Frost durability of Canadian clay bricks

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Frost durability of Canadian clay bricks

Kung, J. H.

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Ser

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5 5 - , &

N21d

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1317

National Research

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Building Research recherches en biltiment

Frost Durability of Canadian Clay Bricks

by J.H. Kung

Reprinted from

Proceedings of the 7th International Brick Masonry Conference

Melbourne, Australia, 17 -20 February 1985 Vol. 1, p. 245

-

251

(DBR Paper No. 1317)

Price $2.00 NRCC 24947

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On a Bvaluk p a r d i v e r s e s mkthodes l a d u r a b i l i t k d e s b r i q u e s d ' a r g i l e exposges au g e l . L ' e s s a i d ' e x p a n s i o n p a r l e g e l de b r i q u e s s a t u r g e s permet d ' g v a l u e r prkciskment l e u r d u r a b i l i t g . Bien que l e s c r i t 2 r e s bas& s u r l e c o e f f i c i e n t de s a t u r a t i o n e t l ' a i r e de s u r f a c e s p k c i f i q u e s o i e n t u t i l e s , i l s dgpendent d e s m a t g r i a u x c o n s t i t u t i f s e t d e s prockdks de f a b r i c a t i o n . Les c o n d i t i o n s de c u i s s o n o p t i m a l e s peuvent t t r e d k d u i t e s d'une s 6 r i e de p o i n t s r e p r k s e n t a n t l e c o e f f i c i e n t d e s a t u r a t i o n

en

f o n c t i o n de l ' a i r e de s u r f a c e s p g c i f i q u e . Le c o n t r b l e de l a q u a l i t k p e u t S t r e amkliork s i on u t i l i s e simultangment l e c o e f f i c i e n t d ' a b s o r p t i o n e t c e l u i de s a t u r a t i o n . La d u d e de l ' e s s a i de c o n t r b l e de l a q u a l i t k , a c t u e l l e m e n t de 48 h e u r e s , p e u t d t r e r g d u i t e 3 _{1 h e u r e ou moins e n procgdant aux e s s a i s}

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FROST DURARILITY OF CANADIAN CLAY BRICKS

J.H.

KUNG R e s e a r c h O f f i c e r

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 Canada, Ottawa, Canada, KIA OR6

ABSTRACT Some methods were used t o a s s e s s t h e f r o s t d u r a b i l i t y of c l a y

b r i c k s . Expansion on f r e e z i n g of s a t u r a t e d b r i c k s p r o v i d e s a v a l i d t e s t f o r t h e a s s e s s m e n t of t h e i r d u r a b i l i t y . Although c r i t e r i a b a s e d on s a t u r a t i o n c o e f f i c i e n t and s p e c i f i c s u r f a c e a r e a a r e u s e f u l , t h e y depend on t h e raw m a t e r i a l s and t h e m a n u f a c t u r i n g p r o c e s s e s . The optimum f i r i n g c o n d i t i o n can b e e s t i m a t e d from a p l o t of s a t u r a t i o n c o e f f i c i e n t a g a i n s t s p e c i f i c s u r f a c e a r e a . Q u a l i t y c o n t r o l can b e improved i f b o t h a b s o r p t i o n and s a t u r a t i o n c o e f f i c i e n t a r e used t o g e t h e r . The c u r r e n t q u a l i t y c o n t r o l t e s t i n v o l v i n g 48 h o u r s can b e reduced t o one h o u r o r less u s i n g s h o r t - t e r m a b s o r p t i o n t e s t s .

1. INTRODUCTION

I n Canada, t h e p r i n c i p a l c a u s e of masonry d e t e r i o r a t i o n i s t h e f r e e z i n g and thawing of c l a y b r i c k s . Although c u r r e n t b r i c k s p e c i f i c a t i o n s c o f i t a i n d u r a b i l i t y c r i t e r i a , t h e tests a r e time-consuming and t h e r e s u l t s a r e n o t r e l i a b l e . An I n d u s t r i a l R e s e a r c h F e l l o w s h i p Program was s p o n s o r e d j o i n t l y by t h e Clay B r i c k A s s o c i a t i o n of Canada and t h e 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 of t h e N a t i o n a l R e s e a r c h C o u n c i l of Canada, i n 1978. The purpose of t h e program was t o i d e n t i f y t h e p e r t i n e n t p h y s i c a l and m i n e r a l o g i c a l p r o p e r t i e s t h a t a r e r e s p o n s i b l e f o r f a i l u r e i n o r d e r t o e s t a b l i s h c r i t e r i a f o r p r o d u c t

