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Alkali metal salts as set accelerators for high alumina cement
CEMENT and CONCRETE RESEARCH. Vol. 23, pp. 177-186, 1993. Printed in the USA. 0008-8846/93. $6.00+.00. Copyright © 1993 Pergamon Press Ltd.
ALKALI
METAL
SALTS
AS
SET ACCELERATORS
FOR
HIGH
ALUMINA
CEMENT
T . M a t u s i n o v i c and N.Vrbos U n i v e r s i t y of Zagreb D e p a r t m e n t of Chemical E n g i n e e r i n g and Technology Marulicev t r g 20, 41000 Zagreb, C r o a t i a
(Sef=eed) (Received Feb. 4; in fnudform March 4, 1992)
ABSTRACT
The effect of alkali metal salts on the setting time of high aluminia cement (HAC) has been studied. The influence of c o n c e n t r a t i o n of the salts, chemical nature of anion and the type of alkali metal cation have been investigated. The results of the research indicate that alkali metal salts are set accelerators of HAC. The lithium cation has more effect on the setting time than other alkali cations because of its ability to form tetrahedral symmetry while the others will form the octahedral type. L i t h i u m salts remove the n u c l e a t i o n barrier, caused by an initially fast precipitation. The influence of pH in mixing water is not important. The effect of hydroxyl group is greater than effect of other i n v e s t i g a t e d anions due to the replacement leading to a further centre for oxobridge formation. The l i t h i u m salts cause d e c r e a s i n g of flexural and compressive s t r e n g t h of H A C mortars but also cause the strength d e v e l o p m e n t at early ages.
Introduction
L i t h i u m salts have been reported as accelerating setting agents for alumina concretes in the patent literature(l-3). Parker r e p o r t e d that the setting time of HAC pastes could be influenced by a d d i t i o n of small amounts of m a n y materials. Double(4) and Currell(5) studied the c h e m i s t r y of hydration of HAC in the p r e s e n c e of accelerating and retarding admixtures. Novinson et ai.(7,8) i n v e s t i g a t e d the effects of lithium salts on r e f r a c t o r y mortars. In chemical terms, the mode of action of these admixtures is not well understood. In this paper alkali metal salts as set accelerators of HAC have been studied. The influence of c o n c e n t r a t i o n of the salts, chemical nature of anions and the type 177
178
T. Matusinovic and N. Vrbos
Vol. 23. No. 1
of a l k a l i m e t a l c a t i o n s h a v e b e e n i n v e s t i g a t e d . T h e r e s e a r c h has b e e n c a r r i e d out to d e v e l o p r a p i d s e t t i n g and h a r d e n i n g m a t e r i a l s for the r e p a i r of c o n c r e t e . We have b e e n c o n d u c t i n g e x p e r i m e n t s to determine the optimal setting time and the strength of the m a t e r i a l s m a d e w i t h l i t h i u m salt a d m i x t u r e s .
