Theory of the setting of gypsum bonding materials

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Kuntsevich, O. V.; Aleksandrov, P. E.; Ratinov, V. B.; Rozenberg, T. I.; Bogautdinova, G. G.

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T i t l e :

NATIONAL RESEARCH COUNCIL OF CANADA

Technical T r a n s l a t i o n TT-685

The t h e o r y of t h e s e t t i n g of gypsum bonding materials

( K voprosu o t e o r i i t v e r d e n i i a gipsovykh viazhushchikh)

Authors : O.V. Kuntsevich, P.E. Aleksandrov, V.3. Batinov, T

.

I. Rozenberg and G .G

.

Bogaut dinova

Reference: Doklady Akad. Nauk SSSB, 104 ( 4 ) : 587-588,

1355

T r a n s l a t o r : G. Belkov, T r a n s l a t i o n s S e c t i o n , N.R. C. L i b r a r y

THE THEORY OF THE SZTTING OF GYPSUM 3ONDING MATERIALS

The s e t t i n g of gypsum bonding m a t e r i a l s according t o t h e t h e o r y of A . A , Baikov h a s t h r e e s t a g e s : imbibition and p a r t i a l d i s s o l v i n g , c o l l o i d formation and c r y s t a l l i z a t i o n , According t o t h i s g e n e r a l l y accepted t h e o r y developed by P . A , Reblnder mainly with regard t o c o a g u l a t i m s t r u c t u r e

formation ( 2 - 4 ) , t h e second and t h i r d s t a g e s begin almost simultaneously but end a t d i f f e r e n t times: t h e d u r a t i ~ n of c o l l o i d formation i s f i g u r e d i n minutes whereas c r y s t a l l i z a t i o n i n hours and even d a y s .

I n t h i s work we attempted t o check t h e important a s s e r t i o n i n t h e theory of A.A, Baikov t h a t t h e r e i s a c o n s i d e r a b l e d i f f e r e n c e i n t h e d u r a t i o n of t h e second and t h i r d s t a g e s ,

The r e s u l t s of i n v e s t i g a t i o n s c a r r i s d out independently by t h e a u t h o r s were i n remarkably good agreement. The i n v e s t i g a t i o n of gypsum bonding m a t e r i a l s prepared by a l l t h e u s u a l l y accepted methods from r a w m a t e r i a l obtained from

13

d i f f e r e n t l o c a t i o n s and a l s o from a s e l e c t e d rock of 97-99% _{p u r i t y , showed t h a t}

h y d r a t i o n and c r y s t a l l i z a t i o n begin and end a t t h e same time

-

less t h a n hour a f t e r mixing with water ( s e e Fig, l ) ,

These d a t a were obtained from s y s t e m a t i c comparison of t h e s e t t i n g k i n e t i c s of v a r i o u s gypsum suspensions (determined by s t a n d a r d methods, l e e , , betiding s t r e n g t h , compression and t e n s i o n and a l s o s p e c i f i c s h e a r i n g s t r e s s using t h e A . A . Simonian

instrument

( 5 ) )

with t h e i r h y d r a t i o n k i n e t i c s (found by t h e

accepted methods(6) : q u a n t i t y of chemically bonded water, h e a t

*

l i b e r a t i o n , c o n t r a c t i o n e f f e c t s and volumetric changes i n t h e system),

*

E d i t o r ' s n o t e : The word "contraction" would appear t o r e f e r t o t h e set p l a s t e r as opposed t o " v o l u m e t r i c c l ~ a n g e s " , which r e f e r s t o t h e period of s e t t i n g ,

It was found t h a t t h e end of s e t t i n g corresponded t o t h e consumption of only 40-50% of t h e chemically bonded water r e q u i r e d by t h e t h e o r y f o r a l l t h e powder of t h e semi-aqueous calcium s u l p h a t e t o be converted t o a d i h y d r a t e g e l .

Fig. 2 shows t h a t during t h e subsequent p e r i o d of t i m e , depending on t h e o r i g i n a l water-bonding m a t e r i a l r a t i o , t h e r e l a t i v e humidity of t h e atmosphere and t h e temperature of t h e d r y i n g o p e r a t i o n , t h e gypsum does not i n c r e a s e i n s t r e n g t h ; on t h e c o n t r a r y t h e r e Is a tendency f o r a s l i g h t r e d u c t i o n i n hard- n e s s , Following t h i s t h e r e i s a n i n c r e a s e i n s t r e n g t h , almost by t h e f a c t o r of two, accompanied by shrinkage (when samples were

k e p t under normal room c o n d i t i o n s t h e i n c r e a s e i n s t r e n g t h occurred on t h e average a f t e r 3-5 d a y s ) , The r e a s o n f o r t h e a b r u p t i n c r e a s e i n s t r e n g t h a t t h i s s t a g e of d r y l n g i s t h e e l i m i n a t i o n of w a t e r from t h e micropores and c a p i l l a r i e s . T h l s a s s e r t i o n i s confirmed by two f a c t o r s : a l t e r n a t e short-term w e t t i n g and drying r e s u l t s i n a corresponding r e v e r s i b l e v a r i a t i o n i n t h e s t r e n g t h of t h e samples till d i s s o l v i n g of t h e calcium s u l p h a t e d i h y d r a t e r e s u l t s i n i r r e v e r s i b l e processes and t h e r e i s no I n c r e a s e i n s t r e n g t h when t h e samples a r e k e p t a t 100% r e l a t i v e humidity o r i n water,

The experimental proof t h a t h y d r a t Lon and c r y s t a l l i z a t i o n of gypsum, being mutually dependent, b e g i n and end almost simult- aneously, removes t h e most s e r i o u s o b J e c t i o n t o t h e theory t h a t d i h y d r a t e c r y s t a l l i z e s from a s o l u t i o n which i s s a t u r a t e d w i t h r e s p e c t t o semi-aqueous calcium s u l p h a t e owing t o t h e d i f f e r e n c e i n s o l u b i l i t y of CaSOk 0.5H20 and CaS04 2H20.

The A l l Union Research I n s t i t u t e

of Reinforced Concrete and Rock Products and the Leningrad I n s t i t u t e of Railway Engineers named a f t e r

V.N.

Obraztsov,

Received,

1, Baikov, A.A, Sobr, trud. Izd. Akad. Nauk SSSB,

5:

111, 194.8; Stroit. Prom, (3): 617, 1925.

2, Rebinder, P,A, Iubilein. sborn. Akad, Nauk posviash. 30-

letiui VOSB (Anniversary ed, of Collected Works of the Academy of Sciences SSSR, dedicated to the 30- year anniversary of the Great October Revolution) 1: 1947,

3,

Segalova, E.E.

,

Bebinder, P,A. and Lukianova, O,I, Vestn,

MGY ( 2 ) , 1954.

4, Bebinder, P.A,

In

book .by Bytt

,

Ia,M. and Berkovich,

T.M.

Viazhushchie veshchestva s poverkhnostno-aktlvnymi

dobavkami (Cementing substances with surface-active additives), Moscow, 1953.

5

Simonian, A.A. Torf. prom. (10) : 24, 1953.

6,

Budnikov,

POP,

Gips, ego lssledovanila 1 primeneniia

Fig. 1

The kinetics of hydration and crystallization of

gypsum bonding material, a

-

specific shear stress,

b

-

bending strength, c

-

chemically bonded water,

d

-

volumetric changes, e

-

temperature rise,

Fig. 2

The kinetics of hardening of dihydrates

of gypsum. a

-

tension strength during

drying, b

-

strength of wet samples,