Moisture Transmission and Moisture Distribution in Building Materials

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Moisture Transmission and Moisture Distribution in Building Materials Johansson, C. H.; National Research Council of Canada. Division of Building Research

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NATIONAL RESEARCH COUNCIL OF CANADA

TRANSLATION TT-189

MOISTURE TRANSMISSION AND

MOISTURE DISTRIBUTION IN BUILDING MATERIALS

Ｈｆｵｫｴｧ･ｮｯｲｮｧｾｧ och Fuktfordelning i Byggnadsmaterial) by

C. H" Johar.sson

Reference

Tidskrift for Varme, vento och sanitet ｬｾ S0670 1948

Translated by Ho Ao Go Nathan

This is the thirteenth of the series of translations prepared for the Division of Building Research

Ottawa

July 1951

The performance of building materials and combinations of building materials depends to a large degree on the

amount and distribution of water in them. Hence the study of the mechanism of water and water vapour movement in building materials is one af great concern to the

Division of Building Research. When staff

and facilities permit, the Division will be

attacking this fundamental problem. In the

meantime, every effort is being made to study the work of others in this field so that the Division's work may proceed on a

sound basis. This paper by C& Ho Johansson

of Sweden has been translated with this end in viewo

R.F. Legget Director

ｾ TRANSMISSION AND ｍｏｉｓｔｕｾ

DISTRIBUTION IN BUILDING

ｍａｔｅｒｉｾＪＩ

Moisture and releted problems have been the object of prime interest in the building trade for man;y- years and extensive research has been carried out in various parts of the world. However, these problems have proved to be complex ones and a lot of work remains to be done before it is possible to give the builder reliable calculation formulas and

material data. In particular, very little is known of the manner in

which the moisture moves through hygroscopic materia.l. This in turn means that the necessary material data are not available since it is neither known what data are required to characterize the material nor how to determine them.

In the ｰｲ･ｳ･ｮｾ paper certain fundamental problems regarding the movement and distribution of moisture in building materials are

discussed. Reference is made to a number of earlier investigations,

some of which the author carried out at the Physics Institute of the Royal Technical College with the assistance of engineer By Bergelin, Bo Pehrsson and the technologists J. Nystrom and La Olentalk, and some at the Defense Research Institute (Division I) together with engineer

q0 Per-aeon, In the latter investigations they were a.ssisted by the

*>

The manuscript is based on notes taken on the occasion of a lecture by ｾｨ･ author before ttJ,e meeting of Svenska Kyltekniska fffreningen J.n December, 1947.

Acknowledgement: The author received valuable help from engine

engineers Lo Larsson and Brita Henriksson

｜ｃＱＭＹＱｾＩ

The investigations at the Royal Technical College were aided by grants from the Swedish Committee for Building Research and the Swedish Technical Research Council0 In connection with these investigations engineer Persson and

the author compiled a card-index of the literature on heat and m6isture problems in bufIdd.ngs, This card-index has been deposited in the

Royal Technical College and in Chalmers University of Technologyo

ｍｯｩｳｴｾｾｾｾＰＮＡＧｕｴｩｯｮ

All building materials are more or less hygroscopic» ｩｯ･ｯｾ when

exposed to damp air they always contain a certain amount of moisturea The hygroscopic moisture can be high or low depending on the

microscopic and submicroscopic structure of the material, but it can

never be eliminated completelyo In general the moisture ratio depends

chiefly on the relative humidity of the atmospherea Curves of the moisture absorption of a number of common heat-insulating materials are sho'WIl in Figa 10 A more complete collection of curves showing the moisture absorption of building materials has been published in Byggmastaren 1.8j 0

Moisture Movement by ｃ｡ｰｾｬｬ｡ｲｩ ty an£!. Va-poura 'p"ifJ,ypion

The movement of moisture through hygroscopic materials is causid partly by diffusion of water molecules in the form of vapour and

partly by capillarity of water in liquid forma The resulting moisture

transmission per unit of time, G, is thus equal to the sum of the

diffusion term Gd and the capillarity term Guo For plane parallel

t)

= 3

-layers the following equations hold: G :;: Gd

+

Gu

= Gd == kd 0 A 0 ］ｇｵ］ｾｯａｯ where dp dx du dx

(1)

(2) (3)

p :; partial pressure of the water vapour u

=

moisture ratio of the material

x

=

position along the normal to the layer A ': area

k_{d and}

ku

=

coefficients of moisture transmission for diffusion and capillarity respectively.

