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A study of mechanical properties of autoclaved calcium silicate
systems
Beaudoin, J. J.; Feldman, R. F.
https://publications-cnrc.canada.ca/fra/droits
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CEMENT and CONCRETE RESEARCH. Vol. 5, p p . 103-1 18, 1975. 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 MECHANICAL P R O P E R T I E S O F AUTO CLAVED CALCIUM SILICATE SYSTEMS
J. J. Beaudoin and R , F. F'eldman, 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 Council of Canada, Ottawa, Canada
(Communicated by
D.
M.
Roy)(Received Aug. 21, 1974; i n f i n a l f o r m Nov. 7, l a 7 4 ) ABSTRACT:
C o m p r e s s i v e s t r e n g t h , modulus of e l a s t i c i t y , and m i c r o h a r d - n e s s m e a s u r e m e n t s w e r e made o n a v a r i e t y of autoclaved c e m e n t - s i l i c a p r e p a r a t i o n s covering a wide r a n g e of porosity. A s p e c t r u m of l i n e a r log m e c h a n i c a l p r o p e r t y - p o r o s i t y functions w a s o b s e r v e d . A n a l y s i s d e m o n s t r a t e d t h a t the s l o p e s of t h e s e functions w e r e dependent on the p r e p a r a t i o n s i l i c a content and d e n s i t y of the h y d r a t e d product. T h e s l o p e s of the l i n e s f o r ' e a c h m e c h a n i c a l p r o p e r t y b o r e a c o n s t a n t r a t i o with s l o p e s c a l c u l a t e d f r o m the c o r r e s p o n d i n g l i n e s of the o t h e r two m e c h a n i c a l p r o p e r t i e s . T h i s r e s u l t e d in e x p r e s s i o n s i n t e r r e l a t i n g m e c h a n i c a l p r o p e r t i e s which w e r e independent of p o r o s i t y and valid f o r a l l p r e p a r a t i o n s studied. C o m p r e s s i v e s t r e n g t h and m i c r o h a r d n e s s f o r p r e p a r a t i o n s studied w e r e shown to be d i r e c t l y r e l a t e d .
L a r C s i s t a n c e
5
l t C c r a s e m e n t , l e module dtClasticitC e t l am i c r o d u r e t e d l u n a s s o r t i m e n t de p r h p a r a t i o n s c i m e n t - s i l i c e autoclave f u r e n t dCter minCs pour une g r a n d e g a m m e de p o r o - sitC. Un s p e c t r e d e fonctions l i n e a i r e s
5
b a s e l o g a r i t h m i q u epropriCtC m h c a n i q u e - p o r o s it6 fut cons tati:. Une a n a l y s e a dCmontrC que l e s pentes de c e s fonctions d t p e n d a i e n t de l a t e n e u r en s i l i c e de l a p r C p a r a t i o n et d e l a d e n s i t 6 d u produit hydratC. L e s p e n t e s d e s c o u r b e s pour chaque propriCt6 mkcanique ont maintenu un r a p p o r t c o n s t a n t aux p e n t e s c a l - culCes
>
p a r t i r d e s c o u r b e s c o r r e s p o n d a n t e s d e s d e u x a u t r e s propriCtCs mCcaniques. I1 e n rCsulta d e s e x p r e s s i o n s r e l i a n t e n t r e e l l e s l e s propriCtCs mhcaniques q u i Ctaient indhpendentes d e l a porositC et v a l a b l e s pour toutes l e s p r C p a r a t i o n s CtudiCes. I1 fut dCmontrC que l a r g s i s t a n c e5
1 ' C c r a s e m e n t e t l a m i c r o - dureti: d e s p r C p a r a t i o n s CtudiCes Ctaient d i r e c t e m e n t r e l i k e sl l u n e
>
l t a u t r e .J . J .
Beaudoin, R. F . Feldrnan Vol.5,
No.2
C o m p r e s s i v e s t r e n g t h , modulus of e l a s t i c i t y a n d m i c r o h a r d n e s s a r e m e c h a n i c a l p r o p e r t i e s t h a t have b e e n s h o w n to be p o r o s i t y dependent for r o o m t e m p e r a t u r e hydrated c e m e n t p a s t e ( 1 to 5). R e c e n t w o r k (6, 7 ) cites p o r o s i t y , morphology and c r y s t a l bonding a s contributing to the m e c h a n i c a l behaviour of autoclaved and r o o m t e m p e r a t u r e h y d r a t e d paste. It a p p e a r s that although p o r o s i t y i s a m a j o r f a c t o r c o n t r o l l i n g m e c h a n i c a l behaviour of p o r o u s c e m e n t h y d r a t e s o t h e r f a c t o r s a l s o play a r o l e .
T h e c h e m i s t r y of autoclaved p a s t e s with and without q u a r t z ( s i l i c a ) additions h a s b e e n studied by v a r i o u s i n v e s t i g a t o r s ( 8 to 14); the p r i n c i p a l p r o d u c t s , depending on i n i t i a l p r o p o r t i o n s of c e m e n t and s i l i c a , a r e c r y s -
e
t a l l i n e a C S h y d r a t e , 11A t o b e r m o r i t e , p o o r l y c r y s t a l l i z e d t o b e r m o r i t e
2
(CSH(1) and CSH(I1)) and s o m e t i m e s h i l l e b r a n d i t e and xonotlite.
