Variation in the volume of plaster during and after setting

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NATIOTJAL RESEARCH COUNCIL OF CANADA

Technical Translation TT-643

Variation in the volume of plaster during and after setting,

Shuyo Ito, Ichiro Teraoka and Seiichiro Yoshihama, Research Laboratory of the Tokyo Shibaura Electric Company, Limited.

K,

Shimizu.

Plaster continues to be

an

important building material in Canada and it is therefore the subject of some of the investigations now being carried out

in

the Building Materials Section

a f

the Division of Building Research,

In

the necessary and essential library research carried out in association with our laboratory work in connection with plaster problems, reference was found to this paper on the variation in the volume of plaster W i n g and after setting from Japan, Study of the paper showed its value and its relevance to current experimental work being carried out by the Division and in other laboratories in North America,

The Division is therefore pleased to be able to include this translation in its series of Technical Trans- lations, by permission of the author, The Division is grate- ful to Mr,

K,

Shimfzu for preparing thf s translation,

Ottawa,

VARIATION IN THE VOLUNE OF PLASTER DURING

AND

AFTER SETTING

1,

Introduction

A

part of this study has been published at the Fall

Symposium of Plaster Research Group in Nagoya on October

25,

1951.

The present paper deals with the results of further research*

In

the past only hardening and expansion of plaster due to hydration

have been studied, However, cont~action

takes place at the be-

ginning of hydration and expansion follows, Thus there is con-

siderable difference in true expansion of plaster due to hydration

between measurements made from the extreme of contraction and

measurements made within the range of expansion, The authors have

been able to measure contraction and expansion by means of a

simple optical dilatometer which has been specially designed for

the present work,

2,

Materials Used

The following types of plaster were used:

(a)

a

and

p

type plaster made from crystals which were obtained

from CaSO,, a residue of the manufacture of hydrofluoric acid at

the Kawaguchi Factory of the Shibaura Electric Co,,

Commercial products

Yoshino Plaster Manufactures, Ltd,

Two products were used (both +type).

Equipment

The equipment was designed to measure thermal contrac-

tion and expansion, This can be used to measure expansion and

contraction in plaster due to hydration, The use of this instru-

ment enabled the authors to discover that regular contraction

takes place before expansion which has been the sole subject of

research in the past,,

blain components of t h e equipment a r e shown schemati- c a l l y i n F i g u r e l a I t c o n s i s t s of a h e a t e r ( n o t used i n t h e p r e s e n t work), a q u a r t z g l a s s d i l n t o m e t e r (need n o t be q u a r t z g l a s s i n t h e p r e s e n t work), a s c a l e and a t e l e s c o p e , The inain components of t h e d i l a t o r a e t e r c o n s i s t of t e s t - m a t e r i a l r e c e i v i n g s t a n d and push b a r b o t h made of q u a r t z g l a s s , The b a r i s p l a c e d on r o l l e r s and p r e s s e d l i g h t l y by two rubber bands, The push b a r i s extremely l i g h t and moves sidetT~ays t o t h e r i g h t and l e f t ,

This movement t u r n s t h e r o l l e r s and a m i r r o r a t t a c h e d t o a r o l l e r . The m i r r o r i s placed a t t h e c e n t r e of t h e curved s c a l e and r e - f l e c t s t h e g r a d u a t i o n s on t h e s c a l e - The g r a d u a t i o n i s observed through a t e l e s c o p e r I n t h i s way b o t h c o n t r a c t i o n and expansion can b e a c c u r a t e l y measured, When t h e p l a s t e r which is t o b e t e s t e d is p l a c e d between t h e r e c e i v i n g s t a n d and t h e push b a r , + t h e change i n t h e volume of p l a s t e r is immediately transformed i n - t o t h e r o t a t i o n

o f

t h e ~;:inlor* Thus by t h i s equipment

i t

i s

p o s s i b l e t o observe continuously the c o n t r a c t i o n i n volume of p l a s t e r b e f o r e s e t t i n g and t h e expansion a f t e r s e t t i n g *

The following experiments were conducted: ( i ) t h e amount of mixing water i s changed; ( i i ) when s a l t s a r e added,

The r e s u l t s of experiments a r e shown below, Fig. 2 sho1vs t h e change i n volume of c o m l e r c i a l l y a v a i l a b l e Y- and S-

p l a s t e r with standard r ~ ~ o u n t of' mixing water ( s e e e d i t o r ' s n o t e ) ? blnx, Coizte$ Iclax,

EX^+%

T o t a l

E-*$

Maxa Temp-

Fig,

3

shows t h e chc~nce i n volune of

a-

_{and @-type}

p l a s t e r of Shibaura due t o h y d r a t i o n w i t h t h e change i n t h e m o u n t of mixing water added,

The folloiving shows t h e change i n volume:

( a ) of a type p l a s t e r with standard water mix ( s e e e d i t o r ' s note)" of 28% when

31%:

35% and

40$

of water was added,

Water $ Max. Cont, $ Max.