An example in Fig. 2 shows hov the moisture transmission through

a single layer is composed of Gd and Guo The temperature distribution

in the sheet and the partial pressUre p on both sides of the sheet are

assumed to be knovn, From the curve for t in Fig. 2a the saturation

pressure of the water vapour (curve for Pm in Fig. 2b) can be calculated. The relation between the partial pressure and the saturation pressure gives the relative humidity of the atnosphere,

ep ,

and from the curve of the moisture, absorption of the material the corresponding moisture

ratio, u» can be calculated. In order to obtain steedy state conditions,

either G

=

G_d

+

Gu

must have the same value at all points of the sheet

or else moisture will accumulate in the shget. If.ku is so small

that

Gu

can be neglected together with Gd, the partial pressure along the Clotted straight line in Fig. 2b decreases and

'f

and u follow the dotted. curve in Figs. 2c and 2d respectively. _{If Gu is appreciable the} curves for p and u are modified until

£J2...

\u

.

du assumes the same value

dx kd dx

the distribution in such a case.

The greatest partial pressure' is obtained at the warm side of a wull and thus the diffusion ｯ｣｣ｾｲｳ in the direction of the cold sideo

The moisture ｲ｡ｴｩｯｾ on the other handj is greatest on the cold surface

of e wall and the moisture is moved in the direction of the warm surface by capillary forces. In this case diffusion and capillarity act in the opposite direction.

In applying equations (l)j (2) and (3) to actual cases the fact seems to have been overlooked so far that not only does the capillarity cause the moisture transmission, as represented by the term Gu' but even affects the coefficient of diffusion kd and thus Gd. It is therefore necessary" to make a distinction between a capillarity which is confined locally and one which has an equalizing effect on the ｮｯｮｾｵｮｩｦｯｲｭ moisture distribution in the material. To make this cLear , the mechanism of

moisture transmission will be studied with reference to a number of geometrically simple cases. The nomenclature will be as follows: - "localized capillarity" for the first-mentioned type of capillarity and "moisture-equalizing capillarity" for the second one.

Calculation of Moisture TransBission for a Number of_{... ... .}

-

_....

1. ｉｨｾｍｯｶ･ｭ･ＡＡＮＮｴ of Moisture in a ..Qzl.indrical Capillag Tube

The transmission of moisture in a cylindrical capillary tube filled with air occurs in an entirely different manner from that· in a capillary tube which is almost full of water. In the first case the water

5

-second case the water vapour condenses at one end of the water column

and evapqrates at the other. During this process the capillary forces

draw water from the condensation side to the evaporation side (Fig. 3). The following symbols are now introduced:

1-

and

ｾ

1

=

the length of the tube and water colunm

respectively

r a radius of the tube

=

,partial pressure at the respective sides of the tube

- internal friction and density of the water

- diffusion of the water vapour in air

For the amount of moisture (G) passing through the tube in the unit of

time

[9J

the following equation holds:

G

=

kD ·J7.r2 Q Pl_-_P.=:2 _

ｃｾＭｩｬＩ

+

q -(1'1 - 1.4r)+ 3r

(1)

where q

=

(2)

is filled with air (11

=

0) If now Gd denotes the value G when the tube

If numerical values are substituted in the expression for q, then at a temperature of lOoe.: k

_n

=

2v 2 x 10-10 sec. (p in dyne per sq.cm.),

7

=

O.Ol} d1Be sec./sq.cm. and ｾ ｾ 1 gm./cc.; whence the following is obtained if r is ･ｸｰｲｾｳｳ･､ ｩｮｾｾ

q ;;; (0.05 )2-r

and

au

when it is completely filled with

ｷｾｴｾｲ

()l

= )

and if,t,.is

G

d _

--

G

u

It is evident ｦｾｯｭ equations (2) and (3) that

Gdｾ G_u when q ｾ 1, Le., when r ｾ ＰＮＰＵＯｾＮ (4)

This means that 0.1

r

is a critical diameter at which the moisture transmission is the same whether the tube is filled with air or water. With smaller diameter a water column has an impeding effect on the moisture transmission, but with greater diameter it facilitates moisture transmission through the tube.

It is also evident from equations (2) and (J) that the pressure drop caused by the water drawn through a capillary tube filled with water is negligible compared with the pressure drop at both ends of the tube if

r

,»

0.03V

t --'

r •

According to equation (5) this pressure drop is less than 1 per cent of the total pressure drop for r> l r when!

=

lOr (short tube) or for r

>

ｬｾ when

l

=

1,000 r (long tube}, In such a case q ｾ 0 and equation (3) becomes

Expressed in words, equation (3a) indicates that if the difference in partial pressure is maintained constant the moisture transmission through a capillary tube increases very considerably as both partial pressures increase so that the tube which was first filled with air fills ｾｰ with water. Hence the longer the tube in proportion to the radius the greater the increase.

