JSCE 令和3年度土木学会全国大会第76回年次学術講演会

第V部門

付着・定着・継手(2)2021年9月10日(金) 11:10 〜 12:30 V-7 (Room24)[V-514] Concrete Cracked by Expansion Agent Filled Pipes in Bond
Test Specimens with Stirrups
Concrete Cracked by Expansion Agent Filled Pipes in Bond
Test Specimens with Stirrups*下河邉 大貴1、Syll Amadou Sakhir1、金久保 利之1 （1. 筑波大学）*Hiroki Shimokobe1, Amadou Sakhir Syll1, Toshiyuki Kanakubo1 （1. Tsukuba University）
キーワード：鉄筋腐食、静的破砕剤、ひび割れ幅、付着、横補強筋
Rebar corrosion, Expansion agent, Crack width, Bond test, Stirrup
付着とは鉄筋と周囲のコンクリートとの相互作用を指す。鉄筋の腐食は、鉄筋とコンクリートの間の付着劣化を引き起こし、 RC構造物の構造性能の低下へと繋がる。コンクリート表面のひび割れ幅は目視での観察が可能なため、鉄筋腐食による付着劣化を評価する上で有効な指標であると考えられる。本研究では、横補強筋が付着強度劣化に及ぼす影響を調査するために、破砕剤充填パイプ（ EAFP）によってひび割れを模擬した試験体の引抜き試験を行い、鉄筋腐食によるひび割れ幅及び横補強筋が付着強度劣化に与える影響について検討を行った。実験に用いた試験体と破砕剤充填パイプによるひび割れの模擬結果を示す。
Rebar corrosion can cause bond deterioration between rebar and concrete which directly affects theserviceability and durability of RC structures.
In this study, to investigate the influence of stirrup on bond strength degradation, specimens cracked byexpansion agent filled pipe (EAFP) are subjected to a pull-out test and a relationship between the bondstrength of bar and surface crack width as a variable is discussed. This part describes the design andcracks simulation results of those specimens.

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Japan Society of Civil Engineers 2021 Annual Meeting

Concrete Cracked by Expansion Agent Filled Pipes in Bond Test Specimens with Stirrups
筑波大学
筑波大学
筑波大学
1.

学生会員
学生会員
正会員

○ 下河邉大貴
Syll Amadou Sakhir
金久保 利之INTRODUCTION
Bond refers to the interaction between reinforcing steel(rebar) and the surrounding concrete, which allows
transferring of tensile stress from the steel into the concrete.
Rebar corrosion can cause bond deterioration between rebar
and concrete which directly affects the serviceability anddurability of RC structures. Indeed, the surface crack width
provides the clearest visual manifestation of reinforcement
corrosion. Easily measurable, it can be a key parameter tosolve this problem by directly correlating the bonddeterioration of the surface crack width. Our previous studies[1,2] are based on specimens without stirrups. However, forFig. 1 Specimen detail (example Series S2)

real concrete structural members stirrups are present. In fact,
the bond deterioration of stirrup-confined specimens is quite
different from specimens without stirrups.
In this study, to investigate the influence of stirrup on bondstrength degradation, specimens cracked by expansion agent
filled pipe (EAFP) are subjected to a pull-out test and a
relationship between the bond strength of bar and surface(a) Series S0(b) Series S1(c) Series S2

crack width as a variable is discussed. This part describes theFig. 2 Specimen framework

design and cracks simulation results of those specimens.

Table 1 Specimen list
StirrupTarget inducedpw
spacing
crack width(%)
(mm)
(mm)
No stirrup
076
1.10
0 to 1.450
1.68

2.

PULL-OUT SPECIMENS OVERVIEW

Series

2.1 Pull-out specimen

The pull-out specimen is designed as shown in Fig.1. The
dimensions of the specimen are 260×170×170 mm, and theS0S1S2D19 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.
The main parameters examined are the induced crack widthand stirrup quantity (see Table 1). D10 rebar is used as astirrup. Two EAFPs are set to 50 mm from the rebar tosimulate the cracking of surrounding concrete. Moreover, anunbonded part was set to avoid cone failure of concrete. TheM6 coupler was fixed 100×50 mm at the upright position toset an LDVT for measuring the slip of the free end of the bar.

Fig. 3 Loading and measurement of pull-out test

Keywords

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

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Japan Society of Civil Engineers 2021 Annual Meeting

The reinforcement is a deformed bar of a nominal diameter of19 mm. The specimen framework is also shown in Fig.2.
2.2 Loading and measurements

Fig. 3 shows the test set-ups for the pull-out test. The
specimen was set on the Teflon sheet and the loading plate on
which the hole with the same diameter corresponding toconcrete cover to not restrict the lateral deformation ofconcrete. The D19 rebar is subjected to monotonic pull-out

Fig. 4 Filling of expansion agent

loading at a speed of 0.5mm/min. The measurement items arepull-out load, crack opening, and slippage of the rebar.
3.

CRACK SIMULATION BY EAFP

3.1 Crack simulation by EAFP

The ratio of the water to an expansion agent was set to 30%.
The specimen was placed to set vertically the axis of the pipe.
As shown in Fig.4, the expansion agent was filled from thetop of the pipe. The crack width increases over elapsed time

(S0-C-0.95mm) (S1-C-0.70mm) (S2-C-0.60mm)

after filling. Thus, this time is controlled to obtain the target

Fig. 5 Example of cracking by EAFPcrack width.

Before loading

After loading

3.2 Cracking patterns induced by EAFP

Fig. 5 shows an example of crack patterns after filling theexpansion agent. The side split type cracks took place in all
specimens. The maximum induced crack width ranges from0.15 to 0.95 mm in S0 specimens, 0.15 to 1.40 mm in S1
specimens, 0.15 to 0.70 mm in S2 specimens.
4.

FAILURE PATTERNS BY PULL-OUT TEST(a) Widening of induced crack

Example of failure pattern is shown in Fig.6. All specimens
failed by splitting of concrete. S0 specimens failed by thewidening of existing crack induced with EAFP. However, S1and S2 specimens failed by a newly generated crack on thecover face despite existing induced crack. It was also
observed that the stirrups can effectively restrain the openingof induced cracks
5.

CONCLUSIONSThis study describes the outline of concrete cracks by(b) New crack on the cover faceexpansion agent filled pipes in bond test specimens withFig. 6 Example of failure pattern by pull-out loading

stirrups. Side split cracks with various widths were simulated
by EAFP in all specimens. By pull-out loading, the specimen

split type specimens ， Summaries of Technical Papers ofeither failed by widening of induces cracks or by a newly

Annual Meeting, AIJ pp. 37～38，2020.9.

generated crack on the cover face.

[2] Syll et al ： Bond Behavior in Cracked Concrete by

REFERENCESExpansion Agent Filled Pipes, Part 2: Bond strength[1] Aburano et al：Bond Behavior in Cracked Concrete bydegradation in side-split type specimens ， Summaries ofExpansion Agent Filled Pipes, Part 1: Concrete cracks in side-

Technical Papers of Annual Meeting, AIJ，pp. 39～40，2020.9.

JSCE 令和3年度土木学会全国大会第76回年次学術講演会© Japan Society of Civil Engineers- V-514 -