Influence of quartz surfaces on the reaction C3A +
CaSO4.2H2O + water
Citation for published version (APA):
Holten, C. L. M., & Stein, H. N. (1977). Influence of quartz surfaces on the reaction C3A + CaSO4.2H2O + water. Cement and Concrete Research, 7(3), 291-296. https://doi.org/10.1016/0008-8846(77)90091-6
DOI:
10.1016/0008-8846(77)90091-6
Document status and date: Published: 01/01/1977
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INFLUENCE OF QUARTZ SURFACES ON THE REACTION C3A + CaSO4.2H20 + WATER.
C.L.M. Holten and H.N. Stein Laboratory of General Chemistry
Technological University, Eindhoven, The N e t h e r l a n d s
(Communicated by H. F. W. Taylor) (Received February 28, 1977)
A B S T R A C T
Quartz surfaces counteract the retarding action of SO~- on the hydration of C3A, by p r e s e n t i n g additional sites for ettringite crystallization. Strong retardation requires the presence of ettringite near the C3A , influencing the local concentrations there.
Q u a r z o b e r f l ~ c h e n w i r k e n der V e r z 6 g e r u n g der Hydration des C3A durch Sulfationen entgegen, indem sie Extrapl~tze f~r die K r i s t a l l i s a t i o n des Ettringits bieten. Eine
starke V e r z ~ g e r u n g erfordert die A n w e s e n h e i t des Ettringits dicht neben dem C3A , w o d u r c h die lokalen K o n z e n t r a t i o n e n dort b e e i n f l u s s t werden.
292 Vol. 7, No. 3 C. L. M. Holten, H. N. Stein I n t r o d u c t i o n In s t u d i e s of the r e a c t i o n C 3 A + C a S O 4 . 2 H 2 0 + }{2 ° in p a s t e s , q u a r t z is f r e q u e n t l y a d d e d as an " i n e r t " f i l l e r in o r d e r to p r e - v e n t d e m i x i n g a n d s e d i m e n t a t i o n (I, 2). The i n e r t c h a r a c t e r of the q u a r t z may, h o w e v e r , be d o u b t e d , if o n l y b e c a u s e the p r e s e n c e of a f o r e i g n s u r f a c e m i g h t i n f l u e n c e n u c l e a t i o n of h y d r a t e s . I n d i c a t i o n s of t h i s h a v e b e e n r e p o r t e d for c e m e n t p a s t e s (3). It w a s t h o u g h t d e s i r a b l e to p e r f o r m s i m i l a r e x p e r i m e n t s w i t h p u r e C 3 A s i n c e t h e y m a y g i v e a c l u e on t h e m e c h a n i s m r e s p o n s i b l e for t h e r e t a r d a t i o n of its h y d r a t i o n by S 0 4 2 - . E x p e r i m e n t a l T h e C a S O 4 . 2 H 2 0 w a s e x M e r c k p r o a n a l y s i . C 3 A , s a m p l e a, h a d 0 . 1 % f r e e C a O a n d B l a i n e s u r f a c e a r e a 0 . 0 7 5 m 2 g - 1 ; s a m p l e b h a d 0 . 3 % f r e e C a O a n d N 2 a d s o r p t i o n s u r f a c e a r e a 0.321 m 2 g -I . T h e s a m p l e s w e r e e i t h e r k e p t in a s e a l e d g l a s s a m p o u l e , or h e a t e d to I 0 0 0 o c f o r 2 h s h o r t l y b e f o r e use. T h e q u a r t z w a s e x R i e d e l de H a h n ; B l a i n e s u r f a c e a r e a 0.60 m 2 g - 1 . On t r e a t i n g w i t h HF + H 2 S O 4 , 0 . 