3. Materials and apparatus

In this study, we used Fujinomori soil (sample 1), three types of glass particles
with uniform sizes (Catalysts and Chemicals Ind. Co., Ltd.: d = 9.7 µm (sample 2), d =5.3 µm (sample 3), d = 2.2 µm (sample 4) and mixture of the glass particles (sample 5).
All water that we used was preliminary distilled, deionized, and degassed.
The sample 1 was actual soil and well-known for its high frost susceptibility.
The particles in the samples 2-4 were spherical with roughly the same diameters andtheir surface had nano-pores with a uniform diameter (figures 6 and 7).

The sample 5

was prepared by mixing the samples 2-4 and two other kinds of glass particles withuniform diameters (Nippon Rikagau Kikai Co., Ltd.: d = 50 µm and d = 200 µm).

In

the case of the sample 5, the particle size distribution was arranged to the distribution ofthe sample 1.

The sample 1 was prepared for observing actual ice lensing in naturalsoils and the samples 2-4 were for observing ideal ice lensing to make model.

Thesample 5 was prepared for comparing the phenomena between actual soil and ideal
porous media and for verifying influence of the uniformity of particles on a model thatwill be shown in chapter 7.

3.1 Characteristics of samples and grain-size distribution
Table 1 lists some characteristics of the samples 1-5.
sample 1 were quoted from Takeda (1988).

Some values for theThe samples 2-4 consisted of Vycor glass

particles, which formed a fine powder.

- 33 -Table 1. Characteristics of the samples 1-5
SampleSample 1

Sample 2

Sample 3

Sample 4

Sample 5

Fujinomori

Glass

Glass

Glass

Mixture(2.00mm~)%00.00.00.00Sand(2.00~0.074mm)%

150.00.00.015Silt(0.074~0.005mm)%

6197.345.912.6

60

Clay(~0.005mm)%

242.7854.1

87.4

25Quartz,

SiO2

SiO2

SiO2

SiO2

Feldspar (little),(99.6%),(99.0%),(99.4%),(99.0%),

GravelMineral components

Kaolin, Mica,

Na2O (little) Na2O(little) Na2O( little)

Montmorillonite,

etc.

etc.

Etc.

etc. (very little)(very little)(very little)(very little)

etc. ( little)

Mean diameterµm-

9.7

5.3

2.2-Specific gravity

-3

2.61

2.12

2.13

2.12-

2 -1

24.5

150.5

146.4

128.6

-

45.3

79.0

79.0

79.0

34.1

gcm

Specific surface areamg

Liquid limit
Plastic limit

46.5

79.0

79.0

79.0

34.1

-3%

Dry density

gm

1.18

0.79

0.82

0.85

0.88

Porosity

n55.0

----

2.22 × 107

5.85×10-6

3.00×10-6>

3.00×10-6>-

2.68 × 10-3

-----

6.8

7.0

6.8

7.0

Hydraulic conductivity

K cm sThermal conductivity-1 -1-1-1

cal cm s ˚CpHFigure 6 shows grain size accumulation curves for the samples.

The sample 1

was mainly consisting of silt.

The grain size of the sample 1 gradually distributed

from 0.3 mm to clay size.

The mean particle diameters of samples 2 and 4

corresponded to silt and clay, respectively.
between the samples 2 and 4.

The particle diameter of sample 3 was justThe coefficient of uniformity Uc of the samples 2 and 3

were 1.81 and 3.18 and the coefficient of curvature Uc’ were 1.02 and 1.19, respectively.
Although, the distribution of sample 4 was not so obvious because of the lack ofmeasurement under the range of a few micrometers, it was found that the particle sizesof samples 2 and 3 were very uniform.

The particle size distribution of the sample 5

imitated the distribution of sample 1.

Figure 6 indicates that the sample 5 had almost

same particle distribution as the sample 1.
- 34 -

sample1 (soil)
glass beads(d = 200 µm)
glass beads(d = 50 µm)
sample2 (d = 9.7 µm)
sample3 (d = 5.3 µm)
sample4 (d = 2.2 µm)
sample5 (mixture)
100806040200.001

Clay.01.1
Grain size (mm)Silt1Fine
sandFig. 6. Grain size accumulation curves for the samples.

- 35 -Coarse
sand3.2 Surface conditions
The surfaces of sample particles were observed by electron microscope.
Figures 7a-d show the electron micrographs of the samples 1-4.

The samples were

coated with thin film of vacuums evaporated gold since a sample must have someelectric conductivity for observation by electron microscope.

Then, the surface wasobserved with resolution of until 50000 but the surface under the film could notobserved. In the micrographs with resolution of 50000, the thin film of gold wasshown as a plane with many cracks.

Such cracks distributed widely throughout thesurface shown in the micrographs.

In the figure 7a (Sample 1), plate-like particles

with diameter of dozens micrometer and a number of micro particles with diameter of afew micrometer were observed.

