thThe 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China

BOND BEHABIOR BETWEEN DEFORMED ARAMID FIBER-REINFORCED
PLASTIC REINFORCEMENT AND CONCRETE
1

2

Yuji NAKAYAMA , Hiroshi NAKAI and Toshiyuki KANAKUBO

3

1

Graduate Student, Graduate School of Systems and Information Engineering
University of Tsukuba, Ibaraki, Japan
2
Maeda Kosen Co., Ltd. , Tokyo, Japan
3
Associate Professor, Graduate School of Systems and Information Engineering
University of Tsukuba, Ibaraki, Japan, Dr. E
Email: nakayama@rcs.kz.tsukuba.ac.jp, nakai@mdk.co.jp, kanakubo@kz.tsukuba.ac.jp
ABSTRACT :Recent years, Fiber-Reinforced Plastic (FRP) reinforcement has been utilized for concrete structures expecting
its high durability to corrosion and insulation property. In this study, pullout loading test and tensile loading test
is performed to investigate the bond behavior between AFRP reinforcement and concrete. The test parameters
are cross sectional size of concrete block, elastic modulus and nominal diameter of AFRP reinforcement. The test
results of pullout loading test show that bond behavior is influenced by surface figure of AFRP reinforcement.
The results of tensile loading test show that crack width depends on elastic modulus. Tension stiffening behaviorof AFRP reinforcement is almost same in spite of the type of AFRP reinforcement.
KEYWORDS:

Pullout loading test, tensile loading test, bond stress-slippage relationship,
local bond behavior, tension stiffening behavior, crack width

1. INTRODUCTION
Generally, steel reinforcing bar is used as reinforcement of concrete structures. However, it is a serious problem
that corrosion of steel reinforcing bar occurs due to cracking. Moreover, since steel reinforcing bar is becamemagnetized, it is difficult to use in medical facility or semiconductor factory. Therefore, in recent years,
Fiber-Reinforced Plastic (FRP) reinforcement has been utilized for concrete structures expecting its highdurability to corrosion and insulation property. Typical types of FRP are Carbon Fiber- Reinforced Plastic(CFRP), Glass Fiber-Reinforced Plastic (GFRP) and Aramid Fiber-Reinforced Plastic (AFRP). Because CFRP
are became magnetized, GFRP generally has a problem in alkali resistance. AFRP has been expected to be
applied to concrete structures. Reinforcement of concrete structures is expected to bear the tensile force andgives enough capacity and ductility to concrete members. It is necessary to have a good unification between
reinforcement and concrete to lead these objectives. It is well known that the unification of reinforcement andconcrete is depended on bond characteristics of the local part of reinforcement and concrete.
In this study, pullout loading test is performed to evaluate the bond behavior of AFRP reinforcement. The test
parameters are cross sectional size of concrete block, elastic modulus and nominal diameter of AFRP
reinforcement. Further, tensile loading test is performed by using specimens with length of 1680mm to inquire
the influence of unification between reinforcement and concrete.
2. PULLOUT LOADING TEST
2.1. Specimen
An example of specimen is shown in Figure 1.The cross section of a specimen is 80mm x 80mm, 100mm x
100mm and 120mm x 120mm. Height is 100mm. Ordinary steel reinforcing bar (D10) or AFRP reinforcement

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The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China

688

is used in the center of concrete block. The nominal diameter of AFRP reinforcement isφ6.0, 7.0 and 13mm.
The coupler is used at the loading end of reinforcement to grip reinforcement by the chuck of testing machine.
Bond length is 4 times of the reinforcement diameter. List of specimen is shown in Table 1. The test parameters
are cross section of concrete block (80mm x 80mm, 100mm x 100mm and 120mm x 120mm), type ofreinforcement (TE, TO and reinforcing bar) and nominal diameter (6.0mm, 7.0mm, 13mm and D10).

