Moisture Absorption Curves for Building Materials

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Moisture Absorption Curves for Building Materials

Johansson, C. H.; Persson, G.; National Research Council of Canada, Divison of Building Research

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PREFACE

The a b s o r p t i o n of m o i s t u r e by b u i l d i n g m a t e r i a l s i s of g r e a t i n t e r e s t i n Canadian c o n s t r u c t i o n p r a c t i c e because of t h e tendency of a l m o s t a l l s u c h m a t e r i a l s t o s w e l l t o some e x t e n t , a s t h e i r m o i s t u r e c o n t e n t i n - c r e a s e s . The f o r c e s developed when d i f f e r e n t elements of a b u i l d i n g swell t o d i f f e r e n t e x t e n t s have a l l t o o o f t e n been r e s p o n s i b l e f o r damage, o f t e n s e v e r e , t o s t r u c t u r a l and f i n i s h i n g components.

A s a c o n t r i b u t i o n t o i n v e s t i g a t i o n s on t h i s sub- j e c t , t h e D i v i s i o n of B u i l d i n g Research i s p l e a s e d t o i s s u e t h i s r e p o r t . It was t r a n s l a t e d by H.A.G. Nathan of t h e T r a n s l a t i o n S e c t i o n , National. Research Council L i b r a r y , t o whom t h e D i v i s i o n of B u i l d i n g Research h e r e r e c o r d s I t s t h a n k s . O t t a w a , A p r i l , 1958 N .B. Hutcheon, A s s 1 s t a n t D i r e c t o r

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NATIONAL

RESEARCH

COUNCIL OF CANADA Technical Translation-747

Title: Moisture absorption curves for building materials.

(Fuktabsorptionskurvor for byggnadsmaterial) Authors : C.H. Johansson and G. Persson

Reference : Byggmgstaren, 17 : 311-314, 1946

Translator: H.A.G. Nathan, Translations Section, N.R.C. Library Translated with permission.

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MOISTURE ABSORPTION CURVES FOB BUILDING MATERIALS Most b u i l d i n g m a t e r i a l s are h y g r o s c o p i c , I . e.

,

t h e y c o n t a i n a c e r t a i n p e r c e n t a g e o f m o i s t u r e i n e q u i l i b r i u m w i t h damp a i r , even i f t h e l a t t e r i s n o t s a t u r a t e d . A d e f i n i t e r e 1 : t t i o n s h i p e x i s t s between t h e h y g r o s c o p i c a l l y bound m o i s t u r e i n t h e m a t e r i a l and t h e r e l a t i v e h u m i d i t y of t h e a t m o s p h e r e . T h i s r e l q t i o n s h i p i s f r e q u e n t l y r e f e r r e d t o as t h e i s o t h e r m f o r w a t e r vapour o r t h e s o r p t i o n i s o t h e r m . However, t h e t e r m i s o t h e r m i s u n s a t i s - f a c t o r y b e c a u s e i t merely i n d i c a t e s t h a t t h e d e t e r m i n a . t i o n re- f e r s t o a c e r t a i n t e m p e r a t u r e . T h i s t e r m had o r i g i n a l l y been a d o p t e d i n c o n n e c t i o n w i t h i n v e s t i g a t i o n s of s o r p t i o n ( a d s o r p t l o n o r a b s o r p t i o n , as t h e c a s e may b e ) of o r g a n i c g a s e s and v a p o u r s i n a c t i v a t e d c a r b o n , where t h e t e m p e r a t u r e p l a y s a n imporvtant r o l e . However, w i t h r e s p e c t t o t h e s o r p t i o n of w a t e r v a p o u r t h e f o l l o w - i n g a p p l i e s . I f t h e r e l a t i v e h u m i d i t y i s k e p t c o n s t a n t , t h e p e r c e n t a g e o f m o i s t u r e i n i n o r g a n i c b u i l d i n g m a t e r i a l s i s v i r t u - a l l y i n d e p e n d e n t of t e m p e r a t u r e and i n o r g a n i c m a t e r i a l s , where t h e p e r c e n t a g e o f m o i s t u r e i n c r e a s e s a s t h e t e m p e r a t u r e d e c r e a s e s , t h e change w i t h t e m p e r a t u r e i s c o m p a r a t i v e l y s l i g h t . I n w h a t f o l l o w s , t h e t e r m m o i s t u r e - a b s o r p t i o n c u r v e i s u s e d f o r t h e r e l a t i o n s h i p between t h e p e r c e n t a g e of m o i s t u r e i n t h e m a t e r i a l and t h e r e l a t i v e h u m i d i t y of t h e a i r when t h e m o i s t u r e i n t h e m a t e r i a l and t h e h u m i d i t y of t h e a t m o s p h e r e a r e i n e q u i l i b r i u m w i t h one a n o t h e r . A knowledge of t h e m o i s t u r e - a b s o r p t i o n c u r v e f o r d i f f e r e n t b u i l d i n g m a t e r i a l s i s i m p o r t a n t f o r e s t i m a t i n g t h e p r o p e r t i e s of a b u i l d i n g w i t h r e s p e c t t o m o i s t u r e . The c u r v e p r o v i d e s a d i r e c t c r i t e r i o n of t h e m o i s t u r e c a p a c i t y o f t h e m a t e r i a l , i . e . , t h e l a t t e r ' s a b i l i t y t o a b s o r b , a c c u m u l a t e and g i v e o f f m o i s t u r e . The c u r v e a l s o makes it p o s s i b l e t o c a l c u l a t e t h e second of t h e s e p r o p e r t i e s from a knowledge o f one q u a n t i t y .

