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Microstructure of calcium silicate hydrates
Ciach, T. D.; Gillott, J. E.; Swenson, E. G.; Sereda, P. J.
https://publications-cnrc.canada.ca/fra/droits
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https://nrc-publications.canada.ca/eng/view/object/?id=c8c174b7-f27b-4c26-b5dc-3361dfb1e767 https://publications-cnrc.canada.ca/fra/voir/objet/?id=c8c174b7-f27b-4c26-b5dc-3361dfb1e767CEMENT
and
CONCRETE RESEARCH.Vol. 1 ,
pp. 13-25, 1971. Pergamon P r e s s , I n c .
P r i n t e d i n t h e United S t a t e s .
MICROSTRUCTURE O F CALCIUM SILICATE HYDRATES* T . D . C i a c h , J . E . G i l l o t t , E . G . Swenson and P. J. S e r e d a Division of Building R e s e a r c h , National R e s e a r c h Council of C a n a d a
(Communicated by D . M. Roy) ABSTRACT
M o r p h o l o g i c a l and m i c r o s t r u c t u r a l c h a n g e s with t i m e of a h y d r a t - ing C3S paste::* w e r e studied by e l e c t r o n m i c r o s c o p y and x - r a y d i f f r a c t i o n . P r o d u c t s c o n s i s t e d of a m o r p h o u s m a t e r i a l , c r u m p l e d f o i l s , f i b r o u s p a r t i c l e s and p l a t e s . T h e p l a t e s a p p e a r t o have a n underlying m e s h s t r u c t u r e of i n t e r l o c k i n g f i b r e s , t h e s p a c e be
-
tween t h e s e having been f i l l e d with a l i m e - r i c h c a l c i u m s i l i c a t e h y d r a t e o r with c a l c i u m hydroxide. T h e p l a t y m o r p h o l o g y o c c u r s f o r t h e s i l i c a t e h y d r a t e s a s w e l l a s f o r c a l c i u m hydroxide. T h i s study included a l s o p o r t l a n d c e m e n t p a s t e to allow a c o m p a r i s o n with t h e C3S s y s t e m . C o n c l u s i o n s a r e given r e g a r d i n g m e c h a n i c a l p r o p e r t i e s of t h e s e c e m e n t i n g s y s t e m s .SOMMAIRE
L e s c h a n g e m e n t s d a n s l e t e m p s d e l a m o r p h o l o g i e e t de l a m i c r o - s t r u c t u r e d u r a n t l ' h y d r a t i o n d'une pbte de C,S ont 6t6 t t u d i t s a u m i c r o s c o p e Clectronique e t p a r d i f f r a c t i o n X. L e s p r o d u i t s c o m p r e n a i e n t d e s m a t 6 r i a u x a m o r p h e s , d e s f e u i l l e s f r o i s s t e s , d e s p a r t i c u l e s f i b r e u s e s e t d e s p a i l l e t t e s . C e s p a i l l e t t e s a v a i e n t une s t r u c t u r e de m a i l l e s de f i b r e s e n c l e n c h g e s e t l ' e s p a c e e n t r e l e s f i b r e s paral't r e m p l i d'une f o r m e de s i l i c a t e de c a l c i u m hydratC r i c h e e n c h a u x ou d'hydroxyde de c a l c i u m . L a m o r p h o - logie en p a i l l e t t e s a l i e u a u s s i bien d a n s l e s s i l i c a t e s h y d r a t t s que d a n s l'hydroxyde de c a l c i u m . C e t t e Ctude c o m p r e n d Cgale- m e n t l a pbte de c i m e n t p o r t l a n d afin de p e r m e t t r e une c o m p a r a i -
son a v e c l e syst'eme de C3S. L e s c o n c l u s i o n s sont t i r 6 e s c o n c e r n a n t l e s p r o p r i C t e s m 6 c a n i q u e s de c e s s y s t k m e s d e c i m e n t a t i o n . :: P r e s e n t e d a t t h e C e m e n t S y m p o s i u m of t h e A m e r i c a n C e r a m i c Society, 72 Annual Meeting P h i l a d e l p h i a , M a y 1970. $::Standard c e m e n t n o m e n c l a t u r e i s u s e d ; e . g. C3S = 3CaO.Si0, ; W/C = w a t e r : c e m e n t r a t i o by weight.
