Seventh International Conference on Geotechnique, Construction Materials andEnvironment, Mie, Japan, Nov. 21-24, 2017, ISBN: 978-4-9905958-8-3 C3051

DEVELOPMENT OF CEMENT-BENTONITE MIXED SOILS BYMIXINGSODIUM CARBONATE
Ko Hashimoto1, Shuichi Kuwahara2, Yukio Uchida3, Tadaomi Eguchi4, Shinya Inazumi5
1Advanced Course of Architecture and Civil Engineering, Akashi College, National Institute ofTechnology, Japan, 2Marushin Co., Ltd., Japan, 3Japan Material Co., Ltd., Japan, 4Department of Civil
Engineering, Akashi College, National Institute of Technology, Japan, 5Department of Civil
Engineering, Shibaura Institute of Technology, Japan

Abstract
Cement milk is used as a grout to fill holes which are resulted from pile extraction. Although cement milk has anadvantage of being able to perform blending and placing according to circumstance of work on site, cement andwater cause segregation, so uniform filling is difficult over the entire length of holes. In addition, there is a
disadvantage that cement milk can’t perform a predetermined strength when diluted by groundwater erosion.
Sodium carbonate is a substance expected to suppress the segregation of cement milk and to speed up thedevelopment of strength. In this study, we conducted an indoor mixing test on fillers mixed with sodium carbonate
into cement milk which is a mixture consisting of water, cement and bentonite, and examined various
characteristics from the viewpoint of physical and chemical aspects. (1) By mixing sodium carbonate, bleeding of
cement milk is suppressed. This is considered to be due to increased swelling of bentonite by receiving sodiumions. (2) By mixing sodium carbonate, the strength development time of cement milk is advanced and the longterm strength also increases. This is considered that calcium carbonate is generated at the initial stage of reaction
from the reaction of bentonite and sodium carbonate.
Keywords: cement, bentonite, sodium carbonate, bleeding, early strength1.

Introduction

1.1.

BackgroundIn demolition work, it is necessary to remove existing
piles in the ground. If new land use is planned, existing
piles must be removed so as not to interfere with pilefoundation of newly built-structures. In addition,
existing piles remaining in the ground are industrial
waste, so troubles often occur in the land saletransaction. Therefore, removal of existing piles is
indispensable. In order to remove an existing piles, adrawing out method is generally adopted. In thedrawing out method, holes are formed in the ground,which adversely affect the ground environment. In thevicinity of the hole, it may cause problems such as
collapse of earth and sand, subduction of thesurrounding ground, weakening, so it is necessary tofill the filling and stabilize the ground quickly.
Depending on the construction site, the properties
required for the filling are different, but there is no
regulation on filling presently. From the above, there
is a demand for constructing a filler that can reliably
fill and secure stable strength.
1.2.

Purposeseparation when filling holes generated by pulling out
existing piles. We aim at sophistication of cement
bentonite typed cavity filling since it is possible toadjust blending filling at the construction site. By
mixing sodium carbonate (Na2CO3), it is expected thatthe strength development of the cement bentonite typecavity filling will be promoted and the bleeding will
be suppressed. We will examine the improvement andusefulness as cavity filling by conducting an indoor
blending test on cement bentonite and sodium
carbonate mixed cement bentonite. For examining theimprovement and usefulness, a comparative test is
conducted in view of strength characteristics, fluidity
and material separation.
1.3.

OutlineIn this research, we carried out uniaxial compression
test, penetration test, bleeding test and flow test on
cement bentonite and cement bentonite mixing sodium
carbonate, and examine usefulness of cement
bentonite typed filling by mixing sodium carbonate. In
addition, we consider the mechanism of thedevelopment of various properties exerted by mixing
sodium carbonate from the physical and chemical
point of view (Fig.1).

We will aim for the development of a filling thatexhibits uniform strength without causing material
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2.

MethodResearch background

2.1.

Materials and Mixing Conditions
Purpose of research(1) Cement
The type of cement used in this study is ordinary
portland cement, and one is having a density of 3.16
g /cm3 and a specific surface of 3200cm2/g. Cement isa main component which exerts a curing function as a
cement bentonite typed cavity filling because it
reaction with hydration and develops initial and longterm strength by the formation of ettringite andcalcium silicate hydrate(C-S-H).

