Carbon Fiber Reinforced Polymer (CFRP) as Reinforcement for Concrete Beam

shootperchUrban and Civil

Nov 26, 2013 (3 years and 10 months ago)

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International Journal of Emerging Technology and Advanced Engineering

Website:
www.ijetae.com

(
ISSN 2250
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2459,

ISO 9001:2008

Certified Journal
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Volume 3
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2013
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6


C
arbon
F
iber Reinforced Polymer (CFRP) as Reinforcement for
Concrete Beam

Norazman Mohamad Nor
1
,
Mohd Hanif Ahmad Boestamam
2
,
Mohammed Alias Yusof
3

1,3
Universiti Pertahanan Nasional
Malaysia, 57000 Kuala Lumpur, Malaysia

2
Malaysian Army, 50634 Kuala Lumpur, Malaysia




Abstract


Damaged or old structures sometime need to be
repaired or reinforced to enhance its structural life and
performances. There are many ways to strengthen structures.
This research investigates the potential of using Carbon Fiber
Reinforced Polymer (CFRP) as

reinforcement to
concrete

beam. In this study, use of CFRP as reinforcement was
explored. The CFRP reinforcement is applied in strip form,
which is more economical compared to wrapping or forming
it into bar shape, because it easier and uses less fiber to

achieve similar performance. Samples of CFRP reinforced
concrete
beam were tested to failure in four point bending
test. The results obtained are compared with performance of
steel reinforced concrete. From the research, we can conclude
that the CFRP rei
nforced
concrete
beam give the required
resistance and strength as designed, with
behavior

similar to
t
hose reinforced with steel bars
.

Keywords


Carbon fiber
, CFRP
,
concrete

reinforcement,
structural repair
, and

strengthening
.

I.

I
NTRODUCTION

Reinforced Concrete is one of the common building
materials in the world. Many structures, such as buildings,
bridges, and highways, use reinforced concrete as its main
construction materials. Concrete lacks tensile strength,
thus, steel is the common ten
sile reinforcement use in
reinforced concrete. Even though steel performance in
reinforce concrete is superb, it does have some set back.
Steel tent to deteriorate, rapidly, especially when expose to
extreme
coastal
weather and sea water.

This research i
s to investigate an alternative non
-
metal
reinforcement for concrete structure, namely using Carbon
Fibre

Reinforced Polymer (CFRP). CFRP, currently, is
being
used for structural repair for damage structure due to
aging or exposure to extreme condition. I
n this study, the
purpose of using CFRP is to enhance the tensile strength of
reinforced concrete, replacing steel, totally. The main
advantage of using CFRP as reinforcement is to avoid
rusting and corrosion of reinforcement.






The main objective of t
his study is to design beam
reinforced with CFRP. Then to study the performance and
behaviour of CFRP reinforced concrete compared with
steel reinforced concrete. This study involved design and
experimental works on CFRP reinforced concrete,
compared to tr
aditional steel reinforced concrete.

Steel is the most widely used reinforcement in concrete.
Use of

steel reinforcement
is to increase

the tensile and
shear strength of concrete. The position and arrangement of
steel bars
are an

important
strengthening factor
in
reinforced
concrete.

The development of reinforcement technology is
becoming more advanced as engineers are not just using
steel reinforced concrete in their design. In recent years,
Fibre

Reinforced Polymer (FRP) has been proposed
as one
of the main material in reinforced concrete
.
The benefits of
using FRP in reinforced concrete depends on some factor
such as shape, length, cross section,
fibre

content and bond
characteristics of FRP.
[1]

CFRP can be produced with higher strength
and higher
modulus of elasticity than steel, hence improving the
flexural, shear strength, and deflection of structural
member. Furthermore, the corrosion resistance
characteristic gives more advantage on using FRP in
reinforced concrete where it can be us
ed for structures
exposed to corrosive condition. The usage of FRP as
reinforcement is very new and restricted to rehabilitation
work on buildings. The main reason is because the lack of
experience in handling this material and cost of using it
.

[2]

P
admar
ajaiah and Ramaswamy
[3]
, shows the effect of
adding
fibres

increased the compressive strength of
concrete. In their research, adding up to 1.5% of
fibres

in
volume
,

increased the compressive strength up to 15%
from normal strength. This shows that the vol
ume of
fibres

in concrete affect the compressive str
ength and strain

of the
concrete.
Figure 1 shows the stress
-
strain curve for
different portion of FRC

(Fibre Reinforced Concrete)

to
indicate ductility and toughness of the mix.



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Figure 1: Effects of
Fi
bres

Content on Compressive Stress
-
Strain
Curve of FRC
.

