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Evaluation of long-term durability of engineered barrier system - - PowerPoint PPT Presentation

Jun 17, 2023 115 likes •568 views

Evaluation of long-term durability of engineered barrier system (EBS) of bentonite and cementitious materials by migration technique K. Nakarai* , M. Watanabe*, T. Sugiyama**, Y. Tsuji* * Gunma University, Japan ** Hokkaido University, Japan

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SLIDE 1

Evaluation of long-term durability

  • f engineered barrier system (EBS)
  • f bentonite and cementitious materials

by migration technique

  • K. Nakarai*, M. Watanabe*, T. Sugiyama**, Y. Tsuji*

* Gunma University, Japan ** Hokkaido University, Japan

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SLIDE 2

Evaluation of long-term durability

  • f engineered barrier system (EBS)
  • f bentonite and cementitious materials

by migration technique

  • K. Nakarai*, M. Watanabe*, T. Sugiyama**, Y. Tsuji*

* Gunma University, Japan ** Hokkaido University, Japan

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SLIDE 3

Contents of this presentation

1.

  • 1. Introduction

Introduction

Concept of EBS for LLW in Japan Degradation of EBS at cement/bentonite interaction

2.

  • 2. Test method

Test method

Acceleration test by electrical migration technique

3.

  • 3. Experimental procedures and results

Experimental procedures and results

  • 1. Investigation of effect of dry density on degradation of

EBS at cement/bentonite interaction

  • 2. Investigation of effect mixed NaHCO3 on degradation
  • f EBS at cement/bentonite interaction

4.

  • 4. Conclusions

Conclusions

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SLIDE 4

Contents of this presentation

1.

  • 1. Introduction

Introduction

Concept of EBS for LLW in Japan Degradation of EBS at cement/bentonite interaction

2.

  • 2. Test method

Test method

Acceleration test by electrical migration technique

3.

  • 3. Experimental procedures and results

Experimental procedures and results

  • 1. Investigation of effect of dry density on degradation of

EBS at cement/bentonite interaction

  • 2. Investigation of effect mixed NaHCO3 on degradation
  • f EBS at cement/bentonite interaction

4.

  • 4. Conclusions

Conclusions

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SLIDE 5

EBS for LLW in Japan

Repository concept of LLW in Japan

50~100m under the ground

Underground cavern type disposal facility to isolate low-level radioactive waste

(http://www.enecho.meti.go.jp/rw/gaiyo/gaiyo03-3.html)

Low conductivity buffer [Bentonite material] Low diffusion layer [Cementitious material]

Extremely long-term stability for several tens thousands years is required.

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SLIDE 6

Ca2+ Ca2+ Ca2+

Durability problem of EBS for LLW in Japan

Low diffusion layer [Cementitious material] Low conductivity buffer [Bentonite material]

Increase in Ca & pH Degradation

Increase in porosity >>>Increase in diffusivity

Ca leaching Degradation

Decrease in swelling capacity >>>Increase in conductivity

Repository concept

  • f LLW in Japan

To evaluate extremely long-term stability during tens thousands of years Na

  • type

Ca

  • type

water

Ca2+ Ca2+ Ca2+

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SLIDE 7

Two experimental plans in this study

Low conductivity buffer [Bentonite material] Low diffusion layer [Cementitious material]

Repository concept of LLW in Japan

Leaching

Increase in Ca & pH

Degradation

Ex) Increase in diffusivity

Degradation

Ex) Increase in conductivity

Reduce negative cement/bentonite interaction Problem of EBS Approach I Control cement/bentonite interaction for increasing stability Approach II Mixing NaHCO3 for creating additional layer of CaCO3

Exp II

To evaluate stability during tens thousands of years

Increase in dry density of bentonite

Exp I

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SLIDE 8

Next topic

1.

  • 1. Introduction

Introduction

Concept of EBS for LLW in Japan Degradation of EBS due to cement/bentonite interaction

2.

  • 2. Test method

Test method

Acceleration test by electrical migration technique

3.

  • 3. Experimental procedures and results

Experimental procedures and results

  • 1. Investigation of effect of dry density on degradation of

EBS due to cement/bentonite interaction

  • 2. Investigation of effect mixed NaHCO3 on degradation
  • f EBS due to cement/bentonite interaction

4.