7

-With respect to the conditions under which the tube contains either air or water the following holdso The tube is completely

filled with air if f

<

Pr' completely filled with water if P2

»

p

I r

and partly filled with water if 'PI> Pr :> P2' Here Pr is the vapour pressure on the liquid meniscus in a capillar,y tube having the radius r, and if

Pm

denotes the saturation pressure on a level surface of water and b is a constant, then

Pr =Pm • e -b/r (6)

Two chambers having the partial pressures ｾｬ and P2 are assumed to be connected by a linear system of pores and capillar,y tubes in the, manner shown in Fig. 40 In such a system the water cannot be drawn from one capillary tube to another if the intermediate pores are filled with air. Capillarity certainly is a necessar,y assumption for moisture

ｴｲ｡ｮｳｭｩｾｳｩｯｮ through capillaries containing water but here it is merely

a question of localized capillarity in each individual ｣｡ｰｩｬｬ｡ｾ tube and the moisture transmission depends not on du/dx but merely on dP!dxQ The resistance to moisture transmission through capillaries depends on

the extent to which the tubes are filled with water in a manner shown by the above exampleo The coefficient of diffusion, which is

proportional. to the inverse value of the sum of the resistance by the capillaries and por-es , thus increases with the moisture content if r

>

0005}-tQ _{Conversely, kd decreases with the moisture content if} r

<

ＰＮＰＵｾＮ

3.. The Hovement of Moisture in a_§tructure Consisting of Tightly Packed Sphere,§

A clear picture of the diff""rence between "moisture equalizing" and "localized" capillnri ties is obtained in a structure consisting of tightly'

packed spheres. Around each point of contact there is.a capillary space

. where the water condenses on an -annular Lamfna

In.

th the meniscoidal radii cos dv

and

i"2

=

r k • tan d... •

This is shown in Fig.

5.

Since the moisture ratio is so small that

-:<..,.<300 the annular capillary Lami.nae around the points of contact are separated from each other. When 0<..

=

300 _{they flow together and}

only then can water be drawn from one Lami.na to another. Hence the moisture-equalizing capillarity does not occur until the moisture

content obtains a certain minimum value. The'pore volume amounts to

25.8 per cent by volume and if "-

=

300 the 1'ater content ameunt.e

to

4.9

Ｎｰｾｲ cent by volume. As long as u is ｳｾｬｬ･ｲ than

4.9

per cent

by volume cnly the diffusion term need be taken into account, but the localized capillerity ｣｡ｵｳｾｳ the coefficient of ｭｯｩｳｴｾｲ･ diffusion to increaEe with the moisture content.

The MOVement of Moisture in a Plane-Parallel Plate Containing Capill§.ries,

Two cpambers having the partial pressures PI and P2 are assumed

to be separated by a plane-parallel plate of ｴｨｩ｣ｫｮ･ｳｳｾＮ This plate

9

-distributed uniformly over the plate. Such a plate has a moisture...;.

absorptton curve similar to that of a hygroscopic materiaL In

general, with ambient moist air the capillary tubes with a smaller radius than a value (rl) determined Qy the relative humidity of

the atmosphere ＨｾＩ are filled with water and the other capillaries

are filled with air. 'According to equation (6) the ｦｯｬｬｯｾｾｮｧ

rela.tion between

cf

and r

l holds: , 1

(6a)

If the area of the capillary tubes', vhose radii are between

r and rTdr, is denoted by f (r) dr, ｣｡ｬ｣ｵｬ｡ｾ･､ per unit of surface

of the plate, then the ｦｯｬｬｯｾｾｮｧＬ expressed in volume elements ＨｾＩＬ

is obtained for the moisture ratio of the plate:

r 1 !' I U ::

)f

(r) dr _(7a) 1 0

and for the saturation value of the moisture ratio (Urn), ioe., when all the capillaries are filled with water,:

Co

J

f (r) dr , o

(7b)

If PI

>

P2 and if all the capillaries for which r

<.

"i are filled with water, then according to equation (1) the moisture transmission per unit of time is

G

=

k_{n .} A

u

Equatioh (8) can also be written in the following forE:

ｾ

l

G

=

_{kd • A}

PJ.-

P2

If

r dr

₊

(I-g) fer) dr ! _{1+3r /{} (q+3r/.1) (l-t-JrjL) 0 0 ₍₉₎

If the distribution function f (r ) and the thiclmess of the plate, ,(, are knowny k

d can be calculated by graphical integration. Numeri9.al calculation was carried out for three examples with the radii of the capillary tubes distributed as ｳｨｯｨｾ in Fig. 6 (curves 1 to 3). The distribution has been chosen such that the total area of the capillaries per urcit of surface is the same in all three cases.

