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Effect of synthesis temperature and cooling conditions of beta-dicalcium silicate on its hydration rate
CEMENT and CONCRETE RESEARCH. 0008-8846/83/010041-08503.00/0
E F F E C T OF S Y N T H E S I S OF B E T A - D I C A L C I U M
Vol. 13, pp. 41-48, 1983. Printed in the USA. Copyright (c) 1982 Pergamon Press, Ltd.
TEMPERATURE AND S I L I C A T E ON ITS
COOLING CONDITIONS HYDRATION RATE
P. F i e r e n s and J. T i r l o c q S e r v i c e de S c i e n c e des M a t ~ r i a u x F a c u l t ~ des S c i e n c e s , U n i v e r s i t ~ de M o n s Belgique
(Communicated by D.M. Roy) (Received June 4, 1982) ABSTRACT Beta-dicalcium s i l i c a t e s are s y n t h e s i z e d b e t w e e n 1050 and 1 5 5 0 ° C and are c h a r a c t e r i z e d w i t h r e s p e c t to their s t r u c ture d e f e c t s by c a t h o d o l u m i n e s c e n c e , thermoluminescence and E . S . R . . P a s t e h y d r a t i o n k i n e t i c s are f o l l o w e d , in the e a r l y stage, by e l e c t r i c a l conductivity and m i c r o c a l o r i m e t r y ; for l o n g e r d u r a t i o n s , D . T . G . and q u a n t i t a t i v e X . R ° D . are used. Experimental r e s u l t s s h o w that s y n t h e s i s t e m p e r a t u r e aff e c t s g r e a t l y the h y d r a t i o n r a t e from the b e g i n n i n g to extended periods, while cooling conditions s e e m to h a v e no s i g n i f i c a n t influence. Hydration rate evolution with firing temperature and s a m p l e s c h a r a c t e r i s t i c s are comp a r e d in the f i n a l d i s c u s s i o n . I.
Introduction
M a n y f a c t o r s m a y i n f l u e n c e the h y d r a t i o n k i n e t i c s of b e t a dicalcium silicate. A m o n g these, the s y n t h e s i s temperature effect has not yet b e e n f u l l y s t u d i e d . O n l y few d a t a a b o u t this s u b j e c t are a v a i l a b l e , for e x a m p l e those of B u t t and T i m a s h e v (|), P a s h c h e n k o and c o - w o r k e r s (2) and K a n t r o and W e i s e (3). In the p r e s e n t work, s a m p l e s of b o r o n s t a b i l i z e d B v a r i e t y are f i r e d at a g i v e n t e m p e r a t u r e b e t w e e n 1050 and 1550°C and c h a r a c t e r i zed by s e v e r a l s o l i d state m e t h o d s w i t h r e s p e c t to their s t r u c t u r e defects. As those t e c h n i q u e s are v e r y s e n s i t i v e to the impurities of the solid, h i g h p u r i t y raw m a t e r i a l s are c h o o s e n and c a r e f u l l y employed. Paste hydration k i n e t i c s are f o l l o w e d f i r s t by e l e c t r i c a l conductivity and c o n d u c t i o n m i c r o c a l o r i m e t r y ; for l o n g e r d u r a t i o n s , D . T . G . and X . R . D . A . are used. F i n a l y , the e f f e c t of s y n t h e s i s t e m p e r a t u r e on the h y d r a u l i c reactivity and the s t r u c t u r a l characteristics of b e t a - d i c a l c i u m s i l i c a t e is d i s c u s s e d . 41
42
Vol. 13, No. i P. Fierens, J. Tirlocq
We have shown e a r l i e r (4) that c o o l i n g c o n d i t i o n s on the end of t r i c a l c i u m s i l i c a t e synthesis are very i m p o r t a n t for its h y d r a u lic r e a c t i v i t y ; this e f f e c t is also i n v e s t i g a t e d on the b e t a - d i c a l cium silicate in the p r e s e n t work. II.
Experimental
procedure
I) Sxnthesis Raw m a t e r i a l s are " S u p r a p u r M e r c k quality" calcium carbonate, " P u r a t r o n i c first grade" J o h n s o n M a t t h e y C h e m i c a l s silica and analytical r e a g e n t b o r o n oxide as s t a b i l i z e r (0.5 atomic p e r c e n t of B~. In the synthesis t e m p e r a t u r e effect study, each s t o e c h i o m e t r i c m i x t u r e is fired in a p l a t i n u m crucible at a given t e m p e r a t u r e : 1050, 1150, 1250, ]350, 1450 or 1550°C. F i r i n g is stopped w h e n the residual free lime c o n c e n t r a t i o n , d e t e r m i n e d by the F r a n k e ' s method, b e c o m e s lower than one percent. All the samples are ground in an agate B.E.T. specific surface area of one sq.m/g.
jar mill
to reach
a
The cooling c o n d i t i o n s effect is i n v e s t i g a t e d by means of three samples s y n t h e s i z e d at 15OO°C and cooled r e s p e c t i v e l y in liquid nitrogen, a m b i e n t air or at a p r o g r a m m e d d e c r e a s e rate (8°/min.). After
grinding,
each
specific
surface
area was
about
0.4
sq~/g
2) A n h l d E o u s _ s a m ~ ! e s _ c h a r a c t e r i z a t i o n D.T.A. the c h o o s e n This tribution
is used to d e t e r m i n e the p o l y m o r p h i c v a r i e t y synthesis t e m p e r a t u r e before air quenching.
present
at
factor could indeed i n f l u e n c e the s t r u c t u r e defects disand the r e a c t i v i t y of boron s t a b i l i z e d d i c a l c i u m silicates.
An X-Ray d i f f r a c t i o n p a t t e r n of each samples is c a r e f u l l y r e c o r d e d to point out some s i g n i f i c a n t shift in the m a i n d i f f r a c tion peaks p o s i t i o n s . P r e v i o u s works (5) in this l a b o r a t o r y have shown the high n u c l e o p h i l i c c h a r a c t e r of t r i c a l c i u m s i l i c a t e surface can be m e a s u red using an e l e c t r o n transfer from surface centers towards tetracyanoethylene adsorbed molecules. The ( T . C . N . E . ) - ions surface c o n c e n t r a t i o n is d e t e r m i n e d by means of the E.S.R. technique. The same p r o c e d u r e is followed in the p r e s e n t study. S t r u c t u r e defects m a y also be bring to light by m e a s u r i n g l u m i n e s c e n c e p r o p e r t i e s of the solids. Thermoluminescence and cathodoluminescence, w h i c h have a l r e a d y been d e s c r i b e d in earlier papers (6,7), are used with the aim to d i f f e r e n t i a t e the dicalcium silicate samples s y n t h e s i z e d at v a r i o u s t e m p e r a t u r e s . 3) E x t e n t
of h x d r a t i o n
measurement
Hydration experimental conditions t e m p e r a t u r e = 25°C and a sealed sphere ions,
Paste aqueous phase c o n t e n t s silicate ions c o n c e n t r a t i o n
are : W/S ratio = 0.6, to avoid c a r b o n a t i o n .
m a i n l y c a l c i u m and h y d r o x i d e b e c o m i n g r a p i d l y very low (8).