  • 4. Conclusions

Conclusions

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SLIDE 9

25 65 10 Direct current voltage (15V) Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Direct current voltage (15V) Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

Acceleration test by electrical migration technique

To accelerate ion transport by applying electric potential gradient

Several studies have been reported. (e.g. Saito et al. 1997)

Ca2+ Ca2+

＋ －

Anode Cathode Ca leaching Degradation

Ca2+ Ca2+ Ca2+

Cement Bentonite Side view

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SLIDE 10

Next topic

1.

  • 1. Introduction

Introduction

Concept of EBS for LLW in Japan Degradation of EBS due to cement/bentonite interaction

2.

  • 2. Test method

Test method

Acceleration test by electrical migration technique

3.

  • 3. Experimental procedures and results

Experimental procedures and results

  • 1. Investigation of effect of dry density on degradation of

EBS due to cement/bentonite interaction

  • 2. Investigation of effect mixed NaHCO3 on degradation
  • f EBS due to cement/bentonite interaction

4.

  • 4. Conclusions

Conclusions

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SLIDE 11

Exp I: Influence of dry density (Specimen)

25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

[Cementitious material] Concrete Cement: OPC W/C = 55% [Bentonite material] Bentonite sand mixture Bentonite: Kunigel V1 Bentonite:Sand = 7:3 Name

  • f specimen

Dry Density g/cm3 Water Content % Compaction times / Layer 28.6 11 19 38 150, 200 26.1 22.6 15.0 Bt16 1.6 Bt17 1.7 Bt18 1.8 Bt19 1.9

4 specimens of bentonite sand mixture

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SLIDE 12

After 13.0kC accumulated electrical charge

Exp I: Measurement after electrical migration test

TGA Ca(OH)2, Swelling capacity Cation concentration EPMA (Bt19)

Concrete Bentonite sand mixture

25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

No. Dry density, g/cm3 Water content, % Bt16 1.6 28.6 Bt17 1.7 26.1 Bt18 1.8 22.6 Bt19 1.9 15.0 Anode Cathode

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SLIDE 13

After 13.0kC accumulated electrical charge

Exp I: Measurement after electrical migration test

TGA Ca(OH)2, Swelling capacity Cation concentration EPMA (Bt19)

Concrete Bentonite sand mixture

25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

No. Dry density, g/cm3 Water content, % Bt16 1.6 28.6 Bt17 1.7 26.1 Bt18 1.8 22.6 Bt19 1.9 15.0

10 5 5 5

Anode

陰極 2 7 1 3 4 5 6 5 10 ・・・ (mm) 10

Cathode (Layer) Center Bt-side

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SLIDE 14

5 10 15 20 25 1 2 3 4

Center Bt-side

5 10 15 20 25 1 2 3 4

Center Bt-side

5 10 15 20 25 1 2 3 4

Center Bt-side

Bt17 Bt18 Bt19

Percentage of Residual Ca(OH)2 (%)

75% 75%

Percentage of Residual Ca(OH)2 (%) Percentage of Residual Ca(OH)2 (%)

Percentage of residual Ca(OH)2: Calcium leached from Bt-side of concrete to bentonite

Center > Bt-side

Decrease in Bt-side was not observed Reduce degradation

Bt17 Bt18 Bt19

Ca(OH)2: leach from concrete first Measurement of residual Ca(OH)2

Result of TGA: Degradation of concrete

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SLIDE 15

low high

Concrete Cathode Concrete Cathode

low high low high

Concrete Cathode Concrete Concrete Cathode Cathode Concrete Cathode Concrete Concrete Cathode Cathode

Na Na Ca Ca

Alteration of bentonite progress from the interface

Profile of Sodium Profile of Calcium

surface analysis and profile

Sodium Ion: Migrated to cathode Calcium Ion: Migrated from concrete

Result of EPMA: Cations in bentonite (Bt19)

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SLIDE 16

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of layer Ca/Na

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of layer Swelling capacity ratio

Bt16

1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

Bt17 Bt18 Bt19

Swelling capacity ratio: Swelling capacity divided by mean value of swelling capacities of 6th and 7th layers

Result of cations and swelling capacity of bentonite

Cation ratio (Ca/Na): Ion ratio of calcium to sodium ions

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SLIDE 17

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of layer Ca/Na

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of layer Swelling capacity ratio

Bt16

1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

Swelling capacities decrease with increase in Ca/Na Change to Ca-type Concrete side: Bt17 Bt18 Bt19

Result of cations and swelling capacity of bentonite

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SLIDE 18

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of Layer Swelling Capacity ratio

2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of layer Ca/Na

0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 6 7 Number of layer Swelling capacity ratio

Bt16

1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

Bt17 Bt18 Bt19 Bt19: Decrease in swelling capacity was reduced Low conductivity can be maintained by using high dry density bentonite

59% 66% 64% 36%

Result of cations and swelling capacity of bentonite

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SLIDE 19

Next topic

1.

