Phase identification during early and middle hydration of tricalciumsilicate (Ca3SiO5)

CEMENT and CONCRETE RESEARCH. Vol. 19, pp. 411-422, 1989. Printed in the USA 0008-8846/89. S3.OO&O0. Copyright (c) 1989 Pergamon Press plc.

PHASE IDENTIFICATION DURING EARLY AND MIDDLE HYDRATION OF TRICALCIUMSILICATE (Ca3SiO 5)

R. Melzer* and E.Eberhard : Institut fur Mineralogie LIniversit~it Hannover, D-3000 Hannover - present address : Institut fiJr Mineralogie und Kristallographie, TtIBerlin, D-1000 Berlin 12

(Refereed) (Received July ]7, 1988; in final form Feb. 23, 1989) Abstract The hydration reaction of tricalciumsilicate was observed during the first 14 days with electron microscopic methods. This investigation aimed mainly at the identification of calcium-silicate-hydrate (CSH) by TEM diffraction techniques. By this method crystalline structural

units in CSH gel

and

four crystalline

CSH

phases could be identified. These phases coexist side by side from 8 hours after the beginning of the hydration until the end of the observation period. Their electron diffraction patterns look similar to that of the l l A - t o b e r m o r i t e but the d-spacings

vary

slightly.

Nevertheless,

the

main

reflections

were

accordingly

indexed to determine lattice constants. The crystalline phases are designated as c~-, {3- , y- und 8-CSH. As a further reaction product, a sheet-like epitaxial intergrowth of different CSH phases and also portlandite parallel to the basal plane was observed. T h e s e layers, about 10 to I00 nm thick, are rotated around the c-axis because of small differences in the lattice c o n s t a n t s .

An interpretation

of the

hydration process of tricalciumsilicate is given, because of the appearance of new phases.

Introduction The reaction product of the hydration of tricalciumsilicate C3S (cement nomenclature: C=CaO, S=SiO 2 and H=H20) are calcium hydroxide (Ca(OH) 2) and calciumsilicate-hydrate phases (CSH). While the structure and appearance of calcium. hydroxide are relatively wellknown, there is a lack of information about the chemical composition and the structure of CSH. The criteria of distinguishing between the C S H phases are based primarily on the morphologies as determined 411

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by e l e c t r o n o p t i c a l m e t h o d s (S,13) and t h e i r c o m p o s i t i o n s . S e v e r a l c o n t r a d i c t o r y d a t a e x i s t r e g a r d i n g t h e c o m p o s i t i o n s o f t h e h y d r a t e s , w h i c h s e e m to vary d u r i n g the h y d r a t i o n p r o c e s s (4,5,19,21). The m a i n o b s t a c l e involved in t h e d e s c r i p t i o n and c h a r a c t e r i z a t i o n o f CSH is i t s s m a l l c r y s t a l l i t e size and i t s p o o r c r y s t a l l i n i t y . Hence, X - r a y d i f f r a c t i o n t e c h n i q u e s f o r s t r u c t u r e d e t e r m i n a t i o n fail due to i n s u f f i c i e n t intensity of characteristic reflections. Electron optical methods yield better results, b e c a u s e t h e d i f f r a c t e d a r e a o f an e l e c t r o n b e a m is m u c h s m a l l e r . T a y l o r (20) c h a r a c t e r i z e d a l a t e CSH p h a s e as having a t o b e r m o r i t e - l i k e s t r u c t u r e , b e c a u s e o f t h e s i m i l a r t r a n s m i s s i o n e l e c t r o n m i c r o s c o p i c ( T I M ) d i f f r a c t i o n p a t t e r n s and l a t t i c e p a r a m e t e r s t o n a t u r a l CSH l l • - t o b e r m o r i t e . U s i n g T i M t e c h n i q u e s as w e l l Gard & T a y l o r (7) r e l a t e t h e s t r u c t u r e o f an e a r l y h y d r a t i o n p r o d u c t to t h a t o f t h e m i n e r a l jennite. This present investigation was initiated because of the previous successes, t h a t t h e T i M t e c h n i q u e s have y i e l d e d in c h a r a c t e r i z i n g CSH p h a s e s .

