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Cement and Concrete Research, 1, 3, pp. 257-271, 1971-05
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Morphology and microstructure of hydrating portland cement and its
constituents. III. Changes in the hydration of a mixture of C3S, C3A and
gypsum with and without triethanolamine and calcium lignosulphonate
present
Ciach, T. D.; Swenson, E. G.
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https://nrc-publications.canada.ca/eng/view/object/?id=b37f1f2d-d2d4-4e3f-8433-7bee67522141 https://publications-cnrc.canada.ca/fra/voir/objet/?id=b37f1f2d-d2d4-4e3f-8433-7bee67522141CEMENT and CONCRETE RESEARCH. Vol
.
1,
pp. 257-271, 1971. 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 .MORPHOLOGY AND MICROSTRUCTURE O F HYDRATLNG PORTLAND C E M E N T AND ITS CONSTITUENTS
111. CHANGES IN T H E HYDRATION O F A MIXTURE O F C3S, C3A AND GYPSUM WITH AND WITHOUT TRIETHANOLAMINE
AND CALCIUM LIGNOSULPHONATE P R E S E N T
T . D. C i a c h and E . G. Swenson
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 Ottawa, 7 , O n t a r i o , Canada (Communicated by G. M. I d o r n ) ABSTRACT S y s t e m a t i c s e q u e n t i a l o b s e r v a t i o n s with t h e e l e c t r o n m i c r o s c o p e w e r e m a d e of t h e m o r p h o l o g i c a l c h a n g e s which o c c u r r e d d u r i n g t h e h y d r a t i o n of a p a s t e m i x t u r e of C3S:k, C3A and g y p s u m . It w a s found t h a t t h i s s y s t e m p r o d u c e d h y d r a t i o n p r o d u c t s s i m i l a r i n n a t u r e t o t h o s e p r o d u c e d by t h e m o n o m i n e r a l s y s t e m s w i t h g y p s u m p r e s e n t . T h e two o r g a n i c a d m i x t u r e s s t u d i e d had s o m e effect on c h a n g e s i n m o r p h o l o g y and m i c r o s t r u c t u r e of t h e h y d r a t - ing m i x t u r e , but they showed a pronounced influence on t h e r a t e of t h e h y d r a t i o n p r o c e s s e s .
S OMMAIRE
D e s o b s e r v a t i o n s au m i c r o s c o p e g l e c t r o n i q u e ont C t C f a i t e s en s g q u e n c e s y s t g m a t i q u e p o u r o b s e r v e r l e s c h a n g e m e n t s m o r p h o l - ogiques qui p r e n n e n t p l a c e a u c o u r s d e l l h y d r a t a t i o n d l u n e pbte composCe d e C,S, C3A e t d e g y p s e . C e syst'eme a d e s p r o d u i t s d l h y d r a t a t i o n s e m b l a b l e s p a r l e u r n a t u r e
B
c e u x p r o d u i t s p a r l e ssyst'emes monominCraux e n p r C s e n c e d e g y p s e . L e s d e u x a d j u - vants o r g a n i q u e s e x a m i n e s ont un lCger effet s u r l a m o r p h o l o g i e e t l a m i c r o s t r u c t u r e du mClange a u c o u r s d e l l h y d r a t a t i o n , m a i s ont une influence prononcCe s u r l a d u r g e du p r o c e s s u s d l h y d r a t - ation.
--
"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. SiO, ;
C3A = 3CaO.Al ,0, ; C,S = 2CaO.Si0,; CSH = c a l c i u m s i l i c a t e h y d r a t e ( s ) ; C A H = c a l c i u m a l u m i n a t e h y d r a t e ( s ) ; w/c = w a t e r : c e m e n t r a t i o by weight.
Val. 1, No.
3
M I C R O S T R U C T U R E , C E M E N T P A S T E , A D M I X T U R E S
This i s the t h i r d paper in a continuing s e r i e s which studies the morphological changes occurring during the hydration of portland cement and i t s pure components in the absence and in the p r e s e n c e of admixtures. The f i r s t dealt with C,A ( 1 ) and the second with C3S and C2S ( 2 ) , and in each the changes with and without gypsum w e r e observed.
The method used in the studies s o f a r c o n s i s t s of taking e l e c t r o n m i c r o g r a p h s of the hydrating p a s t e s on a sequential b a s i s , and reporting
only those changes and s t r u c t u r e s which appear to be dominant. E l e c t r o n m i c r o g r a p h s a r e included t o i l l u s t r a t e different f o r m s of m i c r o s t r u c t u r e
and changes in morphology which affect the m a i n components. P r o p o r t i o n s of phases a r e to be considered on a qualitative b a s i s .
