Pore structure and frost susceptibility of building materials

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Pore structure and frost susceptibility of building materials

Litvan, G. G.

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1

-

L i t v a n

P O R E

S T R U C T U R E

AND

F R O S T

S U S C E P T I B I L I T Y

OF

B U I L D I N G

M A T E R I A L S

G. _{G. L i t v a n} D i v i s i o n of B u i l d i n g R e s e a r c h N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , Ottawa, C a n a d a

ABSTRACT

It i s shown t h a t t h e i n a b i l i t y of w a t e r c o n t a i n e d in p o r e s t o c r y s t a l l i z e i n s i t u l e a d s t o g r a d u a l and c o n t i n u o u s r e d i s t r i b u t i o n of t h e a d s o r b a t e on c o o l i n g t o below 0 ° C . F r o s t d a m a g e o c c u r s when t h e p r o c e s s c a n n o t p r o c e e d b e c a u s e t h e a m o u n t of c a p i l l a r y w a t e r t h a t i s b e c o m i n g u n s t a b l e i n u n i t t i m e i s g r e a t e r t h a n t h e flux. T h e e s t a b l i s h e d h a r m f u l e f f e c t of t h e i n t e r m e d i a t e - s i z e p o r e s , l a r g e s a m p l e d i m e n s i o n s . h i g h d e g r e e of s a t u r a t i o n and r a p i d cooling r a t e a r e t o b e e x p e c t e d . C o r - r e l a t i o n b e t w e e n n i t r o g e n s u r f a c e a r e a and f r o s t r e s i s t a n c e of b r i c k s w a s found t o b e good; t h i s c a n a l s o b e e x p l a i n e d b y t h e t h e o r y . L 8 a u t e u r m o n t r e que l'inaptitude d e l a e a u c o n t e n u e d a n s l e s p o r e s s e c r i s t a l l i s e r i n s i t u e n t r a f n e u n e r e d i s t r i b u t i o n g r a d u e l l e e t c o n t i n u e l l e du p r o d u i t a d s o r b 6 l o r s du r e f r o i d i s s e m e n t a u - d e s s o u s d e 0 ° C . L e s d o m m a g e s d u s a u g e l s e p r o d u i s e n t l o r s q u e l e procCdC n'aboutit p a s du f a i t q u e l a quantit6 d a e a u c a p i l l a i r e qui d e v i e n t i n s t a b l e p a r unit6 d e t e m p s e s t p l u s g r a n d e que l e flu,:. On d o i t s s a t t e n d r e ?I l'effet nCfaste connu d e s p o r e s d e g r a n d e u r i n t e r m h d i a i r e , d e s Cchantillons d e g r a n d e d i m e n s i o n , dlune s a t u r a t i o n ClevCe e t d l u n e g r a n d e v i t e s s e d e r e f r o i d i s s e - m e n t . Ll y a bonne c o r r k l a t i o n e n t r e l ' a i r e d e s u r f a c e d'azote e t l a

2

-

L i t v a n It h a s long b e e n r e c o g n i z e d t h a t f r o s t s u s c e p t i b i l i t y of p o r o u s b o d i e s i s r e l a t e d t o s o m e f e a t u r e s of t h e i r i n t e r n a l s t r u c t u r e . T a b e r (1) on d i s c u s s i n g f r o s t h e a v i n g i n s o i l s i n 1928 s t a t e s t h a t t h e chief c o n t r o l l i n g f a c t o r s a r e s i z e of s o i l p a r t i c l e , s i z e and p e r c e n t a g e of voids, a m o u n t of w a t e r a v a i l a b l e and cooling r a t e . A c c o r d i n g l y , t h e m o s t e f f e c t i v e p r a c t i c a l m e t h o d f o r p r o v i d i n g r e s i s t a n c e a g a i n s t f r o s t d a m a g e in c o n c r e t e i s t o m o d i f y t h e p o r e s t r u c t u r e t h r o u g h t h e i n c o r p o r a t i o n of a i r bubbles i n t h e m i x . T h e m e c h a n i s m l e a d i n g t o i m p a i r m e n t d u e t o f r o s t a c t i o n i s , h o w e v e r , not fully u n d e r s t o o d , a d e f i c i e n c y t h a t p r e v e n t s t h e s o l u t i o n of t h e two m o s t i m p o r t a n t c u r r e n t p r o b l e m s of c o n c r e t e technology: d e t e r i o r a t i o n of b r i d g e d e c k s and t h e d e s t r u c t i v e effect of d e - i c i n g s a l t s . U n d e r s t a n d a b l y , no fully r e l i a b l e t e s t f o r t h e e v a l u a t i o n of f r o s t r e s i s t a n c e h a s b e e n developed. F u r t h e r w o r k in t h i s f i e l d w a s c o n s i d e r e d w e l l w a r r a n t e d and h a s b e e n c a r r i e d out in t h i s l a b o r a t o r y . In t h e p r e s e n t p a p e r f u r t h e r d e v e l o p ~ n e n t s of a p r o p o s e d t h e o r y ( 2

-

4 ) w i l l b e d i s c u s s e d . F o r m u l a t i o n of t h e T h e o r y

C o n s i d e r a p o r o u s body of unit weight f u l l y s a t u r a t e d with w a t e r .