Experimental
Methods
T h e h i g h a l u m i n a c e m e n t u s e d was a n o r m a l p r o d u c t i o n of " G i u l i o R e v e l a n t e " , Pula, C r o a t i a . T h e g e n e r a l a n a l y s i s of s u c h c e m e n t was: CaO, 40.2%, A1203, 39.0%, FeO, 4.3%, Fe203, 11.7%. T h e a d m i x t u r e s used were commercial Analar grade reagents dissolved in d e m i n e r a l i z e d w a t e r p r i o r to m i x i n g w i t h HAC. LizS a n d R b O H w e r e prepared in o u r l a b o r a t o r y (9-11). The s e t t i n g t i m e of HAC in d e p e n d e n c e of the pH of l i t h i u m salts in m i x i n g w a t e r has b e e n measured. T h e pH of e a c h s o l u t i o n w a s m e a s u r e d w i t h a s t a n d a r d g l a s s e l e c t r o d e . T h e e l e c t r o d e was c a l i b r a t e d w i t h b u f f e r s o l u t i o n at 25°C at pH 4 a n d 9. The salt s o l u t i o n was p o u r e d into the b o w l a n d the HAC w e r e a d d e d to the water. T h e s e w e r e m i x e d t o g e t h e r b y means of m e c h a n i c stirrer for p r e s c r i b e d time intervals. All experiments used a water/cement (w/c) r a t i o of 0.24. T h e s e t t i n g time was determined using a modification of the JUS ~ m e t h o d B.C8.023. In o u r m o d i f i c a t i o n the p e n e t r a t i o n of the n e e d l e into h a r d e n i n g p a s t e was m e a s u r e d e v e r y 5 s e c o n d s due to e x t r e m e l y r a p i d setting time for l i t h i u m salt m o d i f i e d . The e x p e r i m e n t s were r e p e a t e d t h r e e times to o b t a i n r e l i a b l e s t a n d a r d d e v i a t i o n s a n d s t a t i s t i c a l means. For d e t e r m i n a t i o n of c o m p r e s s i v e a n d f l e x u r a l s t r e n g t h the s p e c i m e n s (40 x 40 x 160 mm) w e r e p r e p a r e d a c c o r d i n g to JUS B . C 8 . 0 2 2 at w/c r a t i o of 0.5. The s p e c i m e n s w e r e t e s t e d at the age of 1,3,7,28, and 90 days. T h r e e s p e c i m e n s w e r e t e s t e d for e a c h age. Results
T h e m e a s u r e m e n t of the i n f l u e n c e of d i f f e r e n t m a s s f r a c t i o n , ( w ) , of l i t h i u m n i t r a t e on the s e t t i n g t i m e of HAC has b e e n d o n e to c h o o s e the f r a c t i o n of the salt w h i c h can give a s e t t i n g t i m e c o n v e n i e n t for t h e r e s e a r c h . The r e s u l t s of the m e a s u r e m e n t are s h o w n in T a b l e i. The m e a s u r e m e n t s of the i n f l u e n c e of d i f f e r e n t a l k a l i m e t a l s a l t s on the s e t t i n g t i m e has b e e n made. The r e s u l t s of the r e s e a r c h are s h o w n in T a b l e 2. *JUS
- Yugoslav
standard
Vol.23,No. I
Lithium
SET ACCEI22ATORS,ALKALIMETAL SALTS,ALUMINATE CEMENT
nitrate:
Lithium
Comparison fractions.
salt
TABLE 1 of s e t t i n g t i m e s
at d i f f e r e n t
w(LiNO~)/%
Setting
mass
time/s
16500
0
LINO 3
179
0.0005
7330
0.001
1650
0.005
710
0.01
440
0.05
F
0.i
M
F - s e t t i n g of HAC w i t h l i t h i u m n i t r a t e d u r i n g the m i x i n g t i m e M - s e t t i n g of HAC i m m e d i a t e l y by a d d i n g of the l i t h i u m n i t r a t e
Alkali
metal
Anions
salts:
OH-
TABLE 2 C o m p a r i s o n of s e t t i n g fraction.
S=
Cations
C03 =
Br"
Setting
time/s
times
at 0.01% m a s s
CI-
NO3 =
SO Z
Li
300
325
370
305
360
440
560
Na
5140
5620
6300
8940
9720
6480
7800
K
7200
7400
7980
10120
10200
7920
8100
Rb
9140
9260
10930
10680
9360
9300
Cs
iiii0
11990
11200
11400
11480
11630
- dash
llne
indicates
The d i f f e r e n t l i t h i u m s h o w n in the T a b l e 3.
that the c h e m i c a l salts
have
been
was
not a v a i l a b l e
tested
and the
results
are
Discussion
T h e r e s u l t s of the r e s e a r c h i n d i c a t e that a l k a l i m e t a l s a l t s are set a c c e l e r a t o r s of HAC. The d a t a in T a b l e 1 d e m o n s t r a t e t h a t L i N O 3 a c c e l e r a t e s the s e t t i n g time of HAC e v e n at the m a s s f r a c t i o n of
T. Mamsinovic and N. Vrbos
180
Lithium
salts:
Lithium
VoL 23. No. 1
TABLE 3 C o m p a r i s o n of s e t t i n g times and pH of 0.01% l i t h i u m salts in m i x i n g water.