6 % of r e s i d u e r e m a i n e d . It w a s h e a t e d to 1 0 0 0 o c f o r 2 h s h o r t l y b e f o r e use. T h e w a t e r w a s t w i c e d i s t i l l e d , a n d t h e n a g a i n d i s t i l l e d u n d e r r e d u c e d p r e s s u r e s h o r t l y b e f o r e use. T h e c o n d u c t i o n c a l o r i m e t e r , m i x i n g a n d X - r a y d i f f r a c t i o n p r o c e d u r e s w e r e the s a m e as d e s c r i b e d p r e v i o u s l y 4). T h e S E M w a s a C a m b r i d g e M K - 2 A i n s t r u m e n t . T h e h y d r a t i o n r e a c t i o n w a s s t o p p e d by w a s h i n g w i t h a b s o l u t e e t h a n o l a n d d r y i n g in a s t r e a m of n i t r o g e n f r e e d f r o m C O 2. In s o m e c a s e s t h e d r y i n g w a s e f f e c t e d by s u c k i n g a i r t h r o u g h t h e p r e c i p i t a t e in a g l o v e - b o x in an a t m o s p h e r e f r e e of C O 2. R e s u l t s In F i g . 1 h e a t e v o l u t i o n r a t e is p l o t t e d a g a i n s t t i m e f o r p a s t e s w i t h C 3 A s a m p l e b, w e i g h t r a t i o s C 3 A : C a S O 4 . 2 H 2 0 : H 2 0 : S i O 2 = 1 . 5 : 1 . 4 3 : 5 . 0 : z (z in c a p t i o n ) . G r o u p s of t h r e e g r a p h s in t h e s a m e h o r i z o n t a l p o s i t i o n r e f e r to o n e e x p e r i m e n t ; t h e b r e a k s c o r r e s p o n d to s c a l e a d j u s t m e n t s . T h e m a i n f e a t u r e s of F i g . 1 w e r e a l s o s h o w n by p a s t e s w i t h C 3 A : C a S O 4 . 2 H 2 0 : H 2 0 : S i O 2 w e i g h t r a t i o s 1 . 5 : 0 . 7 7 : 5 . 0 : z ( 0 < z < 5 . 0 ) , for b o t h C 3 A s a m p l e s . F o r z~0, t h e e f f e c t s of i n c r e a s i n g q u a r t z c o n t e n t c a n be s u m m a r i z e d as f o l l o w s : I) T h e f i r s t h e a t e v o l u t i o n r a t e p e a k (A) is i n t e n s i f i e d a n d s h i f t e d s l i g h t l y f o r w a r d . 2) A f t e r s o m e t i m e t h e h e a t e v o l u t i o n r a t e d e c r e a s e s f u r t h e r ( s h o r t l y a f t e r s t a g e B). F o r 0 . 8 2 < z < 1 , 6 5 , a p e a k is f o u n d at s t a g e B. A t ~ r g e z v a l u e s the t r a n s i t i o n to t h e l o w h e a t e v o l u t i o n s t a g e C is s m o o t h . 3) T h e t r a n s i t i o n to s t a g e C s t a r t s e a r l i e r , a n d o n c e s t a r t e d is f a s t e r w i t h i n c r e a s i n g z. 4) T h e ~ n a l h e a t e v o l u t i o n p e a k D o c c u r s e a r l i e r . E x p e r i m e n t s w i t h p a s t e s m i x e d in a g l o v e - b o x in an a t m o s p h e r e f r e e of C O 2 d i d n o t s h o w s i g n i f i c a n t d i f f e r e n c e s f r o m
o ~ ~ ~ICqC~A~' z = o o ~ i m 1o ,o io ~ 7, c ~ z J ~ , c i o l o !~1 ~c - - t ~ s m E ,, ~ 10 i0 7o c o " • ~ ' ~ - ~ , o ?s 6 m . ~ o o z 7 ~o [ _ : , 0 m l o ~o . . . ,co 2o c o to o . ~ ~o F I G I
H e a t e v o l u t i o n rate ~8. time for p a s t e s C 3 A + C a S O 4 . 2 H 2 0 + H20 + SiO2, w e i g h t r a t i o s 1.50:1.43: 5.00:z; C 3 A s a m p l e b. The v e r t i c a l bars i n d i c a t e the r e a c t i o n s t a g e s up to w h i c h i n t e g r a t i o n of the c u r v e s was
c a r r i e d out (see text).