Indoor mixing test
Arrangement andconsideration of test results

Investigation of usefulness as
filling(2) Bentonite
The chemical components of the bentonite used on
our test are shown in Table 1. Bentonite has the effectof suppressing material separation of cement andwater by swelling property due to take water into theone1). Bentonite is a smectite clay mineral containing
montmorillonite as a main component and has alayered structure in which thin plate crystals arestacked. The crystal is negatively charged andelectrical equilibrium is maintained by adsorbing
cations between crystal layers. The interlayer cationsof montmorillonite are mainly composed of sodiumion (Na+), calcium ion (Ca2+), potassium ion (K+),
magnesium ion (Mg2+), and the properties of bentonite
vary depending on the type of the one. The type isdivided into two types, one is called Na type where alarge number of monovalent cations such as Na + andK+ are adsorbed, and the other is called Ca type wherea large number of divalent cations such as Ca2+ andMg2+ are adsorbed2). The bentonite used in thisexperiment is a Na type bentonite having many Na + ininterlayer cations.

Consideration aboutmechanism of upgrading

Fig.1

Table 1 Chemical components of bentonite
Chemical Components
SiO2
Al2O3
Fe2O3
MgO
CaO
Na2O
K2O
Ignition loss

Content (%)
67.1
16.8
3.7
3.3
2.7
2.2
1.3
2.9

Table 2 Chemical components of the admixture(3) Sodium carbonate
When we mix sodium carbonate as an admixture intoa cement bentonite typed cavity filling in thisexperiment, we use anhydrous salt obtained by heating
at a high temperature of 300°C. Table 2 shows thechemical components of the admixture, and it contains
Na2CO3 of 99.41%. Sodium carbonate is expected topromote the hydration reaction between cement andwater and exert the effect of early strength
development3).
(4) Mixing condition
Table 3 shows the mixing conditions of each material
used in the series of tests. The target strength is set to
0.5N/mm2 on the mixing condition. In the precast piledriving method prescribed in the "Public BuildingStandards Manual"4), since the pile circumferential
fixing liquid is set to 0.5N/mm2 at the compression
strength after 28 day material age and is considered tobe the same as the ground strength, the strength isgenerally adopted as a standard. In blend A and B,
cement bentonite and cement bentonite mixing sodium

Procedure of study

Chemical Components
Na2Co3NaCl
Fe2O3
Insoluble matter

Content (%)
99.41
0.35
0.003 or less0.001or lessIgnition loss

0.15

Table 3 Mixing conditions of each material
No.
A-1
A-2
B-1
B-2
C
D
E
F
G

B
(kg/m3)
50
50
50
50
50
50
50
50
50

C
(kg/m3)
240
240
300
300
180
200
220
250
260

S
(kg/m3)
0
20
0
20
20
20
20
20
20

W
(kg/m3)
905
897
886
878
916
910
903
894
891

W/C
(%)
377
374
295
293
509
455
410
358
343

carbonate whose weight ratios C/B=5, 6 of cement (C)and bentonite (B) were prepared, and we investigate
the properties of cement bentonite mixing sodium
carbonate perform. In blend C, D, E, F and G, only theamount of cement (C) is changed to prepare cement
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bentonite mixing sodium carbonate and the correlation
between sodium carbonate and cement is examined. In
the mixing procedure, water (W) and bentonite (B)were added to a stirrer having a rotation speed of 1,500rpm/min and stirred for 3 minutes, then ordinary
portland cement (C) was added and stir for 3 minutes
and sodium carbonate was added and stir for 3 minutes(Fig.2).
2.2.

Strength Test

The strength development of cement bentonite
mixing sodium carbonate will be examined according
to the Japanese Industrial Standard (JIS A 1216)"uniaxial compression test". Each material is mixed
according to mixing conditions and it is poured into amold having a diameter of 50mm and a height of
100mm to prepare a sample. Curing is performed for7, 14, 28, 60, 90, 120 days in a thermostatic chamber
at 20°C, and a uniaxial compression test is performedat each curing day (Fig.3).
In order to investigate the change about the action of
cement bentonite due to mix sodium carbonate, we
conduct a simple penetration test on samples of A and
B. Penetration resistance values in immediately after
sample mixing and 30 minutes, 1, 2, 3, 4, 5, 6, 7, 8, 12,
24 hours are measured using a simple measuring
instrument (Fig.4).
2.3.