Experimental The C3S u s e d f o r t h e h y d r a t i o n e x p e r i m e n t s w a s m a d e f o l l o w i n g the get m e t h o d o f H a m i l t o n & H e n d e r s o n (11). As a f i r s t s t e p , C a C O 3 w a s d e s o l v e d in d i l u t e nitric acid. The n i t r a t e s w e r e r e m o v e d t h r o u g h on e v a p o r a t i n g to a g e l - l i k e s u b s t a n c e . This m a s s , t h e n d i s s o l v e d in w a t e r , w a s m i x e d w i t h t h e a p p r o p r i a t e q u a n t i t y o f t e t r a e t h y l o r t h o s i l i c a t e . A h o m o g e n e o u s s o l u t i o n w a s f o r m e d by a d d i t i o n o f a l c o h o l . F o r t h e g e l p r o c e s s 33% a m m o n i a s o l u t i o n was u s e d . The g e l was d r i e d at SO, 70 a n d 100 ° C a t each t e m p e r a t u r e f o r 24 h o u r s . T h e s y n t h e s i s was c a r r i e d o u t by f i r i n g at 1400 °C. The p r o d u c t gave t h e s a m e p o w d e r p a t t e r n s as t h e t r i c l i n i c C3S p h a s e i n v e s t i g a t e d b y J e f f r e y (19S2, JCPDS-No.31-301). SEM p h o t o g r a p h s o f this s y n t h e t i c p r o d u c t d i s p l a y no r e g u l a r s h a p e and t h e a v e r a g e g r a i n size w a s 2 ~zm. F o u r d i f f e r e n t h y d r a t i o n e x p e r i m e n t s s h o w n in t a b l e 1 w e r e c a r r i e d out.

Table 1

Experimental conditions of the four hydration experiments

w/s ratio

hydration atmosphere

storage time before hydration

test series A

0.7

argon

-

test series B

1.4

argon

-

test series C

1.4

argon

80 d a y s

test series D

1.4

air

80 d a y s

The e x p e r i m e n t a l c o n d i t i o n s m e n t i o n e d a b o v e s h o u l d s h o w t h e e f f e c t o f w / s r a t i o s , s t o r a g e t i m e s and c a r b o n i c a c i d g a s on t h e f o r m a t i o n o f t h e d i f f e r e n t CSH phases. F r o m e a c h t e s t s e r i e s s p e c i m e n s w e r e t a k e n a f t e r 1, 2, 4, 8, 12, 24, 48, 96, 168 a n d 336 h o u r s ( d u r i n g a 14 day p e r i o d ) a f t e r t h e b e g i n n i n g o f t h e h y d r a t i o n r e a c t i o n for X-ray and electron microscopical investigations. Quantitative X-ray analysis was used to determine the kinetics of the hydration r e a c t i o n s . T h e r e f o r e , t h e d e c r e a s e o f t h e a m o u n t o f C3S a n d t h e i n c r e a s e o f Ca(OH) 2 w e r e d e t e r m i n e d . This q u a n t i t a t i v e a n a l y s i s w a s c a r r i e d o u t w i t h a Guinier c a m e r a

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413 C3H HYDRATION,

C-S-H CRYSTALLINITY,

TEM

using the film method. Quartz was used as an internal standard. The hydration products were examined with a transmission electron microscope (TEM) model H 800 and a scanning electron microscope (SEM) model S 530 from Hitachi during the first 14 days of the hydration reaction. For the TEM investigation the samples were suspended in isopropyl alcohol and transferred to a copper grid (O=3mm) overlain with a thin carbon film. Specimens for SEM investigation were sputtered with an ~ 1SOA thick gold layer. Results The main result of this investigation was the characterization of different CSH phases during the hydration process by diffraction techniques. Furthermore, it was proved, that these phases coexist t o g e t h e r . In this respect, the evaluation of the four test series showed no significant differences. As the objective of this paper lies in the presentation of the newly formed phases, only the results of one test series of the quantitative X-ray analysis will be shown. They will d e m o n s t r a t e the kinetics of the investigated hydration reactions. The results including the kinetics will be the subject of another report. 1.Quantitative X-ray analysis The kinetics of test series A determined by the quantitative X-ray analysis was shown in Fig.1. This figure exhibits the decrease of the amount of C3S and the increase of the amount of Ca(OH) 2. An extrapolation of the C3S curve s h o w s , that the hydration would be complete after 59 hours. Fig.1 also presents the onsets of the formation of the CSH phases observed by electron optical methods. 2. TEM Investigation It was possible to distinguish with the TEM two different formation processes concerning newly formed phases. In the first case, there is the radial g r o w t h of 100

100

o 80

80

o 60

60

C3S

[ -..~]

°\

40

Ca(OH) 2

40 o

"j'j

20

i

~

1

2

to

4

,

,

i

8

12

24

1.

