A study of the state of water and stoichiometry of bottle- hydrated Ca3SiO5

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Cement and Concrete Research, 4, March 2, pp. 155-166, 1974-03-01

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A study of the state of water and stoichiometry of bottle- hydrated

Ca3SiO5

Feldman, R. F.; Ramachandran, V. S.

https://publications-cnrc.canada.ca/fra/droits

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CEMENT and CONCRETE RESEARCH. V o l . 4, pp. 155-166, 1974. Pergamon Press, I n c . P r i n t e d i n t h e U n i t e d S t a t e s .

A STUDY O F T H E S T A T E O F WATER AND STOICHIOMETRY O F B O T T L E - H Y D R A T E D Ca, SiO,

R . F. F e l d m a n and V

.

S. R a m a c h a n d r a n

D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l of C a n a d a , Ottawa, O n t a r i o , K1A OR6

(Communicated by P. J. Sereda) (Received November 12, 1973) A B S T R A C T T h e s t a t e of w a t e r i n h y d r a t e d C, S is s t u d i e d b y D i f f e r e n t i a l T h e r m a l A n a l y s i s a n d T h e r m o G r a v i m e t r i c A n a l y s i s t e c h n i q u e s . S a m p l e s w e r e c o n d i t i o n e d a t s e v e r a l r e l a t i v e h u m i d i t i e s f o r l e n g t h y p e r i o d s s t a r t i n g f r o m d - d r y , 1 0 0 p e r c e n t R. H. a n d 1 1 p e r c e n t R . H. I t w a s found t h a t t h e s t o i c h i o m e t r y of t h e b o t t l e - h y d r a t e d C - S - H g e l a t 1 1 p e r c e n t R. H. a p p r o a c h e d f r o m 100 p e r c e n t R. H. is 3 . 2 8 C a O : 2 S i 0 , : 3 . 9 2 H 2 0. R e s u l t s s u g - g e s t e d t h a t a t h i g h e r h u m i d i t i e s h i g h e r h y d r a t e s e x i s t w h i c h d e - c o m p o s e d o n d r y i n g a t r e l a t i v e h u m i d i t i e s b e l o w 4 0 p e r c e n t R . H. D e c o m p o s i t i o n m i g h t o c c u r a t h u m i d i t i e s a b o v e t h i s l e v e l . On Ctudie 1lCtat d e lt e a u d a n s l e C, S h y d r a t C B l t a i d e d e l l a n a l y s e t h e r m i q u e d i f f C r e n t i e l l e e t d e l l a n a l y s e t h e r m o g r a v i m C t r i q u e . D e s C c h a n t i l l o n s s o n t conditionnCs B d i v e r s d e g r C s dl h u m i d i t 6 r e l a t i v e (h. r. ) p e n d a n t d e l o n g u e s p e ' r i o d e s B p a r t i r d e l f C t a t " d - d r y " , d f u n e h. r . d e 100 p o u r c e n t e t d l u n e h . r . d e 1 1 p o u r c e n t . L a s t o e c h i o m b t r i e d u g e l C - S - H h y d r a t C e n b o u t e i l l e , B u n e h. r . d e 1 1 p o u r c e n t a t t e i n t e B p a r t i r d l u n e h. r . d e 100 p o u r c e n t , e s t 3, 2 8 C a O : 2 S i 0 , : 3, 92 H, 0. L e s r C s u l t a t s s u g g ' e r e n t q u f i l e x i s t e , B d e s d e g r C s d f h u m i d i t C p l u s ClevCs, d e s h y d r a t e s s u p C r i e u r s q u i s e d e ' c o m p o s e n t e n s C c h a n t B u n e h. r . d e m o i n s d e 4 0 p o u r c e n t . L a d C c o m p o s i t i o n p o u r r a i t s e p r o d u i r e B u n e h u m i d i t 6 d e p l u s d e 4 0 p o u r c e n t .

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V o l . 4, No. 2

STOICHIOMETRY, TRICALCIUM SILICATE, BOTTLE HYDRATION

Introduc tion

A study of the s t o i c h i o m e t r y of h y d r a t e d C, S and the r e a c t i o n of C, S with w a t e r h a s always b e e n difficult b e c a u s e of the p r o b l e m of s e p a r a t i n g and e s t i m a t i n g quantitatively the v a r i o u s p r o d u c t s and the r e a c t a n t s . The e q u a - tion f o r the r e a c t i o n i s of the f oilowing f o r m :

3 C a 0 . SiO, f xH2 0 -+ YCaO. SiO, ( x t Y - 3 ) H 2 0 f ( 3 - Y ) C a ( O H ) ,

I t h a s b e e n difficult to d e t e r m i n e the a m o u n t of CaO a s s o c i a t e d with e a c h of the two p r o d u c t s and thus the amount of w a t e r a s s o c i a t e d with Ca(OH),

.