A s y s t e m a t i c study of the m e c h a n i c a l p r o p e r t i e s of the c e m e n t - s i l i c a s y s t e m u n d e r autoclaved conditions on a p o r o s i t y b a s i s may h e l p i n elucidat- ing the c o n t r i b u t o r y r o l e of morphology, c r y s t a l bonding and c h e m i s t r y of the h y d r a t i o n p r o d u c t a s c h a r a c t e r i z e d by s o l i d d e n s i t y ; this s y s t e m i s e s p e c i a l l y good f o r t h i s type of study b e c a u s e of the w i d e v a r i a t i o n p o s s i b l e i n p o r e d i s t r i b u t i o n and morphology. M i n d e s s (15) s t u d i e d s t r e n g t h porosity r e l a t i o n s h i p s f o r autoclaved l i m e - s i l i c a m i x t u r e s but a s s u m e d a c o n s t a n t v a l u e f o r the s o l i d d e n s i t y i n calculating p o r o s i t y making any a s s e s s m e n t of r e s u l t s difficult.
T o a s s e s s the c e m e n t i n g p r o p e r t i e s of v a r i o u s w a s t e p r o d u c t s s u c h a s fly a s h i t would b e useful to b a s e s e l e c t i v i t y o n f a c t o r s affecting a univer- s a l l y r e c o g n i z e d e n g i n e e r i n g p r o p e r t y s u c h a s p o r o s i t y . P r e v i o u s w o r k ( 6 ) c l e a r l y showed t h a t c o m p r e s s i v e s t r e n g t h and modulus of e l a s t i c i t y c u r v e s f o r r o o m t e m p e r a t u r e h y d r a t e d p a s t e w e r e significantly d i s p l a c e d f r o m t h o s e r e p r e s e n t i n g autoclaved c e m e n t p a s t e . It w a s thought that a b e t t e r defined s y s t e m ( c e m e n t - s i l i c a ) under autoclaved conditions would p r o v i d e a s p e c t r u m of m e c h a n i c a l p r o p e r t y v s p o r o s i t y functions that would a s s i s t in c h a r a c t e r i z i n g t h e e n g i n e e r i n g p r o p e r t i e s of fly a s h e s f r o m d i f f e r e n t sources. T h e r e l a t i o n s h i p s between m i c r o h a r d n e s s , s t r e n g t h and modulus of e l a s t i c i t y and t h e i r dependence on p o r o s i t y would b e f u r t h e r elucidated.
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MECHANICAL PROPERTIES, AUTOCLAVING, CALCIUM SILICATE HYDRATES
E x p e r i m e n t a l M a t e r i a l s
T h e following m a t e r i a l s w e r e used:
1. N o r m a l T y p e I C e m e n t w a s mixed with v a r y i n g p r o p o r t i o n s of s i l i c a and h y d r a t e d a t w a t e r - s o l i d s r a t i o s f r o m 0. 26 to 0 . 4 5 .
2. S i l i c a , p r e p a r e d by g r i n d i n g Ottawa s i l i c a s a n d and r e t a i n i n g t h a t w h i c h p a s s e d t h r o u g h a 1 0 0 - m e s h s i e v e , w a s mixed w i t h c e m e n t ( 5 , 1 0 , 20, 30; 50 and 6 5 p e r cent by weight) p r i o r to autoclaving. T h e p a r t i c l e s i z e d i s - t r i b u t i o n was a s follows: 150 p m
-
75 p m (40 p e r c e n t ) ; 7 5 p m - 4 5 p m ( 1 6 p e r c e n t ) ; 45 p m-
25 p m ( 1 4 p e r c e n t ) ; 25 p m-
12 p m (10 p e r c e n t ) ; 12 y m-
6 p m (10 p e r c e n t ) ; 6 p m-
1. 5 p m ( 5 p e r c e n t ) ; and f i n e r t h a n 1. 5 p m ( 5 p e r c e n t ) .3. F l y A s h c o m p o s e d a s follows: 56 p e r c e n t s i l i c a , 23 p e r cent a l u m i n a , 4 p e r c e n t f e r r i c o x i d e , 13 p e r c e n t CaO and 4 p e r cent m i s c e l l a n e o u s o x i d e s . It w a s used a s a 50 p e r c e n t r e p l a c e m e n t f o r c e m e n t i n t h e cement- fly a s h m i x t u r e s . Eighty-five p e r cent of t h e p a r t i c l e s w e r e 45 p m
-