  • 1. Introduction

Introduction

Concept of EBS for LLW in Japan Degradation of EBS due to cement/bentonite interaction

2.

  • 2. Test method

Test method

Acceleration test by electrical migration technique

3.

  • 3. Experimental procedures and results

Experimental procedures and results

  • 1. Investigation of effect of dry density on degradation of

EBS due to cement/bentonite interaction

  • 2. Investigation of effect mixed NaHCO3 on degradation
  • f EBS due to cement/bentonite interaction

4.

  • 4. Conclusions

Conclusions

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SLIDE 20

Exp II: Utilization of cement/bentonite interaction

Exp I: Negative effect

Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+

Ca leaching Degradation

Exp II: Utilization

Ca2+ Ca2+ Ca2+

HCO3

  • HCO3
  • HCO3
  • Ca2+

Ca2+ Ca2+

HCO3

  • HCO3
  • HCO3
  • Ca2+

Ca2+

HCO3

  • HCO3
  • Reduction of degradation

Additional barrier of CaCO3 Mixing NaHCO3 into bentonite

Mixing of NaHCO3 Low conductivity buffer

[Bentonite material]

Low diffusion layer

[Cementitious material]

Low conductivity buffer

[Bentonite material]

Low diffusion layer

[Cementitious material]

CaCO3

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SLIDE 21

Reference: Reduce leaching by HCO3-

Kurashige et al. (2005) have shown that HCO3

  • in ground water

reduce leaching of cementitious materials.

Immersion time (week) Accumulated amount of leached OH- (mg/L)

In this study, we aim to get this additional effect intentionally in the proposed artificial system.

Reduction

  • f

leaching

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SLIDE 22

25 65 10 Direct current voltage (15V) Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Direct current voltage (15V) Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

Exp II: Acceleration test by electrical migration technique

To accelerate ion transport by applying electrical gradient

Ex) Saito et al. investigated calcium leaching

Ca2+ Ca2+

HCO3

  • HCO3
  • ＋

－

Anode Cathode Ca leaching Degradation

Ca2+ Ca2+ Ca2+

Cement Bentonite

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SLIDE 23

Exp II: Influence of mixing NaHCO3 (Specimen)

25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

[Cementitious material] Cement paste Cement: OPC W/C = 60% [Bentonite material] Bentonite sand mixture Bentonite: Kunigel V1 Bentonite:Sand = 7:3 Dry density = 1.6 g/cm3 Name

  • f specimen

NaHCO3 mass % Concentration g/litter Remarks No mixing Saturation 10 103 103 C0 C0.4 0.4 C4 4.1 C7 7.1

4 specimens of bentonite sand mixture

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SLIDE 24

After 140 hours electrical migration

Exp II: Measurement after electrical migration test

TGA Ca(OH)2, CaCO3 Swelling capacity Cation concentration

Cement paste Bentonite sand mixture

25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

No.

NaHCO3 mass % Concentration g/litter C0 C0.4 0.4 10 C4 4.1 103 C7 7.1 103

Anode Cathode

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SLIDE 25

After 140 hours electrical migration

Exp II: Measurement after electrical migration test

TGA Ca(OH)2, CaCO3 Swelling capacity Cation concentration

Cement paste Bentonite sand mixture

25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution 25 65 10 Bentonite Sand Mixture Concrete Steel mesh Steel mesh Saturated Calcium solution

No.