A m o r e p r o b l e m a t i c a l question i s to d i s t i n g u i s h quantitatively the u n r e a c t e d w a t e r f r o m the constitutional w a t e r i n the c a l c i u m s i l i c a t e h y d r a t e product, v i z . ( x

+

Y - 3) m o l e c u l e s .

No r e a l a t t e m p t h a s b e e n m a d e p r e v i o u s l y to e s t i m a t e the t o t a l h y d r a t e w a t e r in the C - S - H p h a s e . ( 1 ) P r e v i o u s l y , the s t o i c h i o m e t r y of the C-S-H p h a s e was d e t e r m i n e d a t the d - d r i e d condition. I t was a s s u m e d t h a t l i t t l e o r no f r e e o r a d s o r b e d w a t e r r e m a i n e d on the s a m p l e a t t h i s condition which was the vapour p r e s s u r e of w a t e r a t the s u b l i m a t i o n t e m p e r a t u r e of solid CO, ( - 7 8 " C) ( 2 ) . In addition i t would be useful to d e t e r m i n e the s t o i c h i o m e t r y a t higher r e l a t i v e humidity conditions, b e c a u s e the s t a b i l i t y of higher hy- d r a t e s if they e x i s t m a y g o v e r n and explain the behaviour of h y d r a t e d p o r t - land c e m e n t under v a r i o u s p r a c t i c a l conditions of load and environment.

In a r e c e n t p a p e r (3) i t was shown by t h e r m a l a n a l y s i s that higher h y d r a t e s do e x i s t a t h u m i d i t i e s above t h e d - d r y s t a t e f o r h y d r a t e d portland c e m e n t ; in t h i s p r e s e n t p a p e r the s t o i c h i o m e t r y and s t a b i l i t y of the h y d r a t e s of C, S a t v a r i o u s conditions of e x p o s u r e a r e examined by that technique. he p o s s i b i l i t y of sulphoaluminates being the c a u s e of v a r i o u s phenomena i s eliminated with C3S. R e l a t i v e humidity of 11 p e r c e n t on d r y i n g f r o m 100 p e r c e n t R. H. was used a s the m a i n r e f e r e n c e f o r the h y d r a t e f o r e x p e r i m e n - t a l convenience and because, a t t h i s point, the e s t i m a t e of a d s o r b e d water c a n be m a d e with s o m e confidence.

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STOICHIOMETRY, TRICALCIUM SILICATE, BOTTLE HYDRATION

E x p e r i m e n t a l M a t e r i a l s T h e h y d r a t e d C , S p r e p a r a t i o n u s e d i n t h i s w o r k w a s o b t a i n e d b y b o t t l e - h y d r a t i n g C, S a t 2 3 " C f o r 17 m o n t h s a t a w a t e r - t o - s o l i d r a t i o of 5. T h e b o t t l e - h y d r a t e d s l u r r y w a s f i l t e r e d a n d d r i e d o v e r 11 p e r c e n t R . H. ( L i C Z s a t u r a t e d s o l u t i o n ) a n d s c r e e n e d o v e r a 1 0 0 - m e s h s i e v e . T h e r e s i d u e of l a r g e Ca(OH), c r y s t a l s w a s g r o u n d a n d r e m i x e d w i t h t h e p o w d e r . I t w a s c o m p l e t e l y h y d r a t e d ; c a r b o n d i o x i d e c o n t e n t w a s 1 . 4 p e r c e n t b a s e d on t h e w e i g h t a t 1 1 p e r c e n t R . H. on f i r s t d r y i u g . T h e s u r f a c e a r e a b y n i t r o g e n a d s o r p t i o n w a s 70. 3 m 2 I g m f o r t h e d - d r i e d s a m p l e . T h e s a m p l e w a s c o n - d i t i o n e d a t 1 1 p e r c e n t R . H. f o l l o w e d by v a c u u m d r y i n g a n d f i n a l l y by h e a t i n g a t 1 1 0 ° C f o r 3 h r p r i o r t o s u r f a c e a r e a d e t e r m i n a t i o n . S a m p l e Conditioning B a s i c a l l y 4 s e r i e s of s a m p l e s w e r e p r e p a r e d a n d d e s i g n a t e d A, B, B ( R ) a n d C. T h e f o l l o w i n g d i a g r a m i l l u s t r a t e s d e s i g n a t i o n of s a m p l e s a n d t h e i r h i s t o r y . T h e b o t t l e - h y d r a t e d p o w d e r w a s c o n d i t i o n e d a t 1 1 p e r c e n t R . H. i n a d e s i c c a t o r f o r 10 m o n t h s a n d d e s i g n a t e d P r e p a r a t i o n A. B o t t l e h y d r a t e d

I

c3s

1

1 1 % R.H.

]

P r e p a r a t i o n A l l l , 3 2 , 4 2 , 5 8 , 6 6

1

4

1 8 4 a n d 100% R . H .