100

38 24 38

12

80

Test Region

800

Unbond80

Cross Section View

Elevational View

Unit:mmFigure 1 Example of specimen
Table 1 List of specimen
Cross
Cross
Cross
Specimen
Type of Diameter
Type of Diameter
Type of Diameter
No.
No. Specimen name section
No. Specimen name section
sectionnamereinforcement (mm)reinforcement (mm)reinforcement (mm)
(mm)
(mm)
(mm)
1 P-80TE-F6.0
φ6.0 11 P-100TE-F6.0
φ6.0 21 P-120TE-F6
φ6.0
2 P-80TE-F7.4
φ7.4 12 P-100TE-F7.4
φ7.4 22 P-120TE-F7.4
φ7.4
TE
TE
TE
3 P-80TE-F13-1
13 P-100TE-F13-1
23 P-120TE-F13-1
φ13 14 P-100TE-F13-2
φ13 24 P-120TE-F13-2
φ13
4 P-80TE-F13-2
80
100
120
5 P-80TE-F13-3
15 P-100TE-F13-3
25 P-120TE-F13-3
XXX
6 P-80TO-F6.0 80
φ6.0 16 P-100TO-F6.0 100
φ6.0 26 P-120TO-F6.0 120
φ6.0
TO
TO
TO
7 P-80TO-F7.4
φ7.4 17 P-100TO-F7.4
φ7.4 27 P-120TO-F7.4
φ7.4
8 P-80SD-D10-1
18 P-100SD-D10-1
28 P-120SD-D10-1
Reinforcing
Reinforcing
Reinforcing
D10 19 P-100SD-D10-2
D10 29 P-120SD-D10-2
D10
9 P-80SD-D10-2
bar
bar
bar
10 P-80SD-D10-3
20 P-100SD-D10-3
30 P-120SD-D10-3

2.2 Employed Material
The shape of AFRP reinforcement is shown in Figure 2. Surface figure of TE and TO is deformed rod andTE-F13 is double spiral structure. The mechanical properties of concrete are shown in Table 2. The tensile test
result for steel reinforcing bar is shown in Table 3. Table 4 shows the characteristic properties of AFRP
reinforcement.
・TE-F13
・SD-D10・TO-F7.0
・TO-F6.0
Figure 2 Shape of AFRP reinforcement
Table 2 Mechanical properties of concreteCompressive strength(MPa)28.6

Elastic modulus(GPa)26.8

Tensile splitting strength (MPa)
2.44

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The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
Table 3 Tensile test result for steel reinforcing bar
Tension strength(MPa)931

Yield strength(MPa)752

Elastic modulus (GPa)197

Table 4 Characteristic properties of AFRP reinforcement
Diameter(mm)Effective cross section area(mm2)

φ6.0

6.43

28.3

φ7.4
φ13
φ6.0
φ7.4

7.88
13.1
6.43
7.88

42.4
133
28.3
42.4

Type
TE

TO

Elastic modulus (GPa)
53.0

90.0

2.3 Method of Loading
The method of loading is shown in Figure 3. The specimen is set on steel plate with a hole which diameter is thehalf of sectional size of specimens. The specimen is subjected to monotonic loading for pulling out thereinforcement. Teflon sheet is inserted between specimen and the steel plate to not restrict lateral displacementof concrete block. Measurement items are tensile load and reinforcement slippage at free end.

Figure 3 Method of pullout loading test
2.4. Test Results
2.4.1 Failure pattern
The damage of AFRP reinforcement after loading is shown in Figure 4. No.5, 6, 7, 16 specimens failed by
splitting of concrete. Slipping out of reinforcement was observed in other specimens. In these specimens,
surface fibers which forms deformed shape of AFRP reinforcement were chipped off due to friction withconcrete.

Figure4 Damage of AFRP reinforcement after loadingth

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
2.4.2 Bond Stress and slippage
The test results are summarized in Table 5. Figure5 shows bond stress-loaded end slippage relationship. Bondstress is calculated by Eq2.1. Assuming that bond stress distribution in the bond section is constant, loaded end
slippage is calculated by adding elongation of reinforcement to the free end slippage obtained by LVDT.

