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Electric freezing potentials in water and soils
Parameswaran, V. R.
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1216
National Research
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Council Canada
de recherches Canada
ELECTRIC FREEZING POTENTIALS I N WATER
-
AND SOILSby V.R. Parameswaran
ANALYZED
Presented at
Third International Symposium on Ground Freezing Hanover, New Hampshire, 21
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24 June 1982,7
p.Printed with permission
DBR Paper No. 1216
Division of Building
ResearcllLes p o t e n t i e l s g l e c t r i q u e s engendrgs pendant l a c o n g g l a t i o n d e l ' e a u pure e t d e s o l s humides o n t &ti5 mesuri5s en l a b o r a - t o i r e . Le p o t e n t i e l de c o n g g l a t i o n de l ' e a u g t a i t p o s i t i f p a r r a p p o r t 3 c e l u i de l a g l a c e e t de l ' o r d r e de quelques v o l t s ; l e s p o t e n t i e l s dans l e s s o l s B t a i e n t de l ' o r d r e de quelques c e n t a i n e s de m i l l i v o l t s (61
V)
e t l e u r s i g n e c h a n g e a i t e n f o n c t i o n du temps s o u s l ' i n f l u e n c e d e s c h a r g e s d e s u r f a c e d e s p a r t i c u l e s mingrales.ELECTRIC FREEZING POTENTIALS I N WATER AND SOILS
V.R. Parameswaran, D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council of Canada, Ottawa, O n t a r i o , K I A 0R6, Canada
ABSTRACT
E l e c t r i c a l p o t e n t i a l s g e n e r a t e d d u r i n g t h e f r e e z i n g o f p u r e w a t e r and moist s o i l s have been measured i n t h e l a b o r a t o r y . The f r e e z i n g p o t e n t i a l i n w a t e r w a s i c e - p o s i t i v e and of t h e o r d e r of a few v o l t s ; t h e p o t e n t i a l s i n s o i l s were of t h e o r d e r of a few hundred m i l l i v o l t s ( ( 1 V), and t h e s i g n changed w i t h t i m e under t h e i n f l u e n c e of s u r f a c e c h a r g e s on t h e m i n e r a l p a r t i c l e s . INTRODUCTION E l e c t r i c a l p o t e n t i a l s t h a t occur d u r i n g f r e e z i n g o f aqueous systems c a n r e s u l t from two d i f f e r e n t e f f e c t s : ( 1 ) e l e c t r i c a l c u r r e n t s and p o t e n t i a l s r e l a t e d t o t h e phase change of w a t e r , a n d ( 2 ) p o t e n t i a l s a r i s i n g o u t of c h a r g e s e p a r a t i o n d u r i n g f r e e z i n g and i o n i n c o r p o r a t i o n , commonly known a s t h e Workman-Reynolds e f f e c t . I n f r e e z i n g s o i l s i t i s d i f f i c u l t t o s e p a r a t e t h e two e f f e c t s , and t h e f r e e z i n g p o t e n t i a l s observed c o u l d v e r y w e l l b e a combination o f both. EARLY WORK ( a ) Aqueous s o l u t i o n s
Workman and Reynolds ( 1 950) were t h e f i r s t t o s t u d y t h e l a r g e p o t e n t i a l s ( u p t o 230 V) developed d u r i n g f r e e z i n g of d i l u t e aqueous s o l u t i o n s c o n t a i n i n g v e r y s m a l l amounts ( 1 0 ' ~ t o m o l l l ) of i o n i c i m p u r i t i e s . T h e i r measurements i n d o u b l e - d i s t i l l e d w a t e r from which ammonia and c a r b o n d i o x i d e had been removed i n d i c a t e d p o t e n t i a l s of a few v o l t s . G i l l and A l f r e y (1952) o f t h e Clarendon L a b o r a t o r y , Oxford, England, immersed a c y l i n d r i c a l b l o c k o f copper c o o l e d by l i q u i d a i r (-193OC) i n d i s t i l l e d w a t e r and measured a t r a n s i e n t e l e c t r i c a l p o t e n t i a l of up t o 50 V between t h e c o p p e r b l o c k a n d a wire k e p t i n t h e w a t e r a s i c e f r o z e on t h e b l o c k , which t h u s a c q u i r e d a p o s i t i v e c h a r g e w i t h r e s p e c t t o water. Following t h e s e i n i t i a l o b s e r v a t i o n s , s e v e r a l i n v e s t i g a t o r s measured e l e c t r i c a l f r e e z i n g p o t e n t i a l s i n p u r e w a t e r (Bayadina 1960, Murphy 1970 and Korkina 1975) a n d i n d i l u t e aqueous s o l u t i o n s c o n t a i n i n g d i f f e r e n t k i n d s o f
