3.Fiber Reinforced Plastics

8/8/2019 3.Fiber Reinforced Plastics

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FIBER REINFORCED PLASTICS (SFRPs) for REPAIR and

STRENGTHENING of CONCRETE BRIDGE STRUCTURES AN

ANALYSISBy

Prof. Cristina T. Coquilla of Adamson University, Philippines

Prof. Junichiro Niwa of Tokyo Institute of Technology

The Problem and Its Background

Damage to concrete bridges may not only be of a material or structural

nature but may have adverse effects on the aesthetic appearance. Whereas it

should be sought to repair the structure in the most effective manner, care

should be taken that the method of repair does not aggravate the situation.

Where upgrading is involved, this may pose a major problem and great ingenuity

may be necessary in some cases to apply strengthening systems that do not

deface the overall aesthetic appearance.

Due to the difficulty and cost involved in strengthening an existing

concrete bridge to new design standards, it is usually not economically justifiable

to do so. Therefore, the goal of this study is often limited to preventing

unacceptable failure. This means that a considerable amount of a structural

damaged during a major earthquake is acceptable provided collapse of the

bridge is prevented. In the case of major concrete bridges, the ability of the

bridge to carry emergency traffic immediately following an earthquake may

require a higher level of performance with less structural damage, the threshold

of damage that will constitute unacceptable failure must therefore be defined by

the engineer by taking into consideration the over-all configuration of the

structure, the importance of the structure as a lifeline following a major

earthquake, the case with which certain types of damage can be quickly repaired,and the relationships of the bridge to other structures that may or may not be

affected during the same earthquake.

It should be noted that cost is also a major issue. Therefore, a

mobilization and traffic control costs represent a major part of the total seismic

repair cost.

Reinforcing fibers will stretch more than concrete under loading.

Therefore, the composite system of fiber reinforced concrete is assumed to work

as if it were unreinforced until it reaches its first crack strength. It is from thispoint that the fiber reinforcing takes over and holds the concrete together.


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For fibers reinforcing, The maximum load carrying capacity is controlled

by fibers pulling out of the composite because fiber reinforcing does not have a

deformed surface like larger steel reinforcing bars. This condition limitsperformance to a point far less than the yield strength of the fiber itself. This is

important because some fibers are more slippery than others when used as

reinforcing and will affect the toughness of the concrete product in which they

are placed.

Toughness is based on the total energy absorbed prior to compete

failure.

It is from this theory, that the authors conducted a research on the repair

of concrete bridges using sprayed fiber reinforced plastics.

In this study, a new, inexpensive, and simple strengthening method for

concrete structures is discussed and suggested in order to improve future

seismic strengthening. This method, using short fibers with vinyl ester, is a new

combination of materials as seismic strengthening. Chopped short fibers of

carbon and glass with vinyl ester/polyester resin are sprayed in place on the

concrete structures. It is called Sprayed Up FRP (Fiber Reinforced Polymer).

The benefit of using vinyl ester resin in this strengthening method is that it takes

shorter time to harden the resin than where epoxy resin is used. In addition, the

mechanical properties of vinyl ester resin are the same as the one of epoxy

resin.

Statement of Purpose:

This research contains procedures for evaluating and upgrading the

seismic resistance of existing highway concrete bridges. Specifically it contains

h the design requirements of the Sprayed Fiber Reinforced Plastics

for increasing the seismic resistance of existing concretebridges.

h to minimize the risk of unacceptable damage during a

design earthquake. Damage is unacceptable if it results in:

the loss of life

the collapse of all or part of the bridge

the loss of use of a vital transportation route

h to investigate the effect of SFRP strengthening to ReinforcedConcrete (RC) member with deterioration such as crack andcorrosion of steel bars.


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h to propose the calculating way of load carrying capacity of RC

member with SFRP

hto improve the peel off of SFRP improve the transformability of SFRP

using the resin that has larger extensibility to strain

using resin that has lower strength

improve the bonding strength

using the uncongealer (rough surface)

using the concrete spike( fix SFRP at some points)

Scope and Delimitations:

This research is intended for use on highway concrete bridges of

conventional steel and concrete girder and box girder construction with spans

not exceeding 500 feet (150 meters). Suspension Bridges, cable-stayed bridges,

arches, and movable bridges are not covered. However, many of the concepts

presented here can be applied to these types of structures if appropriate

judgment is used. Although specifically developed for highway bridges, this

research may also have applicability to other type of bridges. Minimum

requirements for evaluation and upgrading will vary based on SPC (Seismic

Performance Category).

