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日本建築学会大会学術講演梗概集（関東） 2020 年 9 月

Bond Behavior in Cracked Concrete by Expansion Agent Filled Pipes
Part 2: Bond strength degradation in side-split type specimens
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Concrete crack
Bond strength

Rebar corrosion
Bond test○Amadou Sakhir Syll *Togo Aburano *Toshiyuki Kanakubo **Juan Jose Castro ***Crack widthSplitting

INTRODUCTION
The fib Model Code 2010 [1] and the Japan Concrete
Institute in its concrete structure rehabilitation researchcommittee report 1998 [2] gave an evaluation of the bonddegradation as a function of crack width due to corrosion.
Also, an overview of the current research indicates thatexisting studies have achieved only primary knowledge
regarding the potential correlation between bond and thesurface crack width. However, there still a research gap inthis respect.
In Part 1, concrete cracked by expansion agent filledpipes in bond test specimens has been presented. In thispaper, those specimens are subjected to a pull-out test anda relationship between the maximum pull-out load ofrebar 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 experienced failure due to splitting. The
specimens without crack failed by single splitting due tothe limited cover thickness. In the crack induced
specimens, most of them failed by side-splitting due to theopening of the pre-existent crack. In side-splitting failure,some specimens presented newly side crack (N1 with one
new crack, N2 with two new cracks).
The pull-out load versus slippage relationships areshown in Fig. 1. From these plots, it is apparent that thestiffness did not decrease in cracked specimens. As thepull-out load increase, the slip seems to increase in analmost linear way. However, as soon as the bond strength
is reached, a steeper descending curve is measured for
uncracked specimens when compared to cracked ones.
Hence a more sudden bond degradation is noted due to theoccurrence of new cracks or the widening of the induced
cracks.
Fig. 2 shows the maximum pull-out load versus crack
width relationship. It can be seen that the maximum loaddecreases as the crack width increases. As expected, there
is a significant correlation between residual bond strength
1.

Table 1 Test result
Specimen
nameS.18.NC.1

Crackwidth(mm)0Load (kN)

At Maximum load
Slip (mm)Remarks

50.51

0.444

Single split

S.18.NC.2

046.36

0.962

Single split

S.18.C.0.08

0.08

31.36

0.508

Side split N1

S.18.C.0.2

0.20

22.87

0.352

Side split N2

S.18.C.0.6

0.60

17.220.832

Side split O

S.18.C.0.65

0.65

25.10

0.121

Side split N1

S.18.C.0.750.75

4.191.102

Side split O

S.18.C.0.85

0.85

4.29

0.676

Side split O

S.30.NC.1

042.970.592

Single split

S.30.NC.2

061.730.166

Single split

S.30.C.0.15

0.15

49.46

0.348

Single split

S.30.C.0.25

0.25

31.25

0.308

Single split

S.30.C.0.35

0.35

26.86

0.468

Side split O

S.30.C.0.50

0.50

33.20

0.610

Side split O

S.30.C.0.60

0.60

19.77

0.488

Side split N1

S.30.C.0.85

0.85

12.53

0.724

Side split O

Fig. 1 Pull-out load vs. slippage

Fig. 2 Max load vs crack width
Bond Behavior in Cracked Concrete by Expansion Agent Filled Pipes
Part 2: Bond strength degradation in side-split type specimens― 39 ―

and induced crack width.
The decrease of the pull-out load is more severe in 18MPa
than in 30 MPa specimens. A possible explanation for this might
be that the 30MPa concrete has a stiffer response than the18MPa concrete in both compression and tension therefore thecrack opening may be delayed.
3. BOND STRENGTH DEGRADATION
The maximum pull-out load is normalized by the pull-out
splitting strength of uncracked specimens. In Fig. 3, our test
results are compared to the fib Model Code and the formula
proposed by the Japan Concrete Institute.
The prediction with fib Model Code 2010 shows good
agreement when the induced crack width is around 0.3mm.
However, for other specimens, our results are overestimated orunderestimated for 18 MPa specimens.
The prediction with Japan Concrete Institute 1998 is in good
agreement with some 18MPa specimens. However, our results
are overestimated for 30 MPa specimens.
An exponential fitting curve gives a better correlation thanlinear or logarithmic fitting. Therefore, the following equation
can be used for prediction of the maximum pull-out load:

18MPa specimens
30MPa specimens
Model Code 2010: upper limit
Model Code 2010: lower limit
JCI 1998

Normalized load

1
0.8
0.6
0.4
0.2
00.2

0.4

0.6

0.8

Crack width (mm)1Fig. 3 Results in comparison with literature

1

Present study 18MPa
Present study 30MPa
Prediction model

Normalized load

0.8
0.6
0.4
0.20e0.2

0.4

0.6

0.8

Crack width (mm)1Fig. 4 Result and prediction modelP(Wcr) = P0 ⋅ -0.46Wcr
Where P(Wcr): Pull-out load; P0: Pull-out load of a
specimen without crack; Wcr: Crack width.
Fig. 4 shows the experimental result and the prediction model.
The concrete crack width can potentially be a good indicator tocharacterize bond strength degradation.
In our previous study [3], a formula expressing thedeterioration of the bond obtained with single splitting type (Fig.
5) specimens has been proposed. In Fig.6, that model iscompared to the one obtained in this paper. It can be seen thatthe deterioration of the bond is more severe in a side-splitting
specimen than in a single-splitting specimen. This result may beexplained by the fact that the number and position of induced
crack can heavily affect the deterioration of the bond.

Single-split

Side-split

Fig. 5 Splitting mode
Side-splitting
Single-splitting

1
Normalized load

0.8
0.6
0.4
0.2

4. CONCLUSIONSThe test is carried out on a side split type specimen. Insummary, these results show that there was a significant
exponential correlation between pull-out strength and surfacecrack width and the decrease of the pull-out load is more severein 18MPa than in 30 MPa specimens. The deterioration of thebond due to the induced cracks was more severe in a sidesplitting specimen than in a single-splitting specimen.
ACKNOWLEDGEMENT
This study was supported by the JSPS KAKENHI Grant
Number 17K18917.

012

Crack width (mm)3Fig. 6 Bond deterioration
REFERENCES [1] fib Model Code 2010, Vol.1. International
Federation for Structural Concrete, Lausanne, Switzerland.
[2] 日本コンクリート工学協会，コンクリート構造物のリ
ハビリテーション研究委員会報告書，1998[3] Syll, A. S., Kanakubo, T., Aburano T., Castro, J. J., BondBehavior in Cracked Concrete by Expansion Agent Filled Pipes,
Summaries of Technical Papers of Annual Meeting, AIJ 2019.9* 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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