NaHCO3 mass % Concentration g/litter C0 C0.4 0.4 10 C4 4.1 103 C7 7.1 103 10 5 5 5

Anode

陰極 2 7 1 3 4 5 6 5 10 ・・・ (mm) 10

Cathode (Layer) Center Bt-side

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SLIDE 26

Result of TGA: Degradation of cement paste

TGA Measurement of Ca(OH)2 Measurement of CaCO3

Cement paste

C0 C0.4 C4 C7

1 2 3 4 Total Ca (mol/l) (=Ca(OH)2+CaCO3)

Initial No mix 0.4% mix 4% mix 7% mix Calculated value as summation of Calcium in Ca(OH)2 & CaCO3 Drop

No drop No drop

Reduce drop 10 5 5 5

Anode

陰極 2 7 1 3 4 5 6 5 10 ・・・ (mm) 10

Cathode (Layer) Bt-side

Total Total

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SLIDE 27

C0 C0.4 C4 C7

1 2 3 4 Total Ca (mol/l) (=Ca(OH)2+CaCO3)

Result of TG-DTA: Degradation of cement paste

Initial No mix 0.4% mix 4% mix 7% mix Initial Ca(OH)2 CaCO3 measured by TG-DTA Ca(OH)2 measured by TG-DTA TG-DTA Measurement of Ca(OH)2 Measurement of CaCO3

Cement paste

10 5 5 5

Anode

陰極 2 7 1 3 4 5 6 5 10 ・・・ (mm) 10

Cathode (Layer) Bt-side Calculated value as summation of Calcium in Ca(OH)2 & CaCO3

Details Details

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SLIDE 28

Details Details

C0 C0.4 C4 C7

1 2 3 4 Total Ca (mol/l) (=Ca(OH)2+CaCO3)

Result of TG-DTA: Degradation of cement paste

No mix 0.4% mix 4% mix 7% mix 初期Ca（OH)2 Ca2+ Ca2+

HCO3

  • HCO3
  • Cement paste Bentonite

By mixing NaHCO3 into bentonite, CaCO3 was precipitated at cement/bentonite interface

Reduction of leaching

CaCO3 measured by TG-DTA Ca(OH)2 measured by TG-DTA TG-DTA Measurement of Ca(OH)2 Measurement of CaCO3

Cement paste

10 5 5 5

Anode

陰極 2 7 1 3 4 5 6 5 10 ・・・ (mm) 10

Cathode (Layer) Bt-side CaCO3

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SLIDE 29

Result of Cations: Degradation of bentonite

1 2 3 4 5 6 1 2 3 4 5 6 7

  • No. of layer

Cation’s ratio (Ca/Na)

1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 1 2 3 4 5 6 7

C0 C0.4 C4 C7

Initial

Cation’s ratio (Ca/Na) Cation’s ratio (Ca/Na) Cation’s ratio (Ca/Na)

In specimen without NaHCO3, cation’s ratio increased at the surface layers In specimens with large NaHCO3,

increase in cation’s ratio were significantly reduced

No mixing 0.4% mix 4% mix 7% mix

  • No. of layer
  • No. of layer
  • No. of layer

Swelling capacity Cation concentration

Bentonite sand mixture

10 5 5 5

Anode

陰極 2 7 1 3 4 5 6 5 10 ・・・ (mm) 10

Cathode (Layer)

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SLIDE 30

Result of swelling capacity: Degradation of bentonite

5 10 15 20 1 2 3 4 5 6 7

5 10 15 20 1 2 3 4 5 6 7 5 10 15 20 1 2 3 4 5 6 7 5 10 15 20 1 2 3 4 5 6 7

Layer Swelling capacity mg/2g

Initial

C0 C0.4 C4 C7

No mixing 0.4% mix 4% mix 7% mix

Initial Initial Initial

In specimen without NaHCO3, swelling capacity decreased at the surface layers In specimens with large NaHCO3,

decrease in swelling capacity were significantly reduced

Swelling capacity Cation concentration

Bentonite sand mixture

10 5 5 5

Anode

陰極 2 7 1 3 4 5 6 5 10 ・・・ (mm) 10

Cathode (Layer)

Layer Swelling capacity mg/2g Layer Layer Swelling capacity mg/2g Swelling capacity mg/2g

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SLIDE 31

Next topic

1.

  • 1. Introduction

Introduction

Concept of EBS for LLW in Japan Degradation of EBS due to cement/bentonite interaction

2.

  • 2. Test method

Test method

Acceleration test by electrical migration technique

3.