Vol. 13, No. i
43 B-C2S, SYNTHESIS, HYDRATION RATE, LUMINESCENCE,
CONDUCTIVITY
So, h y d r a t i o n c a n be f o l l o w e d by the e v o l u t i o n of the p a s t e trical conductance m e a s u r e d b e t w e e n two p l a t i n u m e l e c t r o d e s n e c t e d to a c o n d u c t i m e t e r . heat
eleccon-
Dicalcium silicate hydration is a e x o t h e r m a l reaction whose liberation r a t e c a n be f o l l o w e d by c o n d u c t i o n m i c r o c a l o r i m e t r y .
However, the c a l o r i m e t r i c p e a k i n t e n s i t y in the case of dicalcium silicate hydration is a b o u t ten times w e a k e r than that dev e l o p p e d by t r i c a l c i u m silicate hydration. T h a t is the r e a s o n why this t e c h n i q u e has not yet b e e n w i d e l y used. The m i c r o c a l o r i m e ter d e v e l o p p e d in our l a b o r a t o r y has a l r e a d y b e e n d e s c r i b e d earlier (9). and
For l o n g e r h y d r a t i o n d u r a t i o n , e v e n t u a l c a r b o n a t e p r o d u c e d are
the a m o n g of c a l c i u m determined by D.T.G.
hydroxide
Quantitative X-Ray diffraction a n a l y s i s is the sole d i r e c t m e t h o d to m e a s u r e an h y d r a t i o n conversion degree. Calibration c u r v e is r e a l i z e d by m e a n s of m i x t u r e s of dicalcium s i l i c a t e w i t h an a r t i f i c i a l h y d r a t e m a d e by T a y l o r ' s m e t h o d (IO). A correction f a c t o r is also a p p l i e d to t r a n s f o r m the w e i g h t f r a c t i o n (x) of C2S in the h y d r a t e d dry r e s i d u e into the h y d r a t i o n c o n v e r s i o n d e g r e e (~). The d i f f r a c t i o n doublet sensitive to the g r a i n s m e a n analysis. ).0~ ~ , \
[
T
I
For k i n e t i c a l m e a s u r e m e n t s , I is the m e a n v a l u e of six d e t e r m i nations with a standard deviation of 3 % ; I o is the i n t e n s i t y of the a n h y d r o u s c o m p o u n d u s e d as e x t e r n a l standard.
\\
0.1.13.2-
III.
~,~
I)
I/.
0
0.2
O/
0.6
FIG. versus
~'H
at
32°09 (2e,CuK~), unis s e l e c t e d for this
F i g u r e 1 shows the r e l a t i o n o b t a i n e d b e t w e e n the c o n v e r s i o n d e g r e e ~ and the r e l a t i v e d i f f r a c tion i n t e n s i t y I/I o.
I
0.8-(X ~ \ 0.5-
at 32°05 and orientation,
"~ 0.8
f.O
1
I/I o e x p e r i m e n t a l relation 1350,
1250
and
I150°C,
Results
Characterization ~!e~arations
of
anh!drous
D.T.A. m e a s u r e m e n t s on b o r o n stabilized dicalcium s i l i c a t e samp i e s s h o w that the v a r i e t i e s present on the end of the f i r i n g p e r i o d are respectively ~ at 1550 and 1450°C,
and
~
at
IO50°C.
Ambient temperature X-Ray diffraction d i a g r a m s let r e c o g n i z e the B v a r i e t y in all the p r e p a r a t i o n s and no s i g n i f i c a n t s h i f t is o b s e r v e d in the m a i n d i f f r a c t i o n positions. Adsorption of T . C . N . E . on the d i c a l c i u m silicate surface gives r i s e to a s t r o n g E . S . R . s i g n a l , but its i n t e n s i t y is of the same o r d e r of m a g n i t u d e for e v e r y B v a r i e t y s a m p l e but also for a p u r e
44
Vol. 13, No. 1 P. Fierens, J. Tirlocq
y variety synthesized at 1650°C. Then, they all p r e s e n t the same strong surface nucleophilic character. T h a n k s to a JEOL coal i n t e r nal s t a n d a r d , the s u r f a c e d e n s i t y of ( T C N E ) - ions could be e s t i m a ted b e t w e e n 150 and 300 ions per s q u a r e m i c r o n . T h a t is far to be a m o n o m o l e c u l a r layer. Concerning luminescence properties, every sample present a cathodoluminescence e m i s s i o n in the v i s i b l e r a n g e w i t h a p r o n o u n ced m a x i m u m at a b o u t 440 nm., r e p r e s e n t e d on f i g u r e 2. No significant difference is o b s e r v e d b e t w e e n those s p e c t r a . On the o t h e r hand, s a m p l e s s h o w d i s t i n c t U.V. e x c i t e d thermoluminescence curves, whose characteristics are s u m m a r i z e d in table I. Samples synthesized at the h i g h e s t t e m p e r a t u r e s present only one p e a k w h o s e m a x i m u m t e m p e r a t u r e diminishes with firing temperature. B e l o w 1350°C, l i g h t e m i s s i o n p e a k s p l i t s off into two t i n c t m a x i m a , and m o r e o v e r , the i n t e n s i t i e s of b o t h 6 1250 are m u c h w e a k e r than all the o t h e r s .
dispeaks
In c o n c l u s i o n , the T.L. c h a r a c t e r i s t i c s p r e s e n t no c o n t i n u e d variation with firing temperature. However, they s h o w that samples synthesized at d i f f e r e n t temperatures are d i s t i n c t w i t h r e s p e c t to their e l e c t r o n t r a p - c e n t e r s . seems cates
So, a m o n g the s e v e r a l tried t e c h n i q u e s , thermoluminescence to be the u n i q u e one a b l e to d i f f e r e n t i a t e dicalcium silii s s u e d from d i f f e r e n t firing temperatures.
04
/-~,,
I (o.u I
./
/~i 0.3
11 I I I I.I I!1 I
\
,
\~i\\ \ \\ \
~
a, = o a 4.
~ ~B ~ /~ ~
m55o 155o 1450 1250 1150 IOSO
TABLE T.L.
peaks
I
characteristics
\" \ \t
02 ¸
•
§ \
\ a\
Sample
*
Max.
Temp. (°C)
Max. (a.
Int. u.)
