Fiber Reinforced Polymers in Concrete Construction and Advanced Repair Technologies

N. Banthia1

Department of Civil Engineering University of British Columbia

2324 Main Mall Vancouver, BC, Canada V6T 1Z4

ABSTRACT

Non-corrosive and lightweight materials like fiber reinforced polymers (FRPs) are fast replacing steel as a material of choice in both new construction and in rehabilitation projects. FRPs are light, non-magnetic, chemically inert, easy to apply and hence have proven especially suitable and economical for strengthening, rehabilitation and seismic retrofit of columns, beams, masonry, joints, and other structures. This paper provides a broad overview of the current use of Fiber Reinforced Polymers (FRPs) in concrete construction and describes our state-of-the-art. Two broad areas are covered: new construction where FRP bars, grids and other innovative shapes are used and repair and strengthening where wraps, jackets and laminates are used. In the context of repair and strengthening, an entirely novel method of Sprayed Fiber Reinforced Polymer (SFRP) coatings pioneered at the University of British Columbia is described. Finally, the paper provides some basic analysis procedures for beams, and discusses some durability related issues. KEYWORDS: FRP, rebars, grids, retrofit, rehabilitation, strengthening, composites, durability, analysis

INTRODUCTION Reinforced concrete has been a successful construction technique that has provided us with aesthetically pleasing, cost-effective and easy-to-construct structures for our residential, transportation and utility facilities. However, reinforced concrete has also had major durability problems stemming in large part from the corrosion of reinforcing steel in aggressive environments. Infrastructure aging and deterioration is now a global crisis, and in almost all countries of the world, existing bridges and other structures need strengthening, rehabilitation or replacement. In Canada alone, presently there are 30,000 bridges and 5,000 parking garages in need of replacement or rehabilitation. Globally, the magnitude of the problem is pegged about $900 billion, and this figure is increasing steadily. Clearly, such a major challenge cannot be undertaken using old technology—new and improved ways of construction, repair, strengthening and rehabilitation are urgently sought.

For both new construction and strengthening of older reinforced concrete structures, the use of fiber reinforced plastics has increased steadily (1-7). Fiber reinforced polymers offer numerous advantages over steel including excellent corrosion resistance, good fatigue resistance, low coefficient of thermal expansion, as well as being lightweight. FRPs also possess a high specific stiffness and an equally high specific strength in the direction of fiber alignment. An

1 Professor and Distinguished University Scholar, Tel: 604-822-9541; Facsimile: 604-822-6901; e-mail: banthia@civil.ubc.ca

2additional advantage of FRPs is in the endless ways in which polymers and fibers can be combined in a material to suit the specific needs of a structure. Use of FRPs provides a high structural efficiency, and their low density makes physical implementation much easier. Unfortunately, FRPs are also expensive, but the higher costs of FRP materials are often offset by savings in reduced periodic maintenance, longer life spans and of reduced labor costs (1).

STRUCTURE OF FIBER REINFORCED POLYMERS A composite is defined as a material system consisting of two chemically dissimilar phases that are separated by a distinct interface. Concrete is a good example of a composite material. Concrete, however, carries reinforcement elements (aggregates) that have a low aspect ratio and hence concrete is often called a ‘particulate’ reinforced composite (see Figure 1). On the other hand, if the reinforcement element were given a fiber-like shape characterized by a high aspect ratio, then the resulting composite is termed a ‘fiber’ reinforced composite (Figure 1) .

In fiber reinforced polymers, the polymer (or the resin) phase constitutes the binding phase and strong and stiff fibers constitute the fiber phase. Two types of polymers are currently in use: thermosetting polymer and the thermoplastic polymers. Thermoplastic polymers (such as polyethylene, polypropylene, thermoplastic polyester, polybutylene, polymethypentene, ethylene-vinyl acetate, etc.) are highly ductile materials with high impact strengths. Unfortunately, these also soften at relatively low temperatures and have high creep and stress relaxation. These are, therefore, not suitable for primary engineering applications where long term load carrying capability is a necessity. The thermosetting polymers, on the other hand, are low molecular weight liquids with very low viscosities. In their case, solidification occurs by using free radicals to cause cross-linking and curing which provides them with a good chemical resistance, enhanced thermal and dimensional stabilities and low creep and stress relaxation characteristics. The thermosetting polymers are ideally suited for FRPs in civil engineering applications. Properties of three commonly used thermosetting polymers (unsaturated polyester, epoxy and vinyl ester) and their typical chemical formulation are given in Table 1. Note that polyester exists both as a thermoplastic polymer as well as a theromosetting polymer, with the latter variety being an unsaturated polymer with at least two double bonds in its monomer. The two double bonds in the monomer offer a wide range of final properties (8).

Of the three resins listed in Table 1, polyester is by far the most used. This is due to their low cost and abundant availability. Vinyl ester is, in fact, a type of polyester resin produced by reacting a monofunctional unsaturated acid (methacrylic or acrylic acid) with bisphenol di epoxide. Epoxies are advanced polymeric resins that involve reactions with epichlorohydrin (5), and are more expensive than the polyester or vinyl ester resins. These are used typically in aerospace and defense applications and are characterized by a highly cross-linked internal structure imparting them a much superior resistance to chemicals and solvents. Epoxies also have low cure shrinkage (Table 1) and no volatile monomers are emitted during their processing.