c a t i o n s a n d a n i o n s (Pruppacher e t a l . 1968, Cobb and Gross 1969, Murphy 1970 and Korkina 1975). The r e s u l t s o f t h e s e e a r l y o b s e r v a t i o n s showed t h a t t h e
magnitude and s i g n o f t h e f r e e z i n g
p o t e n t i a l s depended upon v a r i o u s f a c t o r s s u c h a s t y p e of i o n s i n s o l u t i o n , t y p e o f e l e c t r o d e s and t h e d i s t a n c e between them,
c o n c e n t r a t i o n of e l e c t r o l y t e s o l u t i o n , r a t e of c o o l i n g , e t c . These p o t e n t i a l s were a t t r i b u t e d t o primary s t r u c t u r a l changes i n w a t e r on f r e e z i n g a n d , i n s o l u t i o n s , t o t h e r a t e o f c a p t u r e and b u i l d - u p of a f r o z e n - i n s p a c e c h a r g e i n t h e i c e , a s w e l l a s t o t h e d i s t r i b u t e d s u r f a c e c h a r g e a l o n g t h e i c e s o l u t i o n i n t e r f a c e . The t y p e o f c h a r g e accumulated depended on t h e c h a r a c t e r i s t i c s of t h e s o l u t e . ( b ) S o i l s a n d r o c k R e p o r t s on f r e e z i n g p o t e n t i a l s i n
s o i l s and r o c k s a r e few and i n c o n c l u s i v e . J u m i k i s (1958) measured p o t e n t i a l s of 40 t o 120 MV d u r i n g f r e e z i n g o f a s i l t y s o i l , and s u g g e s t e d t h a t s u c h p o t e n t i a l s c o u l d enhance m o i s t u r e t r a n s p o r t i n t h e m a t e r i a l . Korkina (1975) s t u d i e d t h e f r e e z i n g p o t e n t i a l s i n s u s p e n s i o n s c o n t a i n i n g p a r t i c l e s less t h a n o n e micron i n s i z e and s a t u r a t e d w i t h d i f f e r e n t k i n d s of c a t i o n s . A t low d e n s i t i e s o f s u s p e n s i o n t h e b e h a v i o u r was s i m i l a r t o t h a t observed i n w a t e r ; t h a t i s , t h e i c e showed a p o s i t i v e c h a r g e . A t h i g h e r d e n s i t i e s t h e i c e w a s c h a r g e d n e g a t i v e l y . S i n c e t h e n a few o t h e r s ( B o r o v i t s k i i 1976, Yarkin 1974, 1978, Hanley and Ramachandra Rao 1980) h a v e measured f r e e z i n g p o t e n t i a l s i n v a r i o u s s o i l s . T h e i r r e s u l t s show t h a t , i n a d d i t i o n t o t h e p o l a r i z a t i o n of w a t e r m o l e c u l e s and t h e a l i g n m e n t of d i p o l e s a c r o s s t h e p o t e n t i a l b a r r i e r a t t h e f r e e z i n g boundary, t h e e x c e s s c h a r g e p r e s e n t a t t h e s u r f a c e s of t h e m i n e r a l p a r t i c l e s a l s o c o n t r i b u t e s t o t h e development of f r e e z i n g p o t e n t i a l s i n s o i l s . The s t u d y of t h e development of c o n t a c t e l e c t r i c a l p o t e n t i a l s i s of c o n s i d e r a b l e i m p o r t a n c e i n many p r a c t i c a l problems. An e l e c t r i c a l p o t e n t i a l g r a d i e n t t h a t developed d u r i n g f r e e z i n g c o u l d enhance m o i s t u r e t r a n s p o r t t h r o u g h t h e s o i l t o t h e f r e e z i n g f r o n t and c a u s e a d d i t i o n a l heave. Also, t h e c a t h o d i c p r o t e c t i o n used on underground p i p e l i n e s t o i n h i b i t c o r r o s i o n c o u l d b e a f f e c t e d by any e l e c t r i c a l p o t e n t i a l r e s u l t i n g from ground f r e e z i n g . Model s t u d i e s h a v e been c a r r i e d o u t by t h e a u t h o r on t h e b e h a v i o u r of p i l e s i n f r o z e n s o i l s and i c e (Parameswaran 1978, 1981). I n t h i s c o n n e c t i o n i t w a s t h o u g h t u s e f u l t o measure t h e e l e c t r i c a l p o t e n t i a l s t h a t may d e v e l o p when w a t e r and s o i l s f r e e z e t o a m e t a l l i c p i l e . Some of t h e r e s u l t s a r e p r e s e n t e d i n t h i s paper. EXPERIMENTAL PROCEDURE Two d i f f e r e n t e x p e r i m e n t a l s e t - u p s ( F i g s . 1 and 2) were u s e d t o measure t h e f r e e z i n g p o t e n t i a l s d e v e l o p e d d u r i n g f a s t and slow c o o l i n g , r e s p e c t i v e l y . I n t h e f i r s t s e t - u p (Fig. l ) , a c y l i n d r i c a l t u b e "A" ( a small p i l e made f r o m c o p p e r o r s t e e l c o a t e d w i t h c o p p e r ) t h r o u g h which a c o o l i n g f l u i d c o u l d b e c i r c u l a t e d w a s p l a c e d i n s i d e a c y l i n d r i c a l
