Drying shrinkage and moisture movement in an autoclaved cellular concrete

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Drying shrinkage and moisture movement in an autoclaved cellular

concrete

DRYING SHPJ NKAGE AND HOI STURE !vIOVETvIENT IN AN AUTOCLAVED CELLULAR CONCRETE

by E.M. Hoyle and E.G. Swenson

This is a report of an investigation to determine the shrinkage and moisture movement properties of a high-pressure

steam-cured cellular concrete. This material will hereafter

be referred to as cellular material ｾａｾＮ This investigation was

carried out by the Division of Building Research at the request of the Canadian manufacturer of the cellular concrete.

A previous report on this material reported the

following data: 24-hour absorption; capillary absorption; vacuum

saturation; absorption at various relative humidities.

The samples specified for testing were specially cut slabs on which thermal conductivity tests had previously been

made by the Building Services Section, of DBR. These samples

had, therefore, been subjected to nrevious drying to constant

weight at 105°c. Although i t is recognized that such

prehe-ating may radically alter the volume change properties of such a material, drying shrinkage and moisture movement tests were carried out on these samples, as originally requested. Consequently they were again dried at 105 C. before testing.

It was decided to depart from existing practices and

methods of test, in Which, for example, a sample is saturated

by soakir.g in water for 24 hours followed by drying at 50 or

55 percent relative humidity. The latter condition was not

considered to be sufficiently desiccating to represent some

field exposures. Soaking for a limited period is also not

considered a reproducible procedure for cellular materials with

very high moisture capacity. It was decided therefore to use

vacuum saturation as the starting point in the Het condition. Specification B.S.2028:1953 of the British Standards Institution for drying shrinkage, for example, requires soaking

in water £or four days followed by drying at 50

!

lOco and at

17 percent relative humidity. Moisture movement determinatiDn

requires resoaking of the dried samples.

Extensive study of reports by Otto Graf (1), and

others (2,3,4) gives insufficient information on volume

change characteristics of high-pressure steam-cured cellular

concretes. Furthermore, literature studies indicate that the

requirements and methods of testing for drying shrinkage and moisture movement vary widely and may be inadequate,

2

-was consequently expanded. Additional experiments were carried

out to investigate certain properties of this material which became evident during this study:

(1 )

(2)

(3)

Length change sensitivity to small moisture

changes during drying at ＱＰＵﾰｾ［

Apparent growth of autoclaved samples containing moisture;

Small difference in volume change between a high-pressure steam-cured material and an air-cured product.

The moisture movement, shrinkage, and Ugrowth" of the

material were found to be very slow processes and i t was thus necessary to place a time limit on these experiments.

2. MATERIALS

The sample bars of cellular material "A'· used in the following tests were cut from 2- by 18- by l8-inch slabs on which thermal conductiVity tests had been previously made. The density of this material was 34.6 lh/ft).

Another cellular material which was cured normally,

hereafter referred to as cellular material

'·B'·,

was used

primarily as a reference material in some of the exneriments.

Samples of cellular material

"B"

were 1- by 1- by 6-inch bars,

fitted with inserts and used for volume change studies in 1954.

These samples were also subjected to drying at 105°c, Cellular

material "B" had a dr-y density of 41.5 lh/ftr3. In experiment s

on thermal expansion, bars made of mortar, haydite concrete,

and ordinary concrete, were also used for reference. All these

bars were 1 by 1 by 6 inches and were fitted with inserts for length measurements.

3.

METHODS OF PREPARATION AND TESTING

3.1 PREPARATION OF BARS WITH INSERTS

Bars of ｾ･ｬｬｵｬ｡ｲ material "A" were cut by ordinary

power saw to the dimensions 2 by 2 by 6 inches. Half-inch

diameter holes were drilled in each end of these bars to such

a depth that the distance between inserts would be 5

±

1/32

inch to accommodate the bars in the standard comparator. The

inserts were cem6nted by a mortar made of one part of fine

sand, specially prepared, and one part of high early strength

cement, and mixed to a creamy consistency. The base of each

insert rested on the bar material so that the cementing material would not be involved in length changes.

The size of the bars was selected for convenience. It

3

-have a bearinc on the results obtained insofar as rates are concerned.

3.2 DRYING TO CONSTANT HEIGHT

After curing the cementing material for one week, the bars were heated in a forced draft oven at 105°c. to constant

weight and length. The bars were cooled in desiccators charged

with magnesium perchlorate.

It was soon found that appreciable linear volume changes occurred with very small gains or losses in moisture

from the nominal dried state. The constant weight and length

values taken were subject therefore to some degree of error

or variation. It was found that a 24-hour heating period

was sufficient providing no accidental moisture gain occurred. Attention is again drawn to the B.S. Specification 2028:1953 in which the method of cooling, after oven drying

at 50 ｾ 10C., requires placing the samples in a desiccator

containing solid calcium chloride or a saturated solution of

calcium chloride. This ｡ｰｰ･ｾｲｳ to cause serious discrepancies

in the dry values for sensitive materials like cellular material

"A".