20

i

|

i

i

48

96

168

336

'("J

FigA. A plot showing the decrease of the amount of C3S (o) and increase of the a m o u n t of Ca(OH) 2 (*) as a function of time and the onset of formation of different C S H phases of test series A O - onset of the formation of a vermicular- to sword-like C S H phase H - onset of the formation sheet-like C S H phases and calcium hydroxide

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needle-like CSH particles out of a gel, which s u r r o u n d s C3S grains. Furthermore, CSH phases with sheet-like morphology and calcium hydroxide crystallize in the solution. (i) Typical reaction products formed directly from pure C3S The collection of the diffraction p h o t o g r a p h s in Figs. 2 b - 4 b exhibits an increasing degree of crystallinity. With increasing crystallinity, a change in morphology is also recognizable. A first ordering in the CSH gel (two diffraction rings) is represented by vermicular particles, then more needle-like (type 1) and at last broader swordlike (type 2) crystals occur (see Figs.2a-¢a). The particles shown in Fig.2a gave only two diffuse interference rings with d - s p a c i n g s of 2.94 and 1.10 A (Fig.2b) . Phases with b e t t e r morphological development gave p a t t e r n s comparable to those of IlAtobermorite (Fig.3b and 4b), however with slightly differing d-spacings. Nevertheless, the reflections are indexed accordingly as 400, 040 and 220 (y*=90°). Thus, the aand b - l a t t i c e c o n s t a n t s are a = 10.1 A and b = 7.8 A Type 1 and type 2 phases are designated both as a-CSH. CSH phases crystallized in the solution are shown in Fig.S . These are ~ypically sheet-like particles with irregular shapes. They often form crystalline conglomerations. Fig.6b nearly c o n s t i t u t e s a single-crystal diffraction photograph. The interferences of this phase, termed I~-CSH in this study, are also similar to those of ll.~-toberm o r i t e , a s c~-CSH. The measured a- and b-lattice c o n s t a n t s are a = 9.75 A and b = 6.85 A . A d d i t i o n a l r e f l e c t i o n s , i n d e x e d as 400, 0 4 0 and 440, c o u l d be r e l a t e d t o a n o t h e r phase, y - C S H , w i t h t h e f o l l o w i n g l a t t i c e c o n s t a n t s : a = lO.SS A

and b = 7.29 A ~- and y - C S H are typically grown epitaxially together. Whereas ~-CSH is found isolated in the solution, 7-CSH was only found t o g e t h e r with ~-CSH. The relation

a

b

Fig.2. a TEM p h o t o g r a p h of a gel-like mass of test series A after a hydration time of 48 hours (lcm=O.4~m) b TEM diffraction p h o t o g r a p h of the gel-like mass (diffracted area marked by "x", represents ordering in the gel)

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415 C3H HYDRATION,

a

C-S-H CRYSTALLINITY,

TEM

b

Fig.3. a TEM p h o t o g r a p h of a needle-like phase of test series B after a hydration time of 12 hours (Icm=--O.4gm) b TEM diffraction p h o t o g r a p h of the needle-like phase (diffracted area marked by "x", represents ordering in the gel and c~-CSH)

of the reflections of the two phases in Fig.6b is schematically subdivided in Fig.7, Because of missing p a r a m e t e r s , the lattice parameter c could not yet be determined. Calcium hydroxide Formed particles with sizes up to 30 ~m. Small crystalIites grew idiomorphically in the form of hexagonal plates. With increasing size, the regular shapes disappear. Simultaneously, m o s t of the diffraction p h o t o g r a p h s show additional diffuse rings or discreet reflections. The diffuse rings are the same as

a

b

Fig.4. a T E M photograph of a sword-like phase of test series A after a hydration time of ! hour (Icm---0.4~m) b T E M diffraction photograph of the sword-like phase (diffracted area marked by "x", represents =-CSH)