τb =

τb
ψ

P
ψ × lb

(2.1)：bond stress(N/mm2)P：tensile load(N)：reinforcement perimeter(mm)lb：bond length(mm)The maximum bond stress ranges from 11.47 to 22.36 N/mm2. In any case of cross section of a specimen, thesteel reinforcing bar (D10) showed the largest value. Bond stress increases again after the maximum bond stress.
It is considered that concrete and ribs of reinforcement is engaged again. Comparing TE and TO of φ6.0
specimen at each cross section of concrete, TO shows a gentle decrement after the maximum bond stress. On theother hand, TE shows large dropping of bond stress. This is considered that rapid failure occurs at matrix of
AFRP surface.
Table 5 Pullout loading test results

P-80TE-F6.0
P-80TO-F6.0
P-80TE-F7.4
P-80TO-F7.4
P-80TE-F13-1
P-80TE-F13-2
P-80TE-F13-3
P-80SD-D10-1
P-80SD-D10-2
P-80SD-D10-3

12.05
16.89
12.83
12.93
11.88
12.08
12.30
22.02
19.88
22.36

P-100TE-F6.0
P-100TO-F6.0
P-100TE-F7.4
P-100TO-F7.4
P-100TE-F13-1
P-100TE-F13-2
P-100TE-F13-3
P-100SD-D10-1
P-100SD-D10-2
P-100SD-D10-3

11.47
15.90
15.20
14.78
11.65
14.12
12.54
17.01
19.46
18.90

Slippageatloaded end
(mm)
0.477
1.647
1.696
1.683
2.336
1.298
1.702
0.534
0.628
0.902

100×100 Specimen
TE-F6
TO-F6
TE-F7.4
TO-F7.4
TE-F13-1
TE-F13-2
TE-F13-3
SD-D10-1
SD-D10-2
SD-D10-3

20

10

0

Bond stress(N/mm2)

Bond stress（N/mm2）80×80 Specimen
TE-F6.0
TO-F6.0
TE-F7.4
TO-F7.4
TE-F13-1
TE-F13-2
TE-F13-3
SD-D10-1
SD-D10-2
SD-D10-320Specimen name

10

0

2

4

6

8

Loaded end slippage （mm）

100Specimen nameBond stress(N/mm2)P-120TE-F6.0
P-120TO-F6.0
P-120TE-F7.4
P-120TO-F7.4
P-120TE-F13-1
P-120TE-F13-2
P-120TE-F13-3
P-120SD-D10-1
P-120SD-D10-2
P-120SD-D10-3

12.11
15.12
15.40
12.55
13.62
16.04
14.15
20.02
20.48
20.43

20

10

0

2
4
6
8
Loaded end slippage （mm）

100Slippageatloaded end
(mm)
0.488
1.481
1.867
1.846
1.702
2.392
2.198
0.625
0.589
0.638

120×120 Specimen
TE-F6
TO-F6
TE-F7.4
TO-F7.4
TE-F13-1
TE-F13-2
TE-F13-3
SD-D10-1
SD-D10-2
SD-D10-3

Bond stress（N/mm2）

Bond stress(N/mm2)

Bond stress（N/mm2）

Specimen name

Slippageatloaded end
(mm)
0.341
1.389
1.773
1.812
1.109
0.897
1.279
0.620
0.604
0.630

0

2
4
6
8
Loaded end slippage （mm）

10

Figure 5 Bond stress versus loaded end slippage curve
2.4.3 Maximum bond stress and fracture energy
Comparisons of maximum bond stress in each parameter are shown in Figure 6. The clear relation between
maximum bond stress and parameters can not be recognized.
Fracture energy-slippage relationship is shown in Figure 7. Fracture energy is calculated as an area of bondstress-slippage curve until focused slippage. The results of specimen No.3, 4 and 5 are not included because of
splitting failure. In any case of cross section of a specimen, the steel reinforcing bar (D10) shows the largest
fracture energy even if the slippage is small. On the other hand, the specimen of TE-F6.0’s fracture energy issmall in totally. In other reinforcement, the significant difference by types of reinforcement or cross section ofth

The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
concrete was not observed.