The object of t h e s e investigations i s to improve the understanding of the n a t u r e of morphological changes occurring in the hydration of p o r t - land cement, and to r e l a t e m i c r o s t r u c t u r e of cement paste to physical and mechanical p r o p e r t i e s of paste and concrete.
The p r e s e n t p a p e r d e a l s with the morphological changes occurring during the hydration of a m i x t u r e of C3S, C3A and gypsum in the absence and in the p r e s e n c e of two organic admixtures.
Introduction
The morphological changes occurring during the hydration of C3S and C 2 S and the effects of gypsum and other a d m i x t u r e s have been briefly referenced in a previous paper in this s e r i e s (2). E x p e r i m e n t s with a m i x - t u r e of C3S, C, A and gypsum a p p e a r t o be e x t r e m e l y limited. F r o m x - r a y studies i t has been found that the formation of ettringite appeared to be accel- e r a t e d when C3S was used in place of Ca(OH), with C3A ( 0 . 7 5 m o l e s C3S t o
1 m o l e C3A) ( 3 ) . The second stage of formation of the low sulphoaluminate and the l a s t reactions with the remaining C3S w e r e found to be affected: the r a t e s of reaction d e c r e a s e d and the products w e r e m o r e poorly crystallized. At m o l a r r a t i o s of 3 t o 1 of C3S and C3A, the second stage w a s r e t a r d e d . In g e n e r a l i t was concluded that the behaviour of t h i s s y s t e m closely resembled that of the orr responding components in the portland cement s y s t e m .
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259
MICROSTRUCTURE
,
C E M E N T PASTE, A D M I X T U R E S
R e c e n t r e v i e w p a p e r s i n d i c a t e t h a t t h e r e i s g e n e r a l a c c e p t a n c e of t h e i d e a t h a t t h e a l u m i n u m , o r s o m e compound of t h i s e l e m e n t d e r i v e d f r o m C3A, e n t e r s r e a d i l y into 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 p r o d u c t of t h e h y d r a t - i o n of C3S ( 4 , 5). S o m e r e s e a r c h e r s c l a i m t h a t t h i s r e s u l t s i n a change i n the m o r p h o l o g y of t h e CSH g e l ( 6 ) and o t h e r s t h a t l i t t l e o r no change o c c u r s ( 7 ) . It i s r e p o r t e d (8, 9) t h a t t h e hydration of a l i t e i s i n c r e a s e d by t h e p r e s e n c e of f r e e C,A. Gypsum a l s o h a s t h i s e f f e c t but in t h i s c a s e t h e sulphate c o n c e n t r a t i o n i s an influencing f a c t o r . The s a m e r e v i e w p a p e r (8) r e p o r t s t h a t i n a d i f f e r e n t i n v e s t i g a t i o n up t o 4 p e r c e n t gypsum had no effect on C3S hydration.I t h a s been noted ( 3 ) t h a t "the behaviour of lignosulphonate i n m o r e c o m p l e x m i x t u r e s d i f f e r s m a r k e d l y f r o m t h e e f f e c t s on h y d r a t i o n of b a s e m i x t u r e s o r on C3S alone. I '
T h e o b s e r v a t i o n s noted above w e r e m a d e on t h e b a s i s of x - r a y , c a l o r i m e t r i c and DTA m e a s u r e m e n t s , with s o m e l i m i t e d evidence f r o m 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 . C o m p a r i s o n i s difficult b e c a u s e t h e v a r i o u s i n v e s t i g a t o r s u s e d d i f f e r e n t p r o p o r t i o n s of m i x w a t e r a s w e l l a s d i f f e r e n t p r o p o r t i o n s of solid components.
M a t e r i a l s and P r o c e d u r e s
T h e C3S and C3A u s e d i n t h i s s e r i e s w e r e supplied by t h e 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 . T h e g y p s u m and t h e two o r g a n i c a d m i x t u r e s ,
t r i e t h a n o l a r n i n e and c a l c i u m lignosulphonate, a r e t h e s a m e a s t h o s e u s e d i n t h e p r e v i o u s s t u d i e s i n t h i s s e r i e s and t h e i r p r o p e r t i e s a r e d e s c r i b e d
t h e r e i n ( 1 , 2).
The d r y m i x t u r e c o n s i s t e d of 76.9 p e r c e n t C,S, 15.4 p e r c e n t C3A and 7 . 7 p e r cent g y p s u m . T h e s e w e r e ground t o g e t h e r i n a p o r c e l a i n - a l u m i n a ball - m i l l .