What h a s b e e n s a i d h e r e r e f e r s t o t h e h y g r o s c o p i c m o i s t u r e of m a t e r i a l s . The r e l a t i o n s h i p changes i f water i s p r e s e n t i n

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l i q u i d form, f o r example, s o i l m o i s t u r e a t a f o u n d a t i o n wall,

wind-driven r a i n on e x t e r n a l w a l l s and on a roof o r condensing wxter vapour from i n s i d e . I n porous m a t e r i a l s t h e " f r e e water1$ c o n t e n t may g r e a t l y exceed t h e h y g r o s c o p i c a l l y bound m o i s t u r e .

A s a n example of t h i s , F i g . l a and l b show t h e quantities of hyigroscopic m o i s t u r e and f r e e w a t e r t h a t may b e absorbed by y e l l n w p i n e and 1.6 b r i c k , r e s p e c t i v e l y . I n t h e s e d i a g r a m s , a b c r e p r e s e n t s t h e m o i s t u r e - a b s o r p t i o n c u r v e and c d t h e f r e e w a t e r c o n t e n t when t h e m a t e r i a l i s soaked w i t h watsr.

A t D i v l s i o n I ( f o r m e r l y t h e Chemical I n s t i t u t e of N a t i o n a l

Defence) of t h e Swedish Defence Research I n s t i t u t e , m o i s t u r e a b s o r p t i o n c u r v e s f o r a number of d i f f e r e n t b u i l d i n g m 3 t e r i a l s were determined i n c o n j u n c t i o n w i t h c e r t a i n m i l i t a r y b u i l d i n g problems, The p r e s e n t a r t i c l e g i v e s a comparison between t h e mois t u r e - a b s o r p t i o n v a l u e s t h u s o b t a i n e d and t h o s e o b t s i n e d by

o t h e r d e t e r m i n a t i o n s and p u b l i s h e d i n t h e literature. A few

m a t e r i a l s which a r e n o t used a s b u i l d i n g m a t e r i a l s have a l s o been i n c l u d e d .

Measuring Methodoloay

The i n v e s t i g a t i o n i n c l u d e s t h e d e t e r m i n a t i o n of t h e hygro- s c o p i c rnolsture c o n t e n t a t +25OC. The sample w a s suspended i n a i r of a c e r t a i n r e l a t i v e humidity w ? t i l e q u i l i b r i u m was a t t a i n e d between t h e m o i s t u r e i n t h e m a t e r i a l and t h e humidity of t h e

atmosphere. The amount of m o i s t u r e absorbed w a s measured by de- t e r m i n i n g t h e i n c r e a s e i n weizht when t h e welght had a t t a i n e d a c o n s t a n t v a l u e .

