Ouchi, M.

BOND STRENGTH OF SELF-COMACTING MORTAR
Masahiro OUCHI, Kazuhisa NAKAOKA, Masato ONO and Hideo MIYAJI
Kochi University of Technology, JAPANABSTRACT: The factors for the bond strength of self-compacting mortar as repairing material to thehardened concrete were experimentally examined. Both tensile and shear bond strength were examined.
It was found that the dominant factor for the bond strength was the supply of water for the hydration ofcement rather than the water to cement ratio of the mortar.
KEYWORDS: self-compacting concrete, self-compacting mortar, tensile bond strength, shear bond strength
1. INTRODUCTION(C/W) resulted in the lower shear bond strength.

The necessity for cheap repairing material for theis possible that the influence of the water to cement

conventional concrete structures is increasing.

ratio on the bond strength was not so large as that ofTo

the jointless specimen of concrete.

make the repairing material cheap, only the commonmaterials

shouldbeused.

Self-compacting
Tensile bond strength (N/mm^2)

concrete is desirable for the necessity because nospecial material is employed.
AstherepairingItmaterialfortheconventional concrete structures, the bond strength
to the existing hardened concrete is indispensable.
However, such kind of research on thebond strength has not been done, especially for the1.5

10.5

0
1

2mortar or concrete without using any special

345C/Wadmixture like polymer mortar.

Fig. 1 Relationship between C/W and tensile bond

The purpose of this study is to clarify thestrength at the age of 3 days by shield curing:factor for the bond strength of self-compacting

average value and standard deviationmortar to the hardened concrete.

Shear bond strength (N/mm^2)

2. WATER TO CEMENT RATIO ON BOND
STRENGTH
From the commonsense of the concrete engineering,the dominant factor for the strength is water tocement ratio.

Therefore, at first the relationshipbetween the water to cement ratio and the tensile
bond strength was experimentally obtained (Fig. 1).

501Also, the relationship between the water to cement

2345C/W

ratio and the shear bond strength was experimentallyobtained (Fig. 2).

10Fig. 2 Relationship between C/W and shear bondHigher cement to water ratio

strength at the age of 7 days by shield curing
1Ouchi, M.
tensile bond strength of the mortar with low C/W of
3. METHOD OF CURING ON BOND STRENGTH

around 2.

As the reference, the tensile and shear strength of thefor hydration of cement.

jointless specimen of concrete were experimentally

That may be because it had sufficient water

It is possible that the dominant factor for thebond strength was the supply of water for hydration ofobtained (Fig. 3 and Fig. 4).

5Tensile bond strength (N/mm^2)

Tensile bond strength (N/mm^2)

cement rather than the water to cement ratio itself.

432
10
12

345C/W

3Water curing
21Shield curing

01

2

3Fig. 3 Tensile strength of the jointless specimen of

5

concrete by shield curing at the age of 3 days:

Fig. 5 Water curing promoted tensile bond strength;

tensile split-cylinder test

Upper: water curing; lower: shield curingAlso, the bond strength of the jointless specimen of

10Shear strength (N/mm^2)

4C/W

concrete by between water and shield curing wascompared (Fig. 6).

The promotion rate of the tensile

strength by water curing was small compared with the5tensile bond strength.

The necessity for water forhydration of cement was verified especially for the012

34bond strength.

5C/W

Tensile bond strength (N/mm^2)

Fig. 4 Shear strength of the jointless specimen of
concrete by shield curing at the age of 7 days

Higher cement to water ratio did not result in the highstrength in case of the shield curing.

That may be dueto the shortage of water for the hydration of cement andWater curing
4Shield curing

201

then that may be the case with the bond strength.

2345C/W

The tensile bond strength was compared bybetween shield and water curing (Fig. 5).

6Fig. 6 Less difference in tensile strength between
water and shield curing than tensile bond strength

The tensile

bond strength by water curing was almost twice asat the of 3 days

much as that by shield curing.
However, water curing did not promote the2Ouchi, M.

(2) Water curing promoted the tensile bond strength
4. SUPPLY OF WATER FOR HYDRATION OFremarkably from that of shield curing.

Also, theCEMENT ON BOND STRENGTH

replacement of cement with limestone powder

Some portion of cement was replaced with limestone

promoted or kept the tensile bond strength despite

powder and the relationship between the cement toof the reduction in the cement content of thewater ratio (C/W) and the tensile bond strength wasmortar.

The volumetric ratio of water to(3) It can be concluded that the dominant factor for

powder (= cement + limestone powder) was constant ofthe bond strength was the supply of water for the100%.

hydration of cement rather than the water toobtained (Fig. 7).

Tensile bond strength (N/mm^2)

cement ratio.
3

It was found that the sufficient supply of water forthe hydration is indispensable in order to make the2Water curing

self-compacting mortar practical in the repairing
1

work of the existing concrete structures, especially to

Shield curing
LS/P = 0.4

0.3

0.2

0.1

promote the tensile bond strength at this moment.

001

2

3

For example, the tensile bond strength of the4polymer cement mortar was almost 2 N/mm2.