\o \
\ \.\ \\| \ 01-
1550 6 1450 B 1350 B 1250
.\
x x#
",-
A~
\
i
\
6 ll50 6 1050
,~"(nm ) ~0o
700
5
FIG.
2
Cathodoluminescence
spectra
II0 95 86 62 I00 71 150 90 105
* Note : Beta-dicalcium synthesized at 1550°C written : ~ 1550.
4 , 1 0 'i 3.2,10 ~ I0 i 2.6,103 1.8,103 3.6,105 3.4,105 3.4,105 3 4,105 silicate is
Vol. 13, No. i
45 ~-C2S , SYNTHESIS, HYDRATION RATE, LUMINESCENCE,
2)
~ Z ~ E ~ - ~ $
the
earlz_~t~$
~
Figure 3 represents typical e v o l u t i o n of the e l e c t r i c a l cond u c t a n c e of the h y d r a t i n g paste. A f t e r an i n i t i a l f a s t r i s i n g step, c o n d u c t a n c e reaches a maxim u m v a l u e , f o l l o w e d by a n o t i c a ble drop, d u e to the b e g i n n i n g of calcium hydroxide precipitation. Calculated saturation level of calcium hydroxide in p u r e w• a t e r is d r a w n on the f i g u r e to p o i n t out that c o n d u c t a n c e goes r a p i dly d o w n this v a l u e as Tong and Y o u n g n o t i c e d e a r l i e r (8). Then, dicalcium silicate hydration p r o c e e d s in u n s a t u r a t e d conditions r e l a t i v e l y to c a l c i u m hydroxide.
~I o'(ms) !
a
!
~] ~I
TABLE
each
sample
2
Times corresponding to maximum supersaturation
Sample 1550
B 1450 1350
B 1250 B 1150 B ]050 y ]650
as
Time
(h)
1 ~I I
~!
!
D u r i n g this e a r l y generally written.
~..
_._
c.2~o~
,~
tlh) '~
S
I0
FIG.
to r e a c h
maximum
15
3
electrical
conductance conductance
are
General evolution is the lower the s y n t h e s i s t e m p e r a t u r e , the longer the time r e q u i r e d for s u p e r s a t u ration. But this v a r i a t i o n is far to be m o n o t o n e and its c o n s p i c u o u s steps h a p p e n b e t w e e n ]450 and 1350°C and b e t w e e n |150 and 1050°C. us r e m e m b e r that b o t h temi n t e r v a l s are p r e c i s e l y the ~ ÷ ~'H and ~'H ÷ L
polymorphic
transitions.
The y v a r i e t y is v e r y s i m i l a r to
stage,
..~.
......... c~
Let perature those of
3 3 I/2 6 6 I/2 6 10 5
\ .,,.-"'"...
I
Paste Times r e q u i r e d by c o l l e c t e d in table 2.
CONDUCTIVITY
the
y variety
is n o t
conductance curve the B v a r i e t y one
as
less
reactive
Microcalorimetric measurements have b e e n c a r r i e d out w i t h all the s a m p l e s , including the y v a r i e t y ; o n l y the B 1550 and B 1450 s a m p l e s and a B 1350 one w i t h a h i g h e r s p e c i f i c s u r f a c e a r e a (= 2.2 s q . m / g . ) d e v e l o p a d e t e c t a b l e e x o t h e r m a l peak. Figure 4 represents the c u m u l a t e d h y d r a t i o n of the three s a m p l e s .
heat
liberated
during
the
Considering a total h y d r a t i o n h e a t of 62 c a l . / g . , a c o n v e r s i o n d e g r e e ~ of the r e a c t i o n is c a l c u l a t e d and s e v e r a l h e t e r o geneous kinetic equations are tried to fit the c o n v e r s i o n d e g r e e evolution.
46
Vol. 13, No. i P. Fierens, J. Tirlocq
olt)
LI (cal/g) I0 9
.J
/~/x -~'~
x
1550 °C
+
IL50° C
0
13T~O° C
/ X ( s.orea = 2,2rr~ / gl
,
/
/
R3 (~l
/
..
5
.
0.5
/÷"'+~÷~
"
ucPl
///
.
+
10"31
x x~
0.3
•x
o x
0.1
o
D3 qeC)
i
i
~
t[h) 5
tO
FIG. Cumulated
L
*
.
•
s
iS
t(h}
~,,x.
FIG.
4
hydration
Hydration
heat
,6
,~
5 kinetics
According to S h a r p ' s n o m e n c l a t u r e (II), A v r a m i ' s n u c l e a t i o n A3(~) , p h a s e - b o u n d a r y c o n t r o l l e d R3(~) and J a n d e r ' s d i f f u s i o n c o n t r o l l e d D3(~) e q u a t i o n s h a v e b e e n c a l c u l a t e d and p l o t t e d v e r sus h y d r a t i o n time. F i g u r e 5 shows the b e s t fit is o b t a i n e d w i t h p h a s e - b o u n d a r y controlled e q u a t i o n but d i f f u s i o n c o n t r o l l e d equation presents also a s h o r t v a l i d i t y p e r i o d on the end of the c a l o r i m e t r i c curve. The v a l i d i t y p e r i o d of R3(~) lies on b o t h sides of the m a x i m u m h e a t l i b e r a t i o n rate, l o c a t e d by an a r r o w on the f i g u r e . Rate
constants
K.
i
of
R 3 ( ~ ) are
shown
on
table
3.
Rate constant values increase with firing temperature ; that is in a g r e e m e n t w i t h the e l e c t r i c a l conductance results. Of c o u r s e , the v a l u e of the 8 ]350 s a m p l e is e n h a n c e d by its h i g h e r s p e c i f i c s u r f a c e area. TABLE 3 Concerning the e f f e c t of c o o l i n g c o n d i t i o n s , times R a t e c o n s t a n t K. r e q u i r e d to r e a c h m a x i m u m c o n K. x 10 3 d u c t i v i t y by the s a m p l e s noSample t i f i e d " l i q u i d N 2 , air and Z(h-1 ) s l o w c o o l i n g " are r e s p e c t i v e l y 4h30 min., 4h45 min. and 6.37 B 1550 4h40 m i n . . M a x i m u m h e a t li3.96 B 1450 b e r a t i o n rate is r e a c h e d after 4.14 B ] 350 a b o u t 6h30 min. in e v e r y case. So, it seems that c o o l i n g (Spec. Surf. A = c o n d i t i o n s h a v e no s i g n i f i c a n t 2.2 s q . m . / g . ) e f f e c t on d i c a l c i u m s i l i c a t e h y d r a t i o n rate. T h a t is q u i t e
Vol. 13, No. i
47 B-C2S, SYNTHESIS, HYDRATION RATE, LUMINESCENCE, CONDUCTIVITY
o p p o s i t e to the results o b t a i n e d in the case of h y d r a t i o n in p r e v i o u s studies (4).