12 ym. Methods H e l i u m C o m p a r i s o n P y c n o m e t r y T h e a p p l i c a t i o n of t h i s technique to t h e h y d r a t e d p o r t l a n d c e m e n t s y s t e m i s d e s c r i b e d e l s e w h e r e ( 1 6 ) . Solid v o l u m e i s m e a s u r e d e n a b l i n g the d e t e r m i n a t i o n of p o r o s i t y a s t h e a p p a r e n t v o l u m e i s c a l c u l a t e d f r o m s a m p l e g e o m e t r y . T h e p r o b l e m of r e h y d r a t i o n e n c o u n t e r e d when w a t e r i s used a s the d i s p l a c e m e n t m e d i u m i s avoided. Using 11 p e r c e n t R . H. a s d a t u m avoids e x c e s s i v e d e c o m p o s i t i o n of t h e h y d r a t e s ( 1 7 ) .C o m p r e s s i v e S t r e n g t h ; Young's Modulus and M i c r o h a r d n e s s
S t r e n g t h w a s m e a s u r e d i n c o m p r e s s i o n on 2-in. (5. 1 - c m ) c u b e s ; two c u b e s w e r e t e s t e d f o r e a c h p r e p a r a t i o n . Young's m o d u l u s w a s m e a s u r e d on 3. 2 - c m d i a m e t e r d i s c s , 1. 3 m m thick; t e n d i s c s f o r e a c h p r e p a r a t i o n w e r e u s e d . T h e p r o c e d u r e i n v o l v e s m e a s u r i n g the d e f l e c t i o n of a s p e c i m e n when i t i s loaded a t i t s c e n t r e and s u p p o r t e d a t t h r e e p o i n t s located a t the c i r c u m f e r e n c e of a c i r c l e 2. 5 c m ( 1 i n . ) i n d i a m e t e r ( 3 ) . A L e i t z m i c r o h a r d n e s s t e s t i n g m a c h i n e with a V i c k e r s i n d e n t e r w a s used f o r t h e m i c r o h a r d n e s s m e a s u r e m e n t s which w e r e m a d e on t h e d i s c s used f o r modulus of e l a s t i c i t y m e a s u r e m e n t s and w e r e c a r r i e d out a t 11 p e r cent R.H T h e r e w e r e t e n h a r d n e s s m e a s u r e m e n t s m a d e on e a c h d i s c and t h r e e d i s c s w e r e t e s t e d f o r e a c h p r e p a r a t i o n . H y d r a t i o n S a m p l e s f o r autoclaving w e r e p r e p a r e d a t w a t e r - s o l i d r a t i o s 0. 2 6 , 0. 30, 0. 35, 0 . 4 0 and 0 . 4 5 . P r e p a r a t i o n s a t e a c h w a t e r - s o l i d r a t i o c o n - s i s t e d of s i x s e t s of s a m p l e s , e a c h s e t having a d i f f e r e n t s i l i c a content. S i l i c a c o n t e n t s e x p r e s s e d a s p e r c e n t by weight of s o l i d w e r e 5, 10, 20, 30, 50 and 6 5 p e r c e n t ; t h i s p r o v i d e d a t o t a l of 30 d i f f e r e n t p r e p a r a t i o n s . Mixes w e r e c a s t i n cube m o l d s and m o i s t c u r e d f o r 2 4 h o u r s ; t h r e e cubes w e r e
Vol. 5, No. 2
J. J.
Beaudoin,
R.
F. Feldman
c a s t f o r e a c h p r e p a r a t i o n . A f t e r d e m o l d i n g s a m p l e s w e r e a u t o c l a v e d at 2 1 b ° C , 21 k g / c m 2 p r e s s u r e f o r 3 h o u r s . Two c u b e s w e r e r e t a i n e d f o r c o m p r e s s i v e s t r e n g t h m e a s u r e m e n t . A 1. 25-in. ( 3 . 2 - c m ) c o r e w a s t a k e n f r o m the t h i r d cube with a d i a m o n d tipped c o r e d r i l l . T e n d i s c s , 0. 050 in.
(. 127 c m ) t h i c k , w e r e s l i c e d f r o m e a c h c o r e f o r m e a s u r e m e n t s of modulus of e l a s t i c i t y and m i c r o h a r d n e s s . R e s u l t s P o r o s i t y T h e l o g a r i t h m s of c o m p r e s s i v e s t r e n g t h , m i c r o h a r d n e s s , a n d modulus of e l a s t i c i t y w e r e plotted a g a i n s t p o r o s i t y ; t h e p l o t s r e s u l t e d in a f a m i l y of s t r a i g h t l i n e s ( e a c h s i l i c a c o n t e n t yielding a d i f f e r e n t l i n e ) with d i f f e r e n t s l o p e s ( F i g u r e s 1
-
3). T h e r e s u l t s of l i n e a r r e g r e s s i o n a n a l y s i s a r e r e c o r d e d i n T a b l e 1. F o r l i n e s r e p r e s e n t i n g e a c h s i l i c a con- t e n t the s l o p e r a t i o s w e r e d e t e r m i n e d . T a b l e 2 g i v e s v a l u e s of the slope r a t i o s f o r the s e m i l o g a r i t h m i c functions r e p r e s e n t i n g t h e t h r e e m e c h a n i c a l FIG. 1 C o m p r e s s i v e s t r e n g t h v s p o r o s i t y f o r v a r i o u s a u t o c l a v e d a n d r o o m t e m - p e r a t u r e h y d r a t e d cement and ce ment-
s i l i c a p r e p a r a t i o n sVol.