20
18
16
14
12

8000
12000
Cross section area of concrete(mm 2)
TE-F6.0、
TE-F7.4、
TE-F13、TO-F6.0
TO-F7.4
SD-D10

22
20
18
16
14
12
6
8
10
12
14
Reinforcement diameter(mm)80-TE,
100-TE,
120-TE,

80-TO,
100-TO,
120-TO,

Maximum bond stress(N/mm2)

22

Maximum bond stress(N/mm2)

Maximum bond stress(N/mm2)

From the test results, in reinforcement of AFRP, the maximum bond stress is not affected by cross section of
concrete, diameter of reinforcement and elastic modulus largely if rapid failure dose not occur at matrix of
AFRP surface. Therefore, it is considered that the local maximum bond stress obtained by pullout loading test isdepended on the bearing action with surface figure of reinforcement between concrete.
22
20
18
16
14
12
50

100
150
200
Elastic modulus(GPa)80-F6.0,
80-D10,100-F13,120-F7.4,

80-SD,
100-SD,
120-SD

80-F7.4,
100-F6.0,
100-D10,120-F13,80-F13,100-F7.4
120-F6.0
120-D10(a) cross section area of concrete(b) reinforcement diameter(c) elastic modulus
Figure 6 Comparison of maximum bond stress with each parameter

60
40
20
0
0

80×80
2

4

TE-F6.0
TE-F7.4
TE-F13
TO-F6.0
TO-F7.4
SD-D10100

6Slippage(mm)

80
60
40
20

100×100

0
0

8

2

4

TE-F6.0
TE-F7.4
TE-F13
TO-F6.0
TO-7.4
SD-D10100

Ftracture energy(N/mm)

80

TE-F6.0
TO-F6.0
TE-F7.4
TO-F7.4
SD-D10Fracture energy(N/mm)

Fracture energy(N/mm)

100

6Slippage(mm)

80
60
40
20
0
0

8

120×120
2

4

6

Slippage(mm)8Figure 7 Fracture energy-slippage relationship
3. TENSILE LOADING TEST
3.1. Specimen
An example of specimen is shown in Figure 8. The cross section of a specimen is 80mm x 80mm, 100mm x
100mm and 120mm x 120mm. Length is 1680mm and steel reinforcing bar (D10) or AFRP reinforcement isused in the center of concrete block. The nominal diameter of AFRP reinforcement isφ6.0, 7.0 and 13. The
couplers in both ends of reinforcement are set to grip reinforcement by the chuck of testing machine. As shownin Figure 8, the sectional number is defined as A to H with intervals of 200mm from the position of 40mm ofspecimen ends. List of specimen is shown in Table 6. The same concrete and reinforcements are utilized withpullout loading test.
60 40 200

200

200

200

1680
200

200

200

200 40 60

A

B

C

D

E

F

G

H

Unit：mmFigure 8 Example of specimen

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The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
Table 6 List of specimen
No.

Specimen name

31
32
33
34
35

T-80TE-F6.0
T-80TE-F7.4
T-80TE-F13
T-80TO-F6.0
T-80TO-F7.4

36

T-80SD-D10

37
38

T-100TE-F6.0
T-100TE-F7.4

39

T-100TE-F13

Cross
section(mm)

Type ofreinforcement

pg*
(%)

No.