tricalcium
silicate
H y d r a t i o n e x p e r i m e n t s have been stopped after 7, ]4, 28 and 42 days and related c o n v e r s i o n degrees have been 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 d i f f r a c t i o n analysis and D.T.G., a c c o r d i n g to p r e v i o u s l y e x p l a i n e d p r o c e d u r e s ; o b t a i n e d values are given in table 4. TABLE 4 Conversion
degrees
over
longer
periods
Sample 7 days B 1550 B 1450 B 1350 1250 8 1150 8 IO5O
14 days
0.19 0.22 0.10 <0.04 <0.04 0.04
28 days
0.33 0.38 0.26 O.ll 0.II 0.08
0.43 O.32 0.20 0.18 0.30
42 days 0.52 0.52 0.66 0.26 0.40 O.61
After two weeks of hydration, the B 1550 and B 1450 samples reach the h i g h e s t c o n v e r s i o n degrees, while d i c a l c i u m silicates s y n t h e s i z e d at lower t e m p e r a t u r e s show far slower h y d r a t i o n rates. This b e h a v i o u r is in a g r e e m e n t o b s e r v e d in the early stage.
with
the r e a c t i v i t y
sequence
For longer d u r a t i o n s , the 8 1350 and 8 1050 h y d r a t i o n i n c r e a s e as high as they show the most advanced c o n v e r s i o n among all the samples.
rates degrees
This enhanced r e a c t i v i t y of the 8 1050 p r e p a r a t i o n has a l r e a d y been o b s e r v e d by P a s h c h e n k o and c o - w o r k e r s (2). On the other hand, the ~ 1250 and vities remain always the weakest. IV.
B 1150
samples
reacti-
Discussion
T h e r m o l u m i n e s c e n c e m e a s u r e m e n t s show that b e t a - d i c a l c i u m silicate s t r u c t u r e defects, in this case e l e c t r o n t r a p - c e n t e r s , are i n f l u e n c e d by the synthesis t e m p e r a t u r e of the compound. Let us also take into a c c o u n t that d i f f e r e n t p o l y m o r p h i c v a r i e t i e s c o r r e s p o n d to the selected firing t e m p e r a t u r e s . This s u p p l e m e n t a r y p a r a m e t e r could indeed p a r t l y c o n d i t i o n the structure defects d i s t r i b u t i o n . Paste e l e c t r i c a l c o n d u c t i v i t y rements show that, d u r i n g the first silicate r e a c t i v i t y increases with c o n s p i c u o u s steps h o w e v e r at about p e r a t u r e ranges are p r e c i s e l y those
and m i c r o c a l o r i m e t r i c m e a s u h y d r a t i o n day, d i c a l c i u m firing t e m p e r a t u r e but with 14OO and IIOO°C. These temof the ~+~'H and ~'H+~'L
48
Vol. 13, No. i P. Fierens, J. Tirlocq
polymorphic transitions. Then, it seems that the p o l y m o r p h i c var i e t y p r e s e n t on the end of the s y n t h e s i s could also i n f l u e n c e the d i c a l c i u m s i l i c a t e h y d r a t i o n r e a c t i v i t y . After longer duration hydration (six w e e k s ) , s a m p l e s s y n t h e sized at 1350 and I050°C r e a c h h i g h e r c o n v e r s i o n d e g r e e s than the 1550 and B 1450 s a m p l e s . That is r a t h e r s u r p r i s i n g : though o n l y b o t h last p r e p a r a t i o n s develop a significant calorimetric peak, they do not r e a c h the b e s t c o n v e r s i o n d e g r e e a f t e r p r o l o n g e d period. To e x p l a i n this point, let us c o m p a r e the c u m u l a t e d h e a t lib e r a t e d by t r i c a l c i u m s i l i c a t e h y d r a t i o n d u r i n g the w h o l e c a l o r i m e t r i c step to that d e v e l o p p e d by d i c a l c i u m s i l i c a t e h y d r a t i o n . The f i r s t one r e p r e s e n t s 60 to 80 % of the w h o l e h y d r a t i o n reaction heat, w h i l e the s e c o n d one r e a c h e s o n l y 20 %, w i t h a s p e c i fic s u r f a c e area of one s q . m . / g , in b o t h cases. ther case
So, d i c a l c i u m silicate hydration calorimetric step has s m a l l e r i m p o r t a n c e on the w h o l e h y d r a t i o n p r o c e s s than of t r i c a l c i u m s i l i c a t e h y d r a t i o n .
a rain the
Finaly, synthesis temperature affects greatly the d i c a l c i u m s i l i c a t e h y d r a t i o n r a t e from the e a r l y stage to p r o l o n g e d p e r i o d s , while cooling conditions, w h i c h are a w e l l - k n o w n reactivity f a c t o r in the case of t r i c a l c i u m s i l i c a t e , do not p l a y any s i g n i f i c a n t p a r t on the h y d r a t i o n r e a c t i v i t y of b e t a - d i c a l c i u m silicate. References I. Y.M.
BUTT,
V.V.
TIMASHEV,
2, A.A, P A S H C H E N K O , Int. Cong. Chem. (1974).
E.A. Cem°
D.L. K A N T R O , C.H. W E I S E , (RD 070.O1 T) (|980).
4.
P. F I E R E N S , J. T I R L O C Q , (4), 363 (1974).
5.
P. F I E R E N S , (1976).
J.P.
6.
P. ~,
FIERENS, (5), 549
J. T I R L O C Q , (1973).
FIERENS,
J.P.
TONG,
J.F.
2,
P.C.A.
J.P.
VERHAEGEN,
Cem.
and
and
Conc.
Ind.,
(|),
Chem.
Soc.,
I|.
J.H. SHARP, G.W. B R I N D L E Y , Soc., 49, (7), 379 (1966).
3682
B.N.
60,
321
1550
Belg.,
39,
(I),
Conc.
17
103
Res.
(1978).
J. T I R L O C Q - " C o n t r i b u t i o n ~ l ' ~ t u d e de la c i n ~ t i q u e de l'hydratation du s i l i c a t e b i c a l c i q u e " - Th~se de d o c t o r a t Universit~ de l ' E t a t ~ M o n s - B e l g i q u e (1981). H.F.W.
Soc.,
and
6,
Ser.
9.
IO.
Cer.
Chim.
Res.,
Cem.
43,
Bul.,
H.S.
J.
J. Am.
Dev.
Ind.
VERHAEGEN,
Sil.
(1961).
8.
TAYLOR,
YOUNG,
Res.
VERHAEGEN,
J.P.
VERHAEGEN,
17-23
th U.P. S E R B I N , Proc. Vl - Section I - 4 - Moscow
STARCHEVSKAYA, - Suppl. P a p e r
3.