t h o s e s h o w n in Fig. I. N e i t h e r had p r e v i o u s s a t u r a t i o n of the w a t e r w i t h C a S O 4 . 2 H 2 0 any i n f l u e n c e . Stage B c o r r e s p o n d s to n e a r l y c o m p l e t e e x h a u s t i o n of the C a S O 4 . 2 H 2 0 . T h i s was f o u n d by X - r a y d i f f r a c t i o n , a g r e e i n g w i t h p r e v i o u s d a t a (2), and by the total e n t h a l p y c h a n g e e x h i b i t e d by the r e a c t i o n to stage B as found by g r a p h i c a l i n t e g r a t i o n of the h e a t
e v o l u t i o n rate curves. In the l a t t e r case, v a l u e s w e r e found in s l i g h t e x c e s s (0.20-0.24 k c a l (g C3A)-I) of the t h e o r e t i c a l v a l u e for total c o n v e r s i o n of C a S O 4 . 2 H 2 0 into e t t r i n g i t e (0.2065 k c a l (g C3A)-I , c a l c u l a t e d f r o m the e n t h a l p i e s of f o r m a t i o n of C3A (5), H 2 0 (6), C a S O 4 . 2 H 2 0 (7) and e t t r i n g i t e (8). This i n d i c a t e s the f o r m a t i o n of some o t h e r p r o d u c t b e s i d e s e t t r i n g i t e . N o p r o d u c t e x c e p t e t t r i n g i t e was f o u n d up to stage C by X - r a y d i f f r a c t i o n , but h y d r a t i o n p r o d u c t s r e s e m b l i n g A F m phases, n o t s h o w i n g the c o r r e s p o n d i n g X - r a y d i f f r a c t i o n l i n e s , h a v e been o b s e r v e d by e l e c t r o n m i c r o s c o p y in o t h e r cases (9, 10, 11). A f t e r stage D, e t t r i n g i t e was still present, in a d d i t i o n to m o n o s u l p h a t e and the 8.2 ~ h e m i c a r b o n a t e , w h i c h is c o n s i d e r e d to be f o r m e d f r o m C 4 A H 1 9 d u r i n g the p r e p a r a t i o n of the sample for X - r a y analysis.
If z = 0, the e n t h a l p y c h a n g e up to stage E (Fig. I) was -0.14 k c a l (g C 3 A ) - I . T h i s i n d i c a t e s i n h o m o g e n e i t y of this paste, b e c a u s e of the h i g h w a t e r / s o l i d s ratio: the C 3 A s e t t l e s m o r e
r a p i d l y t h a n the C a S O 4 . 2 H 2 0 and a SO42- s h o r t a g e a r i s e s n e a r the C 3 A g r a i n s b e f o r e e x h a u s t i o n of the C a S O 4 . 2 H 2 0 . W i t h large z, h o w e v e r , no d e m i x i n g o c c u r e d ; this was c h e c k e d in a s e p a r a t e e x p e r i m e n t w i t h C 3 A (sample b; w e i g h t r a t i o s 1 . 5 : 1 . 4 3 : 5 . 0 : 2 . 9 7 ) , c a r r i e d out in a g l a s s v e s s e l of d i m e n s i o n s s i m i l a r to t h o s e of the c a l o r i m e t e r v e s s e l s . S h o r t l y a f t e r b e i n g m i x e d , the paste had a r e f l e c t i n g top surface, but after 8 m i n u t e s the top s u r f a c e had b e c o m e n o n - r e f l e c t i n g . A p p a r e n t l y , c o a g u l a t i o n c a u s e d the s e d i m e n t v o l u m e to c o i n c i d e p r a c t i c a l l y w i t h the t o t a l paste volume. S e p a r a t e X - r a y a n a l y s e s of top and b o t t o m m a t e r i a l , in a r e a c t i o n stage w h e r e o n l y s m a l l a m o u n t s of C a S O 4 . 2 H 2 0 r e m a i n e d , s h o w e d g o o d m u t u a l a g r e e m e n t . D i s c u s s i o n An i n c r e a s i n g q u a r t z c o n t e n t of the p a s t e has a d i s t i n c t i n f l u e n c e w h i c h , at l e a s t for z>2.97, c a n n o t be a s c r i b e d to c o u n t e r a c t i o n of d e m i x i n g . An e v e r i n c r e a s i n g c o u n t e r a c t i o n of d e m i x i n g w i t h i n c r e a s i n g z m i g h t be h e l d r e s p o n s i b l e for the