Fig.2 Mixing and stirring of materials

Bleeding Test

A test is carried out according to the JSCE Standards(JSCE-F522) "Bleeding Rate and Expansion Rate Test
Method of grouting Mortar of Prepacked concreat(Polyethylene Bag Method)" in order to evaluate
material separation of water and cement (Fig.5). The
Sample mixing each material put to a height of 200mm
in a polyethylene bag with a diameter of 50mm and theamount of bleeding water after 1, 3, 24 hours ismeasured, and the bleeding rate is obtained using thefollowing formula.

𝐁𝐫 = (

Fig.3 Uniaxial compression test𝑾𝒃
) × 𝟏𝟎𝟎𝑽

Br (%) is the bleeding rate, Wb (ml) is the amount of
bleeding water at each elapsed time, and V (ml) is thevolume of the whole sample.
2.4.

Fluidity Test

The fluidity of cement bentonite mixing sodium
carbonate is evaluated according to JSCE-F521"Fluidity Test Method of grouting Mortar of
Prepacked concreat (Method of P Funnel)". The
Sample mixing each material is filled in a P-funnel
tester having an outflow pipe inner diameter of 13mm,
an outflow pipe length of 38mm and a funnel portion
height of 192mm. The sample is allowed to flow by
releasing a finger from the flow pipe, and we measure

Fig.4 Simple penetration test
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the time until the flow of sample is interrupted for the
first time with a stopwatch (Fig.6).

3.
3.1.

Consideration
Consideration on Strength Test

(1) Initial strength development
From the uniaxial compression test results in Fig.8(a), compare the initial strength of cement bentonite
and cement bentonite mixing sodium carbonate. A-1
has the 7th day strength of 0.09N/mm2, and A-2 has aseven-day strength of 0.30N/mm2, so A-2 is stronger
than A-1. Similarly in the comparison between B-1
and B-2, the 7th day strength of B-1 is 0.37N/mm2 andthe 7th day strength of B-2 is 0.59 N/mm2, so mixing
sodium carbonate makes cement bentonite stronger
than when it does not mix. Therefore, it can be said
that the initial strength of cement bentonite increases
by mixing sodium carbonate. In addition, since nosignificant difference is observed in the strength
development behavior up to the 28th day of age, it isthought that sodium carbonate influence the strength
development before the 7th day of age.
In Fig.7, the results of the penetration test showedthat the resistance values of cement bentonite of A-1
and B-1 rise about 8 hours after mixing and stirring ofeach material, but the values of cement bentonite
mixing sodium carbonate of A-2 and B-2 rise about 1
hour after mixing and stirring. Since the setting
initiation time of cement bentonite is accelerating, it
can be said that mixing sodium carbonate affects thesolidification performance at the one-day of age.
Exercising solidification performance in 1 hour after
filling prevents the invasion of groundwater in the
ground and helps developing stable strength cement
bentonite type cavity filling.
From the above, mixing sodium carbonate into
cement bentonite promotes the solidification
performance immediately after mixing and stirring ofeach material, and exerts a useful effect as a filling.

Fig.6 fluidity test
7

resistance value(kgf/cm2)(2) Long-term strength
From the uniaxial compression test results in Fig.8(a), compare the long-term strength of cement
bentonite and cement bentonite mixing sodium
carbonate. In comparing A-1 and A-2, B-1 and B-2,
the strength of mixing sodium carbonate is stronger
than not mixing at any age. However, as for thetendency of strength development, there is a tendency
that the strength increases up to about the 28th day of
age in any samples, and the strength hardly increase
after that. In addition, Fig.9 shows the values
normalized by the strength of 28th day of age(hereinafter referred to as compression strength ratio).
Comparison of each sample from Fig.9 (a) showed nosignificant difference in long-term strength
development behavior after 28th day of age, and theFig.5 Bleeding test

A-1

6

A-2

B-1

B-2

5
4
3

2
1
0
0

3

6

9

12

15

18

21

24

elapsed time (h)Fig.7 Result of penetration test

compressive strength ratio is around 1.0, except for
B-1. There is not effect on the long-term strength
development due to mix sodium carbonate, so thereason why the strength is larger on each age at the175

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time mixing sodium carbonate is considered that theincrease of the initial strength affects the long-term
strength development.