I

32, 42, 58, 66, 84 11, 32, 42, 58, 66, 84%

b

_{a n d 10070 R . H.} S e r i e s B

+

11% R. H. S e r i e s B ( R )

E h

O n e p o r t i o n of P r e p a r a t i o n A w a s s p r e a d 2 t o 3 mm t h i c k i n d i s h e s a n d d - d r i e d i n a l a r g e d e s i c c a t o r f o r 5 w e e k s . T h e m a t e r i a l w a s t h e n p l a c e d i n a v a c u u m v e s s e l a n d h e a t e d f o r 3 h r a t 1 0 0 ° C . T h i s s a m p l e w a s

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2 STOICHIOMETRY, TRICALCIUM SILICATE, BOTTLE HYDRATION

d e s i g n a t e d P r e p a r a t i o n B. A n o t h e r p o r t i o n of P r e p a r a t i o n A w a s p l a c e d i n a d e s i c c a t o r f o r two m o n t h s a t 100 p e r c e n t R.H. and w a s d e s i g n a t e d P r e p a - r a t i o n C. E a c h of t h e s e p r e p a r a t i o n s w a s divided i n t o s m a l l p o r t i o n s and one p o r t i o n (two p o r t i o n s f o r P r e p a r a t i o n B) p l a c e d i n e a c h of s e v e r a l d e s i c - c a t o r s conditioned a t 11, 32, 42, 58, 66, 84 and 100 p e r c e n t R. H. Conditioning t i m e in e v e r y c a s e w a s 2 _months. _{One of t h e p o r t i o n s of P r e p a r a t i o n B w a s}

r e m o v e d f r o m e a c h d e s i c c a t o r a n d p l a c e d f o r two m o n t h s i n 1 1 p e r c e n t R. H.;

t h i s was d e s i g n a t e d S e r i e s B ( R ) . The d i f f e r e n t g r o u p s of DTA r u n s w e r e l a b e l l e d S e r i e s A, B, C a n d B ( R ) a s p r e v i o u s l y shown.

T h e r m a l a n a l y s i s

-

In t h i s work, DTA and TGA of s a m p l e s p r e p a r e d a s p r e v i o u s l y d e - s c r i b e d w e r e c a r r i e d out u n d e r c o n t r o l l e d conditions of humidity. The d e t a i l s h a v e b e e n p u b l i s h e d e l s e w h e r e . _{(3) N o r m a l TGA r u n s w e r e p e r f o r -} m e d a t a heating r a t e of 1 O 0 C / m i n under vacuum. S t a t i c r u n s w e r e a l s o p e r f o r m e d by heating a t 1 0 0 " f o r 3 h r under v a c u u m . S a m p l e s w e r e c o m - p a c t e d a t 5000 p s i t o p r e v e n t blowing and l o s s of powder d u r i n g e v a c u a t i o n and heating. In t h e DTA r u n s , the c e l l w a s p l a c e d i n a gloved box c o n t r o l l e d a t the r e q u i r e d humidity. In e a c h e x p e r i m e n t 16 m g of t h e s a m p l e w e r e weighed i n a b a l a n c e p l a c e d i n t h e gloved box. A l u m i n u m c u p s w e r e u s e d a s s a m p l e h o l d e r s and the r e m o t e DTA c e l l supplied by DuPont Co. w a s adopted f o r t h i s work. T h e r m a l c u r v e s w e r e obtained a t heating r a t e s of 10 and 2 0 " C / m i n .

D e t e r m i n a t i o n of F r e e CaO a n d C S ,

-

F r e e l i m e w a s d e t e r m i n e d b y the s o l v e n t v a r i a t i o n m e t h o d (SVM) ( 4 ) .

The a c t u a l a m o u n t of Ca(OH), w a s d e t e r m i n e d b y taking i n t o a c c o u n t t h a t which had r e a c t e d with CO, t o f o r m C a C 0 3 a n d t h a t which had d i s s o l v e d i n t h e w a t e r d u r i n g b o t t l e hydration.

CO, w a s d e t e r m i n e d by adding s u l f u r i c a c i d t o t h e s a m p l e and a b s o r

-

bing t h e evolved CO, i n Ba(OH),

.

E x c e s s Ba(OH), was e s t i m a t e d by t i t r a t i n g with HC &. The e x p e r i m e n t w a s c a r r i e d out i n a c l o s e d s y s t e m .

