reinforced concrete structures;

2. to facilitate the use of innovative and sustainable building materials and systems in the construction industry; and

3. to provide guidance to students seeking additional information on this topic. Much of the material presented herein is not currently

part of a national or international code, but is based mainly on the results of ongoing research studies and FRP field applications conducted in Canada and around the world, as well as the experience of FRP manufacturers, suppliers, and applicators over the past 15 years. As such, this module should not be used as a design or implementation document, and it is intended for educational use only. Future engineers and practitioners who wish to specify or use FRP materials are encouraged to consult more complete documents (refer to Section 6 of this module).


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Additional ISIS Educational Modules Available from ISIS Canada (www.isiscanada.com) Module 1 Mechanics Examples Incorporating FRP Materials Nineteen worked mechanics of materials problems are presented which incorporate FRP materials. These examples could be used in lectures to demonstrate various mechanics concepts, or could be assigned for assignment or exam problems. This module seeks to expose first and second year undergraduates to FRP materials at the introductory level. Mechanics topics covered at the elementary level include: equilibrium, stress, strain and deformation, elasticity, plasticity, determinacy, thermal stress and strain, flexure and shear in beams, torsion, composite beams, and deflections. Module 2 Introduction to FRP Composites for Construction FRP materials are discussed in detail at the introductory level. This module seeks to expose undergraduate students to FRP materials such that they have a basic understanding of the components, manufacture, properties, mechanics, durability, and application of FRP materials in civil infrastructure applications. A suggested laboratory is included which outlines an experimental procedure for comparing the stress-strain responses of steel versus FRPs in tension, and a sample assignment is provided. Module 3 Introduction to FRP-Reinforced Concrete The use of FRP bars, rods, and tendons as internal tensile reinforcement for new concrete structures is presented and discussed in detail. Included are discussions of FRP materials relevant to these applications, flexural design guidelines, serviceability criteria, deformability, bar spacing, and various additional considerations. A number of case studies are also discussed. A series of worked example problems, a suggested assignment with solutions, and a suggested laboratory incorporating FRP-reinforced concrete beams are all included. Module 4 Introduction to FRP-Strengthening of Concrete Structures The use of externally-bonded FRP reinforcement for strengthening concrete structures is discussed in detail. FRP materials relevant to these applications are first presented, followed by detailed discussions of FRP-strengthening of concrete structures in flexure, shear, and axial compression. A series of worked examples are presented, case studies are outlined, and additional, more specialized, applications are introduced. A suggested assignment is provided with worked solutions, and a potential laboratory for strengthening concrete beams in flexure with externally-bonded FRP sheets is outlined.

Module 5 Introduction to Structural Health Monitoring The overall motivation behind, and the benefits, design, application, and use of, structural health monitoring (SHM) systems for infrastructure are presented and discussed at the introductory level. The motivation and goals of SHM are first presented and discussed, followed by descriptions of the various components, categories, and classifications of SHM systems. Typical SHM methodologies are outlined, innovative fibre optic sensor technology is briefly covered, and types of tests which can be carried out using SHM are explained. Finally, a series of SHM case studies is provided to demonstrate four field applications of SHM systems in Canada. Module 7 Introduction to Life Cycle Engineering & Costing for Innovative Infrastructure Life cycle costing (LCC) is a well-recognized means of guiding design, rehabilitation and on-going management decisions involving infrastructure systems. LCC can be employed to enable and encourage the use of fibre reinforced polymers (FRPs) and fibre optic sensor (FOS) technologies across a broad range of infrastructure applications and circumstances, even where the initial costs of innovations exceed those of conventional alternatives. The objective of this module is to provide undergraduate engineering students with a general awareness of the principles of LCC, particularly as it applies to the use of fibre reinforced polymers (FRPs) and structural health monitoring (SHM) in civil engineering applications. Module 8 Durability of FRP Composites for Construction Fibre reinforced polymers (FRPs), like all engineering materials, are potentially susceptible to a variety of environmental factors that may influence their long-term durability. It is thus important, when contemplating the use of FRP materials in a specific application, that allowance be made for potentially harmful environments and conditions. It is shown in this module that modern FRP materials are extremely durable and that they have tremendous promise in infrastructure applications. The objective of this module is to provide engineering students with an overall awareness and understanding of the various environmental factors that are currently considered significant with respect to the durability of fibre reinforced polymer (FRP) materials in civil engineering applications.


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Section 1

Introduction and Background Modern societies rely on complex and sophisticated systems of infrastructure for economic health and prosperity. These infrastructure systems are comprised of the roads, bridges, tunnels, towers, sewers, and buildings that make up our urban landscapes. In recent years, our infrastructure systems, many components of which are nearing the end of their useful service lives, have been deteriorating at an increasing and alarming rate. This threatens our current high quality of life.

In an effort to slow and/or prevent ongoing infrastructure deterioration, engineers are looking for new materials that can be used to prolong and extend the service lives of existing structures, while also enabling the design and construction of durable new structures. Fibre reinforced polymers (FRPs), a relatively new class of non-corrosive, high-strength, and lightweight materials, have recently emerged as innovative but practical materials for a number of structural engineering applications.

FRP materials have demonstrated strong promise in several important applications. One of these involves the use of FRP reinforcing bars in lieu of steel reinforcing bars as internal reinforcement for concrete. The primary advantage of FRPs in this application is that they are non-corrosive, and are not susceptible to rusting in the same manner as steel. Corrosion of conventional steel reinforcement in concrete structures is a major factor contributing to infrastructure deterioration around the world. The use of FRP reinforcing bars for concrete (discussed in more detail in Section 2) has the potential to significantly improve the longevity of reinforced concrete structures.

Another promising application of FRP materials is in the strengthening and/or rehabilitation of existing deteriorated or under-strength reinforced concrete structures. In these applications, FRP plates, strips, sheets, or in some cases bars, are bonded to the exterior of reinforced concrete structures using high-strength adhesives. The FRP materials provide external tension or confining reinforcement for the existing concrete members, thus increasing their strength and preventing further deterioration. These applications are described in more detail in Section 2.

Additional information on the use of FRP materials in both of the aforementioned applications is available from various sources, many of which are listed in Section 6 of this module.

The reader is encouraged to review ISIS Educational Modules 3 and 4 for background information before continuing with the current document.

The focus in the present discussion is specifically on the handling and application of FRP materials for use with concrete. The goal is to provide an awareness and understanding of the significant issues associated with the use of these materials in typical construction projects. It is important to recognize that a number of different products, manufacturing techniques, component shapes, and end-use applications are available for FRP materials, and that this document cannot adequately discuss them all. More complete discussions of different FRP materials and applications are available from specific FRP manufacturers and suppliers (refer to Appendix A) and specialized texts (refer to Section 6).

WHAT ARE FRPs? FRPs are a subgroup of the class of materials referred to more generally as composites. Composites are defined as materials created by the combination of two or more materials, on a macroscopic scale, to form a new and useful material with enhanced properties that are superior to those of the individual constituents alone. More familiar composite materials include concrete (a mixture of cement paste, sand, and gravel), and wood (a natural combination of lignin and cellulose).

An FRP is a specific type of two-component composite material consisting of high strength fibres embedded in a polymer matrix. This is shown schematically in Figure 1-1.

Fig. 1-1. Schematic showing combination of fibres and matrix to form an FRP composite. Polymer Matrices The polymer matrix is the binder of the FRP and plays many important roles. These include: binding the fibres together; protecting the fibres from abrasion and environmental

degradation; separating and dispersing the fibres within the

composite;

Polymer (Resin)

Fibre Reinforcement


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transferring force between the individual fibres; and providing shape to the FRP component.

Various polymer matrix materials are currently used in FRP materials for concrete reinforcement or strengthening applications; however, one of two specific types is typically used depending on the intended end-use for the FRP component. A class of polymers called vinylesters is commonly used as matrices in the fabrication of FRP reinforcing bars for concrete, due to their superior durability characteristics when embedded in concrete. In external strengthening applications, polymers called epoxies have emerged as the preferred choice, due primarily to their very good adhesion characteristics. A more detailed discussion of polymer matrix types and properties is provided in ISIS Educational Module 2. Fibres The fibres provide the strength and stiffness of an FRP. Those used in most structural FRPs are continuous and are oriented in specified directions. FRPs are thus much stronger and stiffer in the direction(s) of the fibres and weaker in directions perpendicular to the fibres. Fibres are selected to have: high stiffness; high ultimate strength; low variation of properties between individual fibres;

and stability during handling. In structural engineering applications, fibres are also characterized by extremely small diameters yielding large length-to-diameter ratios. Many different types of fibres are available for use. In civil engineering applications, the three most commonly used fibre types are glass, carbon, and aramid. The suitability of the various fibres for specific applications depends on a number of factors, including the required strength, the stiffness, durability considerations, cost constraints, and the availability of component materials.