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R. Melzer and E. Eberhard

f~

a

b

Fig.& a TEM p h o t o g r a p h o f c o n g l o m e r a t e d C S H of t e s t s e r i e s B a f t e r a h y d r a t i o n t i m e o f 7 h o u r s (lcm=-O.4~m) b TEM d i f f r a c t i o n p h o t o g r a p h o f t h e c o n g l o m e r a t e d CSH ( d i f f r a c t e d a r e a m a r k e d by "x", r e p r e s e n t s ~ - C S H ) t h o s e o b s e r v e d a t t h e m a r g i n o f C3S g r a i n s . The d i s c r e e t r e f l e c t i o n s in F i g . 8 b b e l o n g p a r t i a l l y to [3- and y - C S H , t h e o t h e r o n e s a r e r e l a t e d to a Fourth p h a s e w i t h the f o l l o w i n g a - and b - l a t t i c e c o n s t a n t s : a = 11.2 and b = 8.0 A . The p o s i t i o n i n g o f t h e r e f l e c t i o n s d e m o n s t r a t e s an e p i t a x i a l i n t e r g r o w t h b e t w e e n t h e p h a s e s . An i n c r e a s i n g i n t e r g r o w t h o f d i f f e r e n t p h a s e s is c o r r e l a t e d with a r o t a t i o n

a

b

Fig.6. a TEM p h o t o g r a p h o f s h e e t - l i k e p l a t e s o f t e s t s e r i e s B a f t e r a h y d r a t i o n t i m e o f 240 h o u r s (lcm-=lgm) b TEM d i f f r a c t i o n p h o t o g r a p h o f t h e s h e e t - l i k e p l a t e s ( d i f f r a c t e d a r e a m a r k e d by "x", r e p r e s e n t s ~- and "(-CSH)

Vol. 19, No. 3

417 C3H HYDRATION,

C-S-H

CRYSTALLINITY,

TEM

t b* o

o÷

Fig.7.

Indexing of the reflections shown in Fig.6b o = [3-CSH + : y-CSH

o

•

o

~

04O

+o

o22O

o

o+

0

o

4-0

0

o÷

÷

•

~;

o

0

*0

of the crystalline plates parallel to the basal plane (see schematic diagramm Fig.9) as demonstrated by an arcuate extension of the reflections. The maximal observed rotation is 2S°. Stacked thin plates have been recognized from the morphological point of view. Solid a - C S H was observed for the first time after I hour of hydration and the phases in the solution after 8 hours. After this period of the hydration process all phases coexist together.

a

Fig.8.

b

a T E M photograph of sheet-like plates of test series B after a hydration time of 240 hours (IcmEO.4pm) b T E M diffraction photograph of the sheet-like plates (diffracted area marked by "'x", represents {3-, ~'- and ~-CSH)

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Vol. 19, No. 3 R. Melzer and E. Eberhard

C-axis

Fig.9. Schematical diagram of the epitaxial intergrowth of portlandite and CSH plates

3. SEM Investigation A specimen hydrated for 12 hours of test series B was chosen, to compare the morphological appearance of the phases with that observed by TEM techniques. Fig.lO is a b a c k s c a t t e r e d SEM photograph, which represents a survey of the various phases. Sword-like particles, c~-CSH, are observed in the middle of the picture coating larger irregular shaped particles. There are also many sheet-like crystals with sizes up to several tzm. Special care was taken on "calcium hydroxide" particles, because of the epitaxial intergrowth of phases found by TEM. There are two different morphologies. The first type are idiomorphical hydrates, while the second type consists of the book-like epitaxial intergrowth of crystal plates (Fig.ll) . The thickness of the plates is in the range of 10-100 nm. Further characterization of the plates is not possible presently, because they can not be seperated from one another.

Discussion A first ordering of CSH gel and the occurence of four crystalline CSH phases were observed by TEM diffraction within the first 14 days of the hydration of C3S. Their appearance and d-spacings are summarized in table 2 . . The needle-like (type I) and sword-like (type 2) crystals of ~-CSH are obviously the main reaction product. Hence, there is a good agreement with other studies (1,S,13,20}. According to Jennings et al. (13) and Diamond (S), similar needles were formed during middle hydration and radiating from C3S grains as well. Comparable

Fig.lO.

SEM survey picture of a 12 hours hydrated specimen

Vol. 19, No. 3

419 C3H HYDRATION, C-S-H CRYSTALLINITY,

Fig.ll.