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M I C R O S T R U C T U R E , C A L C I U M - S I L I C A T E - H Y D R A T E , M O R P H O L O G Y
Vol. 1 , No. 1
Introduction
T h e o b j e c t of t h e p r e s e n t w o r k i s t o e l u c i d a t e t h e m i c r o s t r u c t u r e an$ n a t u r e of t h e h y d r a t i o n p r o d u c t s of p o r t l a n d c e m e n t , t h e chief component of which i s c a l c i u m s i l i c a t e h y d r a t e . T h i s m i c r o s t r u c t u r e i s thought t o be. a k e y t o a b e t t e r u n d e r s t a n d i n g of the p h y s i c a l and m e c ' h a h i c a l p r o p e r t i e s of t h e c e m e n t .
M a n y a u t h o r s ( 1
-
20) have studied the s t r u c t u r e and m o r p h o l o g y of CSH ( c a l c i u m s i l i c a t e h y d r a t e ) . S o m e have p r e s e n t e d evidence f o r t h e s e m i c r y s - t a l l i n e f i b r o u s f o r m s of the h y d r a t i o n p r o d u c t s , and o t h e r s ( 5-
7 ) have d i s - c u s s e d the f i b r o u s p a r t i c l e s which a p p e a r a s b u n d l e s , a g g r e g a t e s , and s o m e - t i m e s a s s h e e t s having a n i n t e r l o c k i n g s t r u c t u r e o r i e n t e d in t h r e e d i r e c t i o n s a t a n angle of about 60". But n e i t h e r t h e i n t e r r e l a t i o n between t h e v a r i o u s o b s e r v e d s h a p e s of p a r t i c l e s , n o r t h e i r r o l e i n t h e f o r m a t i o n of t h e f i n a l m i c r o s t r u c t u r e of h a r d e n e d p a s t e , have been e s t a b l i s h e d . T h e f i n a l f o r m of t h e m i c r o s t r u c t u r e of c e m e n t p a s t e a f t e r long h y d r a t i o n t i m e , a p p e a r i n g a s c l e a v e d t a b u l a r m a s s e s h a s often b e e n identified a s c a l c i u m hydroxide.R e c e n t w o r k i n t h e l a b o r a t o r i e s of DB@RC h a s involved t h e s t u d y of t h e c h a n g e s i n m o r p h o l o g y of t h e h y d r a t i o n p r o d u c t s of the v a r i o u s p u r e c o n - s t i t u e n t s , singly and i n c o m b i n a t i o n s , a s w e l l a s of c e m e n t p a s t e . A s p a r t of t h i s s t u d y t r i e t h a n o l a m i n e and o t h e r compounds w e r e included t o o b s e r v e the e f f e c t s of a d d i t i v e s on p o r t l a n d c e m e n t . T h i s p a p e r i s c o n c e r n e d with m i c r o - s t r u c t u r e ; a s e p a r a t e s e r i e s of p a p e r s will d e a l with s p e c i f i c m o r p h o l o g i c a l c h a n g e s o c c u r r i n g with d i f f e r e n t c o m b i n a t i o n s of the c o n s t i t u e n t s . E x p e r i m e n t a l M e t h o d s C h a n g e s with t i m e i n t h e m o r p h o l o g y and n a t u r e of t h e h y d r a t i o n p r o d u c t s of c e m e n t and C3S p a s t e , of 0. 5 w a t e r t o c e m e n t r a t i o , w e r e studied by e l e c t r o n m i c r o s c o p y , x - r a y and e l e c t r o n d i f f r a c t i o n . T h e m i c r o s t r u c t u r e w a s examined a t d i f f e r e n t i n t e r v a l s of h y d r a t i o n .from 5 m i n u t e s t o 6 m o n t h s . The hydration w a s stopped by t r e a t i n g the s a m p l e