Glass fibres are the most inexpensive, and consequently the most commonly used fibres in structural engineering applications. They are often chosen for structural applications that are non-weight-critical (glass FRPs are heavier than carbon or aramid) and that can tolerate the larger deflections resulting from the comparatively low elastic modulus of glass fibres. Glass fibres are commonly used in the manufacture of FRP reinforcing bars and structural wraps. Carbon fibres are more expensive than glass fibres. Several grades, with varying strength and elastic modulus, are available. Carbon fibres are typically much stiffer, stronger, and lighter than glass fibres, and they are thus used

in weight and/or modulus-critical applications, such as prestressing tendons for concrete and structural FRP wraps for repair and strengthening of concrete structures. In addition, carbon fibres display outstanding resistance to thermal, chemical, and environmental effects. Aramid fibres, while popular in other parts of the world, are not extensively used in North America. Additional information on fibre types and properties is presented in ISIS Educational Module 2. FRPs Although the strength and stiffness of an FRP material or component are governed predominantly by the fibres, the overall properties also depend on the properties of the matrix, the fibre volume fraction (the volume of fibres per unit volume of matrix), the fibre cross-sectional area, the orientation of the fibres within the matrix, and the method of manufacturing. It is the interaction between the fibres and the matrix that gives FRPs their unique physical and mechanical characteristics. The orientation of the fibres within the matrix is a key consideration in the design and use of FRP materials. In the present discussion the focus is on unidirectional FRPs FRPs in which all of the fibres are aligned in a single direction. Figure 1-2 shows various FRP products currently used for reinforcement or rehabilitation of concrete structures. The reader is encouraged to consult ISIS Educational Modules 2, 3 and 4 for additional information on FRP properties and manufacturing methods.

Fig. 1-2. Assorted FRP products used for reinforcement or rehabilitation of concrete structures.


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Section 2

Applications of FRP Materials in Construction MOTIVATION: INFRASTRUCTURE DETERIORATION Existing infrastructure systems are falling into a state of disrepair, and this is threatening the high quality of life that we currently enjoy in North America. This deterioration, combined with shrinking government budgets and increased urbanization, is forcing the development and use of advanced materials and cost-effective solutions to repair, strengthen, and rebuild our infrastructure systems. FRP materials have emerged as important materials in several construction applications, particularly applications in conjunction with reinforced concrete, and they are now considered materials of choice in many cases. WHY USE FRPs? Rapid increases in the use of FRP materials for structural engineering applications have occurred over the past 15 to 20 years. This can be attributed, in part, to continuing reductions in material costs and to the numerous advantages of FRPs as compared with conventional structural materials. Some of the more commonly cited advantages of FRP materials over more conventional materials such as steel include: resistance to electrochemical corrosion (rusting); high strength-to-weight ratios; outstanding durability in a variety of environments; ease and speed of installation, flexibility, and

application techniques; electromagnetic neutrality, which can be important in

certain special structures such as magnetic imaging facilities; and

the ability to tailor mechanical properties by appropriate choice and direction of fibres.

These advantages have resulted in the widespread use of FRP materials in numerous construction applications, including: FRP bars, rods, and tendons for internal or external

reinforcement or prestressing of reinforced concrete structures;

FRP plates, sheets, strips, bars and wraps for externally-bonded strengthening and rehabilitation of reinforced concrete, steel, timber, and masonry structures;

FRP structural sections and panels for all-FRP structures; and

FRP shapes, sections, and tubes for use in novel hybrid structures.

In the current discussion, the focus is on specific applications related to the first two bullets listed above, namely reinforcement and strengthening of concrete. It is important to recognize that FRP materials also have a number of potential disadvantages with respect to their use as structural materials in construction applications. Foremost among these disadvantages is the high initial material cost of many FRPs, which can be several times that of steel. When the cost of a structure is considered over its entire life cycle, however, the improved durability offered by FRP materials often makes them the most cost-effective choice. Furthermore, savings in installations costs and downtime can easily offset higher initial costs in time-critical construction projects (particularly in strengthening and rehabilitation projects). Other potential disadvantages include uncertainties associated with the long-term durability of FRP materials, the poor performance of most FRPs at high temperature, and the overall lack of awareness of FRPs in the construction industry. These concerns are all currently being addressed within the FRP community.

INTERNAL FRP REINFORCEMENT FOR CONCRETE STRUCTURES Because FRP materials do not corrode electrochemically, FRP bars, rods, and tendons are increasingly being used in lieu of conventional reinforcing steel for internal reinforcement of concrete. Figure 2-1 shows typical FRP bars that are currently available in North America.

Fig. 2-1. Assorted carbon and glass FRP reinforcing bars for reinforcement of concrete.


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Concrete reinforcement applications for which these materials are particularly suited include: prestressed and reinforced concrete beams exposed

to deicing salts, including bridge decks, barrier walls, approach slabs, parking garages, railroad crossings, and salt storage facilities;

prestressed and reinforced concrete beams in marine environments, including seawalls, buildings and structures near waterfronts, aquaculture operations, harbours, wharfs, artificial reefs, offshore structures, and floating marine docks;

concrete portions of various tunneling and mining structures;

externally and internally-restrained deck slabs; and glass FRP bars may be used in any concrete structure

requiring non-ferrous reinforcement due to electromagnetic considerations, including magnetic resonance imaging facilities and high-voltage applications.

Both glass and carbon FRP bars and reinforcing grids

have been used successfully as internal reinforcement in concrete beams and slabs, as have various hybrid two and three-dimensional FRP grids composed of both glass and carbon fibres. Research and field applications using FRP bars in concrete bridge decks have indicated that these materials perform well in the harsh Canadian climate.

The major design issues requiring consideration in the design of FRP-reinforced concrete members include the fact that FRPs are linear-elastic to failure, unlike steel which exhibits a well-defined yield plateau, and the fact that FRP reinforcements generally have elastic moduli that are less than steel. Thus, serviceability (cracking and deflection) requirements often govern the design of FRP reinforced concrete. Figure 2-2 shows glass FRP reinforcement being installed in a concrete bridge deck in Quebec (shown just prior to placement of the concrete). A detailed discussion of design methodologies for reinforcing concrete with FRP bars is beyond the scope of this document. The reader is encouraged to consult ISIS Educational Module 3 for additional information in this area.

FRP Reinforcing Bar Properties Unidirectional FRP materials currently used in concrete reinforcing applications are linear elastic to failure. This behaviour is shown in Fig. 2-3, which demonstrates the significant differences in the tensile behaviour of FRPs as compared with steel. FRP materials commonly have much higher strengths than reinforcing steel but have strains at failure that are considerably less. The differences in behaviour between various FRPs and steel have important consequences for the design of FRP-reinforced concrete members, as discussed in detail in ISIS Educational Modules 3 and 4.

The specific properties of FRP materials vary a great deal from product to product. It is beyond the scope of this module to discuss properties of available FRP reinforcing materials in detail. However, Table 2-1 and Fig. 2-3 give material properties for a number of available FRP reinforcing products for concrete. It is extremely important in the design of FRP-reinforced concrete members that the Engineer specifies which FRP product is to be used and what minimum properties are required.

Fig. 2-2. Glass FRP reinforcing bars placed in bridge deck forms before placing the concrete (courtesy Vector Construction Group).

Strain [%]

0 1 2 3

Stre

ss [M

Pa]

0

500

1000

1500

2000

2500SteelISOROD CFRPISOROD GFRPNEFMAC GFRPNEFMAC CFRPNEFMAC AFRPLeadlineTM CFRP

Fig. 2-3. Stress-strain plots for various reinforcing materials. EXTERNALLY-BONDED FRP REINFORCEMENT FOR CONCRETE During the 1990s, a number of preservation, rehabilitation, and strengthening techniques that use FRP materials have been applied to a variety of concrete, steel, aluminum, masonry and timber structures. In the current discussion, the focus is placed on strengthening of concrete structures using externally-bonded FRP plates and sheets, which remains the most common application of these materials for strengthening concrete structures.