In the figure 7b (Sample 2), spherical particles withdiameters from 3 to 20 micrometers were observed.
matters less than 0.3 micrometer on the surface.

The particles had many granular

In the figure 7c (Sample 3), sphericalparticles with diameters from 1 to 15 micrometers were observed.
similar to the sample 2.

The aspects wereThe particle surface shown in the figure 7c also had granularmatters less than 0.3 micrometer.

In the figure 7d (Sample 4), spherical particles withdiameters from 0.1 to 6 micrometers were observed.

Some of these particles gathered

and aggregated. The surface also had some granular matters- 36 -

- 37 Fig. 7. (a) Electron micrograph of sample 1 (Fujinomori soil: × 1000).

10µm

- 38 -Fig. 7. (b) Electron micrograph of sample 2.

(i) × 500, (ii) × 5000.

- 39 -Fig. 7. (b) Electron micrograph of sample 2.

(iii) × 10000, (ii) × 50000.

- 40 Fig. 7. (c) Electron micrograph of sample 3.

(i) × 500, (ii) × 5000.

- 41 -Fig. 7. (c) Electron micrograph of sample 3.

(iii) × 10000, (ii) × 50000.

- 42 Fig. 7. (d) Electron micrograph of sample 4.

(i) × 500, (ii) × 5000.

- 43 -Fig. 7. (c) Electron micrograph of sample 3.

(iii) × 10000, (ii) × 50000.300(a)200

1000300(b)2001000300(c)20010001234 5 6 78 102030

Pore radius (nm)Fig. 8.

Distribution curves of nano pores of the samples 2-4 obtained by the nitrogen

adsorption method.
4 (d = 2.2 µm).

(a) Sample 2 (d = 9.7 µm), (b) Sample 3 (d = 5.3 µm), (c) Sample

Each curve has strong peak at 3.3 nm.

- 44 -3.3 Specific surface area and distribution of pores
The specific surface area and distribution of nano-pores were determined bynitrogen adsorption method.

Nitrogen gas tends to adsorb to a surface as monolayer.

The method consists of the measurement of the amount of nitrogen gas adsorbed andsubsequent calibration of this amount with the specific surface area.

Table 1 shows thespecific surface area of the samples measured by using auto gas adsorption apparatus(Nihon Bell Co. Ltd.: BEL SORP36).

A sample that has higher specific surface area

may have more amount of unfrozen water during freezing.

Each specific surface areaof the samples 2-4 was over 120 (m2/g), which was greater than the value ofmontmorillonite (80 m2/g).

These high specific surface areas imply that the samples

might have a lot of unfrozen water at subzero temperature.

Figure 8 shows distribution

curves of nano pores of the samples 2-4 obtained by the nitrogen adsorption method.
Each curve had strong peak at 3.3 nm.

The high specific surface areas of samples will

come from the presence of nano pores.

3.4 Unfrozen water content
3.4.1 NMR methods
The unfrozen water content can be defined as ratio of liquid water (g) tosample (100 g).

Since all the water melt, the content of unfrozen sample remains

constant value, which corresponds to normal water content (wt%).

The unfrozen watercontent was measured using pulsed NMR technique. A proton bears a slight magnetic
moment originating from its spin, and acts as magnet that tends to align along a fixed
external magnetic field.

The magnetic moment orients when pulse is applied to asample set in fixed magnetic field and it returns to the initial direction when the pulse iseliminated.

An NMR measured a change in magnetic field arising at the time as

voltage decay.

The voltage decay curve is called a free-induction decay (FID).

- 45 -FID

peak value proportional to the number of protons of water and ice in the sample.

TheFID signal resulting from ice, however, decreases much rapider than the signal fromliquid water.

Therefor, we can estimate amount of liquid water in a sample from theFID.

3.4.2 Test procedure
We used a pulsed NMR instrument PRAXIS-2 shown in figure 9 andphotograph 3.

The applied magnetic filed was 2.5 kG, the radio frequency was 10.7

MHz and the pulse width was 12 µm.

Samples were prepared by placing soil or glass

particles in a desiccator with water, evacuating the desiccator, allowing a few days forthe solid-vapor equilibrium to be established, adding liquid water, and allowing thesystem to equilibrate for one day.

The initial water content of the sample 1 was 50%

and of the samples 2-4 were 80 %, respectively.

The prepared samples werecompacted in a Teflon tube with diameter of 25 mm for NMR measurements and sealed
off with rubber stopper to prevent water evaporation.
–40 ˚C.

The samples were first frozen atThen, series of unfrozen water content of the samples were measured during

the sample thawing from –40 ˚C to 10 ˚C.

3.4.3 Unfrozen water content
Figure 10 shows unfrozen water content in the frozen samples measured using
the NMR technique.
near 0 ˚C.

The unfrozen water content in each sample decreased steeply

The unfrozen water content of the sample 1 almost reached 0 % at –20 ˚C.