salt
pH values
Setting
LiOH
12.3
300
Li~S
11.8
325
Li2CO ~
11.2
370
LiBO 2
10.4
390
Li2SO 4
6.4
560
LiNO~
5.9
440
LiCI
5.6
360
LiBr
5.4
305
TABLE 4 F l e x u r a l s t r e n g t h s of HAC m o r t a r s and HAC m o r t a r s alkali metal salts. Time/ days
Flexural HAC + LiNO I
HAC + NaNO~
time/s
made with
0.01%
strength/MPa
HAC + KNO~
HAC + RbNO~
HAC + CsNO~
HAC
1
7.32
7.44
7.68
7.92
8.14
8.62
3
7.92
8.30
8.15
8.35
8.72
8.95
7
8.99
9.88
10.12
10.30
10.67
11.10
28
9.65
10.12
10.51
10.72
10.94
11.20
90
10.68
10.77
10.91
11.03
11.25
11.36
C o m p r e s s i v e s t r e n g t h s of 0.01% alkali metal salts.
TABLE 5 mortars
Compressive
Time/ days
HAC
HAC + LiNO~
HAC + NaNO~
1
49.18
52.09
3
61.87
7
HAC + KNO~
and
HAC
mortars
made
with
strength/MPa HAC + RbNO~
HAC + CsNO~
HAC
53.62
55.42
56.45
58.70
62.12
63.78
64.95
66.35
67.97
70.10
73.71
75.05
79.55
82.66
84.50
28
76.25
79.85
82.29
86.90
88.75
92.60
90
82.08
85.73
88.75
91.15
93.12
96.25
Vol. 23, No. 1
SET ACCELERATORS,AI.,KALIMETAL SALTS, ALUMINATECEMENT
181
TABLE 6 C o m p r e s s i v e and flexural strengths of HAC mortars and HAC mortars made w i t h 0.05% Li2CO3. Time/h
C o m p r e s s i v e strength/MPa HAC
HAC+ Li~CO 3
Flexural s t r e n g t h / M P A HAC
HAC+ Li2CO 3
0.5
X
1.82
X
X
1.0
X
3.86
X
X
1.5
X
4.89
X
X
2.0
X
5.93
X
1.42
2.5
X
8.96
X
2.44
3.0
X
12.60
X
3.11
3.5
X
13.12
X
3.93
X
4.21
4.0
2.65
18.33
4.5
8.80
20.02
2.19
4.37
5.0
24.58
21.25
2.64
4.56
6.0
36.65
23.87
3.34
4.96
i0.0
43.83
30.62
4.61
6.48
15.0
46.77
32.16
6.95
6.88
20.0
48.12
36.56
7.22
7.15
x - test could not be p e r f o r m e d because specimens were too soft to be removed from the mold 5xi0-4%. With increasing the fraction of LiNO~, the setting time decreases. With the fraction of 0.1% setting occurs i m m e d i a t e l y by a d d i n g of LiNO~. The principal hydraulic constituent in HAC is CaAl204 (CA). The h y d r a t i o n process of CA is generally believed to occur through initial dissolution, formation of a metastable gel and s u b s e q u e n t p r e c i p i t a t i o n p r i n c i p a l l y CaAI204xlOH20 (CAHI0), but also Ca2Al2OsxSH20 (C2AHB), and their c o n v e r s i o n to Ca3A1206x6H20 (C3AH6) (12). The c o m p o s i t i o n of the hydration products shows a t i m e - t e m p e r a t u r e dependency: the l o w - t e m p e r a t u r e hydration products (CAHI0) is t h e r m o d y n a m i c a l l y unstable e s p e c i a l l y in w a r m and humid storage c o n d i t i o n w h e n a more stable compound, C~AH6, is formed. L a b o r a t o r y and field experience with HAC concretes show that on p r o l o n g e d storage the hexagonal CAHI0 and C2AH 8 phases tend to convert to the cubic C3AH 6 (13). After d i s s o c i a t i o n of CA, the formed m e t a s t a b l e gel will acquire stability by c o n d e n s a t i o n of m o n o c o o r d i n a t e d OH groups linked to A1 to form oxobridges b e t w e e n
182
T. Matusinovic imdN. Vrbos
Vol. 23, No. 1