improvement, t o improve q u a l i t y c o n t r o l and t o p r o v i d e a b e t t e r and f a s t e r t e s t f o r t h e f r o s t d u r a b i l i t y of c l a y b r i c k s . Nine t y p e s of commercially marketed b r i c k s manufactured by s i x p l a n t s were s t u d i e d . The program i n c l u d e d a s t u d y of t h e e f f e c t s of raw m a t e r i a l s , forming methods and h e a t g r a d i e n t i n k i l n s . The h i g h l i g h t s of t h e program from 1978 t o 1982, and i n f o r m a t i o n p e r t i n e n t t o m a n u f a c t u r e r s , a r e p r e s e n t e d h e r e .

2. MICROSTRUCTURAL CHARACTERISTICS AND DURABILITY

The m i c r o s t r u c t u r a l p r o p e r t i e s t h a t may b e r e l e v a n t t o t h e d u r a b i l i t y of c l a y b r i c k s , i.e. s a t u r a t i o n c o e f f i c i e n t , s p e c i f i c s u r f a c e a r e a and p o r e s t r u c t u r e , a r e d e s c r i b e d below. 2.1 S a t u r a t i o n C o e f f i c i e n t S a t u r a t i o n c o e f f i c i e n t i s t h e r a t i o of t h e twenty-four h o u r s c o l d w a t e r a b s o r p t i o n v a l u e t o t h e f i v e h o u r s b ~ i l i n g a b s o r p t i o n v a l u e of a b r i c k . It i s an approximate i n d i c a t i o n of t h e s p a c e a v a i l a b l e i n t h e b r i c k t o accommodate t h e e x p a n s i v e p r e s s u r e of f r e e z i n g water. The lower t h e s a t u r a t i o n

c o e f f i c i e n t , t h e more s p a c e t h e r e i s f o r t h e f r e e z i n g p r e s s u r e t o b e r e l i e v e d ; t h u s i t i s less l i k e l y t h a t t h e b r i c k w i l l b e damaged. The s a t u r a t i o n

c o e f f i c i e n t i s t r a d i t i o n a l l y used as a measure of d u r a b i l i t y i n b r i c k

s p e c i f i c a t i o n s and q u a l i t y c o n t r o l . The development of s a t u r a t i o n c o e f f i c i e n t

i

w i t h r e s p e c t t o h e a t work (combined e f f e c t of peak t e m p e r a t u r e and s o a k i n g

t i m e ) , a s measured by t h e s h r i n k a g e of f i r e c h e k k e y s ( I ) , e x p r e s s e d i n t h e a r b i t r a r y B R I u n i t , i s shown i n F i g u r e 1 f o r v a r i o u s Canadian brickmaking m a t e r i a l s and i n F i g u r e 2 f o r b r i c k s made of t h e same raw m a t e r i a l b u t by d i f f e r e n t forming methods. These f i g u r e s i n d i c a t e t h a t t h e c r i t i c a l s a t u r a t i o n c o e f f i c i e n t r e q u i r e d f o r f r o s t r e s i s t a n c e depends on t h e raw m a t e r i a l s and t h e m a n u f a c t u r i n g p r o c e s s and v a r i e s from b r i c k t o b r i c k .

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0 . 1

-

0 - - 2 + 4 0 1 - 0 W H I T E M U D 0 Q U E E N S T O N H I G H L l M E - Q U E E N S T O N - L O W L l M t O U N D A S - 9 P E N N S Y L V A N I A N 0 . 1 ' \ 0 1 0 2 0 3 0 4 0 5 0 0 0 7 0 8 0 9 0 H E A T W O R K . B R I U n l l r F I G U R E 1 S A T U R A T I O N C O E F F I C I E N T O F B R I C K S M A D E O F V A R I O U S C A N A D I A N B R I C K M A K I N G M A T E R I A L S A S A F U N C T I O N O F H E A T W O R K H E A T W O R K B R I U n i l i F I G U R E 2 S A T U R A T I O N C O E F F I C I E N T O F B R I C K S M A D E O F T H E S A M E R A W M A T E R I A L B U T B Y D I F F E R E N T F O R M I N G M E T H O D A S A F U N C T I O N O F H E A T W O R K

.