Exp.

%

Total

Exp.

%

31

-0,022 +0, 250 0,272

35 -Or 010 + O m

197

0,207

40 -0,038

+o,

125 0,163

( ~ o o m temp. 26,5Oc.> )

( b ) of a type p l a s t e r with standard water mix ( s e e e d i t o r ' s n o t e ) * of

3Mr

when 40%: 50% and 60% of water was added,

Water

%

Max. Con%*

%

Max, Exp,

%

Total

Exp,

%

Room T ~ w *

A t 57@* t h e r e

i s

an e x t r a o r d i n a r i l y l a r g e c o n t r a c t i o n ; however, t h e r e i s a decrease i n t o t a l expansion with i n c r e a s e i n water,

Fig,

3

( c ) sho~vs t h e change i n volume of f3-type p l a s t e r with standard water mix ( s e e e d i t o r ' s note)* of _{50% with change i n} amount of water,

Water $ Max, Cont,

%

Max, Exp.

%

Total Exp.

%

-0,025

+Os337

0,362

-or

062 +Om 212 0'

274

-0,036 +O, 112 0,148 -0,- 035

+o.

060 0,095 -0.012 +01 045 0, 057 ( ~ v e r a g e Room Temp. 1 2 , 2 O ~ , ) * E d i t o r ' s note:- The phrase "standard amount of mixing water" and

"standard . : ~ a t e r mix1' would appear t o be equivalent t o t h e phrase "standard c o n s i s t encyql,

Figure

4

shows the change in volume with the change in

water of

(B)

and

(c)

type of Yoshino Plaster Manufactures, Ltd,

(a) Change

in

the volume of P-type plaster

(B)

with the standard

water

mix

(see editor's note)* of

45,8%

when mount of water is

changed,

Waters Max, Cont.

$

Max,

Exp,

%

TotalExp.

%

R o o m T e W a

The result shows that measured from the initial position,

the expansion does not decrease in the order of increasing amount

of water,

(b) Shows the change in volume of @-type plaster

(c)

with the

standard water mix (see editorPs

note)* of

48.5%

when the amount

of water is changed.

Water

$

Max, Cont,

%

Max.

E q e

%

Total E a *

%

Room

The result, as in

(a),

shows that the expansion measured

from the initial position does not decrease with the increase in

the amount of water,

Fig.

5

(a) shows the change in volume of Shibaura a-type

plaster with sodium citrate added;

30%

water,

0.01

and

0.03%

of

sodium citrate was used,

Sodium citrate

%

Max,

Cant,$ Max, Exp.%

Total

Exp,%

Room Temp,

(

80

min,)

0,Ol

-0,025

+O*

275

0,300

20. O°Ce

0.03

-0,014

+O. 241

0.255

21,

O°Ce

*See footnote on page

4,

Fig.

5

(b) shows the change in volume due to hydration

of Shibaura a-type plaster with

50%

water and

1%

sodium citrate*

Fig,

6

shows the change in volume due to hydration of

Shibaura a-type plaster with sodium alginate added.

It is seen

that in all cases there is lengthening in the "apparent completion1'

time,

Water

%

Ratio of

Mix

Max.

Cant.%

Max,

Exp.%

Total Exp.%

Sodium alginate to

plaster

5,

Analysis

By means of a newly designed dilatometer the authors

measured the change in volume of plaster at the time of setting,

They discovered that the volume contracts during the setting

process and were able to measure the expansion in volume after

setting, The review of the present work shows that the experiments

can be summarized roughly

by

such

a

curve as shown in Fig,

7,

Hydration in plaster is a reaction in which crystalline gy-psum is

evolved and heat is generated as shown in the following equation:

CaSO,

o

1/2H20

+

1 4 ~ ~ 0

=

CaSO,

2H20

+

X

cal.