two A1 c e n t e r s l e a d i n g to the c r y s t a l l i n e CAHI0 (6). To produce such an o x o b r i d g e s condensation structure it is n e c e s s a r y to b r i n g the OH g r o u p in a p o s i t i o n that a lone p a i r on the o x y g e n can o v e r l a p w i t h a d o r b i t a l of AI, r e s u l t i n g in the f o r m a t i o n of an o x o b r i d g e and a m o l e c u l e of w a t e r w h i c h w o u l d r e m a i n h y d r o g e n b o n d e d to the o x y g e n atom. S o l i d - s t a t e N M R d a t a i n d i c a t e that a l u m i n i u m in CA is e n t i r e l y 4c o o r d i n a t e d but the p r i n c i p a l h y d r a t i o n p r o d u c t s of CA, CAHI0, C2AHs, AH~ and C3AH 6 c o n t a i n 6 - c o o r d i n a t e d a l u m i n i u m . The 27AI N M R w o r k shows that the h y d r a t i o n of c a l c i u m a l u m i n a t e c e m e n t s p r o c e e d s as a c o n v e r s i o n of 4- to 6- f o l d - c o o r d i n a t e d a l u m i n i u m (14). In situ 2VAl N M R s t u d i e s of the h y d r a t i o n p r o c e s s w e r e c a r r i e d out on c e m e n t s a m p l e s h y d r a t e d w i t h d e m i n e r a l i z e d w a t e r and w i t h a s o l u t i o n of Li2CO 3 in d e m i n e r a l i z e d w a t e r (8). W i t h o u t any a d d i t i v e , the A1 c o n v e r s i o n s t a r t s o n l y a f t e r a p p r o x i m a t e l y 3-4 h i n d u c t i o n p e r i o d and a p p e a r s to end a f t e r 18-20 h. At a w/c r a t i o of 0.5 the f r a c t i o n of 4 - c o o r d i n a t e d a l u m i n i u m in the final p r o d u c t a m o u n t s to approximately 30% to 40% of the e n t i r e A1 content. The d a t a o b t a i n e d w i t h the a d d i t i v e are in s h a r p c o n t r a s t to the h y d r a t i o n w i t h d e m i n e r a l i z e d water, the c o n v e r s i o n of AI(4) to AI(6) s t a r t s i m m e d i a t e l y a f t e r mixing, if f r a c t i o n of 0.5% a q u e o u s l i t h i u m c a r b o n a t e s o l u t i o n is u s e d as the h y d r a t i o n medium. H o w e v e r , the rate constant of the a l u m i n i u m conversion process is w i t h i n e x p e r i m e n t a l error, i d e n t i c a l to that found in the a b s e n c e of the l i t h i u m a d d i t i v e . Thus, the a c t i o n of l i t h i u m - c o n t a i n i n g s e t t i n g a c c e l e r a t o r s is b a s e d on a s h o r t e n i n g of the i n d u c t i o n p e r i o d w h i l e h a v i n g no e f f e c t on the rate of the p h a s e t r a n s f o r m a t i o n p r o c e s s . The i n d u c t i o n p e r i o d d u r i n g the p r e c i p i t a t i o n of CAHI0 and C2AH 8 from a s u p e r s a t u r a t e d s o l u t i o n is a r e f l e c t i o n of the n u c l e a t i o n b a r r i e r to the f o r m a t i o n of t h e s e c o m p o u n d s . D o u b l e et al. (5) a t t r i b u t e the a c c e l e r a t i n g e f f e c t of l i t h i u m salts to a r e m o v a l of this n u c l e a t i o n b a r r i e r , c a u s e d by an i n i t i a l l y fast p r e c i p i t a t i o n of l i t h i u m h y d r o m e t a a l u m i n a t e . This c o m p o u n d is t h e n t h o u g h t to act as a h e t e r o g e n e o u s nucleation substrate, thus e l i m i n a t i n g the i n d u c t i o n period. This v i e w is e n t i r e l y c o m p a t i b l e w i t h N M R r e s u l t s p r e s e n t e d by N o v i n s o n (8), w h i c h i n d i c a t e that the a c c e l e r a t o r a f f e c t s o n l y the i n d u c t i o n but not the rate of p h a s e c o n v e r s i o n once the n u c l e a t i o n b a r r i e r has b e e n broken. The N M R r e s u l t s s u g g e s t f u r t h