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MECHANICAL PROPERTIES, AUTOCLAVING, CALCIUM S I L I C A T E H Y D R A T E S
10 2 0 3 0 4 0 5 0 6 0 P O R O S I T Y . % F I G . 3 Modulus of e l a s t i c i t y v s p o r o s i t y f o r v a r i o u s a u t o c l a v e d and r o o m t e m p e r a t u r e h y d r a t e d c e m e n t and c e m e n t - s i l i c a p r e p a r a t i o n s F I G . 2 M i c r o h a r d n e s s vs p o r o s i t y f o r v a r i o u s a u t o c l a v e d and r o o m t e m p e r a t u r e hy- d r a t e d c e m e n t and c e m e n t - s i l i c a p r e p a r a t i o n s
J. J. Beaudoin, R . F. Feldrnan C o m p r e s s i v e s t r e n g t h , m i c r o h a r d n e s s , a n d m o d u l u s of e l a s t i c i t y f o r r o o m t e m p e r - a t u r e h y d r a t e d p a s t e obey t h e g e n e r a l r e l a t i o n s h i p , S, E , H = w h e r e S ,
E,
H r e f e r t o s t r e n g t h m o d u l u s of e l a s t i c i t y and m i c r o h a r d n e s s a n d p r e p r e - s e n t s p o r o s i t y . T h i s a p p e a r s to be t r u e a l s o f o r a u t o c l a v e d c e m e n t - s i l i c a m i x t u r e s . T h e m e a n s l o p e r a t i o s f o r t h e r a n g e of s i l i c a c o n t e n t s s t u d i e d a r e a s f o l l o w s : It c a n be e a s i l y s h o w n t h a t : V o l . 5, No. 2 T A B L E 1 R e g r e s s i o n A n a l y s i s of M o d u l u s of E l a s t i c i t y , C o m p r e s s i v e S t r e n g t h a n d M i c r o h a r d n e s s v e r s u s P o r o s i t y D a t a :; g i v e s 9 0 p e r c e n t c o n f i d e n c e l i m i t st
c o r r e l a t i o n c o e f f i c i e n tVol.
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109MECHANICAL PROPERTIES, AUTOCLAVING, CALCIUM SILICATE HYDRATES
T A B L E 2 E q u a t i o n s 1 , 2 a n d 3 apply w i t h i n R a t i o of S l o p e s of S t r e n g t h , M i c r o h a r d n e s s a n d M o d u l u s of E l a s t i c i t y v s P o r o s i t y D a t a the s t a t i s t i c a l bounds of t h e r a t i o s b b~
,
b~ and S a n d the v a l i d i t y of-
- -
b~ b~ b~ the g e n e r a l e q u a t i o n f o r S , E a n d H. T h e y a l s o i m p l y t h a t p o r o s i t y g e n - e r a l l y i n f l u e n c e s t h e p r o p e r t i e s S , E a n d H i n a s i m i l a r way f o r r a n g e of c o m p o s i t i o n s a n d m o r p h o l o g i e s . T h e c o n s t a n t of p r o p o r t i o n a l i t y i n Eq. ( 3 ) h a s a p h y s i c a l s i g n i f i c a n c e . I t i s t h e r a t i o of m i c r o h a r d n e s s to c o m p r e s s i v e s t r e n g t h a t z e r o p o r o s i t y . Solid d e n s i t i e s w e r e d e t e r m i n e d a t 11 p e r cent R. H. by h e l i u m d i s - p l a c e m e n t f o r a l l p r e p a r a t i o n s s t u d i e d . T h e s p e c i f i c v o l u m e i n c r e a s e s t o am a x i m u m value a s s i l i c a content i n c r e a s e s and t h e n d e c r e a s e s a t l a r g e s i l i c a c o n t e n t s ( F i g u r e 4 ) . T h e h i g h d e n s i t y v a l u e s c o r r e s p o n d to the p r e s - e n c e of cuC S h y d r a t e ( d e t e r m i n e d by X - r a y d i f f r a c t i o n ) a n d low v a l u e s of 2 c o m p r e s s i v e s t r e n g t h . S i m i l a r l y t h e low d e n s i t y v a l u e s c o r r e s p o n d to t h e p r e s e n c e of p o o r l y c r y s t a l l i z e d h y d r o s i l i c a t e a n d o p t i m u m s t r e n g t h . T h e above o b s e r v a t i o n s a r e a l s o t r u e f o r m a x i m u m a n d m i n i m u m values of modulus of e l a s t i c i t y and m i c r o h a r d n e s s . I n t e r r e l a t i o n s h i p of Mechanical P r o p e r t i e s F i g u r e s 5 a n d 6 a r e plots of modulus of e l a s t i c i t y a n d m i c r o h a r d n e s s v s c o m p r e s s i v e s t r e n g t h . F i g u r e 7 plots modulus of e l a s t i c i t y vs m i c r o - h a r d n e s s . As e x p e c t e d f r o m E q u a t i o n s ( 1 ) and ( 2 ) , F i g u r e s 5 and 7 a r e non- l i n e a r r e l a t i o n s w h e n the o r i g i n i s included i n the population of e x p e r i m e n t a l points.