I n o r d e r t o o b t a i n a c o n s t a n t r e l a t i v e h u r n i ~ l t t y of t h e a i r w i t h known v a l u e s , saturated s a l t s o l u t i o n s were used. The va- ?our p r e s s u r e above t h e s a t u r a t e d s a l t s o l u t i o n s I s lower t h z n t h s t above pure w a t e r , and by s e l e c t i n g s u i t a b l e s a l t s a s e r i e s of v a l u e s f o r t h e r e l a t i v e humidity of t h e a i r may be o b t a i n e d i n a simple Pray. A t room t e m p e r a t u r e t h e s e v a l u e s l i e between

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w i t h , f o r example, m i x t u r e s of s u l p h u r i c a c i d and w a t e r , s i n c e t h e vapour p r e s s u r e of t h e former i s n o t changed by e v a p o r a t i o n o r c o n d e n s a t i o n a s l o n g as t h e s o l u t i o n c o n t a i n s s a l t c r y s t a l s . S a t u r a t e d s a l t s o l u t i o n s have t h e added advantage t h a t t h e r e l s - t i v e humidity of t h e a i r above them changes comparatively l i t t l e with t e m p e r a t u r e . The f o l l o w i n g s a l t s o l u t i o n s were used f o r t h i s

i n v e s t i g a t i o n : S a l t L i C l M€5ClZ Mg (NO3 NaCl B e l s t i v e humidity of t h e a i r a t 25OC.

The samples were p l a c e d i n weighing g l a s s e s which i n t u r n were p l s c e d on s t e e l - w i r e r a c k s w i t h room f o r s i x samples. The

i n o r g a n i c b u i l d i n g m a t e r i a l s were crushed down t o a maximum

g r a i n s i z e of two m i l l i m e t r e s . Each of t h e s t e e l - w i r e r a c k s w a s

suspended i n o n e - l i t r e g l a s s jars, which could b e h e r m e t i c a l l y s e a l e d with g l a s s c o v e r s and r u b b e r r i n g s ( " p r e s e r v i n g j a r s t 1 ) .

The s a l t s o l u t i o n s were p l a c e d i n t h e bottom of t h e jars. The bottom and walls had been a s p h a l t e d t o a h e i g h t of 20 m i l l i m e t r e s

i n o r d e r t o prevent t h e s a l t from c r e e p i n g up on t h e walls. The s e a l e d jars were p l a c e d i n a t h e r m o s t a t , which was kept a t + 2 5 ' ~ . The t e s t w a s u s u a l l y c a r r i e d o u t w i t h o u t p r e v i o u s l y d r y i n g t h e samples. They were weighed each day u n t i l t h e i r weight remained c o n s t a n t . A s a r u l e , t h i s took approximately 14 days. The d r y weight w a s determined s u b s e q u e n t l y by d r y i n g t o a c o n s t a n t weight

a t + 1 0 5 O ~ . T h i s u s u a l l y took two hours.

The l a b o r a t o r y t e s t s were c a r r i e d o u t by B r i t a Henriksson. M o i s t u r e - A b s o r ~ t i o n Curves

The m o i s t u r e - a b s o r p t i o n c u r v e s a r e shown i n F i g . 3

-

11 w i t h m o i s t u r e r a t i o s i n p e r c e n t by w e i g h t , i . e . , t h e m o i s t u r e c o n t e n t

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i n p e r c e n t by weight of d r y m a t e r i a l , a s a f u n c t i o n of t h e r e l a t i v e hurnldity of t h e a i r . (The p e r c e n t a g e of m o i s t u r e

g i v e s t h e m o i s t u r e c o n t e n t i n r e l a t i o n t o moist m a t e r i a l . ) For t h e d e t e r m i n a t i o n s of t h e p r e s e n t investigation, measuring p o i n t s have been p l o t t e d i n t h e diagrams. F o r t h e o t h e r v a l u e s , r e f e r - e n c e s t o t h e l i t e r a t u r e a r e g i v e n i n t h e t e x t f o r t h e f i g u r e s , where, f o r example, (L7) means no. 7 i n t h e l i s t o f r e f e r e n c e s a t t h e end of t h i s a r t i c l e .