C/WFig. 7 Promoted hydration of cement by limestone---------------------------------------------

powder; LS/P: volumetric ratio of limestone powder

MATERIALS IN USE

to total powder

Cement: ordinary portland cement (specific gravity:3.15)
Despite of the replacement with limestone powder andFine aggregate: mixture of limestone crushed sandthen the reduction in the cement content of the mortar,(specific gravity: 2.69; F. M.: 2.73) and sea sandthe tensile bond strength was almost constant in case of(specific gravity: 2.59; F. M.: 2.22) :(8:2 byshield curing and promoted in case of water curing.

volume)Superplasticizer: Poly-carboxylate type ofThat may be because the retained water by limestone

superplasticizer

powder was consumed for the hydration of the cement
and then it promoted the tensile bond strength.

MIX PROPORTIONING OF
5. CONCLUSIONSSELF-COMPACTING MORTAR

The dominant factor for the bond strength ofFine aggregate content in mortar: 45% by volume

self-compacting mortar to the base material concrete

Dosage of suerplasticizer: adjusted to obtain themortar flow value of 290 to 310 mm

was experimentally examined for both tensile and shear
strength. The conclusions are summarized as follows:

FLOWABILITY(1) Higher cement to water ratio did not always result

OFSELF-COMPACTING

MORTARin the higher bond strength compared with theThe flow value of the mortar was 290 to 310 mm sostrength of jointless specimen of concrete.

that the sufficient contact with the existing concrete
3

Ouchi, M.

may be obtained and also the segregation between

compatibility with the conventional strength testing

paste and mortar may be prevented (Fig. 8).

methods.

The lower portion was the base material

concrete and self-compacting mortar was cast to theupper portion without vibration (Fig. 9).

BASE MATERIAL CONCRETE TO WHICH

No segregation was observed in all theMORTAR WAS BONDED
The

base

material

self-compacting

concretemortar

wastowhichmixes of the mortar in this series of experiment.

thebondedwas

conventional concrete of W/C of 45%.

Toeliminate the influence of the hydration of the basedmaterial concrete itself on the bond strength, only
the concrete specimen with the age of over 28 days
was employed.

The compressive strength wasaround 44 N/mm2 at the age of 28 days.

Fig. 9 Specimen for bond strength: common in

The interface to the mortar was grinded byboth tensile and shear bond strength; upper:

the grinding machine for the top and bottom surface

self-compacting mortar; lower: base materialof the specimen for compressive strength test.

concrete (conventional concrete)

The base material concrete was in water
until just before the casting of the self-compacting
mortar and the interface was wiped just before theIn case of shield curing, the mould having thecasting of the mortar.

specimen was wrapped after the casting of themortar until the strength test.

In case of water

curing, the mould was removed at the age of 1 day.
TENSILE BOND TESTING METHOD
The conventional tensile split-cylinder test is notsuitable for the tensile bond strength test because of
the existence of the joint between the base material
concrete and the self-compacting mortar.

The

strength of the joint itself has to be tested to evaluate
the repairing material.

So, chuck type of testing

apparatus was employed, which the authors havemortar flow

newly developed (Fig. 10 and Fig. 11).

Fig. 8 Flow of self-compacting mortar of around
300 mmSPECIMEN FOR BOND STRENGTH TESTAND CURING
The conventional specimen of the cylinder of φ100 *200 mm was employed for the convenience and the4Ouchi, M.

PPPPPPP

Fig. 10 Concept of direct tensile testPFig. 12 Concept of direct pure shearing apparatus:
not by compression but by tension

Fig. 11 Chuck type of tensile testing apparatus

Fig. 13 Direct pure shearing testing apparatus: notby compression but by tension

This testing apparatus was employed in the tensile
bond strength test only in this research.

The tensile

strength of the jointless cylinder of concrete wasobtained by the conventional split-cylinder test.
SHEAR STRENGTH TESTING METHOD
A direct pure shear testing apparatus was employed,
which the authors have newly developed. The conceptof the testing method and the testing apparatus itself are
shown in Fig. 12 and Fig. 13.

Fig. 14 Shear failure of jointess specimen ofconcrete by the apparatus
5Ouchi, M.
FAILURE MODE OF TENSILE BOND TESTIn this research, no breaking of the base material
concrete or self-compacting mortar was observed in thetensile bond strength test. All of the specimens werefailed on the interface between the base material
concrete and the elf-compacting mortar in this series ofexperiment.

REFERENCES

1) Okamura, H., Maekawa, K., and Ozawa, K.: Highperformance concrete (written in Japanese),
Gihodo-shuppan, September 1993.
2) Okamura, H. and Ouchi, M.: Self-compacting
concrete,

JournalofAdvanced

Concrete

Techmology, Vol. 1. No. 1, pp.5-15, April 2003.
3) Ouchi, M., Hibino, M., Sugamata, T. andOkamura, H.: Quantitative evaluation methodfortheeffectofself-compacting concrete,JapanConcrete

superplasticizer

inProceedings of theInstitute,Vol.21,

No.1,

pp.129-134, 1998.
4) Sugamata, T., Edamatsu, Y. and Ouchi, M.:
Quantitative evaluation for retaining in diepsersing
effect by superplasticizer, Proceedings of theJapan Concrete Institute, Vol.22, No.2, pp.163-168,
2000.

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