Fig. 7 shows kq/k_Das a function of the "noiGture ratio" Uo For

small values of u, kd decreases with u anc,if a considerable part of the capillary volume consists of capillaries \nth ｲｾｏＢｏｾ｣ｵｲｶ･ 1), this tendency to decrease greatly affects large values of u. For greater ｣｡ｰｩｬｬ｡ｾｊ ､ｩｾｾ･ｴ･ｲｳ the increase of k with u begins even with

d

small values of u. Furthermore it is evident from the calculations tha.t only if 3 r/( is negligible compared ldth 1, or with q, is k

d independent ｾ［ the thickness of the plateo Fig. 8 shows kd/kD as a function of u for various values ofｾ when the capillary radii are distributed according to curve 3 of Fig. 6. Fig. 9 shows kd/kD af a function of the thickness of the plate for u/um

=

0.75 when the capillary distribution is the same as in Fig. 8. It is evident from the curves that kd increases ｾｮｴｨ the thickness of the plate and

- 11 ｾ..

approaches an upper limiting value, which in this case is renched when

"t:;

0.1 mm , However, the region where the thickness affects k_{d ｩｾ} shifted with larger values of.e, if the distribution curve for the capillary radii has large r values.

Experimental ialues for the Coefficient.of Moisture TransmissioI! The structure of a hygroscopic material is a great deal more complicated than that of the model structures discussed above. However, it is an interesting fact that the experimentally obtained

curves shown in Figs. 10 and 11 have the ｳＦｾ･ form as curves of plotted calculated values shawn in Fig. 7. In order to represent heterogeneous materials in one and the same diagram the experimental curves have been plotted with ｾＧＱｮｳｴ･｡､ of u as abscissa, thus denoting the relative humidity of the atmosphere which is equivalent to the moisture ratio u, A change from u to

f

causes only an unimportant

change in the form of the curve and is without significance for purposes of comparison.

Figs. 10 and 11 show curves of some of the ｣ｯｾｾｯｮ building materials. Some of the experimental values were taken from the author's measurements and some from Edenholm's ｭ･｡ｳｾ･ｭ･ｮｴｳ (E). In view of the difficulties encountered in ｡｣｣ｵｲ｡ｴ･ｾ determining the coefficient of moisture transmission, the agreement must be considered satisfactory. However, this does not apply to the interpretation of results. Edenholm ｡ｳｳｾ･ｳ that the increase in the value of k with the moisture ratio is due to capillarity, and from it he derives a coefficient of capillarity for the moisture-equalizing capillarity.

Whereas the author's experimental investigations have shown that the moisture-equalizing capillarity is negligible compared with the vapour

diffusion within the range of hygroscopic moisture applying here. The

fact that the vapour diffusion is combined with the capillarit,y does not change the situation since here it is a case of localized capillarity which does not contribute to the moisture-equalizing capillarity.

In order to facilitate comparison the moisture diffusion values (in gmu/sq. m. hr. rom. Hg at ＲＰｯｃｾ in thin sheets OT films of different materials and in sheets of building materials 1 em. thick have been

compiled in Tables I and II

ｲ･ｳｰ･｣ｴｩｶ･ｾＮＪＩ

To convert the figures shown

in Table II into w.uJm. hr. nun. Hg they must be mu?-tiplied by 0.01.

Table II Moisture diffusion value,

lcd,

in aheets of material 1 em.

thick, in gm./Sq. m, hr. mm, Hg at 20oC.

-Material kd

Wax

10-5

Rubber of various typef!. 10-4 to 10-3

Hard masonite _{0.05 to OJ.}

Pine wood (.L. grain)

Concrete

_--

0.1 to 1

Cement mortar and sandlime mortar

Plywood 0.5 to 1

Brick _{1 to 3}

Porous fibre sheets; ｰｲ･ｳｳｾ､ mineral wool Pine wood (1/.gnatn)

Aerate6'conerete _{3 to 6}

Mineral wool. 100 to 200 kzm , per cu. m.

Air, stationary layer 8 tolD

*)

A similar compilation can be found il'1o nIngenjorshandboken" _{I Al:I.mSnna}

13

-Table I Moisture diffusion value k<J. for thin sheets or films of different materials ｾｮ gm./sq. m. hr. mm. Hg at 20°C.

Material

ｾ＼ＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭｾＭＭＭＧＭＭＭＭＭＭＫＭＭＭＭＭＭｴ

Al foils, Ou009 romo on ｾｰ･ｲ

Al foils on paraffin paper

Cellophane "Wetterfest" (weather proof) 35 gm./sq. m. Asphalt, 0.025 rom.

"Isoglasyr", 150 gm(sq. m.

Cardboard, impregnated and coated with asphalt

Cardbeard, black, impregnated, unfinished <0.02

Kraft paper, 150 gm.7sq. mo

Bitumen lining, 325 gm./sq. m, (impregnated with

asphalt)

Gasproof paper m/42, 350 gm./sq. m. (impregnated with asphalt and paraffin)

Newsprint, "impregnated with 115 gm, of paraffin/sq. m•

. /

Vinyl-chloroacetate 0.025 mm.

Varnish, "long oil" with Al powder 0.025 rom.

Varnish, "short oil" _{0.02 to 0.1..}I f

Gold shellack

""Ocear." paper, 170 gm./sq. m, (with ,50 gm , asphalt per squ tn.)