Table 2

SEM photograph showing the assumed plate-like o f P o r t l a n d i t e and C S H - p h a s e s

TEM

construction

CSH p h a s e s w i t h t h e f o l l o w i n g l a t t i c e c o n s t a n t s o r d - s p a c i n g s and t h e i r m o r p h o l o g i c a l a p p e a r a n c e , o b s e r v e d d u r i n g t h e f i r s t 14 d a y s o f t h e h y d r a t i o n o f C3S by TEM d i f f r a c t i o n t e c h n i q u e s are l i s t e d below

phase

lattice constants or d-spacings

morpological appearance

gel-like phase

diffuse rings with d ~ 2.94 A a n d d ~ 1.10 A

vermicular-like, quasi crystalline size ~ 1 ~m

=-CSH

a = 10.1 A b=7.8A

f r o m C3S g r a i n s r a d i a l g r o w n type I : needle-like type 2 : sword-like (higher degree of crystallinty) size ~ 1 gm

[3-CSH

a = 9,75 A b = 6.85 A

i)sheet-like particles, often conglomerated ii)epitaxial intergrowth with p o r t l a n d i t e a n d / o r y - and

8-CSH size ~ 1 gm y - CSH

a = 10.SS A b= 7.29A

epitaxially grown together with ~ - C S H a n d / o r p o r t l a n d i t e and

8-CSH S - CSH

a = 11.2 • b = 8.0 A

epitaxially grown together with p o r t l a n d i t e , (3- a n d T - C S H

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h y d r a t e s are d e s c r i b e d by Bailey & S t e w a r t (1). S t u c k e & Majumdar (20) and Ghose et al. (8). Bailey & S t e w a r t (1) o b s e r v e d a t r a n s f o r m a t i o n of a n e e d l e - l i k e to a s h e e t - l i k e p r o d u c t a f t e r 24 hours. Jennings & P a r r o t t (14) found no c l e a r division b e t w e e n two d i f f e r e n t m o r p h o l o g i c a l p h a s e s and s u g g e s t e d , t h a t the p h a s e s b e l o n g to one type of CSH. These o b s e r v a t i o n s s u p p o r t the division of ct-CSH into types 1 and 2 and the e x i s t e n c e of an o r d e r e d gel as an i n t e r m e d i a t e stage. By SEM t e c h niques, the i d e n t i f i c a t i o n of {3-CSH, the s o l u t i o n r e l a t e d phase, is a l m o s t impossible. There are no criteria for d i s t i n g u i s h i n g b e t w e e n {3-CSH and calcium hydroxide, because the p a r t i c l e s are too small f o r energy d i s p e r s e d X - r a y analysis EDXA and t h e i r c o m p o s i t i o n s are unknown. Jennings et al. (13) d e s c r i b e d " p a r t l y c r u m b l e d i n t e r l o c k e d foils" by TEM. Diamond (S) c o n s e q u e n t l y o b s e r v e d no c o m p a r a b l e p r o d u c t s by SEM. The a- and b - l a t t i c e c o n s t a n t s of T-CSH are nearly identical with those of jennite, whereas the cell a n g l e s deviate m a r k e d l y (2). T h e r e f o r e , there seem to be no s t r u c t u r a l s i m i l a r i t i e s b e t w e e n the CSH phase and the mineral jennite, as p r o p o s e d p r e v i o u s l y by Gard & Taylor (6). Moreover, Gard & T a y l o r (5) d e s c r i b e d the m o r p h o l o g y as a n e e d l e - l i k e phase, which from this s t u d y a p p e a r s to be ~-CSH. The l a t t i c e c o n s t a n t b = 7.29 • of T-CSH can be r e l a t e d to a D r e i e r k e t t e as in l l ] ~ - t o b e r m o r i t e (10). C o n s e q u e n t l y the f o r m a t i o n of ~/-CSH s u p p o r t s the p r o p o s a l of the p r o g r e s s i v e s i l i c a t e polyrrferization as found by Dent G l a s s e r et al. (4). At p r e s e n t , f u r t h e r a s s e r t i o n s a b o u t the s t r u c t u r e of the CSH p h a s e s are not possible. It m u s t be s t r e s s e d , t h a t in spite of the s i m i l a r TEM d i f f r a c t i o n p a t t e r n s , there was no indication, t h a t the s t r u c t u r e s are i d e n t i c a l to t h a t of l l A - t o b e r m o r i t e , a l t h o u g h c e r t a i n s t r u c t u r a l units may be r e l a t e d . Combined s t u d i e s involving TEM and EDXA techniques c o u l d yield new r e s u l t s which allow s t r u c t u r a l c o n c l u s i o n s from b o t h the c o m p o s i t i o n s and l a t t i c e p a r a m e t e r s to be drawn. Kurczyk & Schwiete (16) p