The m a t e r i a l s i n c l u d e d have bzen c l a s s i f i e d as f o l l o w s :

I . B u i l d i n g m a t e r i a l s w i t h t h e f o l l o w i n g s u b d i v i s i o n s : ( a ) b u i l d i n g m a t e r i a l s i n c l u d i n g b r i c k ( F i g . 3 and 4 ) ;

( b ) wood ( F i g . 5a and b )

,

( c ) Porous and s i m i l s r s h e e t m a t e r i a l ( F i g . 6 ) , ( d ) Highly porous s h e e t s and b a t t s w i t h t h e e x c e p t i o n of f i b r e b o a r d ( F i g . 7 ) , ( e ) wood- f ibre-board. 11. O t h e r m a t e r i a l s , d i v i d e d i n t o t h e f o l l o w i n g g r o u p s , t h e d i v i s i o n depending c h i e f l y on t h e i n i t i a l m a t e r i a l : ( a ) v e g e t a b l e ( F i g . 9 a n d

l o ) ,

( b ) animal ( F i g . 11). A comparison of t h e r e s u l t s of d i f f e r e n t r e s e a r c h e r s g e n e r a l l y shows s a t i s f a c t o r y agreement. I n g e n e r a l t h e a b s o r p t i o n i n p u r e l y o r g a n i c m a t e r i a l s is c o n s i d e r a b l y h i g h e r t h a n t h a t i n p u r e l y in- o r g a n i c b u i l d i n g m a t e r i a l s , i f t h e m o i s t u r e r a t i o i s g i v e n i n per- c e n t by weight. However, t h e f a c t t h a t t h e m o i s t u r e r a t i o i n per- c e n t by volume i s t h e d e t e r m i n i n g f a c t o r f o r t h e u s e of t h e mater-

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References

1. McBain. The sorption of gases and vapours by solids. London,

1932

2. Frisk,

P. Textilteknisk luftbehandling (Textile air treatment

in industry)

.

Flakten,

4 (9) :

170-187, 1944.

3.

Haller, P.

Die Austrocknung von Baustoffen (Drying of build-

ing materials).

EMPA, Ziirich, 1942. Disk. bericht no.139.

4.

Hggglund, E.

Holzchemie (Wood chemistry). Le,ipzig

,

1928.

5. Johansson, C.H. Fuktighetens absorption och vandring 1

byggnadsmaterial (Absorption and movement of moisture in

building materials). Tekn. Tidskr.

H

.42, Stockholm, 1944.

6.

Kollmann, F.

Technologic

des Holzes (Technology of wood).

Berlin, 1936.

7.

~tglhane,

B.

and

Pyk, S.

~ l e k t r o v ~ r r n e i n s t i t u t e t ,

1923-1933.

p *

612.

8.

Wilson,

B. and Fuwa, T.

J. Ind.

Eng.

Chem. 14: 915, 1922.

9.

Heating, Ventilating, Air Conditioning Guide, 1946.

10. Thunell, B. Trg, dess byggnad och felaktigheter (Wood, its

structure and shortcomings). Byggstandardiaeringen.

Stockholm, 1945.

11. Thunell, B. and Lundquist

,

H. Trztorkning

I

-

I11

(Wood

dessication

I

-

111).

Svenska Trgforsknings-

institutet

,

Meddelande

,

No.

4-6.

Stockholm,

1945.

12. Edenholm, H. and Malmqvist,

L. Meddelsnde Statens ~ommitt6

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Yellow p i n e 1.6 B r i c k

Fig. l a F i g . l b

M O I S T U I I C RATIO . g - O t W E ! G " r _ _ .

Hygroscopic moisture and f r e e w a t e r i n yellow p i n e and 1.6 b r i c k , r e s p e c t i v e l y . I . , F i g . 2 ' r l 1 . . R e l a t i v e humfdity of t h e a i r above s a t u r a t e d s a l t s o l u t i o n s l-. .l l-l .l, --.. ." - . . I " ( " . . , . L. . . . i ... I . ...,.,., Y I... -

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Fig. 3

Inorganic b u i l d i n g m a t e r i a l s : 1. Tretong (1 cement: 4 Tretong)

,

2 . Cement ( P o r t l a n d cement w i t h 40% w a t e r ) ( L 7 ) , 3. Ytong,

4. Slag c o n c r e t e ( c o k e ) , 5. G a s c o n c r e t e , * 6. Foam c o n c r e t e , *

7. Tretong (1 cement: 2 sand: 2 T r e t o n g ) , 8. Slporex 0.4, 9 . S l a g c o n c r e t e ( b l a s t furnace s l a g ) , 1 0 . Hollow cement blocks