v e s s e l "B" made from p o l y v i n y l c h l o r i d e (PVC) and i n s u l a t e d w i t h s t y r o f o a m "D". The c e n t r a l t u b u l a r metallic p i l e , which
was c o n n e c t e d t o t h e p o s i t i v e t e r m i n a l s of a two-pen c h a r t r e c o r d e r , a c t e d a s t h e i n n e r e l e c t r o d e t o which t h e m a t e r i a l ( w a t e r o r m o i s t s o i l ) f r o z e . Two c o n c e n t r i c o u t e r e l e c t r o d e s "C"
,
made from p e r f o r a t e d c o p p e r s h e e t r o l l e d i n t o c y l i n d e r s , were c o n n e c t e d t o t h e n e g a t i v e t e r m i n a l s of t h e two pens. COOLANT-
=
,
11
-
scale U 1 in. F i g u r e 1. Schematic drawing o f e x p e r i m e n t a l s e t - u p t o s t u d y f r e e z i n g p o t e n t i a l s a t f a s t c o o l i n g r a t e s V a r i o u s m a t e r i a l s , s u c h a s d i s t i l l e d w a t e r , a q u a r t z s a n d from Ottawa, I l l i n o i s , h a v i n g u n i f o r m g r a i n s i z e (0.2 -0.6 mm) and c o n t a i n i n g 14 and 20% m o i s t u r e by w e i g h t , a n d a s i l t y s a n d c o n t a i n i n g 20% w a t e r , were p l a c e d one a t a t i m e i n t h e v e s s e l t o measure t h e i r f r e e z i n g p o t e n t i a l s . P r e c o o l e d methanol (-30°c and - 5 0 ' ~ ) was c i r c u l a t e d t h r o u g h t h e p i l e and t h e v o l t a g e which r e s u l t e d when t h e w a t e r o r s o i l f r o z e t o t h e p i l e was r e c o r d e d . For some t e s t s , f r e e z i n gwas a c h i e v e d by p o u r i n g l i q u i d n i t r o g e n d i r e c t l y i n t o t h e h o l l o w p i l e i n s t e a d o f c i r c u l a t i n g c o l d methanol. The e x p e r i m e n t a l s e t - u p and p r o c e d u r e a r e d e s c r i b e d i n d e t a i l e l s e w h e r e (Parameswaran 1982). A d i a g r a m of t h e equipment u s e d i n t h e s e c o n d s e t - u p t o s t u d y t h e e l e c t r i c a l p o t e n t i a l s and c u r r e n t s g e n e r a t e d d u r i n g v e r y s l o w c o o l i n g of m o i s t s o i l s i n s i d e a c o l d room i s shown i n F i g u r e 2. A
I
p r o b e "A", made from a PVC t u b e a n dr i n g e d w i t h copper e l e c t r o d e s "C" I i n s t a l l e d i n g r o o v e s , w a s embedded i n m o i s t s o i l i n a c y l i n d r i c a l v e s s e l "B" made o f PVC and i n s u l a t e d w i t h g l a s s
i
wool "D". C o a x i a l c a b l e s were a t t a c h e d t o t h e e l e c t r o d e s and e x t e n d e d t h r o u g h t h e c e n t r a l c o r e of t h e t u b e s . Three d i f f e r e n t s o i l s were used: a s a n d f r o m Ottawa, I l l i n o i s , mixed w i t h 14% w a t e r by w e i g h t , a s i l t y s o i l from Norman Wells,Northwest T e r r i t o r i e s (Canada), mixed w i t h 20% water by weight, and a very f ine-grained c l a y from Thompson,
Manitoba, mixed w i t h 30% water by weight. The a p p a r a t u s was k e p t i n s i d e a c o l d room maintained a t -2.2 f O . l ° C , and t h e
e l e c t r i c a l p o t e n t i a l g e n e r a t e d a t e a c h e l e c t r o d e a s t h e f r e e z i n g f r o n t g r a d u a l l y moved through t h e s o i l from t h e t o p
downwards was measured by a a l t i m e t e r . The bottom-most e l e c t r o d e , numbered "OM,
was connected t o t h e n e g a t i v e , o r ground, t e r m i n a l of t h e meter and t h e o t h e r
e l e c t r o d e s were connected s u c c e s s i v e l y t o t h e p o s i t i v e t e r m i n a l through a r o t a r y switch. The v o l t a g e r e a d i n g s a t each e l e c t r o d e and t h e corresponding
temperatures were recorded.