In this reaction, plaster dissolves at first, and gypsum crystall-

izes from the supersaturated solution; heat is generated followed

by the development of crystals and expansion proceeds rapidly,

It

appears that after the crystals are fully developed, contraction

In volume due to the drying of solid matter takes place,

(i)

0 -+

A:

Momentary contraction to A is observed, It appears

as if plaster is mostly in solution during this period and tenslon

predominates.

( i i ) A + B: This a l s o takes place i n a s h o r t i n t e r v a l of time. Dissolution 1 s r a p i d l y 'akfng place; h e a t

is

a l s o gener- ated,

( i i i ) B + C: C r y s t a l l i zatfon of small c r y s t a l s of CaSO, a 2H,O

g r a d u a l l y takes p l a c e and h e a t i s generated i n g r e a t e r quantity,

A t C the c ~ y s t a l l i z a t i o n ceases. I t appears a s i f t h i s is the p o i n t of "apparent comp.le tlon",

( i v ) C + D: Short s t a t i o n a r y s t a t e ,

( v ) D -, E -+ Fu, Development of c r y s t a l s t a k e s p l a c e r a p i d l y ;

volume expands r a p i d l y with t h e generation o f heat, Heat reaches a maximum i n the neighbowhood of Eo The temperature g r a d u a l l y d e c l i n e s , but expansion continues and a t F i t s r a t e begins t o decline, D -+ E t h e curve i s concave up and E -+ F i t i s convex,

( v f ) F -+ G -+

Hs

From

F

the c w v e , whose g r a d i e n t was low,

r i s e s a l i t t l e , and reaches a t s maximum a t H,

( v i i ) H + I: Expansion s t a y s a t a constant value f o r a while

then slow c o n t r a c t ion takes place,

N a t u r a l l y the shape of the curve depends on the proper- t i e s of t h e p l a s t e r ; f u r t h e r , depending on the condition under which the p l a s t e r was poured, them. a r e cases where A -+ B can hardly be recognized; st111 i n o t h e r cases, C and D coincide,

F w t h e r examination of t h e diagram suggests t o the authors t h e p o s s i b i l i t y tha% c e r t a i n explanations can be made with regard t o

t h e s t a r t of s e t t i n g , apparenX comp%etion, and completion of s e t t i n g , doe,, p o i n t B indicates the beginning, and p o i n t C

"apparent comple%ioni'. F u r t h e r , i f t h e completion i s i n d i c a t e d by t h e h i g h e s t p o l n t on the thermomete~, i t must l i e somewhere i n the neighbourhood of E, the p o i n t of i n f l e c t i o n , If the com- p l e t i o n i s t o b e taken a s t r u e expansion, p o i n t H must be taken a s the completion af sett5ng. Secondly, i t i s seen from the re- s u l t s of the p r e s e n t experiments t h a t t h e i n c r e a s e i n the amount of water r e s u l t s g e n e r a l l y i n the decrease i n t o t a l expansion ( ~ i g , 8 )

-

t h i s cannot be found from the consideration of contrac- t i o n (-) and expansion ( a ) separately. I t can only be known from

the sum of absolute values (total expansion),

Further, it was

found that the presence of organic salts has considerable effect

on the change in volume.

6.

Conclusion

Tile authors were able to study the change in volurne of

plaster due to hydration by means of the optical telescope and

using small quantity of test material, Our investigation is

un-

doubtedly incomplete; however, we feel that our investigation

gave us some insight into the problem, Further studies are under-

way on the effect of such factors as heat and strength, and others

on the amount of water added and on the change in volume,

The authors wish to thank the Yoshino Plaster Manufac-

tures,Ltd. for supplying them with test materials.

References

(a) Louis Chassevent, Variation in the volume of plaster during

and after setting, Rev, mat&riaux construction et trav,

publ.,

Ed, C., NO,

407*

276-72,

1949;

NO.

408,

304-308,

1949. @.A.