294 Vol. 7, No. 3 C. L. M. Holten, H. N. Stein
i n t e n s i f i c a t i o n of the f i r s t p e a k a n d the s h i f t i n g f o r w a r d s of s t a g e B, b u t n o t for the f a c t t h a t the t r a n s i t i o n to s t a g e C, o n c e s t a r t e d , is q u i c k e r (i.e., the h y d r a t i o n of C 3 A is s l o w e d d o w n faster) in the p r e s e n c e of m o r e q u a r t z . The e x p e r i m e n t a l e v i d e n c e a g a i n s t d e m i x i n g at z = 2.97 has a l s o b e e n m e n t i o n e d . T h r e e p o s s i b l e m e c h a n i s m s for the r e t a r d a t i o n of h y d r a t i o n in the p r e s e n c e of S 0 4 2 - w i l l be c o n s i d e r e d :
I. T h e s o l u t i o n b e t w e e n the C 3 A g r a i n s is s a t u r a t e d t o w a r d s the a n h y d r o u s C 3 A , and C 3 A r e a c t s o n l y to the e x t e n t t h a t
r e a c t i o n r e p l a c e s ions w i t h d r a w n f r o m the s o l u t i o n by p r e c i p i t a t i o n of h y d r a t e s . S O 4 2 - l o w e r s the s o l u b i l i t y of C 3 A , c a u s i n g a s l o w e r p r e c i p i t a t i o n of e t t r i n g i t e as c o m p a r e d w i t h the p r e c i p i t a t i o n of A F m p h a s e s f r o m a m e d i u m less r i c h in SO. 2-. H y d r a t e p r e c i p i t a t i o n is the r a t e - d e t e r m i n i n g s t e p (12, 15). II. C 3 A r e a c t s o n l y w h e r e its s u r f a c e is m e t by d i s l o c a t i o n s ; the h y d r a t i o n is a c c o m p a n i e d by m o v e m e n t of the d i s l o c a t i o n s , and ions a d s o r b e d o n t o the s u r f a c e i m p e d e this m o v e m e n t (14).
III. A h y d r a t i o n p r o d u c t , e.g. e t t r i n g i t e (15), f o r m s a p r o t e c t i v e layer.
M e c h a n i s m II is c o n t r a d i c t e d by the fact t h a t q u a r t z has a n y i n f l u e n c e at all. C 3 A and C a S O 4 . ~H20 d i s s o l v e q u i c k l y in w a t e r , as s h o w n by e l e c t r i c a l c o n d u c t i v i t , d a t a in s y s t e m s C 3 A + H 2 0 (16) a n d C 3 A + C a S O 4 . 2 H 2 0 + H 2 0 (17), a n d by the f a c t t h a t no
d i f f e r e n c e is seen b e t w e e n p a s t e s p r e p a r e d w i t h p u r e w a t e r and w i t h w a t e r p r e v i o u s l y s a t u r a t e d t o w a r d s C a S O 4 . 2 H 2 0 . The r e a c t i o n of q u a r t z w i t h the ions c o n c e r n e d is m u c h s l o w e r (quartz has n o i n f l u e n c e on the c o n c e n t r a t i o n s in C 3 A s u s p e n s i o n s d u r i n g the i n i t i a l s t a g e s (16)). Thus, the p r e s e n c e of q u a r t z c a n n o t
r e a s o n a b l y be s u p p o s e d to i n f l u e n c e e i t h e r the c o n c e n t r a t i o n s of ions in the s o l u t i o n , or t h e i r a d s o r p t i o n o n t o the C3A.