P a s t e s w e r e p r e p a r e d with a p r o p o r t i o n of w a t e r t o d r y powder of 0. 5 by weight. A d m i x t u r e d o s a g e s w e r e 0. 5 p e r c e n t by weight of t h e d r y m i x t u r e s . F u r t h e r c h a r a c t e r i s t i c s of t h e m a t e r i a l s and a d e s c r i p t i o n of t h e
2 6 0
MICROSTRUCTURE, CEMENT PASTE, ADMIXTURES
V o l . 1, No. 3
methods and p r o c e d u r e s used in preparing and examining the t e s t specimens a r e given in the f i r s t two p a p e r s (1, 2).
At i n t e r v a l s of 5 m i n u t e s , 1, 4 and 8 h o u r s , 1 , 2, 3 and 7 days, and 1, 2 and 3 months, s a m p l e s w e r e taken and t e s t e d , To stop hydration, the s a m p l e s w e r e f r o z e n by t r e a t i n g t h e m with acetone a t about -18°C and then drying t h e m in vacuum,
Single stage r e p l i c a s f r o m broken s u r f a c e s of the p a s t e w e r e m a d e using the platinum carbon technique. The e l e c t r o n m i c r o g r a p h s shown a r e those that depict the average and g e n e r a l morphology.
Results and Observations
1. Hydration of C3A, C3S and gypsum with no admixture p r e s e n t .
After 5 m i n u t e s of hydration, the m i c r o s t r u c t u r e of t h i s t h r e e
-
m i n e r a l paste with no admixture p r e s e n t displayed a m i x t u r e of unhydrated g r a i n s with s o m e v e r y thin crumpled foils of hydration products around them. At 1 hour, ettringite -type rod-like p a r t i c l e s appeared ( F i g . 1 ) . Between 4 and 8 hours s o m e i r r e g u l a r p a r t i c l e s w e r e a l s o p r e s e n t (Fig. 2); t h e s e and the ettringite-type phase w e r e the m a j o r hydration products t o 1 day of hydration,At the age of 1 day, between the r o d s of ettringite (high sulpho- aluminate hydrate), some hexagonal plates of low sulpho-aluminate hydrate appeared (Fig. 3). Semi-amorphous ' f i b r e s , which w e r e probably CSH in a three-dimensional a r r a n g e m e n t of p l a t e s , w e r e a l s o p r e s e n t (Fig. 4 ) . Usually these interlocking s t r u c t u r e s of fibrous p a r t i c l e s displayed ribbon- like aggregates a t the edges of plates ( F i g . 5). After 2 days of hydration, the paste had the quite c l o s e , p a r t l y unoriented m i c r o s t r u c t u r e m a d e up of a v a r i e t y of plate f o r m s ( F i g . 6)-
During the whole period f r o m 2 days t o 6 weeks t h e s e platy hydration products w e r e dominant. Sometimes they displayed s t r i a t e d o r hexagonal f o r m s , and s o m e t i m e s t h r e e -dimensional cleavage. The m o s t c h a r a c t e r
-
i s t i c f o r m s of the hydration products during the t i m e f r o m 3 days t o 3 months a r e shown in the e l e c t r o n m i c r o g r a p h s ( F i g s . 7-9).Vol.
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261
:EMENT PASTE, ADMIXTURES
FIG. 1
M i c r o s t r u c t u r e of C,S, C3A and gypsum p a s t e , w/c = 0.5. Age 1 h r . L a r g e plate c r y s t a l s of gypsum and i r r e g u l a r g r a i n s of C3S and C 3 A c o v e r e d by s m a l l e t t r i n g i t e -type rod like p a r t i c l e s . FIG. 2 M i c r o s t r u c t u r e of C3S, C,A and gypsum p a s t e , w/c = 0. 5. Age 8 h r . Some s m a l l i r r e g u l a r p a r t i c l e s of hydration p r o d u c t s on the s u r f a c e s of unhydrated g r a i n s . FIG. 3 M i c r o s t r u c t u r e of C3S, C3A and gypsum p a s t e , w/c = 0.5. Age 1 day. E t t r i n g i t e -type rod -like p a r t i c l e s and s o m e p l a t e s of low c a l c i u m sulpho-aluminate hydrate.
FIG. 4
M i c r o s t r u c t u r e of C3S, C3A and gypsum p a s t e , w/c = 0. 5. Age 1 day. Between the r o d s of e t t r i n g i t e and the p l a t e s of CSH and CAH t h e r e a p p e a r s o m e s e m i c r y s t a l l i n e f i b r o u s p a r t i c l e s of CSH f o r m i n g basket-like f r a c t u r e on the s u r f a c e s of p l a t e s of hydration p r o d u c t s .
262 V o l .
1 , .
N o . 3 MICROSTRUCTURE, CEMENT PASTE, ADMIXTURESFIG. 5 FIG.