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Table 2-1. Selected Properties of Typical Currently Available FRP Reinforcing Products

Reinforcement Type Designation Diameter [mm] Area [mm2]

Tensile Strength [MPa]

Elastic Modulus [GPa]

Deformed Steel #10 11.3 100 400* 200 Aslan 100 GFRP Bar #3 9.5 84 760 41 Aslan 200 CFRP Bar #3 9.0 65 2068 124 V-ROD CFRP Rod #10 9.3 71 1596 111 V-ROD GFRP Rod 3/8 9.3 71 691 40 NEFMAC GFRP Grid G10 N/A 79 600 30 NEFMAC CFRP Grid C16 N/A 100 1200 100 NEFMAC AFRP Grid A16 N/A 92 1300 54 LEADLINETM CFRP Rod -- 12 113 2255 147

* specified yield strength

Typical Applications FRP materials are becoming increasingly popular for repair and strengthening of reinforced concrete structures, and they are now materials of choice for flexural, shear, and axial strengthening of reinforced concrete members. In these applications, FRP plates or sheets are bonded to the exterior of reinforced concrete members to provide tension or confining shear reinforcement which typically supplements reinforcement provided by existing internal reinforcing steel. Three specific applications are common, namely flexural, shear, and axial (confinement) strengthening. Flexural Strengthening FRP materials are bonded to the bottom and/or side faces of a concrete beam to provide tensile reinforcement and to increase the strength of the member in bending. The fibres are oriented along the longitudinal axis of the beam. Figures 2-4 and 2-5 provide schematic and actual applications of the use of externally-bonded FRPs in flexural strengthening applications

Fig. 2-4. Typical flexural strengthening of a reinforced concrete beam using externally-bonded FRP reinforcement. Shear Strengthening FRP materials are bonded to the side faces of a concrete beam (often in the form of U-shaped wraps) or continuously around a column to provide shear reinforcement which supplements the internal steel stirrups or ties. The fibres are typically oriented perpendicular to the longitudinal axis of the member. Figures 2-6 and 2-7 show the use of FRPs as externally-bonded shear reinforcement for concrete.

Fig. 2-5. Two-way flexural strengthening of a reinforced concrete slab using carbon FRP strips (courtesy Sika Corp.).

Fig. 2-6. Typical shear strengthening of a reinforced concrete beam using externally-bonded FRP reinforcement.

Fig. 2-7. Shear strengthening of a reinforced concrete bridge girder using carbon FRP sheets.

Elevation Section A-A

A

A

Elevation Section A-A

A

A

ISIS Canada Educational Module No. 6: Application and Handling of FRP Systems for Concrete

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Confining Reinforcement Concrete members are wrapped in the circumferential (hoop) direction with FRP sheets. Under compressive axial load, the column expands (dilates) laterally and the FRP sheets develop a tensile confining stress that places the concrete in a beneficial state of triaxial stress. This significantly increases the strength and deformation capacity of the concrete. The fibres are most commonly oriented perpendicular to the longitudinal axis of the member (refer to Figures 2-8 and 2-9).

Fig. 2-8. Typical axial strengthening of a circular reinforced concrete column using an externally-bonded FRP wrap.

Fig. 2-9. Axial strengthening of a reinforced concrete bridge column using carbon FRP sheets. For the purposes of external reinforcement of concrete, there are essentially two classes of FRP strengthening materials that are commonly used, namely plates and sheets. Plates are rigid FRP strips that are manufactured using a process called pultrusion (refer to ISIS EC Modules 2 or 3). The plates are bonded to the exterior of reinforced concrete structures using an epoxy adhesive. Sheet FRPs are supplied as flexible fabrics of raw (or pre-impregnated) fibres. The sheet FRP materials are applied by saturating the fibres with an epoxy resin and laying-up the sheets onto the concrete

surface. Figure 2-10 shows some currently available plate and sheet FRP materials for strengthening concrete structures.

Fig. 2-10. Assorted carbon and glass FRP reinforcing materials used as externally-bonded reinforcement for concrete members. Installation Techniques Although a variety of techniques can be used to apply external FRP reinforcement to reinforced concrete structures, the most widely used is referred to as lay-up, which can be performed in wet or dry configurations with either plate or sheet FRPs. In the wet lay-up technique, flexible sheets or fabrics of raw or pre-impregnated fibres are saturated with an epoxy adhesive resin and placed on the surface of the concrete. As a result, the resin acts both as the adhesive and as the FRP matrix. The dry lay-up technique involves the adhesion of pre-cured rigid FRP strips or plates (or dry fibre fabrics) to the surface of the concrete using an epoxy adhesive. The second technique is more akin to conventional rehabilitation techniques using steel plates, but does not offer the flexibility enjoyed by the wet lay-up procedure. Both procedures have been used with success in field applications.

The reader should note that most external FRP reinforcing applications are referred to as bond critical, which means that adequate bonding of the FRP to the

A A

Elevation

Section A-A


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concrete is paramount in ensuring that the FRP strengthening system will function as desired. Thus, the quality of the concrete surface prior to bonding the FRP reinforcement is very important. The need for adequate surface preparation, quality control, and adequate curing conditions for the adhesive, as discussed later in this document, cannot be overstated.

Properties Unidirectional FRP materials used in external strengthening applications are linear elastic up to failure. As is the case for FRP reinforcing bars discussed above, the specific properties of different FRP strengthening materials vary a great deal from one manufacturer to another. Table 2-2 and Fig. 2-11 give material properties for a number of typical currently available FRP strengthening materials. A more complete discussion of the use of FRPs for strengthening concrete structures, including other applications and important aspects of FRP materials for strengthening concrete, steel, timber, and masonry structures, is provided in ISIS Educational Module 4.

Strain [%]

0.0 0.5 1.0 1.5 2.0 2.5

Tens

ile S

tress

[MPa

]

0

1000

2000

3000

4000SteelTyfo SEH-51 MBrace CF 530 MBrace AK 60 Hex 103C CarboDur S CarboDur H Replark HM

Fig. 2-11. Stress-strain plots for various FRP strengthening systems

Table 2-2. Selected Properties of Typical Currently Available FRP Strengthening Systems*

FRP System Fibre Type Weight [g/cm2] Thickness

[mm] Tensile

Strength [MPa] Tensile Elastic Modulus [GPa]

Strain at Failure [%]

Fyfe Co. LLC [www.fyfeco.com] Tyfo SEH-51 Glass 930 1.3 575 26.1 2.2 Tyfo SCH-35 Carbon -- 0.89 991 78.6 1.3

Mitsubishi [www.mitsubishichemical.com] Replark 20 Carbon 200 0.11 3400 230 1.5 Replark 30 Carbon 300 0.17 3400 230 1.5 Replark MM Carbon -- 0.17 2900 390 0.7 Replark HM Carbon 200 0.14 1900 640 0.3

Sika [www.sikacanada.com] Hex 100G Glass 913 1.0 600 26.1 2.2 Hex 103C Carbon 618 1.0 960 73.1 1.3 CarboDur S Carbon 2240 1.2-1.4 2800 165 1.7 CarboDur M Carbon 2240 1.2 2400 210 1.2 CarboDur H Carbon 2240 1.2 1300 300 0.5

Watson Bowman Acme [www.wabocorp.com] MBrace EG 900 Glass 900 0.35 1517 72.4 2.1 MBrace CF 530 Carbon 300 0.17 3500 373 0.94 MBrace AK 60 Aramid 600 0.28 2000 120 1.6