The samples 2-4 had 5 % or more unfrozen water even under –30 ˚C. The samples 2-4
had similar water content curves.
particles.

Unfrozen water presence exists on the surface of

Therefor, the amount of unfrozen water of a sample will be proportional toits surface area and highly depend on the surface condition.

- 46 -

Since the samples 2-4 hadsimilar nano-pore distribution and similar specific surface area in spite of different
diameters, the samples would have similar curves of unfrozen water content shown in
the figure 10.

Large amount of unfrozen water of the samples also would come fromtheir high specific surface area and the nano-pores.

3.4.4 Effect of solute on unfrozen water content
Unfrozen water content of the sample 1 saturated with solution instead of
distilled water was also measured.

We can find the effect of solute on the soil freezing

from the measurements of the unfrozen water.
and MgCl 2.

The solutes we used were NaCl, KCl

The solutes were mixed with distilled water and 9 kinds of solutions (10,3, 2, 1, 0.5, 0.1, 0.05, 0.01, 0 wt%) were prepared.

Figures 11a-c show the unfrozen

water curves of samples 1 saturated with NaCl, KCl and MgCl2 solutions, respectively.
In the figures, FJ indicates the sample 1 saturated with distilled water, and 10 % and
1 % indicate the samples saturated with the concentration of solutes, respectively.

The

unfrozen water contents were maintained the initial water content a few degrees lower
than 0 ˚C because of the depression of freezing point induced by the solutes.

Thesample, which had high concentration of solute, had large amount of unfrozen water.
Such dependence of solute on the unfrozen water amount was shown in other samples
saturated with different solutes (Watanabe and Mizoguchi, 1997).

- 47 -

Photograph 3. A pulsed NMR instrument PRAXIS-2.

- 48 -Fig. 9. Schematic diagram of NMR setup, a sample and a resulting NMR signal.

- 49 -

UNFROZEN WATER CONTENT (%)

80

Sample 1
Sample 2
Sample 3
Sample 4

60

40

20

0-40

-30

-20

-10

010

TEMPERATUREFig. 10.

Unfrozen water content in the frozen samples measured using the NMRtechnique.

- 50 -

Fig. 11.

Unfrozen water curves of samples 1 saturated with NaCl, KCl and MgCl2solutions.

- 51 -

3.5 Unidirectional freezing apparatus
In this study, the sample was frozen using the unidirectional freezing apparatus
shown in photograph 4, which is basically the same as that designed by Uhlmann et al.
(1964), Uhlmann and Jackson (1985), Köber et al. (1992) and Nagashima andFurukawa (1997).

The advances of using the apparatus are that we can easily control

temperature gradient and freezing rate for a sample and that we can observe near thecrystal growth surface continuously, directly and microscopically.
Schematic diagrams of the apparatus are shown in figure 12.
prepared was set into the sample cell.
holder indicated by a star mark;☆.

The sample

The sample cell was placed in a Teflon cell

Opposite ends of the cell were held at different

temperatures, T H and TL, by using two copper blocks kept at constant temperatures byPeltier thermoelements.

The thermoelements were controlled by a computer at each 6-second. This established a temperature gradient α in the sample cell.

The left side of

the figure is warmer and the right side is colder.
The cell holder was moved toward the cold side at a constant rate from 0 to 40µm/sec by a computer controlled pulse motor.

When the cell was moved with constantrate V s, the sample was cooled with keeping established temperature gradient α.

Theadvancing rate of isotherms in the sample Vf corresponded to the constant rate of thesample moving Vs (V f = -V s: figure 13).

In this time, the freezing front in the sample

did not move against the observation filed of microscope since the sample was moved
relative to the freezing. Consequently, continuous direct observation was available
with a microscope.

- 52 -Photograph 4.

Unidirectional freezing apparatus.

- 53 -- 54 Schematic diagram of unidirectional freezing apparatus (freezing portion).

A: sample cell, B: teflon holder, C: copper block, D: thermoelement

Fig. 12a.

- 55 Schematic diagram of unidirectional freezing apparatus.

E: pulse motor, F: translational stage, G: microscope.

Fig. 12b.

TemperatureTemgra per
die aturent

αTL Cold chamber
０℃

Vf
Warm chamber Rate of advancing
of freezing frontTHFig. 13.

VsRate of movingof sample cell

Schematic diagram of temperature gradient and freezing rate given to thesample on the unidirectional freezing apparatus.
The temperature of each chamber is controlled by thermoelement.
temperature gradient, α, is maintained in the sample.

Then a constant

The sample cell is pushed

toward the cold chamber at a constant speed, Vs by a computer-controlled pulse motor.
When Vs is zero, the isotherms moved immediately after lowering the temperature.
When V s is not zero, the freezing rate of advancing of freezing front, Vf is equal to therate of moving of sample cell, Vs.

- 56 -