E q u a t i o n ( 3 ) d e s c r i b e s t h e r e l a t i o n b e t w e e n m i c r o h a r d n e s s and s t r e n g t h a s l i n e a r a n d p a s s i n g t h r o u g h t h e o r i g i n . R e g r e s s i o n a n a l y s i s of t h e e x p e r i m e n t a l d a t a , which i n c l u d e s r e s u l t s f r o m the 30 p r e p a r a t i o n s a s w e l l a s r o o m t e m p e r a t u r e h y d r a t e d p a s t e but d o e s not i n c l u d e the o r i g i n in
110 J. J. Beaudoin, R . F. Feldman 0. 36 0 10 20 30 40 5 0 60 7( S I L I C A . % F I G . 5 Modulus of e l a s t i c i t y v s c o m p r e s s i v e s t r e n g t h f o r v a r i o u s a u t o c l a v e d a n d r o o m t e m p e r a t u r e h y d r a t e d c e m e n t a n d c e m e n t - s i l i c a p r e p a r a t i o n s V o l . 5, No. 2 FIG. 4 S p e c i f i c v o l u m e of s o l i d p h a s e v s s i l i c a content f o r v a r i o u s a u t o c l a v e d c e m e n t - s i l i c a p r e p a r a t i o n s 0 200 400 600 800 1000 1200 1400 C O M P R E S S I V E S T R E N G T H . K G l C M t h e p o p u l a t i o n of e x p e r i m e n t a l p o i n t s , g i v e s t h e f o l l o w i n g r e l a t i o n : T h e m i c r o h a r d n e s s i n t e r c e p t 6. 853 k g / m m 2 i s s m a l l a s the p o p u l a t i o n of 2 m i c r o h a r d n e s s v a l u e s c o v e r s t h e r a n g e 0
<
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80 k g / m m.
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MECHANICAL PROPERTIES, AUTOCLAVING, CALCIUM SILICATE HYDRATES
tion coefficient 0 . 9 60 P R O O M T E M P E R A T U R E H Y D R A T E D 2 P A S T E ( R E F . 6.2.1 ) i n d i c a t e s a good l i n e a r r o 6 0 fit. Any d i s p a r i t y a 3 w 0 6 e5 between E q s . ( 3 ) and ( 4 ) 20.6
a
O 4 W / ( C + S i ) NO. S i , % i s negligible and i s o 0.26 I l 0 . 3 0 2 1 0 probably i n h e r e n t i n o 0 . 3 5 3 20 1 P 3 0 . 4 0 4 3 0 e r r o r s a s s o c i a t e d with I A A 0.45 5I
5 0 6 6 5 the t h i r d d e g r e e of 0 I I I I I I I I 1 1 1 I I 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 f r e e d o m ( p o r o s i t y ) on C O M P R E S S I V E S T R E N G T H , K G I C M ~which the d e r i v a t i o n of FIG. 6
M i c r o h a r d n e s s vs c o m p r e s s i v e s t r e n g t h f o r Eq. ( 3 ) i s b a s e d . T h e v a r i o u s autoclaved and r o o m t e m p e r a t u r e . d a t a plotted i n F i g u r e h y d r a t e d c e m e n t and c e m e n t - s i l i c a p r e p a r a t i o n s 5 include: 30 p r e p a r a - tions of autoclaved c e m e n t - s i l i c a mixtures; 5 p r e p a r a t i o n s of auto- claved c e m e n t - f l y a s h m i x t u r e s ; p r e p a r a t i o n s r e p r e s e n t i n g r o o m t e m p e r a t u r e h y d r a t e d p a s t e ; and, p r e p a r a - tions of autoclaved p a s t e without s i l i c a addition. With the e x - ception of autoclaved p a s t e without s i l i c a the d a t a a r e w e l l d e s c r i b e d by a s m o o t h c u r v e r e p W / ( C + S i ) 0 0 . 7 6 l 0.30 0.35 0 . 4 0 A 0 . 4 5 N O . - I 2 3 4 5 S i , % - 5 10 2 0 3 0 5 0 6 6 5 P R O O M T E M P E R A T U R E H Y D R A T E D P A S T E ( R E F . 6,2,1 ) 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 M I C R O H A R D N E S S . K G ~ M M ~ FIG. 7 Modulus of e l a s t i c i t y vs m i c r o h a r d n e s s f o r v a r i o u s autoclaved and r o o m t e m p e r a t u r e h y d r a t e d cement and c e m e n t - s i l i c a p r e p a r a t i o n s r e s e n t i n g Eq. ( 1 ) . T h e d a t a for autoclaved p a s t e without s i l i c a lie on a line of constant s l o p e ; the data f o r autoclaved p a s t e with s i l i c a l i e below the l i n e which r e p r e s e n t s s a m p l e s with p r o d u c t d e n s i t i e s between 2. 7 5 and 2. 88.
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of points having low s i l i c a c o n t e n t s l i e s n e a r e r the high d e n s i t y l i n e than t h o s e having h i g h e r s i l i c a c o n t e n t s . An e x t e n s i o n of t h e d a s h e d s e g m e n t of t h e high d e n s i t y l i n e ( F i g u r e 5) likely i n c l u d e s d a t a r e p r e s e n t i n g h o t - p r e s s e d h y d r a t e d c e m e n t . D a t a on t h i s l i n e a t s t r e n g t h l e v e l s l e s s than 200 k g / c m 2
may be c o n s i d e r e d t o be within the s a m p l e population d e s c r i b e d by E q . ( 1 ) . T a b l e 3 l i s t s v a l u e s of t h e r a t i o E /S ( t h e r a t i o of modulus of e l a s -
0 0
t i c i t y a t z e r o p o r o s i t y to s t r e n g t h a t z e r o p o r o s i t y ) , c a l c u l a t e d f r o m data obtained by e x t r a p o l a t i o n of t h e m e c h a n i c a l p r o p e r t y - p o r o s i t y d a t a . It will be noted t h a t t h e r e i s v a r i a t i o n i n the v a l u e s of E /S a n d H /S f o r the
0 0 0 0 d i f f e r e n t p r e p a r a t i o n s ; t h i s i s c o n s i s t e n t w i t h the d i s t r i b u t i o n of d a t a for v a r y i n g s e t s of p r e p a r a t i o n s i n F i g u r e 5. T h e high d e n s i t y T A B L E 3 R a t l o of Modulus of E l a s t ~ c ~ t y a n d M ~ c r o h a r d n e s s at Z e r o P o r o s ~ t y line to S t r e n g t h a t Z e r o P o r o s i t y t h a t r e p r e s e n t t h e R o o m T e m p e r a t u r e H y d r a t e d P a s t e A u t o c l a v e d P a s t e C e m e n t - F l y A s h 50/50 A u t o c l a v e d P a s t e 0 % S i l i c a 5% S111ca 10% S ~ l i c a 2070 S i l i c a 3090 S i l i c a 5 0 % S l l i c a 6590 S i l i c a h i g h e s t value of t h e r a t i o
E ~ / s ~ .