3.3 VACUUH SATURATION

Vacuum saturation was achieved by an apparatus con-sisting of a vacuum pump connected, through double traps of calcium chloride, to a large vacuum desiccator by means of a

two-way stopcock. The latter was connected to a distilled

water supply by tubing previously filled with water. After

evacuation of the dry samples the vacuum system was shut off

and the water introduced to a level just below the top of the

samples. Following a period of several hours to allow water

to penetrate, the samples were completely covered with water

and allowed to stand for at least one day. The percentage

of water was calculated from the difference between the surface dry weight and the original dry weight.

Another procedure was found to be just as effective for this material, that of using a tap aspirator operated

from the water line. A cycling technique was used and the

values obtained were comparable with the first method. Readings

of volume and weight changes were taken three days after the sample was first wetted and thus constituted normal vacuum saturation procedure.

3.4 CONDPrIONING AT PRESCRIBED rvrOIS'I'URE CONTENTS

The "wetting series" involved the adding of calculated amounts of water to the dried samples by soaking and aspiration,

4

-air was evacuated by mouth, to collaDse the bag around the sample

and the open end then secured by a clamp. These samples were

left sealed in this fashion for about six to seven weeks at

72

to

75

0_{F . until constant length Has obtained. Because of a very}

small vapour loss through the nolythene bags, weiGht constancy

could not be achieved. The moisture content was calculated

from the weight at each selected time for constant length.

In the "drying series", the bEll's were dried from the

vacuum- saturated condi ti on by exoosur-e to laboratory condi ti ons

(72

to

75°R

and

20

to

30

percent relative humidity), using a

fan. This was sufficient to dry down to the lowest moisture

content required. The bars were then placed in double

Doly-t.ne ne bavs and conditioned in the same manner as the "wet t Lng

series" to obtain equilibrium conditions.

3.5

CONDITIONING AT VARIOUS RELATIVE HUI'1IDITh,S

Eighty percent relative humidity was obtained by

means of a specially built box re_0ulated by an electronic

controlling ｡ｄｾ｡ｲ｡ｴｵｳＮ This aDparatus operates, altern8tely as

required, a humidifying and dehll.111idifyin:- chamber by means of

an Aminco-Dunmore cell and electronic relay. The system was

buffered with a saturated solution of aim.on Lum suLphat e and

the air was stirred by a fan. Regular wet- and dry- bulb

readings gave values'of

80

i

Ii

percent relative humidity.

The temperature in this chamber was constant at

75°F.

A condition of

50

percent relative humi.dl t.y Has

obtained in a controlled hluuidity room ｯｰ･ｲ｡ｴ･ｾ nt

50

ｾ 1

ner-cent r-e Lat(. l ve humf.d Ltr'J. . -' • andc.L _ " / ' ) 0 ', L , /.' 1 . ,ＧＺＺ［ﾷｮｩｬＮＧｾＮ1_" •..ｾ ' . '.• - •.!., Y'''I('Y''.• ' I I , "C)l-,n-n' ..._ ... , .I ' : · ,.J -...J \ ＬＧｾｴ.A

10

:!:

3

percent relative humic!ty ano '(c:!.u F'.

3.6

LENGTH AND HEIGHT TvIEASUREI,IL-:NTS

Standard length comparators were used, with an accuracy

of 0.0001 inch. Reproducibility was in the order of 0.0001 to

0.0002

inch. A standard reference bar Has used during all

measurements, which were ｾｐＰ･ at room temperatures varying from

7')_{/{_} to_ｾＢＭ 7')0"_{_,.L. ..} " 0 l "_{ＬＧｪｾｾ} ＧｾＬｴｳ '-'orp _i-<",nn to _1-'}(, ne ar-o st 0 1 -'r"m

I _ J I . ;'j ...j , . ) ( , , - , , - . - , _ _ -,, i . , .. " J ; - . , - ' o . J U ｾ ... ｌｾｽ Cl io

1:. .:.:, , _- Ｌ｢ｾ

r

ＢｦＮＡｆｾｊＬ｟ｲｦＲ 1\Ii

.n.v

ｩ｜ＮｾﾷＧ［ｔ ｾ -.TＮｬｾＺｇｔｊｾｾＩ :.;TOl-r

_."'-"-- ..•

.--,-_._---The sam-ole e wer-c (]ried to cons tant length, this being

the nractice required by the B.S. Specification

2028:1953

for

precast concrete blocks. Constant Height usually followed as

a matter of course. It was found that evon very slivht0,' , _ )

moisture gains after drying, resulting from exposure during

handling or from a lowered efficiency of the desiccant, were reflected in considerable lenp:th changes in cellular material

5

-"A" s oe cLmen s , From exper-Lenc e it '"Jas f':lunc' that 21f hours

wa s suff' ic ient fo r drying: to minimum Lerig th arid Height , but the extreme sonsitivity of linear chane to moisture made it necessary to rene at daily drying and measuring for about one

week. Dry weights and lengths were 81so extremely sensitive

to small variation in the drying temperatures.