7. P.
Tsement,
(|977).
-
(1950).
NARAHARI
ACHAR,
J.
Am.
Cer.
-
E F F E C T OF S Y N T H E S I S OF B E T A - D I C A L C I U M
Vol. 13, pp. 41-48, 1983. Printed in the USA. Copyright (c) 1982 Pergamon Press, Ltd.
TEMPERATURE AND S I L I C A T E ON ITS
COOLING CONDITIONS HYDRATION RATE
P. F i e r e n s and J. T i r l o c q S e r v i c e de S c i e n c e des M a t ~ r i a u x F a c u l t ~ des S c i e n c e s , U n i v e r s i t ~ de M o n s Belgique
(Communicated by D.M. Roy) (Received June 4, 1982) ABSTRACT Beta-dicalcium s i l i c a t e s are s y n t h e s i z e d b e t w e e n 1050 and 1 5 5 0 ° C and are c h a r a c t e r i z e d w i t h r e s p e c t to their s t r u c ture d e f e c t s by c a t h o d o l u m i n e s c e n c e , thermoluminescence and E . S . R . . P a s t e h y d r a t i o n k i n e t i c s are f o l l o w e d , in the e a r l y stage, by e l e c t r i c a l conductivity and m i c r o c a l o r i m e t r y ; for l o n g e r d u r a t i o n s , D . T . G . and q u a n t i t a t i v e X . R ° D . are used. Experimental r e s u l t s s h o w that s y n t h e s i s t e m p e r a t u r e aff e c t s g r e a t l y the h y d r a t i o n r a t e from the b e g i n n i n g to extended periods, while cooling conditions s e e m to h a v e no s i g n i f i c a n t influence. Hydration rate evolution with firing temperature and s a m p l e s c h a r a c t e r i s t i c s are comp a r e d in the f i n a l d i s c u s s i o n . I.
Introduction
M a n y f a c t o r s m a y i n f l u e n c e the h y d r a t i o n k i n e t i c s of b e t a dicalcium silicate. A m o n g these, the s y n t h e s i s temperature effect has not yet b e e n f u l l y s t u d i e d . O n l y few d a t a a b o u t this s u b j e c t are a v a i l a b l e , for e x a m p l e those of B u t t and T i m a s h e v (|), P a s h c h e n k o and c o - w o r k e r s (2) and K a n t r o and W e i s e (3). In the p r e s e n t work, s a m p l e s of b o r o n s t a b i l i z e d B v a r i e t y are f i r e d at a g i v e n t e m p e r a t u r e b e t w e e n 1050 and 1550°C and c h a r a c t e r i zed by s e v e r a l s o l i d state m e t h o d s w i t h r e s p e c t to their s t r u c t u r e defects. As those t e c h n i q u e s are v e r y s e n s i t i v e to the impurities of the solid, h i g h p u r i t y raw m a t e r i a l s are c h o o s e n and c a r e f u l l y employed. Paste hydration k i n e t i c s are f o l l o w e d f i r s t by e l e c t r i c a l conductivity and c o n d u c t i o n m i c r o c a l o r i m e t r y ; for l o n g e r d u r a t i o n s , D . T . G . and X . R . D . A . are used. F i n a l y , the e f f e c t of s y n t h e s i s t e m p e r a t u r e on the h y d r a u l i c reactivity and the s t r u c t u r a l characteristics of b e t a - d i c a l c i u m s i l i c a t e is d i s c u s s e d . 41
42
Vol. 13, No. i P. Fierens, J. Tirlocq
We have shown e a r l i e r (4) that c o o l i n g c o n d i t i o n s on the end of t r i c a l c i u m s i l i c a t e synthesis are very i m p o r t a n t for its h y d r a u lic r e a c t i v i t y ; this e f f e c t is also i n v e s t i g a t e d on the b e t a - d i c a l cium silicate in the p r e s e n t work. II.
Experimental
procedure
I) Sxnthesis Raw m a t e r i a l s are " S u p r a p u r M e r c k quality" calcium carbonate, " P u r a t r o n i c first grade" J o h n s o n M a t t h e y C h e m i c a l s silica and analytical r e a g e n t b o r o n oxide as s t a b i l i z e r (0.5 atomic p e r c e n t of B~. In the synthesis t e m p e r a t u r e effect study, each s t o e c h i o m e t r i c m i x t u r e is fired in a p l a t i n u m crucible at a given t e m p e r a t u r e : 1050, 1150, 1250, ]350, 1450 or 1550°C. F i r i n g is stopped w h e n the residual free lime c o n c e n t r a t i o n , d e t e r m i n e d by the F r a n k e ' s method, b e c o m e s lower than one percent. All the samples are ground in an agate B.E.T. specific surface area of one sq.m/g.
jar mill
to reach
a
The cooling c o n d i t i o n s effect is i n v e s t i g a t e d by means of three samples s y n t h e s i z e d at 15OO°C and cooled r e s p e c t i v e l y in liquid nitrogen, a m b i e n t air or at a p r o g r a m m e d d e c r e a s e rate (8°/min.). After
grinding,
each
specific
surface
area was
about
0.4
sq~/g
2) A n h l d E o u s _ s a m ~ ! e s _ c h a r a c t e r i z a t i o n D.T.A. the c h o o s e n This tribution
is used to d e t e r m i n e the p o l y m o r p h i c v a r i e t y synthesis t e m p e r a t u r e before air quenching.
present
at
factor could indeed i n f l u e n c e the s t r u c t u r e defects disand the r e a c t i v i t y of boron s t a b i l i z e d d i c a l c i u m silicates.
An X-Ray d i f f r a c t i o n p a t t e r n of each samples is c a r e f u l l y r e c o r d e d to point out some s i g n i f i c a n t shift in the m a i n d i f f r a c tion peaks p o s i t i o n s . P r e v i o u s works (5) in this l a b o r a t o r y have shown the high n u c l e o p h i l i c c h a r a c t e r of t r i c a l c i u m s i l i c a t e surface can be m e a s u red using an e l e c t r o n transfer from surface centers towards tetracyanoethylene adsorbed molecules. The ( T . C . N . E . ) - ions surface c o n c e n t r a t i o n is d e t e r m i n e d by means of the E.S.R. technique. The same p r o c e d u r e is followed in the p r e s e n t study. S t r u c t u r e defects m a y also be bring to light by m e a s u r i n g l u m i n e s c e n c e p r o p e r t i e s of the solids. Thermoluminescence and cathodoluminescence, w h i c h have a l r e a d y been d e s c r i b e d in earlier papers (6,7), are used with the aim to d i f f e r e n t i a t e the dicalcium silicate samples s y n t h e s i z e d at v a r i o u s t e m p e r a t u r e s . 3) E x t e n t
of h x d r a t i o n
measurement
Hydration experimental conditions t e m p e r a t u r e = 25°C and a sealed sphere ions,
Paste aqueous phase c o n t e n t s silicate ions c o n c e n t r a t i o n
are : W/S ratio = 0.6, to avoid c a r b o n a t i o n .
m a i n l y c a l c i u m and h y d r o x i d e b e c o m i n g r a p i d l y very low (8).