with a c e t o n e a t - 1 8 ° C and d r y i n g i n vacuum. S i n g l e - s t a g e r e p l i c a s f r o m the f r e s h l y b r o k e n s u r f a c e s of c e m e n t and C3S p a s t e w e r e m a d e using t h e
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p l a t i n u m - c a r b o n technique ( 1
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5 ) . The m i c r o s t r u c t u r e of 6 - m o n t h - o l d s a m - p l e s w a s m o r e c l e a r l y r e v e a l e d by etching t h e s a m p l e s u r f a c e with ethylene glycol. T h e effect of etching on h y d r a t i o n p r o d u c t s w a s a l s o studied by x - r a y d i f f r a c t i o n .R e s u l t s
In p o r t l a n d c e m e n t p a s t e t h e i n i t i a l p r o d u c t s of h y d r a t i o n a r e a m o r - phous -looking thin f o i l s and f i b r o u s p a r t i c l e s ( F i g . 1 ) . T h e s e p r o d u c t s a p p e a r m a i n l y on the s u r f a c e of u n h y d r a t e d g r a i n s , filling i n void s p a c e s a s t h e y g r o w . T h e f i b r e s b r i d g e u n h y d r a t e d g r a i n s , often m e e t i n g a t about 6 0 " a n g l e s ( F i g . 2 ) , and c r e a t i n g a n i n t e r l o c k i n g m e s h . S p a c e between f i b r e s b e c o m e s f i l l e d in s o t h a t t h e f i n a l p r o d u c t s a r e p l a t e s with m a r k e d c l e a v a g e ( F i g ; 3 ) . S u r f a c e s of t h e p l a t e s often r e v e a l t h e u n d e r l y i n g f i b r o u s s t r u c t u r e . T h i s p a p e r w i l l a t t e m p t t o e s t a b l i s h t h e r e l a t i o n between t h e i n i t i a l p r o d u c t s ,
a p p e a r i n g a s f i b r e s and thin s h e e t s , and the f i n a l , t a b u l a r , m a s s i v e s t r u c t u r e . It w a s believed t h a t the v i t a l s t e p s i n t h e f o r m a t i o n of t h e f i n a l m i c r o - s t r u c t u r e of p o r t l a n d c e m e n t would be b e s t r e v e a l e d by studying t h e e s s e n t i a l c o n s t i t u e n t s individually. F o r t h i s r e a s o n t h e f o r m a t i o n of t h e m i c r o s t r u c - F I G . 1 F I G . 2 C e m e n t p a s t e , W/C = 0. 5, 3 d a y s C e m e n t p a s t e , W/C = 0 . 5, 3 d a y s h y d r a t i o n . F i b r o u s h y d r a t i o n p r o d - h y d r a t i o n . F i b r o u s p a r t i c l e s f o r m - u c t s with i n t e r l o c k i n g a r r a n g e m e n t . ing c r i s s - c r o s s connection between
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F I G . 3 F I G . 4
C e m e n t p a s t e , W/C = 0. 5, 28 days C3S p a s t e , W/C = 0 . 5 , 7 days hydration. Close - t e x t u r e d , t a b u l a r , hydration. S e m i c r y s t a l l i n e f i b r e s m a s s i v e s t r u c t u r e composed of of c a l c i u m s i l i c a t e h y d r a t e covering p l a t e s which show cleavage and unhydrated g r a i n s .
s t r i a t e d a p p e a r a n c e
F I G . 5 F I G . 6
C3S p a s t e , W/C = 0. 5, 1 m o n t h C3S p a s t e , W/C = 0. 5, 1 m o n t h hydration. Hydration product show- hydration. Hydration products show- ing cleavage and p a r a l l e l cleavage ing f i b r o u s s t r u c t u r e m e r g i n g into f a c e ; the interlocking a r r a n g e m e n t p l a t e s m a d e up of f i b r e s i n t e r s e c t i n g of f i b r e s in t h i s f a c e i s evident. a t a p p r o x i m a t e l y 60" a n g l e s .