L c t

-

r b e t h e p o r e s i z e p a r a m e t e r of a p a r a l l e l - s i d e d void l e s s t h e t h i c k n e s s of t h e m o l e c u l a r l z y e r s ,.dsorbed on t h e s u r f a c e , a n d % a n u - m e r i c a l f n c t o r dependent on t h e g e o m e t r y of t h e void ( 5 ) s u c h that:

r .

a

= v ( t h e v o l u m e of t h e void). ( 1 ) If t h e n u m b e r of voids i n t h e body h a v i n g t h e s a m e

L

i s

5,

t h e n V r , t h e volume of w a t e r t h a t b e c o m e s u n s t a b l e when t h e r e l a t i v e p r e s s u r e , p / p 0 , c h a n g e s f r o m ( p / p 0 ) t o ( P / P " ) ~ - ~ ~ ~ i s r T h e v a l u e of N f o r a l l

-

r i s given by t h e p o r e - s i z e d i s t r i b u t i o n , v ( r ) . T h e t o t a l c a p z l a r y v o l u m e , V, i s

A l i n k between r and p/po is e s t a b l i s h e d by t h e Kelvin equ;\lion:

LV

a

I' - c o s

c.

( 4)

3

-

Litvan

-

w h e r e V = m o l a r volume of liquid U : s u r f a c e tension R = gas constant 8 = contact angle, 90" T = t e m p e r a t u r e .

E x p e r i m e n t s indicated that not only t h e a d s o r b e d l a y e r s ( 6 , 7) but a l s o t h e c a p i l l a r y - h e l d liquid (8) d o e s not f r e e z e in situ. T h e s e r e s u l t s c o n f i r m e d p r e v i o u s findings on t h e liquid-like n a t u r e of the f i r s t two a d s o r b e d l a y e r s (9-12) and c a p i l l a r y condensed liquid (13, 14), and lead t o t h e r e a l i z a t i o n that t h i s behaviour m u s t b e c h a r a c t e r i s t i c of a l l p o r o u s s y s t e m s . The fact that t h e a d s o r b a t e i s in a liquid-like s t a t e and h a s a s a t u r a t i o n p r e s s u r e s i m i l a r t o that of undercooled bulk liquid (8), while bulk ice h a s f o r m e d on t h e e x t e r n a l s u r f a c e s r e s u l t s in a non-equi- l i b r i u m situation c h a r a c t e r i z e d by t h e vapour p r e s s u r e d i f f e r e n c e . Equilibrium c a n be achieved by e i t h e r solidification of the liquid in t h e p o r e s , which a p p a r e n t l y cannot o c c u r , o r by r e d u c t i o n of t h e vapour p r e s s u r e of t h e a d s o r b a t e through desorption. When t h e a d s o r b a t e r e - maining in t h e p o r e s h a s a vapour p r e s s u r e equal t o t h a t of i c e a t a given t e m p e r a t u r e , equilibrium conditions have been r e s t o r e d . T h e amount of a d s o r b a t e in t h i s s t a t e i s a p p r o p r i a t e f o r the value of t h e p r e v a i l i n g p/p0

P

and i s defined by t h e n u m e r i c a l value of a t t h e t e m p e r a t u r e in w a t e r

question. T h e r a t i o of the p r e s s u r e of i c e t o that of undercooled w a t e r d e c r e a s e s with descending t e m p e r a t u r e s (151, s o that

1. 1489t - 1. 330 ( 1 0 - ~ t ~ ) :

9.

084 ( l ~ - ~ t ~ ) (5) 273. l t t

w h e r e t = t e m p e r a t u r e , " C ,

and consequently continuous d e s o r p t i o n i s r e q u i r e d f o r maintaining equi- l i b r i u m on t r a v e r s i n g t e m p e r a t u r e s below 0" C.

On cooling f r o m t e m p e r a t u r e T t o T t h e r e l a t i v e p r e s s u r e r - d r l

changes f r o m (P/P")r t o (p/h0 ) r - d r and t h e liquid contained in p o r e s of t h e d i m e n s i o n s defined by t h e equation:

LT

r - ( r

-

d r ) =

-

1 1

R

T a n ( P / P ' ) , - ~ ~ r - d r b e c o m e s unstable.

E q u a t i o n ( 5 ) m a y b e w r i t t e n a s : a n d s u b s t i t u t e d i n E q u a t i o n (6), r e s u l t i n g i n F o r t h e p u r p o s e s of t h i s d i s c u s s i o n t h e c h a n g e s of

o

_{a n d}

_V

_{w i t h} T a r e n e g l e c t e d . C o m b i n i n g E q u a t i o n s (3) a n d (8) a n d r e m e m b e r i n g t h a t a t r = m, T - 2 7 3 " _{t< w e o b t a i n} V =

y'

v ( T )

&

f ( T ) d T ( 9 )

T

R

E q u a t i o n

(9)

s p e c i f i e s t h e a m o u n t of a d s o r b e d w a t e r t h a t b e c o m e s u n s t a b l e w h e n 1 p o r o u s b o d y f u l l y s a t u r a t e d a t 0°C i s c o o l e d t o l o w e r t e m p e r a t u r e s ( T ) . It h a s b e e n s h o w n t h . ~ t t h e o c c u r r e n c e of m e c h a n i c a l d a m a g e i s r e l a t e d t o t h e r a t e of m a s s t r a n s f e r ( 3 , 4). F r o m E q u a t i o n