Varnish, "long oil"

I

Doubly corrugated cardboard, impregnated with asphalt ,0.10 to 0.2C

Sheathing felt < I

Cellophane, 0.025 mIDo Rayon, 0.025 rom.

VinyJ acetate; 0.025 mm.

Viscose cellulose "cellophane", 60 gm./sq. m. Acetate cellulose "df.ophane'", 90 gm./s4.In.

Wax paper, 'finished and unfinished, 22 gm./sq. m. (impregnated with 5gm. of wax'per sq. ro.)

Black impregnated, finished Kraft paper, 200gm./sq.m.

0.20 to 1.0

1 to 4

I

I

Cellophane, untreated, 25 gm./sq. ro. Non-impregnp.ted cardboard

Kraft paper, 1, 2 or 3 layers of 0.1 rom. Newsprint, 55 gm./sq. m. Filter paper " . , 4 tel> 6

I

---O"'---

----L..._-. __

<_< __.__

ｾ

Moisture Distribution in Walls Consisting of Several Layers when the

ｍｯｩｳｴｵｲ･ｾｅｱｵ｡ｬｩｺｩｮｧ ｃ｡ｰｩｬｬ｡ｾ Movement is ｎ･ｧｾｩｧｩ｢ｬ･

When the moisture-equalizing capillary movement is negligible so that only the diffusion term need be taken into account the curve of the partial pressure in walls consisting of several layers can be

obtained in the same manner as the temperature curves. Hence for the

decrease of the partial pressure in e.g. the layer of thickness dk' the moisture diffusion value kdk and the resistance to moisture

diffusion ｾ

=

_{dk : kdkrthe following equation applies:}

m k

where ｾｭｫ

=

total resistance to moisture diffusion, i.e., the sum

of the values of mk for all the layers.

The transition resistance on both sides of the wall is negligible in this caseo Since the curves for t and p have been determined the curves

for p , c( and u are obtained in the same manner as those for a

plane-m <

parallel sheet of a material (cf. p.

3).

Figu 12 shows the curves of t, Pm ｡ｮｾ p obtained for a wall of concrete and light-weight brick, partly with concrete, and partly with

brick on the cold side. From the moisture point of view it is

expedient to ｡ｰｰｾ brick to the cold side because in that case the

relative humidity of the atmosphere can be very high on the warm side, without moisture condensing in the construrction. This is due to the

fact that ｉＱｴｮｴＭｷｾｩｧｨｴ｢ｲｩ｣ｫ has a higher heat resistance compared

with concrete, whereby the curves of t and

Pm

are bent upward and the

=

15

-view it is ｰ｡ｲｴｩ｣ｵｬ｡ｲｾ disadvantageous to ｾｰｰｾ brick to the warm side

since the p curve is then bent upward and intersects the Pm ｣ｵｲｶ･ｾ

which in this case-is bent downward ･ｶ･ｮｷｨ･ｾ the humidity of the

in-side air is lowo It is advantageous to place the bricks on the cold side also from the standpoint of heat capacdty , However, in order to obtain good results it is essential to protect the bricks against penetration of water from the out sdde by an ext.ernal, waterproof layer, which is either permeable to ｷｾｴ･ｲ vapour or is separated from the

｢ｲｩ｣ｾｳ by a space which is in contact with the outside air at the top and at the bo.ttomo

Curve Showiry; the Distribution of the Partial Pressure when the Water Vapour Condenses in the Wall

The flow of water vapour due to diffusion is subject to the

condition p

'Pm'

Le., the partial pressure can never exceed the

saturation pressure at the temperature in questiono If the

calculated curve of p intersects the curve of ｾ as in Fig. 12, it

cannot correspond to the actual distribution of the partial pressure, but the result is valuable just the same since it shows that water vapour condenses in the walL

To obtain a better idea of how the condition p ｾ Pm affects the moisture diffusion it is interesting to see what information can be obtained from a similar case where the water flows through a gutter

having sidewalls of decreasing height. It is assumed that the gutter

is provided with a layer of sand or other granular material having strong resistance to flow so that the water level decreases along the

follows the horizontal line ABCD. It is now assuned tha.t the height

of the sidewalls decreases along the line ABC'Di of Fig. 13 b. The

latter line is partly below the level abcde. Since the water level

ce.nnot be higher than the side walls, the we.ter must flow over the borders and the modified level abc'de with the water flowing over

the borders at the point c'

=

Cl is obtained.

Conditions obtaining at diffusion flow for the above case,

which is shown in Fig. 12, have been reproduced in Fig. 14. Similar

to the gutterj the p curve in Fig.14a is assumed to follow the line

abctd , Lns'tead of abed, with condensa.td.on at the poirit ct , However, lt must then be ftl3sUDled that the condensate can flow off in the

boundary surf'ace at c ' without being absorbed by the brick or concrete. Because of the capillarity the line abc'c'c'de in Fig. 140 should

123

｡ｰｰｲｯｸｩｭ｡ｴ･ｾ correspond to the p curve actually obtained.