P E N N S Y L V A N I A N

.

Q U E E N S T O N L O W L l M E a Q U E E N S T O N H l G H L I M E 0 O U N D A S 0 W H I T E M U D 1 0 2 0 3 0 4 0 5 0 6 0 1 0 8 0 90 1 0 0 H E A T W O R K B R I U n l l l F I G U R E 3 S P E C I F I C S U R F A C E A R E A O F B R l C K S M A D E O F V A R I O U S C A N A D I A N B R I C K M A K I N G M A T E R I A L S A S A F U N C T I O N 0 1 H E A T W O R K

Although the saturation coefficient criterion

has some merit, it fails, by itself, to take

this variation into account. As can be seen

from these results, Canadian Standard CSA A82.1

is of questionable value since five out of the

nine products studied achieved a saturation

coefficient of 0.88 when fired to about 900°C.

These underfired bricks have the specified

saturation coefficient and will pass the CSA

Standard but they do not possess adequate

durability characteristics to withstand either

laboratory freeze-thaw tests or natural

weathering.

2.2 S~ecific

Surface Area

Typically, the specific surface area value of

burnt Canadian clay bricks is between 0.5 and

3.0 /g. Litvan (2) found that the specific

surface areas of twenty-seven bricks collected

from different masonry structures correlated

well with their field performance. Further

results from the Fellowship research indicate

that durability can be assessed on the basis of

specific surface area measurement. But the

effect of raw materials and manufacturing

processes must be considered. Figure 3 shows

the variation of specific surface area of

extruded bricks made from different raw

materials with respect to heat work. The region

of heat work between 35 and 70 BRI units

corresponds to peak firing temperatures between

1030°C and 1080°C. This is where the durability

of the five bricks develops. It can be seen

that the curves are apart and do not cross in

this region. Thus, Figure 3 reveals that the

critical surface area corresponding to the

durable limit of each product may vary.

Similarly, Figure

4 indicates that different

manufacturing processes may also result in

different critical surface areas for equal

durability, even though the same raw materials

were used. Thus the relative durability of

bricks manufactured from raw materials of

different composition and by different processes

cannot be predicted solely on the basis of a

direct comparison of the absolute value of the

specific surface area. Specific surface area is

useful for quality control purposes only when

applied to a particular raw material formed by

the same process.

2.3 Pore Structure

References in the literature suggest that the

existence of coarse pores (greater than

1 micron) result in an enhancement of durability

whereas the intermediate pore sizes (say,

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o S T I F F E X T R U S I O N

.

D R Y P R E S S H E A T W O R K , B R I U n l l r F I G U R E 4 S P E C I F I C S U R F A C E A R E A O F B R I C K S M A O E O F T H E S A M E R A W M A T E R I A L B U T B Y D I F F E R E N T F O R M I N G M E T H O D A S A F U N C T I O N O F H E A T W O R K S A T U R A T I O N C O E F F I C I E N T F I G U R E 5 R E L A T I O N S H I P B E T W E E N T H E A M O U N T O F I N T E R M E D I A T E S I Z E P O R E S A N D S A T U R A T I O N C O E F F I C I E N T O F B R I C K S F R O M P R O J E C T B P m U N B U R N E D B

between

0 . 1

_and

1

_{micron) have a lower}

frost resista~ce

(2,3,4).

In natural

weathering conditions, coarse pores are

rarely filled with water because, although

they are easily filled with water, it

dries out quickly. Small pores do not

fill or dry easily. Since water in small

pores does not freeze until very low

temperatures are reached, it has very

little effect on the frost susceptibility

of bricks. Intermediate pores are most

susceptible to freeze-thaw action since

they are most frequently filled with water

and the water dries more slowly than in

larger pores. This detrimental effect is

illustrated in Figure 5, which shows that

the saturation coefficient is proportional

to the amount of intermediate-sized pores

in bricks, as determined by mercury

intrusion porosimetry. In general, large

pores lower the saturation coefficient,

whereas small pores increase it. It is

perhaps feasible to use pore structure as

a durability test, but more analysis is

needed.