Vol. 13, No. i
43 B-C2S, SYNTHESIS, HYDRATION RATE, LUMINESCENCE,
CONDUCTIVITY
So, h y d r a t i o n c a n be f o l l o w e d by the e v o l u t i o n of the p a s t e trical conductance m e a s u r e d b e t w e e n two p l a t i n u m e l e c t r o d e s n e c t e d to a c o n d u c t i m e t e r . heat
eleccon-
Dicalcium silicate hydration is a e x o t h e r m a l reaction whose liberation r a t e c a n be f o l l o w e d by c o n d u c t i o n m i c r o c a l o r i m e t r y .
However, the c a l o r i m e t r i c p e a k i n t e n s i t y in the case of dicalcium silicate hydration is a b o u t ten times w e a k e r than that dev e l o p p e d by t r i c a l c i u m silicate hydration. T h a t is the r e a s o n why this t e c h n i q u e has not yet b e e n w i d e l y used. The m i c r o c a l o r i m e ter d e v e l o p p e d in our l a b o r a t o r y has a l r e a d y b e e n d e s c r i b e d earlier (9). and
For l o n g e r h y d r a t i o n d u r a t i o n , e v e n t u a l c a r b o n a t e p r o d u c e d are
the a m o n g of c a l c i u m determined by D.T.G.
hydroxide
Quantitative X-Ray diffraction a n a l y s i s is the sole d i r e c t m e t h o d to m e a s u r e an h y d r a t i o n conversion degree. Calibration c u r v e is r e a l i z e d by m e a n s of m i x t u r e s of dicalcium s i l i c a t e w i t h an a r t i f i c i a l h y d r a t e m a d e by T a y l o r ' s m e t h o d (IO). A correction f a c t o r is also a p p l i e d to t r a n s f o r m the w e i g h t f r a c t i o n (x) of C2S in the h y d r a t e d dry r e s i d u e into the h y d r a t i o n c o n v e r s i o n d e g r e e (~). The d i f f r a c t i o n doublet sensitive to the g r a i n s m e a n analysis. ).0~ ~ , \
[
T
I
For k i n e t i c a l m e a s u r e m e n t s , I is the m e a n v a l u e of six d e t e r m i nations with a standard deviation of 3 % ; I o is the i n t e n s i t y of the a n h y d r o u s c o m p o u n d u s e d as e x t e r n a l standard.
\\
0.1.13.2-
III.
~,~
I)
I/.
0
0.2
O/
0.6
FIG. versus
~'H
at
32°09 (2e,CuK~), unis s e l e c t e d for this
F i g u r e 1 shows the r e l a t i o n o b t a i n e d b e t w e e n the c o n v e r s i o n d e g r e e ~ and the r e l a t i v e d i f f r a c tion i n t e n s i t y I/I o.
I
0.8-(X ~ \ 0.5-
at 32°05 and orientation,
"~ 0.8
f.O
1
I/I o e x p e r i m e n t a l relation 1350,
1250
and
I150°C,
Results
Characterization ~!e~arations
of
anh!drous
D.T.A. m e a s u r e m e n t s on b o r o n stabilized dicalcium s i l i c a t e samp i e s s h o w that the v a r i e t i e s present on the end of the f i r i n g p e r i o d are respectively ~ at 1550 and 1450°C,
and
~
at
IO50°C.
Ambient temperature X-Ray diffraction d i a g r a m s let r e c o g n i z e the B v a r i e t y in all the p r e p a r a t i o n s and no s i g n i f i c a n t s h i f t is o b s e r v e d in the m a i n d i f f r a c t i o n positions. Adsorption of T . C . N . E . on the d i c a l c i u m silicate surface gives r i s e to a s t r o n g E . S . R . s i g n a l , but its i n t e n s i t y is of the same o r d e r of m a g n i t u d e for e v e r y B v a r i e t y s a m p l e but also for a p u r e
44
Vol. 13, No. 1 P. Fierens, J. Tirlocq
y variety synthesized at 1650°C. Then, they all p r e s e n t the same strong surface nucleophilic character. T h a n k s to a JEOL coal i n t e r nal s t a n d a r d , the s u r f a c e d e n s i t y of ( T C N E ) - ions could be e s t i m a ted b e t w e e n 150 and 300 ions per s q u a r e m i c r o n . T h a t is far to be a m o n o m o l e c u l a r layer. Concerning luminescence properties, every sample present a cathodoluminescence e m i s s i o n in the v i s i b l e r a n g e w i t h a p r o n o u n ced m a x i m u m at a b o u t 440 nm., r e p r e s e n t e d on f i g u r e 2. No significant difference is o b s e r v e d b e t w e e n those s p e c t r a . On the o t h e r hand, s a m p l e s s h o w d i s t i n c t U.V. e x c i t e d thermoluminescence curves, whose characteristics are s u m m a r i z e d in table I. Samples synthesized at the h i g h e s t t e m p e r a t u r e s present only one p e a k w h o s e m a x i m u m t e m p e r a t u r e diminishes with firing temperature. B e l o w 1350°C, l i g h t e m i s s i o n p e a k s p l i t s off into two t i n c t m a x i m a , and m o r e o v e r , the i n t e n s i t i e s of b o t h 6 1250 are m u c h w e a k e r than all the o t h e r s .
dispeaks
In c o n c l u s i o n , the T.L. c h a r a c t e r i s t i c s p r e s e n t no c o n t i n u e d variation with firing temperature. However, they s h o w that samples synthesized at d i f f e r e n t temperatures are d i s t i n c t w i t h r e s p e c t to their e l e c t r o n t r a p - c e n t e r s . seems cates
So, a m o n g the s e v e r a l tried t e c h n i q u e s , thermoluminescence to be the u n i q u e one a b l e to d i f f e r e n t i a t e dicalcium silii s s u e d from d i f f e r e n t firing temperatures.
04
/-~,,
I (o.u I
./
/~i 0.3
11 I I I I.I I!1 I
\
,
\~i\\ \ \\ \
~
a, = o a 4.
~ ~B ~ /~ ~
m55o 155o 1450 1250 1150 IOSO
TABLE T.L.
peaks
I
characteristics
\" \ \t
02 ¸
•
§ \
\ a\
Sample
*
Max.
Temp. (°C)
Max. (a.
Int. u.)
\o \
\ \.\ \\| \ 01-
1550 6 1450 B 1350 B 1250
.\
x x#
",-
A~
\
i
\
6 ll50 6 1050
,~"(nm ) ~0o
700
5
FIG.