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2 STOICHIOMETRY, TRICALCIUM SILICATE, BOTTLE HYDRATION

R e s u l t s a n d D i s c u s s i o n

(i) S t a t e of W a t e r

-

W a t e r Content

-

R e l a t i v e Humidity Relationship-

As w a s found p r e v i o u s l y f o r h y d r a t e d p o r t l a n d c e m e n t (3) t h e d y n a m i c TGA did n o t show a s c l e a r a d e l i n e a t i o n of d i f f e r e n t t y p e s of w a t e r a s t h e DTA c u r v e s . However, u n d e r s'tatic conditions, heating i n v a c u u m a t 1 0 0 ° C f o r 3 h o u r s g i v e s a condition a p p r o x i m a t e l y e q u i v a l e n t to the d - d r y condition

s o t h a t q u a n t i t a t i v e i n f o r m a t i o n could b e obtained a n d r e l a t e d t o t h e i n t e n s i t y of the DTA c u r v e s of e a c h s a m p l e . In a d d i t i o n s o r p t i o n a n d p a r t i a l s c a n n i n g i s o t h e r m s (5) c a n b e c o n s t r u c t e d by d e t e r m i n i n g t h e a m o u n t of w a t e r held i n e a c h of the s a m p l e s e x p o s e d to t h e d i f f e r e n t h u m i d i t y conditions b y t h e s t a t i c TGA d e s c r i b e d p r e v i o u s l y . E q u i l i b r i u m a t e a c h p o i n t i s a s s u r e d due t o t h e lengthy p e r i o d s allowed f o r i t to b e attained. T h e s e r e s u l t s a r e p r e s e n t e d i n F i g u r e 1. The o u t e r b o u n d a r y s o r p t i o n c u r v e i s obtained f r o m the s a m p l e s of S e r i e s B, and the a p p r o x i m a t e s c a n n i n g c u r v e s , dotted l i n e s , a r e d r a w n in f r o m t h e points obtained on r e t u r n i n g e a c h p o i n t t o 11 p e r c e n t R. H., S e r i e s B ( R ) . P r e p a r a t i o n C, S e r i e s C r e p r e s e n t s the o u t e r b o u n d a r y d e - s o r p t i o n c u r v e . The s l o p e of t h i s c u r v e , i n the low h u m i d i t y r e g i o n f r o m 4 2 to 11 p e r c e n t R. H., i s m u c h g r e a t e r than the s l o p e of the s c a n n i n g c u r v e s a n d t h a t of t h e r e a d s o r p t i o n c u r v e obtained f r o m r e a d s o r p - P R E P . C

/,"

- 1 6 - - 1 4 - 0 _{SORPTION. SERIES B}

SORPTION. PREP. A. SERIES A

A DESORBED FROM 1Wk RH. SERIES C

tion on P r e p a r a t i o n A, S e r i e s A. T h i s 0 c a n n o t b e explained by c a p i l l a r y c o n d e n s e d 1

,

0 20 4 0 6 0 80 1 0 0 R H . % w a t e r i n P r e p a r a t i o n C. S e r i e s A h a s t h e FIG. 1 s a m e s l o p e a s t h e scanning c u r v e s up to S o r p t i o n i s o t h e r m of b o t t l e about 60 p e r c e n t R. H. I t i s p e r t i n e n t t h a t _{h y d r a t e d C,}S

the s a m p l e of S e r i e s B(R) which had b e e n

exposed to 100 p e r c e n t R. H. h a s a l m o s t r e a t t a i n e d the w a t e r c o n t e n t of the o r i g i n a l P r e p a r a t i o n A a t 11 p e r c e n t R. H. In o t h e r w o r d s m o s t of t h e i n t e r -

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2 STOICHIOMETRY, TRICALCIUM SILICATE, BOTTLE HYDRATION

l a y e r w a t e r h a s r e t u r n e d t o the s a m p l e of P r e p a r a t i o n B ( R ) ; i n addition, i t i s c l e a r f r o m t h e scanning c u r v e s t h a t t h i s r e t u r n of i n t e r l a y e r w a t e r t a k e s p l a c e over t h e f u l l r a n g e a s t h e s a m p l e i s exposed t o d i f f e r e n t humidities thus invalidating the u s e of t h e s e c u r v e s f o r B E T s u r f a c e a r e a c a l c u l a t i o n s .

The phenomenon of the scanning c u r v e s was a l s o o b s e r v e d f o r hydrated p o r t - land c e m e n t (5) but t h e r e was a p o s s i b i l i t y t h a t r e h y d r a t i o n of s o m e c a l c i u m sulphoaluminate o r other alurninates m i g h t be p a r t l y r e s p o n s i b l e f o r this. T h e s e r e s u l t s on hydrated C,S c l e a r l y show t h a t scanning c u r v e s owe t h e i r o r i g i n t o the C-S-H phase.