During the firing of a brick, its

durability is improved because the total

porosity is reduced by grain growth and

particle fusing. Also, as the firing

temperature increases, coarsening of the

pores takes place, as shown in Figure

6 .

By comparing water absorption results and

the total theoretical porosity determined

by mercury intrusion porosimetry, the

following important conclusions can be

drawn: a) Some bricks are easier to

saturate than others. For example, after

soaking for one hour in water, bricks from

projects BP and NW achieved~the

highest

level of saturation, i.e.

80%,

whereas

HC

and VD bricks had the lowest degree of

saturation, i.e. below

60%.

_{b) Bricks}

fired at higher temperatures (thus with

greater frost resistance) are more

difficult or slower to saturate by soaking

in water than those fired at lower

temperatures. Such different rates of

saturation have an important practical

significance in considering the

weatherability of bricks in service.

P O R E O I I M i T E Q n l c r o n l

l l b 1 1 9 t h

3. FREEZING EXPANSION AS A FROST

E W C ~ or F I W I U L r t m ~ r ~ ~ ~ u i l ~ s nu vnrt r ~ z t o a r r a r s u r ~ o a

DURABILITY TEST

It is desirable to establish a test

method that is fast and reliable. One

promising method is to measure expansion

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of a wet brick specimen during freezing. The method involves measuring the

expansion of a small (8 mm in diameter

x 13 mm

in length) vacuum-saturated

brick specimen during one cycle of freezing and thawing that could be carried

out in a few hours. It is based on the concept that expansion is caused by

the stress developed when the water freezes, and that there is a relation

between the difference in freezing expansion and thawing shrinkage (called

residual expansion) and the damage suffered (Figure 7).

The results obtained

rated samples of known relative durability in the proper order. Figure 8

presents the residual expansion plotted against the total expansion on

freezing of seventy-seven bricks. Higher freezing expansion is accompanied by

larger residual expansion in general. This behaviour becomes more pronounced

as the freezing expansion exceeds the

0.15%

level. Using

0.10%

expansion as

the threshold, the prediction is

100%

accurate with

15%

rejection of possibly

durable products. Taking

0.15%

as the threshold value, the prediction of

non-durable products is

93%

correct with a 2% rejection of possibly durable

products. Since there is a reasonable correlation between the freezing

expansion and the residual expansion, the method can be simplified by

measuring the residual expansion after freeze-thaw tests. This correlation

improves with specimens of larger size.

The freezing expansion test also provides information on the effect of

the manufacturing process on the frost resistance of bricks. There is an

indication that beyond a critical saturation level, which lies between

75

and

80%,

extruded clay bricks show a marked increase in freezing expansion,

whereas bricks made from dry-press and soft mud methods do not, as can be seen

in Figure

9.

This behaviour in extruded bricks may be related to the pore

structure.

4. OPTIMIZATION OF BRICK FIRING

Where frost durability is concerned, firing is the most important process

in the production of clay bricks. Since frost resistance increases with

greater heat work, it is advantageous for the industry to optimize the firing

conditions.

An

empirical laboratory procedure was developed that estimates

the optimum heat work for a given brick, based on saturation coefficient,

specific surface area and the heat work. The specific surface areas of fired

samples at different heat works are plotted against the corresponding

saturation coefficients, as shown in Figure

10.

The result could be described

' l ' l ' I ' I k

1

- 4 0 - 2 0 0 2 0 40 T E M P E R A T U R E . " C F I G U R E 7 T Y P I C A L E X P E R I M E N T A L L E N G T H C H A N G E R E S U L T S F R O M T H E R M O M E C H A N I C A L M E A S U R E M E N T o N O N - F R O S T R E S I S I A N T

:

:::::::.