e r that the m e a s u r e m e n t s of s e t t i n g time a p p e a r s to be m o s t c l o s e l y r e l a t e d to the end of the i n d u c t i o n period, at w h i c h p o i n t the A I ( 4 ) - to -AI(6) c o n v e r s i o n is a b o u t to begin. The r e s u l t s of such a m e a s u r e m e n t in the p r e s e n t s t u d y p r o v e it. The o x o b r i d g e s c o n d e n s a t i o n s t r u c t u r e s w i l l be a f f e c t e d by a l k a l i m e t a l c a t i o n s f o r m i n g c o - o r d i n a t i o n l i n k a g e w i t h the h y d r o x y l groups. Of the ions studied, Li* s h o u l d be d i f f e r e n t in b e h a v i o u r from the o t h e r c a t i o n s b e c a u s e of the a b i l i t y to form t e t r a h e d r a l symmetry w i t h OH groups, w h i l e Na ÷, K ÷, Rb ÷, and Cs ÷ w i l l f o r m the o c t a h e d r a l type (15). This is p r o v e d by our e x p e r i m e n t a l r e s u l t s
Vol. 23, No. 1
SET ACCELERATORS, AIJfAIJ METAL SALTS, ALUMINATE CEMENT
183
(Tables 2 and 3), l i t h i u m h a v i n g a d r a s t i c effect, but d i f f e r e n c e s b e t w e e n the o t h e r c a t i o n s are not g r e a t and e x h i b i t a d e f i n i t i v e trend. T h e s e t t i n g t i m e of HAC w i t h the d e c r e a s e s in the f o l l o w i n g order: Cs
>
Rb
>
K
>
same
Na
salts
>>
data
on the a l k a l i
Parameter Crystal
radii/nm
Hydrated Hydration
radii/nm number
-AHh/kJ mol -l
TABLE metal
7 cations
Na
K
Li
alkali
metal
Li
The s e q u e n c e f o l l o w s the t r e n d of c r y s t a l radii, and e n t h a l p i e s of h y d r a t i o n .
Hydration
of
hydration numbers
(16).
Rb
Cs
0.068
0.098
0.133
0.148
0.167
0.340
0.276
0.232
0.228
0.228
25
16
10
-
10
530
420
340
315
280
T h e c o m p r e s s i v e s t r e n g t h of HAC m o r t a r s c o u l d not be m e a s u r e d w i t h i n 4 h o u r s b e c a u s e the s p e c i m e n s w e r e too soft to be r e m o v e d from the mold. A f t e r 4 h, w h e n the p e r i o d of i n d u c t i o n time e n d e d the s p e c i m e n s had the m i n i m a l c o m p r e s s i v e s t r e n g t h of 2.65 MPa. It can be s e e n from t a b l e 6 that t h e r e is a s u d d e n i n c r e a s e in s t r e n g t h for HAC m o r t a r s up to the age of 4 h. A f t e r 20 h HAC m o r t a r h a d a c o m p r e s s i v e s t r e n g t h of 48.12 MPa, a p p r o x i m a t e l y 50% v a l u e s of the i n f i n i t i v e c o m p r e s s i v e s t r e n g t h . HAC m o r t a r s w i t h l i t h i u m c a r b o n a t e s h o w e d a f t e r 30 m i n a c o m p r e s s i v e s t r e n g t h of 1.82 M P a and i n c r e a s e s r a p i d l y w i t h aging. T h e s e r e s u l t s s u p p o r t the r e s u l t s of r e s e a r c h m a d e by D o u b l e (5) as w e l l as N o v i n s o n (8). The results of the m e a s u r e m e n t s of c o m p r e s s i v e and flexural s t r e n g t h of a l k a l i m e t a l n i t r a t e s (Tables 4 and 5) s h o w t h a t a l k a l i m e t a l s a l t s d e c r e a s e the s t r e n g t h of HAC. It is a p p a r e n t that the s t r e n g t h i n c r e a s e s w i t h an i n c r e a s e in age of H A C m o r t a r s as w e l l as HAC m o r t a r s w i t h a l k a l i m e t a l salts. T h e i n v e s t i g a t e d l i t h i u m salts can be c l