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t u r e d u r i n g the h y d r a t i o n i n C,S p a s t e w a s studied i n g r e a t d e t a i l and the e s s e n t i a l o b s e r v a t i o n s a r e p r e s e n t e d h e r e . D u r i n g t h e f i r s t 7 d a y s of h y d r a t i o n , t h e s u r f a c e of the C3S g r a i n s b e - c a m e c o v e r e d by r a d i a t i n g f i b r o u s p a r t i c l e s of c a l c i u m s i l i c a t e h y d r a t e ( F i g . 4 ) . T h e s e f o r m e d a n i n t e r l o c k i n g m e s h i n the s p a c e between g r a i n s . A s t i m e of h y d r a t i o n i n c r e a s e d , t h e f i b r o u s s t r u c t u r e developed into a p l a t y f o r m ( F i g s . 5 and
6 )
s i m i l a r in a p p e a r a n c e to t h a t o b s e r v e d i n c e m e n t ( F i g . 3 ) , although t h e f i b r o u s s t r u c t u r e of t h e p l a t e s i n C3S p a s t e w a s c l e a r - e r than t h a t s e e n in p o r t l a n d c e m e n t . T h e t r i a n g u l a r d i s p o s i t i o n of the f i b r e s i s c l e a r l y s e e n in F i g u r e6.
A f t e r6
m o n t h s ' h y d r a t i o n , t h e p a s t e d i s p l a y e d a m a s s i v e t a b u l a rs t r u c t u r e w i t h platy and o c c a s i o n a l l y f i b r o u s h y d r a t i o n p r o d u c t s between l e s s well-defined m a s s e s which a p p e a r e d like p s e u d o m o r p h s of g r a i n s of C3S ( F i g . 7 ) . E t c h i n g of t h i s t a b u l a r m a t e r i a l f o r h r w i t h ethylene g l y c o l r e v e a l e d t e x t u r a l d e t a i l s . A s shown i n F i g u r e 8 the a p p e a r a n c e w a s s t r i k - ingly s i m i l a r t o t h a t of C 3 S i n e a r l y s t a g e s of h y d r a t i o n ( F i g . 4 ) . P l a t y h y d r a t i o n p r o d u c t s c o r r o d e d by g l y c o l d i s p l a y e d a pseudohexagonal f o r m r e s u l t i n g f r o m t h e i r u n d e r l y i n g f i b r o u s s t r u c t u r e ( F i g s 9 and 10). F o r c o m p a r i s o n a s t u d y w a s m a d e of a n e t c h e d s u r f a c e of n a t u r a l t o b e r m o r i t e f r o m Skye. It showed t h a t the g l y c o l a l s o a t t a c k e d the n a t u r a l c r y s t a l l i n e f o r m of c a l c i u m s i l i c a t e h y d r a t e and r e v e a l e d t h e pseudohexagonal platy
s t r u c t u r e ( F i g . 1 1 ) .
X - r a y d i f f r a c t o g r a m s showed t h a t the g l y c o l r e a c t e d w i t h a l l t h e h y d r a t - ion p r o d u c t s of C,S although a t d i f f e r e n t r a t e s . P e a k s a t t r i b u t e d t o both Ca(OH), and C -S-H w e r e m a r k e d l y weakened; s o m e of t h e p e a k s , p a r t i c u l a r l y t h o s e a t about 3.07A, w e r e b r o a d e n e d . T h i s m a y have b e e n the r e s u l t of s m a l l c r y s t a l l i t e s i z e , o r i n t e r n a l r e s i d u a l s t r e s s i n the c r y s t a l s , o r of both. E t c h i n g a p p e a r s to have d e c r e a s e d t h e c r y s t a l l i n i t y of t h e m a t e r i a l w h i c h
r e m a i n e d a f t e r glycol t r e a t m e n t ( F i g . 1 2 ) .