1.40

unconfined cimpression
strength(N/mm2)

1.20(3) Increase mechanism of initial and long-term
strength
The amount of cement is changed in C, D, E, F, and
G of cement bentonite mixing sodium carbonate. From
Fig.8 (b), there is a trend that the smaller the watercement ratio is, the stronger the strength is at each age.
In addition, from Fig.9 (b), there is no clear differencein the tendency of strength development in any
samples except for C, and the compressive strength
ratio at 90th day of age is about 1.15. There is nodifference in behavior of initial and long-term strength
development of cement bentonite mixing sodium
carbonate by difference in cement amount, so it can besaid that sodium carbonate has no effect on cement.
Therefore, the initial strength increase of cement
bentonite by mixing sodium carbonate does notpromote the hydration reaction between cement andwater, and it is considered that forms a cured bodydifferent from cement hydrate.
Here, attention is paid to sodium carbonate andbentonite. Bentonite has different properties
depending on the type of interlayer cation ofmontmorillonite, but bentonite easily changes its
properties by ion exchange with other types of cations
since it has ion exchange properties. The interlayer
cation exchangeability increases in the following
order5).

B-1

B-2

0.60
0.40
0.20

0.00
20

40

60

80

100

120

140

material age (day）(a)

Comparison by mixing sodium carbonate

unconfined compression
strength(N/mm2)

0.60

C

D

E

F

G

0.50
0.40

0.30
0.20

0.10
0.00

0

20

40

60

80

100

material age (day)(b) Comparison by changing cement amountFig.8 Result of uniaxial compression test

compressibe strength ratio( σ/σ28)

1.400
1.200
1.000
0.800
0.600
0.400
0.200

A-1

A-2

B-1

B-2

0.000
0

20

40

60

80

100

120

140

material age (day)(a) Comparison by mixing sodium carbonate
compressive strength ratio(σ/σ28)1.400

Consideration on Breathing Test

Table 4 shows the results of the bleeding test. In
Cement bentonite of A-1 and B-1, the bleeding rateincrease with the passage of time, but in cement
bentonite mixing sodium carbonate of A-2 and B-2,
about 0.5% bleeding is only confirmed after 1 hour,
and there is no moisture on the surface of the specimen.
Similarly, in C, D, E, F, and G, it can be confirmed thatthe bleeding rate becomes 0% within 24 hours fromthe mixing of the materials. The decrease in the
bleeding rate of cement bentonite due to the mixing

A-2

0.80

0

𝑵+ < 𝑲+ < 𝑪𝒂𝟐+ < 𝑴𝒈𝟐+
When sodium carbonate (Na2CO3) dissolve in water,
it ionizes to sodium ion (2Na+) and carbonate ion(CO32-).Therefore, Ca2+ contained in the interlayer
cations in the bentonite and Na+ ionized from thesodium carbonate perform ion-exchange, and Ca2+ andCO32- are bonded to form calcium carbonate (CaCO3).
Calcium carbonate is a water-insoluble substance, andforms a cured body by binding molecules with eachother. The early strength development of cement
bentonite by mixing sodium carbonate and theincrease in long-term strength are attributed to theformation of a cured body of calcium carbonate
immediately after mixing of materials.
3.2.

A-1

1.00

1.200
1.000
0.800
0.600

0.400
0.200

C

D

E

F

G

0.000
0

20

40

60

80

100

material age (day)(b) Comparison by changing cement amountFig.9 Compressive strength ratio
sodium carbonate is attributed to the increase in theswellability of bentonite and the initial strength
development of cement bentonite. Bentonite exerts
swellability by interlayer cations of montmorillonite
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Table 4 Results of bleeding and fluidity test
No.