(9)

dV = v ( T )

&

f ( T )

-

d 7 R d 7 w h e r e T

-

t i m e . T h u s t h e flow r a t e i s a f u n c t i o n of t h e c o o l i n g r a t c . I n o r d c r t o a v o i d d a r n a g e i n a g i v e n s o l i d t h e c o o l i n g r a t e h a s t o b e l e s s that1 ;I l i m i t i n g v a l u e w h i c h i s d e t e r m i n e d b y i t s p e r m e a b i l i t y . M e c h a n i c a l d a m a g e i s c a u s e d by s e v e r a l m e c h i i n i s m s . (;I) T h e esudecl w a t e r c o l l e c t s i n e x i s t i n g f i s s u r e s , c r ; ~ c k s , e t c .

.

\ \ , h e r e it f l - c e z e s ancl b e c a u s e of i t s s p e c i f i c v o l u m e i n c r e ; ~ s e or1 s o l i d i f i c a t i o n , c r y s t - t l l i z a t i o n p r e s s u r e c ; t u s e s t h e c r a c k t o [>rop:tgatc. T h i s r n e c h a n i s l n is p a r t i c u l a r l y d e s t r u c t i v e b e c a u s e it i s c o n c e n t r ; i t e d o n t h e n i e c h ; ~ n i c a l l y \re.lkc.r a r e a of t h e body. ( b ) T h e d a m a g e i s c a u s e d by t h e r a p i d ; i c c u r n u - 1.ition of w a t e r below a d r i e d - o u t s u r f a c e r e g i o n w h i c h i m p e d e s m o i s t u r e f l o w . T h i s conditiorl i s s i m i l a r t o t h a t a r i s i n g i n w a l l s d u r i n g f i r e ( 1 6 ) and lcnd-; i n b o t h c a s c s t o s p z ~ l l i n g . ( c ) If t h e p o r e - s i z c d i s t r i h u t i o t l i s s u c h t h a t I largc: a m o u n t of w a t e r b e c o m e s u n s t a b l e a t low t e m p e r ; i t u r e s w h e r e t h e v i s c o s i t y i s h i g h , e v e n a t n l o d e r a t e l y rapicl c o o l i n g r a t e s t h e w;ttc:r c a n n o t r e ; ~ c h t h e e x t e r n a l s u r f a c e a n d s o l i d i f i e s , probal.)ly ;is a g l a s s , in l a r g e r c a v i t i e s . T h i s p r o c e s s i s ; i s s o c i n t c d w i t h l a r g e e x p a t l s i o n of t h e s y s t e t n o c c a s i o n a l l y r e s u l t i n g i n d a m a g e .

E x p e r i m e n t a l R e s u l t s and P r a c t i c a l Implications

R e s u l t s obtained i n t h e l a b o r a t o r y a r e in good a g r e e m e n t with t h e d e s c r i b e d m e c h a n i s m . T h e f e a t u r e of t h e d i m e n s i o n a l change and h e a t content c u r v e s proved t o h e e a s i l y explained ( 3 , 4 ) . In F i g u r e 1 t h e changes in dimensions and h e a t content of a fully s a t u r a t e d p o r o u s s i l i c a g l a s s s p e c i m e n during a cooling-warming c y c l e a r e shown. On t1.e a b s c i s s a , b e s i d e t h e t e m p e r a t u r e , the v a l u e s of t h e l i m i t i n g r c l a t l v e p r e s s u r e p o

ice' ''water a r e indicated t o g e t h e r with the r a d i u s of t h e p o r e s (calculated f r o m t h e Kelvin equation) which empty at t h e r e l a t i v e p r e s s u r e in question. It i s significant t h a t t h e p o r e - s i z e d i s t r i b u t i o n c u r v e a s c e n d s at t h o s e values of r ( o r T o r p/po ) at which e x o t h e r m i c h e a t effects w e r e o b s e r v e d .

T h e l a r g e body of field e x p e r i e n c e a l s o l e n d s s u p p o r t t o t h e model. Beyond t h i s , t h e i m p l i c a t i o n s of Equation ( 1 0) r e n d e r guidance f o r m i n i - m i z i n g f r o s t d a m a g e .

D e e r e e of s a t u r a t i o n

It i s , of c o u r s e , t r i v i a l t h a t in t h e a b s e n c e of w a t e r no f r o s t d a m a g e o c c u r s . At t h e o t h e r end of s c a l e the d e v a s t a t i n g e f f e c t of f r e e z i n g in t h e fully s a t u r a t e d s t a t e i s a l s o well recognized. E x p e r i e n c e h a s shown, however, that even at r e l a t i v e l y high w a t e r contents no f r o s t action will t a k e p l a c e if t h e d e g r e e of s a t u r a t i o n i s l e s s than a c r i t i c a l value. T h e o r e t i c a l l y it w a s p r e d i c t e d , b y c o n s i d e r i n g t h e volume i n c r e a s e of w a t e r on f r e e z i n g . t h a t t h e c r i t i c a l value i s 0. 917 but T . C . P o w e r s emphasized r e p e a t e d l y t h a t t h i s n u m b e r i s not t o be taken a s an unequivocal c r i t e r i o n between s a f e and unsafe conditions (17, 18), although MacInnis and Beaudoin (19) found i t valid f o r m o r t a r m i x e s . Vuorinnen (20), on the o t h e r hand, e s t a b l i s h e d t h a t good f r o s t r e s i s t a n c e of c o n c r e t e can be expected only if s a t u r a t i o n

i s l e s s than 60 p e r cent. W a r r i s (21) and subsequently F a g e r l u n d ( 2 2 )

p r o p o s e d a method of p r e d i c t i n g f r o s t d u r a b i l i t y by e s t i m a t i n g the a c t u a l d e g r e e of s a t u r a t i o n which i s attained in different e n v i r o n m e n t s in r e l a t i o n to t h e c r i t i c a l one.