Ff.gur-e 1 shows the effect of such small moisture

ch arige s on the lengths of cellu.lar mat e r-La I "A" bars. 'I'hes e

results emphasize the importance of rigid control of

techn-iques of dryinc to constant length and Height for such materials.

The B.S. Specification (2028:1953) requiring drying

at 50 ｾ 100. and 17 percent relative humidity (over-saturated

c a.Lc Lum chloride) is probably de s l gne d to prevent the danger of

phy s Lc a L c hange s in the material wh Lc h may occur in 1050_{c . , and}

which may change absorption ｾｲｯｰ･ｲｴｩＸｳＮ The samples of cellular

mat e r-La I

"A"

on wh i.ch tests Here oricinAlly requested had

pre-viously been heated to 1050 0 . , _{and this rnater-La I had been cured}

under hieh pressure steam conditions. For these reasons, a

different procedure wus followed in ｴｾ･ present tests. Saturated

calcium chioride at 5000., is expected to provide a relative

humidi ty of 17 Dercent in the procedure outlined in the B. S.

Specification but wou Ld give a relative hum.i.d L

t:r

of about 35

-oercent at 18.500. _{- the approximate temperature of measuring}

Le ngth s ,

!+.2 SLO\'J' GRO\JTH OF VACUUN-SA'rTJRA'rED ｓａｉｶｉｐｌｪｾｓ

'I'vlO 2- by 2- by 6-inch bars of cellular material "A"

wer-e Lmme r s ed in water except for the top Ｎｾ inch. Vacuum was

then applied by aspirator for 3 hours, broken for ｾ ｾｯｵｲＬ again

as pi r-ate d for 3 hours, anri f Lnal.Ly left imrnersed ov..r-nl ght at

normal air nressure. This procedure was repeated four to five

times Der Heek for about six weeks. The samples Here measured

and weighed periodically. The gradunl growth of these samnles,

as distinguished from the normal length increase ｾｵｯ to moisture

content, is shown in Fig. 2. The actual increase in expansion

Dbove the normal vacuum saturation value is 23.9 percent for a

J.12-day period, and appears to continue at a diminishing rate.

Figure 2 also shows the gercent increase in moisture content over this neriod.

The lack of reproducibility in tho vacuum-saturated moisture content data is due to the inherent difficulty in reproducing saturated surface dry conditions.

It was first assumed that the growth was caused by

mech ani ceI extension of the s amp Le due to ne r-LodLc :jPD1ics.tlon

of v ac uum , 'rho slight increase in moisture content j;; not

com-patible however, with the considerable growth. The truo

6

-into the finer gel pores of the hardened cement paste.

Sub-sequent results indirectly bear out this hypothesis.

4.3

ｖｏｌｕｉｾ CHANGE AT VARIOUS MOISTURE CONTENTS

Seventeen cellular material ItA It bars fitted with inserts

were dried at

105°C.

to constant weight and length. Seven of

the bars were used in a wetting series test and the remainder in a drying series test.

directly contents values. and then moisture

In the wetting series, water was added to the dry bars

by pipette, or by soaking, to give a range of moisture

from about

5

to about 90 percent of vacuum-saturated

In the drying series the bars were vacuum-saturated dried in the open laboratory to obtain a range of

contents from about 90 to about

5

percent.

The bars so adjusted were ｩｾｾ･､ｩ｡ｴ･ｬｹ sealed in

double polythene bags and stored at room temperature for 6

weeks to attain equilibrium. Measurements of length and weight

were taken at

6

and

7

weeks. Determinations of moisture movement

and shrinkage for cellular material nAil were made first at 8

weeks and finally at 6 months.

For purposes of comparison a wetting series was

car-ried out on cellular material "BII

•

The data are recorded in Table I for cellular material

"An and in Table II for cellular material ItEn, the latter based

on two months' measurements only. The plotted values for the

two materials are shown in Figs.

3

and

4

respectively.

For cellular material "A" the initial wetting series gave a length change considerably greater than the corresponding drying series.

To check this anparent contradiction, selected samples

from both series were re-dried and their cycles reversed.

These samples, together with the uninterrupted samples, were

finally weighed and measured after approximatel

_b

six months.

