V-371

Japan Society of Civil Engineers 2022 Annual Meeting

Bond Strength Degradation due to Corrosion Cracking in Concrete Specimens without Stirrups
筑波大学
筑波大学
1.

○ Syll Amadou Sakhir
金久保 利之学生会員
正会員

INTRODUCTION
Rebar corrosion can deteriorate the bond between the rebar

specimen was set on the Teflon sheet and the loading plate on

and the concrete, directly affecting the serviceability andwhich the hole with the same diameter corresponding todurability of RC structures. The surface crack provides theconcrete cover to not restrict the lateral deformation ofclearest visual manifestation of reinforcement corrosion.

concrete. The D19 rebar is subjected to monotonic pull-out

Easily measurable, it can be a key parameter in solving thisloading at 0.5mm/min.

problem by directly correlating the bond deterioration of thesurface crack width. However, due to the ambiguity related tocorrosion, the bond deterioration remains unclear.
This study aims to cast deep sight on the bond strength of
concrete cracked by corrosion. To investigate the isolated
influence of cracks on bond strength degradation, specimens
cracked by electrical corrosion or by expansion agent-filled

Fig. 2 Loading and measurement of pull-out test

pipe (EAFP) are subjected to a pull-out test. The relationshipbetween the bond strength and surface crack width as aDirect
Current
Supply+variable is discussed.
2.

DirectCurrent
Supply+DirectCurrent
Supply+Filling of expansion agent

PULL-OUT SPECIMENS OVERVIEW
Copperplate

2.1 Pull-out specimen

The pull-out specimen is designed as shown in Fig.1. The

TestedRebar

dimensions of the specimen are 260×170×170 mm, and the3᧡NaClwater

D19 rebar is embedded at 47.5 mm from the specimen coverside. A short bond length of 4 times the diameter of the rebar
equal to 76 mm is chosen to focus on the local bond behavior.

(a)(b)
Fig. 3 Crack simulation: (a) electrical corrosion; (b) EAFP

Two rebars or EAFPs are set to 50 mm from the main tested

3.

100

170100EAFPconcrete. In
rebar to simulate the cracking of surrounding

CRACK SIMULATION METHOD

3.1 Crack simulation by electrical corrosion

D19 rebar(Tested bar)

addition, an unbonded part was set to avoid cone failure ofFig.3 (a) shows the setup for electrical corrosion. Theconcrete. The compressive and splitting strengths of thespecimen was immersed in a 3% NaCl solution and a direct

concrete were 22.4 MPa and 2.2 MPa, respectively.

current was separately impressed in the three rebars using

EAFP

47

Casting

50

76

47

Unit: mmdirection

EAFP orD19 rebar

M6coupler
260

100

applied to simulate cracking in a reasonable time.

D19 rebar(Tested bar)

47.5

Induced cracks

3.2 Crack simulation by EAFP
Loading
direction

3835 50 50 35
170

three different current supplies. An intensity of 0.3 A was100

Fig.3 (b) shows the setup for crack simulation by EAFP. It

Unbonded
170730Fig. 1 Specimen detail
2.2 Loading and measurements
Fig. 2 shows the test set-ups for the pull-out test. The

consists of inserting an aluminum pipe into the concrete andthen filling it with an expansion agent to simulate thevolumetric expansion of the bar due to corrosion. More details
can be found in a previous paper [1].

Keywords

Pull-out test, Bond strength, Induced crack width, Electrical corrosion, Expansion agent filled pipe

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JSCE 令和4年度土木学会全国大会第77回年次学術講演会© Japan Society of Civil Engineers- V-371 -V-371

Japan Society of Civil Engineers 2022 Annual Meeting

Mass loss (%)
5.2

7.2

10.2

Free end
tested rebar

Considered
induced crack(a)b)(c)Fig. 4 Crack simulation :(a) Rebar after corrosion (b) Electrical corrosion; (c) EAFP
indicator that can be measured on the outer concrete surface.

3.3 Crack simulation result

Fig. 4 (b) and (c) shows an example of crack patterns byHowever, more research is necessary to investigate theelectrical corrosion and EAFP, respectively. The side split

influence of other involved parameters such as concrete

type cracks took place in all specimens. The considered crackstrength, cover/diameter ratio, confinement effect, and so on,

width ranged from 0.15 to 1.10 mm in specimens cracked by

to develop a predictive model for general applicability.

corrosion was calculated for electrically corroded specimens.
An example of the change in the rebar surface can be seen inFig.4(a). Moreover, Fig.5 shows that the relationship between

121086420

the mass loss and induced crack width is unclear.
4.

BOND DEGRADATION IN CRACKED SPECIMEN
The residual bond strength ratio associated with theResidual bond strength ratioelectrical corrosion. After loading, the mass loss due to14

Mass loss on bond length (%)

EAFP and from 0.15 to 0.65 mm in specimens cracked by

0.2

0.4

0.6

Induced crack width (mm)0.8Fig. 5 Mass loss versus crackwidth
5. CONCLUSIONS

1EAFP
Electrical corrosion
Prediction model

0.8
0.6
0.4
0.2000.2

0.4

0.6

0.8

Induced crack width (mm)Fig. 6 Residual bond strength
ratio versus crack width

induced crack width is obtained by normalizing the bondTo investigate the bond degradation in cracked concrete

strength of the cracked specimens to that of the uncracked

without stirrup, pull-out bond test was conducted onreference specimen. Fig. 6 shows the relationship between thespecimens cracked by electrical corrosion or EAFP. The

residual bond strength ratio and the induced crack width. With

results showed that the deterioration trend is almost identicalincreasing induced crack width, residual bond decreases inin both induced crack method (electrical corrosion and EAFP).

most specimens. Also, the residual bond strength ratio can be

The reduction in bond strength can be related directly tocorrectly estimated by considering the single effect of

induced crack width while ignoring the ambiguity resultant

cracking,from corrosion (rebar shape change or rust accumulation).

ignoring

therebar

profilechange.

Thisdemonstrates that the bond mechanism through interlocking

ACKNOWLEDGEMENT

ribs is predominant with respect to frictional influence after

This study was supported by the JSPS KAKENHI Grant

cracking. Furthermore, it is confirmed that a direct

Number JP21H01472. The authors acknowledge Mr. Masato

relationship between interlock reduction and crack width canNagai for his contribution to this project.

ignore ambiguity related to the accumulation of corrosion

REFERENCES

products. The result also suggests that a crack-based approach

1. Syll, A.S., Aburano, T., and Kanakubo, T. (2021) Bondcan lead to more accurate results because corrosion-induced

strength degradation in concrete cracked by expansion

surface cracks represent the net amount of corrosion. In

agent filled pipes. Structural Concrete, 22 (5), 3156–3172.

addition, it is practical to have a direct and visible damage

JSCE 令和4年度土木学会全国大会第77回年次学術講演会© Japan Society of Civil Engineers- V-371 -1