6
M i c r o s t r u c t u r e of C3S, C3A and M i c r o s t r u c t u r e of C,S, C3A and gypsum p a s t e , w/c = 0.5. Age 1 gypsum p a s t e , w/c = 0.5. Age 2
day. Hydration p r o d u c t s of f i b r o u s d a y s . Various f o r m s of hydration o r rod-like habit f o r m a n i n t e r l o c k - p r o d u c t s with d e n s e unoriented ing s t r u c t u r e of p l a t e s which d i s p l a y m i c r o s t r u c t u r e .
ribbon-like a g g r e g a t e s a t the e d g e s .
FIG. 7 FIG. 8
M i c r o s t r u c t u r e of C3S, C3A and M i c r o s t r u c t u r e of C3S, C3A and gypsum p a s t e etched with glycol f o r f y p s u m p a s t e etched with glycol f o r
1
2 h r . , w/c = 0. 5. Age
6
weeks. 2 h r . , w/c = 0 . 5 . Age6
weeks. F i b r o u s p a r t i c l e s of r o s e t t e -like Unoriented p l a t e s of l a v calcium f o r m a r e a r r a n g e d on p l a t e - l i k e , sulpho -aluminate hydrate and b i n d e r s s t r i a t e d f o r m s . between pseudomorphous o r p a r t l yV o l . 1 , No. 3 263 MICROSTRUCTURE, CEMENT PASTE, ADMIXTURES
In this period i t was v e r y difficult t o d i s t i n g u i s h between some of the hydration products because of t h e i r v e r y s i m i l a r plate-like f o r m s . F o r this r e a s o n , a t the end of
6
weeks the p a s t e was t r e a t e d with glycol f o r 30 minutes and p a r t of the r i c h calcium hydroxide phase w a s removed. Many plates then showed the t h r e e -dimensional interlocking o r r o s e t t e -likea r r a n g e m e n t s of s e m i c r y s t a l l i n e fibrous p a r t i c l e s that a r e s o c h a r a c t e r i s t i c
I
of CSH ( F i g . 7 ) . The s m a l l hexagonal plates of low sulpho-aluminate
hydrate of m a n y different orientations w e r e a l s o p r e s e n t (Fig. 8 ) . P s e u d o - m o r p h s of individual m i n e r a l components can be observed where the
hydration products w e r e p a r t l y o r a l m o s t e n t i r e l y removed. The essentially amorphous binders can a l s o be seen between each of t h e s e g r a i n s .
At the next t i m e s of observation, 2 and 3 months, the m i c r o s t r u c t u r e did not show any f u r t h e r c l e a r changes ( F i g .
9 ) .
2. Hydration of C3A, C3S, gypsum and triethanolamine.
At 5 minutes' hydration, the m i c r o s t r u c t u r e of a p a s t e of C,A, C3S, gypsum and 0. 5 p e r cent triethanolamine (w/c = 0.5) displayed a m i x t u r e of unhydrated g r a i n s of m i n e r a l components. T h e r e w e r e some amorphous, crumpled foils around t h e s e components and a l s o unoriented hexagonal plates of hydration products on t h e i r s u r f a c e s . The s m a l l , rod-like p a r t i - c l e s of ettringite w e r e a l s o visible. Up to 1 h o u r ' s hydration t h e r e was no significant change in the m i c r o s t r u c t u r e (Fig. 10). During the next few hours s m a l l rounded p a r t i c l e s appeared mainly on the s u r f a c e s of C,S g r a i n s . These new hydration products w e r e probably the r e s u l t of nucleations of calcium silicate hydrate, which was a l s o p r e s e n t i n the f i b r o u s f o r m . D u r - ing the next period until 1 day of hydration, m o r e hydration products of this f o r m , and a l s o l a r g e thin hexagonal plates developed ( F i g . 11). At 3 days, the m i c r o s t r u c t u r e had a m o r e closed s t r u c t u r e of plate -like f o r m s , but r o s e t t e - l i k e aggregates of ettringite rods w e r e p r e s e n t a s well (Fig. 12). Very often l a r g e plates of hydration products displayed the three-dimensional, interlocking s t r u c t u r e of fibrous p a r t i c l e s that i s so significant of CSH.
These products a l s o appeared a s loose bundles. Between them one could distinguish the s m a l l , single hexagonal rods of ettringite
.
264 V o l . 1 , N o . 3 MICROSTRUCTURE, CEMENT PASTE, ADMIXTURES
FIG.