* Additional information can be obtained from the specific FRP manufacturers


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Section 3

Handling and application of FRP Reinforcement for Concrete Structures GENERAL The use of FRP reinforcement for reinforced concrete (RC) structures is now relatively well accepted within the civil engineering community, and various codes and guidelines exist for use by engineers in designing and specifying these types of systems (refer to Section 6 of this module for more information on codes and guidelines for the use of FRP materials). Major differences in design requirements as compared with steel reinforcement are a result of the linear elastic behaviour of FRPs and the fact that their elastic moduli are typically less than that of steel. These differences can appropriately be accounted for in most situations. From a handling and application point of view, construction and installation practices required when using FRP reinforcing bars are similar to those used with conventional steel bars. In most cases, the lightweight properties of FRP bars actually make the placement of reinforcement in formwork less time consuming. The following sections very briefly outline some of the important issues that must be kept in mind when handling and installing FRP reinforcing bars. GRADES, SIZES, BAR IDENTIFICATION Unlike conventional reinforcing steel, which has a relatively long history of use in construction projects, FRP reinforcement for concrete is considered, by some, to be an emerging technology. However, certain specific grades and sizes of steel reinforcement have emerged as industry standards, such that any engineers can easily specify the grade and size of bars required for a particular application. Because FRP reinforcing bars are a newer technology, and since slight variations in the composition and manufacturing processes of these bars can lead to significant differences in physical and mechanical properties, the same degree of standardization does not yet exist for FRP reinforcing bars. However, all FRP bars for use as reinforcement for concrete are manufactured to meet certain performance requirements and they are typically graded and marked accordingly. Strength, Modulus & Durabilty Grades ISIS Canada (ISIS, 2006) recommends a grading system for FRP reinforcing bars for concrete which is based on fibre type, tensile strength and elastic modulus, and durability of the bars in concrete. Strength is gradad based on the ultimate tesnile strength of the bar (in MPa), as determined by testing

peroformed in accordance with appropriate standards (see ISIS, 2006). Modulus is graded accoring to the fibre type and based on three categories as desribed in Table 3-1. Table 3-1. Modulus Grades for FRP Bars (ISIS, 2006)

Minimum Tensile Modulus (GPa) Fibre Type

Grade III Grade II Grade I Carbon 80 110 140 Glass 35 40 50 Aramid 50 70 90 ISIS Canada durability grading depends on the physical and durability properties defined in ISIS Canadas Specifications for Product Certification of Fibre Reinforced Polymers (FRPs) as Internal Reinforcement in Concrete Structures (ISIS, 2006). Using these procedures, FRPs with high durability are classified as D1, and FRPs with moderate durability are classified as D2. FRPs made with vinylester and epoxy are classified as D1 or D2 based on ISIS requirements, and FRPs made with polyester matrix, which are known to have inferior durability characterisitics, are classified as D2.

The American Concrete Institute (ACI, 2003) recommends that FRP bars be graded (unfortunately using imperial units) according to both their ultimate tensile strength and their tensile modulus of elasticity. An FRP bar with a tensile strength of 60 ksi would be designated as F60 in the ACI system, whereas a bar with a strength of 3000 ksi would be F3000. Similarly, a bar with a tensile elastic modulus of 5.7 ksi would be graded as E5.7. This grading system is recommended but has not yet been codified. ISIS Canada is also currently developing a grading system through its Committee on Standardization. Surface Geometry Various surface geometries currently exist for FRP bars, including spiral braids, sand coatings, and surface ribs (refer to Figure 2-1). There is currently no standard classification for these treatments. Manufacturers should be consulted if questions regarding surface treatments arise. Bar Sizes Various bar sizes are available from specific FRP bar manufacturers. No standard bar sizes currently exist,


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although ACI (2003) recommends the use of a system wherein bar size designations correspond to their nominal diameter in increments of an eighth of an inch, similar to the current bar designation system for steel reinforcing bars used in the United States. Bar Identification While the various FRP bar manufacturers are not currently bound by any identification requirements for their products, both ISIS Canada (2006) and ACI (2003) have suggested the use of a designation systems that would provide necessary information to users of their products.

The ISIS Canada designation system is as follows:

Xa Eb Dc Where: X is A, C or G for aramid, carbon or glass fibres a is the tensile strength of the FRP (MPa) E is the modulus of elasticity b is the modulus grade of the FRP (Table 3-1) D stands for durability c is the durability designation (explained previously)

The ACI designation system includes information on: the bars producer; the type of fibre; the bar size (using the system currently used for

conventional steel reinforcing bars); and the strength and modulus grades (using the F# and E#.#

system noted above). For example, a half-inch diameter, 1000 ksi tensile strength, 4 ksi tensile elastic modulus, glass FRP bar manufactured by Acme FRP Co. (AFC) would be marked with the following identification:

AFC G#4 F1000 E4.0 HANDLING AND STORAGE As discussed previously, FRP reinforcing bars are comprised of high strength fibres (typically of carbon or glass) embedded in a polymer matrix (typically vinylester). Because the bars are unidirectional, their strength and stiffness in the fibre (longitudinal) direction are much greater than in the transverse (off-axis) direction. Thus, while inherently durable once embedded in concrete, FRP bars are susceptible to surface damage if abused during handling and installation. Deep scoring of the bars surface will reduce their durability and load-carrying capacity and must be avoided. Fibre reinforced polymer bars can thus be considered similar to epoxy-coated steel reinforcing bars caution is required during handling and application to ensure

that the surface coating is not damaged. Specific storage, handling, and installation guidelines vary somewhat from manufacturer to manufacturer, and it is important to check the manufacturers requirements for any specific FRP reinforcement which is being contemplated for use. The following are common storage and handling guidelines that should be observed in most cases. Table 3-2 provides a basic checklist of handling and storage issues for FRP reinforcing bars for concrete. Table 3-2. Checklist: Handling and Storage of FRP Bars

; Store bars in a clean environment Protect bars against: ; - UV radiation ; - High temperature ; - Damaging chemicals ; Lift bundles of bars with care ; Do not shear bars when cutting

SAFETY* Work gloves should be worn at all times * In addition to typical safety precautions and procedures

Gloves The fibres contained in FRP reinforcing bars can cause splinters, cuts, and skin irritation. FRP bars should be always be handled with heavy-duty work gloves. On-Site Storage FRP bars should be kept clean and free of oil, dust, chemicals, or other contaminants. They should not be stored directly on the ground, but should be placed on timber pallets to ensure cleanliness and easy handling. Access should be provided for easy inspection of materials. Ultra-Violet Radiation While FRP bars are highly corrosion resistant, most FRP polymer matrix materials are susceptible to slight degradation under prolonged exposure to ultra-violet (UV) radiation. All FRP reinforcing materials should thus be protected from exposure to UV radiation. When stored outdoors, FRP bars should be covered with opaque plastic or otherwise protected. High temperatures FRP materials are sensitive to degradation at high temperatures and should generally not be stored in elevated temperature environments.


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Moisture and Chemicals Protection of FRP bars from moisture is not needed. Certain specific chemicals can damage FRP bars, however, and chemical exposure should thus be avoided. Manufacturers should be consulted in this regard. Lifting and Hoisting FRP bars are lighter (about 75% lighter) and more flexible that conventional reinforcing steel, and can thus be hoisted and placed with much less effort (Figures 3-1 and 3-2). Hoisting should be performed with care until operators are familiar with the behaviour of these materials upon lifting. In some cases, spreader bars are needed to prevent excessive bending due to their low-stiffness.

Fig. 3-1. Large sections of preassembled reinforcing grids can be installed with ease (photo courtesy Vector Construction Group). Cutting FRP bars can easily be cut with high-speed diamond grinding discs or fine-blade saws. FRP bars should never be sheared as this typically causes matrix cracking and fibre damage. Appropriate safety measures should be taken when cutting FRP bars due to airborne fibre fragments. This includes the strict use safety glasses and dust masks. Sealing of the end of the bar is not typically required.

Fig. 3-2. Lightweight bundles of FRP bars are easily moved on site (photo courtesy Vector Construction Group).

PLACEMENT AND ASSEMBLY Placement and assembly of FRP reinforcing bar cages in formwork is performed in much the same manner as for steel reinforcement, and very little adjustment is typically required in the construction process. Manufacturers guidelines, which may differ somewhat, should be followed at all times when placing FRP reinforcement. Typical guidelines for the placement of FRP reinforcing bars are as follows. Table 3-3 provides a basic checklist of issues in placement and assembly of FRP reinforcing bars for concrete structures. Table 3-3. Checklist: Placement and Assembly of FRP Bars

; Oil, grease, dirt, removed from bars ; Bars placed as specified by Engineer ; Ties type as specified by Engineer ; Bar chair type as specified by Engineer ; No direct contact between CFRP and steel ; No mechanical bar splices (lap splices only) ; Reinforcement tied down to prevent floating ; Care taken during concrete vibrating ; Walking on bars allowed? (ask Site Engineer) ; Bends/hooks may not be fabricated on-site

SAFETY Work gloves and eye protection must be worn at all times* * In addition to typical safety precautions and procedures

Oil and Grease Oil or grease on the surface of the bars will adversely affect their bond strength to concrete and should be avoided. Oil or grease on the bars surface should be removed prior to placement by wiping or spraying with a manufacturer specified solvent. Bar Placement Unless otherwise specified by the engineer, FRP bars should be placed in accordance with tolerances set out in applicable guidelines for conventional reinforcing steel. Because FRP bars are considerably lighter than steel bars, care is needed to ensure that FRP bars are not displaced by concrete or construction workers during concrete placement operations. Care should also be taken to ensure that FRP bars are not unnecessarily abraded by dragging or rubbing against


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other bars, as this may degrade their bond properties and tensile strength. Figure 3-3 shows FRP bars being installed in a bridge deck using standard bar placement methods.