]

F R O S T R E S I S T A N . 0 H A N D M O L O 0 = F R E E Z I N G E X P A N S I O N . % F I G U R E 8 R E L A T I O N S H I P B E T W E E N R E S I D U A L E X P A N S I O N A N D F R E E Z I N G E X P A N S I O N O F F R O S T R E S I S T A N T A N D N O N - F R O S T R E S I S T A N T B R I C K S

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E X T R U D E D B R I C K S D. 1. G 0 5 H A N D M O L D B R I C K , DEGREE OF S A T U R A T I O N , % F I G U R E 9 EFFECT OF M A N U F A C T U R I N G M E T H O D S O N F R E E Z I N G B E H A V I O R OF C L A Y B R I C K S S A T U R A T I O N C O E F F I C I E N T F I G U R E 1 0 E S T I M f l T I O N OF O P T I M U M F I R I N G C O N D I T I O N FOR P R O J E C T V D B A S E D O N S P E C I F I C S U R F A C E AREA A N 0 S A T U R A T I O N C O E F F I C I E N I

by two intersecting lines. The optimum heat work and firing condition are

approximately those corresponding to the intersection of the two lines. This

optimum value can be more clearly defined by the derivative of the curve of

specific surface area with respect to saturation coefficient. This method

could also be used to assess the intrinsic tolerance of a brickmaking material

to frost action or to indicate how much improvement could be achieved in a

product by modifying the present process.

5.

QUALITY CONTROL

The procedures for the present quality control tests have limitations,

since they are based on tests for absorption characteristics and saturation

coefficients which are time-consuming and depend on the variation in raw

materials. Thus, the maximum allowable and the optimum values of absorption

and saturation coefficients must be established for each product.

5.1 Short-Term Absorption Tests

Correlation between the short-term absorption and the saturation

coefficient has been found, as shown in Figures 11 and 12. The degree of

correlation is a function of the mixing or homogeneity of the raw materials:

it is best when only one source of consistent raw material is used (Figures 13

and 14) and is poor when different materials are blended (Figure 15).

Thus,

the standard quality control tests could be shortened considerably from the

usual forty-eight hours (required in the case of saturation coefficient) to

within an hour by using short-term absorptions, such as one minute or one hour

cold absorptions. In order to ensure best correlation, the short-term

absorption tests should be done with half bricks or a fraction of a whole

brick in order to avoid the "tight-skin effect" which increases the scattering

of data. Although the initial rate of absorption could be measured in a

minute, it has a poorer correlation than the one hour absorption tests and is

more affected by surface texture.

5.2 Absorption and Saturation Coefficient

Cold absorption and saturation coefficients have been used separately for

quality control, but their values vary depending on the raw material. The

inadequacy of using either one independently for quality control can be seen

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L O 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 9.2

-

- Z 8.4

-

z - 0 1.6 - + L - 2 6.8- w - 6 0 - 0 - " 5.2-

-.

w 3 - p 4.4

-

- 1 6 -

.

- 2.8

-

. I I I I I I I I I - 2.0 I I I I I I I I I I 0.54 0.58 a 6 2 O.M o m 0.14 0.16 0.8 0.1 0.90 0.91 S A T U R A T I O N C O E F F I C I E N T F I G U R E 1 1

C O R R E L A T I O N BETWEEN ONE HOUR COLD A B S O R P T I O N A N D S A T U R A T I O N C O E F F I C I E N T FOR B U R N T B R I C K S F R O M P R O J E C T R I I I 1 , - 0 5 0 0.58 0 . 6 6 0.14 0 . 8 2 0 . 9 0 S A T U R A T I O N C O E F F I C I E N T F I G U R E 1 3 R E L A T I O N S H I P BETWEEN S A T U R A T I O N C O E F F I C I E N T A N D A B S O R P T I O N OF B R I C K S MADE F R O M A S I N G L E S O U R C E OF RAW M A T E R I A L F I G U R E I 2 C O R R E L A T I O N BETWEEN ONE M I N U T E C O L D A B S O R P T I O N A N D S A T U R A T I O N C O E F F I C I E N T FOR B U R N T B R I C K S F R O M PROJECT R S A T U R A T I O N C O E F F I C I E N T F I G U R E 1 4 R E L A T I O N S H I P BETWEEN S A T U R A T I O N C O E F F l C I L N T A N 0 A B S O R P T I O N OF B R I C K S M A D E W I T H A D D I T I V E S I N T R O D U C E D I N S L U R R Y I I I I I I I 8 . 0 8.5 9.0 9 5 1 0 0 10.5 1 1 . 0 C O L D A B S O R P T I O N . 5 F I G U R E 15 R E L A T I O N S H I P B E T l E E N S A T U R A T I O N C O E F F I C I E N T A N 0 A B S O R P T I O N OF B R I C K S M A D E F R O M B L E N D I N G A SHALE A N 0 A C L A Y F I G U R E 1 6 P R O P E R T I E S OF B R I C K S PROOUCED I N A P L A N T OVER A P E R I O D OF THREE M O N T H S

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13

-

I I I I * 13 - z 0 5 - LIMESTONE CONTfNl - E > D > C > B > A 3

-

I I I I 0 . 6 0 0 6 8 0 . 1 6 0 . 8 4 0 P Z 1 0 0

in Figure 16. In a production plant, bricks of

similar saturation coefficient but different

absorption values, and similar absorption but

different saturation coefficient values are both

produced. These bricks have different properties.