Following this they were all dried again at

105

C.to constant

length and weight. The final length and weight were considerably

different from the initial oven-dried values.

The calculated values of drying shrinkage and moisture

movement, as shown in Fig.

3,

indicate that volume change is,

in general, independent of the method Whereby the various

moisture content conditions are obtained. The exception appears

to be the initial wetting series, which may have received a slightly more severe initial heating.

7

-The differences in percent volume change calculated in

initial dry Heights and final dry ｾＮＬｲ･ｩｌｬｬｴｳ are quite ma r-ke d ,

sUG[esting that heating and wetting treatments affect subsequent

volume changes (Table I).

The value of drying shrinkage and moisture movement for

cellular material "A" over the 5 to 90 percent moisture content

ranges is, therefore, a minimum of

0.3

percent, and is probably

near 0.4 percent for untreated samples of this material. The

value obtai ned for cellular material "BIt was 0.41 percent.

4.4

DRYING SHRINKAGE AND MOISTURE MOVEMENT AT VARIOUS RELATIVE

HUMIDlrrIES

Two series of cellular material ftAft

bars were subjected

to relative

humidities of 80, 50 and 10 percent, with two or

three bars at each condition o

In the wetting series, the bars were first dried to

constant length, then placed in the various conditions of relative

humidi ty for determining moisture movement. Lengths and weights

were measured periodically until a/parent equilibrium was

reached, usually in about

6

weeks.

In the drying series, the bars were vacuum saturated,

then placed in the various conditions of relative humidity for

drying shrinkage determination. 'I'he d at um for this series was

the ｾｲ｣･ｮｴ expansion after 42 days in the vacuum-saturated state

in order

to

include the Ｚｾｯｷｴｨ factor described in (b).

The data are given in Table III. Figure 5 shows the

considerable hysteresis between the wetting and drying series which is similar to the hysteresis observed in the next section

on moisture content versus relative humidityo

Since the growth in the samples was not complete at

42 days, the drying shrinkage shown in the data is somewhat

less than the absolute value would be.

Figure

6

shows a very simple relationship between the

logarithm of relative humidity and percent expansion for both

the drying and wetting series for periods of time ｢･ｾｯｮ､ 11 dayso

485

MOls'rURE CONTENT

AN"])

RELATIVE HD:"IIDITY

ｒｦＮｾ［ｉｎｉＱｉ ONSHIPS

The data in Tables IV and V on the relationship between moisture content and relative humidity are derived from the same tests carried out for shrinkage and moisture movement at relative

humidities of 80,50, and 10 pe r-c ent , These data are p Lot t.ed

S

-The hysteresis between wetting and drying appears to

increase Hi.th incre asine; r-eLat t vc hurm :' i ty (Fig. 79.) 0 The

straight line relationships in Figs. 8a and Sb, plotting the

Loga rLt.hm of moisture content against relative humidity, appears

to indicate a simple r-elatioDship between these two conditions.

In Fig. 7b 1s plotted the decrease in moisture content

with increase in pF, based on suction determinations. This

shows that a very slight drop in relative humidity (from 100 to

99092

percent) corresponds to a loss of nearly 60 percent of the

total moisture that the material is ｾ｡ｰ｡｢ｬ･ of taking up. The

wetting nortion of this curve was net determined for cellular

material· "All, but with cellular material HB" there was found in

previous tests to be a very pronounced hysteresis in this region.

During this investigation i t was observed that the

initial oven-dry length could not be reproduced.after intermediate

wetting. An irreversible expansion had occurredo This is

illustrated by the data in '}'able VI.

Since all oven drying Twas done ｾ｟ｮ a f'or c ed draft oven

at lOsoG. this irreversible length change was recognized as a

function of the wetting and dryinG cycle, and not as a result

of fluctuations in the c"eg1":,e of drying. From thi s i t follows

that the magnitude of shrink2[!e and molsture ｭｯｶ･ｭ･ｮｴｾ expressed

as a difference between wet and dry lengths: would decrease

wi th the number' of cycle s , This is true senerally for

cement-itious ｾｲｯ､ｵ｣ｴｳＮ

Superimnosed upon this irreversible lenpth change due

to ovening is the slow growth of cellular material

"A"

in-the

moist state.

For cellular-type materials it would appear necessary to develop a nrocedure to determine drying shrinkage and moisture

movement on samp Le s not pr-evLo us Ly conditioned in any way.

Actual calculations would then be made on data obtained from

companion specimens which had been dried in the c onverrt LonaL

manner.