The three commonly used fibers for producing FRPs for concrete applications are glass, aramid and carbon/graphite with their properties given in Table 2. These are all strong ceramic materials with that depict both a stiff and a brittle behavior. Glass is an amorphous silica and available as

3

(a) (b)

Figure 1(a) Particulate Reinforced and 1(b) Fiber Reinforced Composite

A-glass, E-glass, ECR-glass, AR-glass and the S-glass. E-glass fiber, with its low cost is one of the most commonly used, but its poor durability in alkaline cementitious environments has caused concern and to improve durability, handling and compatibility with the matrix, a sizing or coupling agent is often placed on the fiber. Carbon fibers are produced from one of the three precursors: polyacylonitrile (PAN), rayon and mesophase/isotropic pitches. These fibers, or their allotropic form graphite, have the most desired properties from the civil engineering applications view point. Graphite has a hexagonal structure, a very strong covalent internal bond and very high specific modulus and strength. Unfortunately, graphite has poor properties in the transverse direction and a low shear modulus. Aramid (Kevlar) is the most commonly used organic fiber in composites. Molecular structure of the para-aramid Kevlar is shown in Figure 2. Stress-strain responses of some commonly used fibers are shown in Figure 3. Note that all fibers have a linear elastic response to failure.

Figure 2. Molecular Structure of Kevlar (8)

4

Figure 3. Stress-Strain Responses of Some Fibers (8)

Compatibility between the fiber and the matrix is an important consideration. Glass fibers

with silane-based sizing are ideally suited for polyester resins as the sizing improves the fiber-matrix bond. The high cure shrinkage of polyester, however, restricts its use in applications where a low performance is needed. Further, polyester resins do not adhere well to both aramid and carbon fibers and hence these combinations are virtually non-existent (8). Epoxies offer a better resin for use with aramid and carbon fibers, but epoxies have high water susceptibility and hence care has to be exercised in this regard. Water absorption also reduces the glass transition temperature [Tg] of epoxies and may affect their thermal performance.

PROPERTIES OF FIBER REINFORCED POLYMERS

Mechanical Properties: Laws of mixtures are often used to calculate the mechanical properties of continuous fiber composites in the longitudinal and transverse directions. As can be imagined, the properties of a continuous fiber reinforced composite are highly anisotropic with the highest strength and stiffness available in the direction of the fiber and only low strength and stiffness (equal to or slightly exceeding those of the matrix) available in a direction perpendicular to the fiber. If subscripts m, f and c refer, respectively, to the matrix, fiber and the composite and Vf represents the volume fraction of fiber in the composite, then one can show that the composite strength in the direction of the fiber alignment, σc, is (8):

( ) ffmfc VV σσσ +−= 1 (1)

5And the composite stiffness in the direction of fiber alignment, , is: cE

( ) ffmfc EVEVE +−= 1 (2)

Similarly, the composite strength in the direction perpendicular to fiber alignment, σc⊥ , is given by: fmc σσσ ==⊥ (3)

And composite stiffness in the direction perpendicular to fiber alignment, Ec⊥, is given by;

f

f

m

f

c EV

EV

E+

−=

⊥

)1(1 (4)

One can also define a critical fiber volume fraction as the minimum fiber volume fraction at which the failure is governed by the fiber and not by the matrix. If the strain at fracture in fiber is given by εf*, and the ultimate conditions are described by the subscript, m, then the critical fiber volume fraction is given by:

*

*

)(

)()(

f

f

mfu

mmu

critfVε

ε

σσ

σσ

−

−= (5)

Mechanical properties of some commonly used FRPs are given in Table 3.

Table 1— Typical Properties of Resins Used in FRPs (5) Resin Specific

GravityTensile Strength [MPa]

Tensile Modulus [GPa]

Cure Shrinkage [%]

Epoxy

1.20-1.30

55.00-130.00

2.75-4.10

1.00-5.00

Polyester

1.10-1.40

34.50-103.50

2.10-3.45

5.00-12.00

Vinyl Ester

1.12-1.32

73.00-81.00

3.00-3.35

5.40-10.30

6

Table 2 —Typical Mechanical Properties of Fibres (5) FIBER TYPE Tensile

Strength [MPa]

Modulus of Elasticity [GPa]

Elongation[%]

Coefficient of Thermal Expansion [x10-6]

Poisson’s Ratio

CARBON High Strength

3500 200-240 1.3-1.8 PAN

High Modulus

2500-4000

350-650 0.4-0.8

(-1.2) to (-0.1) 7 to 12

-0.2

Ordinary 780-1000 38-40 2.1-2.5 Pitch High Modulus

3000-3500

400-800 0.4-1.5 (-1.6) to (-0.9) N/A

ARAMID Kevlar 29 3620 82.7 4.4 N/A Kevlar 49 2800 130 2.3 -2.0

59 Kevlar 129 4210

(est.) 110 (est.) -- N/A

Kevlar 149 3450 172-179 1.9 N/A Twaron 2800 130 2.3 (-2.0), 59 Technora 3500 74 4.6 N/A

0.35

GLASS E-Glass 3500-

3600 74-75 4.8 5.0 0.2

S-Glass 4900 87 5.6 2.9 0.22 Alkali Resistant Glass

1800-3500

70-76 2.0-3.0 N/A N/A

Table 3 —Properties of Composites and Comparison with Steel (5) Property Steel AFRP CFRP GFRP

Tensile strength, MPa 300-450 1720-2540 600-3690 480-1600 Elastic modulus, GPa 200 41-125 120-580 35-51 Rupture strain, % 7-13 1.9-4.4 0.5-1.7 1.2-3.1

Limiting strain, ∈ .0035 .002 0.01 0.02 Performance factor, φ .75 .9 0.8 0.4

7Durability of Composites: Significant issues remain unresolved with respect to the long term durability of composites in concrete construction. There are two major concerns: one relates to the longevity of the composite itself in a deleterious environment, and the other relates to the durability of the bond between the FRP and concrete. A synopsis of our understanding with respect to the durability of the composites is presented in Tables 4 and 5 (10, 11). A compendium of papers related specifically to the durability of the bond is given in Table 6. A detailed treatment of bond durability appears elsewhere (12)

Table 4 — Durability of Composites (Part A)

MATERIAS Water Absorption (%/24 hr.)