2
Cathodoluminescence
spectra
II0 95 86 62 I00 71 150 90 105
* Note : Beta-dicalcium synthesized at 1550°C written : ~ 1550.
4 , 1 0 'i 3.2,10 ~ I0 i 2.6,103 1.8,103 3.6,105 3.4,105 3.4,105 3 4,105 silicate is
Vol. 13, No. i
45 ~-C2S , SYNTHESIS, HYDRATION RATE, LUMINESCENCE,
2)
~ Z ~ E ~ - ~ $
the
earlz_~t~$
~
Figure 3 represents typical e v o l u t i o n of the e l e c t r i c a l cond u c t a n c e of the h y d r a t i n g paste. A f t e r an i n i t i a l f a s t r i s i n g step, c o n d u c t a n c e reaches a maxim u m v a l u e , f o l l o w e d by a n o t i c a ble drop, d u e to the b e g i n n i n g of calcium hydroxide precipitation. Calculated saturation level of calcium hydroxide in p u r e w• a t e r is d r a w n on the f i g u r e to p o i n t out that c o n d u c t a n c e goes r a p i dly d o w n this v a l u e as Tong and Y o u n g n o t i c e d e a r l i e r (8). Then, dicalcium silicate hydration p r o c e e d s in u n s a t u r a t e d conditions r e l a t i v e l y to c a l c i u m hydroxide.
~I o'(ms) !
a
!
~] ~I
TABLE
each
sample
2
Times corresponding to maximum supersaturation
Sample 1550
B 1450 1350
B 1250 B 1150 B ]050 y ]650
as
Time
(h)
1 ~I I
~!
!
D u r i n g this e a r l y generally written.
~..
_._
c.2~o~
,~
tlh) '~
S
I0
FIG.
to r e a c h
maximum
15
3
electrical
conductance conductance
are
General evolution is the lower the s y n t h e s i s t e m p e r a t u r e , the longer the time r e q u i r e d for s u p e r s a t u ration. But this v a r i a t i o n is far to be m o n o t o n e and its c o n s p i c u o u s steps h a p p e n b e t w e e n ]450 and 1350°C and b e t w e e n |150 and 1050°C. us r e m e m b e r that b o t h temi n t e r v a l s are p r e c i s e l y the ~ ÷ ~'H and ~'H ÷ L
polymorphic
transitions.
The y v a r i e t y is v e r y s i m i l a r to
stage,
..~.
......... c~
Let perature those of
3 3 I/2 6 6 I/2 6 10 5
\ .,,.-"'"...
I
Paste Times r e q u i r e d by c o l l e c t e d in table 2.
CONDUCTIVITY
the
y variety
is n o t
conductance curve the B v a r i e t y one
as
less
reactive
Microcalorimetric measurements have b e e n c a r r i e d out w i t h all the s a m p l e s , including the y v a r i e t y ; o n l y the B 1550 and B 1450 s a m p l e s and a B 1350 one w i t h a h i g h e r s p e c i f i c s u r f a c e a r e a (= 2.2 s q . m / g . ) d e v e l o p a d e t e c t a b l e e x o t h e r m a l peak. Figure 4 represents the c u m u l a t e d h y d r a t i o n of the three s a m p l e s .
heat
liberated
during
the
Considering a total h y d r a t i o n h e a t of 62 c a l . / g . , a c o n v e r s i o n d e g r e e ~ of the r e a c t i o n is c a l c u l a t e d and s e v e r a l h e t e r o geneous kinetic equations are tried to fit the c o n v e r s i o n d e g r e e evolution.
46
Vol. 13, No. i P. Fierens, J. Tirlocq
olt)
LI (cal/g) I0 9
.J
/~/x -~'~
x
1550 °C
+
IL50° C
0
13T~O° C
/ X ( s.orea = 2,2rr~ / gl
,
/
/
R3 (~l
/
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.
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"
ucPl
///
.
+
10"31
x x~
0.3
•x
o x
0.1
o
D3 qeC)
i
i
~
t[h) 5
tO
FIG. Cumulated
L
*
.
•
s
iS
t(h}
~,,x.
FIG.
4
hydration
Hydration
heat
,6
,~
5 kinetics
According to S h a r p ' s n o m e n c l a t u r e (II), A v r a m i ' s n u c l e a t i o n A3(~) , p h a s e - b o u n d a r y c o n t r o l l e d R3(~) and J a n d e r ' s d i f f u s i o n c o n t r o l l e d D3(~) e q u a t i o n s h a v e b e e n c a l c u l a t e d and p l o t t e d v e r sus h y d r a t i o n time. F i g u r e 5 shows the b e s t fit is o b t a i n e d w i t h p h a s e - b o u n d a r y controlled e q u a t i o n but d i f f u s i o n c o n t r o l l e d equation presents also a s h o r t v a l i d i t y p e r i o d on the end of the c a l o r i m e t r i c curve. The v a l i d i t y p e r i o d of R3(~) lies on b o t h sides of the m a x i m u m h e a t l i b e r a t i o n rate, l o c a t e d by an a r r o w on the f i g u r e . Rate
constants
K.
i
of
R 3 ( ~ ) are
shown
on
table
3.
Rate constant values increase with firing temperature ; that is in a g r e e m e n t w i t h the e l e c t r i c a l conductance results. Of c o u r s e , the v a l u e of the 8 ]350 s a m p l e is e n h a n c e d by its h i g h e r s p e c i f i c s u r f a c e area. TABLE 3 Concerning the e f f e c t of c o o l i n g c o n d i t i o n s , times R a t e c o n s t a n t K. r e q u i r e d to r e a c h m a x i m u m c o n K. x 10 3 d u c t i v i t y by the s a m p l e s noSample t i f i e d " l i q u i d N 2 , air and Z(h-1 ) s l o w c o o l i n g " are r e s p e c t i v e l y 4h30 min., 4h45 min. and 6.37 B 1550 4h40 m i n . . M a x i m u m h e a t li3.96 B 1450 b e r a t i o n rate is r e a c h e d after 4.14 B ] 350 a b o u t 6h30 min. in e v e r y case. So, it seems that c o o l i n g (Spec. Surf. A = c o n d i t i o n s h a v e no s i g n i f i c a n t 2.2 s q . m . / g . ) e f f e c t on d i c a l c i u m s i l i c a t e h y d r a t i o n rate. T h a t is q u i t e
Vol. 13, No. i
47 B-C2S, SYNTHESIS, HYDRATION RATE, LUMINESCENCE, CONDUCTIVITY
o p p o s i t e to the results o b t a i n e d in the case of h y d r a t i o n in p r e v i o u s studies (4).