9
FIG. 10M i c r o s t r u c t u r e of C3S, C3A and M i c r o s t r u c t u r e of C,S and C3A g y p s u m p a s t e , w/c = 0.5. Age 2 p a s t e with g y p s u m and t r i e t h a n o l - m o n t h s . C l o s e , u n o r i e n t e d , p a r t l y m i n e , w/c = 0.5. Age 1 h r . s t r i a t e d m i c r o s t r u c t u r e of hydration Unhydrated g r a i n s of c e m e n t m i n - p r o d u c t s . e r a l s with p l a t e s o r r o d s of e t t r i n g - i t e - t y p e h y d r a t i o n p r o d u c t s and s o m e v e r y s m a l l rounded p a r t i c l e s . FIG. 11 FIG. 12
M i c r o s t r u c t u r e of C 3 S and C3A p a s t e M i c r o s t r u c t u r e of C 3 S and C3A p a s t e with g y p s u m and t r i e t h a n o l a m i n e , with g y p s u m and t r i e t h a n o l a m i n e , w/c = 0.5. Age 17 h r . L a r g e p l a t e s w/c = 0.5. Age 3 d a y s . F r a c t u r e of of hydration p r o d u c t s and s o m e 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 on t h e s m a l l f i b r o u s p a r t i c l e s . s u r f a c e s of p l a t e s .
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F r o m 3 to 7 d a y s , ribbons of aggregate radiated out f r o m the edges of m a n y p l a t e s that had a n interlocking f i b r o u s s t r u c t u r e ( F i g . 13). The t h r e e - d i m e n s i o n a l a r r a n g e m e n t of the f i b r o u s p a r t i c l e s on the s u r f a c e s could a l s o be observed.
During the t i m e of hydration f r o m 7 d a y s t o 1 month, no c l e a r
changes in m i c r o s t r u c t u r e appeared. Occasionally one could s e e the p a r t l y p a r a l l e l orientation of the p l a t e s of hydration products and t h e i r interlocking t h r e e -dimensional f i b r o u s s t r u c t u r e ( F i g . 14). S m a l l e r hexagonal p l a t e s of low sulpho-aluminate hydrate w e r e a l s o d i s c e r n a b l e .
After 6 weeks' hydration the p a s t e with triethanolamine w a s a l s o t r e a t e d with glycol in the s a m e way that the p a s t e with no a d m i x t u r e had been t r e a t e d . The r i c h c a l c i u m hydroxide p h a s e s w e r e removed by t h i s t r e a t m e n t but to a l e s s e r extent than had been r e m o v e d f r o m the paste with no admixture. A l a r g e proportion of the r a d i a l l y - a r r a n g e d f i b r o u s p a r t i c l e s of CSH and of the plate -like f o r m s a r r a n g e d in a t h r e e -dimensional i n t e r - locking f i b r o u s s t r u c t u r e was s t i l l p r e s e n t . S o m e t i m e s the plate-like f o r m s w e r e a l s o pseudohexagonal i n shape.
Between 6 weeks and 3 m o n t h s of hydration no c l e a r changes in
m i c r o s t r u c t u r e w e r e o b s e r v e d (Fig. 15). The d e n s e l y packed m i c r o s t r u c t u r e w a s built up f r o m different f o r m s of hydration products; among t h e m one could distinguish p l a t e s o r f i b r e s of CSH, p l a t e s of low sulpho-aluminate hydrate, and l a r g e r single hexagonal r o d s of e t t r i n g i t e .
3. Hydration of C,A, C,S, gypsum and c a l c i u m lignosulphonate.
During t h e f i r s t 4 h o u r s of hydration, t h e m i c r o s t r u c t u r e of a paste of C,A, C3S and gypsum with 0.5 p e r cent calcium lignosulphonate, displayed a m i x t u r e of unhydrated g r a i n s with thin c r u m p l e d foils around t h e m
(Fig. 16). Rod-like p a r t i c l e s had a l s o begun t o a p p e a r .
At 8 h o u r s of hydration, unoriented p a r t i c l e s of ettringite-type r o d s a p p e a r e d on the s u r f a c e s of g r a i n s , but between the r o d s the l a r g e c r y s t a l s of gypsum w e r e s t i l l p r e s e n t . At 1 day hydration m o r e hydration products developed and t h e s u r f a c e s of s o m e l a r g e c r y s t a l s of gypsum became p a r t l y eroded.