Thermal Expansion (*10-6 ° C)

Heat UV radiation

Fiber Phase Glass E-Glass S-2 Glass AR-Glass

5.4 1.6 6.5

GR GR GR

GR GR GR

Carbon PAN-type Pitch-based

GR GR

GR GR

Aramid 0.05 -5.2 A A

Concrete Steel

10-13 10.5

Matrix Phase Polyester resin

0.15~0.60

A

Vinylester resin 0.1~0.2 A A

Epoxy resin 0.1 A GR

(Legend-- GR: Generally Resistant; A: Attacked; SA: Slightly Attacked)

Figure 4. Some FRP Rebar and 2-D Grids Available Commercially

8Table 5 — Durability of Composites (Part B)

MATERIAS Weak Acids

Strong Acids

Weak Alkalis

Strong Alkalis

Organic Solvents

Oxygen/Ozone

Fiber Phase Glass E-Glass S-2 Glass AR-Glass

SA GR GR

A

SA SA

SA GR

A A

SA

GR GR GR

Carbon PAN Pitch-based

GR GR

GR GR

GR GR

GR GR

GR GR

GR GR

Aramid GR SA A SA A A Matrix Phase Polyester resin

SA

A

A

A

SA

A

Vinyl ester resin GR GR GR GR GR SA Epoxy resin GR SA GR GR GR GR (Legend-- GR: Generally Resistant; A: Attacked; SA: Slightly Attacked)

FIBER REINFORCED POLYMER IN NEW CONSTRUCTION: REBARS, GRIDS AND OTHER SHAPES

Figure 4 shows some FRP rebars and grids available for reinforcement. These products are produced by pultrusion (Figure 5, Ref. 5), and available in various shapes and configurations. All three fibers (carbon, glass and aramid) are used in these products along with stabilized thermosetting matrices. In some products a hybrid combination of fibers (glass and carbon) are also used. Their bond with concrete remains an issue and hence their surfaces are either deformed by winding an additional strand in a helical pattern on the surface or by coating them with sand particles of a specific grain size distribution. The fiber volume fraction in these bars varies between 30% and 75% and their stress-strain curves are linear elastic to failure (Figure 6, Ref. 5). Applications of FRP rods and girds are shown in Figures 7-13 (19).

9

Table 6 — Summary of Studies Related to Interface Bond

Researcher System studied Variables Major findings Tighiouart et al (13)

GFRP bar- Concrete Bond

- Type of rebar - Diameter - Anchored length

- For steel bar, the bearing mode controls the bond strength. However for GFRP, mostly the adhesion and friction provide the bonding strength. - For larger diameters, smaller bond strength is reported.

Sen et al (14) CFRP bar- Concrete Bond

- Environmental Conditions (Tidal/Thermal cycles)- Effect of moisture absorption

- Moisture absorption results in swelling of the CFRP composite and it leads to tensile stresses around the CFRP rods lead to cracking and bond degradation.

Katz et al (15) FRP bar- Concrete Bond

- Temperature - Severe reduction in the bond strength with a temperature rise was reported. - The reduction happens at the Tg of the polymer and it was sharper for the less cross-linked matrix polymers.

Toutanji et al (16)

FRP sheet- Concrete Bond

- Type of fiber - Type of surface treatment (water jet and sanding)

- The surface preparation by water jet produces a better bonding strength. - Specimens with high modulus carbon fiber showed higher average tensile than those of lower modulus and those with glass fiber.

Karbhari et al (17)

FRP plate- Concrete Bond

-Environmental conditions - Type of resin - Type of composite plate

- Systems with low glass transition temperatures and severe drop in instantaneous result in significant deterioration. - CFRP lead to more durable retrofits.

Toutanji et al (18)

FRP plate- Concrete Bond

- Environmental conditions) - Type of fiber - Type of epoxy

- Specimens conditioned under wet/dry cycles produced less improvement. - Selection of suitable epoxy is very important.

10

Figure 5. Process of Pultrusion

0

2550

0

770

0

1300

0

600

0

1500

0

1400

0

500

1000

1500

2000

2500

3000

0 0.005 0.01 0.015 0.02 0.025 0.03

Strain

Stre

ngth

[MPa

]

CFRP Leadline tendon

CFRP ISOROD bar

CFRP NEFMAC gridAFRP NEFMAC grid

GFRP C-bar

HFRP NEFMAC grid

Figure 6. Stress-Strain Curves for Some FRP Products

.

Figure 7. FRP Grids as Reinforcement for Tunnel Lining Prior to Shotcreting

11

Figure 8. Marine GFRP Fender Panels

Figure 9. Innovative FRP Bridge Deck

12

Figure 10. Underground Precast Chamber for Utilities

Figure 11. GFRP Dowels Shear Transfer in Slabs on Grade

13

Figure 12. FRP in Bridge Deck Applications

Figure 13 CFRP Stirrups for Bridge Girder

FIBER REINFORCED POLYMER IN STRUCTURAL STRENGTHENING: SHEETS, WRAPS AND LAMINATES

Steel plates glued to the structure using epoxies have been used extensively in the past for strengthening of concrete structures. Steel plates, however, are prone to corrosion which ultimately leads to bond deterioration and plate debonding. FRPs, with their non-corrosive nature are significantly more suitable for strengthening and rehabilitation. In fact, strengthening and rehabilitation applications of FRPs have far surpassed their application in new construction as bars and grids. For repair and strengthening unidirectional FRP sheets (Figure 14, Ref. 19) are generally used. All three fibers, carbon, aramid or glass are employed with an appropriate thermosetting resin (polyester, vinyl ester or epoxy). The sheets can be impregnated in place with

14the resin, or impregnated and cured outside with the hardened laminate applied to the structure using adhesives with or without pre-stress (Figure 15). In some other cases, fiber tapes and strands have also been used for wrapping. Some commercial strengthening products are listed in Table 7, and applications are shown in Figures 15-17.