In a s t u d y c o n c e r n e d w i t h the effect of t r i e t h a n o l a m i n e additive on t h e m o r p h o l o g y of C,S h y d r a t i o n p r o d u c t s , i t w a s o b s e r v e d t h a t the s t e p s i n the d e v e l o p m e n t of m i c r o s t r u c t u r e w e r e m o r e c l e a r l y defined; t h e e s s e n t i a l
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FIG. 7 FIG. 8
C3S p a s t e , W/C = 0. 5, 6 m o n t h s h y d r a - C,S p a s t e , W/C = 0. 5, 6 m o n t h s tion. M a i n h y d r a t i o n p r o d u c t i s m a s - h y d r a t i o n . E t c h e d with glycol
$
h o u r .s i v e t a b u l a r s t r u c t u r e showing s t r o n g P l a t y f o r m of h y d r a t i o n p r o d u c t d i s
-
p a r a l l e l c l e a v a g e . T h e t a b u l a r m a s s e s p l a y s f i b r o u s m o r p h o l o g y . connect t o g e t h e r l e s s d e f i n e d m a s s e s a p p e a r i n g a s p s e u d o m o r p h s of u n h y d r a - t e d g r a i n s . FIG.9
F I G . 10 C,S p a s t e , W/C = 0. 5, 6 m o n t h s C3S p a s t e , W/C = 0. 5, 6 m o n t h s h y d r a t i o n . E t c h e d with g l y c o l$
h y d r a t i o n . E t c h e d with g l y c o l h o u r . h o u r . P s e u d o h e x a g o n a l p l a t e s I n t e r g r o w i n g f i b r e s of h y d r a t i o n c o m p o s e d of i n t e r l o c k i n g f i b r e s p r o d u c t a r e s e e n f o r m i n g the t a b u l a r m e e t i n g a t about 60". m a s s e s .Vol. 1 , No. 1
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FIG. 11 - 5 4 5 0 4 6 4 2 3 8 3 4 3 0 26 2 2 1 8 14 20 F I G . 12 N a t u r a l t o b e r m o r i t e f r o m Skye e t c h - X - r a y d i f f r a c t o g r a r n s of C3S p a s t e , 1 e d by glycol f o r
z
h o u r . M i n e r a l W/C = 0. 5, 180 d a y s h y d r a t e d . d i s p l a y s f i b r e s with i n t e r s e c t i o n s f o r m i n g pseudohexagonal angle. f e a t u r e s a r e p r e s e n t e d h e r e t o add t o t h e u n d e r s t a n d i n g of t h e m i c r o s t r u c - t u r e of c e m e n t p a s t e . A full r e p o r t on t h i s study will b e p r e s e n t e d l a t e r .T h e p r o d u c t s d u r i n g t h e e a r l y s t a g e s of h y d r a t i o n of C,S with t r i e t h a n o l a m i n e additive w e r e r a d i a t i n g f i b r e s and s h e e t s of f i b r o u s s t r u c t u r e between u n h y d r a t e d g r a i n s ( F i g . 13). T h e m o r p h o l o g y w a s v e r y s i m i l a r t o t h a t shown in F i g u r e 10. T h e f i b r o u s t e x t u r e of t h e u n o r i e n t e d i n t e r g r o w i n g p l a t e s i s shown v e r y c l e a r l y i n F i g u r e 14. A f t e r about 1 m o n t h of h y d r a t i o n t h e f i b r o u s t e x t u r e w a s s t i l l v i s i b l e on the s u r f a c e of p l a t e s , which s o m e - t i m e s d i s p l a y e d pseudohexagonal m o r p h o l o g y ( F i g s . 1 5 and 16). F i g u r e 17 shows m o s t c l e a r l y how t h e f i b r o u s h y d r a t i o n p r o d u c t s f o r m e d t h e p l a t e s . The p l a t e s had p a r a l l e l o r i e n t a t i o n and w e r e s t a c k e d t o f o r m t h e t a b u l a r m a s s e s .
F r o m t h e s e r e s u l t s i t i s c l e a r t h a t t h e pseudohexagonal m o r p h o l o g y r e s u l t e d f r o m t h e t r i a n g u l a r d i s p o s i t i o n of the f e l t e d f i b r e s of c a l c i u m s i l - i c a t e h y d r a t e . T h e p l a t y m o r p h o l o g y would s e e m t o have been t h e r e s u l t of infilling between f i b r e s .