a s s i f i e d in t w o g r o u p s , a l k a l i n e l i t h i u m salts, from l i t h i u m h y d r o x i d e and v e r y w e a k a c i d s (K^ ~ i0 -7 mol dm -3) and a c i d l i t h i u m salts d e r i v e d f r o m s t r o n g and v e r y s t r o n g a c i d s (K A ~ 10 -2 mol dm -3) (17). The d a t a w e r e p l o t t e d as s e t t i n g times v_ss. pH of the s o l u t i o n . Figs. 1 a n d 2 i l l u s t r a t e the r e l a t i o n s h i p b e t w e e n s e t t i n g t i m e and pH for a l k a l i n e salts and a c i d salts. Alkaline lithium salts, salts (hydroxide, carbonate, sulfide
of and
weak and very weak metaborate) have a
acids linear
184
VoL 23,No. 1
T. Matusinovlc and N. Vrbos
E 0 u3
r-
I;3t) 0 v
400
SETTING TIME 1 -O.059pH + 3.2116 t=lO I00 I
I
I0
II
pilaf
I
12
0.001°/o tithium salt in mixing water
FIG. 1 Setting times of paste v_ss. pH for alkaline lithium salts.
u') QU,
E
A
.,,.,
or) r-.
-$
E} L) Lt} 133 0
u~
s<
600 _
4O0
cC Br~- ~ ' ~ ' ' /
j
J
r SETTING TIME L t= 100"2599pH+1,0935
200
l
55 pilaf
I
I
6 6.5 0.001°/o [ithium sort in mixing water
FIG.2 Setting times of paste v__ss, pH of acid lithium salts.
Vol. 23, No. 1
SET ACCELERATORS, ALKALI METAL SALTS. ALUMINATE CEMENT
185
e x p r e s s i o n w i t h a negative slope and follow the equation t
=
1 0 -°'°sgPs +
3.2116
w h e r e t is the setting time. The acids salts (bromide, chloride, nitrate, sulphate) follow a linear plot w l t h a positive slope and seem to obey the e q u a t i o n t
=
1 0 0"2599pH + 1.0935
The effect of hydroxyl group is greater than the effect of the other i n v e s t i g a t e d anions due to the replacement of m o l e c u l e s H20 by hydroxyl groups in the A1 environment leading to a further centre for o x o b r i d g e formation. The other investigated anions have a lesser effect w h i l e they substitute OH groups in the c o o r d i n a t i o n sphere of AI, w h i c h leads to the removal of a hydroxyl group n e c e s s a r y In the process of oxolation. Acknowledqment
The authors a c k n o w l e d g e financial support from the M i n i s t r y of science, t e c h n o l o g y and informatics of Croatia. References
I.
"Fluldizlng M o d l l n g Material for M a n u f a c t u r i n g Cores and Molds and a M e t h o d Therefor", U.S. Patent 3,600.203. 2. "Verfahren zur V e r k ~ r z u n g der A b b l n d e z e l t von T o n e r d e z e m e n t e n " R e l c h s p a t e n t a m t Patentschrlft, Deutschland, Nr. 648851. 3. "Setting and H a r d e n i n g of Alumlnous Cement", U.S. Patent 3,826.665. 4. T.W.Parker, Proc. Third Int. Symp. C h e m i s t r y of Cement, L o n d o n 1952, p512 (5), Cement and Concrete A s s o c i a t i o n (1954). 5. S . R o d g e r and D.D.Double, Cem. Concr. Res., 14, 73 (1984). 6. B.R.Currell, R.Grzeskowlak, H . G . M i d g l e y and J.R.Parsonage, Cem. Concr. Res., Z, 420 (1987). 7. T . I . N o v i n s o n and J.Crahan, Am. Concr. Inst. Mater. J., !, 12 (1988). 8. T.Luong, H.Mayer, H.Eckert and T.I.Novlnson, J. Am. Ceram. Soc., 72 (ii) 2136 (1989). 9. R.Juza and P.Laurer, Z. anorg, allgem. Chem., 275, 79 (1954). 10. R.Juza and P.Laurer, Z. anorg, allgem. Chem., 287, 113 (1956). ii. G.Brauer, H a n d b u c h der Praparatlven A n o r g a n l s c h e Chemle, F e r d i n a n d Enke Verlag, Stuttgart, (1960).