Obviously, if t h e p/po at which a p o r o u s body i s equilibrated with w a t e r above 0 ° C i s s m a l l e r than that i m p o s e d on t h e s y s t e m by cooling t o low t e m p e r a t u r e s , n o f r o s t damage will occur.

P o r e s t r u c t u r e

On t h e b a s i s of the p r o p o s e d m e c h a n i s m it i s t o be expected t h a t p o r o s i t y affects durability and s o m e p r e d i c t i o n s c a n be m a d e .

6

-

L i t v a n F i g u r e 1. Top: D i m e n s i o n a l c h a n g e s a n d t t ~ c r m o g r ~ i t n of a p o r o u s s i l l c , ~ g l a s s c o n l p l e t e l y s a t u r a t e d with w ~ t t e r d u r l r ~ g .I t c n l p e r c t t u r e c y c l e ( 0 3 3 ~ C / m i n . ) . B o t t o m c u r v e : p o r e s i z e d i s t r i b u t i o n of t h c s a m e a d s o r b e n t clrsterrnined f r o m n i t r o g e n i s o t h a r r n . ( O r d i n a t e : p o r e v o l u l n e p e r p o r e r a d i u s ~ n c r e m r n t ) . On t h e a b s c i s s a t e m p e r a t u r e , t h e r a t i o of t h e v a p o r p r e s s u r t . of Lce t o th,tt of u n d e r c o o l e d w a t e r a t s e l e c t e d t r n l p e r ; t t u r c v . + l u c s . 'tnd. t h c p o r e r.tdius c o r r e s p o n d i n g t o c e r t a i n r e l a t i v c p r c s s u r e v , ~ l u e s it r e i n c l ~ c < i t ecl.

A a r e e m p t y ( F i g . l ) , thus, u n l e s s s p e c i a l conditions p r e v a i l , t h e p r e s e n c e of s u c h p o r e s d o e s not enhance t h e d a n g e r of f r o s t d a m a g e . On t h e c o n t r a r y , by acting a s r e s e r v o i r s , t h e y c a n a c c o m m o d a t e t h e w a t e r expelled f r o m t h e s m a l l e r c a p i l l a r i e s on cooling t o low t e m p e r a t u r e s . T h i s m o d e of p r o t e c t i o n , known a s a i r e n t r a i n m e n t , c r e a t e s an e s s e n t i a l l y e x t e r n a l s u r f a c e within t h e body of t h e p a s t e t h u s e l i m i n a t i n g t h e need for m i g r a t i o n o v e r long d i s t a n c e s t o t h e o u t e r s u r f a c e .

P o r e s of v e r y s m a l l d i a m e t e r s a r e a l s o h a r m l e s s b e c a u s e w a t e r contained in t h e m b e c o m e s u n s t a b l e only at v e r y low t e m p e r a t u r e s which s e l d o m if e v e r o c c u r in n a t u r e . F r o m t h e point of view of f r o s t action, p o r e s with r a d i i in t h e r a n g e of 300 to 40

A

can c a u s e f r o s t d a m a g e m o s t often.

T h e effect of p o r o s i t y on d u r a b i l i t y i s well documented. M a m i l l a n (23) showed t h a t in t h e c a s e of s t o n e s t h e value of c r i t i c a l s a t u r a t i o n i s i n v e r s e l y p r o p o r t i o n a l t o that of p o r o s i t y .

D i m e n s i o n s of s p e c i m e n s

P o w e r s (17) e m p h a s i z e d t h e concept of c r i t i c a l t h i c k n e s s in addition t o c r i t i c a l s a t u r a t i o n a s t h e m o s t i m p o r t a n t p a r a m e t e r s that d e t e r m i n e f r o s t r e s i s t a n c e in t h e a b s e n c e of <lir voids. T r e m p e r and S p e l l m a n (24) show that t h e l a r g e r t h e s i z e of t h e a g g r e g a t e t h e g r e a t e r t h e p r o b a b i l i t y of being v u l n e r a b l e . S i m i l a r c o n c l u s i o n s w e r e r e a c h e d by MacInnis and Lau (25), V e r b e c k and L a n d g r e n ( ~ 6 ) and T o u r e n q (L7).

T h e s i z e e f f e c t i s a s s o c i a t e d with t h e need of r e d i s t r i b u t i o n of w a t e r . T h e d i m e n s i o n of r o c k s , which contain no a i r voids

o ores

with r

>

1 ~ m ) , d e t e r m i n e s t h e length of t h e m i g r < l t l o n path. In f a c t , p ~ l r a m e t e r s of t h e p o r o u s body, t h e contained liquid <lnd t h e e n ~ i r o n m e n t ~ ~ l conditions which affect t h e r e d i s t r i b u t i o n n r o c e s s . ) r e k n o ~ b n to ,\ffect t h e f r o s t r e - s i s t a n c e of s y s t e m s . In t h i s c a t e g o r y belong cooling r a t e , p e r m e a b i l i t y , and v i s c o s i t y . T h e influence of v i s c o s i t y w,ls d r < i m < ~ t i c a l l y shown by t h e f.lct that 5 - m m .