Hoisture Distribution as Influt'!llced by MoistUre-EqualiziJ1g Ce.pilla'!y. Movemen.t

A calculation of the moisture distribution when the moisture ratio is so high that the moisture-equaiizing capillarity is noticeable or

simply is the dominating factor is not possible. One reason among

others is the lack of necessary material data. In order to obtain some

information 8S to how in such a case the moisture is distributed in a

material the author carried out certain preliminary investigations. The experiments were made with prismatic test bars of briok with the dimension 35 x 8 x 8 ｭｭＬｾＮ Each test bar ｾｳ moistened until a certain desired moisture ratio was obtained and then provided Jdth a moisture-resistant wrapping consisting of an inner layer of elastic rubber tape,

17

-an intermediate layer of thin aluminium foil -and -an outer layer of

paraffinQ Four test bars with their individual wrappings were

arranged together between two heating plates controlled by

thermostats, each having its constant temperature. By good heat

insulation of the experimental set-up it was possible to obtain an approxlmately rectilinear temperature drop in the test bars.

Preliminary experiments showed that the temperature distribution was a.pproximately stationary after a few days. During the experiments the test bars"were left in the apparatus for a week. Then they were

removed and the,moisture distribution was determined. So as to

remove the moisture-resistant wrappings as rapidly as possible, the bars were cut lengthwise into four or five parts and each part placed

in a weighing tube with a ground cover. The moisture ratio was then

determined in the usual manner by weighing before and after drying at 110oC.

Fig. 15 shows the result obtained from a determination of moisture dd.sbrdbutdon for three test bars of l.8-brick. ,Without capillarity the moisture would diffuse towards the'"cold end" until all the pores were

filled up with water. This would correspond to a rectangular curve of

moisture distribution with a moisture ratio of approximately 30 per cent at the "cold end". The ｭｯｩｳｴｵｲ･ｾ･ｱｵ｡ｬｩｺｩｮｧ capillarity thus has a

decisive influence on the form of the moisture-distribution curve. The

present experimental results indicate that the method employed is I

suitable for the determination of the capillarity value as a function

of the moisture ratdo, However, the author has not yet been-able to

Of special interest is the fact that up to a mean moisture ratio of approximatelY 4 to 5 per cent it is found that at the warm side

there 1s a region which oontains onlY hygroscopic moisture. This

result confirms the fact that the moisture-equalizing capillarit,y is negligible as long as the moisture ratio is low in the hygroscopic region.

19

-Bibliograp&

List of papers by the author and colleagues on moisture problems. 1. Temperatur och fuktighet i bergskyddsrum vid olika

avfuktningssystemu (Temperature and moisture in air raid

shelters in rocks with different air drying systems.) Tekn. Tidskrift 73 (1943) p. 368-376, (special number for underground shelters in rocks.)

2. Luftfuktighetens diffusion genom ｳｭｾ oppningar. (Diffusion of the humidity of the atmosphere through small openings.)

(Joint report by the author and S. Persson.) IVA 1943, no. 2 p.

160-162.

3. FWctighetens absorption och vandring i byggnadsmaterial. (Absorption and movement of moisture in building materials.) Tekn. Tidskrift 74 (1944) p. 1205-1216.

4. Avfuktningssystem for ｳｾＺｦｏｲｲ､､Ｌ som sakna elstrom, varme och daglig tillsyn. (Air-drying system for small stores without electricity, heat and daily inspection.)

Varme, ｶ･ｮｾ och sanitet 16 (1945) p. ＶＷｾＶＹＮ

5. Temperatur och fukthalt i ett friskluftventilerat bergskyddsrum med innerb,rggna9. (Temperature and mOIsture content of a

com-pletely finished rock air raid shelter with fresh air ventilation.) (Joint report by the author, G. Persson Bnd L. Larsson.)

Varme, vent. och sanitet 16 (1945) p. 49-52.

6. Fukt i byggnader: orsaker - verkningar- hotemedel. (Moisture in buildings - causes - effects - remedies.)

Byggnadsvarlden 1945 p. 409 and 422.

7. Fdktighetens inverkan pa varmeledningen i tegel. (Influence of moisture on heat conduction in bricks.)

Byggmastaren 1946 p. 117-124.

8. Fuktabsorptionskurvor fOr byggnadsmaterial. (Curves of moisture absorptio.p for various building materials.)

(Joint report by the author and G. Persson.) Eyggmastaren 1946 p. 311-14.