186
12. 13. 14. 15. 16. 17.
T. Matuslnovlc and N. Vrbos
Vol. 23, No. 1
F.M.Lea, The Chemisty of Cement and Concrete, Edward Arnold Ltd., London (1976). P.K.Mehta, Concrete Structure, Properties and Materials, Prentice-Hall., Engelwood Cliffs, New Jersey (1986). D.Muller, A.Rettel, W.Gessner and G.Scheler, J. Magn. Reson., 57, 152 (1984). A.F.WelIs, Structural Inorganic Chemistry, Oxford Press, London (1962). F.A.Cotton and G.Wilkinson., Advanced Inorganic Chemistry: A Comprehensive Text, Interscience Publishers, New York, (1972). J.C.Bailar, H.J.Emeleus, R.Nyholm and A.F.Trontman-Dickenson (Eds.), Comprehensive Inorganic Chemistry, Volume i, Pergamon Press, New York (1973).
ALKALI
METAL
SALTS
AS
SET ACCELERATORS
FOR
HIGH
ALUMINA
CEMENT
T . M a t u s i n o v i c and N.Vrbos U n i v e r s i t y of Zagreb D e p a r t m e n t of Chemical E n g i n e e r i n g and Technology Marulicev t r g 20, 41000 Zagreb, C r o a t i a
(Sef=eed) (Received Feb. 4; in fnudform March 4, 1992)
ABSTRACT
The effect of alkali metal salts on the setting time of high aluminia cement (HAC) has been studied. The influence of c o n c e n t r a t i o n of the salts, chemical nature of anion and the type of alkali metal cation have been investigated. The results of the research indicate that alkali metal salts are set accelerators of HAC. The lithium cation has more effect on the setting time than other alkali cations because of its ability to form tetrahedral symmetry while the others will form the octahedral type. L i t h i u m salts remove the n u c l e a t i o n barrier, caused by an initially fast precipitation. The influence of pH in mixing water is not important. The effect of hydroxyl group is greater than effect of other i n v e s t i g a t e d anions due to the replacement leading to a further centre for oxobridge formation. The l i t h i u m salts cause d e c r e a s i n g of flexural and compressive s t r e n g t h of H A C mortars but also cause the strength d e v e l o p m e n t at early ages.
Introduction
L i t h i u m salts have been reported as accelerating setting agents for alumina concretes in the patent literature(l-3). Parker r e p o r t e d that the setting time of HAC pastes could be influenced by a d d i t i o n of small amounts of m a n y materials. Double(4) and Currell(5) studied the c h e m i s t r y of hydration of HAC in the p r e s e n c e of accelerating and retarding admixtures. Novinson et ai.(7,8) i n v e s t i g a t e d the effects of lithium salts on r e f r a c t o r y mortars. In chemical terms, the mode of action of these admixtures is not well understood. In this paper alkali metal salts as set accelerators of HAC have been studied. The influence of c o n c e n t r a t i o n of the salts, chemical nature of anions and the type 177
178
T. Matusinovic and N. Vrbos
Vol. 23. No. 1
of a l k a l i m e t a l c a t i o n s h a v e b e e n i n v e s t i g a t e d . T h e r e s e a r c h has b e e n c a r r i e d out to d e v e l o p r a p i d s e t t i n g and h a r d e n i n g m a t e r i a l s for the r e p a i r of c o n c r e t e . We have b e e n c o n d u c t i n g e x p e r i m e n t s to determine the optimal setting time and the strength of the m a t e r i a l s m a d e w i t h l i t h i u m salt a d m i x t u r e s .