[3]

Khaled Soudki et al,
[4]
,

investigate the load

deflection
of fibrous concrete and compared with plain concrete. In
their research, carbon
fibre

was added into concrete mix
design with difference percentage of
fibre

volume. It can be
seen that different amount of
fibres

gave different
deflections to the concrete. Figure 2
shows that
fibre

added
concrete mix samples performed significantly better t
han
their control samples.


Figure 2: Load
-
Deflection Curves for Strengthened and
Unstrengthened Beams
. [4]

Ot
her research done by
Wasan and Akar Abdulrazaq,
[5]
, highlighted that the addition of carbon
fibres

causes a
significant increase in splitting tensile strength relative to
normal plain concrete. From the research, it can be seen
that the percentage of splitting tensile strength increase by
about 45% of normal strength with 0.5%
fibre

volume
fraction.
Ta
ble
I

shows the tensile strength test result for
carbon
fibre

reinforced concrete relative to volume of
fibre

fraction and age of specimen.


TABLE
I

S
PLITTING
T
ENSILE
S
TRENGTH FOR
C
ARBON
F
IBER
R
EINFORCED
C
ONCRETE
.

[5]


Gadve et al,
[6]
,

investigated about rehabilitation of steel
reinforcement using CFRP. In that study, CFRP used as an
anode while the steel reinforcing bar used as cathode. The
result shows that the reinforcing bar is still in good
condition after the sample were immersed
in salt water for
a particular period. This proposed technique has been very
effective in avoiding the corrosion of steel.

II.

M
ETHODOLOGY

In this research, the main material to be used as the
concrete reinforcement is CFRP. Six types of CFRP strip
samples wi
th zero degree orientation were fabricated and
tested using tensile strength test according to ASTM D 638.
The process is required to determine the mechanical
properties of the CFRP

strip
. The next step is preparation
of the concrete samples. There are three types of concrete
samples fabricated.
Eight

samples of CFRP reinforced
concrete with and without cover were prepared. Another
four

samples of conventional steel reinforced concrete we
re
prepared as control samples.
Cubes are prepared for each
mix to ensure the concrete grade.
Table
II

shows the type
of samples used for this research.

TABLE
II

T
YPES OF
S
AMPLES

[7]

Type

Sample

Quantity

Beam

Cube

1

Control (Conventional Steel
Reinforced Concrete)

4

4

2

CFRP Reinforced Concrete (CFRP
Strip with Cover)

4

4

3

CFRP Reinforced Concrete (CFRP
Strip without Cover)

4

4

For the samples Type 2, the technique of the
reinforcement was similar to the steel reinforcement which
has cover of 25 mm. The only different is the CFRP strips
are rectangular in shape, unlike the round steel bars, as
shown on Figure 3 and Figure 4. The
CFRP were
prefabricated with epoxy before used as reinforcement for
the concrete. For samples Type 3, the technique of concrete
reinforcement was different from the previous samples.


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There were no concrete cover for the reinforcement and
the CFRP was put
in the concrete using wet lay
-
up process.
The size of CFRP for
Type 1 and Type 2

samples is 450
mm (length) x 60 mm (width) x 4.5 mm (thick).












Figure 3: Steel Reinforced Concrete Beam
,

Type

1












Figure 4: CFRP Reinforced Concrete Beam
, Type 2 and 3

III.

R
ESULT
A
ND
D
ISCUSSION

The steel bars used for this research is 12 mm mild steel
round bars. The tensile test results for the steel bar are
shown in Table
III
. Average ultimate strength for the steel
bar is at 371 MPa.

TABLE
III

P
ROPERTIES OF THE
S
TEEL
R
EINFORCEMENT
B
AR

[7]

Sample

Ultimate Tensile
Strength (MPa)

Modulus of
Elasticity
(kN/mm²)

1

380

207

2

371

201

3

363

205

4

371

203

Mean

371

204





For tensile test on CFRP strips, six types of CFRP
sampl
es were prepared with different
layers
, O
o

only,

for
each type of sample. Samples preparation is done through
wet hand lay
-
up. The result of this test is shown in Table
IV

and graphically presented on Figure 5. Figure 5 could
be used to estimate the strength and modulus of CFRP strip
produced similarl
y, base on sample thickness.

Provided
same materials being used.

TABLE
IV

P
ROPERTIES OF
CFRP

S
TRIP

[7]

Type of
Sample

Cross
Sectional
Area (mm²)

Maximum
Load (kN)

Tensile
Strength at
Break
(MPa)

Modulus
of
Elasticity
(MPa)

1
layer

A

30

25.193

840

64076

B

30

19.721

657

86468

2
layers

A

55

23.820

433

32557

B

55.2

29.825

540

49691

3
layers

A

48.4

32.077

661

45119

B

62.4

33.229

532

57079

4
layers

A

69

36.847

534

68683

B

69

34.967

507

51392

5
layers

A

90

38.217

425

57048

B

87.5

39.008

446

56570

6
layers

A

115

42.753

372

68221

B

117

42.458

363

46127



Figure 5: CFRP Thickness verses Tensile Strength and Modulus of
Elasticity

Four point bending test were conducted

on all the beam
samples
. Figure 6 shows the experimental results obtained.
The experimental results are compared to calculated
strength based on stress diagram, as tabulated on Table
V
.