M e c h a n i s m I m i g h t a c c o u n t for the i n t e n s i f i c a t i o n of the f i r s t peak, a n d the s h i f t i n g f o r w a r d s of s t a g e B w i t h i n c r e a s i n g z. A l t h o u g h q u a r t z c a n n o t c h a n g e the c o n c e n t r a t i o n s in a
s o l u t i o n s a t u r a t e d t o w a r d s C 3 A and C a S O 4 . 2 H 2 0 , the q u a r t z s u r f a c e s c o u l d f a c i l i t a t e n u c l e a t i o n of h y d r a t e s , t h u s
a c c e l e r a t i n g w h a t is, a c c o r d i n g to t h i s m e c h a n i s m , the r a t e - d e t e r m i n i n g step. H o w e v e r , the f o l l o w i n g a r g u m e n t s are a d d u c e d a g a i n s t m e c h a n i s m I: I) qhe c o n c e n t r a t i o n s in a s o l u t i o n s a t u r a t e d t o w a r d s C~A, as c a l c u l a t e d f r o m t h e r m o d y n a m i c d a t a (18), are at l e a s t 100 t z m e s l a r g e r t h a n t h o s e f o u n d e x p e r i m e n t a l l y in C 3 A + C a S O 4 + H 2 0 s y s t e m s (2). 2) The c o n c e n t r a t i o n s f o u n d e x p e r i m e n t a l l y c o r r e s p o n d to the s o l u b i l i t i e s of the h y d r a t e s . T h e large d i f f e r e n c e b e t w e e n the e n t h a l p i e s of d i s s o l u t i o n of the h y d r a t e s on the one hand, a n d of C 3 A on the other, l e a d to the e x p e c t a t i o n t h a t the s o l u b i l i t y of C 3 A s h o u l d be m u c h l a r g e r t h a n t h o s e of the h y d r a t e s .
3) If s u c h S O 4 2 - c o n c e n t r a t i o n s as are p r e s e n t in a s o l u t i o n s a t u r a t e d t o w a r d s C a S O 4 . 2 H 2 0 w o u l d r e d u c e the s o l u b i l i t y of C 3 A
2- m u s t s t r o n g l y to the e x t e n t r e q u i r e d by the m e c h a n i s m , t h e n SO4
i n c r e a s e the a c t i v i t y c o e f f i c i e n t s of the o t h e r ions p r e s e n t . T h i s is n o t k n o w n in the t h e r m o d y n a m i c s of e l e c t r o l y t e s o l u t i o n s
p r e s e n c e of S 0 4 2 - (19)).
A c c o r d i n g to m e c h a n i s m III, the q u a r t z p r e s e n t s a d d i t i o n a l sites for e t t r i n g i t e c r y s t a l l i z a t i o n and p r e v e n t s f o r m a t i o n of e t t r i n g i t e on the C 3 A surface. This is c o m p a t i b l e w i t h the h e a t e v o l u t i o n rate data; h o w e v e r , e t t r i n g i t e l a y e r s as f o r m e d in h y d r a t i n g p a s t e s a r e too i n c o h e r e n t for c o m p l e t e s c r e e n i n g of the C 3 A (13).