-

t h i c k p o r o u s s i l i c a g l a s s , which c'ln e n d u r e t e m p e r a t u r e cycling when s a t u r a t e d with w a t e r , was c o m p l e t e l y d e s t r o y e d under

s i m i l a r conditions when it ~ o n t ~ i i n e d an aqueous glycerine solutlon of a n y c ~ n c e n t r ~ i t i o n below 60 p e r c e n t (28).

Evaluation of F r o s t R e s i s t a n c e and P r e d i c t i o n of P e r f ~ r m ~ l n c c

I n d u s t r y n e e d s a s i m p l e and rapid t e s t , by which m a t e r i a l s c a n be unequivoc;~lly approved o r r e j e c t e d with r e g a r d t o f r o s t r e s i s t a n c e . It i s abundantly c l e a r , h o w e v e r , that t h i s demand cannot be m e t fully b e c a u s e no rnateriiil i s i n h e r e n t l y f r o s t r e s i s t a n t and i t s behaviour c a n be p r e d i c t e d only if t h e e n v i r o n m e n t a l f a c t o r s d u r i n g e x p o s u r e a r e e x a c t l y known, which

8

- Litvan

i s a l m o s t n e v e r the c a s e . F o r t u n a t e l y , helpful guidance b a s e d on t h e d e s c r i b e d m o d e l can be offered.

It i s p o s s i b l e t o a s s e s s t h e s e v e r i t y of the p r o s p e c t i v e environment by c o n s i d e r i n g the following questions:

-

Is high d e g r e e of s a t u r a t i o n

provided due t o e x p o s u r e t o p e n e t r a t i n g r a i n , poor d r a i n a g e o r condensation? What i s the anticipated cooling r a t e c o n s i d e r i n g the c l i m a t i c conditions, t h e h e a t capacity and the coefficient of heat conduction of the s t r u c t u r e ? How p r o n e i s t h e m a t e r i a l t o f r o s t d a m a g e judged f r o m i t s absorptivity, p o r e -

s i z e d i s t r i b u t i o n and p e r m e a b i l i t y ?

Although the individual p a r a m e t e r s c a n be d e t e r m i n e d quantitatively t h e s e n u m b e r s s t i l l cannot be utilized f o r p r e d i c t i n g the p e r f o r m a n c e of a m a t e r i a l i n a given environment. T h i s i s s o b e c a u s e t h e v a r i a t i o n of t h e c l i m a t i c p a r a m e t e r s c a n r e s u l t in a n infinite number of conditions affecting t h e d e g r e e of s a t u r a t i o n , the r a t e of evaporation, t h e absolute t e m p e r a t u r e , the r a t e of cooling, d e g r e e of humidity, and s o on. N e v e r t h e l e s s , evaluation i n a qualitative s e n s e of the s e v e r i t y of t h e environment and s u s c e p t i b i l i t y of t h e m a t e r i a l i s p o s s i b l e and one c a n judge t h e adequacy of t h e m a t c h .

T h e t e s t i n g m e t h o d s now in u s e r a n k t h e s p e c i m e n s a c c o r d i n g t o t h e i r a b i l i t y t o e n d u r e f r e e z e - t h a w c y c l e s under a r b i t r a r i l y s e l e c t e d conditions, a s well a s t h e i r behaviour judged against that of m a t e r i a l s with known and proved r e c o r d s . T h i s information and p e r s o n a l judgement e n a b l e s t h e evaluator t o a s s e s s " f r o s t durability of s p e c i m e n s . " T h i s p r o c e d u r e i s , by no m e a n s , e n t i r e l y s u c c e s s f u l but it w a s p o s s i b l e t o i m p r o v e t h e quality of and s h o r t e n t h e t i m e r e q u i r e d for the p e r f o r m a n c e of t h e conventional t e s t by utilizing t h e d i s c u s s e d p r i n c i p l e s ( 3 3 ) .

In the c a s e of b r i c k s f u r t h e r p r o g r e s s w a s m a d e by using a p r a g m a t i c a p p r o a c h b a s e d on the following working hypothesis.

Notwithstanding t h e c o m p l e x n a t u r e of t h e f r o s t action phenomenon s o m e p a r a m e t e r s m u s t be of dominant i m p o r t a n c e . If t h i s i s t r u e ,

v a l u e s c h a r a c t e r i z i n g t h e p o r e s t r u c t u r e a r e m o s t probably such p a r a m e t e r s . Accordingly, t h e nitrogen B. E. T . s u r f a c e a r e a s of L 7 _{c o m m e r c i a l p r o d u c t s}

w e r e d e t e r m i n e d . S o m e of t h e s a m p l e s w e r e obtained f r o m b r i c k s i n t h e field which failed i n s e r v i c e , o t h e r s f r o m unexposed o r exposed b r i c k s u s e d locally. The a s s e s s m e n t of f r o s t r e s i s t a n c e w a s b a s e d on t h e reputation of t h e p a r t i c u l a r product c o n s i d e r i n g the f r e q u e n c y of f a i l u r e i n s e r v i c e t h a t c a m e t o o u r attention. P r o d u c t s t h u s w e r e c l a s s i f i e d a s d u r a b l e (no incidence of f a i l u r e ) , questionable ( s o m e known c a s e s of f a i l u r e of p r o d u c t ) and unsound ( s a m p l e originating f r o m b r i c k t h a t failed in s e r v i c e ) . In T a b l e I the r e s u l t s a r e a r r a n g e d in o r d e r of i n c r e a s i n g s u r f a c e a r e a values.