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FIG. 1 3 F I G . 14
C3S p a s t e , with 0 . 570 t r i e t h a n o l a m i n e , C3S p a s t e w i t h 0 . 5% t r i e t h a n o l a m i n e , W/C = 0 . 5, 1 day hydration. M a i n hy- W/C = 0. 5 , 2 d a y s hydration. Hy- d r a t i o n product a p p e a r s a s r a d i a t i n g d r a t i o n p r o d u c t s a p p e a r a s i n t e r g r o w - f i b r e s and u n o r i e n t e d i r r e g u l a r s h e e t s ing p l a t e s o r s h e e t s composed of (which s o m e t i m e s d i s p l a y f i b r o u s t e x - i n t e r l o c k i n g f i b r o u s s t r u c t u r e . t u r e ) between unhydrated g r a i n s .
F I G . 1 5 FIG. 16
C3S p a s t e with 0 . 5% t r i e t h a n o l a m i n e , C B S p a s t e with 0. 5% t r i e t h a n o l a m i n e , W/C = 0. 5, 2 m o n t h s hydration. Fi- W / C = 0. 5, 2 m o n t h s hydration. Hy- b r ~ u s h ~ d r a t i o n p r o d u c t s f o r m t h e u n - d r a t i o n p r o d u c t s s h o w f i b r o u s t e x t u r e d e r l y i n g s t r u c t u r e of p l a t e s which in and pseudohexagonal morphology. t u r n a r e s t a c k e d a s p a r a l l e l l a y e r s
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FIG. 17 C,S p a s t e with 0. 5% t r i e t h a n o l a m i n e , W/C = 0. 5, 3 m o n t h s hydration. Hydration p r o d u c t s d i s p l a y a n i n t e r l o c k i n g m e s h of f i b r e s giving a p s e u d o - hexagonal p l a t e m o r p h o l o g y t o t h e c a l c i u m s i l i c a t e h y d r a t e . T r i e t h a n o l a m i n e a c c e l e r a t e d t h e h y d r a t i o n of C,S. P r e s e n t w o r k showed t h a t when t h i s additive i s u s e d it a l s o c a u s e d t h e m o r p h o l o g y of t h e h y d r a t i o n p r o d u c t s t o b e m o r e c l e a r l y defined.2 2
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D i s c u s s i o n
M a n y o t h e r w o r k e r s have o b s e r v e d and r e p o r t e d t h e v a r i o u s f o r m s of h y d r a t i o n p r o d u c t s of p o r t l a n d c e m e n t and C3S, d e s c r i b e d a s c r u m p l e d f o i l s , f i b r o u s p a r t i c l e s and p l a t e s , but n o evidence h a s b e e n p r e s e n t e d t o show the i n t e r r e l a t i o n between t h e m and t h e s t e p s involved i n t h e f o r m a t i o n of t h e f i n a l m i c r o s t r u c t u r e . T h i s study t a k e s evidence f r o m t h e h y d r a t i o n of p o r t l a n d
c e m e n t p a s t e , C3S, and C3S with t r i e t h a n o l a m i n e p a s t e t o provide t h i s m i s s
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ing link. The i n i t i a l h y d r a t i o n p r o d u c t s of C3S f o r m e d i n t h i s condition w e r e v e r y p o o r l y c r y s t a l l i z e d c a l c i u m s i l i c a t e h y d r a t e s i n t h e f o r m of c r u m p l e d f o i l s , f i b r o u s p a r t i c l e s and p l a t e s . T h e s e f o r m s w e r e m o s t often o b s e r v e d and r e p o r t e d when p o r t l a n d c e m e n t and C3S g r a i n s w e r e allowed t o h y d r a t e i n e x c e s s w a t e r (1.- 10).In t h e e a r l y s t a g e s of h y d r a t i o n t h e u n h y d r a t e d g r a i n s of c e m e n t o r C3S a r e r e a d i l y identified. When h y d r a t i o n i s n e a r l y c o m p l e t e d t h e s p a c e o c c u p - i e d by unhydrated g r a i n s s e e m s to be r e p l a c e d by p s e u d o m o r p h s ( F i g . 7 ) of n o p a r t i c u l a r distinguishable morphology; t h e y m a y w e l l be c o m p o s e d of t h e s a m e m a t e r i a l t h a t f i l l s the s p a c e between the i n t e r l o c k i n g f i b r o u s p a r t i c l e s .