The low s l o p e of t h e c u r v e r e p r e s e n t i n g r e a d s o r p t i o n of P r e p a r a t i o n A ( S e r i e s A), c o m p a r e d t o the o u t e r boundary d e s o r p t i o n ( S e r i e s C) c u r v e i n d i c a t e s t h a t s o m e d i s s o c i a t i o n of a h y d r a t e o c c u r s above t h e 11 p e r c e n t R. H. l e v e l d u r i n g d r y i n g of P r e p a r a t i o n C m o s t of which r e c o m b i n e s above 66 p e r c e n t R. H. on rewetting ( S e r i e s A). In t h i s work, however, a n a t t e m p t was m a d e t o obtain t h e s t o i c h i o m e t r y of the h y d r a t e only a t the 11 p e r c e n t R.H. l e v e l on t h e outer boundary d e s o r p t i o n c u r v e ( P r e p a r a t i o n A), f o r r e a s o n s mentioned above. The h y s t e r e s i s shown h e r e between the a d s o r p t i o n and d e s o r p t i o n c u r v e s i s s i m i l a r quantitatively and qualitatively to t h a t of Helrnuth (6) and c o n t r a r y to t h a t of H a g y m a s s y (7). This work thus v e r i f i e s t h e e x i s t e n c e of scanning loops and the s e c o n d a r y h y s t e r e s i s , and c o n f i r m s t h a t t h i s i s a p r o p e r t y of the c a l c i u m s i l i c a t e h y d r a t e . P r e v i o u s w o r k (1, 3, 5 ) on c e m e n t h a s shown t h a t t h e h y s t e r e s i s i s due t o r e h y d r a t i o n of t h e d - d r i e d m a t e r i a l .

(ii) S t a t e of Water

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Differential T h e r m a l A n a l y s i s

R e s u l t s f o r S e r i e s A, B and C f o r a heating r a t e of 1 O 0 C / m i n a r e p r e s e n t e d on F i g u r e 2. S e r i e s B, the d - d r i e d sample, shows a s i m u l t a n e o u s growth of two e n d o t h e r m i c p e a k s a t 7 5 " and 110" C p r o b a b l y d u e to a d s o r b e d and i n t e r l a y e r w a t e r r e s p e c t i v e l y . The p e a k a t 1 1 0 ° C i s f i r s t of higher i n - t e n s i t y b u t a t h i g h e r h u m i d i t i e s the 7 5 ° C peak e x c e e d s i t and a g e n e r a l m e r g - ing of the p e a k s o c c u r s f r o m 66 p e r c e n t R. H. T h e r e i s evidence f o r o t h e r e n d o t h e r m a l effects a t a p p r o x i m a t e l y 200 and 300" C but, d u e to s e v e r e b a s e - l i n e shifting in t h i s t e m p e r a t u r e r a n g e , i t cannot b e c l e a r l y seen. This i s

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0 I50 300 450 0 150 300 450 0 I50 300 450

T E M P , O C T E M P , O C T E M P , O C

FIG. 2

DTA t h e r m o g r a m s a t 1 O 0 C / m i n ( a ) S e r i e s A

( b ) S e r i e s B ( c ) S e r i e s C

m o r e c l e a r l y o b s e r v e d when the heating r a t e i s 2 O 0 C / m i n a s shown on F i g u r e

3 S e r i e s (B) although t h e p e a k s have shifted to h i g h e r t e m p e r a t u r e s r e l a t i v e to 1O0C/min. T h e s e peaks a r e probably due to decomposition of hydroxyl groups within the s i l i c a t e . The p e a k s tend to m e r g e a t the h i g h e r humidities. F i g u r e 2 S e r i e s (A) p r e s e n t s the DTA t r a c e s of the o r i g i n a l m a t e r i a l , P r e p - a r a t i o n A, which h a s been e q u i l i b r a t e d a t 11 p e r c e n t R . H. The t r a c e a t 11 p e r c e n t

R.

H. shows a m u c h l a r g e r peak a t 11 0" C than the t r a c e f o r the d - d r i e d S e r i e s ( B ) a t 11 p e r c e n t R.H. This i s b e c a u s e t h e l a t t e r d o e s not contain a s m u c h i n t e r l a y e r w a t e r a t this humidity s i n c e i t h a s been d - d r i e d .

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Vol. 4, No.

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S e r i e s (A) s h o w s t h e low t e m p e r a t u r e p e a k a t 7 5 ° C r e p r e s e n t i n g a d s o r b e d w a t e r growing l a r g e l y by i t s e l f until i t h a s m e r g e d with t h e o t h e r p e a k s a t t h e high h u m i d i t i e s . At e a c h humidity above 42 p e r c e n t R. H. t h e i n t e n s i t y of t h e 7 5 ° C p e a k f o r S e r i e s (A) c l e a r l y e x c e e d s t h a t of S e r i e s ( B ) . T h i s i s p e r h a p s d u e to t h e f a c t t h a t S e r i e s (A) h a s n o t b e e n d - d r i e d and p r o b a b l y h a s a h i g h e r s u r f a c e a r e a t h a n t h e d - d r i e d s a m p l e S e r i e s ( B ) .