266
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V o l . 1, N o . 3
F I G . 1 3
M i c r o s t r u c t u r e of C 3 S and C3A p a s t e with g y p s u m and t r i e t h a n o l a m i n e , w/e = 0. 5. Age 7 d a y s . Radial a r r a n g e m e n t a t e d g e s of p l a t e s i n f i b r o u s i n t e r l o c k i n g s t r u c t u r e of CSH. FIG. 1 4 M i c r o s t r u c t u r e of C3S and C3A p a s t e w i t h g y p s u m and t r i e t h a n o l a m i n e , w/c = 0. 5. Age 1 m o n t h . P l a t e s of h y d r a t i o n p r o d u c t s with f i b r o u s f r a c t u r e s , s o m e t i m e s of p a r a l l e l o r i e n t a t i o n , a r o u n d g r a i n s of u n - h y d r a t e d c e m e n t m i n e r a l s w i t h r o u g h f r a c t u r e . FIG. 1 5 M i c r o s t r u c t u r e of C3S and C3A p a s t e with g y p s u m and t r i e t h a n o l a r n i n e , w/c = 0. 5. Age 3 m o n t h s . P l a t e l e t s and f i b r o u s u n o r i e n t e d m i c r o s t r u c t u r e of hydration p r o d u c t s d i s p l a y m a n y d i f f e r e n t f o r m s . FIG. 1 6 M i c r o s t r u c t u r e of C 3 S and C3A p a s t e w i t h g y p s u m and c a l c i u m l i g n o s u l - phonate, w/c = 0. 5. Age 4 h o u r s . S e m i c r y s t a l l i n e f o i l s and r o d - l i k e p a r t i c l e s of h y d r a t i o n p r o d u c t s .
V o l .
1,
No. 3 267 MICROSTRUCTURE, CEMENT PASTE, ADMIXTURESFIG. 17 FIG. 18
M i c r o s t r u c t u r e of C 3 S and C 3 A p a s t e M i c r o s t r u c t u r e of C 3 S and C3A p a s t e with g y p s u m and c a l c i u m l i g n o s u l - with g y p s u m and c a l c i u m l i g n o s u l - phonate, w/c = 0.5. Age 1 day. phonate, w/c = 0.5. Age 2 d a y s . F i b r o u s p a r t i c l e s of CSH f o r m p l a t e s L o o s e , u n o r i e n t e d s t r u c t u r e of with i n t e r l o c k i n g s t r u c t u r e . f i b r o u s p a r t i c l e s .
FIG. 19 FIG. 20
M i c r o s t r u c t u r e of C,S and C3A p a s t e M i c r o s t r u c t u r e of C3S and C3A p a s t e with g y p s u m and c a l c i u m l i g n o s u l - w i t h g y p s u m and c a l c i u m l i g n o s u l - phonate, w/c = 0. 5. Age 7 d a y s . phonate, w/c = 0.5. E t c h e d with M a s s i v e s t r i a t e d s t r u c t u r e d i s p l a y e d g l y c o l f o r
$
h o u r . Age6
w e e k s . between m a n y of t h e v a r i o u s f o r m s of P l a t e s of CSH and c l e a r binder b e - hydration. t w e e n p a r t l y h y d r a t e d g r a i n s ofc e m e n t c 2mponents. S o m e of t h e g r a i n s d i s p l a y c l e a r zonal s t r u c t u r e .
V o l .
1,
No. 3 MICROSTRUCTURE, CEMENT PASTE, ADMIXTURESA f t e r 1 d a y of h y d r a t i o n , t h e f i b r o u s p a r t i c l e s of CSH w e r e f o r m e d , u s u a l l y with a n i n t e r l o c k i n g s t r u c t u r e ( F i g . 1 7 ) . S o m e t i m e s s o m e l a r g e h e x a g o n a l p l a t e s w e r e a l s o v i s i b l e . S o m e of t h e p l a t e s had a f i b r o u s i n t e r - locking s t r u c t u r e with a r i b b o n - l i k e p a r a l l e l a r r a n g e m e n t a t t h e i r e d g e s . At 2 d a y s , m o r 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 a p p e a r e d ( F i g . 1 8 ) , a n d d u r i n g t h e p e r i o d f r o m 3 t o 7 d a y s t h e y d i s p l a y e d m a i n l y a p l a t y o r f i b r o u s habit ( F i g . 19). A f t e r 1 4 d a y s of h y d r a t i o n , t h e p a s t e had d e v e l o p e d a d e n s e m i c r o - s t r u c t u r e of p a r t i c l e s of both p l a t y and f i b r o u s h a b i t . D e f i n i t e c h a n g e s of m i c r o s t r u c t u r e d u r i n g t h i s p e r i o d of h y d r a t i o n w e r e not o b s e r v e d . A f t e r t r e a t m e n t w i t h g l y c o l a t
6