r o p o s e d an e p i t a x i a l i n t e r g r o w t h of the t o b e r m o r i ~ e like phase of Taylor (21) and calcium h y d r o x i d e b e c a u s e of s i m i l a r d - s p a c i n g s . Their p r o p o s a l is verified by this investigation. Groves (9) examined a m i c r o c r y s t a l line form of calcium hydroxide in P o r t l a n d c e m e n t p a s t e s o f low w a t e r / s o l i d r a t i o s by TEM. The typical p a r t i c l e m o r p h o l o g i e s c o n s i s t of p l a t e s 10 nm thick, growing p a r a l l e l to the b a s a l plane. The s t a c k i n g along the c - a x i s is variable. Groves (9) e x p l a i n e d this to be due to i m p e r f e c t i o n s in the s t r u c t u r e r e l a t e d to rapid c r y s t a l l i s a t i o n . Diffuse s c a t t e r i n g around calcium h y d r o x i d e r e f l e c t i o n s was explained to be c a u s e d by a coating of the p l a t e s in the CSH gel. This i n v e s t i g a t i o n shows an e p i t a x i a l i n t e r g r o w t h of d i f f e r e n t p l a t e s , whereby the d i s o r i e n t a t i o n of the p l a t e s can be e x p l a i n e d by d i f f e r e n t l a t t i c e p a r a m e t e r s , in c o n t r a s t to Groves (9). Differing m o r p h o l o g i e s of calcium hydroxide have a l s o been r e p o r t e d by Marchese (17) and J e n n i n g s & P a r r o t t (14). As a r e s u l t of this investigation, t h e d e t e r m i n a t i o n of C / S mole r a t i o s of the p r o d u c t s of c a l c i u m - s i l i c a t e - h y d r a t e c o m p o s i t i o n t h r o u g h i n d i r e c t c a l c u l a t i o n , with values derived from the d e c r e a s e of C3S and t h e increase of calcium hydroxide, as d e t e r m i n e d by q u a n t i t a t i v e X - r a y analysis, e x t r a c t i o n or t h e r m o g r a v i m e t r a l m e t h o d s (3,15,18,19) has to be c o n s i d e r e d d o u b t f u l . The n e c e s s a r y c o n d i t i o n of having one phase at a given time during h y d r a t i o n is no l o n g e r valid, b e c a u s e of the c o e x i s t a n c e of four d i f f e r e n t CSH p h a s e s as shown by our o b s e r v a t i o n . F u r t h e r m o r e , a l t h o u g h there were r e m a r k a b l e d i f f e r e n c e s in the k i n e t i c s of the four t e s t s e r i e s (Melzer, u n p u b l i s h e d r e s u l t s ) , the same p h a s e s are found in each t e s t series. Thus, d e t e r m i n a t i o n s of the C / S m o l a r r a t i o s of the C3S h y d r a t i o n p r o d u c t s have to be done using new techniques, which p e r m i t t h e d e t e c t i o n of d i s t i n c t micron or s u b m i c r o n p a r t i c l e s in the bulk mixture. On the b a s i s of this i n v e s t i g a t i o n a h y d r a t i o n model can be c o n s t r u c t e d (Fig.12). We p r o p o s e t h a t at the beginning of the r e a c t i o n gel was f o r m e d on the surface of

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C3H HYDRATION, C-S-H CRYSTALLINITY, TEM C3S grains. With increasing order in the gel TEM diffraction p a t t e r n s can be observed and c o n c o m i t a n t developments in m o r p h o l o g y are noticeable. The first step is a vermicular-like formation, with two diffuse rings shown in TEM diffraction. Higher orders of crystallinity give the diffraction p a t t e r n s of ct-CSH, whose morphological habit is needle-like (type 1) or s w o r d - l i k e (type 2). This phase was observed during the entire investigation period. After 8 hours and probably the end of the induction period, phases began to crystallize from the solution. E3-CSH, a s h e e t - l i k e phase, is often c o n g l o m e r a t e d or epitaxially grown t o g e t h e r with other phases. T- and ~-CSH grow only epitaxially with o t h e r phases. Calcium hydroxide crystallizes in two differing forms: a. c o m p a c t plates, often idiomorphical in f o r m of hexagonal plates b. plate-like epitaxial i n t e r g r o w t h with L3-, T- and $-CSH .

/~-CSH

Ca(OH) 2

\

/ Ca(OH) 2 CSH

Fig.12.