Related Literature:

Portland Cement Concrete is considered to be a relatively brittle material.

When subjected to tensile stress, unreinforced concrete will crack and fail. Since

the mid 1800s steel reinforcing has been used to overcome this problem. As a

composite system , the reinforcing steel is assumed to carry all tensile loads.

Placing an external reinforcement on a structure is a common practice

either to improve its performance during an earthquake or to repair it after anearthquake. This can be used also for under-designed structure. The materials

can be of reinforcement consisted either of concrete materials placed by

spraying or coating and/or steel plate or jackets bounded. However, the

materials needed to develop is a lightweight, high strength materials with

superior durability and corrosion resistance that can also be applied with relative

case to take place in. The use of fiber-reinforced polymers (FRPs) fulfills that

need. Polymers and fibers can be combined in a material to suit the specific

needs of a structure.FRP carrying continuous fiber is that they are highly anisotropic.


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Properties in the direction of fiber alignment , such as tensile strength, elastic

modulus and the thermal stability are far superior to those in the direction

perpendicular to fiber alignment. In addition, continuous fiber composite areessentially brittle and show poor toughness both in the direction of the fiber and

perpendicular to it.

Vinyl Ester Resins are known for their chemical resistance, excellent

wetting, toughness and high temperature properties for composite parts. It is a

resin consisting of an epoxy backbone, for chemical resistance and high strength,

combined with vinyl groups, for high reactivity, and styrene monomer, for low

viscosity. The vinyl groups (carbon to carbon double bonds) and ester linkages

are only at the ends of the resin molecule. This controls the cross linking density,

providing flexibility to the resin matrix. Also these groups are less likely to remain

unreacted in the composite, providing less sites for chemical attack. The ester

linkages are adjacent to methyl groups, making them less susceptible to

breakdown through hydrolysis. These resins are used in composites for

corrosion resistant applications.

Fiber Reinforced Plastics are low weight, high strength, ease of erection,

and corrosion resistance. These factors combined lead to lower installation costs

and lower maintenance costs. When the manufacturing process is perfect and

the standards have been developed, the initial costs may be lower as well. All of

these factors could lead to lower-life cycle costs than using traditional materials.

Nowadays, strengthening by post casting concrete, steel plate jacketing,

fiber reinforcement such as carbon, aramid, and glass are utilized as seismic

strengthening methods for concrete structures. Recently, a seismic

strengthening method by wrapping continuous fiber sheets has often been used,

since the constructibility and durability is superior. However, materials using

continuous fiber are expensive. On the spread of seismic strengthening for

buildings and infrastructures in the future, simple methods of strengthening withlow cost should not only be suggested, but also seismic behaviors should be

cleared.

Definition of Terms:

Glass Fiber is manufactured by Owens Corning, has a diameter of 11 microns,

a tensile strength of 3400 Mpa, an elastic modulus of 81 Gpa, and

elongation at break of 4.6%. It has a high performance , silane-based

sizing that is applied to fiber filaments to improve handling and optimizethe fiber-resin bond in the composite.


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Vinyl Ester Resin(R802)- consisting of an epoxy backbone, for

chemical resistance and high strength, combined with vinyl groups, for high

reactivity, and styrene monomer, for low viscosity. The vinyl groups (carbon tocarbon double bonds) and ester linkages are only at the ends of the resin

molecule. This controls the cross-linking density, providing flexibility to the resin

matrix. Also these groups are less likely to remain unreacted in the composite,

providing less sites for chemical attack. The ester linkages are adjacent to

methyl groups, making them less susceptible to breakdown through hydrolysis.

These resins are used in the composites for corrosion resistant applications.

Vinyl Ester Resin R806- a special type of Vinyl ester resin and they

have the same purpose of R802 as a polymer.

Polyester Resins- are homopolymers based on p-oxybenzol repeat

units and are linear thermoplastics. They are highly crystalline polymers but

have no observed melting point even at up to 900 to 1000 degrees Farenheit.