ELECTRODE THERMOCOUPLE PROBE PVC VESSEL INSULATION COPPER ELECTRODES Scale U 1 In.
Figure 2. Schematic drawing of s e t - u p i n s i d e c o l d room f o r u n i d i r e c t i o n a l f r e e z i n g a t slow r a t e s
RESULTS AND DISCUSSIONS
The r a p i d c o o l i n g of t h e m a t e r i a l s i n t h e f i r s t set-up provided t h e
following r e s u l t s (Figs. 3 t o 6). In F i g u r e s 3 ( a ) and ( b ) , which show t h e v a r i a t i o n of f r e e z i n g p o t e n t i a l w i t h t i m e
( i n seconds) f o r p u r e w a t e r when c o l d methanol and l i q u i d n i t r o g e n were used i n
t u r n a s t h e c o o l a n t , t h e copper p i l e can be seen t o have a h i g h e r peak f r e e z i n g v o l t a g e t h a n t h e c o p p e r p l a t e d s tee1 p i l e . It can a l s o be s e e n t h a t a t lower t e m p e r a t u r e s t h e c o o l a n t caused t h e f r e e z i n g p o t e n t i a l s t o i n c r e a s e and t h e
peak t o occur sooner. T h i s may b e due t o t h e f a s t e r r a t e of f r e e z i n g caused by t h e lower-temperature c o o l a n t .
5 - COPPER-PLATED STEEL PILE. - N a C
15 - COPPER PILE. -N°C
18 - COPPER PILE. -45°C
-
>
0 50 100 150 200
T I M E , s
Figure 3(a). Freezing p o t e n t i a l s i n d i s t i l l e d w a t e r u s i n g methanol a s c o o l a n t
6 - COPPER-PLATED STEEL PlLE I N WATER
19. 20 - COPPER PlLE IN WATER
1
T I M E , s Figure 3(b). Freezing p o t e n t i a l s i n d i s t i l l e d w a t e r u s i n g l i q u i d n i t r o g e n a s c o o l a n t Figure 4 shows t h e f r e e z i n g p o t e n t i a l s g e n e r a t e d i n sand c o n t a i n i n g 14% by weight of m o i s t u r e when cooled by methanol a t -30°C. The i n i t i a l p o s i t i v e peak v o l t a g e up t o 30 mV i s probably due t o t h e f r e e z i n g of t h e water a d j a c e n t t o t h e p i l e , which forms t h e f i r s t t h i n i c e l a y e r . The s u r f a c e c h a r a c t e r i s t i c s of sand p a r t i c l e s soon e x e r t t h e i r i n f l u e n c e and cause a n e g a t i v e f r e e z i n g p o t e n t i a l of up t o -80 mV f o r m o i s t sand.