ｾ｟Ｎ 70 1 Dry Stateon Bars of cellulnr rnat er-LaI t',.'\'1 dried to

constant length and wo lgnt wer-e measured at lOSOG., cooled to

5

0 G_{•. ano}-J _{8 aBlYl}• ._measure.d _{\,omnara t.v e c.e er-nn na .a on s were ma ce}r< t · ,

t

.

t l ,

ｊ Ｇ ｾ L

on bars of cellular material

"B'",

mortars c onc r-e t.e , and haydi te

concrete. The calculated coefficient8 of bhe rmal, .sxpan s l bn in the

'I'he s e da.t:B. ｾＱ re

L_{t n705} 'I'her-maL Expansion at Var101.:Ls i\ioistUI'EO ｃｯｮｴ･ｮｴｳｮｾ The bars

ｾ ｾｬｬｾｾＮｔｾｾＧＱＢｦａｾｾＺ＼［＼ｾｲＭ､ｾＭｉｉＢＬＬｾＬＬＭＬＭＬＭ｡ｊＬﾷ ＢＧｦＭＢｴｾＧｴＢＢ､ＭＢＧｾｾｲＭｲ］ＺＺ［ＢｾＭｾｾｾＺＱｾｾ］ ..., dO

0.:. ｣ﾷｾＮＬ u i a r rnavel le-..:.. l.L·U .in -"0., ,,_.1 '''l.d..:l:1 n a o o e e n c o n : 1<=

tioned in double pclythene bag3 ｡ｾ various moisture ｣ｯｮｴ･ｮｴｳｾ

(1) by adding moisture to oven-dried samples ［ｷ｡ｴｾｩｮｧ series)p

and (i1) by dryi.ag I'rorn the vacuum-ss at ur-at ed st ate in the open

laboratory

t

dry:Lng series)i' "';El::"e cooLed to SoC. and heat e d to

55°c.

resnGstivelY9 in each case length and weight measurements

being taken"

Pfter on ini::.181 condition:i.nr" period these samples

were weighed and mea sur-e d about onee a week for six weeks by

whi.c h time appar-e nt equi LtｾｊｊＢｬＱＩｭｪ｡､ been r-eac.hed0 The grmvth

or e.xpans l.on previously obs erve c had dLrai.nishe d to snch a

degree that it was po s s Lb Le to nredict9.cGc.U:'f-lteJ,y any Lncre a s e

in length with time. Below a certain moisture ｣ｯｮｴ･ｬＧｾｄ however;

small lOSSeS in moisture ｴｾｬＺｩＧｲＩｾ｟Ｌｾｨ the DO:.ythene b22)3 resulted In

definite cecPGases Iii Lerigtn as wou:u':i. oe eX'j,3 ted . s ee 403).

These changds ＦｾＲ ｾｲ｡Ｘ･､ in Figs. 10 and II for

cellular mater-LaI JlA［ｩＢｾＬｮ 1;')1'1iGh t.n0 percent expansion is

plotted against t.Lme " and :In:·,'h'"_:,h. l.he vo Lurne oharige clue to

｣ｯｯＱＱｾｧ and heating is showno

In Fig. 10, for ＳＸｾｮＱＸＸ with moisture contents from

approximately ･Ｚｾ to 9 r)Clcent" i,',1)··1 tc i:J··5) the thermal expansion

is unlf'or-m , At 101.vcr moi.stur-e contents" as in ＱｲＮｪｾＬＶＮ small losses

in rnoi.st ur-e nr-oduc e a c or.si de r-abI.e decrease in lengths thus

count er-act l ng anY' t ne rme l expens:!.o!:l in th9 met e r t s L, The datum

for this fieul's 1;-Jas c st ab l lshe d .cLt 710Fnr 2l:d ＺＳＺＺＧｭｾＬｊＮ｡ｲｊＮＮｹ for

subS G Cll18n t f 1｛Ｚ｜ｬｉｾ･ So

In FiZ0 11,; for the d:r'y:1.n'." s e.ru e s f""()lil 1)··1 tel ｮＭｾＬ

the t.her-ma; expansion VUl1JAS Dr-O

L!rlf";;;ln

ＢｾＳＺ［ｩｯｾｾ

;bout 'U'/')G;'GeJlt

moistlIT8 ｣｣ｾｴｇｮｳＧｾ ｄ｣ｾＬＵｾ the ncrnsl ､Ａｾｹ ｳｨＬｲｩｮｬｾＺｮｾＳ n ｇｦｦｳ･ｾ

the t.her-meL eXDaY131ori ,

:n

ｧＶｮ･ｲ･ｬｾ for both materials. the thsrmal coefficient

i s L n d epo n d en t o i' t e-nper - a. .c u r - e ｛ｾＺＭ･｡､ｩ･ｮＬｴ v l J " lth i , n ｴｨﾷＺＮｾ l"'ange o ba e r-ved ,

5°0.

