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THEBES: KYT project investigating bentonite 1 st THEBES workshop, Aalto University 11 th December 2015 The behaviour of bentonite based materials: insight into nano and micro-structure Pierre Delage Ecole Nationale des Ponts et Chausses, Paris

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The behaviour of bentonite based materials: insight into nano and micro-structure

Pierre Delage Ecole Nationale des Ponts et Chaussées, Paris Laboratoire Navier/CERMES THEBES: KYT project investigating bentonite 1st THEBES workshop, Aalto University 11th December 2015

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2

Outline of the presentation

  • Bentonite materials in nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
  • Nanostructure issues during hydration
  • Consequences on water retention
  • Consequences on water transfer
  • Consequences on technological voids
  • Conclusions
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3

Outline of the presentation

  • Bentonite materials in nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
  • Nanostructure issues during hydration
  • Consequences on water retention
  • Consequences on water transfer
  • Consequences on technological voids
  • Conclusions
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4

Role of the disposal

  • To impede water circulation

– Canister – Engineered barrier – Geological barrier – Structure of the disposal

  • To immobilise radionuclides into the canisters
  • To delay and attenuate the migration of

radionuclides (> 500 000 y.) Multibarrier concept including engineered barrier and host rock

ANDRA 2005

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Multi-barrier system (vertical deposit)

SKB

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SKB concept

SKB, Posiva

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Swiss concept

Opalinus clay Compacted bentonite High Level Waste Intermediate Level Waste

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SLIDE 8

Deep geological disposal: French concept

ANDRA 2005

(EDZ)

Saturation

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SLIDE 9

COx Claystone

Ø Stable geological context (155 Ma) Ø Very low permeability: 10-20 10-21 m2 Ø Good ability for radionuclides retention Ø Porosity : 14 – 19% Ø Clay fraction: 48-50% at 490 m

Photo ANDRA

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Blocks of compacted bentonite

FEBEX project (1996), Grimsel URL FEBEX project (2005)

Technological voids Closed after 9 years hydration

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11

Pellets

Posiva

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NAGRA Concept

Bentonite blocks Bentonite pellets

Nagra

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13

HE-E experiment (Nagra)

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14

Outline of the presentation

  • Bentonite materials in nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

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Clay FoCa7 clay (F) Kunigel (J) MX 80 (US) Mineralogy Kaolinite- smectite 64% Na smectite 85% Na - Ca smectite wL (%) 112 474 520 wP (%) 50 27 62 IP 62 447 458 ρs 2.67 Mg/m3 2.79 Mg/m3 2.65 Mg/m3 Activity 0.78 6.9 5.4 Specific surface 300 m2/g 687 m2/g 700 m2/g Cation Exchange Capacity 54 mEq/100 g 73,2 mEq/100 g 68 mEq/100 g

Some typical characteristics of bentonites

Tessier et al. (1998), Komine & Ogata (1992), Pusch (1992)

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SEM Photo, Compacted Kunigel clay

5 µm 2 µm

Cui et al. (2002)

Clay aggregates Inter-aggregates DRY pores ρ = 2 Mg/m3 w = 8% s = 57 MPa Cui, Loiseau and Delage 2002

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Sand (35%) - MX80 (65%) mixture

20 40 60 80 100 0.0001 0.001 0.01 0.1 1 10

Grain size (mm) Percentage passing (%)

Sand grains Bentonite grains Deflocculated bentonite (hydrometer)

Sand Bentonite grains Deflocculated bentonite

Saba, Delage et al. Eng. Geol 2014

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SLIDE 18

0.01 0.1 1 10 100 0.00 0.01 0.1 1 10 100 0.0 0.1 0.2 0.3 0.4

b

Porosity Entrance pore diameter (µm)

Laplace’s law : Cylindrical pore : r1 = r2 Higher Hg (non wetting) pressure penetrates smaller pores

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + =

2 1

1 1 r r cos p θ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ 1 =

1

2 r cos p θ

in smaller and smaller pores

increasing Hg pressure

200 MPa 3.5 nm

Mercury intrusion pore size distribution

Hg penetrating

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Mercury intrusion pore size distribution

0.01 0.1 1 10 100 0.00 0.05 0.10 0.15

dV/d(logD)

a

0.01 0.1 1 10 100 0.0 0.1 0.2 0.3 0.4

b

Porosity Entrance pore diameter (µm)