C e m e n t i t i o u s m a t e r i a l between p s e u d o m o r p h s and g r a i n s of p a r t l y h y d r a t e d c e m e n t o r C,S c o n s i s t s of t a b u l a r m a s s e s c o m p o s e d of platy h y d r a - tion p r o d u c t s ( F i g s . 3 , 7, 1 5 and 1 6 ) . B e c a u s e of i t s m o r p h o l o g y and c l e a v - a g e t h i s h a s commonly b e e n r e g a r d e d a s Ca(OH),
.
A s shown by t h e p r e s e n t w o r k ( F i g . 1 7 ) , h o w e v e r , t h e s e p l a t e s a p p e a r t o have a n u n d e r l y i n g p s e u d o - hexagonal m e s h s t r u c t u r e of i n t e r l o c k i n g o r f e l t e d f i b r e s . T h e s e f i b r e s f r e q u e n t l y i n t e r s e c t one a n o t h e r with a n a p p r o x i m a t e i s o s c e l e s - t r i a n g l e type of a r r a n g e m e n t . The s p a c e between f i b r e s b e c o m e s f i l l e d with a n a p p a r e n t l y a m o r p h o u s m a t e r i a l c o m p o s e d of e i t h e r a l i m e - r i c h f o r m of c a l c i u m s i l i c a t e h y d r a t e o r c a l c i u m hydroxide. The infilling m a t e r i a l w a s g e n e r a l l y m o r e s u s c e p t i b l e t o etching by glycol t h a n w e r e t h e f i b r e s . The above evidence t h a t t h e C -S-H m a t e r i a l h a s varying f o r m s and m o r p h o l o g y and even d i f f e r e n t r e s p o n s e t o etching by glycol, l e a d s t o t h e c o n c l u s i o n t h a t the h y d r a t i o n p r o d - u c t s cannot be r e g a r d e d a s s e p a r a t e c r y s t a l l i n e p h a s e s of f i x e d s t o i c h i o m e t r i c c h e m i c a l composition, but r a t h e r , a r e s o l i d solutions of c a l c i u m s i l i c a t eVol.
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i d e a s p r e s e n t e d by T a y l o r ( 1 2 ) and the evidence of D. M . Roy (13) showing that the C a / s i r a t i o v a r i e s within the hydrated product.
Morphological evidence that the hydration products a r e of poor c r y s - tallinity i s supported by x - r a y and e l e c t r o n diffraction data. Only ab -plane reflections w e r e detected f r o m the calcium s i l i c a t e h y d r a t e s . The absence of a definite c - a x i s spacing f o r the calcium silicate h y d r a t e s suggests that C a , OH and H 2 0 m a y be held in s h e e t s of CSH of variable thickness and poor crystallinity. Analogous situations a r e known in s o m e of the clay m i n e r a l s where monoclinic and t r i c l i n i c s t r u c t u r e s of pseudohexagonal s y m m e t r y e x i s t
The s a m e morphological f o r m of c a l c i u m s i l i c a t e hydrate a s found in the products of C,S hydration was a l s o found in hydrated cement. This s y s t e m i s , however, m u c h m o r e complex because of the m o r e v a r i a b l e composition.
F r o m the standpoint of m e c h a n i c a l p r o p e r t i e s of hydrated c e m e n t , the m i c r o s t r u c t u r e of the cementing s y s t e m i s r e a l l y a composite m a t e r i a l i n which a f i b r o u s network i s imbedded in an amorphous m a t e r i a l . Such a
s t r u c t u r e should provide a m a t e r i a l having v e r y good m e c h a n i c a l p r o p e r t i e s ; the high c o m p r e s s i v e s t r e n g t h of the dense (low p o r o s i t y ) hydrated cement m a y well be a reflection of t h i s . It would be expected that the t e n s i l e s t r e n g t h of such a composite would be high a l s o , but such i s not the c a s e and g e n e r a l l y the t e n s i l e s t r e n g t h i s only 1/10 that of the c o m p r e s s i v e strength. To account f o r t h i s , the work p r e s e n t e d h e r e shows that the m a s s e s of the cementing m a t e r i a l appearing a s t a b u l a r s t r u c t u r e s a r e not usually interconnected with
e a c h other but r a t h e r a r e joined t o a r e a s r e p r e s e n t i n g the o r i g i n a l unhydrated g r a i n s (pseudomorphs, e t c . ), s o that what might be c o n s i d e r e d a s i n t e r p a r t i - cle connections m u s t be defined a s m a t e r i a l that apparently l a c k s the r e i n - f o r c e m e n t of the f i b r e s .