φ6.0
φ7.4
φ13
φ6.0
φ7.4

0.44
0.66
2.08
0.44
0.66

43
44
45
46
47

T-120TE-F6.0
T-120TE-F7.4
T-120TE-F13
T-120TO-F6.0 120x120
T-120TO-F7.4

D10

1.11

48

T-120SD-D10

φ6.0
φ7.4

0.28
0.42

40
41

φ13

1.33

42

T-100TO-F6.0
T-100TO-F7.4 100x100
T-100SD-D10

TE
80x80

TO
Reinforcing
bar

100x100

Cross
section(mm)

Diameter(mm)

TE

SpecimennameDiameter
(mm)

pg*
(%)

φ6.0
φ7.4
φ13
φ6.0
φ7.4

0.20
0.29
0.92
0.20
0.29

Reinforcing
bar

D10

0.50

TO

φ6.0
φ7.4

0.28
0.42

Reinforcing
bar

D10

1.33

Type ofreinforcement
TE
TO* Sectional area of reinforcement divided by sectional area of concrete
3.2 Method of Loading
The monotonic tensile loading are applied. Measurement items are load, crack width by LVDTs which areassembled both sides of specimen and whole deformation of specimen by LVDTs. The positions of LVDTs areshown in Figure 9. The tensile loads at the crack occurring and crack patterns are also recorded.
East

40 250

200
200

200
200

1680
200 100 200200

250 40UpsideDownside
West
North

80×80×1280 Specimen

UpsideWhole deformation

DownsideSouth

Figure9 Position of LVDT
3.3 Test Results
3.3.1 Failure progress
Tensile loading test results are shown in table 7. The failure progress was categorized into two patterns. The firstone is that a crack around the bottom end of specimen took place and then cracks around the center of thespecimen with almost equal interval took place. The second one is that a crack around the bottom end took place
as same as first one then the next crack occurs around the opposite end of specimen, and cracks by turns by theupper and lower positions toward the center of specimen. Finally, both crack patterns reached nearly same ones
from the center. The final crack number decreases with increases of sectional area of specimen. It is consideredthat initial crack loading of concrete increases with increase the cross section of concrete. Therefore, the numberof crack decrease. In the case of the specimen at the same cross section area, the number of crack tends toincrease and crack spacing is smaller when reinforcement diameter is larger. However, the specimen with steel
reinforcing bar has difference tendency. Even if the diameter is 10mm which is smaller than φ13, the numberof crack is same or bigger than φ13 specimen.

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The 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, China
Table 7 Tensile loading test results
Number Crack
SpecimenNo.
ofspacing
name
crack
(mm)
31
80TE-F68187
32 80TO-F6
8187
33 80TE-F7.4
14112
34 80TO-F7.4
7210
35 80TE-F13
11140
36 80SD-D10
22
73.0

Initial
crack
(kN)
17.52
14.81
17.23
17.22
14.32
12.53

No.
37
38
39
40
41
42

Number Crackof
spacing
crack(mm)100TE-F6
4
336
100TO-F6
4
336
100TE-F7.4
7210100TO-F7.4
6240
100TE-F1313120100SD-D10
14
112
Specimen
nameInitial
crack
(kN)
23.13
19.23
21.11
23.07
25.79
18.09

No.
43
44
45
46
47
48

Number Crackof
spacing
crack(mm)
120TE-F6
1
840
120TO-F6 nothing－
120TE-F7.4
4336
120TO-F7.4
3
420
120TE-F1310153120SD-D104
336
Specimen
nameInitial
crack
(kN)
28.37
－
34.76
34.46
35.96
40.21

3.3.2 Tension stiffening behavior
Tensile loading and whole deformation relationship is shown in Figure 10. In the case of AFRP reinforcement,
whole deformation is calculated by using Eq.3.1 in order to subtract the elongation of reinforcement at theregion from concrete edge and the coupler. For steel reinforcing specimen, elongation of this region is evaluatedby the tension test results of bare reinforcement considering elastic-plastic behavior.