w e e k s of h y d r a t i o n , one could o b s e r v e p l a t e s of l o w s u l p h o - a l u m i n a t e h y d r a t e , s i n g l e h e x a g o n a l r o d s of e t t r i n g i t e t y p e , a n d c l e a r b i n d e r s b e t w e e n t h e i n d i v i d u a l g r a i n s of t h e h y d r a t e d m i n e r a l c o m p o n e n t s . S o m e of t h e s e g r a i n s d i s p l a y e d c l e a r z o n a l s t r u c t u r e ( F i g . 20). T h e CSH a p p e a r e d a s f i b r e s o r c i g a r - s h a p e d p a r t i c l e s which f o r m e d a c o m p l e t e l y u n o r i e n t e d m a s s . At 3 m o n t h s ' h y d r a t i o n t h e r e w e r e s t i l l n o c l e a r c h a n g e s of m i c r o - s t r u c t u r e t o be o b s e r v e d . D i s c u s s i o n a n d C o n c l u s i o n s 1. U n d e r t h e c o n d i t i o n s of t h e s e e x p e r i m e n t s and with t h e p r o p o r-
t i o n s of c o m p o u n d s u s e d , i t w a s found t h a t t h e s y s t e m C,S, C,A and g y p s u m p r o d u c e d CSH p r o d u c t s of s i m i l a r n a t u r e a n d a t about t h e s a m e r a t e s a s had b e e n p r o d u c e d by t h e C,S and g y p s u m s y s t e m ( 2 ) . D i f f e r e n c e s t h a t did o c c u r w e r e t h e r e f o r e e i t h e r of a n a t u r e d i f f i c u l t t o o b s e r v e o r of m i n o r i m p o r t a n c e . 2. With no a d m i x t u r e p r e s e n t t h e f i r s t h y d r a t i o n p r o d u c t s a p p e a r e d a f t e r t h e f i r s t f e w m i n u t e s of h y d r a t i o n a s t h i n , c r u m p l e d f o i l s a n d s m a l l , r o d - l i k e e t t r i n g i t e - t y p e p a r t i c l e s . B e t w e e n 8 a n d 17 h o u r s s o m e s m a l l i r r e g u l a r g r a i n s a l s o developed. A f t e r 1 d a y of h y d r a t i o n the m i c r o s t r u c t u r e w a s m a d e up of s e m i c r y s t a l l i n e f i b r o u s p a r t i c l e s of CSH which h a d a n i n t e r - locking a r r a n g e m e n t of p l a t e s , p l a t e s of l o w s u l p h o - a l u m i n a t e h y d r a t e and r o d s of e t t r i n g i t e . D u r i n g t h e n e x t p e r i o d of h y d r a t i o n t h e m i c r o s t r u c t u r eV o l . 1,
No.
3MICROSTRUCTURE, CEMENT PASTE, ADMIXTURES
b e c a m e m o r e close-knit and m o r e hydration products a p p e a r e d . After the t r e a t m e n t with glycol and removed the r i c h l i m e p h a s e s , the predominant s t r u c t u r e was then the f i b r o u s r o s e t t e s ; the interlocking a r r a n g e m e n t of CSH and the unoriented p l a t e s of low sulpho CAH w e r e a l s o evident. No new f o r m s of hydration products a p p e a r e d a f t e r 2 d a y s of hydration.
3. The influence of e a c h of triethanolamine and c a l c i u m ligno- sulphonate on the hydration p r o c e s s of a m i x t u r e of C3A, C3S and gypsum w a s v e r y pronounced, but s i m i l a r t o t h e i r effects on the s i m p l e r s y s t e m s of C3S plus gypsum o r C3A plus gypsum ( 1 , 2).
4. The hydration p r o c e s s with triethanolamine p r e s e n t w a s s i m i l a r t o that without an a d m i x t u r e , but f a s t e r . S e m i c r y s t a l l i n e f o i l s and e t t r i n g i t e - type hydration products w e r e the dominant f o r m s up t o 4 h o u r s of hydration. After t h i s t i m e nucleation of CSH became visible, and by 8 h o u r s ' hydration CSH p a r t i c l e s w e r e p r e s e n t in the f o r m of interlocking f i b r o u s p l a t e s . CSH and l a r g e thin p l a t e s of CAH w e r e the dominant f o r m s f o r the f i r s t 3 d a y s of hydration. At 3 d a y s , m o r e e t t r i n g i t e -type r o d s a p p e a r e d in a r o s e t t e a r r a n g e m e n t . After t h i s t i m e the m i c r o s t r u c t u r e w a s quite d e n s e , and no f u r t h e r significant change i n morphology took place. The t r e a t m e n t with glycol removed s m a l l e r amounts of the r i c h l i m e p h a s e s of the hydration products than i t had when no a d m i x t u r e w a s p r e s e n t . After t r e a t m e n t the m i c r o s t r u c t u r e displayed a t h r e e - d i m e n s i o n a l f i b r o u s a r r a n g e m e n t of CSH, and a l s o s o m e r o s e t t e f o r m a t i o n s .