Not intruded < 3.5 nm s = 75.5 MPa

Saba, Delage et al. Eng. Geol 2014

Sand-bentonite compacted powder ρd = 1.8 Mg/m3 , w = 10%, Sr = 55%, s = 75.5 MPa

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SLIDE 20

Simona SABA - PhD Defense – 9 Dec 2013 20 /48

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.001 0.01 0.1 1 10 100 1000 Entrance pore diameter D (µm) dV/d(logD) 0.019 µm 22 µm

Micropores: intra-granular Macropores: inter-grains

2- Microstructure at initial state

Micropores

Grain Platelet

Macropores

Pore size distribution curve

Sand-bentonite compacted powder ρd = 1.8 Mg/m3 , w = 10%, Sr = 55%, s = 75.5 MPa

Saba, Delage et al. Eng. Geol 2014

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Microfocus X-Ray Computed Tomography (µCT)

http://navier.enpc.fr

Imager/Detector X-Ray Source Sample Rotation disk Translation rails

Saba, Delage et al. Eng. Geol 2014

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Simona SABA - PhD Defense – 9 Dec 2013 22 /48

10 mm 50 mm 4 mm

2- Microstructure at initial state

Saba, Delage et al. Eng. Geol 2014

Sand-bentonite compacted powder

30 µm voxel size

65% MX80 bentonite, 35% sand, ρd = 1.8 Mg/m3, s = 76 MPa, Sr = 55%

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Simona SABA - PhD Defense – 9 Dec 2013 23 /48

Horizontal µCT cross section

50 mm

Bentonite Sand Pore Well defined bentonite grains Aggregation of bentonite grains

2- Microstructure at initial state

Saba, Delage et al. Eng. Geol 2014

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Simona SABA - PhD Defense – 9 Dec 2013 24 /48

Image analysis (ImageJ)

▌ Segmentation

73 Logarithmic Linear 73 Logarithmic Linear

3D Median filter (2x2x2 vox) Threshold Segmented image 73 Image histogram « Mixture Modelling» function

2- Microstructure at initial state

Saba, Delage et al. Eng. Geol 2014

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Simona SABA - PhD Defense – 9 Dec 2013 25 /48

5 10 15 20 25 30 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Porosity (> 30 µm) Distance fron centre (mm)

Heterogeneity in porosity

Mean value = 0.016 Pores > 30 µm (voxel size)

2- Microstructure at initial state

0.05 0.1 0.15 0.2 0.25 0.3 0.001 0.01 0.1 1 10 100 1000 Entrance pore diameter D (µm) Cumulative porosity

30 µm 0.026

1 3 4 5 2

Saba, Delage et al. Eng. Geol 2014

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26

Outline of the presentation

  • Bentonite materials in nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
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Sand-bentonite mixture PSD

0.01 0.1 1 10 100 0.00 0.05 0.10 0.15

dV/d(logD)

a

0.01 0.1 1 10 100 0.0 0.1 0.2 0.3 0.4

b

Porosity Entrance pore diameter (µm)

Not intruded < 3.5 nm s = 75.5 MPa

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0.001 0.01 0.1 1 10 Porous radius (µm) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Intruded mercury void ratio, em 0.597 0.812 0.293 0.230 w = 12.5 % w = 28.5 % e = 1.008

Effect of water content

MX 80 clay ρ = 2 Mg/m3 w = 12.5%, s = 30 MPa w = 28.5% s = 2 MPa

Delage et al., Géot. 2006

SAMPLE AT HIGHER WATER CONTENT AND LOWER SUCTION HAS MORE WATER LOCATED IN VERY SMALL PORES (< 35 nm)

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As compacted Calcigel

Agus and Schanz, 2005

ρd = 2 Mg/m3, w = 9%, s = 22.7 MPa Total pore volume

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Oven drying, Calcigel clay

Agus and Schanz, 2005

Oven-dried,w = 0%, s = 1 GPa OVEN-DRYING (s from 22 MPa to 1GPa) HAS LITTLE EFFECT ON MICROSTRUCTURE AND NANOPORES

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SLIDE 31

Hydration – swelling, Calcigel clay

Agus and Schanz, 2005

Hydrated and swollen w = 19%, s = 0 MPa SWELLING CONCERNS BOTH NANO PORES (< 3.5 nm) AND LARGE PORES (around 1 µm)