  • 3. Experimental procedures and results

Experimental procedures and results

  • 1. Investigation of effect of dry density on degradation of

EBS due to cement/bentonite interaction

  • 2. Investigation of effect mixed NaHCO3 on degradation
  • f EBS due to cement/bentonite interaction

4.

  • 4. Conclusions

Conclusions

slide-32
SLIDE 32

Conclusions

In this study, the long-term durability of the engineered barriers system was investigated by the migration technique. Firstly, the effect of dry density of bentonite-sand mixtures was investigated. The experimental results showed the use of the bentonite sand mixture having high dry density was effective with regard to the reduction in the risk of the alteration. Secondly, the effect of mixing of NaHCO3 to the bentonite- sand mixture was investigated. The experimental results showed the mixing of NaHCO3 clearly reduced the degradation of cementitious materials and bentonite because of precipitation of CaCO3.

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SLIDE 33

Thank you for your kind attention!

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SLIDE 34

Specimens

150 50 730 100 50 25 100 100 Cut

  • Fig. 1 Dimensions of concrete (mm)

150 50 730 100 50 25 100 100 Cut 150 50 730 100 50 25 100 100 Cut

  • Fig. 1 Dimensions of concrete (mm)
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SLIDE 35

2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of Layer Ca/Na 2 4 6 8 10 1 2 3 4 5 6 7 Number of layer Ca/Na

Bt16

1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

Swelling capacity decrease with increase in Ca/Na Change to Ca-type Concrete side: Bt17 Bt18 Bt19

Result of cation’s ration in bentonite

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SLIDE 36

ベントナイトのおける膨潤力と陽イオン量の関係

0.0 0.2 0.4 0.6 0.8 1.0 1.2 500 1000 1500 C0 C0.4 C4 C7

膨潤力比（＝試験後／試験前） Ca+10Na（meq/100g）

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1 2 3 4 5 C0 C0.4 C4 C7

膨潤力比（＝試験後／試験前） Ca/Na 炭酸水素ナトリウム混合では Ca/Naが高いが膨潤力低下はわずか CaとNaの膨潤への貢献度合いを 足し合わせることにより膨潤力を 統一的に評価できる可能性も

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SLIDE 37

電流の経時変化

15 25 35 45 2 4 6 C7 C4 C0.4 C0

試験期間 （日） 電流（mA）

25 65 10 (mm) ベ ン ト ナ イト 砂混合土 陰極 コ ン クリート 飽和水酸化 カル シ ウム 溶液 陽極 25 65 10 (mm) ベ ン ト ナ イト 砂混合土 陰極 コ ン クリート 飽和水酸化 カル シ ウム 溶液 陽極 25 65 10 (mm) ベ ン ト ナ イト 砂混合土 陰極 コ ン クリート 飽和水酸化 カル シ ウム 溶液 陽極 セメ ン ト ペ ース ト

φ100

C0 13.7 C0.4 13.0 C4 12.3 C7 12.7 試験期間 h 積算電気量 kC 140 供試体名

電気泳動試験結果

slide-38
SLIDE 38

合計Ca量の分布

中央 界面

5 10 15 20 25 30 1 2 3 4 5 供試体名 Ca(OH)2、 CaCO3含有量（ ％） 1 2 3 4 5 合計Ca量（ kmol/ m

3)

Ca(OH)2 CaCO3 Ca合計

初期値 C0 C0.4 C4 C7

5 10 15 20 25 30 1 2 3 4 5 供試体名 Ca(OH)2、 CaCO3含有量（ ％） 1 2 3 4 5 合計Ca量（ kmol/ m

3)

Ca(OH)2 CaCO3 Ca合計

初期値 C0 C0.4 C4 C7

CaCO3 Ca(OH)2 Ca(OH)2 CaCO3 合計Ca量 Ca合計 合計Ca量

セメントペースト単位体積あた りのCa(OH)2とCaCO3の物質量 の和

合計Ca量：

slide-39
SLIDE 39

ベントナイトの試験

日本ベントナイト工業標準試験方法に準拠 浸出陽イオン量・・・CaイオンとNaイオンの浸出陽イオン量比（Ca/Na）で評価 膨潤力・・・150μmに粉砕したベントナイト砂混合土の試料2.0gを，蒸留水100mlを入 れた100mlのメスシリンダーに加え，24時間静置後，容器内に堆積した試料の見掛け容 積を読みとることで測定 膨潤力測定例（C0の1～4層目）