A£
t e r t h i s n e g a t i v e peak t h e f r e e z i n g p o t e n t i a l decays towards zero. With t i m e i t may c r o s s i n t o t h e p o s i t i v e r e g i o n , a s w i l l be s e e n l a t e r i n t h i s s e c t i o n . Figure 5 shows t y p i c a l c u r v e s of t h e f r e e z i n g p o t e n t i a l s i n Ottawa sand c o n t a i n i n g 20% m o i s t u r e by weight when cooled by l i q u i d n i t r o g e n . I n i t i a l l y,
p o s i t i v e p o t e n t i a l s of up t o 400 mV wereobserved which t h e n d e c r e a s e d t o a s low r a n g e of -100 t o -160 mV. The r e v e r s a l a s -220 mV. The f a c t t h a t t h e s e i n i t i a l of p o t e n t i a l a s s e e n i n c u r v e s a and b p o s i t i v e p o t e n t i a l s a r e h i g h e r t h a n t h o s e h a s a l s o been r e p o r t e d by B o r o v i t s k i i i n Figure 4 may be due t o t h e lower (1976) and Yarkin (1978).
c o o l a n t t e m p e r a t u r e which r e s u l t s i n a f a s t e r r a t e of c o o l i n g . 80
0
TIME. rnin -100 I I 1 1I
a 2 d 6 4 10 TIME, min Figure 4. Freezing p o t e n t i a l s i n g r a n u l a r sand c o n t a i n i n g 1 4 % m o i s t u r e , u s i n g methanol a s c o o l a n t (Numbers correspond t o d i f f e r e n t r u n s of experiment ) noor
,
I I I 1 -300 L I ! I I !I 5 10 15 20 r l M E , m i n Figure 5. Freezing p o t e n t i a l s i n g r a n u l a r sand c o n t a i n i n g 20% m o i s t u r e , u s i n g l i q u i d n i t r o g e n a s c o o l a n t (Numbers correspond t o d i f f e r e n t r u n s of experiment)Figure 6 shows t y p i c a l curves of t h e change of f r e e z i n g v o l t a g e w i t h time i n t h e n a t u r a l s i l t y s o i l c o n t a i n i n g 20% w a t e r by weight and cooled by methanol a t -30°C. The wide v a r i a t i o n among t h e samples may b e due t o t h e i r nonhome g e n e i t y and t o t h e random n a t u r e of formation of i c e l e n s e s d u r i n g f r e e z i n g of t h i s fine-grained s o i l . The maximum f r e e z i n g v o l t a g e s observed were i n t h e
Figure 6. Freezing p o t e n t i a l s i n n a t u r a l s i l t y sand c o n t a i n i n g 20% m o i s t u r e , u s i n g methanol a s c o o l a n t (A, B and C r e p r e s e n t
3 d i f f e r e n t r u n s of experiment) Figure 7 shows t h e f r e e z i n g
p o t e n t i a l s measured d u r i n g slow f r e e z i n g of Ottawa sand c o n t a i n i n g 14% m o i s t u r e ( c u r v e a ) and Norman Wells s i l t y sand c o n t a i n i n g 20% m o i s t u r e ( c u r v e b) i n s i d e a c o l d room a t -2.2OC. The dashed c u r v e s
( a ' , b' ) show t h e change i n temperature of t h e s o i l w i t h time a t a p o i n t n e a r t h e corresponding e l e c t r o d e . F i g u r e 8 shows s i m i l a r c u r v e s f o r f r e e z i n g p o t e n t i a l s i n a s i l t y c l a y from Thompson, Manitoba, mixed w i t h 30% water. The v o l t a g e decays a s t h e f r e e z i n g f r o n t p a s s e s t h e
e l e c t r o d e on which t h e measurements a r e made. T h i s i n d i c a t e s t h a t t h e p r o g r e s s of t h e f r e e z i n g f r o n t down through t h e s o i l column can be determined by
o b s e r v i n g t h e f r e e z i n g p o t e n t i a l s
developed on e l e c t r o d e s p l a c e d a t r e g u l a r i n t e r v a l s
.
The peak p o t e n t i a l s observed
measured about 200 mV i n sand, 220 mV i n s i l t y sand and a b o u t 320 mV i n c l a y , a l l
i c e - p o s i t i v e . I t was mentioned e a r l i e r ,
t h a t , under f a s t c o o l i n g by methanol o r l i q u i d n i t r o g e n , t h e s e s o i l s e x h i b i t e d
i c e - n e g a t i v e p o t e n t i a l s ( s e e F i g s . 4 I
t o 6 ) which decayed t o z e r o and t h e n changed t o a p o s i t i v e p o t e n t i a l .