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32

Outline of the presentation

  • High level nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
  • Nanostructure issues during hydration
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Saturated intra-aggregates swelling mechanisms

Saiyouri, Hicher & Tessier (2000), using Pons et al. (1981)

  • X ray scattering at low angles
  • Probabilistic analysis

Interlayer distances as a function of decreased suction

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Sayiouri, Hicher & Tessier (2000)

Water adsorption along smectites

  • 4 layers : 20.6 Å
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  • Adsorption of water vs suction, MX 80

inside the saturated aggregates

50 MPa

18.6 Å 15.6 Å 12.6 Å

7 MPa Sayiouri, Hicher & Tessier (2000)

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Hydration from a dry state

Sayiouri, Hicher & Tessier (2000)

inside the saturated aggregates

high suction (> 50 MPa) 100 layers low suction (< 7 MPa) 10 layers possible double layer

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Hydration from a dry state, MX80

  • 50 MPa

7 MPa 18.6 Å 15.6 Å 12.6 Å

Sayiouri, Hicher & Tessier (2000)

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Hydration from a dry state

Suction (MPa)

inside the saturated aggregates

7 MPa 50 MPa

inter particles water, between 20 and 100 Å 0.001 0.01 0.1 1 10 100

Sayiouri, Hicher & Tessier (2000)

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SLIDE 39
  • Laplace’s law :
  • Planar pores : r2 = ∞

The same pressure corresponds to a twice smaller radius

Mercury intrusion in planar pore

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + =

2 1

1 1 r r cos p θ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ 1 =

1

r cos p θ

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Planar pores in particles

4 layers = 20.6 Å : 2d = 11 Å, d = 5.5 Å 3 layers = 18.6 Å : 2d = 9 Å, d = 4.5 Å 2 layers = 15.6 Å : 2d = 6 Å, d = 3 Å 1 layers = 12.6 Å : 2d = 3 Å, d = 1.5 Å

  • 4 layers : 20.6 Å
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0.001 0.01 0.1 1 10 Porous radius (µm) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Intruded mercury void ratio, em 0.597 0.812 0.293 0.230 w = 12.5 % w = 28.5 % e = 1.008 9 Å 3 layers 1.5 Å : 1 layer

inter particles water, between 20 and 100 Å

Compacted MX80

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42

Outline of the presentation

  • Bentonite materials in nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
  • Nanostructure issues in compacted bentonites

during hydration

  • Consequences on water retention
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SLIDE 43

Water retention curve, FoCa clay

10 20 30 40 50

Gravimetric water content (%)

0.1 1 10 100 1000

Suction (MPa)

Compacted samples Powder samples 50 MPa 7 MPa si

1 layer 2 layers 3 layers

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Water retention with swelling impeded

Wang et al., Soils and Found. 2013

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Water retention curve, constant volume

10 20 30 40 50

Gravimetric water content (%)

0.1 1 10 100 1000

Suction (MPa)

Free swelling condition Prevented swelling condition

50 MPa 7 MPa si

1 layer 2 layers 3 layers ? Constant volume Free swelling 3 layers

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Kunigel (70%) – sand (30%) mixture

4 6 8 10 12 14

w (%)

0.1 1 10 100

s (MPa)

7 MPa

3 layers ? Constant volume

Cui et al., Phys. Chem. Earth 2008

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Compacted MX80 and powder

  • 7 MPa

3 layers ? Constant volume

Delage et al., Géot. 2006

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Swelling

FoCa clay

0.1 1 10 100 1000

Suction (MPa)

0.4 0.8 1.2 1.6

Void ratio

Various suction cycles under no stress : Reversibility

50 MPa 7 MPa Si = 116 MPa

1 layer Less thicker particles 2 layers 3 layers, Many more thinner particles

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SLIDE 49

Simona SABA - PhD 49 /48

50 mm

Sand Empty inter-grains pores containing water Exfoliation Gel around hydrated bentonite grains Bentonite

70% bentonite and 30% sand ρdb = 0.94 Mg/m3 , Sr = 85%

4- Swelling pressure anisotropy

Hydrated sand-bentonite mixture

Saba 2013

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50

Hydrated Pellet-bentonite mixture - µtomo

Van Geet et al. App. Clay Sc. 2005 Two weeks One month Two months (5 bars) Dry

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Investigation of gel formation

Pressure measurements Pressure measurements Flow/Hydration/Gel Flow/Hydration/Gel Inflow, 2 MPa Planar free space Marcial, Delage & Cui, Geomech. Geoeng. 2006