S e r i e s (C), t h e o u t e r b o u n d a r y d e s o r p t i o n c u r v e , shows t h e f e a t u r e o b s e r v e d f r o m t h e i s o t h e r m that, a t e a c h humidity, m o r e w a t e r i s p r e s e n t t h a n f o r S e r i e s (A). The p e a k s , however, a r e g e n e r a l l y m e r g e d and l i t t l e c a n b e l e a r n e d c o n c e r n i n g t h e r e l a t i v e s i z e of t h e p e a k s .

DTA c u r v e s f o r S e r i e s B(R), i n which s a m p l e s e x p o s e d t o v a r i o u s h u m i d i t i e s h a v e a l l b e e n r e t u r n e d t o 1 1 p e r c e n t R . H., a r e shown on F i g u r e 3. I t i s c l e a r f r o m t h e f i r s t c u r v e t h a t t h e f i r s t p e a k i s v e r y s m a l l , while t h e s e c o n d p e a k i s r e l a t i v e l y l a r g e . E a c h c u r v e e x h i b i t s a n i n c r e a s e i n t h e s e c o n d peak, ( e x c e p t p o s s i b l y a t 100 p e r c e n t and 84 p e r c e n t R. H . ) and thus c o n f i r m s t h e g r a v i m e t r i c r e s u l t s , ( F i g u r e l ) , t h e r e s u l t s obtained by s e v e r a l t e c h n i q u e s f o r h y d r a t e d c e m e n t , and the non-unique n a t u r e of t h e 1 1 p e r c e n t R. H. condition a n d t h e change i n p e a k a r e a ( F i g u r e 3, S e r i e s B ( R ) ) . E l e v e n p e r c e n t t o 32 p e r c e n t t o 42 p e r c e n t R. H. e x p o s u r e c o n d i t i o n s a g a i n c o n f i r m t h e f a c t t h a t i n t e r l a y e r w a t e r i s r e - e n t e r i n g a t t h e l o w e r h u m i d i t i e s ; d e s p i t e a long conditioning p e r i o d t h e n o n r e v e r s i b i l i t y a t low h u m i d i t i e s i s a p p a r e n t . T h i s i n v a l i d a t e s t h e u s e of H, 0 _{a s a n a d s o r b a t e f o r s u r f a c e a r e a m e a s u r e -}

m e n t s f o r t h i s s y s t e m . C o m p a r i n g S e r i e s B ( R ) F i g u r e 3, w i t h s e r i e s (A) F i g u r e 2 ( s a m p l e w a s n o t d - d r i e d ) w h e r e t h e l o w e r t e m p e r a t u r e peak, alone, g r o w s with the i n c r e a s i n g humidity, and S e r i e s ( B ) F i g u r e 2, ( s a m p l e w a s d - d r i e d ) w h e r e both p e a k s grow, e m p h a s i z e s the point on i n t e r l a y e r r e - e n t r y , i. e . , a t high h u m i d i t i e s m o s t of t h e w a t e r h a s r e - e n t e r e d .

(iii)

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H y d r a t e s Beyond t h e D - D r i e d S t a t e

Making t h e r e a s o n a b l e a s s u m p t i o n f o r a t y p e I1 i s o t h e r m t h a t a t 11 p e r c e n t R. H., on t h e o u t e r b o u n d a r y s o r p t i o n c u r v e ( S e r i e s B), one m o l e - c u l a r l a y e r of a d s o r b e d w a t e r e x i s t s on the f r e e s u r f a c e of t h e d - d r i e d m a t e r i a l , one m a y e s t i m a t e how m u c h h y d r a t e w a t e r i s a s s o c i a t e d with t h e

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s a m p l e a t t h i s h u m i d i t y a f t e r t h e s a m p l e h a s b e e n e x p o s e d t o 100 p e r c e n t R . H. M u c h w o r k , (8, 9 ) involving h e l i u m f l o w t e c h - n i q u e s h a s s h o w n t h a t a t 1 1 p e r c e n t R. H. a l a r g e p o r t i o n of t h e s o r b e d w a t e r r e - e n t e r s t h e i n t e r l a y e r s t r u c t u r e . T h e s u r f a c e a r e a , m e a s u r e d b y n i t r o g e n , of t h e d - d r i e d m a t e r i a l is 7 0 . 3 m 2 / g m w h i c h c o r - r e s p o n d s t o 1.93 p e r c e n t of w a t e r t o c o v e r t h e s u r - f a c e with one m o n o l a y e r a s s u m i n g one m o l e c u l e of H, 0 _{c o v e r s 1 0 . 8 ~ " . A f t e r} e x p o s u r e t o 100 p e r c e n t R . H . and r e d r y i n g t o 11 p e r c e n t R. H., t h e s a m p l e c o n t a i n s 6. 87 p e r c e n t of w a t e r a b o v e t h e d - d r i e d p o s i t i o n . A s s u m i n g t h e s u r f a c e a r e a i s unchanged b y r e w e t t i n g a n d s e c o n d T E M P , " C FIG. 3 DTA t h e r m o g r a m s f o r ( a ) S e r i e s B a t 2 O 0 C / m i n ( b ) S e r i e s B ( R ) a t 1 O 0 C / m i n T E M P , 'C d r y i n g , t h i s l e a v e s 6. 87