Flow and creep are virtually non-existant below their crystal translation

temperature of 625 degrees. Polyester has a density of 1.44 gm/cc. Polyester

possess a compressive strength of 15,000 psi. The high strength results is an

excellent load bearing capacity. Polyester has a thermal conductivity of 3.9

BTU/hr./ft2 /degrees ft/in. Its coefficient of thermal expansion (3.3x10-5

in/in/degrees F) is approximately linear from room temperature to 575 degrees F.

Polyester is a very thermally stable wholly aromatic polymers.

Methodology:

Spraying of fiber reinforced concrete plastics (SFRP) is conducted by

the Vantec Laboratory through the help of Fuji P.S. Testing is done at Tokyo

Institute of Technology. The tensile strength, bending capacity, shearing capacity

and the bond stress are done using samples of concrete with and without SFRP.

The key element of the spray equipment is the nozzle unit that injects thecatalyzed polymer of the spray stream. Attached to the nozzle is a fiber chopper

unit that cuts the incoming fiber strand to various length (13,26,52 mm.) and

injects it in the spray stream along with the catalyzed polymers(see Fig. 1 to 4).

Before applying the spray, the surfaced concrete is coated with a layer of

bonding agent (vinyl ester resin combined with catalyst methyl ethyl keytone

peroxide (MEKP). The polymetric matrix and the fiber are simultaneously

sprayed at a high speed on the surface of a concrete structured to be repaired

(see Fig.5 to 6). The sprayed composite is compacted pneumatically on theapplication surface, and is then finish with a roller (see Fig. 7 to 8) The length of


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the fiber can be adjusted in the process along with the type of polymer and the

sprayed thickness. In this study, we use three (3) types of polymers namely,

Vinyl ester resin, Vinyl ester resin (R806), 50% Vinyl ester resin (R806) and 50%polyester resin (bb 100) and the polyester resin (bb 100).

Figure 1. Spray machine

To spraying gun

Resin tank

Conpression air

Spray machine

Rolling cutter

1/4inch(6mm)

Figure 2. Fiber gun


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Figure 3. The structure of spraying gun

Resin gun

Glass fiber

Cutting andspraying part

Figure 4. Roller (to drive out the air)


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Figure 5. Spraying situation 1

resinGlass fiber

Mixed in the air

Figure 6 Spraying situation (2)

FFiibbeerrss aarree jjuummppiinngg oouutt ffrroomm

rreessiinn

We can adjust the angle of fiber nozzle

TThheerree iiss oorrggaanniicc ssoollvveenntt ssmmeellll


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Figure 7 Driving out the air using roller

roller

Figure 8 Driving out the air using roller


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Fig. 12 Beam Bending Test Outline

Fig.14- load displacement curve w/ and w/o spraying of SFRP

B e a m b e n d in g te s t o u t lin e

2 5 0

1 5 0

2 0 0

1 2 0 0

4 7 5 4 7 5

3

CL

1 25

1 00

1 00

S t r a in g a g e

S p r a y i n gs u r f a c e

R e s i n

P e a l o f f

W i re b r u s h i n g& s p i k in gr e t a r d e rC h i p p i n gW ir e b r u s h i n gN o t h i n g

P o l y e s t e r B B - r e s i nV i n y l e s t e rN o n e

T h i s t im eL a s t t im e


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Fig. 15- Load Crack and Crack-Displacement Curve


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Table1-Stresses of the Specimens

Reinforcement arrangement A B C

Diameter of steel bar 15.9 22.2 22.2

Reinforcement ratio (area) 0.794 1.548 2.323

Stirrup diameter (mm) 6.35

Bending capacity (KN) 71.6 132.6 187.9

Shear capacity (KN) 216.2 117.7 134.8Without SFRP

Failure mode Flexural tension Diagonal tension Diagonal tension

Bending capacity (KN) 91.2 1.27 150.4 1.13

Shear capacity (KN) 216.2 117.7

Shape of SFRP

a type

thickness Failure mode Flexural tension Diagonal tension

Bending capacity (KN) 104.0 1.45

Shear capacity (KN) 216.2

Shape of SFRP

a type

thickness 5 Failure mode Flexural tension

Bending capacity (KN) 140.3 1.06 194.4 1.03

Shear capacity (KN) 297.7 2.53 314.8 2.34

Shape of SFRP

b type

thickness Failure mode Flexural tension Flexural tension

Bending capacity (KN) 100 1.40 157.8 1.19 210.1 1.19

Shear capacity (KN) 396.2 1.83 297.7 2.53 314.8 2.34Shape of SFRP

c type

thickness Failure mode Flexural tension Flexural tension Flexural tension

Yielding point of steel bar is 380MPa, and youngs modulus is 200,000MPa

Compressive strength of concrete is 35MPa

Assume SFRP at bottom resist not to the shear but to the bending.