T A B L E I S U R F A C E A R E A O F BRICKS R E L A T E D T O F R O S T D U R A B I L I T Y S a m p l e NO. 2 6 L 3 1 9 1 3 3 17 7 1 8 1 5 L L 9 1 4 8 6 1

L

4 L 1 1 L 1 1 L 7 L 5 10 1 6 5 L ₁ L 0 A r e a mag-' 0. 21 0. 3 5 0 . 4 5 0. 52 0 . 5 7 0. 6 3 0. 76 0. 7 8 0. 8 5 0 . 9 8 1 . 0 1 1 . 0 1 i 1 . 1 1 1. 1 4 1 - 2 5 1. 35 D u r a b l e

+

t t t

+

t i t

+

+

+

1 1. 50 1. 68 2 . 65 L. 88 3 . 00 5. 60 8.

L 5

Q u e s t i o n a b l e i U n s o u n d

+

i t

+

i t

It i s a p p a r e n t that d u r a b l e b r i c k s h a v e low s u r f a c e a r e a and b r i c k s with high s u r f a c e a r e a h a v e poor s e r v i c e r e c o r d s . It i s not implied that a t h r e s h o l d value f o r s u r f a c e a r e a c a n be e s t a b l i s h e d o r t h a t i t even e x i s t s . It can b e s t a t e d , however, that i n c e n t r a l and s o u t h e r n O n t a r i o good p e r f o r m a n c e can be expected f r o m b r i c k s which h a v e a s u r f a c e a r e a l e s s than 0. 5 m 2 / g.

In h i s extensive review, B u t t e r w o r t h (29) d i s c u s s e s r e p o r t s on a t t e m p t s t o r e l a t e f r o s t r e s i s t a n c e of b r i c k s t o p o r e - s i z e distribution. He had t o conclude t h a t , c o n t r a r y t o the c l a i m s of t h e a u t h o r s , no method p r o v e d t o b e c o n s i s t e n t l y s u c c e s s f u l . Although, h e adds, "no doubt e x i s t s that t h e p o r e s of a c l a y body become c o a r s e r a s t h e f i r i n g t e m p e r a t u r e i n r r e a s e s ( ~ 9 , 30) and that "hard" f i r i n g i s e s s e n t i a l for f r o s t r e s i s t a n c e . I t In view of t h i s i t i s s u r p r i s i n g that p o r e - s i z e d i s t r i b u t i o n could not have been utilized t o g r e a t e r advantage.

In an excellent but a p p a r e n t l y overlooked p a p e r Blaine, Hunt and T o m e s (31) show good r e l a t i o n s h i p between n i t r o g e n s u r f a c e a r e a and f r o s t r e s i s t a n c e of building s t o n e s and b r i c k s . T h e y p e r h a p s weakened t h e i r c a s e by attempting t o extend the validity t o h y d r a t e d c e m e n t . It m u s t b e r e m e m b e r e d that the magnitude of t h e s u r f a c e a r e a , p e r s e , d o e s not d e t e r m i n e f r o s t r e s i s t a n c e but i t s value i s a function of p a r a m e t e r s which do, t h u s i t s u s e should b e r e s t r i c t e d to b e t t e r defined and s i m p l e r s o l i d s such a s b r i c k and stone. According t o the t h e o r y now suggested p o r o s i t y and p e r m e a b i l i t y h a v e d e c i s i v e effects on f r o s t r e s i s t a n c e and t h e s e p r o p e r t i e s in t u r n a r e r e l a t e d t o s u r f a c e a r e a . F o r example, if t h e s u r f a c e a r e a i s low t h e Kozeny (32) equation i s applicable:

w h e r e I<, = coefficient of p e r m e a b i l i t y k = d i m e n s i o n l e s s constant € = p o r o s i t y

S = s u r f a c e a r e a

and t h e documented c o r r e l a t i o n between s u r f a c e a r e a and f r o s t d u r a b i l i t y i s t o be expected on t h e o r e t i c a l grounds. F u r t h e r w o r k i s in p r o g r e s s in t h i s l a b o r a t o r y and will be published s h o r t l y .

Conclusions

It is g e n e r a l l y a g r e e d that f r o s t action in p o r o u s m a t e r i a l s i s a s s o c i a t e d with expansion and r e d i s t r i b u t i o n of w a t e r leading t o m e c h a n i c a l f a i l u r e . All the t h e o r i e s attempting t o explain t h e phenomenon h a v e been based a t l e a s t p a r t l y on t h e s p e c i f i c volume i n c r e a s e of w a t e r on f r e e z i n g with

1 1 - Litvan

v e r y few exceptions, such a s , T a b e r (1) and E v e r e t t (34).