Figure 14. An FRP Wrap for Strengthening and Repair

Table 7— Some Commercially Av ducts (19)

PRODUCT

Thickness per layer

(mm)

Tensile Strength(MPa)

Elastic Modulus

(GPa)

Ultimate Strain (%)

Mitsubishi Type HM

0.143 1900 640 0.3

MBrace CF130

0.165 3465 229 1.5

Fibrwrap SEH51

1.3 552 27.6 2.0

SIKA CarboDur M

1.4 2000 210 1.1

ailable Reinforcing Pro

15

Figure 15. An FRP Laminate Applied for Strengthening of a Timber Bridge Girder

Figure 16(a). Flexural Strengthening with FRP Figure 16(b). Shear Strengthening with FRP

16

FIBER REINFORCED POLYMER SPRAY FOR STRUCTURAL STRENGTHENING ajority of projects using FRP strengthening have involved the use

f laminated plates or wraps bonded to the concrete surface. An entirely new method of repair

of British Columbia (20-23).

Figure 17. Seismic Strengthening of a Column using FRP

As discussed above, the vast mousing Sprayed Fiber Reinforced Polymer (SFRP) coatings has been developed at the University

Figure 18. The Spray Operation

17The technique consists of spraying polymconcurrently on the surface of concrete to bdistribution of fibers is obtaineingredients of the final comspraying equipment. The resin amixed and then sprayed as a single comTwo strands of roving are fed inpass between a pair of rointervals around its circumference.dependent entirely upon the spacing of blades on consistent length, adjustable fromresin/catalyst mixture fromfibers from the top-mounted chopper unit. Thesspraying surface togethencapsulated by a fullymaterial to whatever thickness is r

er and short, randomly distributed fibers e repaired such that a 2-dimensional random

d on the application surface (Figure 18). There are three basic posite, which are handled simultaneously by the pumping and

nd catalyst are fed separately into a spray gun, where they are pound. The glass fiber is implemented in a roving format.

to a chopper unit mounted on top of the spray gun, wherein they llers. One of these rollers has a series of blades mounted at equal

The blades break the fiber into short lengths, with that length the wheel. This allows production of fibers of

8 to 48 mm. As shown in Figure 18, the gun sprays the the lower spray nozzle while, at the same time, spraying the chopped

e two streams combine and continue on to the er. The result is a two dimensional random distribution of fibers

catalyzed resin. This approach allows the operator to build up the FRP After spraying, a ribbed aluminum roller is used to

orce out any entrapped air voids and to work the material into a consistent thickness. In both the laboratory trials a sin and chopped, randomly distributed glass fiber. The polyester ate tensile strength of 75 MPa and a modulus of 6 GPa when fully hardened. The glass fiber used was manufactured by O his

Figure 19. Safe Bridge, British Columbia

equired.f

nd field application so far, the spray consisted of a polyester reresin developed an approxim

wens Corning under the brand name of Advantex Glass Fiber 360RR Gun Roving. Tfiber has a diameter of 11 microns, a tensile Strength of 3400 MPa, an elastic modulus of 81

18

of pplying the Sprayed FRP was to enhance their shear resistance. In order to demonstrate the ffectivenes e at got replaced in 1999 after 50 years of service were tested in the laboratory. The tested

irders were identical to those in the Safe Bridge in every respect including concrete strength, roperties of reinforcement steel, section and span.

Of the three channel beams salvaged from the old bridge, one was rehabilitated with the prayed GFRP technique while a second was retrofitted using a commercially available ontinuous fiber wrap system, also composed of E-glass (25). The third specimen was tested in s original unretrofitted state to serve as a control specimen. The deteriorated sections with issing cover concrete were repaired, thus creating a continuous flat surface to which the retrofit aterials could be applied. Such surface preparation is particularly important for the continuous ber wrap systems, which would dramatically suffer in efficiency should the material not be pplied to a flat surface. The sprayed technique, on the other hand, is much less susceptible to ese regions of missing concrete. Following a 24-hour moist curing period, the grouted surfaces ere sandblasted. For the channel beam retrofitted with the sprayed technique, the GFRP aterial was applied to all bottom surfaces of the member (slab and leg) as well as to the insides

f the legs, as depicted in Figure 22. The beam retrofitted with the commercially available ontinuous wrap system was also precoated with a primer or coupling agent. After allowing the rimer to cure for a full 24 hours, the wrap was applied in two different orientations, as indicated Figure 23. Fiber orientation is specified with respect to the longitudinal axis of the member,

which is designated as 0o. , was applied to the lower urface of the deck portion of the member and to the bottoms of the two vertical legs. Next, the ame wrap was applied to the inside of the vertical legs, though this time the wrap was turned

GPa, and an elongation at break of 4.6%. The fiber is manufactured from a collection of continuous glass filaments gathered into a single bundle. The “360” designation refers to a high performance, silane-based sizing that is applied to fiber filaments to improve handling and optimize the fiber-resin bond in the composite. Before applying the spray, the outer surface of the structure is coated with a layer of a suitable secondary bonding agent (for example, a two-component elastomer modified vinyl-ester primer system with a methyl ethyl keytone peroxide (MEKP) catalyst). After this bonding agent had dried sufficiently, the spray is applied. With a 20% by volume of 48 mm long fiber, a composite with a density of 1400 kg/m3, a secant tensile modulus of 12 GPa, a tensile strength of 110 MPa and a tensile elongation capacity of 1.25% can be obtained.

The technique of sprayed composites was applied to the Safe Bridge on the Vancouver Island (near Duncan, British Columbia) that needed shear strengthening. The 7.2 m long single span bridge was built in 1955 (Figure 19) and has 11 precast channel beams each 0.35 m wide (see Figure 20). The girders were cast from 35 MPa structural lightweight concrete and the average steel strength was of 356 MPa. The reinforcement details are shown in Figure 21. The 9 m wide bridge includes a sidewalk separated from traffic by a concrete curb. The clearance under the bridge is about 1.2 m at the upstream end and 2.1 m at the downstream end.