With 25 mm cover

Cross
-
Section

Plan View

With and without 25
mm cover

Cross
-
Section

Plan View


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Figure 6: Flexural Strength of Beams

[7]

The tested strength for Type 1 and Type 2 samp
les
seems to be slightly lower than the calculated values,
probably due to imperfection in sample preparations.
While for Type 3 samples, the tested strength is too low
compared to the calculated value, due to de
-
bonding of
CFRP from the concrete surface.

TABLE 5

F
LEXURAL
S
TRENGTH
:

C
ALCULATED AND
T
ESTED

Type


Calculated
Flexural
Strength
(MPa)

Average
Maximum
Applied
Load (kN)

Tested Flexural
Strength


Average (M偡)

1
-

Steel

11

20.2

9

2


CFRP
with cover

12

22.1

10

3


CFRP
w/out
cover

22

27.2

(de
-
bond)

12

This study also investigated the
failure pattern
of CFRP
reinforced concrete beam compared to the conventional
steel reinforced concrete beam.


Figure 7: Failure Pattern of Sample Type 1

[7]

Referring to Figure 7, crack line was observed
close to
the center of the beam where maximum bending moment
developed. The crack is due to yielding of the steel
reinforcement in the tension zone.

Figure 8 shows

the failure pattern of sample T
ype 2.
Crack line was observed
closer to the center of th
e beam
where maximum bending moment developed. The crack is
due to the strain in the CFRP reinforcement in the tension
zone.


Figure 8: Failure Pattern of Sample Type 2

[7]

It was

observed that the failure pattern
of samples Type
2 were

similar to the s
ample
s

Type 1.

Eventhough CFRP
do not yield the same way steel does
.


Figure 9: Failure Pattern of Sample Type 3

[7]

Flexural strength test on samples Type 3 show that it can
support higher load than Type 2. This is expected as
without cover the sample will developed higher resistance
to bending, due to the longer lever arm,
z
. However,
experimental result does not reac
h the value as per the
calculated strength expected. This is due to the CFRP de
-
bonded from the concrete surface. This can be observed on
Figure 9. Even though this type of sample has the highest
flexural strength, the failure pattern is the worst.

0
2
4
6
8
10
12
14
Type of Sample
Flexural Strength (MPa)

Steel Reinforced
Concrete
CFRP Reinforced
Concrete (With
Cover)
CFRP Reinforced
Concrete (Without
Cover)

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The

sample was totally split into 2 pieces. The failure of
this sample is mainly because the concrete and CFRP
experienced de
-
bonding, where the CFRP snap off the
concrete surface at the failure load.

IV.

C
ONCLUSION

The objective of this
research

which is to
inve
stigate

the
performance and behaviour of CFRP reinforced concrete
beams under flexural compared to the steel reinforced
concrete beams has been achieved. As expected, sample
Type 3 can support the highest load, even though the CFRP
reinforcement slips off. Howev
er, its failure pattern is
point for concern, where it just snaps suddenly and such
failure behaviour is not good for structures.

Samples Type 2 shows the crack pattern similar to

Type 1. Therefore, this type of sample, reinforced with
CFRP with cover, can be considered to be utilised where
ever steel reinforcement were not preferred. However, the
question of durability is still need to be ventured.

Overall, from this study some c
onclusions can be made:

1.

The use of CFRP as reinforcement for concrete
can perform intended function to strengthen the
concrete in tension zone.

2.

CFRP reinforced concrete is good at supporting
and resisting flexural loading.

3.

The bond between concrete and CFR
P played the
main role in strengthening the concrete. Thus,
CFRP with cover prevent de
-
bonding and better
for structures.

4.

The performance and behaviour of CFRP
reinforced concrete beam is comparable to the
conventional steel reinforced concrete beam.

Based

on the analysed result, some recommendations
were made for further study:

1.

To design the CFRP reinforced concrete beam
with tension and compression reinforcement. In
this study, the beam only design with tension
reinforcement.

2.

To study the durability of C
FRP reinforced
concrete due to extreme condition such as exposed
to
concrete’s alkaline environment, coastal
environment, or submerge in sea
-
water.


3.

To determine suitable safety factors for CFRP use
in reinforced concrete.

A
cknowledgement

S
pecial gratitude

to
the
Faculty of Engineering, National
Defence University of Malaysia for supporting this
research.

R
EFERENCES

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Carbon Fiber Reinforced
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[3 ]

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Comparative Study on
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