In

c o n t r a s t , t h e p r e s e n t t h e o r y a c c e p t s that c r y s t a l l i z a t i o n d o e s not o c c u r in t h e p o r e s in situ, and c o n s i d e r s the consequences and implications of t h i s e x p e r i m e n t a l finding. It should be noted that beyond t h e o r i g i n of t h e m a s s t r a n s f e r no contradiction e x i s t s between the suggested explanation and m o s t of the c u r r e n t l y accepted t h e o r i e s .

In

a s e n s e it i s a f u r t h e r development of t h e t h e o r i e s due t o T. C. P o w e r s who showed t h a t m a s s t r a n s f e r d o e s t a k e p l a c e and identified t h e f a c t o r s , s u c h a s d e g r e e of s a t u r a t i o n , c r i t i c a l s i z e , a i r e n t r a i n e d bubbles, r a t e of cooling, and s o on, which affect it. At t h e s a m e t i m e , t h e new insight m a k e s it p o s s i b l e t o i m p r o v e t h e t e s t i n g p r o c e d u r e s and t o understand t h e h i t h e r t o u n - explained phenomena.

Acknowledgment

T h e e x p e r i m e n t a l w o r k w a s c a r r i e d out by R. E. M y e r s and H. Schultz. Helpful d i s c u s s i o n s with P. J. S e r e d a , Dr. E. A. Flood, D r . T . Z. H a r m a t h y and T . Ritchie, who a l s o supplied s a m p l e s of

known h i s t o r i e s , a r e gratefully acknowledged. T h i s p a p e r i s a contribution f r o m the Division of Building R e s e a r c h , National R e s e a r c h Council of Canada and i s published with t h e approval of the D i r e c t o r of t h e Division.

R e f e r e n c e s

1. T a b e r , S., F r o s t Heaving, J. of Geology,

37,

428-61 (1929). 2. Litvan, G. G . , F u r t h e r C o m m e n t s on the Mechanism of F r o s t Action

i n C e m e n t P a s t e , RILEM, Int. Syrnp. Durability of C o n c r e t e

-

1969 F i n a l Report B-139.

3. Litvan, G. G . , P h a s e T r a n s i t i o n s of A d s o r b a t e s 111. Heat Effects and Dimensional Changes in Non-equilibrium T e m p e r a t u r e C y c l e s , J. Coll. I n t e r f a c e Sci.

38,

75 (1972).

4. Litvan, G. G., P h a s e T r a n s i t i o n s of A d s o r b a t e s IV. Mechanism of F r o s t Action i n Hardened Cement P a s t e . J. Am. C e r a m . Sot.

55.

38 (197L).

5. E v e r e t t , D. H . , S o m e P r o b l e m s in the Investigation of P o r o s i t y by Adsorption Methods. In "The S t r u c t u r e and P r o p e r t i e s of P o r o u s M a t e r i a l s t 1 D. H. E v e r e t t and F. S. Stone, eds. ( B u t t e r w o r t h s , London. 1958) p. 95.

12

-

Litvan

6. Litvan, G. G. and McIntosh,

R . ,

P h a s e T r a n s i t i o n s of W a t e r and Xenon Adsorbed i n P o r o u s Vycor G l a s s . Can. J. Chem. 41, 3095

-

(1963).

7. Litvan, G. G . , P h a s e T r a n s i t i o n s of A d s o r b a t e s 1. Specific H e a t and D i m e n s i o n a l Changes of t h e P o r o u s G l a s s

-

Water S y s t e m , Can. J. C h e m . 44, 2617 (1966).

8.

Sidebottom, E. W. and Litvan, G. G.

,

P h a s e T r a n s i t i o n s of A d s o r b a t e s P a r t 2

-

Vapour P r e s s u r e and E x t e n s i o n I s o t h e r m s of t h e P o r o u s

-

G l a s s

t W a t e r S y s t e m below O°C, T r a n s . F a r a d a y Soc.

2,

2726 (1972).

9. F r e d e r i k s e , H. P.

R . ,

On t h e Specific H e a t of A d s o r b e d H e l i u m , P h y s i c a , 15, 860 (1949).

-

10. M o r r i s o n , J, A. and D r a i n , L. E . , T h e H e a t C a p a c i t y of M u l t i - m o l e c u l a r L a y e r s of Adsorbed Argon, J. C h e m . P h y s . 1 2 1063 (1951). 11. M o r r i s o n , J . A . , D r a i n , L. E. and Dugdale, J. S., P h a s e T r a n s i t i o n s i n M u l t i - m o l e c u l a r L a y e r s of A d s o r b e d N2, Can. J. Chem. 30, 890 (1952).

-

12. Dennis, K.S., P a c e , E. L., and Baughman, Ch. S . , J. Am. Chem.

SOC. 75, 3267 (1953).

_-

13. A m b e r g , C. H . , E v e r e t t , D. H . , R u i t e r , L.H. and S m i t h , F. W., S t u d i e s i n t h e T h e r m o d y n a m i c s of A d s o r p t i o n and Adsorption H y s t e r e s i s . P r o c . 2nd Int. Congr. S u r f a c e Activity ( B u t t e r w o r t h s , London. 1957) Vol. 11, p. 3.