5. The hydration p r o c e s s began m o r e slowly when calcium
lignosulphonate was p r e s e n t than when no a d m i x t u r e w a s p r e s e n t . The t h i n c r u m p l e d foils which a p p e a r e d in the f i r s t f e w m i n u t e s of hydration w e r e dominant up t o 8 h o u r s . At t h i s t i m e m o r e hydration p r o d u c t s , with m o s t l y ettringite-type r o d s between t h e m , a p p e a r e d . By t h e end of one d a y of
hydration, CSH f i b r e s f o r m e d a n interlocking s t r u c t u r e . The m i c r o s t r u c t u r e then became m o r e d e n s e a s m o r e hydration products developed. The t r e a t - m e n t with glycol removed l a r g e r amounts of hydration p r o d u c t s , with the
r e s u l t that the remaining products exhibited an unoriented f i b r o u s s t r u c t u r e . Comparing t h e s e r e s u l t s with those p r e v i o u s l y r e p o r t e d ( 2 ) f o r the s y s t e m
MICROSTRUCTURE, CEMENT PASTE, ADMIXTURES
V o l . 1 , No. 3
C 3 S , C,S p l u s g y p s u m w i t h a d d e d l i g n o s u l p h o n a t e , one c o n c l u d e s t h a t t h e p r e s e n c e of C,A d o e s , t o s o m e e x t e n t a t l e a s t , r e d u c e t h e r e t a r d i n g a c t i o n of t h e l i g n o s u l p h o n a t e on t h e h y d r a t i o n p r o c e s s of C3S. T h i s i s e s s e n t i a l l y i n a g r e e m e n t w i t h o t h e r s , and h a s been m o s t r e c e n t l y s u b s t a n t i a t e d by Young
( 9 ) .
6 .
F r o m t h i s and t h e p r e v i o u s s t u d i e s i n t h i s s e r i e s (1, 2 ) a p r e l i m i n a r y p i c t u r e of t h e f o r m a t i o n of t h e u l t i m a t e m i c r o s t r u c t u r e of s u c h s i l i c a t e - a l u m i n a t e s y s t e m s b e g i n s t o e m e r g e . T h e e a r l y , t h i n , a m o r p h o u s f i l m s c o n v e r t m o r e o r l e s s r a p i d l y t o v e r y t h i n c r u m p l e d f o i l s and t o n e e d l e s h a p e s o r f i b r e s . T h e s e a r r a n g e t h e m s e l v e s b e t w e e n t h e p s e u d o m o r p h s of t h e o r i g i n a l m i n e r a l s i n b u n d l e s o r a g g r e g a t i o n s w h i c h g r a d u a l l y f i l l i n w i t h h y d r a t i o n p r o d u c t s t o f o r m p l a t e s . T h e p l a t e s i n t u r n a r r a n g e t h e m s e l v e s i n t o t a b u l a r m a s s e s w h i c h t h e n c o n s t i t u t e t h e m i c r o s t r u c t u r e . T h e two o r g a n i c a d m i x t u r e s u s e d , while t h e y s t r o n g l y a f f e c t t h e r a t e s of r e a c t i o n s , d o not a p p e a r t o s i g n i f i c a n t l y i n f l u e n c e t h i s f o r m of t h e f i n a l s t r u c t u r e . S e p a r a t e e x p e r i m e n t s c a r r i e d out i n t h i s l a b o r a t o r y have c o n f i r m e d t h a t t h e m e c h a n i c a l p r o p e r t i e s of c e m e n t p a s t e s a t a d v a n c e d a g e s of h y d r a t i o n a r e not g r e a t l y a f f e c t e d by t h e p r e s e n c e of t h e s e and o t h e r a d m i x t u r e s . 7 . T h e e t c h i n g e x p e r i m e n t s p e r f o r m e d i n t h i s and t h e p r e v i o u s s t u d y ( 2 ) p r o v e r a t h e r c o n c l u s i v e l y t h a t t h e p l a t e s c o n s t i t u t i n g t h e t a b l e t s had evolved f r o m a f i b r o u s f o r m . M o r e w o r k i s r e q u i r e d t o t h r o w light on p r e c i s e l y w h a t t a k e s p l a c e i n t h i s f i l l i n g - i n p r o c e s s ( 1 0 ) . A c k n o w l e d g e m e n t s We acknowledge g r a t e f u l l y t h e i n v a l u a b l e 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 w e a r e a l s o m o s t g r a t e f u l . T h i s i s a c o n t r i b u t i o n 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 , 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 , and i s p u b l i s h e d w i t h 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 D i v i s i o n .Vol. 1, No. 3
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