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Pressure build up

2000 4000 6000 Time (mn) 300 600 900 1200 1500 1800 2100 p (kPa)

pp sp1 sp2 sp3

33h 66h 99h Time (h) Pressure (kPa)

Marcial, Delage & Cui, Geomech. Geoeng. 2006

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Outline of the presentation

  • Bentonite materials in nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
  • Nanostructure issues in compacted bentonites

during hydration

  • Consequences on water retention
  • Consequences on water transfer
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Unsaturated permeability

Instantaneous profile method suction (MPa) Curve slopes give hydraulic gradient i at various suctions

lower gradient Water infiltration in a column Water retention curve determined Suction monitoring along column

Daniel 1984

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Corresponding water contents given by water retention curve Changes in water content with time provide water unit flow q Unsaturated permeability K given by :

A is the sectional area

t dx dx A q

L x t L x t t

i i

Δ θ θ

Δ

∫ ∫

− =

+

( )

t t t

i i 5 , q A 1 K

Δ +

+ − =

Daniel 1984

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Instantaneous profile method, Kunigel

10 20 30 40 50 60 s ( MPa) 50 100 150 200 250 h (mm) t = 0 h t = 200 h t = 400 h t = 600 h t = 800 h t = 1000 h t = 1200 h t = 1400 h t = 1600 h t = 1800 h t = 2000 h t = 2200 h

Suction (MPa)

Infiltration constant volume

Cui et al., Phys. Chem. Earth 2008

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Darcy’s law?

20000 40000 60000

i (-)

0.0x100 4.0x10-13 8.0x10-13 1.2x10-12 1.6x10-12 2.0x10-12

q (m3/s)

s = 45 MPa s = 43 MPa s = 41 MPa s = 39 MPa s = 37 MPa s = 35 MPa

Cui et al., Phys. Chem. Earth 2008

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Unsaturated permeability (2)

10 20 30 40 50 60 s (MPa) 0.0x10 4.0x10

  • 14

8.0x10

  • 14

1.2x10

  • 13

k (m/s) h = 50 mm h = 100 mm h = 150 mm h = 200 mm T01

Suction (MPa) Permeability (m/s)

Cui et al., Phys. Chem. Earth 2008

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59

Outline of the presentation

  • Bentonite materials in nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
  • Nanostructure issues in compacted bentonites

during hydration

  • Consequences on water retention
  • Consequences on water transfer
  • Consequence on technological voids
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Effects of technological voids

Technological voids Closed after 9 years hydration Estimated 6.6% in FEBEX, 9% in the French concept (ANDRA) and 14% in the Sealex test (IRSN, France)

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Technological voids

Wang et al. Sand Found. 2013

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Swelling pressure development

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 10 20 30 40 Time (h) Vertical stress (MPa)

SP-01 SP-02 SP-03 SP-04

ρd = 1.93 Mg/m3 ρd = 1.96 Mg/m3 ρd = 1.96 Mg/m3 ρd = 1.98 Mg/m3

σ

Water escaping Gel formation Clogging Wang et al. Sand Found. 2013

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Final swelling pressure vs saturated density

0.01 0.1 1 10 100 1 2 3 4 Bentonite void ratio (-) Vertical stress (MPa)

Mixture 70/30 (Present work) Mixture 70/30 (Karnland et al., 2008) Pure bentonite (Karnland et al., 2008) Pure bentonite (Dixon et al., 1996) Pure bentonite (Komine et al., 2009) Pure bentonite (Borgesson et al., 1996)

Initial technical void

Wang et al. Sand Found. 2013

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Outline of the presentation

  • High level nuclear waste disposals
  • Microstructure issues in compacted bentonites

and sand bentonite mixtures:

  • Hydration of compacted bentonites
  • Nanostructure issues in compacted bentonites

during hydration

  • Consequences on water retention
  • Consequences on water transfer
  • Consequences on technological voids
  • Conclusions
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Conclusions

  • Smectites are very active materials/water
  • Microstructure examined at various levels:

µtomo MiP and SEM

  • Hydration mechanisms further understood

through nanostructure considerations

  • Generation and role of gel
  • Water retention and transfer illustrated through

adsorption of water layers

  • Swelling pressure always conditioned by final

saturated density

  • Bentonite based material are safe and reliable

with respect to water tightness