to :1'.5')Co It is a l s c i!iCle.peflc=te11t of mo ' st.: ..ＱＱｾ･ cont ent T,'lfithirl

the foL'lowLnrr limLt s : for ＸｳＱｾＮｬａｊＮＸＮｲ ｲｮ｡ｾＸｲｩ｡ｬ "-A.'I ,. about Go percent

tuc ｃｬＮＮｾＩnl'C1.J"'_\,.! 41-,;:'·'r·-':.n+:, J " J . L -..JV J U 9 . ! . . . l . 18 ....(0 _L '--.'.f'cr (...r.e.L...Ll.A. ...Tlulorc : ＬＮＬｯＢｴ･ｬＧｬＬｾＢＱJ.lltJ _ ....-".J ｾｬﾷｯｩｴ ; ) . t :... '1'00. ＭｾｮＢＢ［ＺＧ･ｮﾷＧＢrJc:-.L ... ..I.. V

inde-- 10 -pendent of drying or wetting.

In summary, the coefficeints of thermal expansion

for cellular material

"A"

are as follows:

bone dry

5.2

x 10-

6

i

_{n • .Ln.}

j"

/0,

.L'.

4

to 80%

M/C

5.6

x 10-

6

_"

V8.c. sat 'd.

6.4

x 10-

6

_"

5.

SUBJ"IARY AND COI1IrIENTS

These experiments deviated in one resDect from most

work in the field, in that the datum for moisture movement and

drying shrinkage was taken from the constant length determined

at the oven-dried state of 105°c. Owing to the previous history

of the materials tested, such a course would seem to be

reaso-nable, but due to the irreversible length changes evolved by such severe drying and small moisture changes at near zero

moisture content, a datum based on dry lengths is obviously

unreliable. This is well illustrated in Fig. 1 and in sections

4.1

&

4.6

of the report.

As an alternative it would appear that a datum based

on vacuum saturation length values would offer a more stable

result yet in section

4.2

it is shown that very large length

changes take place with time at this condition.

Section

4.7

and Figs. 10 to 13 show that length

equilibrium is not achieved at intermediate moisture contents

over a wide range. The rate of change is, however, smallest at

such moisture contents. The datum for cellular concretes should

be established from the most stable condition possible, and this

would confine the selection to preconditioning at either a constant relative humidity or a constant degree of saturatiou.

ｾｲｯｭ section

4.3

the shrinkage and moisture movement

values at various relative humidities are similar, in the case

nf' cellular material

"A",

though length equilibrium requires

a waiting Deriod of about six months. The moisture contents

referred to in

4.3

are almost all in excess of the moisture

contents corresDonding to relative humidities as high as 80 percent.

The relationship between volume change due to drying shrinkage or moisture movement at various relative humidities

is per-h ap s the most relevant for a cellular concrete, for i t

is under conditions of fluctuating relative humidity that the

material is most likely to be used. Sections

4g3, 4.4,

and

4g5

show that volume change reaches a maximum at 80 to 100

percent relative humidity from oven dry and that this value

- 11

-a moisture content of

5

percent gives apnroximately the ｳ｡ｾ･

volume change as a moisture content of 100 percent. There ｩｳｾ

of course, the slow growth wi th time uhe nomerion which has already

been discussed, and under this influence volume changes would

differ very much between the high and Low moisture content

material. Section

4.6

again emphasizes the need to ensure that

lnaterials subjected to testing do not receive excessive heating

or wetting prior to testing. It would also seem to infer that

any previous mild wetting 8Ild drying cycling Hould tend to reduce the magnitude of the volume change assessed at the time

of test. For cellular material

"A"

the vacuum-saturated moisture

content is

134

percent of the oven-dry weight. Assuming vacuum

saturation to represent 100 percent moisture content the lnaterial can lose 60 percent of its moisture by suction methods with a corresponding drop of only 0.08 percent in relative humidity. For this large loss of moisture the volume change is practically

negligible. A further loss in moisture accounting for about

96

percent of that at vacuum saturation results in a slight

volume change. This latter condition would apply to the

moisture content at 80 percent relative humidity. Regarding

the thermal expansion of cellular material "All, experimental

evidence shows no definite variation between the dry state and a large range of intermediate moisture contents through to the

vacuum-saturated state. For cellular material "Bit there is some

evidence of increased thermal expansion at intermediate moisture

contents. In general, the values for cellular material "A" are

similar to those of other concretes while those of cellular

material !tBtt _is

₃₀

_to

₄₀

_{percent higher (Fig.}

_9).

It is now proposed to develop a procedure for moisture movement and drying shrinkage determination using control samples

for moisture content and dry weight. Thus the volume change

testing would be made on samples which had received no previous conditioning.