(Vibro) (L5). . . / C I 0 20 'U 40 5 0 6 0 10 A0 3U Hum or THE 4111 F i g . 4 I n o r g a n i c S u l l d l n g materials: 1. Kieselguhr ( L a ) . 2 . B a s t s r d s t u c c o

(30$ cement p l a s t e r

+

70% lime p l a s t e r ) ( L 1 2 ) . 3 . Cement p l a s t e r (1 cement: 3 sand) ( ~ 1 2 ) 4 . Concrete (1 cement: 2 . 6 sand: 2 . 6 broken . s t o n e ) ( L 5 ) . 5. Gypsum ( L 7 ) . 6 . Lime p l a s t e r (1 lime: 3 sand) ( L I Z ) . 7 . Kaolin (L8). 9. Asbestos ( L 8 ) . 9. 1.2-9rlck ( L 5 ) . 1 0 . 1.6-3rick

(L5)

*

T r a n s l a t o r ' s Note: Various European languages make a d i s t i n c t i o n between t h r o e types of l i g h t w e i g h t c o n c r e t e which a r e u n f o r t u n a t e l y lumped t o g e t h e r i n E n g l i s h under onc heading such a s c e l l u l a r

,"

o r foamedn c o n c r e t e s . ' ' h e t y p e s a r e " g a s

,"

ltfoarn,n and t t l i g h t

limen

c o n c r e t e s , depending 011 t h e i r manufacture.

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REL. Hurl. or THf R I R F i g . 5a

(L6)

1 . M o i s t e n e d r e d b e e c h . 2. D r i e d r e d b e e c h . 3 . M o i s t e n e d y e l l o w p i n e . 4 . D r i e d y e l l o w p i n e . 5 . M o i s t e n e d o a k . 6 . D r i e d oak R E L . H U M . O F T N I R l R F i g . 5b (L5) S w e d i s h y e l l o w pine, d r i e d

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Fig. 6

Porous s h e e t m a t e r i a l except wood f i b e r board. 1. Arki b a t t s ( s e a grass). 2. Dyhonit (woodwool boards impregnated w i t h cement). 3 . S t r a m i t

(straw

b o a r d ) . 4. T r a u l l i t (woodwool board impregnated with cement). 5. Woodwool boards ABT (impregnated w i t h cement).

6. S e r p o n i t (woodwool boards impregnated with cement).

20 I 14 12 ,

.

-*- I : Q -

"

,

, . , I ' , 2 ,.,I '1' H3 '111 l i l C #EL. H u n OF r l r F A I R Fig. 7

Highly porous m a t e r i a l s . 1. K r a f t e l i t ( l a m i n a t e d , Impregnated K r a f t P a p e r ) . 2. Kramfors s h e e t s . 3. W e l l i t . 4. I s o f l e x ( t r a n s p a r e n t ) .

5. I s o f l e x ( A l ) . 6. Cork. 7. G l a s s wool. 8. G l a s s wool s h e e t s . 9. Rock wool. 10. S l a g wool.

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Wood f lbre-board. 1. Bockhammer wallboard, porous. 2. T r e e t e x , porous. 3. T r e e t e x , semi-hard. 4. K a t r i n i t

,

semi-hard. 5. K a t - r i n i t , hard. 6. T r e e t e x , hard. 7. Masonlte, semi-hard. 8. Maso-

n i t e , hard. 9. Masonite hardened

Fig. 9

Vegetable m t e r i a l s . 1. Tobacco ( L 8 ) . 2. Activated carbon "Norit" (own r e s u l t s ) . 3. S i l i c a g e l ( i n o r g a n i c ) (L8).

4 . Macaroni ( ~ 8 ) . 5. Sawdust ( L 1 2 ) . 6. White bread ( ~ 8 ) .

7 . Rusks ( L 8 ) . 8. S t a r c h (L8). 9. Charcoal, 0-7mm. (L12).

(14)

F i g . 1 0 (La)

Vegetable m a t e r i a l s . 1. J u t e . 2. N a t u r a l s i l k . 3 . Viscose rayon. 4 . Hemp. 5. Cotton. 6 . Linen. 7 . F i l t e r paper. 8. C e l l u l o s e

a c e t a t e s i l k . 9. Rubber ( s o l i d Goodyear automobile t i r e s ) .

F i g . 11 (La)

M a t e r i a l s of

animal

o r i g i n . 1. S o l e l e a t h e r . 2. White soap.