Assume the direction of diagonal tension crack is 45 , and SFRP can resist till it

ruptured in Shape of SFRP b and c


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Figure 18- Spraying thickness of 3.5 mm of 26 mm fiber length

Note: The dimension of specimen sprayed is 100 square mm. with a length of

450 mm. and a reinforced with no. 23 bars

This 3.5 mm. thickness is recommendable. There is no peeling occurs on

the surface.

Figure 19- Spraying thickness is 5mm of 26 mm. fiber length

Note: From Figure 19, you will notice the peel-off of the sprayed fiber from the

specimen.


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stress-strain curve of bb 13

0

10

20

30

40

50

6070

80

0 5000 10000 15000 20000 25000

strain(

stress(M

P

a)

bb13

bb132

bb133

bb134

bb135


0

10

20

30

40

50

60

70

80

0 5000 10000 15000 20000 25000

strain(

stress(M

P

a)

bb26

bb262

bb263

bb264bb265


0

10

20

30

40

50

60

70

80

0 5000 10000 15000 20000 25000

strain(

stress(M

P

a)

bb52

bb522

bb523

bb524

bb525


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Figure 17-Stress- Strain Diagram of the different length in Fiber

Note that from figure 17, polyester (bb) with a length of 26 mm will give better

result of stress-strain curve.

stress-strain curve

0

10

20

30

40

50

60

7080

0 5000 10000 15000 20000 25000

strain(

stress(M

P

a)

bb13

bb26

bb52


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shearing test

Table Concrete compressive strengthfc (MPa) ft (MPa)

Design

strength

41.4 3.47

Design

strength

65.5 4.20

Table 3 Bond shearing experimental result

Actual thickness of

SFRP

(mm)

Maximum load

(kN)

Fracture morphology

2mm 1.20 22.70 SFRP rupture


3.5mm 1.70 31.35 SFRP rupture

3.5mm 3.20 4.034 SFRP rupture

5mm 5.70 49.65 Peeling


5mm 50MPa 4.10 46.06 Peeling

Concrete design strength of 30MPa are used except for 5mm.

Figure 20- Spraying thickness Maximum load relationship

0

10

20

30

40

50

60

0 1 2 3 4 5 6

MaximumloadkN

Actual spraying thicknessmm

PeelingPeeling


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Figure 21- Strain distribution on SFRP surface

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100

2mm

0%20%40%80%60%Peakor

()

(mm)Distance from center

2mm

Strain

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100

2mm

0%20%40%60%80%Peakor

()


2mm

Strain

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100

3.5mm

0%20%40%60%80%Peakor

()


3.5mm

Strain

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100

3.5mm

0%20%40%60%80%Peakor

()


3.5mm

Strain

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100

5mm

0%20%40%60%80%Peakor

()

(mm)

Distance from center

5mm

Strain

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100

5mm

0%20%40%60%80%Peakor

()


5mm

Strain

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100

5mm

0%20%40%60%

80%orPeak

()


5mm

Strain


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1. Calculation of bond shearing strength

Bond shearing strength is calculated from the following equation.

( )( )

dx

xd

b

Ax

SFRPSFRP

=

Then, we try to calculate the bond shearing strength from the strain distribution of the

specimen which was destroyed by peeling.

Table 4

5mm 5mm Average

Maximum stress

slope

dx

dSFRP

(MPa/mm)1.495 1.475

Cross section ofSFRP

SFRPA (mm2)

420 380

Width of SFRP

b (mm)100 100

Bond shearingstrength

max (MPa)6.28 5.61 5.95


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Figure 28-Load Displacement Curve of type A

0

20

40

60

80

100

120

0 10 20 30 40 50

Displacement (mm.)

Load(KN)

Type A-a5mm

TypeA-a3mm

TypeA(w/oSFRP)

Type Ac-3mm

Figure 29-Load Displacement Curve

0

50

100

150

200

250

0 10 20 30 40

Displacement (mm.)

Load

(KN

)

TypeB(w/oSFRP)

TypeBb3mmTypeBa3mm

TypeBc3mm


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Figure 30-Load Displacement Curve of Type C

0

50

100

150

200

250

0 10 20 30 40

Displacement (mm.)