Fig. 3-3. Placement of glass FRP bars in a bridge deck (photo courtesy Vector Construction Group). Contact between Steel and FRP bars When electrically-conductive materials that have different electro-potentials come into contact with one another, a small electrical current is generated. This can lead to an undesirable phenomenon known as galvanic corrosion. Carbon fibres are highly electrically conductive and have electro-potentials that are significantly different than conventional steel reinforcement. It is therefore important that carbon fibres not come into direct contact with conventional reinforcing steel in a structure, and care should be taken to ensure that these materials are electrically isolated from one another. This is not a concern for glass or aramid FRP bars.

Fig. 3-4. Glass FRP bars tied with nylon zip-ties and glass FRP chairs to eliminate all corrosion (photo courtesy Vector Construction Group).

Ties and Bar Chairs Plastic, nylon, or other non-corrosive ties and bar chairs should be used in applications where it is desirable to completely eliminate corrosion from a structure (Figure 3-4). When carbon FRP reinforcement is used, plastic or nylon ties and chairs should be used in all cases to prevent galvanic corrosion. Glass bars may be tied using conventional steel ties if desired (Figure 3-5), although plastic ties or plastic-coated steel ties are preferred. The type of chairs and ties to be used should be clearly stated in the project specifications.

Fig. 3-5. Glass FRP bars tied with standard steel ties and using plastic chairs (photo courtesy Vector Construction Group). Splices Neither mechanically-connected nor welded splices are possible when using FRP reinforcement. Lapped bar splices should be used when continuity of reinforcement is required in a structure. Applicable design guidelines and manufacturer specifications should be consulted when designing splices. Glass FRP bars can be spliced to steel reinforcement, provided that mechanical splices are not used (which might damage the FRP bars). Carbon FRP bars should not be spliced to steel reinforcement because of the potential for galvanic corrosion. Reinforcement Cage Floating FRP reinforcement is light and must be adequately tied to formwork to prevent it from floating during concrete placing and vibrating operations (Figure 3-6). Vibrating Care must be taken when vibrating FRP reinforced concrete to ensure that the FRP reinforcement is not damaged (plastic protected vibrators should be used where possible).


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Fig. 3-6. Glass FRP bars tied down with plastic-coated steel ties (photo courtesy Vector Construction Group). Bends and Hooks Currently available FRP reinforcing bars are fabricated using thermosetting resin matrices and consequently cannot be bent on site. Bends and hooks, when required, must be produced by the bars manufacturer during the fabrication process. It is possible to obtain bends and hooks in virtually any geometry from current FRP bar manufacturers (Figure 3-7), although minimum bend radii are typically larger than for steel bars due to significant weakening of FRP bars around tight corners. Typical minimum allowable bend radii for FRP bars are 3.5 to 4 times the bars diameter, and these bends are accompanied by up to 50% reduction in the tensile strength of the bar at the bend.

Fig. 3-7. Bends in Glass FRP bars for concrete barrier wall reinforcement (photo courtesy Vector Construction Group). Walking on FRP Bars Some existing design codes and guidelines state that workers should not be permitted to walk on FRP bars prior to

placement of the concrete. This is only a precaution, however, which may not be necessary provided that the workers are aware of damage mechanisms for FRP reinforcing bars (Figure 3-8).

Fig. 3-8. A construction worker stands on glass FRP bars while tying them together (photo courtesy Vector Construction Group).

QUALITY CONTROL AND QUALITY ASSURANCE Quality control and quality assurance are critically-important at each step of the construction process, particularly when using materials with which there is historically less experience. Prior to construction, the Engineer and owner shall decide if the manufacturer specified properties of the FRP reinforcement are sufficient and acceptable or if independent tests are required. When required, tests should be conducted according to recommended procedures (ACI, 2004). Commonly available FRP bars are manufactured under strict conditions, and routine sampling, inspection, and quality control tests are conducted by all manufacturers. Some FRP bar manufacturers colour-code their production runs to allow for easy tracing of individual bars properties, and most bar manufacturers will provide certification of their materials upon request. Typical properties that are of interest to the Engineer may include:


15

dimensional tolerances; mechanical properties including tensile strength, tensile

elastic modulus, fatigue strength, and ultimate strain; bond strength in concrete; fibre volume fraction; hardness, die wicking properties, shear properties in

flexure and in direct shear; and durability in alkaline environments.

Prior to Construction It is important that all parties involved in a particular construction project are educated as to the specific handling and application requirements for a particular FRP reinforcing product, particularly with respect to new and/or unusual construction procedures and design innovations. All uncertainties should be resolved before construction begins. During Construction It is important that all interested parties work together to ensure the proper and adequate transport, storage, handling,

and placement of materials and assemblies. Regular inspections should be conducted by trained and certified engineers who are knowledgeable in the use of FRP materials (in addition to standard construction practices and tolerances). COMMON SAFETY PRECAUTIONS Because the use of FRP reinforcing bars is similar to the use of conventional steel reinforcement, few additional safety precautions are required beyond the common precautions that are typically observed when using conventional steel reinforcement. In most cases, the only additional precautions that are necessary are: heavy-duty work gloves should be worn at all times

when handling FRP bars; and dust masks and eye protection should be worn when

cutting FRP bars.


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Section 4

Handling and Application of FRPs for Strengthening Concrete Structures

GENERAL The effective use of externally-bonded FRPs for strengthening reinforced concrete structures, while derived from conventional steel-plate bonding technologies, is currently much less familiar than the use of FRP reinforcing bars to most engineers, inspectors, and construction workers. Installation of FRP strengthening systems for concrete structures thus requires that particular care be taken at all stages of the design and construction process. In most FRP strengthening applications, bond between the concrete and the FRP is a key factor in the success of the strengthening system; however, in many confinement applications only contact is required. Furthermore, unlike internal FRP reinforcement externally-bonded FRP systems represent somewhat of a departure from conventional building systems and strengthening methods. Handling and application of these systems is thus an extremely important topic that requires special training and certification.

HANDLING AND STORAGE Externally-bonded FRP systems are comprised of several distinct chemicals and components, including various primers, putties, and adhesives, as well as the fibre fabrics and epoxy saturants that eventually become the FRP material. It is extremely important that the various components not be mixed-up or otherwise contaminated during handling and storage, and manufacturers guidelines should be followed in all cases. The following are typical guidelines for the proper handling and storage of the various system components (refer also to the basic checklist provided in Table 4-1): All products should be delivered and stored in unopened

original containers which should be clearly and unambiguously marked. Materials should be inspected immediately upon delivery.

Stored fibre fabrics and epoxy components must be protected from moisture, dust, chemical exposure, and other potential contaminants or harmful compounds.

Epoxy components must be stored in a controlled environment, typically with a temperature of between 10C and 24C, and away from direct sunlight, flames, or other hazards. Many uncured epoxy components are flammable and environmentally hazardous, and appropriate care should be taken in their transport and storage.

Most epoxy component chemicals have finite shelf lives as specified by their manufacturers. Expired resin components may not meet required performance expectations and should not be used.

Fibre fabrics and precured FRP laminates should be handled with care to avoid damage.

Material Safety Data Sheets (MSDSs) should be retained for all materials received. Any individual who may come in contact with the materials should familiarize themselves with these MSDSs.

Table 4-1. Checklist: Handling and Storage of Externally-bonded FRP Systems

; All products delivered and stored in unopened original containers ; All materials inspected immediately upon delivery ; Stored materials protected from potential contaminants or harmful compounds ; Epoxy components stored in a controlled environment ; Fibre fabrics and precured FRP laminates handled with care to avoid damage ; Expired resin components not used

SAFETY*Take special care in transport of potentially harmful compounds (check Material Safety Data Sheets (MSDSs))

* In addition to typical safety precautions and procedures

INSTALLATION Because installation of FRP strengthening systems is a somewhat specialized operation, only trained and certified contractors should be used. Each of the system manufacturers has developed individual application procedures that may differ slightly in some cases. The following is a general outline of the steps in a typical externally-bonded FRP strengthening application on a reinforced concrete member. Manufacturer specifications should be followed when using any specific FRP strengthening system. Figure 4-1 shows a basic overall summary of the sequence of events in the application of a typical externally-bonded FRP strengthening system for concrete.


