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日本建築学会大会学術講演梗概集（北陸） 2019 年 9 月

Bond Behavior in Cracked Concrete by Expansion Agent Filled Pipes
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Regular Member
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Regular Member
Expansion agent

Table 1 Test result list
SpecimennameBiggest

M aximumSlippagecrack

Loadatwidth(kN)maximum(mm)

Remarksload(mm)

S-1-L1

0.15

7.985

0.088

New crack

S-2-L1
S-3-L1

0.1

8.386

0.146

Crack opening

0.2

6.959

0.218

New crack

S-4-L1S-2-L2
S-1-L2

0.35

5.793

0.144

0.5

6.142

0.198

1.06.994

0.890

New crack
New crack
New crack

S-1-L3

1.5

4.110

0.262

Crack opening

S-2-L3S-3-L3

3.0

2.123

0.804

Crack opening

2.0

3.767

0.572

Crack opening

S-4-L3
S-5-L3
S-6-L3

1.8

4.693

0.658

Crack opening

2.0

3.919

0.768

Crack opening

2.6

2.298

1.380

Crack opening

S-1-L1S-2-L1
S-3-L1
S-4-L1

6

S-1-L2S-2-L28

Load (kN)

8

64

42200

12Free-end slip(mm)03(a) Level 1 specimen

64200

12Free-end slip(mm)(c) Level 3 specimen
Fig. 1 Pull-out load vs. slip

Bond Behavior in Cracked Concrete by Expansion Agent Filled Pipes― 301 ―

12Free-end slip (mm)310S-1-L3
S-2-L3S-3-L3S-4-L3
S-5-L3
S-6-L380(b) Level 2 specimen

Maximum load (kN)

1. INTRODUCTION
A rough correlation between bond strength reduction
and surface crack width is suggested by fib Model
Code 2010 [1], also an overview the current research
indicates that existing studies has achieved a primaryknowledge regarding the potential correlation between
bond and the surface crack width. However, there still a
research gap in this respect.
In our previous works [2], concrete cracked byexpansion agent filled pipes in bond test specimens has
been presented. In this paper, those specimens are
subjected to pull-out test and a relationship between themaximum pull-out load of bar and surface crack width
as a variable is discussed.
2. PULL-OUT TEST RESULT
Test results of pull-out tests are shown in Table 1. All
specimens failed by splitting of concrete. A group ofspecimens failed by newly generated splitting crack
despite existing longitudinal crack due to corrosion andother specimens failed by widening of existing crack
induced with the expansion agent. The pull-out load
versus free end slippage relationships are shown in Fig.
1.The maximum pull-out load versus crack width
relationship is shown in Fig. 2. It can be seen that themaximum load decreases as the crack width increases.
The maximum pull-out load is normalized by
calculated pull-out splitting strength reported inprevious study [3] as non-corroded specimen using
following equation:
τb,max = 0.601⋅σt ⋅ (ru/db ) ⋅ cotα
Where, τb,max : bond splitting strength, σt:splitting tensile strength of concrete, ru:C+d b/2,d b: diameter of pipe (19mm), C: thickness ofcover concrete, α :angle between longitudinal axis
and splitting force (=34 degree).
To calculate the pull-out splitting strength, splitting
surface in the entire embedded bar length (82mm) is
assumed.

Load (kN)

Rebar corrosion
Bond test

Load (kN)Concrete crack
Bond strength○Amadou Sakhir Syll *Togo Aburano *Toshiyuki Kanakubo **Juan Jose Castro ***38642012

Crack width (mm)3Fig. 2 Max load vs. crack width

0.8
0.6
0.4
0.2
023Fig. 3 Result in comparison with M odel Code 2010

1R2
0.79
0.83
0.90

Present study
Prediction model

0.8
0.6
0.4
0.2

4. CONCLUSIONS
It is clarified that the maximum pull-out load reduces
exponentially as surface crack width caused by thecorrosion of rebar increases. A simple formula to predict thebond degradation is proposed by using the surface crack
width as a variable. More research is necessary toinvestigate the influence of other involved parameters (e.g.
cover/diameter ratio, confinement, bar profile) to develop a
predictive model for general applicability.
ACKNOWLEDGEMENT
This study was supported by the JSPS KAKENHI Grant
Number 17K18917.
REFERENCES [1] fib Model Code 2010, Vol.1.
International Federation for Structural Concrete, Lausanne,
Switzerland.
[2] Kanakubo, T., Syll, A. S., Aburano T., Castro, J. J.,
Concrete Cracks by Expansion Agent Filled Pipes in Bond
Test Specimens, Summaries of Technical Papers of Annual
Meeting, Architectural Institute of Japan, 2019.9[3] Yasojima, A., Kanakubo, T., Bond Splitting Strength ofRC Members Based on Local Bond Stress and SlipBehavior, 11th International Conference on Fracture,
No.4486, 2005 .

1

Crack width (mm)Table 2 Regression analysis results
Analysis
EquationsLinear-0.28 Wcr + 1
Logarithmic-0.17ln(Wcr) + 0.54
Exponential
e-0.46Wcr

Normalized loadeExperimental values
Model Code 2010: upper limit
Model Code 2010: lower limit

1Normalised load

3. BOND STRENGTH DEGRADATION
In fib Model Code 2010[1], the reduction in bond strength
depending on the surface crack width was introduced. For acertain range of surface crack width, the possible variationof the pull-out load degradation can be predicted. In thisstudy the suggested relationship is compared with the test
results in Fig. 3. The prediction with Model Code 2010 is ingood agreement with Level 1 (crack width ≤ 0.5mm) andfor specimen with 2.6 and 3mm as crack width as an
extrapolation. However, for Level 2 (crack width 0.5mm to1.0mm) fib Model Code gives underestimation.
As can be seen from regression analysis results in Table 2
exponential equation gives the better correlation than linear
or logarithmic fitting. Therefore, the following equation canbe used for prediction of the maximum pull-out load:P(Wcr ) = P0 ⋅ -0.46Wcr
Where P(Wcr): Pull-out load; P0: Pull-out load of
specimen without crack; Wcr: Crack width.
Fig. 4 shows the experimental result and the prediction
model comparison. The calculated and experimental results
are compared in Table 3. The ratios of the experimental tocalculated values are close to one, which indicates that theconcrete crack width can potentially be a good indicator tocharacterize bond strength degradation.

01

23

Crack width (mm)Fig. 4 Result and prediction model
Table 3 Comparison of the calculated and experimental values
Specimen
nameBiggestExperimental

Calculated

crack

maximum

maximum

width(mm)

load
(kN)

load(kN)

S-1-L1S-2-L1

0.15
0.1

7.985
8.386

8.386
8.582

0.95
0.97

S-3-L1
S-4-L1S-2-L20.2
0.35
0.5

6.959
5.793
6.142

8.196
7.649
7.139

0.85
0.76
0.86

S-1-L2
S-1-L3S-2-L3

1.0
1.5
3.0

6.994
4.110
2.123

5.672
4.507
2.260

1.23
0.91
0.94

S-3-L3S-4-L3
S-5-L3

2.0
1.8
2.0

3.767
4.693
3.919

3.581
3.926
3.581

1.05
1.19
1.09

S-6-L3

2.6

2.298

2.717

0.84

* Master Program ,Dept. of Eng. Mechanics and Energy, University of Tsukuba** Prof., Dept. of Eng. Mechanics and Energy, University of Tsukuba, Ph.D.
*** Prof, Architecture and Building Engineering Program, University of the Ryukyus, Ph.D.

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Exp /Cal