-

1 . 9 3 = 4 . 9 4 p e r c e n t of w a t e r a s a h i g h e r h y d r a t e ; t h i s i s e q u i v a l e n t t o 5 . 9 8 p e r c e n t on t h e i g n i t e d b a s i s and c o n v e r t s to 1. 52 m o l e s of h i g h e r h y d r a t e w a t e r a s s o c i a t e d i n t h e r e a c t i o n with two m o l e s of

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( i v ) T h e O v e r - a l l S t o i c h i o m e t r y of t h e R e a c t i o n

T h e l o s s i n weight on ignition of the h y d r a t e d C 3 S conditioned a t 11 p e r c e n t

R.

H. i s 29. 61 p e r c e n t of t h e ignited weight. C o r r e c t i o n f o r t h e d e c o m p o s i t i o n of t h e c a r b o n a t e r e s u l t s i n the l o s s being 28. 54 p e r c e n t . F r o m 1 1 p e r c e n t R. H. to the d - d r y position, 8. 33 p e r c e n t of t h e ignited weight (6. 87 on d - d r y b a s i s , F i g u r e 1) i s l o s t s o t h a t t h e weight l o s s f r o m t h e d - d r y s t a t e to the ignited s t a t e i s 20.2 1 p e r c e n t , o r 0. 2021 g H, O / g m C, S. _{T h i s v a l u e c o m p a r e s well with t h a t given by o t h e r a u t h o r s , (10, 11)}

a n d c o r r e s p o n d s to 2 . 5 6 m o l e s H a O / m o l e C 3 S r e a c t e d up t o the r e f e r e n c e of t h e d - d r y s t a t e o r 5. 12 m o l e s H, 0 1 2 m o l e s C 3 S. Taking t h e a d d i t i o n a l con- s t i t u t i o n a l w a t e r a t t h e 1 1 p e r c e n t

R.

H. into a c c o u n t r e s u l t s in a t o t a l of 6. 64 m o l e s H, 0 combining with 2 m o l e s C 3 S.

T h e e s t i m a t i o n of f r e e l i m e i s n e c e s s a r y f o r the e s t a b l i s h m e n t of the CaO/SiO, a s w e l l a s the r e a c t i o n equation, s i n c e f r o m it, one a l s o d e t e r - m i n e s t h e l i m e and w a t e r c o n t e n t a s s o c i a t e d with t h e s i l i c a t e h y d r a t e . In t h i s w o r k the well-known SVM m e t h o d (4) w a s used a s i t i s shown to g i v e f a i r l y a c c u r a t e r e s u l t s . The v a l u e obtained a f t e r c o r r e c t i o n s f o r c a r b o n a t i o n w a s 3 3 . 4 1 p e r c e n t , yielding a v a l u e of 1. 64 f o r CaO/SiO, r a t i o of t h e

h y d r a t e d s i l i c a t e . T h i s v a l u e a p p r o x i m a t e s the h i g h e r v a l u e s obtained by L o c h e r (10) f o r C 3 S- p a s t e s a t high w a t e r - c e m e n t r a t i o s .

T h e equation f o r t h e r e a c t i o n using the d - d r i e d r e f e r e n c e condition m a y b e w r i t t e n thus:

T h e d i f f e r e n c e b e t w e e n the CaO/SiO, and H 2 O/SiO, of t h e d - d r i e d h y d r a t e d s i l i c a t e i s thus 0 . 4 4 which a g a i n i s s i m i l a r to t h e v a l u e d e t e r m i n e d by o t h e r w o r k e r s (10, 1 1 ) . The equation f o r the condition a t 1 1 p e r c e n t R. H. on d r y i n g f r o m 100 p e r c e n t

R.

H. m a y b e w r i t t e n a s follows:

T h i s y i e l d s a v a l u e f o r CaO/SiO,-H, O/SiO, of - 0 . 32 with a H, O/SiO, of 1 . 9 6 . If the s t o i c h i o m e t r y of the hydrate was m e a s u r e d a t higher humidities t h e e x c e s s of H, O/SiO, o v e r CaO/SiO, m i g h t b e e v e n g r e a t e r . The u s u a l