44:

299, 1950),

(b

) Louis Chassevent, ~atgriaux

construction et trave pml-9

Ed*

C,, No,

4059

188-94,

(c.A. 44;

12449

1950)*

D I L A T O M E T E R UARTZ T U B E S _{C U R V E D S C A} ( R A D I U S

-

I M U B B E R B A N D S SCREW TO F A S T E N Q U A R T Z T U B E S T H E R M O C O U P L E S U P P O R T I N G S U P P O R T I N G S T A N D DILATOMETER R A I L S

QUARTZ GLASS PUSH BAR ELECTRIC FURNACE

/'-

X X CROSS-SECTION

- - -

- - - - - - - Y I _---

,-

Y Y CROSS-SECTION X - - - - - - - - - - --- Z Z CROSS-SECTION -TEST M A T E R I A L R E C E I V I N G S T A N D O F OUARTZ G L A S S A

\

THERMOCOUPLE

7

S T E E L R O L L E R

FIGURE I

S PLASTER

-

nAxlnun H E A T (WATER ADDED GENERATED IS TYPE) 66.6% MAXIMUM H E A T GENERATED ( Y TYPE) Y PLASTER l l l l l l l # l l 0 10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 100 110 TlME IN MINUTES

-

WATER ADDED 31% WATER ADDED 40°k 0 10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 TIME IN MINUTES

FIGURE

2

FIGURE

30

CHANGE

IN VOLUME OF

CHANGE IN VOLUME

OF

SHJBAURA

COMMERCIAL PLAST ER

DUE

oC

-

_{T Y P E}

_PLASTER

_{WITH CHANGE}

TO

HYDRATION WITH

CHANGE

IN THE

AMOUNT

OF WATER

ADDED

FIGURE

3 ( b )

CHANGE

IN

VOLUME

OF

SHIBAURA

d,

-

TYPE

PLASTER

WITH CHANGE

IN THE AMOUNT OF WATER

ADDED,

(STANDARD

WATER MIX OF

& -

TYPE

PLASTER

-

30°h)

-

-

WATER ADDED 4 5 '10

L

-

-

-

-

-

-

-

-

---.I.--..---.---_ t

'

* W A T E R ADDED 60°/0

-

-

W A T E R ADDED 7 0 _O/o +WATER ADDED 8

o

I I I 1 I 1 1 I 1 I I 8 I r 10 2 0 3 0 40 5 0 6 0 70 8 0 90 100 110 120 130 140 150 T I M E (MINUTES)

FIGURE

3(c)

CHANGE

IN

VOLUME

OF

-

TYPE

PLASTER OF

STANDARD

WATER

MIX

5 0 %

WITH

CHANGE

IN

THE

AMOUNT

OF

FIGURE

4(a)

CHANGE

IN

VOLUME OF

(3

-TYPE PLASTER

OF STANDARD

WATER

MIX

OF

45*8°/o

WITH

-

WATER ADDED 60°A

- L

-

,

WATER ADDED 5 5 %

-

-

WATER ADDED 65 Oh

-

0 10 20 30 40 5 0 60 70 80 90 100 TIME ( MINUTES)

FIGURE 4 ( b )

0 10 2 0 3 0 4 0 5 0 6 0 70 8 0 9 0 100 TlME (MINUTES)

FIGURE 5(a)

CHANGE IN VOLUME OF SHIBAURA

oC

-

_{TYPE PLASTER DUE TO HYDRATION}

WHEN SODIUM CITRATE I S ADDED

TlME (MINUTES)

10 2 0 3 0 4 0 5 0 6 0 TO _{8 0 9 0 100} 110 120 130 140 150

1 1 1 1 1

I

FIGURE

5(b)

CHANGE IN VOLUME OF SHIBAURA

d

- T Y P E PLASTER WITH AN ADDITION

SODIUM ALGINATE : P L A S T E R : 5 : 9 5

(WATER ADDED

SODIUM ALGINATE :

PLASTER : 10 : 9 0 (WATER ADDED 70°/o)

0 2 0 4 0 6 0 8 0 100 1 2 0 1 4 0 160 T I M E (MINUTES)

FIGURE

6

CHANGE

IN VOLUME

OF

SHIBAURA

d

-

TYPE PLASTER DUE TO HYDRATION

WHEN SODIUM ALGINATE IS ADDED

T I M E

b

FIGURE

7

H

I

HEAT

G/

GENERATED

0 / / e)

'u/

.

C

0

CHANGE

IN

VOLUME OF PLASTER

FIGURE

8

0.8 0.7 h 9 L Oo6 2 0

-

V) 2

a

0.5 a X W 0 - 4 W b-

a

a _0.3 J

2

0 t- 0.2 0.1

TOTAL

EXPANSION

AND CHANGE

IN

THE AMOUNT

OF

WATER

ADDED

V E R T . DASHED LINES I N D I C A T E STANDARD O/o

C

X

_P

d

PLASTER ( a )

R

0 10 20 30 40 5 0 6 0 70 80