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Fig. 4-1. Overall sequence of events in the installation of a typical externally-bonded FRP strengthening system for concrete.

s Curing Conditions

The following factors must be carefully monitored and controlled during curing of the epoxy saturant/adhesive: Temperature Relative Humidity Mechanical disturbances

r Protective Coatings

Aesthetics, fireproofing, UV radiation, or otherwise protective coatings are often applied to installed FRP systems

n Concrete Preparation

Concrete substrate must be in a clean and sound condition Remove unsound concrete Repair corroding reinforcing steel Patch large voids Inject large cracks

o Surface Preparation

The surface must be prepared to receive the FRP system Level the concrete surface with epoxy putty Round sharp edges where required

p Adhesive mixing

Well mixed resin is critically important, and manufacturer recommendations should be followed

Bond Critical Functionality depends on bond between FRP and

concrete Surface must be profiled to a specific roughness

Contact Critical Functionality depends on contact between FRP

and Concrete Surface roughness is less critical

q FRP Installation

FRPs are bonded to the surface of the concrete

Pre-cured Laminate and Strip Systems

Rigid FRP plates or strips are bonded to the surface of the concrete with an epoxy adhesive

Fabric Systems Flexible fibre fabrics are bonded to the concrete using epoxy

adhesives/saturants

Wet Lay-up Systems Fabric is saturated before

lay-up operation

Dry Lay-up Systems Fabric is saturated during

lay-up operation


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n Concrete Preparation Because most FRP strengthening applications are bond-critical, it is of paramount importance that the concrete substrate is in a clean and sound condition prior to FRP installation. Improperly or poorly prepared substrate concrete can lead to debonding or delamination of the FRP systems. The following are important considerations in ensuring a sound bonding surface: Unsound areas of concrete such as broken or

delaminated regions must be removed to reveal sound material (Figure 4-2). Any low-strength materials such as plaster must be completely removed.

Fig. 4-2. Removal of severely damaged substrate concrete. Corroded reinforcing steel should be repaired according

to guidelines suggested by the International Concrete Repair Institute (ICRI, 2003). Some research suggests that FRP strengthening systems should not be used to cover corroding reinforcing steel, since the expansive forces that result from ongoing corrosion could potentially lead to damage of the FRP system. Other research has shown that this may not be a concern.

Large voids in the concrete must be patched using an appropriate repair mortar as specified by ICRI (1997, 2003).

Large cracks in the concrete surface should be pressure injected with epoxy (Figure 4-3), particularly if there is the potential for water leakage through these cracks.

Fig. 4-3. Crack injection using epoxy.

It is desirable to perform pull tests on the concrete surface to ensure soundness of the substrate concrete (see QC&QA below).

Detailed information on the repair and preparation of the substrate concrete can be found in ACI 546R (ACI, 1996) and ICRI 03730 (ICRI, 2003). o Surface Preparation Once the overall member is ready for FRP installation, the bonding surface must be prepared to receive the adhesive. The end goal of the surface preparation activities is typically to provide a freshly-exposed, clean, sound, open, dry, and roughened texture. The following items should be addressed: The surface of the concrete should be leveled using

mortar or epoxy putty (as specified by the FRP manufacturer) to ensure that any surface irregularities are smoothed typically to less than 1 mm in size.

In cases where FRP systems are applied around corners, the corners must be rounded to a minimum radius as specified in the construction documents (Figure 4-4). This is done to avoid stress concentrations at sharp edges. Typical minimum radii for corners in FRP strengthening applications are between 15 and 35 mm, depending on the specific system being used and applicable code regulations. Corners need not be rounded in cases where the fibre direction runs parallel to the sharp edge.

Fig. 4-4. Rounding of sharp corners to specified minimum radius using a concrete grinder. Bond Critical Applications In applications where bond between the FRP and the concrete is critical for satisfactory performance of the FRP strengthening system (typically these are situations in which the concrete member is not completely encased in FRP, such as flexural and shear strengthening of concrete beams), the surface must be profiled to a specific surface roughness to promote optimal bonding. This is typically achieved by using sand or water blasting, or a hand grinder, to expose the fine and coarse aggregate surfaces. Surface preparation should be in accordance with ACI 546R (ACI, 1996) and ICRI 03730 (ICRI, 2003). Surface contaminants, dust, and debris must subsequently be completely removed by brushing or air or water blasting.

Minimum radius


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Fig. 4-5. Concrete surface preparation by water blasting, sandblasting, or grinding.

Contact Critical Applications In cases where the concrete member is completely encased in FRP (in column wrapping, for instance), surface preparation is less critical. In these applications it is necessary only to ensure intimate contact between the FRP and the concrete. The bonding surface should thus be convex or flat and should be cleaned of debris and contaminants. p Adhesive Mixing Accurate measuring and uniform mixing of adhesive components is critically important for successful application of FRP strengthening systems, and manufacturers recommendations should be strictly observed. The various FRP manufacturers specify mixing methods and times for their adhesives. Depending on the resin supplier and the amount of material required, various mixing techniques may be used, including small drill-mounted mixing blades, special mixing machines, or even hand agitation. Well-mixed resins should be of uniform colour and free of air bubbles. Application of the FRP systems must be completed within the manufacturer specified pot-life of the resin at the applicable ambient temperature. Pot-lives of resins under various ambient temperature conditions are available from FRP strengthening system suppliers. q FRP Installation Environmental conditions must be satisfactory for installation of the FRP system to begin. Precise specifications in this regard vary from manufacturer to manufacturer. The ambient temperature should typically not be less than 4C to 10C, nor above 30C to 55C, depending on the specific resin system being used. The surface of the substrate concrete should be free of moisture and condensation. Exterior installation should be avoided if rain is expected in the near future. Several methods are currently available to bond FRP materials to concrete members. The two most common

methods involve the use of adhesively bonded pre-cured laminates or laid-up fabric systems.

Fig. 4-6. Various conditions that must be avoided during installation of external FRP systems. Pre-cured Laminates and Strip Systems FRP Preparation: The FRP strip is cut to length using

a high-speed cutting wheel or a fine blade hacksaw. Some manufacturers have developed special cutting rigs for this purpose. The strip is cleaned to ensure that its bonding surface is free of contamination. This is typically accomplished by wiping it with acetone.

Application: A layer of mixed adhesive, typically 1 mm to 3 mm thick, is applied to both the substrate (over the area to be bonded) and the FRP strip. Again, some FRP manufacturers have developed special systems for adhesive application. The FRP is then carefully placed in position on the concrete member and is pressed against its surface using a hard rubber roller to achieve a void-free bond line with a thickness of between 2 mm and 3 mm. Excessive adhesive should be removed before curing.

Fig. 4-7. Pressing a carbon FRP strip into adhesive using a small roller (photo courtesy Sika Corp.). Fabric Systems FRP Preparation: The fibre fabric (which is delivered

in standard widths, typically between 300 mm and 600 mm) is cut to length using commercial quality heavy-duty scissors. Blunt scissors and other types of

Moisture Vapor Transmission

Temperatures below 40 F

Surface poresfilled with water

Potential water leakage


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cutting tools can damage the fibres and should not generally be used.

Fig. 4-8. Unidirectional carbon fibre fabric sheet, with paper backing, before installation on concrete structure. Application: Two slightly different methods exist for

the application of FRP fabric strengthening systems for concrete, namely wet lay-up and dry lay-up. These two techniques are similar, however, and consist of the following steps:

1. A low viscosity epoxy primer is applied to the concrete,

using a standard paint roller, to seal and strengthen the concrete surface and to provide the optimal surface for bonding to the FRP material. The coverage rate and curing time for the primer should be as per manufacturer recommendations.

Fig. 4-9. Roller application of epoxy primer on areas (dark areas) where fibre fabric is to be bonded to the underside of a bridge (photo courtesy Vector Construction Group).

2. The surface of the concrete is leveled, where necessary,

with a squeegee or trowel using a non-sag epoxy putty. Any minor voids or surface irregularities should be leveled.

Fig. 4-10. Application of epoxy putty (light gray) on areas where fibre fabric is to be bonded (photo courtesy Vector Construction Group).

3. A layer of mixed epoxy resin saturant is applied to the

surface of the concrete member using a brush, roller, or trowel (again, coverage rates should be in accordance with recommendations).