Shear stirrups in the girders of Safe Bridge are spaced at varying intervals along the length of the beam, ranging from a minimum spacing of 125 mm at the ends of the beam to a maximum spacing of 760 mm at midspan. Thus, like many other bridges in British Columbia and Alberta, the girders of Safe Bridge are considered shear deficient (24), and the purposeae s of sprayed composites at enhancing shear resistance, girders from another bridgthgp

scitmmfiathwmocpin

Initially, a single layer of wrap, oriented at 0o

ss

190o so that the fibers ran vertically. This application was lapped over the 0o wrap at both the

oratory Tests on Full-Scale Bridge Girders

9top and bottom of the channel legs. At the top, it was lapped over the underlying layer by two inches while at the bottom it was continued across the entire width of the stem soffit. The fiber mass applied per m2 in the wrap was comparable to that present in a 10 mm thickness of spray utilizing a 20% fiber volume. These two systems therefore could be compared directly.

All three of the beams were tested under third-point loading using four large hydraulic jacks as load actuators, Figure 24. LVDTs were used to record the deflection of the beam while the hydraulic pressures in the jacks were monitored to provide load information. Results are shown in Figure 25 and also presented in Table 8.

Table 8. Results of Lab

Retrofit Type

Initial Stiffness (kN/mm)

Peak Load

Ultimate Moment Capacity (kNm)

Absorbed Energy To Peak Load

(N·m)

None 6.69 214 237 11559

Wra 323 p 7.67 284 31644

Spray 9.00 419 470 34095

Results indicate that both retrofit techniques have the ability to increase member stiffness. The

pable of producing superior results. Both retrofit

peak load results followed a similar trend, with the continuous fiber wrap producing a 33% increase in ultimate load carrying ability while the improvement due to the sprayed GFRP technique was nearly triple that at 96%. The very large difference between the two techniques is indicative that the sprayed technique is indeed ca

ting approaches produced very large improvements in the energy absorption characteristics of the channel beams; the wrap increased energy absorption to peak load by 174% while the sprayed GFRP technique increased it by 195%. All three of the beams displayed the characteristic bilinear behavior typical of the reinforced concrete beams. However, in the plastic range, the specimen with the Sprayed GFRP retrofit depicted the greatest ability to strain-harden. Results indicated a clear potential of Sprayed GFRP as an effective material for retrofit.

Before the application of GFRP Spray to the Safe Bridge, the bridge was fully instrumented. Strain gauges were placed on all eleven girders at midspan and these were then sealed for long term monitoring. The bridge was then tested and calibrated for its response prior to placement of GFRP Spray retrofit by loading it at various locations using a fully loaded 28 Ton dump truck (Figures 26(a) and 26(b). Once the instrumentation had been placed and tested, and the benchmark response of the bridge recorded, girders that showed severe spalling were repaired using a hybrid fiber reinforced cementitious mortar employing 0.1% each of polypropylene and carbon fiber (Table 9). The use of hybrid fiber reinforcement in the cementitious mortar was made in order to enhance resistance against plastic shrinkage cracking, increase strain capacity, and improve bond with the substrate.

20

Table 9. Properties of Fibers Used in Hybrid Fiber Reinforced Mortar for Patching Girders

Fibers

Type

Average Diameter

Length (mm)

Tensile Strength

Young’s Modulus

Volume Fraction

(mm) (MPa) (GPa) in the Patching Mortar

rbon Ca

Pitch-Based 9 to 11

12.5

2111.1

232

0.1%

Carbon Microns

ene Polypropyl

Surface Coated

Polypropylene

2 Denier*

12.5 375 3.5

1%

0.

* Weight of a meters long fib rams

inally, the fiber reinforced polymer spray was applied using the spray equipment mounted on a

9000 er in g

Ftruck (Figures 27 and 28) using the scheme in Figure 22. The mass of the discharged fiber was continuously monitored in order to control the in-situ fiber volume fraction to 20%. The placement rate was about 4m2/hour. All eleven girders were sprayed in less than a week.

After the application of the spray, the bridge was load tested again by loading it at various locations using a 28 Ton dump truck (Figures 26a and 26b). The benefits of the spray are indicated in Table 10 in terms of maximum recorded strain in the rebar and deflection in the girders. Results are given from both static and roll tests. Notice the overall effectiveness of the spray.

21

Test B fore Application

ray A n

enc

Table 10. Results of Load Test on Safe Bridge

e After Sprayof Sp

pplicatio of PercRedu

t tion

Max. Rebar Strain (micro strain)

Girder # 6

101.76 65.55 36%

Max. Deflection (mm) G

%

irder # 6

1.55 1.08 30

Max. % of Yield Capacity Reached

8.0 5.2 36%

Max. Rebar Strain (micro strain)

%

Girder # 6

72.12 54.94 24

Max. Deflection 1.34 (mm)

0.89 34%

Girder # 6

Max. % of Yield Capacity Reached

5.8 4.4 24%

DESIGNING WITH FIBER REINFORCED POLYMERS

Significant efforts are currently underway to develop design guidelines to design concrete elements with FRP both in new construction and in strengthening. ISIS guidelines (Ref. 5,6) are prominent among these efforts and these are presented in Appendices I, II and III.

CONCLUDING REMARKS

In this paper, the properties and applications of fiber reinforced polymers (FRPs) are described in the context of both new concrete construction and repair and strengthening of older deteriorated structures. FRPs offer numerous advantages over steel in that they are: non-corrosive, lightweight, non-magnetic and easy to apply. A broad overview of the properties of some commonly used FRPs is presented and issues surrounding the choice of resin system and fibers, long term durability in aggressive environments, etc. are discussed. An entirely original method of SFRP coatings pioneered at the University of British Columbia is described in the repair and strengthening context. Finally, the paper provides some basic beam analysis procedures.