T h e 5 p e r cent s i l i c a p r e p a r a t i o n has t h e next h i g h e s t value. T h e r e m a i n i n g c e m e n t - s i l i c a p r e p a r a t i o n s have s i m i l a r v a l u e s . The a c c u r a c y of E q s . ( l ) , ( 2 ) a n d ( 3 ) i n d e s c r i b i n g the d a t a i s a l s o dependent on a v e r a g e v a l u e s of H /S.
T h e s e v a l u e s a r e i n c l u d e d in T a b l e 3. It 0 0 a p p e a r s t h a t a high d e n s i t y s o l i d p h a s e c o n t r i b u t e s to g r e a t e r r a t e s of change of modulus of e l a s t i c i t y with r e s p e c t to c o m p r e s s i v e s t r e n g t h .It i s noteworthy that the d a t a plotted in F i g u r e s 5 , 6 and 7 include r e s u l t s r e p r e s e n t i n g p r e p a r a t i o n s containing v a r y i n g p r o p o r t i o n s of c r y s
-
t a l l i n e cuC S h y d r a t e , p o o r l y c r y s t a l l i z e d h y d r o s i l i c a t e (CSH(1)) and t o b e r -2
m o r i t e like c a l c i u m s i l i c a t e h y d r a t e .
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f o r s e v e r a l c o n c r e t e s ( 1 8 ) h a s the g e n e r a l f o r m E = a s b , w h e r e 0 . 4 5
<
b<
0. 78. T h i s r e l a t i o n , independent of p o r o s i t y , w a s shown to be valid f o r hy- d r a t i o n p e r i o d s up to five y e a r s . F o r c o n c r e t e , p o r o s i t y s e e m s to affect the m e c h a n i c a l p r o p e r t i e s of c o m p r e s s i v e s t r e n g t h and modulus of e l a s t i c i t y i n a s i m i l a r way.
O p t i m u m S i l i c a Content
T h e t h r e e m e c h a n i c a l p r o p e r t i e s i n v e s t i g a t e d - c o m p r e s s i v e s t r e n g t h , m i c r o h a r d n e s s and modulus of e l a s t i c i t y
-
had m a x i m u m v a l u e s a t s i l i c a contents between 20 and 30 p e r cent ( s e e F i g u r e 8 f o r c o m p r e s s i v e s t r e n g t h r e s u l t s ; m i c r o h a r d n e s s and modulus of e l a s t i c i t y showed s i m i l a r dependence on s i l i c a content). X - r a y d i f f r a c t i o n r e s u l t s i n d i c a t e that m o s t of the s i l i c a h a s r e a c t e d a t the m a x i m u m position. The c h a r a c t e r i s t i c s h a p e f o rs t r e n g t h v s s i l i c a content o b s e r v e d by Menzel ( 1 9 ) w a s o b s e r v e d f o r e a c h m e c h a n i c a l p r o p e r t y . F I G . 8 W C o m p r e s s i v e s t r e n g t h >
-
"1 v s s i l i c a content f o r V, 4 W v a r i o u s autoclaved @z a c e m e n t - s i l i c a z 0 3 U p r e p a r a t i o n s 2 S I L I C A . %J. J . Beaudoin,
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In addition it was a l s o found that this type of c h a r a c t e r i s t i c o c c u r r e d with two other p a r a m e t e r s .
( a ) The s p e c i f i c volume ( a s determined by helium d i s p l a c e m e n t ) yielded a maximum value a t a s i l i c a content between 30 and 40 p e r cent ( F i g u r e 4). ( b ) The i n v e r s e of the s l o p e s of the l o g a r i t h m of modulus of e l a s t i c i t y , s t r e n g t h and m i c r o h a r d n e s s v s porosity functions ( F i g u r e 9) exhibit a maximum value a t a s i l i c a content of approximately 30 p e r cent.