A-1
A-2
B-1
B-2
C
D
E
F
G

flowing
downtime (s)

1hour

7.7
7.6
7.8
7.6
7.7
7.7
7.7
7.7
7.7

3.6
0.5
4.0
0.4
0.9
0.7
0.5
0.5
0.5

bleeding rate (%)
3hour
24hour
9.3
0.0
9.5
0.0
0.8
0.5
0.0
0.0
0.0

9.5
0.0
9.8
0.0
0.0
0.0
0.0
0.0
0.0

adsorbing water molecules. As compared with Ca typebentonite, the Na type bentonite has a weak electricalattraction between the unit layers, and so it is likely toswell when adsorbing water molecules. As describedabove, sodium carbonate in water is ionized togenerate Na+, which is exchanged with Ca2+ contained
in interlayer cations in bentonite. It is considered thatthe swelling property of bentonite is improved,
because the interlayer cations become more inclusiveof Na+. In addition, a hardened body is formed quickly
since calcium carbonate is produced, and movement ofwater molecules in cement bentonite is inhibited.
There is also a decrease of the amount of water due tothe hydration reaction with cement. Therefore, it isconsidered that various phenomena such as increase ofswellability with bentonite due to mixing of sodium
carbonate, early strength development of cement
bentonite, and hydration reaction of cement and water
are involved, and the bleeding does not occur after
several hours from mixing.
3.3.

Consideration on Fluidity Test

Table 4 shows the results of the fluidity test. In eachsample, the flowing down time is about 7.7s, and nodecrease in fluidity of cement bentonite due to mixing
sodium carbonate is observed. As described above,since curing started in about one hour after mixing thematerials, the early strength development performancedoes not affect the fluidity at the time of filling.
Although there is a possibility that material separation
may occur due to flowing down, since bleeding hardly
occurs, it can be said that the samples are having
moderate fluidity. Therefore, it is able to say that thecement bentonite mixing sodium carbonate has
ensured workability as a cavity filling.

4.

Conclusions

In this study, the usefulness of the cement bentonite
typed cavity filling mixing sodium carbonate was
examined from the viewpoint of strengthcharacteristics, material separation and fluidity. The
obtained results are shown below.
(1) From the uniaxial compression test, mixing
sodium carbonate increases the initial and longterm strength of cement bentonite. The earlystrength development helps stabilizing the
ground as soon as possible.
(2) From the penetration test, by mixing sodium
carbonate, cement bentonite exerts curingperformance from about 1 hour after mixing
materials. The rapid gelation prevents invasion ofgroundwater into the filling in the ground, andthe filling can stably exhibit the predetermined
strength.
(3) From the bleeding test, bleeding of cement
bentonite is suppressed by mixing sodium
carbonate. When it fills into the hole made bypulling out piles in the ground, the materials is
kept homogeneous and the strength is not differ
depending on the depth direction.
(4) From the fluidity test, the fluidity of cement
bentonite is not lost by mixing sodium carbonate.
Workability is assured in filling holes in the
ground.
In the future, it is necessary to clarify the mechanismof various characteristics development by verifying
from a physicochemical point of view.

References[1] Kouken Horii, Masaaki Nishi, Tsutomu
Yamazaki, Junichi Sakamoto, Michimae Taizou,
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bentonite complex solidified bodies using
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Academic Lectures of the Japanese Association ofArchitectural Conferences, 2007.
[2] Yashima Takashi, “Estimation of smectite
exchangeable cations by powder X-ray regression
method”, JGCA Technical Forum 2011 lecturecollection, No. 40, 2011.
[3] Kiyoshi Kato, Naoki Kato, Toshio Yuzawa, Isao
Masukawa, “A Study on Rapid Evaluation ofLong-term Strength and Unit Cement Volume by
Ultimate Initial Strength of Rapid HardeningPromoted Concrete”, Report of ConcreteEngineering Annual Papers Report, pp. 343 - 346,
1990.
[4] Ministry of Land, Infrastructure and Transport,“Public
Building
Construction
Standard
Specification (Building Construction), Heisei
20th edition, Ministry of Land, Infrastructure andTransport, 2014.
[5] Masanobu Ogata, “Characteristics of bentonite
and its application”, Clay science vol. 46, No.2,
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