RHEOLOGY MEASUREMENTS ON SMECTITE CLAY GELS

Ulf Nilsson Magnus Hedström Clay Technology AB

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Asha

20g/l 5mM 1V 1

20g/l 5mM 1V 2

20g/l 5mM 1V 3

20g/l 10mM 1V 1

20g/l 10mM 1V 2

20g/l 10mM 1V 3

20g/l 50mM 1V 2

20g/l 50mM 1V 3

20g/l 100mM 1V 1

Setup The clay fraction of the Ashapura (505) bentonite was extracted by centrifugation, oven dried at 60°C, milled and then mixed with deionized water to correct concentration. The test samples were prepared by adding equal volumes of adequate concentration of sodium chloride solution and clay suspension. They were mixed through shaking and then rested for 1 day and 1 week, respectively, until testing. Longer periods will be tested. Testing was made in a Brookfield Viscometer with V-73 and V-74 vanes. Testing speed 0.05 rpm.

Comments Gel formation is the only bentonite-specific mechanism that can prevent erosion of clay at a transmissive fracture. The present tests show strong sensitivity to the salinity of the external water. For Ashapura(505) a NaCl concentration of ~5 mM is needed to form a gel. However, at that rather low concentration the present tests show that the yield stress is significant. Care at preparation and the testing is necessary. According to manual a vane inserted to half depth can be used to measure samples if full depth is above the range. This have been tested and this is not applicable to these samples. This is probably due to sedimentation during the gelling process. Consolidation of the gel may also contribute. Reference: Nilsson U, Hedström M., 2016. Rheology of dilute montmorillonite gels. Applied Clay Science. To be submitted Acknowledgements European Atomic Energy Community’s Seventh Framework Programme (FP7/2007-2011) under Grant Agreement no 295487, the BELBaR project. and SKB Svensk Kärnbränslehantering AB.

Preparation of 10 g clay/litre, rest time 1 day, three samples per concentration. Earlier result in background.

Two samples with similar maximum yield stress but corresponds to different phases. Blue (gel) retains the impression of the vane. Black (paste) instantly selfheals due to repulsion forces.

Preparation of 20 g clay/litre, rest time 1 day, three samples per concentration. Earlier result in background.

Preparation of 20 g clay/litre, rest time 1 week, three samples per concentration. Earlier tests in the background.

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Asha 20g/l 0mM 1d 1

20g/l 0mM 1d 2

20g/l 5mM 1d 1

20g/l 5mM 1d 2

20g/l 5mM 1d 3

20g/l 10mM 1d 1

20g/l 10mM 1d 2

20g/l 10mM 1d 3

20g/l 20mM 1d 1

20g/l 20mM 1d 2

20g/l 20mM 1d 3

20g/l 50mM 1d 1

20g/l 50mM 1d 2

20g/l 50mM 1d 3

20g/l 100mM 1d 1

20g/l 100mM 1d 2

20g/l 100mM 1d 3

Results The increase of maximum shear stress (yield stress) with salinity is nonlinear. The effect of increasing salinity is largest between 5 and 20 mM. Further increase in NaCl concentration gives a relatively limited effect. Longer resting times increases the shear strength. This is also expected for clay particles where there are both positive rim charges and negative layer (face) charges. The build-up of a network through edge-face interaction is a slow process and the tests show that the first formed network is not necessarily the strongest. The effect of ageing is strongest for the 5 and 10 mM concentration. Tests with different stock solutions are repeatable: giving both similar characteristic behaviour and quantitative values.

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Asha 10g/l 0mM 1d 1

10g/l 0mM 1d 2

10g/l 5mM 1d 1

10g/l 5mM 1d 2

10g/l 5mM 1d 3

10g/l 10mM 1d 1

10g/l 10mM 1d 2

10g/l 10mM 1d 3

10g/l 20mM 1d 1

10g/l 20mM 1d 2

10g/l 20mM 1d 3

10g/l 20mM 1d 4

10g/l 20mM 1d 5

10g/l 20mM 1d 6

10g/l 50mM 1d 1

10g/l 50mM 1d 2

10g/l 50mM 1d 3

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Asha 505 <2µm, 10 g/l

0 mM

5 mM 1

5 mM 2

5 mM 3

10 mM 1

10 mM 2

10 mM 3

20 mM 1

20 mM 2

20 mM 3

50 mM 1

50 mM 2

50 mM 3

100 mM 1

100 mM 2

100 mM 3

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Asha 505 <2µm, 20 g/l, 1 week rest

5 mM 1

5 mM 2

5 mM 3

10 mM 1

10 mM 2

10 mM 3

20 mM 1

20 mM 2

20 mM 3

50 mM 1

50 mM 2

50 mM 3

100 mM 1

100 mM 2

100 mM 3

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Asha 505 <2µm, 20 g/l, 1day rest

0 mM 1

0 mM 2

5 mM 1

5 mM 2

5 mM 3

10 mM 1

10 mM 2

10 mM 3

20 mM 1

20 mM 2

20 mM 3

50 mM 1

50 mM 2

50 mM 3

100 mM 1

100 mM 2

100 mM 3

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Asha 505 <2µm, 20 and 40 g/l

0 mM 40g/l

20 mM 20g/l