Stat

ic T

ests

R

oll T

ests

22

anne am Reinforcement Details (Imperial Size

Figure 23. FRP Wrapping Scheme

Figure 20. Channel Beam Section and Dimensions

Figure 21. Ch l Be s)

Figure 22. Spraying Scheme

23

Figure 24. Laboratory Tests on Full-Scale Bridge Girders

Figure 25. Re ale Bridge Girders

sults of Laboratory Tests on Full-Sc

24

Figure26(a). Tests on Bridge with Fully Loaded Truck Prior to Strengthening

25

Figure 26(b). Various Positions of the Loaded Truck on the Bridge

26

Figure 27. Spray Equipment Mounted on a Truck

Figure 28. FRP Spray Being Applied to the Bridge

27

REFERENCES

. Meier, U., Carbon Fiber-Reinforced Polymers: Modern Materials in Bridge Engineering. Structural Engineering International, Vol. 1, No. 12, 1992, pp 7-12.

. Ehsani, M.R., Rehabilitation of the Infrastructure with Advanced Composite Materials. Repair and Rehabilitation of the Infrastructure of the Americas, Proceedings. NSF, Mayaguez, Puerto Rico, 1994, pp 193-205.

. Nanni, A., M.S. Norris and N.M. Bradford, Lateral Confinement of Concrete Using FRP Reinforcement. Fiber-Reinforced-Plastic Reinforcement for Concrete Structures, International Symposium. ACI SP-138, 1993, pp 193-209.

. Neale, K. W. and Labossiere, P. State-of-the-art Report on Retrofitting and Strengthening by Continuous Fiber in Canada, Japan Concrete Institute, 1, 1997, pp. 25-39.

. ISIS Canada, Reinforcing Concrete Structures with Fiber Reinforced Polymers, Manual #3, ISIS Canada Corporation, Winnipeg, Canada, 2001.

. ISIS Canada, Strengthening Reinforced Concrete Structures with Externally Bonded Fiber Reinforced Polymers, Manual #4, ISIS Canada Corporation, Winnipeg, Canada, 2001.

. ACI Committee 440, State of the Art Report on Fiber Reinforced Plastic Reinforcement for Concrete Structures, ACI 440R-96, American Concrete Institute, 1999.

. Mangonon, P.L., The Principles of Materials Selection for Engineering Design, Prentice Hall, 1999.

. Engineering Materials Handbook, Vol 1., Composites, AM International, 1987. 0. Banthia, N., and Macdonald, R. Durability of Fiber Reinforced Polymer Composites, Report

to CHBDC Committee 16, The University of British Columbia, Vancouver, 1996. Canadian Highwa Canadian Standards Association, 2000.

2. Banthia, N. and Khalighi, Y., FRP-Concrete Bond: Issues and Challenges, Indian Concrete Institute Journal, Special Issue on FRP, 3(4), January 2003, pp. 35-41.

3. Tighiouart B., Benmokrane B. and Gao D. Investigation of bond in concrete member with fibre reinforced polymer (FRP) bars. Construction and Building Materials, Vol. 12, 1998, pp 453-462.

4. Sen R., Shahawy M., Sukumar S and Rosas J. Durability of Carbon Fiber Reinforced Polymer (CFRP) Pretensioned Elements under Tidal/Thermal Cycles, ACI Structural Journal, Vol. 96 No. 3, May-June 1999, pp 450-459.

5. Katz A. and Berman N. Modeling the effect of high temperature on the bond of FRP reinforcing bars to concrete. Cement and Concrete Composites, Vol. 22, 2000, pp 433-443.

6. Toutanji H. and Qritz G. The effect of surface preparation on the bond interface between FRP sheets and concrete members. Vol. 53, 2001,

7. Karbhari V. M. and Engineer M. Effect of Environment Exposure on the External Strengthening of Concrete with Composites-Short Term Bond Durability, Journal of Reinforced Plastics and Composites, Vol. 15, December 1996, pp 1194-1216.

8. Toutanji H. A. and Gomez W. Durability Characteristics of Concrete Beams Externally Bonded with FRP Composite Sheets, Cement and Concrete Composites, Vol. 19, 1997, pp 351-358.

9. ISIS Seminar Series Material, ISIS Corporation, Winnipeg, 2001.

1

2

3

4

5

6

7

8

91

11. y Bridge Design Code, CAN/CSA-S6-00, Chapter 16,

1

1

1

1

1

1

1

1

280. Banthia, N., C. Yan and N. Nandakumar, Sprayed Fibre Reinforced Plastics (FRPs) for

Repair of Concrete Structures, Advanced Composite Materials in Bridges and Structures, 2nd International Conference, CSCE, Montreal, QC, Canada, 1996, pp 537-545.

Authors thankfully acknowledge the support of Intelligent Sensing of Innovative Structures ciences and

Uni otographs

2

21. Banthia, N. and A.J. Boyd, Sprayed Fiber Reinforced Plastics for Repairs, Canadian Journal of Civil Engineering, Vol. 27, No. 5, 2000, October, pp 907-915.

22. Boyd, A.J. and Banthia. N, Shear Strengthening of Reinforced Concrete Beams with Sprayed GFRP. Proceedings, Structural Faults & Repair, 8th International Conference. London, England, July 1999.

23. Boyd, A.J. Rehabilitation of Reinforced Concrete Beams with Sprayed Glass Fiber Reinforced Polymers. Ph.D. Thesis The University of British Columbia, Vancouver, Canada, 2000.

24. CAN/CSA-S6-00, “Canadian Highway Bridge Design Code”, National Standard of Canada, Dec. 2000, Published by CSA International, Canada.

TM25. MASTER BUILDER TECHNOLOGIES, ‘MBrace Fiber Reinforcement Systems for the MBraceTM composite strengthening system’ (Product Information). TM Trademark of MBT Holding A.G., Master Builders, Inc. Cleveland, Ohio, 1998.