5.0 6.5 11.0 15.0

slide-40
SLIDE 40

ベントナイトにおける浸出陽イオン量

表－6 浸出陽イ オン量測定の結果 1層目 2層目 3層目 4層目 5層目 6層目 7層目 Ca 40.5 92.3 73.3 69.9 43.8 41.0 53.0 73.0 Na 59.3 18.6 21.5 28.4 55.5 72.0 84.3 97.8 Ca 41.0 77.5 82.9 40.1 34.3 27.4 26.9 25.4 Na 66.0 16.7 24.9 61.1 71.9 83.9 82.5 99.4 Ca 42.9 92.8 55.1 37.6 35.1 40.3 39.8 38.9 Na 93.4 22.2 56.2 98.1 80.4 95.6 95.7 116.4 Ca 44.2 112.8 48.9 46.4 48.3 48.0 46.8 43.6 Na 113.4 38.8 91.2 107.3 108.3 107.4 121.0 135.1 C0.4 C4 C7 浸出陽イ オン量 meq/ 100g 供試体名 イ オン C0 初期値 電気泳動試験後 表－6 浸出陽イ オン量測定の結果 1層目 2層目 3層目 4層目 5層目 6層目 7層目 Ca 40.5 92.3 73.3 69.9 43.8 41.0 53.0 73.0 Na 59.3 18.6 21.5 28.4 55.5 72.0 84.3 97.8 Ca 41.0 77.5 82.9 40.1 34.3 27.4 26.9 25.4 Na 66.0 16.7 24.9 61.1 71.9 83.9 82.5 99.4 Ca 42.9 92.8 55.1 37.6 35.1 40.3 39.8 38.9 Na 93.4 22.2 56.2 98.1 80.4 95.6 95.7 116.4 Ca 44.2 112.8 48.9 46.4 48.3 48.0 46.8 43.6 Na 113.4 38.8 91.2 107.3 108.3 107.4 121.0 135.1 C0.4 C4 C7 浸出陽イ オン量 meq/ 100g 供試体名 イ オン C0 初期値 電気泳動試験後

slide-41
SLIDE 41

Swelling Capacity

Swelling Water Molecule Interlayer Cations Layer Crystal Structure

Main component is montmorillonite

slide-42
SLIDE 42

Results of XRD (Bentonite)

Na-type 2θ=7.0~7.5° Ca-type 2θ=5.7~6.0°

Bt19: 1st to 3rd Layer Ca-type Bt16, Bt17, Bt18: 1st and 2nd Layer Process of change to Ca-type ? Changing of type start from concrete side

1 2 3 4 5 6 7

Peak range of angle of reflection in XRD curves shows type of bentonite (Kurosawa, 2002)

Bt19 Na-type Ca-type 1st layer 2nd layer 3rd layer 4th layer 5th layer 6th layer 7th layer 2θ/degree 2 4 6 8 10

2 4 6 8 10

2θ/degree Bt16 Na-type Ca-type 1st layer 2nd layer 3rd layer 4th layer 5th layer 6th layer 7th layer

2 4 6 8 10

Bt17 Na-type Ca-type 1st layer 2nd layer 3rd layer 4th layer 5th layer 6th layer 7th layer 2θ/degree

2 4 6 8 10

Bt18 Na-type Ca-type 1st layer 2nd layer 3rd layer 4th layer 5th layer 6th layer 7th layer 2θ/degree

slide-43
SLIDE 43

2g add to 100ml water Bentonite Sand Mixture Powder (150μ)

After leaving for 24 hour

Cations and Swelling Capacities (Bentonite)

Method of Measurement of Swelling capacity

13 ml/2g 8 ml/2g

Na-type Ca-type

Swelling capacity Swelling capacity

Swelling Capacity Ratio: Swelling capacity divided by mean value of swelling capacity of 6th and 7th in each layer

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SLIDE 44

7.5m 10.5m 12.5m Radioactive Waste Radioactive Waste 7.5m 9m

Cementitious Materials Backfill material

A Horizontal Section A Vertical Section Size of Geological Disposal Structure (Low-Level)

Na-Bentonite Sand Mixture

0.5m 0.5m

Backfill material

Size of a section is 7.5m wide, 7.5m high, and 9m deep.