H o w e v e r , t h e r e is no n e e d to a s s u m e such a c o m p l e t e s c r e e n i n g . If e t t r i n g i t e is the sole h y d r a t e formed, and
c o u n t e r a c t s the t r a n s p o r t of ions f r o m the b u l k s o l u t i o n t o w a r d s the v i c i n i t y of the C 3 A s u f f i c i e n t l y for a c o n c e n t r a t i o n g r a d i e n t to e x i s t b e t w e e n those regions, there w i l l arise a local SO42- s h o r t a g e n e a r the C3A. If i n i t i a l l y the s o l u t i o n is s a t u r a £ e d t o w a r d s C a S O 4 . 2 H ~ O , H?O and C a S O 4 r e a c h the C 3 A in a w e i g h t to w e i g h t r a t i o of ~ 0 0 : 1 7 if e t t r i ~ g i t e p r e c i p i t a t e s as the sole h y d r a t e , H20 and C a S O 4 are w i t h d r a w n f r o m the s o l u t i o n in a w e i g h t to w e i g h t r a t i o of 14:1. Thus, p r e d o m i n a n t e t t r i n g i t e f o r m a t i o n leads to a local S O 4 2 - s h o r t a g e n e a r the C3A. N e v e r t h e l e s s , the r e a c t i v i t y of C 3 A is lower than in S O 4 2 - - f r e e pastes. It has b e e n s u g g e s t e d (2) that a m o r p h o u s AI(OH) 3 is f o r m e d b e c a u s e the
e t t r i n g i t e c r y s t a l s t e n d to g r o w f u r t h e r w h e n there is no S O 4 Z - - at hand, w i t h 2OH- r e p l a c i n g SO42- , c a u s i n g a l o c a l l y low pH and Ca 2+ c o n c e n t r a t i o n n e a r the C3A. A l t h o u g h m i x e d c r y s t a l s
C a 6 A I 2 ( O H ) 1 2 ( S O 4 2 - ) ~ ( O H - ) ~ _ 2 5 H 2 0 are n o t k n o w n the e f f e c t
- - X x
s u g g e s t e d here m a y de a s u r f a c e e f f e c t r a t h e r than a b u l k effect. E a r l i e r (2) it was s u p p o s e d that the a m o r p h o u s AI(OH) 3
p r e c i p i t a t e s f r o m solution. H o w e v e r , r e c e n t d a t a on the h y d r a t i o n of C 3 A in N a O H s o l u t i o n s (10, 20) s u g g e s t the f o r m a t i o n of a
d i s t u r b e d s u r f a c e layer on the C 3 A , a p p r o a c h i n g Ca(OH) 2 in
c o m p o s i t i o n , by p r e f e r e n t i a l e x t r a c t i o n of a l u m i n a t e ions f r o m the C 3 A and t h e i r r e p l a c e m e n t by OH-. It w o u l d be m o r e in line w i t h t h e s e d a t a to t h i n k in the p r e s e n t case of a d i s t u r b e d s u r f a c e layer on the C 3 A a p p r o a c h i n g AI(OH) 3 in c o m p o s i t i o n , f o r m e d by p r e f e r e n t i a l e x t r a c t i o n of Ca 2+ and its r e p l a c e m e n t by H +.
The o c c u r e n c e at stage B of a p e a k at small v a l u e s of z, and a q u i c k e r and s m o o t h e r t r a n s i t i o n to stage C at l a r g e r values, can be e x p l a i n e d thus. As long as S042- d i f f u s e s b e t w e e n the e t t r i n g i t e c r y s t a l s t o w a r d s the C 3 A , the e t t r i n g i t e r e m a i n s stable. The SO42- r e p l a c e s OH- in or on e t t r i n g i t e , and the h y d r a t i o n of C 3 A c o n t i n u e s slowly. If, h o w e v e r , no S O 4 2 - r e a c h e s the CqA, the e t t r i n g i t e is c o n v e r t e d into m o n o s u l p h a t e and C 4 A H 1 9 , but n S t C 2 A H 8 (2, 17). If C A A H I ~ p r e c i p i t a t i o n d o m i n a t e s , the pH and Ca 2+ c o n c e n t r a t i o n n e a r ~he ~3 A d e c r e a s e again (Ca 2+ and a l u m i n a t e ions e n t e r the s o l u t i o n in 3:2 m o l a r ratio, but are w i t h d r a w n f r o m it in 2:1 ratio), l e a d i n g to a r a p i d n e w
r e t a r d a t i o n . This w i l l o c c u r when, on e t t r i n g i t e c o n v e r s i o n , l i t t l e SOJ 2- is f r e e d for m o n o s u l p h a t e f o r m a t i o n ; i.e w h e n a large f r a c t i o n of the e t t r i n g i t e is not f o r m e d n e a r the C3A , but on the SiO 2 s u r f a c e s ; i.c. at large z.
S E M e v i d e n c e s u p p o r t e d e t t r i n g i t e f o r m a t i o n on q u a r t z s u r f a c e s and the i n c o h e r e n t c h a r a c t e r of the e t t r i n g i t e l a y e r s n e a r the C 3 A , a l t h o u g h it was d i f f i c u l t to be sure t h a t no a r t e f a c t s w e r e i n t r o d u c e d d u r i n g s a m p l e p r e p a r a t i o n .