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165 STOICHIOMETRY, TRICALCIUM SILICATE, BOTTLE HYDRATION

a s s u m p t i o n i s t h a t t h e r e a r e 3 m o l e s of w a t e r i n t h e s i l i c a t e h y d r a t e , and a H 2 O/SiO, of 1. 50, one of t h e t h r e e m o l e c u l e s of w a t e r , r e s i d i n g b e t w e e n t h e s h e e t s . At t h e 1 1 p e r c e n t R. H. condition, i t a p p e a r s t h a t 1. 52 m o l e s m a y e x i s t between t h e s h e e t s and m o r e a t h i g h e r h u m i d i t i e s . C o n c l u s i o n s T h e condition a t 11 p e r c e n t R. H. ( d r y i n g f r o m 100 p e r c e n t R. H. )

i s a good b a s e f o r studying the s t o i c h i o m e t r y of c a l c i u m s i l i c a t e h y d r a t e . The s t o i c h i o m e t r y of t h e b o t t l e - h y d r a t e d C-S-H g e l a t 1 1 p e r c e n t R. H. a p p r o a c h e d f r o m 100 p e r c e n t R. H. i s 3 . 2 8 CaO: 2SiO2 : 3. 92H2 0. R e s u l t s s u g g e s t t h a t a t h i g h e r h u m i d i t i e s , h i g h e r h y d r a t e s m a y e x i s t . I n t e r l a y e r w a t e r r e - e n t e r s t h e d - d r i e d C - S - H s t r u c t u r e below 11 p e r c e n t R. H. and throughout t h e h u m i d i t y r a n g e . At t h e 100 p e r c e n t R . H. e x p o s u r e , a l m o s t c o m p l e t e r e - e n t r y s e e m s t o o c c u r . When s p e c i m e n s a r e d r i e d f r o m 100 t o 10 p e r c e n t R . H . d e h y d r a t i o n o c c u r s . This i s v e r y evident a t humidities of 40 p e r c e n t and l o w e r , but m i g h t even o c c u r b e t w e e n 100 and 40 p e r c e n t ; t h i s could not b e a s c e r t a i n e d b e c a u s e of c a p i l l a r y c o n d e n s a t i o n i n t h i s r e g i o n .

T h e r m o g r a m s d e l i n e a t e t h e f r e e and i n t e r l a y e r w a t e r and t h e i r r e l a t i v e i n t e n s i t i e s f o r s a m p l e s exposed to d i f f e r e n t c o n d i t i o n s show a good r e l a t i o n s h i p with t h e a d s o r p t i o n i s o t h e r m s .

Acknowledgment

T h e a u t h o r s w i s h t o acknowledge t h e v a l u a b l e a s s i s t a n c e of S. Dods and G. P o l o m a r k i n p e r f o r m i n g e x p e r i m e n t s and g a t h e r i n g d a t a . T h i s p a p e r i s a c o n t r i b u t i o n f r o m t h e Division of Building R e s e a r c h , National R e s e a r c h Council of Canada, and i s published with t h e a p p r o v a l of t h e D i r e c t o r of t h e Division.

R e f e r e n c e s

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( 2 ) L. E . Copeland and J. C. Hayes, The D e t e r m i n a t i o n of N o n - e v a p o r a b l e W a t e r i n H a r d e n e d P o r t l a n d C e m e n t P a s t e , ASTM Bull. 194, (1953).

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R. F. F e l d m a n and V. S. Ramachandran, Differ entiation of I n t e r l a y e r and A d s o r b e d W a t e r in H y d r a t e d P o r t l a n d C e m e n t by T h e r m a l

A n a l y s i s , C e m e n t and C o n c r e t e R e s e a r c h

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4, 607 (1971).

E. P r e s s l e r , S. B r u n a u e r , D. L. K a n t r o and C. M. Weise, D e t e r m i n - a t i o n of t h e Contents of F r e e C a l c i u m E y d r o x i d e in Hydrated P o r t l a n d C e m e n t s and C a l c i u m S i l i c a t e s , Analyt. C h e m .

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33, 877 (1961). R. F. Feldman, Sorption and Length Change Scanning I s o t h e r m s of Methanol and W a t e r on H y d r a t e d P o r t l a n d Cement, P r o c . , F i f t h Int. Symp. on t h e C h e m i s t r y of Cement, P a r t 111,

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R. F. Feldman, Changes to S t r u c t u r e of Hydrated P o r t l a n d C e m e n t on Drying a n d Rewetting O b s e r v e d by H e l i u m Flow Techniques ( t o b e published).

R. F. Feldman, Helium Flow C h a r a c t e r i s t i c s of Rewetted Specimens of D r i e d P o r t l a n d C e m e n t P a s t e (to b e p u b l i s h e d ) .

F. W. L o c h e r , S t o i c h i o m e t r y of T r i c a l c i u m S i l i c a t e Hydration, Highway R e s e a r c h B o a r d Sp. R e p o r t 90, 300 (1966).

S. B r u n a u e r and D. L. Kantro, The Hydration of T r i c a l c i u m Silicate and _BD i c a l c i u m S i l i c a t e f r o m 5 " C to 5 0 ° C , The C h e m i s t r y of Cement, H. F. W. Taylor Ed.,

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Ch. 7, 287. A c a d e m i c P r e s s , London and New Y o r k (1964).