14. Kiselev, A . V. and Kulichenko, V. V., A d s o r p t i o n of B e n z e n e Vapour a t T e m p e r a t u r e s above and below i t s m e l t i n g point on A d s o r b e n t s with V a r i o u s S t r u c t u r e s (in Russian). Zhur. F i z . Khim. 29, 663 (1955).

-

15. D o r s e y , N. E . , i n " P r o p e r t i e s of O r d i n a r y W a t e r - S u b s t a n c e " (Reinholds,

New York, 1940) p. 562.

16. H a r m a t h y , T. Z .

,

Effect of M o i s t u r e on t h e F i r e E n d u r a n c e of Building E l e m e n t s . Am. Soc. T e s t . Mat. Spec. Techn. P u b l . No. 385, 1965 p.74. 17. P o w e r s , T . C . , B a s i c C o n s i d e r a t i o n P e r t a i n i n g t o F r e e z i n g

-

and

-

Thawing T e s t s . Am. Soc. T e s t . Mat. P r o c e e d i n g s ,

55,

1132 (1955). 18. P o w e r s , T. C . , D i s c u s s i o n of a p a p e r by C. M a c l n n i s and E. C. Lau.

19. MacInnis, C. and Beaudoin, J. J . , Effect of D e g r e e of S a t u r a t i o n on the F r o s t R e s i s t a n c e of M o r t a r M i x e s . A m . C o n c r . Inst. J. P r o c . 65, LO3 (1968)

-

LO. Vuorinnen, J . , On U s e of Dilatlon F a c t o r and D e g r e e of S a t u r a t i o n in T e s t i n g C o n c r e t e f o r F r o s t Resistance, N o r d i s k Betong 1970 p. 37.

21. W a r r i s , B . , T h e Influence of A i r - E n t r a i n m e n t on t h e F r o s t - R e s i s t a n c e of C o n c r e t e . P a r t B. H y p o t h e s i s and F r e e z i n g E x p e r i m e n t s . P r o c . S w e d i s h C e m . and C o n c r . R e s . Inst. P r o c . NO. 36 Stockholm 1964.

22. F a g e r l u n d , G . , DegrC c r i t i q u e d e s a t u r a t i o n . Un o u t i l p o u r l D e s t i m a t i o n d e l a r C s i s t a n c e au g e l d e s m a t C r i a u x d e c o n s t r u c t i o n . Mat. e t C o n s t r . 4, (23), 271 (1971).

-

23. M a m i l l a n , M., L a gClivitC d e s matCriaux. Ann. L'Inst. T e c h . BZtiment e t T r a v a u x P u b l . 20, 1020 (1967).

_-

24. T r e m p e r , B., and Spellman, D. L . , T e s t s f o r F r e e z e - T h a w D u r a b i l i t y of C o n c r e t e A g g r e g a t e s . Highway R e s . B o a r d . Bull. NO. 305, 28 (1961).

25. MacInnis, C . , and Lau, E. C., M a x i m u m A g g r e g a t e S i z e E f f e c t on F r o s t R e s i s t a n c e of C o n c r e t e . Am. C o n c r . Inst. J. P r o c . 68, 1 4 4 (1971).

_-

26. Verbeck, G . , and L a n d g r e n , R . , Influence of P h y s i c a l C h a r a c t e r i s t i c s

of A g g r e g a t e s on F r o s t R e s i s t a n c e of C o n c r e t e . Am. Soc. T e s t . M a t . P r o c . 60, 1063 (1960).

_-

27. T o u r e n q , C . , L a gClivitC d e s r o c h e s . Lab. d e s P o n t s e t C h a u s s C e s , Rapp. R e c h e r c h e No. 6. (1970).

28. Litvan. G. G . , P h a s e T r a n s i t i o n s of A d s o r b a t e s V. Aqueous Sodium C h l o r i d e Solutions A d s o r b e d in P o r o u s S i l i c a G l a s s , s u b m i t t e d t o J. Coll. I n t e r f a c e S c i . L9. B u t t e r l ~ o r t h , B . , T h e F r o s t R e s i s t a n c e of B r i c k s and T i l e s , J. _{B r i t .} C e r a m . Soc. 1, LO3 (1964).

_-

30. May, J. O . , and B u t t e r w o r t h , B . , S t u d i e s of P o r e S i z e D i s t r i b u t i o n 111. T h e Effect of F i r i n g T e m p e r a t u r e i n "Science of C e r a m i c s " ( A c a d e m i c P r e s s , 1961) Vol. 1 p. 201.

31. Blaine, R. L., Hunt, C. M. and T o m e s , L . A . , U s e of I n t e r n a l S u r f a c e

-

A r e a M e a s u r e m e n t s i n R e s e a r c h on F r e e z i n g and Thawing of M a t e r i a l s . P r o c . Highway Res. Board

32,

298 (1953).

32. P o w e r s , T . C. and B r o w n y a r d , T. L . , Studies of t h e P h y s i c a l P r o p e r t i e s of Hardened P o r t l a n d C e m e n t P a s t e .

J.

_{Am. Concr. h s t . P r o c .}

43,

866 (1947).

33. Litvan, G, G . , F r o s t Action i n C e m e n t P a s t e , Mat. Const. i n p r e s s . 34. E v e r e t t , D. H . , T h e T h e r m o d y n a m i c s of F r o s t Damage t o P o r o u s Solids.