The final p e a k (stage D) at z~0 can be u n d e r s t o o d by
296 Vol. 7, No. 3 C. L. M. Holten, H. N. Stein
c o n v e r t e d too, c o n v e r t i n g C 4 A H 1 9 i n i t i a l l y f o r m e d into m o n o s u l p h a t e a n d i n c r e a s i n g local pH n e a r the C3A.
The p r o p o s e d m e c h a n i s m is r e g r e t t a b l y c o m p l i c a t e d , but the c o m p l i c a t e d h e a t e v o l u t i o n rate c u r v e s c a n n o t be e x p l a i n e d by a s i m p l e m e c h a n i s m .
A c k n o w l e d g e m e n t s
We t h a n k M i s s B l i j l e v e n s for a s s i s t e n c e w i t h SEM, and Mr. S p i e r i n g s for p r o v i d i n g one of the C 3 A s a m p l e s .
R e f e r e n c e s
I E.E. S e g a l o v a , E.S. S o l o v ' e v a a n d P.A. R e b i n d e r , Koll. Zh. 23, 194 (1961).
2. H.N. Stein, J. Appl. Chem. (London) 15, 314 (1965).
3. G.D. de Haas, P.C. K r e i j g e r , E . M . M . G . Ni@l, J.C. S l a g t e r , H.N. Stein, E.M. T h e i s s i n g a n d M. v a n W a l l e n d a e l , Cem. C o n c r . Res. 5, 295 (1975).
4. W.A. C o r s t a n j e , H.N. S t e i n a n d J.M. S t e v e l s , Cem. C o n c r . Res. 3, 791 (1973). 5. F. M a s s a z z a a n d M. C a n n a s , Ann. Chim. 51, 904 (1961). 6. M.Kh. K a r a p e t ' y a n t s and M.L. K a r a p e t ' y a n t s , T h e r m o d y n a m i c C o n s t a n t s of I n o r g a n i c a n d O r g a n i c C o m p o u n d s , p. I06, A n n A r b o r - H u m p h r e y S c i e n c e P u b l i s h e r s , A n n A r b o r - L o n d o n (1970). 7. L a n d o l t - B ~ r n s t e i n , Z a h l e n w e r t e u n d F u n k t i o n e n aus P h y s i k , C h e m i e etc., p.211, S p r i n g e r - V e r l a g , B e r l i n etc. 2 (4) (1961). 8. H.A. B e r m a n and E.S. N e w m a n , Proc. 4th Int. Symp. Chem. C e m e n t ,
W a s h i n g t o n 1960, p.247.
9. E. B r e v a l , Cem. Concr. Res. 6, 129 (1976).
10. G . A . C . M . S p i e r i n g s a n d H.N. Stein, Cem. C o n c r . Res. 6, 265 (1976) .
11. P. Gupta, S. C h a t t e r j i a n d J.W. J e f f e r y , Cem. Tech. I--, 59 (1970) .
12. W. Lerch, Proc. Am. Soc. Test. Mat. 46, 1252 (1946). 13. P.K. M e h t a , Cem. Concr. Res. 6, 169 (1976).
14. R.F. F e l d m a n and V.S. R a m a c h a n d r a n , Mag. C o n c r . Res. 18, 185 (1966) .
15. H.N. Stein, Rec. Tray. Chim. P a y s - B a s 81, 881 (1962).
16. H.N. Stein, H i g h w a y R e s e a r c h B o a r d , W a s h i n g t o n , S p e c i a l R e p o r t 90, 368 (1966).
17. W.A. C o r s t a n j e , H.N. S t e i n a n d J.M. S t e v e l s , Cem. C o n c r . Res. 4, 581 (1974).
18. H.N. Stein, Cem. C o n c r . Res. 2, 167 (1972). 19. J . M . T . M . G i e s k e s , Z. P h y s i k . Chem. 50 78 (1966).
20. G . A . C . M . S p i e r i n g s and H.N. Stein, Cem. C o n c r . Res. 6, 487 (1976) .