ACKNOWLEDGMENT

(ISIS), Canada, a Network of Centers of Excellence Program of the Natural SEngineering Research Council of Canada. Help of Yashar Khalighi, Doctoral Student at the

versity of British Columbia is appreciated. The permission of ISIS to use project phis also thankfully acknowledged.

29

ent

Assthe concrete compression fiber is 3500 x 10-6 .

tress-strain relationship for FRP is linear up to failure

ne after deformation.

Mo of concrete

- Compression failure in concrete - Tension Failure of FRP

APPENDIX I

Analysis of Beams with FRPs using ISIS Guidelines: FRP Rebar as Tension Reinforcem

umptions: - Maximum strain at - Perfect bond between the concrete and the FRP - Tensile strength of concrete is ignored5 - The s- The strain in concrete and FRP is proportional to the distance from the neutral axis. - A plane cross section before deformation remains pla

des of Failure: - Balanced failure (simultaneous rupture of FRP and crushing

1.1. BALANCED FAILURE REINFORCEMENT RATIO The balanced failure strain conditions occurs when the concrete strain reaches its ultimate value ε , while the outer layer of FRP reaches its ultimate strain ε . From the strain compatibility in the cross section

cu frpu (Fig 1) and the force equilibrium in the cross section (Cn=Tn)

we will have:

ρfrpb = α1 β1 f’c /ffrpu (εcu / εcu + εfrpu ) (A-1) α1: ration of average concrete strength in rectangular compression block to the specified concrete strength: α1= 0.85 – 0.0015 f’c ≥ 0.67 (A-2) β1: ratio of depth of rectangular compression block to the depth of the neutral axis: β1= 0.97 – 0.0025 f’c ≥ 0.67 (A-3) f’c : compressive strength of concrete, MPa ffrpu : ultimate tensile strength of FRP, MPa

30

Fig 1: Failure at balanced condition

1.2. FAILURE DUE TO CRUSHING OF CONCRETE:

hen flexural failure is induced by the crushing of concrete without rupture of the d. The strain with the top fiber strain equal pression is shown in Fig. 2.

Wreinforcement, the section is said to be over-reinforce

the ultimate compressive strain of concrete in comto

Fig 2: Strain/Stress Distribution at ultimate failure due to crushing of concrete

r this section can be calculated as follows:

(A-4)

T= Afrp φfrp ffrp (A-5)

n iteration process may be used and the assumed value of depth of neutral axis should be e equilibrium condition: T=C.

When the equilibrium is satisfied, the moment of resistance of the section is given by: Mr= C(d - β1c/2) (A-6)

The ultimate moment resistance fo C= α1 φfrp f’c β1 cb

Achanged till it satisfies th

311.3. TENSION FAILURE In this type of failure, the steel yields before the failure and the curvature increases rapidly until the strain in concrete reached the ultimate value. The strain in the reinforcement will be: εfrpu = ffrpu / Efrp . (A-7) The corresponding strain εc at the last compressive fiber will be less than εcu and the traditional rectangular block can not idealize the distribution of the compressive stress in the concrete zone and α and β will be derived for εc varying up to 3500 x 10-6. The resultant of the compressive stress in concrete, C, is then calculated as: C= α φc f’c β1 cb (A-8)

nd β can be obtained from Fig 4 and 5.

in which α a

Fig 3: Strain/Stress Distribution at ultimate failure due to rupture of FRP.

Fig 4: Equivalent stress-block parameter α for concrete strength of 20 to 60 MPa.

32

Fig 5: Equivalent stress-block parameter β for concrete strength of 20 to 60 MPa.

The tensile force in reinforcement is calculated as: T=Afrpφfrp εfrpu Efrp (A-9)

Equilibrium in a cross section is found by equating the equations for tensile and compressive forces: α1 φfrp f’c β1 cb = Afrp φfrp εfrpu Efrp (A-10)

Several iterations with different values of the depth of neutral axis should be made until two n equilibrium.

he moment of resistance of the member can be calculated from:

Mr= C(d - βc/2) (A-11)

forces are i T

33APPENDIX II

Analysis of Beams with FRPs using ISIS Guidelines:

FRP Plates for Flexural Strengthening

RESISTANCE FACTORS Resistance factors are required to compute the flexural strength of reinforced concrete and are show in Table 1. Table 1: Resistance Factors for Concrete, Steel and FRP reinforcement Structure Bridge Concrete 0.6 0.75 Steel 0.85 0.9 FRP Different value are suggested between 0.7 to 0.78 FLEXURAL A LU E M

F I R ODES

3- Steel yielding followed by FRP rupture 4- ment near or at the concrete/FRP interface.

ur or not.

1- Concrete crushing 2- Steel yielding followed by concrete crushing

Debonding of the FRP reinforce It may be difficult to determine the failure mode so one must assume a particular failure mode nd then verify if it will occa

Fig 6: Stress and strain Distribution (Tension Steel Reinforcement Only)

.1 Steel reinforcement in tension

ased on Figure 6, the following relation can be established:

εc /c = εs / (d – c) = εfrp + εbi / (h – c) (A-12)

2 B

34 The internal forces acting on the sec C= α1 φ f’c β cb (A-13) Ts= φ (A-14) Ts= φsfyAs ; for (A-15) Where fs is the stress in the steel, As is the area of tension steel reinforcement, and fy and εy are

el and the yield strain of the steel respectively. For the FRP,

frp ≥ εfrpu (A-17)

C =Ts + Tfrp and the resis nt, Mr , is given by: -a/2) + Tfrp (h-a/2) (A-18)

ompression failure of concrete:

is case, the flexural failure m c = cu = 0.0035 for ructures and 0.003 for bridges), the actual FRP and Steel strain can be determined as follows:

(A-19) εbi (A-20)

The eutral axis, , is obtained from equilibrium: Ass

alculated as: Mr = φsfsAs (d – a/2) + φfrp Efrp εfrp Afrp (h – a/2) (A-22)