/

I

/

1

solution

\

/ -CSH '-CSH

Hydration model of C3S during the first 14 days of the reaction

Acknowledgement We wish to thank you Dr. S.A. Hamid for the preparation of the TEM pictures and Dr. C. Geiger for reading the manuscript. References 1. Bailey, J.E., Stewart, H.R. (1984): C3S Hydration Products viewed in a Cryo Stage in SEM. Journal of Materials Science Letters 3, 411-414 2. Carpenter, A.B., Chalmers, R.A., Gard, J.A., Speakman, K., Taylor, H.F.W. (1968): Jennite, a New Mineral. Am. Min. $|, 56-74 3. Chatterji, S. (1980): C/S Mole Ratio of Fully Hydrated Tricalcium Silicate Pastes. Cem. Con. Res. 10, 783-787 4. Dent Glasser, L.S., Lachowski, E.E., Mohan, K., Taylor, H.F.W. (1978):A Multi-

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S. 6. 7. 8. 9. 10. 11. 12. 13. 14. IS. 16. 17. 18. 19. 20. 21. 22.

Diamond, S. (1976): Hydraulic C e m e n t Pastes: Their S t r u c t u r e s and Properties. Cem. Con. Assoc., Wexham Springs, Slough, p.SS Gard, J.A., Mohan, K., Taylor, H.F.W. (1980): Analytical Electron Microscopy of C e m e n t Pastes: I. Tricalcium Silicate Pastes. J. Am. Ceram. Soc. 63, 336-337 Card, J.A., Taylor, H.F.W. (1976): Calcium Silicate Hydrate tI("CSH(II))"). Cem. Con. Res. 6, 667-678 Ghose, A., Jennings, H.M., Pratt, P.L., Barnes, P. (1980): Fibrous Growth Products in the Hydration of Portland C e m e n t and Related Systems. 7th Intl. Congress on the Chemistry of Cements, Paris, vol. IV, 599 Groves, G.W. (1981): Microcrystalline Ca(OH) 2 in Portland C e m e n t Pastes of Low W a t e r / C e m e n t Ratios. Cem. Con. Res. 11, 713-718 Hamid, S.A. (1981): The Crystal S t r u c t u r e of the I1A Natural T o b e r m o r i t e Ca2.2S(Si307.s(OH)I.S).IH20. Z e i t s c h r i f t fur Kristallographie 1S4, 189 Hamilton, D.L., Henderson, C.M.B. (1968): The Preparation of Silicate C o m p o s i t i o n s by a Gelling Method. Mag. 36, 832-838 Jeffrey, J.W. (1952): The Crystal S t r u c t u r e of Tricalcium Silicate. Acts Cryst., Published for the Intl. Union of Cryst. S, 26-35 Jennings, H.M., Dalgleish, B.J., Pratt, P.L. (1981): M i c r o s t r u c t u r a l Analysis of Hydrated Alite Pastes, Part 2 Microscopy and Reaction Products. J. Material Science 21, 4053 Jennings, H.M., Parrott, L.J. (1986), J. Mareial Science 21, 40S3 Khan, Mohan, K., Taylor, H.F.W. (1985): Pastes of Tricalcium Silicate with Rice H u s k Ash. Cem. Con. Res. 1S, 89-92 Kurczyk, H.G., Schwiete, H.E. (1960): Tonindustrie und Keramische Rundschau 84, $85-598 Marchese, B. (1978): Microstructure of Mature Alite Pastes. j. Am. Ceram. Soc. 61, 349 Odler, I., SchUppstahl, J. (1981): Early Hydration of" Tricalcium Silicate Ill. Control of the Induction Period. Gem. Con. Res. 11, 76S Shebl, F.A., Helmy, F.M., Ludwig, U. (198S): A New Approach on the Hydration Mechanism of Tricalcium Silicate. Cem. Con. Res. 1S, 747 Stucke, M.S., Majumdar, A.J. (1977): The Morphology and Composition of an I m m a t u r e Tricalcium Silicate Paste. Cem. Con. Res. 7, 711-718 Taylor, H.F.W. (1964): The Chemistry of Cements. Academic Press, London and New York, 1964 Taylor, H.F.W., Newburry, D.E. (1984): Calcium Hydroxide Distribution and Calcium Silicate Hydrate Composition in 03S and {3-02S Pastes. Cem. Con. Res. 14, 93-98