F i g u r e s 7 and 8 show o n l y t h e long-term
1
I p o s i t i v e p o t e n t i a l s developed under slowr a t e s of c o o l i n g . Yarkin (1978) a t t r i b u t e d t h e r e v e r s a l of t h e s i g n of t h e f r e e z i n g p o t e n t i a l i n s o i l s t o a combination of exchange a b s o r p t i o n p r o c e s s e s o c c u r r i n g on t h e s u r f a c e of s o i l g r a i n s and m o i s t u r e m i g r a t i o n i n t h e presence of an e l e c t r i c f i e l d g e n e r a t e d d u r i n g f r e e z i n g . S i n c e t h e s u r f a c e of t h e m i n e r a l m a t r i x i s charged n e g a t i v e l y i n most n a t u r a l s o i l s (Yarkin, 1978), t h e
I t 1
I
1 ( a )-
O T T A W A S A N D + 1 4 % W A T E RL
( b )-
S I L T Y S A N D + 2 0 % W A T E R Y I ( a ' ) , ( b ' ) - T E M P E R A T U R E \I-
I
-
-
-
-
-.---__
3 I---:
T I M E , hFigure 7. Freezing p o t e n t i a l s developed under slow c o o l i n g i n s i d e c o l d room a t -2.2OC ( a ) f o r g r a n u l a r sand c o n t a i n i n g 14% m o i s t u r e and ( b ) f o r n a t u r a l s i l t y sand c o n t a i n i n g 2 0 %
m o i s t u r e (Dashed c u r v e s i n d i c a t e temperature)
T I M E , h
Figure 8. Freezing p o t e n t i a l s developed i n a n a t u r a l c l a y c o n t a i n i n g 30% m o i s t u r e i n s i d e c o l d room a t - 2 . 2 O C (Dashed c u r v e s i n d i c a t e temperature. Numbers correspond t o e l e c t r o d e s on which measurements were made)
i n i t i a l f r e e z i n g p o t e n t i a l i s n e g a t i v e ( s e e F i g s . 4 t o 6 ) . However, a s f r e e z i n g p r o g r e s s e s a n d m o i s t u r e m i g r a t i o n t a k e s p l a c e under t h e i n f l u e n c e of e l e c t r o - o s m o t i c f o r c e s , f l o w p o t e n t i a l s ( o r s t r e a m i n g p o t e n t i a l s c a u s e d by t h e f l o w of a l i q u i d c o n t a i n i n g e x c e s s i o n s o f o n e s i g n ) arise which compensate f o r t h e
i n i t i a l n e g a t i v e p o t e n t i a l . T h i s r e s u l t s , i n t h e long-term, i n a p o s i t i v e p o t e n t i a l ( s e e F i g s . 7 and 8 ) . A d e t a i l e d d i s c u s s i o n of t h e r e s u l t s and c a l c u l a t i o n s o f t h e f i e l d and c h a r g e d e n s i t i e s i s p r e s e n t e d e l s e w h e r e (Parameswaran 1982). CONCLUDING REMARKS When w a t e r o r m o i s t s o i l s f r o a e r a p i d l y on a c o l d m e t a l l i c p i l e , e l e c t r i c a l f r e e z i n g p o t e n t i a l s were o b s e r v e d , t h e magnitude of which were of t h e o r d e r of 4 t o 1 2 v o l t s i n p u r e w a t e r and a b o u t -100 t o -220- mV i n m o i s t s o i l s .
Under slow c o o l i n g i n s i d e a c o l d room a t
-2.2'C, m o i s t s o i l s showed f r e e z i n g p o t e n t i a l s of t h e o r d e r of 200 t o 300 mV
.
These p o t e n t i a l s c o u l d be a t t r i b u t e d t o primary s t r u c t u r a l c h a n g e s o c c u r r i n g d u r i n g f r e e z i n g of p u r e w a t e r and, i n s o i l s , t o a combination of exchange a b s o r p t i o n p r o c e s s e s on t h e s u r f a c e of s o i l g r a i n s and of m o i s t u r e m i g r a t i o n i n t h e e l e c t r i c f i e l d g e n e r a t e d d u r i n g f r e e z i n g . ACKNOWLEDGEMENTS The a u t h o r a p p r e c i a t e s t h e h e l p of C o l i n Hubbs i n s e t t i n g u p t h e e x p e r i m e n t and c a r r y i n g o u t t h e measurements. S i n c e r e t h a n k s a r e a l s o e x t e n d e d t o Marcel Roy and Andrew C h e v r i e r f o r t h e i r c o n t r i b u t i o n t o t h e s e measurements.REFERENCES
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