9. Theoretical investigation of ,the effect of capillary suction on transmission of moisture in hygroscopic ｭ｡ｴ･ｲｩ｡ｬｾＮ

Discussion

T. ｈ｡ｧ･ｾｮＬ PH.D.g The research institute of the brick industry

.

ha.s been confronted even with problems of building technique along with others ｡ｮ､ｾ after consultation with Dr. Johansson, has·begun a

number of experiments on the movement of moisture in brickwork. The

reason for this was the fact that in buildings faced with slabs of compact stone ｳｵｾｨ as marble there is a danger that the brickwork behind the slabs will crack due to freezing unless precautions are

taken during the construction. An extreme ｾ｡ｳ･ is a bUilding where

in eight t9 ten.years a free surface of water and insufficient ventilation had caused a large ·amount of water to pass through the concrete wall and to ｾｯｲｭ a frozen layer in the light-weight concrete

behind the slabs and back moulding. In another case where the wall

consisted of only single-stone 1.2 -bricks with slab trimming, the

damage in the bricks occurred right up to the back moulding. It must

be assumed that the q.amage was qaused by frost. ｈｯｷ･ｶ･ｲｾ there was some doubt in this case as to whether the moisture in the ｪｯｾｮｴｳ

between the slabs originated from within or without. This type of

Wall was therefore made the obj ect of study in the first labors.tory experiment, which was arranged in the following manner.

A test wall of the above type was constructed and put into an

opening cut into the wall of a refrigerator. On the cold side,

therefore, the brick wall was tr1mmedwith a 3-cm. marble slab mounted

on mortar and on the warm side it was plastered. Thermo elements were

attached to the warm side, a few centimetres inside the material, in the centre of the wall and a few centimetres inside the brick on the

21

-cold side. In the first stage the temperature on the warm side was

+

200C. _{and the rele.tive humidity of the atmosphere 50 per cent.}

The temperature on the cold side was about - lSoC. during a period of approximately 130 days. At different times moisture samples were taken from the ｾＮｬｬ at various depths by drilling with a core drill. As expected the moisture had increased ｣ｯｮｳｩ､･ｲ｡｢ｾ towards the cold side, but the values did not give uniform results for the same zone of depth but gave reason to assume that the accumulation of moisture ､･ｰ･ｲｾｳ to a great extent on the condition of the material', esg , the degree of burning, and thus on the system of

pores of different bricks. During the experiments the temperatures at the various point of measurement were ｲ･ｭ｡ｲｫ｡｢ｾ constant. It had been assumed that the K value would show a marked decrease but this did not occur in the above experiment. Such an ･ｾｦ･｣ｴ may perha.ps be expected a.t first since "complete water connection is obtained from a communicating system of pores. It is of course of the greatest interest to know precisely for the various materials in what manner the K value changes with changed moisture content.

The interest taken by the refrigeration experts in the analysis and perhaps in the standardization of insulating material was

Dlentioned earlier during the meeting. No less than in the case of brick and light-weight concrete, this entails a lot of work. The pore system of the various types of brick undoubtedly depends on the quality of the raw materia.l and on the method of production. All the various ideas regarding the manner in which the insulation is carried out also have some influence. For organic materials sufficient

allowance must also'be made for ageing under various moisture ｣ｯｮ､ｩｴｩｯｮｳｾ

The valuable ｣ｯｮｴｲｩ｢ｵｾｩｯｮ which Doctor Johansson has made to the study of the fundamental probLems of moisture transmission in var-Lous materials are a great advantage for the continuation of the

investigations in this field. It is regretted that because of changed working conditions Dr. Johansson himself has no longer a chance to

continue these investigations. Engineer B. .Ax

At the STAL we had the opportunity of investigating cork insulations which for many years had been attached to plate tanks containing brine.

o The temperature of the la.tter was nea.rly always lower than 0 C.

Strangely enough, we observed neither accumulation of water or ice nor any damage to the insulation.

- 23

-Moisture ratio in per cent by weight

2

3

ＭＧＭｾｾＮ

I

.

.

｟ＬＮＮＮＮＮＮＮＮＭ｟Ａ｟ＭｾＭ

ｾＭｾＭ｟ＭＭＭＭｉ

Ii.

If

"

'l·'.It

50

eo

70

60 '0

.,C/J ."

10

10

30

c

e

6

14

B

'fa

2!

" ---.,.---'T""-..,.----,..--.-....-.--r--.--,

-- -1

"Isoflexl ' (Al); 12 kgm./cu.m. Corki 95 kgm./cu.m. Concrete

Glass wool; 100 kgm./cu.m. 1.6 - brick

Glass-wool sheets; 120 kgm./ cu.m.

Rock wool; 150 kgm.!cu.m. Slag wool; 135 kgm./cu.m. 9. 10. 11. 12. 13. 14. 15. 16.

Relative humidity in the atmosphere

Fig. 1 Curves showing the moisture absorption of various building

materials.

1. "Kraftelit" (laminated, impregnated Kraft paper); 125 kgm./cu.m.

2. Sawdust; 211 kgm./cu.m. 3. Drying pine

4. "Treelex", porous; 260 k&m./cu.m. 5. Kramfors sheets; 60 kgm./cu.m.

6. "Wellit"; 40 kgm./cu.m.