Fig. 4-11. Application of epoxy saturant layer on areas where fibre fabric is to be bonded (photo courtesy Vector Construction Group).

4. The FRP material is bonded to the surface of the

concrete using the wet or dry lay up technique: Wet Lay-up The fibre fabric is saturated with resin before being bonded to the concrete. This is typically accomplished using a paint roller on a clean plastic drop sheet, or by using a specialized saturating roller assembly. The saturated FRP sheet is then placed onto the surface of the concrete and smoothed out by hand or using a squeegee to ensure intimate contact. Dry Lay-up Unsaturated (dry) fibre fabric is placed into the initial layer of saturant applied to the surface of the member. In some cases, the fibre fabric may have a paper backing which is removed once the fabric has been placed against the member. The dry fibres are pressed into the saturant to impregnate the fibre fabric with resin.


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Fig. 4-12. Carbon fibre fabric (black) is pushed into the saturant layer and impregnated with epoxy (photo courtesy Vector Construction Group).

5. Air bubbles beneath the surface of the FRP sheet should

be rolled or pressed out by hand. 6. A second layer of saturant is applied with a roller over

top of the fibre fabric. Full saturation of the fibres is critical.

Fig. 4-13. A second layer of epoxy saturant is applied on top of the carbon fibre fabric (photo courtesy Vector Construction Group).

7. The process can be repeated for multiple layers of FRP.

If the resin is allowed to cure between installations of multiple FRP layers, a light sanding of the FRP surface may be required between applications. Figure 4-14 shows the various layers of materials in a typical lay-up application of an externally-bonded FRP strengthening system.

Spacing and Positioning: The primary fibre direction

of the installed FRP system is a key factor influencing the strengthening systems performance. The specified design orientations of the FRP sheets should be strictly observed. Fabric with misaligned fibres should not be used, or should be removed if fibre misalignment occurs during or after installation. Fibre misalignments of less than about 5 can normally be ignored, at the discretion of the engineer.

Fig. 4-14. Layers of materials in a typical lay-up application of an externally-bonded FRP system. r Protective Coatings In some cases, an epoxy coating, decorative elastic polymer, paint, or fire protective coating may be applied to the exterior of the FRP strengthening system. This may be done for aesthetic reasons, to protect the FRP from UV exposure, or to provide a fire barrier or fire insulation. s Curing Conditions Because curing of epoxy resins used in FRP strengthening applications is a time dependent phenomenon, FRP systems must be cured for an adequate period of time under acceptable conditions of temperature and humidity. The recommendations of the manufacturer should be followed. While specifications for different FRP strengthening systems differ somewhat, the temperature during the curing process must typically be maintained above 4C to 10C for some specified duration, and condensation or contamination on the surface of the FRP must be prevented during curing. In some cases, auxiliary heat sources and temporary shelters can be used to heat the substrate concrete to allow installation in colder environments. The ambient relative humidity (RH) must typically be less than 85%. Most FRP systems also have specified maximum cure temperatures, which are typically in the range of 35C to 55C. The reader should note that the pot-life of epoxies may be significantly reduced at higher ambient temperatures. It is important that the FRP not be disturbed during the early stages of the curing process (typically during the first 24 hours). Common epoxy resins reach their design strength in about seven days. The temperature and humidity conditions should be monitored and recorded throughout the installation and curing process. Research suggests that typical vibrations and strains due to traffic loads are not a concern during curing of FRP strengthening applications on concrete bridges.

Protective coating

2nd resin coating

Fibre fabric

1st resin coating

Leveling putty

Primer

Concrete substrate


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Equipment Many FRP manufacturers have developed specialized equipment for the installation of their specific FRP strengthening systems. Specialized items such as mixers, sprayers, resin impregnators and winding machines are used in some instances. All workers should be trained in the safe and effective operation of such equipment prior to use. Alternative Techniques Various additional techniques are available, and have been used, to apply externally-bonded FRP strengthening systems to reinforced concrete structures. These include (but are not limited to) near surface mounted (NSM) systems, filament wound FRP wraps, and UV curing systems. These techniques are not discussed in detail in the current document, and the reader is encouraged to consult the references listed in Section 6 for further information.

Fig. 4-15. A fibre saturation machine being used to impregnate glass FRP sheets with clear epoxy resin for a wet lay-up FRP strengthening application (courtesy Sika Corp.). QUALITY CONTROL AND QUALITY ASSURANCE The performance and durability of externally-bonded FRP strengthening systems depends to a large extent on the quality of the materials used and the care taken by the applicators. Because currently available FRP strengthening systems often have slightly different installation procedures, detailed specifications should be developed and followed for any specific FRP application. It is also important when using FRP strengthening systems that comprehensive quality control (QC) and quality assurance (QA) programs be put in place and observed throughout the installation process. Most FRP system suppliers and design codes/guidelines provide similar guidance in this regard. The following is a summary

of typical QC and QA recommendations (refer to Table 4-2). Manufacturers should be consulted regarding requirements for FRP specific systems. Table 4-2. Basic Checklist: Quality Control & Quality Assurance

; FRP systems and materials qualified by the Engineer ; Engineers, contractors, and site inspectors appropriately educated and certified in the use

of FRP systems

; Inspections conducted regularly by trained personnel

Pre-installation: Concrete FRP

During Installation: quantities of materials used, rates of application environmental conditions fibre alignment witness panels

Post-installation:

voids and delaminations cured FRP thickness bond testing load testing

Material Qualifications All FRP materials must be qualified for use based on the project specifications decided upon by the Engineer. The FRPs must meet qualifications in terms of mechanical, physical, and chemical design requirements. While most FRP suppliers provide detailed information on the properties of their strengthening systems, qualification tests are typically performed on the materials by an independent testing authority to confirm manufacturer-specified physical and mechanical data. These may include tests to verify: Tensile strength and elastic modulus; Strain at failure; Resin glass transition temperature; Resin pot-life; and Bond strength to concrete. Contractor/Applicator Qualifications Because significant care is required when FRP strengthening systems are used, installation of these systems should only be performed by trained and certified personnel. Installation specialists who have been trained in the application and handling of the specific FRP systems should be used. Training is typically the responsibility of the FRP suppliers.


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Inspections and Field Quality Control Inspections should be carried out before, during, and after application of the FRP materials, to ensure that the strengthened structure will perform as desired. Inspections should be conducted by a trained and certified site engineer. Items of interest during such inspections will typically include the presence and extent of delaminations, the adequacy of resin cure, adhesion, FRP thickness, fibre alignment, bond properties, and as-installed material properties. Pre-Installation Both the concrete substrate and the FRP materials should be inspected prior to application. The concrete surface should be inspected with respect to soundness and adequacy of surface preparation, as outlined previously. This should include examinations of the surface roughness, holes, cracks, protrusions, sharp corners or other imperfections. The FRP material should be examined to ensure that it meets the specifications of the Engineer with respect to mechanical and physical properties. The Engineer must ensure that all relevant information on the FRP system has been supplied by the manufacturer or determined through testing. During Installation During installation it is important to carefully control and monitor the quantities of materials being used to ensure adequate coverage rates for primers, putties, and saturants. Mixing and installation times, temperatures, and relative humidities should also be monitored and recorded. A trained field supervisor should be present at all times. Fibre directions and alignments should be verified during the installation process. Various samples are often taken during application of FRP strengthening systems. This may include small samples of the various resins or sample panels of FRP (called witness panels) that can be tested at a later date to verify as-installed FRP properties. The American Concrete Institute (ACI, 2002) recommends the following items for inclusion in daily inspections of FRP installations: Date and time of installation; Ambient temperature, relative humidity, and general

weather; Surface temperature of concrete; Surface dryness; Surface preparation methods and resulting surface

roughness; Qualitative description of surface preparation and

cleanliness; Type of auxiliary environmental control, if any; Widths of existing cracks not repaired by epoxy

injection; Details of the specific FRP materials batch numbers

and locations on the structure;

Batch numbers, mixing ratios, mixing times and methods, description of appearance of all mixed resins (primers, putties, saturants, adhesives, topcoats);

Observations on cure of the resins; As-installed fibre orientations; Conformance with recommended procedures for

installation; Results of tensile tests performed on FRP witness

panels, where required; Results of delamination surveys and pull-off tests; and General progress of the work. Post-Installation Various tests are typically performed after installation of FRP strengthening systems to provide assurances that the systems have been installed properly and that they will be able to perform as desired over the long term. The following QC tests are common: Inspection for voids and delaminations: Once the

resin has undergone its initial hardening (usually within the first 24 hours after application), a visual and acoustic tap test inspection should be performed on the bonded FRP to check for debonded areas, air pockets, and voids beneath the FRP (Figure 4-16). Various other inspection techniques, including ultra-sonic inspection and thermography, are available and may be used if agreed upon by all parties.