The need for such an undertaking has become obvious

from a review of the available literature on the subjecto There

is at present a marked inconsistency of opinion on what ｣ｯｮｳｴｾ

itutes a comprehensive procedure. Previous work has, in genera19

failed to ive information on behaviour at Low moisture contents

TABLE I

VOLUI\lli CHANGE Arr VARIOUS NOIS'rURE CONTENTS

Cellular Material "A"

... _-0-'"._,_' _{"-._._-}....-,'....｟ＭｾＮ

---

.

'--"----

...,...ｾＮＮＬＬｾＭ｟ ..ｾ...

---INITIAL DRYING

(2

Months)

FINAL DRYING

(6

Months)

-

ｾＭ｟Ｎ

__

.

Dry Ht.

Moisture

_%

EXPI:'lnsion

Moisture

_%

Expansion

Reversed Cycle

gm.

Content

from

Content

from

\'1-

Now hTetting

%

of Vac.

Oven Dry

_1a

of Vac.

Oven Dry

D- Now Drying

Sample No.

ｓ｡ｴｾ

Sat.

1

237.6

_ＳＮｾ

.318

1.8

_{ＮＲｾＭＴ}

2

230.5

31.

.334

27.4

.302

w

3

225.1

62.8

.332

57.3

.318

w

7

236.8

16.8

.300

4.1

.276

8

236.9

74.8

•

ＳＰｌｾ

53.8

.290

9

238.7

47.2

.306

28.5

.286

10

239.1

_{-_.}

__

88.6

_...

_.334

_66.4

.292

｟ＭＭＭｾＭＭＭ｟ＮＢＬ ...ｾＮ｟ ...ｾＭ -...,

..

ＭＬＮＮＮ｟ＮＧｾＮＢＮＬＮＢＢＮＭＮＭ ..,ｾＮ｟ｾＮｾＢＢ ...Ｍｾ ...ＧｾＮＭＭＢＧＭ •••ｾＬ••••• --_.-••._... , _...｟ＭＭＭＭｾ ...［ＮＭＮＮＭＭ＼ＧＮｾｾ ."'.- -,'••• - . , _ .• , ' - _. . . • , ＮＢｾ ...- '" .. ><"'"'"" ...•••.,, .

-INITIAL WE'rTING

FINAL WE'rTING

- ｾＭＭＭ｟ ...

_

...'_..

13

ＲｌｾＳＮ

7

2.3

.320

1.8

.254

11-1-

238.7

16.0

.368

3.4

0288

-15

242.6

16.8

.360

-

-

-16

238.3

31.9

.372

27.1

.288

D

17

238,,1

34.1

• 35L

I·

23.4

ＮＲｭｾ

18

240.0

52.7

.368

31.5

.300

_I

19

244.0

70 09

.392

67.0

0306

D

I

20

_{242 08}

89 .. 3

.410

84.9

.304

D _It

21

24-3.5

7702

0396

60.9

.296

i

22

238.1

91.7

.406

7203

.306

i • _ _ _ _. ｟ｾＮＬ ... .,___...,.,_, _ _ ,Ｎ｟ＮｾｯＮＮＭ｟ ... _..._ ...ｾ__ｾ Ｎ ____Ｎ｟ｾ .... __,__ ...ｾ... _ •.ｾ｟Ｎ . J

TABIE

II

VOLUHE CHANGE AT

VAHIOUS HOISTURE

CONTENT'S

-CelI "

'. ＧＬＭｾ ＭｾｴＮ･Ｎ 1.I•.d

T1

Moisture Content

;&

of vcc , Sat, 'I

I

c170 ,E -"--.xnsnSlon I

From Oven Dry

,308

e

306

.302

T3

T5

T9

T13

T16

87.8

90.0

93.9

97.8

12.8

11.6

10.5

28.3

26.6

24.9

41.3

39.4

37.5

73.6

72.0 71.0

87

01

85.8

84.3

TABLE III

MOISTURE l\10VEl'-fSNT

&

DRYING SHRCNKAGL<:: OF CELLULAR

ｾＧｬｬ｜ｔｅｒｉａｌ

IIA II

A'l'

VARIOUS

ｾ｟ｾＮｾＮ｟ｾｬＡＮ

VALUES

1+.

-I

R

!1i.!.!

80%

Moisture Move-ment ---- .--..｟ＭＭＭＭＭｾＬＭｾ｟Ｎ｟Ｎ｟Ｎ｟ＭＮ｟Ｎ -

-

_{ＭＭＭＭＭＭｾＭ}

T>!OISTURE IVJOVEMENT FROH OVEN DRY

ＨＨｾＩ

--: -. _ - - - . _ - _ . , . , . , . _ - _ . _ , - - - _ . _ - - - - _ . -.• __ •.•ｾＬＮＮＬＮＮ ...｟ ｾ ｟ ..ＭＭｾ .._ . -...Ｍ Ｎ Ｎ Ｎ Ｍ Ｍ Ｍ Ｍ Ｍ Ｎ Ｌ ｟ Ｎ ｾ ｟ .•_ - _ .•ｾｾ ...ｾ... -.,.._ ... "-,,-,>,., ••-,... ,-_ ...｟ＭＭＭＮ｟ＭＭｾ .•.. - .... I

TINE (DAYS)

;

I

I ｬｾ

39

42

i

1

lL.-1L.