7. "Masonite", semi-hard; 690 kgm./ cu.m.

8. "Isoflex" (transparent); 12 kgm./ cu.m.

-d} Moisture ratio 1

•

.,

o

2

.

..

c} Relative humidity of the atmos-phere C ...- - - 1 2:

0.

-b} Vapour pressure

..

,..

-,

a} Temperature

.10

Fig. 2 Temperature and moisture in single sheets (Siporex).

The dotted curves for p, ｾ and u apply to cases where

the "moisture-equalizing" capillarity is negligible and the solid curves to oases where Gd is appreciable

together with Gu•

Condensation

Diffu.s ion Eva oration

Fig. 3 Moisture transmission through a capillary tube partly

- 25

-Fig •. 4 Capillaries and pores which impede the movement of

moisture from one capillary to another.

\ \ \ \

\

\

I-coso;

ＧｾＢＢＢＧＭＧＭＣＧＭＭＧＭ

CO.

GC'

,

/

I

, /

/

Fig. 5 Annular laminae of liquid around points of contact in

2

1

o

Fig. 6

o

ＭＭＭＭｾＭＭＭＭＭｾＭＭ

U",

u as a function of the radius of the capillary tube

27

-o

eo

60

_'0

₁₀₀

i'

- ••-JL ·

fOf)

"",

Fig. 7 The coefficient of moisture diffusion as a function of

the moisture ratio in a plate as shown in Fig. 6 with

ｾ

q.,...---.,

ClJ

t

ｾＬ

1-.·..

o

o

20

JO

40

_ｾｯ

_ ..._ltJ; .

u'"

fo¢

100

Fig. 8 The moisture diffusion as a function of the moisture

ratio for case 3 of Fig. 6 for various thicknesses of the-plate.

29 -, • 00 ＭｾＭＭＭＭｾＭＭ｟

...

_---o

o

QOl

ｾＰＸ

",,'"

-

{

Fig. 9 The moisture diffusion as a function of the thickness

10

o

1

o

ＭＫＭｾＭＭＫＭＭ｟Ｍ］ｩＺＭ __---4_--+--+--_ _""

Relative humidity of the atmosphere

Fig. 10 Moisture diffusion values in gm./sq.m. hr. rom. Hg for

1 em. thick sheets of material.

*)

31 -1 1.G-brick I _ - -<' 1.2-brick

I

.'

,

I sandl1lne morta!'" I

I' concrete Ie: 98 (E)*)

I J

;' _.,... l.a-brick

I"'"

I' sandl1me mortar II

ｾ

｢ｾｳｴ｡ｲ､

stucco (E)

ｦｾＧ cement mortar (E)

cement mortar I

.-:..1'- / cement mortar III

,,/

ｾ

ｾＢｖｩ｢ｲｯＢ

concrete

ｾ

Ｇ ｾ concrete lc: 4s (E) ", - cement mortar II

__

ｾＭＭＭＭＭＭ

..:c:--.

hard masonite "'---4---4---+---f----4-- - -+ - -_ -_-+-

--J

o

ｾｏ 60

'0

Be '0

toe",

2.,

Ie

₂

t:I

1,e

'."

ｾＢ

ｾＲ

1

q,

q.

ｾｾ

ql

Or;

_to

_eo

_JO

Relative humidity of the atmosphere

Fig. 11 Moisture diffusion values in gm./sq. m. hr. mrn. Hg

for 1 em. thick sheets of material. {!o )

(E)

=

taken from Edenholm's measurements

a) Concrete on the cold surface b) Brick on the cold surface

Temperature Vapour Pressure Temperature Vapour Pressure

·C

4) Q)

ｾＭｾ

Q)

""'"''''I

ｾ ｾ ｾ _ｾ

.,

ｾ _ｾ Q) o Q) o 10 Q) ()

₂₀

ｾ oM H ] r: p.(t} H _..-l

..

ｾｏ o H _I ()

.,

,

o _H

s::

.0 t::

.

s:: .0

,-'1(;

.-0 0 0

.'0

o o '$ o ' 1$

.1C

C _/

.

DCf,O·:J 0 "('0\,'

Fig. 12 Temperature and vapour pressure in a wall of concrete

c

D

n

A

•

•

/(7z/z/zz27/zz/

Fig. 13 Flow in a gutter.

a) Constant height of the side walls of the butter b) Decreasing height of the side walls of the gutter

a .--....·...

ＭｾｌＮＮＮＮｬＮ｟Ｍｌ

a

_.- .J;

b

---a

Fig. 14 Curves showing the distribution of the partial pressure

for the same wall as in Fig. 12 a, but taking into account the condensation in the wall.

- 33

-ｕｾｉ

_'0

8

I

t

_I

?

₆

!

5

2

c

Fig. 15 AveraEe moisture distribution in test bars of 1.8

brick surrounded by a moisture-proof wrapping and exposed to moisture.