FIG. 9
I n v e r s e slope of the log mechanical p r o p e r t y - p o r o s i t y r e l a t i o n s as a function of s i l i c a content
D i s c u s s i o n
The c o m p r e s s i v e s t r e n g t h - p o r o s i t y functions f o r r o o m t e m p e r a t u r e hydrated paste and autoclaved p a s t e a r e not colinear ( 6 ) but i n t e r s e c t at approximately 2 8 p e r cent porosity. S i m i l a r l y the modulus of e l a s t i c i t y vs porosity functions i n t e r s e c t at approximately 40 p e r cent porosity. For autoclaved c e m e n t - s i l i c a m i x t u r e s a family of mechanical property-porosity
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f u n c t i o n s e x i s t . As t h e s i l i c a c o n t e n t i s v a r i e d t h e s l o p e of t h e l i n e c h a n g e s ; e a c h l i n e a l s o r e f l e c t s a c h a n g e i n p r o d u c t d e n s i t y and h e n c e m o r p h o l o g i c a l and c h e m i c a l c h a n g e . T h e s e c h a n g e s i n s l o p e a n d d e n s i t y a t a given p o r o s i t y s u p p o r t t h e view t h a t a n o p t i m u m a m o u n t of p o o r l y c r y s t a l l i z e d h y d r o s i l i c a t e a n d w e l l c r y s t a l l i z e d d e n s e m a t e r i a l p r o v i d e m a x i m u m v a l u e s of s t r e n g t h a n d m o d u l u s of e l a s t i c i t y . T h e l i n e f o r a u t o c l a v e d p a s t e e x t r a p o l a t e d t o z e r o p o r o s i t y i n c l u d e d p u b l i s h e d v a l u e s ( 2 0 ) f o r c o m p r e s s i v e s t r e n g t h of h o t 2 p r e s s e d p a s t e up to 9 0 , 000 p s i ( 6 3 0 0 k g / c m ). D i v e r g e n c e b e t w e e n l i n e s i n t h e low p o r o s i t y r e g i o n r e s u l t s f r o m a n i n t i m a t e s u r f a c e to s u r f a c e b o n d i n g of h i g h d e n s i t y u n i t s w e l d e d t o g e t h e r w i t h a n o p t i m u m a m o u n t of p o o r l y c r y s t a l l i z e d h y d r o s i l i c a t e . In the h i g h p o r o s i t y r e g i o n p o o r bonding b e t w e e n t h e d e n s e c r y s t a l s a n d i n s u f f i c i e n t p o o r l y c r y s t a l l i z e d h y d r o s i l i c a t e a c c o u n t s f o r t h e d i v e r g e n c e b e t w e e n l i n e s a n d r e s u l t i n g low s t r e n g t h of t h e a u t o c l a v e d p r o d u c t w i t h o u t s i l i c a . P o r o s i t y , c r y s t a l bonding a n d p r o d u c t d e n s i t y a n d m o r p h o l o g y a l l p l a y a r o l e i n d e t e r m i n i n g v a l u e s of c o m p r e s s i v e s t r e n g t h , m i c r o h a r d n e s s , and m o d u l u s of e l a s t i c i t y . A d d i t i o n s of s i l i c a h e l p p r e s e r v e to s o m e e x t e n t t h e p o o r l y - c r y s t a l l i z e d s t r u c t u r e . It h a s b e e n o b s e r v e d (1) t h a t the s l o p e of t h e l i n e a r l o g m e c h a n i c a l p r o p e r t y - p o r o s i t y f u n c t i o n f o r r o o m t e m p e r a t u r e h y d r a t e d p a s t e c h a n g e s w h e n t h e p o r o s i t y e x c e e d s 50 p e r c e n t ; t h i s is p o s s i b l y due to a c h a n g e i n m o r p h o l o g y w i t h h i g h w a t e r - c e m e n t r a t i o s , It i s p o s s i b l e t h a t a s i m i l a r c h a n g e i n s l o p e would h a v e b e e n o b s e r v - e d f o r a u t o c l a v e d p r e p a r a t i o n s h a d p o r o s i t y e x c e e d e d 50 p e r c e n t . P u r t o n ( 2 1 ) a s c r i b e s the 20 p e r c e n t d e c r e a s e i n s o l i d v o l u m e upon f o r m a t i o n of a C S h y d r a t e and x o n o t l i t e a s t h e m a j o r f a c t o r r e s p o n s i b l e f o r low c o m - 2 p r e s s i v e s t r e n g t h . O b s e r v e d c h a n g e s i n c o m p r e s s i v e s t r e n g t h , modulus of e l a s t i c i t y and m i c r o h a r d n e s s ( w h e n a C S h y d r a t e i s p r e s e n t ) a t a c o n s t a n t 2 p o r o s i t y s u g g e s t t h a t t h e s e v o l u m e c h a n g e s c a n n o t a l o n e a c c o u n t f o r o b s e r v e d c h a n g e s i n s t r e n g t h . P u r t o n ( 2 2 ) c o r r e l a t e d d r y i n g s h r i n k a g e w i t h t h e a m o u n t of h y d r o - s i l i c a t e f o r m e d ( d e f i n e d a s h y d r a t e g i v i n g D T A e x o t h e r m a t 820 " C
<
T<
870 "C) b u t h y p o t h e s i z e d t h a t s t r e n g t h w a s m o r e p r o b a b l y r e l a t e d t o t h e d e g r e e t o w h i c h the c e m e n t i n g m a t e r i a l f i l l e d t h e v o i d s . T h i s s e e m s i n a c c o r d w i t h t h e p r e v i o u s d i s c u s s i o n of a n o p t i m u m m i x t u r e of c r y s t a l l i n eJ. J.
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and poorly c r y s t a l l i n e m a t e r i a l being r e s p o n s i b l e for o p t i m u m m e c h a n i c a l behaviour.