Assuming yielding of the tension steel: α1 φc f’c β1 c2 b + (φfrpEfrpAfrp (εcu + εbi ) – φsfyAs )c – φfrpEfrpAfrp εcu h = 0 (A-23) Mr = φsfyAs (d – a/2) + φfrp Efrp εfrp Afrp (h – a/2) (A-24) 2.3. Tension failure of FRP When the FRP tension occurs first, the strain in steel will be greater than the yield strain. And the strain in concrete and steel will be calculated as the following: εs = (εfrpu + εbi) ( d – c / h - c) (A-25) εc = (εfr (A-26)

he distance c from the neutral axis to the top compression face is given by:

/ α1 φc f’c β1 b (A-27)

frp (h – a/2)

tion are as follows: frp 1

sfsAs ; for εs < εy εs ≥ εy

the yield stress of the ste Tfrp = φfrp Efrp εfrp Afrp ; for εfrp ≤ εfrpu (A-16) Tfrp = 0; for ε The equilibrium of internal forces gives: s

ting mome Mr= Ts(d

2.2. C

thIn ode is initiated by concrete crashing (ε εst εs = εcu ( d – c / c) εfrp = εcu ( h – c / c) –

distance c from the top compression face to the n

uming that the tension steel has not yielded: α1 φc f’c β1 c2 b + (φsEsAsεcu + φfrpEfrpAfrp (εcu + εbi))c – (φsEsAsd + φfrpEfrpAfrph)εcu = 0 (A-21) The factored resisting moment can ba c

pu + εbi) ( c / h - c) T c = ( φsfyAs + φfrp Efrp εfrp Afrp ) and the factored moment: Mr = φsfyAs (d – a/2) + φfrp Efrp εfrp A (A-28)

35II

eams with FRPs using ISIS Guidelines: Plates for Shear Strengthening

APPENDIX I

Analysis of BFRP

Fig 7: Effective length of reinforcements:

=0.2 f

(A-30)

(A-31)

frp, wfrp and β are the spacing, width and angle of the FRinfo nal axis of the member, respectively. The effective strain

btained from:

fr c frp frp 2 (A-32)

p (A-33)

The factored shear resistance, Vr is given by: Vr =Vc + Vs + Vfrp in which Vc √ c bwd (A-29) The steel contribution is: Vs= φsfyAvd / s And the contribution of FRP is:

Vfrp = φfrpEfrpεfrp Afrp dfrp (sin β + cos β) / sfrp Where A = 2 tfrfrp p frp w ; Here the s P shear re rcement to the longitudi εfrpe is o

ε = Rε where R is given by: R= α λ (f’ 2/3 / ρ E )λ frpe pu 1 and

ρ frpb = 2 tfrp wfrp / bw sfr

36λ1 and λ2 are 1.35 and 0.3 for CFRP for AFRP rupture. The effecti nding in which:

k1= (f’c / 27.65)2/3 (A-34)

= 0.8 and ne is the number of free ends of the FRP stirrups on one side of the beam.

The effective anchorage length, Le , can be found using the following equation: Le= 25350 / (tfrp Efrp )0.58 (A-35) STRENGTHENING LIMITS When shear strengthening is required, the maximum band spacing should be limited to: sfrp ≤ wfrp + d/4 (A-36) Also the factored shear resistance is limited to: Vr =Vc + Vs + Vfrp Vc + 0.8 λ φc√fc bwd (A-37)

rupture and 1.23 and 0.47

ve FRP strain should also be less than α φfrp k1 k2 Le /9225 to avoid debo

and k = (d – n L ) / d2 frp e e frp

α

37

— Typical Properties of Resins Used in FRPs

rison with Steel

vailable Reinforcing Products ratory Tests on Full-Scale Bridge Girders Using Sprayed

Composites able 9 — Results of Load Test on Safe Bridge

ulate Reinforced and

t

igure 5. Process of Pultrusion igure 6. Stress-Strain Curves for Some FRP Products

Figure 7. FRP Grids as Reinforcement for Shotcreted Tunnel Lining Figure 8. Marine GFRP Fender Panels Figure 9. Innovative FRP Deck Figure 10. Underground Precast Chamber Figure 11. GFRP Dowels for Slabs in Grade Figure 12. FRP in Bridge Deck Applications Figure 13 CFRP Stirrups for Girder Figure 14. An FRP Wrap for Strengthening and Repair Figure 15. An FRP Laminate For Flexural Reinforcement of Timber Bridge Girder Figure 16(a). Flexural Strengthening with FRP Figure 16(b). Shear Strengthening with FRP Figure 17. Seismic Strengthening of a Column using FRP Figure 18. The Spray Operation Figure 19. Safe Bridge, British Columbia Figure 20. Channel Beam Section and Dimensions Figure 21. Channel Beam Reinforcement Details (Imperial Sizes) Figure 22. Spraying Scheme Figure 23. FRP Wrapping Scheme Figure 24. Laboratory Tests on Full-Scale Bridge Girders Figure 25. Results of Laboratory Tests on Full-Scale Bridge Girders Figure 26(a). Tests on Bridge with Fully Loaded Truck Prior to Strengthening Figure 26(b). Various Positions of the Loaded Truck on the Bridge Figure 27. Spray Equipment Mounted on a Truck Figure 28. FRP Spray Being Applied to the Bridge

LIST OF TABLES AND FIGURES Table 1Table 2 — Typical Mechanical Properties of Fibres Table 3 — Properties of Composites and CompaTable 4 — Durability of Composites (Part A)

t B) Table 5 — Durability of Composites (ParTable 6 — Summary of Studies Related to Interface Bond Table 7 — Some Commercially ATable 8 — Results of Labo T Figure 1(a) Partic

Fiber Reinforced Composite Figure 1(b) Figure 2. Molecular Structure of Kevlar Figure 3. Stress-S rain Responses of Some Fibers Figure 4. Some FRP Rebar and Grids Available Commercially. FF