δw =δ1，δ 2 ：deformation by LVDT (mm),ab ：sectional area of reinforcement(mm2),

δ1 + δ 2
2−

P ⋅120ab ⋅ E b(3.1)

P ：tensile load(kN)Eb ：elastic modulus of reinforcement (GPa)30

TE-F13

20

40
80×80
100×100
120×120
Reinforcement

200TE-F13
80×80
100×100
120×12001020Whole deformation(mm)

10
0

-10
0 10 20 30 40 50
Whole deformation(mm)Figure 10 Tensile loading-whole deformation curve

40
Pinc (kN)60

Pinc (kN)

Tensile load(kN)

The tension stiffening behavior was recognized in all specimens. The pseudo tensile force carried by concrete(Pinc) is defined as the tensile load which is calculated by subtracting the load carried by bare reinforcementfrom the obtained tensile load under the same whole deformation. Pinc-whole deformation relationships is shownin Figure 11. For all specimens, Pinc increases with decreases of the reinforcement ratio. It is considered thatratio of tensile load carried by concrete increases by increase of the sectional area of concrete. Comparing with
TE-F13 and SD-D10 in a 120mm x 120mm specimen, Pinc of SD-D10 is larger than TE-F13 in the samedeformation. Considering the local bond behavior of TE-F13 and SD-D10, the fracture energy of SD-D10 islarger than TE-F13 in small slippage. It is considered that these differences of local bond behavior affects
tension stiffening behavior.

30

120×120
TE-F13
SD-D10

20
10
0

2
4
6
8
10
Whole deformation(mm)Figure 11 Pinc-whole deformation curve

3.3.3Crack width
Tensile load-crack width relationship is shown in Figure 12. In this figure, the crack width measured in B
section is plotted and the curve shows until second crack occurring in the same measurement section. The
remarkable difference is not observed by the difference of cross section of specimen. The test result of thepullout loading test that the local bond behavior is not influenced by cross section of specimen holds thisphenomenon. The crack width of SD-D10 and TE-F13 at the same load is small. The clear difference is notobserved in other specimens. It is considered that large elastic modulus, and good local bond behavior of
SD-D10 lead small crack width. In the case of TE-F13, it is considered that a sectional area of reinforcement is

thThe 14 World Conference on Earthquake Engineering
October 12-17, 2008, Beijing, Chinalarger so that crack width is controlled. The difference in other specimen’s is not so large even if the elastic
modulus is different.

40
TO-F6
TO-F74TE-F13
SD-D1020
0

1
2Crack width(mm)3

60 100-δB
40

TO-F6.0
TE-F7.4
TO-F7.4
TE-F13
SD-D10Tensile load(kN)

60 80-δB

Tensile load(kN)Tensile load(kN)

Reinforcement strain-crack width relationship is shown in Figure 13. It is considered that crack width at thesame reinforcement strain is almost equal when reinforcement shows similar local bond behavior.

20
0

1
2
Crack width(mm)60 120-δB
40
TE-F7.4
TO-F7.4
TE-F13
SD-D10

20

3

0

1
2
Crack width(mm)

3

1

0

80-δB

TO-F6.0
TO-F7.4
TE-F13
SD-D10

1
2
Crack width(mm)

3

2

1

0

100-δB

TO-F6.0
TE-F7.4
TO-F7.4
TE-F13
SD-D10

1
2
Crack width(mm)3Reinforcement strain(%)

2

Reinforcement strain(%)

Reinforcement strain(%)

Figure 12 Tensile load- crack width relationship2120-δB

10

TE-F7.4
TO-F7.4
TE-F13
SD-D10

1
2
Crack width(mm)3Figure 13 Reinforcement strain-crack width relationship
4. CONCLUSIONS
From the test results, the following are summarized.
(1) The local maximum bond stress obtained by pullout loading test is depends on the bearing action withsurface figure of reinforcement between concrete.
(2) The tension stiffening behavior is recognized in the tensile loading test. The behavior is influenced by the
local bond behavior of reinforcement.
(3) Crack width at the same reinforcement strain is almost equal when reinforcement has similar local bondbehavior.