V-612

Japan Society of Civil Engineers 2020 Annual Meeting

Bond Strength Degradation in Cracked Concrete by Expansion Agent Filled Pipes
筑波大学

1.

○Syll Amadou Sakhir

学生会員

INTRODUCTION
concrete.

学生会員 油野 登梧
正会員 金久保 利之

adopted to investigate the effect of cover on bond

Bond at the steel-concrete interface is a critical property ofreinforced

筑波大学
筑波大学

Rebar

corrosioncausesdeterioration. The bond length of 51.6mm was chosen tobond

avoid the rupture of the pipe by tensile force. Moreover,deterioration between rebar and concrete which directly

adhesive tape was used to make unbonded part to avoid cone

affects the durability of RC structures. Evidence suggests that

failure of concrete. Table 1 shows the mechanical properties

the surface crack width is among the most important factorsof concrete obtained from concrete cylinder test on the day offor solving this problem by directly correlating it to the bondfilling of expansion agent.

deterioration. In previous research [1] [2], the simulation of
the cracking of concrete due to corrosion of reinforcing bars
by using an expansion agent filled pipe (EAFP) was proposedas a novel method. Moreover, a pull-out test was carried out
to establish a simple formula for predicting the bondFig. 1 Aluminum pipe with rib

degradation with surface crack width as a variable. Despite
the importance of the induced crack width, there remains a
paucity of evidence on the influence of other parameters(concrete strength and cover).
In this paper, a concrete cracked by an EAFP in bond test
specimens has been designed with a smaller concrete cover.
Those specimens with different crack width are subjected toa pull-out test. This study sets out to investigate the influenceFig. 2 Specimen detailof the concrete cover on bond deterioration.
2.

Table 1 Concrete mechanical properties
Compressivestrength(MPa)28.2

PULL-OUT SPECIMENS OVERVIEW

2.1 Aluminum pipe with ribs

Fig. 1 shows an overview of a processed aluminum pipe

Young’smodulus(GPa)22.8

Splitting tensile
strength(MPa)2.17with ribs set according to JIS G 3112. An aluminum pipe with21.7 mm as outer diameter and 2.5mm thickness was used toimitate D19 rebar. The fundamental properties of thealuminum pipe and the expansion agent filled pipe have beenreported by authors [1].
2.2 Pull-out specimen

Pull-out specimen was designed as shown in Fig. 2.
Dimensions of the specimen are 260×260×82mm and theFig. 3 Loading and measurement in pull-out test
2.3 Loading and measurement

aluminum pipe with ribs was embedded at 28.5mm from theFig. 3 shows the test set-ups for pull-out test. The specimen

specimen side. A concrete cover as 28.5mm (1.5Db) have been

was set on the Teflon sheet and the loading plate on which theused in the previous study [2], here a 19mm (Db) cover washole with the same diameter corresponding to concrete coverKeywords

Rebar corrosion，Expansion agent，Crack width，Bond test.

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V-612

Japan Society of Civil Engineers 2020 Annual Meeting

to not restrict the lateral deformation of concrete. The pipe

may be the most important parameter when evaluating bondwas subjected to monotonic pull-out loading at a speed ofdeterioration.

0.5mm/min. The measurement items are pull-out load,
slippage of the pipe at the free end, and crack opening. . A π-

Table 2 Experimental result listSpecimen

Max. crackwidth (mm)

S-1
S-2
S-3
S-4
S-5
S-6

0.30
0.85
0.95
1.00
1.10
1.50

type displacement transducer was placed on the concrete
cover to measure the crack opening as shown in Fig.3.
3.

EXPERIMENTAL RESULTS AND DISCUSSIONS

3.1 Crack simulation by EAFPThe specimen was placed as the axial direction of the pipe
was set vertically, and expansion agent was filled from the topof the pipe. The details of the EAFP simulation method have

Failure mode

Crack opening
Crack opening
New crack
New crack
New crack
Crack opening

Past study (cover 28.5mm)
Present study(cover 19mm)

1

been reported by authors [1]. The results of the cracking

Max.
load(kN)
5.55
3.75
4.47
4.92
5.78
2.50

Normalized load

0.8

simulation and pull-out test are summarized in Table 2.
Initially, the influence of concrete cover on crack

0.6

propagation is insignificant, but later there exists a tendency

0.4

that the crack width increases at a faster rate for specimens
with a smaller concrete cover. This has contributed to the0.2

difficulty to obtain a crack width between 0.3mm and 0.85mm.

0Also, in some specimens with 19mm cover presented multiple

12

Crack width (mm)3cracks. These results are likely to be related to the fact that
Fig. 4 Max. load vs. crack width

larger concrete cover offers more resistance to the formation
4.

of cracks due to the volumetric expansion of rebar.

CONCLUSIONS
The maximum pull-out load reduces exponentially as

3.2 Influence of the concrete cover on bond degradation

All specimens failed by splitting of concrete in pull-out

surface crack width increases even in the case of smallloading. A group of specimens failed by newly generated

concrete cover. The concrete cover has no significant

splitting crack despite existing longitudinal crack due toinfluence on the bond deterioration due to cracking of theEAFP and other specimens failed by the widening of existing

cover. However, it plays a fundamental role in limiting thecrack.

cracking due to corrosion.

The results, as shown in Table 2, indicate that theACKNOWLEDGEMENT

maximum load decreases exponentially as the crack widthThis study was supported by the JSPS KAKENHI Grantincreases when new crack did not occur at failure.

Number 17K18917.

To better observe the deterioration of the bond, theREFERENCES

maximum pull-out load is normalized by calculated bond

[1] Kanakubo, T., et al., Concrete Cracks by Expansion Agent

splitting strength reported in previous study [3].

Filled Pipes in Bond Test Specimens, Summaries of TechnicalFig. 4 shows the normalized maximum pull-out load versus

Papers of Annual Meeting, AIJ, 2019.9

crack width relationship. It can be seen that the concrete cover[2] Syll, A.S., et al., Bond Behavior in Cracked Concrete byshows no significant influence on the relationship between

Expansion Agent Filled Pipes, Summaries of Technicalbond deterioration and the surface crack width. This result

Papers of Annual Meeting, AIJ 2019.9

may be explained by the fact that once cracking develops,[3] Yasojima, A., Kanakubo, T., Bond Splitting Strength ofappreciable loss of bond strength may be due to the lack of

RC Members Based on Local Bond Stress and Slip Behavior,confinement. The opening of cracks during the loading

11th International Conference on Fracture, No.4486, 2005

severely affects the confinement. Therefore, the crack width© Japan Society of Civil Engineers- V-612 -