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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

Concrete Cracks by Expansion Agent Filled Pipes in Bond Test Specimens
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Concrete crack
Expansion agent

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

1. INTRODUCTION
Rebar corrosion basically causes bond deterioration between
rebar and concrete which directly affects the serviceability anddurability of RC structures. Indeed, the surface crack width
provides the clearest visual manifes-tation of reinforcementcorrosion. Easily measurable, it can be a key parameter to solve
this problem by directly correlating the bond deterioration of thesurface crack width. Moreover, corrosion-induced crack has
been clarified to be more dominant than corrosion productand change of rebar profile in bond deterioration
mechanism [1]. In our previous study [2], the simulation of
the cracking of concrete due to corrosion of reinforcing
bars by using an aluminum pipe embedded in concrete andfilled with an expansion agent has been proposed as amethod to simulate reinforcing bars which volume expands
due to corrosion. In this paper, a novel crack simulation
method to investigate the bond behavior of concrete
corrosion-induced cracks is presented and test specimens
are prepared for the pull-out test using expansion agent
filled pipes.
2. PULL-OUT SPECIMENS OVERVIEW
2.1 Aluminum pipe with ribs
Fig. 1 shows an overview of a processed aluminum pipewith ribs set according to JIS G 3112. An aluminum pipewith 21.7 mm as outer diameter and 2.5mm thickness wasused to imitate D19 rebar. The fundamental properties ofthe aluminum pipe and the expansion agent filled pipe havebeen reported by authors [3].
2.2 Pull-out specimen

loading. Table 1 shows the mechanical properties of concreteobtained from concrete cylinder test at the day of filling ofexpansion agent.
2.3 Loading and measurement
Fig. 3 shows the test set-ups for pull-out test. The specimen wasset on the Teflon sheet, and the loading plate on which the holewith the same diameter corresponding to concrete cover in order(unit: mm)
Fig. 1 Aluminum pipe with rib

Fig. 2 Specimen detailTable 1 Concrete mechanical properties
Compressive
strength(MPa)Young’smodulus(GPa)Splitting tensile
strength(MPa)

17.8

22.8

1.78

Pull-out specimen was designed as shown in Fig. 2.
Dimensions of specimen are 260×260×82mm and thealuminum pipe with ribs was embedded at 38mm from thespecimen side. The bond length of 51.6mm was chosen toavoid the rupture of the pipe by tensile force. Moreover,adhesive tape was used to make unbonded part to avoid
cone failure of concrete. A M6 coupler was fixed 100×100
mm at up left position to set a LDVT for measuring the slipof pipe. A π-type displacement transducer was placed on
the concrete cover to measure the opening of crack during

Fig. 3 Loading and measurement in pull-out test

Concrete Cracks by Expansion Agent Filled Pipes in Bond Test Specimens― 299 ―

to not restrict the lateral deformation of concrete. The pipe wassubjected to monotonic pull-out loading at a speed of
0.5mm/min. The measurement items are pull-out load, crack
opening and slippage of the pipe at the free end.
3. CRACK SIMULATION BY ALUMINUM PIPE
FILLED WITH EXPANSION AGENT
3.1 Filling of expansion agent
Expansion agent is mainly used for destruction of rocks and RC
structures, in powder form, and it expands when humified. Dueto this expansion, cracks are generated in the concrete (Fig. 4).
The ratio of the water to expansion agent was set to 30%. The
specimen was placed as the axial direction of the pipe was set
vertically, and expansion agent was filled from the top of thepipe as shown in Fig. 5.
3.2 Cracking patterns induced by expansion agent
Fig. 6 shows examples of crack patterns after filling theexpansion agent. The reaction of the expansion agent washeavily influenced by the ambient temperature around thespecimens. To control the width of induced crack, specimens
were placed in variable temperature conditions such as in an airconditioned room or in the testing laboratory with same
temperature of outside. Also, because of the increasing of crack
width over elapsed time from filling of expansion agent,
maximum crack width was measured by a crack scale after a fullstop of crack width increasing. Crack width as parameter isorganized into 3 levels as shown in Table 2. The maximum
crack width in every specimen is summarized in Table 3. As theresults, crack width ranges from 0.1mm to 3.0mm.
4. CONCLUSIONSThis study describes a crack simulation method to investigate thebond behavior of reinforcing bars in corroded reinforced concrete.
Ribbed aluminum pipe filled with an expansion agent cansimulate concrete cracks due to bar corrosion.
ACKNOWLEDGEMENT
This study was supported by the JSPS KAKENHI Grant Number
17K18917.
REFERENCES[1] Yang ,Y., Nakamura, H., Miura, T., Yamamoto, Y., Effect ofCorrosion-Induced Crack and Corroded Rebar Profile on Bond
Stress and Slip Relationship, Proceedings of the Japan Concrete
Institute, Vol. 40, No. 1, pp.927-932, 2018[2] Syll, A. S., Kawamura, Y.，Kanakubo, T., Simulation ofConcrete Cracks due to Bar Corrosion by Aluminum Pipe Filledwith An Expansion Agent, Summaries of Technical Papers ofAnnual Meeting, AIJ, Structure IV, pp.55-56, 2018.9

Fig. 4 Concrete cracking
with expansion agent

Fig. 5 Filling of expansion agent(a) Bottom view (free end)(b) Side view (cover side)
Fig. 6 Cracking of concrete before pull-out test
Table 2 Crack level

Table 3 Maximum crack width

Level

Crack width
range

Specimen Maximum
namecrack width(mm)

Level 1

≤ 0.5mm

S-1-L1

0.15

Level 20.5mm to 1. 0mm

S-2-L1

0.1

Level 3

> 1. 0mm

S-3-L1
S-4-L1S-2-L2
S-1-L2
S-1-L3S-2-L3S-3-L3S-4-L3
S-5-L3

0.2
0.35
0.5
1.0
1.5
3.0
2.0
1.8
2.0

S-6-L32.6

Specimen name explanation[3] Aburano, T., Syll, A. S., Castro, J. J., Kanakubo, T., Tensile
Characteristics of Expansion Agent Filled Pipes for Simulation ofConcrete Cracks due to Bar Corrosion, Summaries of TechnicalPapers of Annual Meeting, AIJ, 2019.9* Prof., Dept. of Eng. Mechanics and Energy, University of Tsukuba, Ph.D.
** Prof, Architecture and Building Engineering Program, University of the Ryukyus, Ph.D.
*** Master Program in GSSIE, University of Tsukuba― 300 ―