T h e l i n e a r c o r r e l a t i o n of m i c r o h a r d n e s s and s t r e n g t h i s i n t e r e s t i n g and significant. Obviously both p r o c e s s e s involve the b r e a k i n g of s i m i l a r bonds. T h e r e s u l t adds confidence to the cube c r u s h i n g t e s t and p r o v i d e s a way to e s t i m a t e c o m p r e s s i v e s t r e n g t h when the making of cubes is incon- venient.
Conclusions
1. T h e o b s e r v a t i o n that d a t a r e p r e s e n t i n g m e a s u r e m e n t s of modulus of e l a s t i c i t y , c o m p r e s s i v e s t r e n g t h , and m i c r o h a r d n e s s f o r a v a r i e t y of auto- claved p r e p a r a t i o n s containing SiO a s w e l l a s r o o m t e m p e r a t u r e hydrated
2
c e m e n t p a s t e , when plotted one against the o t h e r , lie o n a single c u r v e s u g g e s t s that the r e l a t i o n s h i p s between t h e s e m e c h a n i c a l p r o p e r t i e s a r e not significantly influenced by the p r e s e n c e or a b s e n c e of varying p r o p o r t i o n s of
0
crC SH, CSH(1) o r 11A t o b e r m o r i t e . T h i s a l s o s u g g e s t s that d i f f e r e n c e s i n
2
the m i c r o s t r u c t u r e of the p r e p a r a t i o n s studied do not significantly inflaence the i n t e r r e l a t i o n of m e c h a n i c a l p r o p e r t i e s . The q u a n t i t i e s of c r y s t a l l i n e and p o o r l y c r y s t a l l i n e m a t e r i a l a r e in s u c h p r o p o r t i o n a s t o i m p a r t to t h e hy- d r a t e d p a s t e c o m p o s i t e s i m i l a r i t i e s of m e c h a n i c a l b e h a v i o u r , i f 5 p e r cent o r g r e a t e r SiO i s added.
2
2 . P o r o s i t y affects the m e c h a n i c a l p r o p e r t i e s of E , S and H qualitatively i n a s i m i l a r way. T h i s follows f r o m the p r e v i o u s s t a t e m e n t a s the relation-
s h i p s between E , S and H a r e independent of porosity.
3 . To a f i r s t a p p r o x i m a t i o n , modulus of e l a s t i c i t y , E , can be e x p r e s s e d a s a n exponential function of s t r e n g t h o r m i c r o h a r d n e s s ; i. e. ,
T h e c o n s t a n t s subject to the a c c u r a c y of e x t r a p o l a t i o n have p h y s i c a l signifi- c a n c e a s
E
S H a r e modulus of e l a s t i c i t y , s t r e n g t h and m i c r o h a r d n e s s0 , 0 , 0
a t z e r o p o r o s i t y r e s p e c t i v e l y .
Vol.
5,
No.
2
117
MECHANICAL PROPERTIES, AUTOCLAVING, CALCIUM SILICATE H Y D R A T E S
S 0
h a r d n e s s ; S =
-
H H. T h i s gives a physical significance to the constant of
0
p r o p o r t i o n a l i t y which i s the r a t i o of the c o m p r e s s i v e s t r e n g t h to m i c r o h a r d - n e s s a t z e r o p o r o s i t y . C o n v e r s e l y S / H can be d e t e r m i n e d f r o m the s l o p e
0 0
of the S vs H plot without extrapolation.
5. F o r e a c h m e c h a n i c a l p r o p e r t y m e a s u r e d (modulus of e l a s t i c i t y , c o r n p r e s s i v e s t r e n g t h , and m i c r o h a r d n e s s ) , t h e r e i s a f a m i l y of s t r a i g h t l i n e s when t h e s e p r o p e r t i e s a r e plotted a s log m e c h a n i c a l p r o p e r t y vs p o r o s i t y ; e a c h line r e p r e s e n t s a d i f f e r e n t s i l i c a content.
6. T h e i n v e r s e s l o p e of t h e s e l i n e s when plotted a s a function of s i l i c a content follows a b e l l - s h a p e d c u r v e s i m i l a r to the Menzel c o m p r e s s i v e s t r e n g t h - s i l i c a content r e l a t i o n s h i p .
7. S i m i l a r l y the i n v e r s e of s o l i d d e n s i t y ( s p e c i f i c v o l u m e ) when p l o t t e d a s a function of s i l i c a content d i s p l a y s a b e l l - s h a p e d c u r v e . The c u r v e s for w a t e r - s o l i d r a t i o s 0. 30, 0. 35, 0 . 4 0 , and 0 . 4 5 a r e w e l l n e s t e d . The c u r v e f o r w a t e r - s o l i d r a t i o 0. 26 h a s a significantly h i g h e r m a x i m a l value p r o b a - bly due to a lower d e g r e e of hydration.
8. M i c r o h a r d n e s s when plotted a s a function of s i l i c a content a l s o d i s - played a b e l l - s h a p e d r e s p o n s e a k i n to that f o r c o m p r e s s i v e s t r e n g t h and modulus of e l a s t i c i t y .
Acknowledgement
T h e a u t h o r s w i s h to thank G. A a r t s , E. Quinn, and T . Doherty f o r t h e i r a s s i s t a n c e with the e x p e r i m e n t a l work. 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 the 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 the a p p r o v a l of the D i r e c t o r of the Division. R e f e r e n c e s
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