tricalcium
silicate
H y d r a t i o n e x p e r i m e n t s have been stopped after 7, ]4, 28 and 42 days and related c o n v e r s i o n degrees have been 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 d i f f r a c t i o n analysis and D.T.G., a c c o r d i n g to p r e v i o u s l y e x p l a i n e d p r o c e d u r e s ; o b t a i n e d values are given in table 4. TABLE 4 Conversion
degrees
over
longer
periods
Sample 7 days B 1550 B 1450 B 1350 1250 8 1150 8 IO5O
14 days
0.19 0.22 0.10 <0.04 <0.04 0.04
28 days
0.33 0.38 0.26 O.ll 0.II 0.08
0.43 O.32 0.20 0.18 0.30
42 days 0.52 0.52 0.66 0.26 0.40 O.61
After two weeks of hydration, the B 1550 and B 1450 samples reach the h i g h e s t c o n v e r s i o n degrees, while d i c a l c i u m silicates s y n t h e s i z e d at lower t e m p e r a t u r e s show far slower h y d r a t i o n rates. This b e h a v i o u r is in a g r e e m e n t o b s e r v e d in the early stage.
with
the r e a c t i v i t y
sequence
For longer d u r a t i o n s , the 8 1350 and 8 1050 h y d r a t i o n i n c r e a s e as high as they show the most advanced c o n v e r s i o n among all the samples.
rates degrees
This enhanced r e a c t i v i t y of the 8 1050 p r e p a r a t i o n has a l r e a d y been o b s e r v e d by P a s h c h e n k o and c o - w o r k e r s (2). On the other hand, the ~ 1250 and vities remain always the weakest. IV.
B 1150
samples
reacti-
Discussion
T h e r m o l u m i n e s c e n c e m e a s u r e m e n t s show that b e t a - d i c a l c i u m silicate s t r u c t u r e defects, in this case e l e c t r o n t r a p - c e n t e r s , are i n f l u e n c e d by the synthesis t e m p e r a t u r e of the compound. Let us also take into a c c o u n t that d i f f e r e n t p o l y m o r p h i c v a r i e t i e s c o r r e s p o n d to the selected firing t e m p e r a t u r e s . This s u p p l e m e n t a r y p a r a m e t e r could indeed p a r t l y c o n d i t i o n the structure defects d i s t r i b u t i o n . Paste e l e c t r i c a l c o n d u c t i v i t y rements show that, d u r i n g the first silicate r e a c t i v i t y increases with c o n s p i c u o u s steps h o w e v e r at about p e r a t u r e ranges are p r e c i s e l y those
and m i c r o c a l o r i m e t r i c m e a s u h y d r a t i o n day, d i c a l c i u m firing t e m p e r a t u r e but with 14OO and IIOO°C. These temof the ~+~'H and ~'H+~'L
48
Vol. 13, No. i P. Fierens, J. Tirlocq
polymorphic transitions. Then, it seems that the p o l y m o r p h i c var i e t y p r e s e n t on the end of the s y n t h e s i s could also i n f l u e n c e the d i c a l c i u m s i l i c a t e h y d r a t i o n r e a c t i v i t y . After longer duration hydration (six w e e k s ) , s a m p l e s s y n t h e sized at 1350 and I050°C r e a c h h i g h e r c o n v e r s i o n d e g r e e s than the 1550 and B 1450 s a m p l e s . That is r a t h e r s u r p r i s i n g : though o n l y b o t h last p r e p a r a t i o n s develop a significant calorimetric peak, they do not r e a c h the b e s t c o n v e r s i o n d e g r e e a f t e r p r o l o n g e d period. To e x p l a i n this point, let us c o m p a r e the c u m u l a t e d h e a t lib e r a t e d by t r i c a l c i u m s i l i c a t e h y d r a t i o n d u r i n g the w h o l e c a l o r i m e t r i c step to that d e v e l o p p e d by d i c a l c i u m s i l i c a t e h y d r a t i o n . The f i r s t one r e p r e s e n t s 60 to 80 % of the w h o l e h y d r a t i o n reaction heat, w h i l e the s e c o n d one r e a c h e s o n l y 20 %, w i t h a s p e c i fic s u r f a c e area of one s q . m . / g , in b o t h cases. ther case
So, d i c a l c i u m silicate hydration calorimetric step has s m a l l e r i m p o r t a n c e on the w h o l e h y d r a t i o n p r o c e s s than of t r i c a l c i u m s i l i c a t e h y d r a t i o n .
a rain the
Finaly, synthesis temperature affects greatly the d i c a l c i u m s i l i c a t e h y d r a t i o n r a t e from the e a r l y stage to p r o l o n g e d p e r i o d s , while cooling conditions, w h i c h are a w e l l - k n o w n reactivity f a c t o r in the case of t r i c a l c i u m s i l i c a t e , do not p l a y any s i g n i f i c a n t p a r t on the h y d r a t i o n r e a c t i v i t y of b e t a - d i c a l c i u m silicate. References I. Y.M.
BUTT,
V.V.
TIMASHEV,
2, A.A, P A S H C H E N K O , Int. Cong. Chem. (1974).
E.A. Cem°
D.L. K A N T R O , C.H. W E I S E , (RD 070.O1 T) (|980).
4.
P. F I E R E N S , J. T I R L O C Q , (4), 363 (1974).
5.
P. F I E R E N S , (1976).
J.P.
6.
P. ~,
FIERENS, (5), 549
J. T I R L O C Q , (1973).
FIERENS,
J.P.
TONG,
J.F.
2,
P.C.A.
J.P.
VERHAEGEN,
Cem.
and
and
Conc.
Ind.,
(|),
Chem.
Soc.,
I|.
J.H. SHARP, G.W. B R I N D L E Y , Soc., 49, (7), 379 (1966).
3682
B.N.
60,
321
1550
Belg.,
39,
(I),
Conc.
17
103
Res.
(1978).
J. T I R L O C Q - " C o n t r i b u t i o n ~ l ' ~ t u d e de la c i n ~ t i q u e de l'hydratation du s i l i c a t e b i c a l c i q u e " - Th~se de d o c t o r a t Universit~ de l ' E t a t ~ M o n s - B e l g i q u e (1981). H.F.W.
Soc.,
and
6,
Ser.
9.
IO.
Cer.
Chim.
Res.,
Cem.
43,
Bul.,
H.S.
J.
J. Am.
Dev.
Ind.
VERHAEGEN,
Sil.
(1961).
8.
TAYLOR,
YOUNG,
Res.
VERHAEGEN,
J.P.
VERHAEGEN,
17-23
th U.P. S E R B I N , Proc. Vl - Section I - 4 - Moscow
STARCHEVSKAYA, - Suppl. P a p e r
3.
7. P.
Tsement,
(|977).
-
(1950).
NARAHARI
ACHAR,
J.
Am.
Cer.
-