Void and delamination repair: Voids and/or delaminations detected after installation and cure of the FRP system should be repaired. The repair technique used will depend on the size and location of the delamination and its effects on the structural performance of the FRP system. The following recommendations would typically be followed:

Delamination areas < 1300 mm2 These small delaminations do not require corrective action in most cases, provided that the area of the delamination is less than 5% of the total bonded area and that there are not more than 10 such delaminations per square metre. Delamination areas > 16000 mm2 Large delaminations should be repaired by selectively cutting away the affected area of cured FRP sheet, reapplying primer and leveling putty, and applying an overlapping patch of FRP sheet that is equivalent to the removed material. Delamination areas 1300 mm2 to 16000 mm2 Moderate delaminations can be repaired either by low-pressure injection of resin saturant into the void beneath the delamination, or using the patching method described above.


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Fig. 4-16. Tap test for voids and delaminations. Cured FRP thickness: Small FRP core samples may be

taken from non-critical areas of the installed FRP systems to measure the as-installed cured thickness of the FRP strengthening system. The cored areas should be repaired with FRP patches.

Bond testing: In bond-critical applications it is common to conduct direct tension bond testing on the installed FRP system in accordance with applicable test methods (ACI, 2004). These tests are performed to verify the adequacy of the FRP-concrete bond, and should not be conducted until the adhesive has cured for at least 24 hours. The desired failure mode in these tests is cohesive failure occurring in the concrete and a typical minimum substrate tensile strength of 1.4 MPa to 1.5 MPa is usually required

Load testing: In some cases, FRP-strengthened structures may be load tested, according to applicable guidelines, to verify the in-service performance of the FRP strengthening system. Such testing must be conducted only by skilled engineers. The advice of an expert engineer should be sought if load tests are required.

Fig. 4-16. Pull-off bond testing using a specialized pull-off rig.

The Engineer must provide a detailed written report on all aspects of the quality control and quality assurance procedures, tests, and results. Samples of as-installed materials should be retained by the Engineer. COMMON SAFETY PRECAUTIONS Epoxy resins used in externally-bonded FRP systems typically contain potentially harmful chemicals, which may be classified as corrosive, flammable, or poisonous, and it is thus important that appropriate health and environmental safety procedures be followed. Manufacturers should be consulted in this regard, and Material Safety Data Sheets should be obtained and reviewed prior to use. When handling epoxies and their components it is typical to observe to following safety precautions: Avoid contact with skin and eyes. Safety glasses,

impermeable gloves, and disposable suits should be worn at all times while handling uncured FRP systems.

High vapour concentrations resulting from epoxy use can cause respiratory irritations. Epoxies should only be handled in well-ventilated areas or approved respirators should be worn.

Gloves should be worn at all times when handling fibre fabrics and FRP sheets, since loose fibres can cause skin irritation.

MAINTENANCE AND REPAIR OF FRP SYSTEMS It is important when using FRP strengthening systems, as with any repair project, to monitor the in-service performance of the repaired member. Long-term inspections and assessments typically include general visual inspections to identify changes in appearance, debonding, delamination, cracking, peeling, blistering, etc. In addition, mechanical testing, which may include pull-off testing or structural load testing, is commonly performed. In cases where repair of the FRP strengthening system is required, the advice of a specialist engineer should be sought to determine the causes and remedies for the observed damage.


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Section 5

Summary and Conclusions Fibre reinforced polymers are now recognized as efficient, effective, and durable materials for use as internal reinforcement or external strengthening materials for reinforced concrete structures. However, because these systems are still relatively new in construction applications, it is important that engineers, technologists, site inspectors, and construction workers be educated as to their handling and application. This module has presented a brief overview of some of the important considerations and procedures that should be kept in mind when using FRP reinforcement and strengthening systems in construction applications with a goal of fostering awareness in the construction industry. It is clear that the novelty of these systems necessitates the

observation of specific handling and application procedures, although none of these are beyond the capabilities of typical concrete repair engineers, technologists, or contractors. The discussion has been kept broad, and the reader is encouraged to consult additional resources and specific FRP manufacturers for further information. A comprehensive list of additional references is presented in the following section. Interested readers are also encouraged to contact ISIS Canada (www.isiscanada.com) for additional information on any of the topics presented herein. Appendix A provides contact information for various current FRP reinforcement and strengthening system manufacturers in North America.

Section 6

References and Additional Guidance Additional information on the use of FRP materials (and Structural Health Monitoring) in civil engineering applications can be obtained in various documents also available from ISIS Canada (www.isiscanada.com). Additional educational modules include: ISIS Educational Module 1: Mechanics Examples Incorporating FRP Materials ISIS Educational Module 2: An Introduction to FRP Composites for Construction ISIS Educational Module 3: An Introduction to FRP Reinforced Concrete ISIS Educational Module 4: An Introduction to FRP-Strengthening of Concrete Structures ISIS Educational Module 5: An Introduction to Structural Health Monitoring ISIS Educational Module 8: Durability of FRP Composites for Construction. In addition, ISIS Canada has published design manuals for the use of FRP materials. The following design manuals are relevant to the current module: ISIS Design Manual No. 2 Guidelines for Structural Health Monitoring ISIS Design Manual No. 3 Reinforcing Concrete Structures with Fibre Reinforced Polymers ISIS Design Manual No. 4 Strengthening Reinforced Concrete Structures with Externally-Bonded Fibre Reinforced

Polymers ISIS Design Manual No. 5 Prestressing Concrete Structures with Fibre Reinforced Polymers ISIS Design Manual No. 6 Civionics Specifications ISIS Canada Specifications for Product Certification of Fibre Reinforced Polymers (FRPs) as Internal Reinforcement in

Concrete Structures Due to the increasing popularity and use of FRP reinforcements in the concrete construction industry, a number of design recommendations have recently been produced by various organizations for the design of concrete structures with internal FRP reinforcement. The following documents can be consulted for additional information, or if design with FRP materials is being contemplated.


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General information on FRPs for infrastructure: Teng, J.G., Chen, J.F., Smith, S.T., and Lam, L. 2002. FRP strengthened concrete structures. Wiley. Hollaway, L.C., and Head, P.R. 2001. Advanced polymer composites and polymers in the civil infrastructure. Elsevier. Design codes and guidelines for the use of FRPs with concrete: CSA 2002. CAN/CSA-S806-02: Design and Construction of Building components with Fibre Reinforced Polymers.

Canadian Standards Association, Ottawa, ON. CSA 2005. CAN/CSA-S06-05: The Canadian Highway Bridge Design Code (CHBDC). Canadian Standards

Association, Ottawa, ON. ACI 2004. ACI 440.4R-04: Prestressing Concrete Structures with FRP Tendons. American Concrete Institute,

Farmington Hills, MI. ACI 2004. ACI 440.3R-04: Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening

Concrete Structures. American Concrete Institute, Farmington Hills, MI. ACI 2003. ACI 440.1R-03: Guide for the design and construction of concrete reinforced with FRP bars. American

Concrete Institute, Farmington Hills, MI. ACI 2002. ACI 440.2R-02: Guide for the design and construction of externally bonded FRP systems for strengthening

concrete structures. American Concrete Institute, Farmington Hills, MI. Additional references used in the current document: ACI 1996. ACI 546R-96: Concrete Repair Guide, American Concrete Institute, Farmington Hills, MI. ICRI 2003. ICRI 03730: Guide for Surface Preparation for the Repair of Deteriorated Concrete Resulting From

Reinforcing Steel Corrosion, International Concrete Repair Institute. ICRI 1997. ICRI 03732: Guideline for Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and

Polymer Overlays, International Concrete Repair Institute.

Acknowledgements The authors would like to thanks the following individuals and organizations for providing information and photographs for use in this educational module:

Mr. Garth Fallis, Vector Construction Group

Mr. Dave White, Sika Corporation


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Appendix: North American FRP Suppliers Additional information on the various currently available FRP materials and systems for reinforcement and strengthening of concrete, as well as materials and systems for more specialized a

ISIS EC Module 6 - Notes (Student)

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