Load

(KN

)

TypeC(w/oSFRP)

TypeC-b3mm

TypeC-c3mm


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Type A under Compressive Stress

Type A under Tensile Stress


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Type B under Compressive Stress

Type B under Tensile Stress


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Type C under Compressive Stress

Type C under Tensile Stress


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Costing:

For vinyl ester resin, the following are the unit cost:

the unit cost of resin;R806- 750/kg.

R802- 750/kg.

BB100-650/kg.

The unit cost of glass fiber- 220/kg.

The unit cost of SFRP spraying- not yet available

Based from Figure 28,29 and 30, the Load Displacement Curve with SFRP

gives better displacement results than without SFRP, it appears that

specimen with SFRP gives more strength than without Spraying which

shows in the said graph. Comparison of using finite element analysis of

Diana software and the actual experimental value in Figure 31, shows that

the finite element analysis and the experimental values will give almost the

same result.

Conclusions:

1. SFRP spray process of strengthening and rehabilitation is a very promising

technique, and continued research will undoubtedly lead to its use in reality.

2. It appears that SFRP have the potential to significantly increase the strength

of existing concrete structures, while at the same time dramatically improving

their fracture energy characteristics.

3. The results indicate that while a number of issues still remain to be

addressed, the use of SFRP for repair and retrofit has advantages over the

traditional wraps on the basis on ease of placement, labor cost and

workmanship requirements.

4. It is highly recommended for highway concrete bridge repair as a form ofretrofitting.

5. The thickness of spraying is 3.5 mm and the length of fiber is 26 mm. To

avoid peel-off.

Recommendations:

The following are the recommendations for future studies:

1. To investigate the actual cost of the SFRP if it is more economical to use.

2. To investigate its durability characteristics under the Philippine weather.. Try to make another mixing type of SFRP using another resin or combination of


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resins.

3. To determine the ability to withstand elements and other detrimental

influences out there in field.

References:

1. N. Banthia, A. Bentur, A. Mufti, Fiber Reinforced Concrete, The Canadian

Society for Civil Engineers, 1998

2. N. Banthia and S. Mindess, Fiber Reinforced Concrete (Modern

Developments), The University of British Columbia, Vancouver,

Canada,1995

3. Thomas W. Berg Fiber Reinforced Concrete, http://www.retail

source.com/information

4. Sprayed-Up FRP Strengthening for Reinforced Concrete Beams,

http://www.tsukuba.ac.com

5. Fiber Reinforced Concrete, http://www.fibermesh.com

6. Stone Solutions Custom Concrete Countertops,

http://www.stone-solutions.com

7. Cary Concrete Products, Inc. Materials, http://www.caryconcrete.com

8. Durastone, http://www.durastone.com

9. Superior Polymer Products Vinyl Ester Resin Technical Data,

http://www.superiorpolymer.com

10. Composites-What is a Vinyl Ester Resin?, http://www.cabot.corp.com

11.http://www.bouyer.net/digests/2000

12. Polyester Resin, http://www.deq.state.la.us/assistance

13. Polyester Resin, http://www.sculpt.com/catalog_98

14. Rule 1162- Polyester Resin Operations, http://www.aqnd.gov/rules/htm

15. Polyester Resin Plastics Products Fabrication,

http://www.dep.state.fl.u/air/permitting/plastics.htm16. 4684-1 Rule 4684 Polyester Resin Operations (Adopted May 19,.),

http://www.valleyair.org/rules/currentrules

Diana Finite Element Analysis, TNO Building and Construction Research, 2000


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ABOUT THE AUTHOR

Engr. Cristina Tanhueco-Coquilla is at present the Chairperson of the Civil

Engineering Department of Adamson University. She earned her Master ofEngineering, major in Civil Engineering from Technological University of the

Philippines and her B.S. Degree in Civil Engineering from the University of the

East. She was at one time also the Chairperson of the Civil Engineering

Department of the University of the East. At present she is taking up Ph.D. in

Technology Management at the Technological University of the Philippines. She

may be contacted at 14 Rd. 7 G.S.I.S. Hills Talipapa, Novaliches, Tel. No.

(02)983-11-41, Cell/Text No. 0917-240-6529, E-mail Address:

[email protected], [email protected].

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3.Fiber Reinforced Plastics