Conclusions
The m o s t i m p o r t a n t conclusions f r o m the p r e s e n t work a r e a s follows: 1. T h e m a i n products of C,S hydrated under t h e s e conditions cannot be r e
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g a r d e d a s c r y s t a l l i n e components of s t o i c h i o m e t r i c c h e m i c a l composition; rather, they a r e solid solutions of c a l c i u m s i l i c a t e h y d r a t e s and calcium hydroxide.Y o l . 1 ,
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2 . A p l a t y m o r p h o l o g y i s n o t a r e l i a b l e c r i t e r i o n f o r t h e identification of Ca(OH), a s a h y d r a t i o n p r o d u c t b e c a u s e t h e f i n a l m o r p h o l o g y of c a l c i u m s i l i c a t e h y d r a t e s i s a l s o p l a t e -like.
3. T h e , p l a t e s of c a l c i u m s i l i c a t e h y d r a t e a r e b a s e d upon a s k e l e t a l s t r u c t u r e of f i b r e s which have a pseudohexagonal a r r a n g e m e n t .
4. T h e s a m e p l a t y m o r p h o l o g y of c a l c i u m s i l i c a t e h y d r a t e i s a l s o found i n h y d r a t e d c e m e n t p a s t e .
5. T h e h y d r a t i o n p r o d u c t s , a s s e m b l e d i n t o t a b u l a r s t r u c t u r e s , a c t a s c e m e n t i n g a g e n t s , fir s t between a d j a c e n t u n h y d r a t e d g r a i n s and s u b s e q u e n t l y b e t w e e n p s e u d o m o r p h s w h e r e u n h y d r a t e d g r a i n s had been. 6. T h e p s e u d o m o r p h s s e e m t o have no definite m o r p h o l o g i c a l s t r u c t u r e ; t h e y a r e s u s p e c t e d t o h a v e a c o m p o s i t i o n s i m i l a r t o t h a t of t h e infilling m a t e - r i a l . 7. T h e c e m e n t i n g s y s t e m c o n s i s t s of a c o m p o s i t e m a t e r i a l i n which a f i b r o u s n e t w o r k i s e m b e d d e d i n a n a m o r p h o u s m a t r i x (infilling m a t e r i a l ) . T h i s m a t e r i a l i t s e l f i s e x p e c t e d t o h a v e e x c e l l e n t m e c h a n i c a l p r o p e r t i e s ; t h e i n t e r p a r t i c l e c o n n e c t i o n s , h o w e v e r , s e e m t o be m a d e u p of t h e p s e u d o m o r p h s of t h e infilling m a t e r i a l ( m a t r i x ) a n d do n o t have t h e r e i n f o r c e m e n t of t h e f i b r e s . Acknowledgements
We acknowledge g r a t e f u l l y t h e invaluable c o n t r i b u t i o n of M r . E . Quinn i n p r e p a r i n g r e p l i c a s f r o m t h e s a m p l e s f o r e l e c t r o n m i c r o s c o p i c e x a m i n a t i o n . T O P o r t l a n d C e m e n t A s s o c i a t i o n f o r supplying t h e p u r e c o n s t i t u e n t s of c e m e n t we a r e a l s o m o s t g r a t e f u l .
T h i s p a p e r i s a contribution f r o m t h e D i v i s i o n of Building R e s e a r c h , National R e s e a r c h C o u n c i l of Canada. and i s published w i t h t h e a p p r o v a l of the D i r e c t o r of t h e Division.
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