Thus, it is recommended that absorption and

saturation coefficients be used in conjunction,

since this composite relationship not only reveals

the quality of the particular brick produced but

also the "history" of the brick, such as the

original raw material composition and the resulting

firing condition, as shown in Figure 17.

S A T U R A T I O N C O E F F I C I E N T

~ I G U R ~ 17

6. CONCLUSIONS

V A R I A T I O N I N RAW M A T E R I A L S E L U C I D A T E D B Y P L O T T I N G C O L D A B S O R P T I O N V S S A T U R A T I O N C O E F F I C I E N T

Present Canadian durability standards for clay

bricks are questionable. Evaluation criteria based

on saturation coefficient and specific surf

ace area must be established for

each product because they vary according to the different raw materials and

manufacturing processes. The optimum firing condition can be estimated by

plotting the specific surface area against saturation coefficient at different

degrees of firing. Freezing expansion seems to provide a valid durability

test for clay bricks independent of the composition and process variables. In

the absence of the criteria mentioned above, quality control should be based

on both absorption and saturation coefficient. Current quality control tests

based on saturation coefficient can be shortened by the dne minute or one hour

absorption test.

7. ACKNOWLEDGEMENT

The author would like to thank Drs. V.S. Ramachandran and P.J. Sereda for

their helpful guidance in this work; the technical officers of the DBR

Building Materials Section for their assistance in the experiments; and the

workers at Canada Brick, Domtar Inc., I-XL Industries Ltd., L.E. Shaw Ltd.,

and Toronto Brick for their participation and cooperation. This Program was

This paper is a contribution from the Division of Building Research,

National Research Council Canada, and is published with the approval of the

Director of the Division.

8. REFERENCES

(1) Newman, H.B., Direct and Indirect Methods of Measuring Body Maturity.

Bull. Amer. Ceram. Soc. 58 (6) 580-586, 1979.

( 2 )

Litvan, G.G., Testing t h r ~ r o s t

Susceptibility of Bricks. ASTM STP 589,

123-132, 1975.

(3) Robinson, G.C., The Relationship Between Pore Structure and Durability of

Brick. Bull. Amer. Ceram. Soc. 63 (2) 295-300, 1984.

(4) Vincenzini, P., Some Laboratory Tests Used to Foresee the Frost Behaviour

(11)

T h i s paper, w h i l e being d i s t r i b u t e d i n r e p r i n t form by t h e D i v i s i o n of B u i l d i n g Research, remains t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It s h o u l d n o t be reproduced i n whole o r i n p a r t w i t h o u t t h e p e r m i s s i o n of t h e p u b l i s h e r . A _{l i s t} _{of a l l p u b l i c a t i o n s a v a i l a b l e from} t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o 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 , O t t a w a , O n t a r i o , K l A _OR6.

C e document est d i s t r i b u g s o u s f orme de tiri5-a-part par l a D i v i s i o n d e s r e c h e r c h e s e n bztiment. Les d r o i t s de r e p r o d u c t i o n s o n t t o u t e f o i s l a proprii5tC de 1 ' C d i t e u r o r i g i n a l . C e document n e p e u t G t r e r e p r o d u i t en t o t a l i t i 5 ou en p a r t i e s a n s l e consentement de l v 6 d i t e u r . Une l i s t e d e s p u b l i c a t i o n s d e l a D i v i s i o n p e u t S t r e obtenue en i5crivant

3

_{l a S e c t i o n} d e s p u b l i c a t i o n s , D i v i s i o n d e s r e c h e r c h e s e n b$timent, C o n s e i l n a t i o n a l de r e c h e r c h e s Canada, Ottawa, O n t a r i o , K1A 0R6.