6

ｾ

10

13

18

19

22

28

I

_.287

.288

.293

.295

.299

.304

.303

.310

.310

.310

.312

I

.248

.263 0267

.270

.270

.273

.277

.277

.277

.278

.115

.lL19

.168

.171

.170

.176

.172

.172

.176

.176

-

- _..｟ｉＭｾ ｟ｾ｟ .. _ _ _ " - - - 0 . _h . -_ _ ... ___

DRl'ING SIilUNKAGE FROM

ｖａｃｕｕｍｾａＧｉＧｕｒａｔｉｏｎ ((il)

(Avg. Vee.

Sat. Expansion of

0.34L1-%

Based on Oven-dry Lengths)

-,..---.- - - ' - " - - '

-

.008

-

.008

-

.004

.008

.008

-

.020

-

.020

-

.020

.020

.020

-

.080

-

.090

-

.092

.086

.086

.016

.020

.010

.012

---.--- ----_·_---1--' -._._..-.--

ＭＭＭＭＭｾＭＭＭ

0 0 0

.0011

0

.010

•

ＰＲＡｾｾ｟Ｎ

｟Ｐｾ｟ＧＭＷ

...0._0_8--'6

.090

ShrinkaQ"et:» Drying

TABLE IV

M!C OF CELLULAR MATERIAL ...A'" AT VARIOUS RH VALUES

Wetting From Oven Dry

Conditioned Original Stable

H!C as

M/C % H/C

%

Sample

Average

Base(!

on

No.

to

RH

Dry Wt. Moist Wt

% Dry Wt.

Of

Sample

Vac , Sac ,

(gm. ) (gm. )

_M!C

sIt

80%

233.0

242.6

g

=

4.12

35

80%

236.5

246.2

_ｾ］

_4.10

23

.5

311

80%

236.6

246.2

9.6

=

4.06

4.3%

3.2%

1236.6

31

80%

670.4

700.0

29.6

=

4.42

lb"(O.Lj.

32

80%

759.3

795.7

36.4

4.79

1759.3

-31

50%

670.4

690.7

3.03

32

50%

759.3

781.5

2.92

3.07%

2.3%

315

50%

243.1

250.7

3.13

324

50%

238.8

246.4

3.18

Sl

22%

670.4

686.6

2.42

32

22%

759.3

776.3

2.24

2.33%

1.7%

S12

10%

239.9

ＲｾＭＴＮＱ

1.75

323

10%

237.4

241.4

1.68

1.71%

1.3%

TABLE

v

Mle

OF CELLULAR MP.TERli\L ItA' t _{AT VATIIOUS BE}

_VALUES

Drying From Vacuum Saturation

Dry

In.

Hie

(gm.)

%

Mle

on

%

Mle

on

'10 RH

Sample (gm. )

Dry

\tit.

Vac. Sat.

s6

236.6

14.2

5.8

4.3

80

s14

238.7

13.4

25

235.5

8.9

3.75

2.79

50

18

240.0

8.8

21

243.5

5.6

2.2

1.64

10

17

238.1

5.0

TABLE VI

IRREVE:RSIBLE LENGTH CHAN GES DUE TO OVENING

ｾｖｅｔｔｅｄ

SAHPLES

Cellular Material ItA n

Gain in

Gain in

Length From Length From

Wt. Gain

Wt. Loss

D

- Drying

Sample

1st to 2nd 2nd to 3rd

From Original From Original

1:J

-

ｾｊ･ｴｴｩｮｧ

Ovening

Ovening

G

L

Series

1

28

L 0.9

gm,

D

2

25

51

L 1.0

gm,

D

- w

3

23

67

L 0.6

gm,

D

_{- w}

7

12

L 0.8

gm, D

8

28

_{L 0.9}

gm.

D

9

22

L 0.8 gm.

D

10

46

G 0.6 gm.

D

13

31

G 0.9

gm,

W

14

42

G 1.9

gm ,

w

16

43

34

G 0.4

gm,

w

- D

17

36

G 0.2

gm, W

18

39

G 1.4 gm.

W

19

47

62

G 0.3 gm.

\-J -

D

20

60

₄₅

G 0.3

gm, _{1rJ -}

D

21

67

G 0.8

gm,

w

22

90

G 1.2 gm.

1:J -

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MOISTURE- CONTE-NT

AT

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