Experimental
Methods
T h e h i g h a l u m i n a c e m e n t u s e d was a n o r m a l p r o d u c t i o n of " G i u l i o R e v e l a n t e " , Pula, C r o a t i a . T h e g e n e r a l a n a l y s i s of s u c h c e m e n t was: CaO, 40.2%, A1203, 39.0%, FeO, 4.3%, Fe203, 11.7%. T h e a d m i x t u r e s used were commercial Analar grade reagents dissolved in d e m i n e r a l i z e d w a t e r p r i o r to m i x i n g w i t h HAC. LizS a n d R b O H w e r e prepared in o u r l a b o r a t o r y (9-11). The s e t t i n g t i m e of HAC in d e p e n d e n c e of the pH of l i t h i u m salts in m i x i n g w a t e r has b e e n measured. T h e pH of e a c h s o l u t i o n w a s m e a s u r e d w i t h a s t a n d a r d g l a s s e l e c t r o d e . T h e e l e c t r o d e was c a l i b r a t e d w i t h b u f f e r s o l u t i o n at 25°C at pH 4 a n d 9. The salt s o l u t i o n was p o u r e d into the b o w l a n d the HAC w e r e a d d e d to the water. T h e s e w e r e m i x e d t o g e t h e r b y means of m e c h a n i c stirrer for p r e s c r i b e d time intervals. All experiments used a water/cement (w/c) r a t i o of 0.24. T h e s e t t i n g time was determined using a modification of the JUS ~ m e t h o d B.C8.023. In o u r m o d i f i c a t i o n the p e n e t r a t i o n of the n e e d l e into h a r d e n i n g p a s t e was m e a s u r e d e v e r y 5 s e c o n d s due to e x t r e m e l y r a p i d setting time for l i t h i u m salt m o d i f i e d . The e x p e r i m e n t s were r e p e a t e d t h r e e times to o b t a i n r e l i a b l e s t a n d a r d d e v i a t i o n s a n d s t a t i s t i c a l means. For d e t e r m i n a t i o n of c o m p r e s s i v e a n d f l e x u r a l s t r e n g t h the s p e c i m e n s (40 x 40 x 160 mm) w e r e p r e p a r e d a c c o r d i n g to JUS B . C 8 . 0 2 2 at w/c r a t i o of 0.5. The s p e c i m e n s w e r e t e s t e d at the age of 1,3,7,28, and 90 days. T h r e e s p e c i m e n s w e r e t e s t e d for e a c h age. Results
T h e m e a s u r e m e n t of the i n f l u e n c e of d i f f e r e n t m a s s f r a c t i o n , ( w ) , of l i t h i u m n i t r a t e on the s e t t i n g t i m e of HAC has b e e n d o n e to c h o o s e the f r a c t i o n of the salt w h i c h can give a s e t t i n g t i m e c o n v e n i e n t for t h e r e s e a r c h . The r e s u l t s of the m e a s u r e m e n t are s h o w n in T a b l e i. The m e a s u r e m e n t s of the i n f l u e n c e of d i f f e r e n t a l k a l i m e t a l s a l t s on the s e t t i n g t i m e has b e e n made. The r e s u l t s of the r e s e a r c h are s h o w n in T a b l e 2. *JUS
- Yugoslav
standard
Vol.23,No. I
Lithium
SET ACCEI22ATORS,ALKALIMETAL SALTS,ALUMINATE CEMENT
nitrate:
Lithium
Comparison fractions.
salt
TABLE 1 of s e t t i n g t i m e s
at d i f f e r e n t
w(LiNO~)/%
Setting
mass
time/s
16500
0
LINO 3
179
0.0005
7330
0.001
1650
0.005
710
0.01
440
0.05
F
0.i
M
F - s e t t i n g of HAC w i t h l i t h i u m n i t r a t e d u r i n g the m i x i n g t i m e M - s e t t i n g of HAC i m m e d i a t e l y by a d d i n g of the l i t h i u m n i t r a t e
Alkali
metal
Anions
salts:
OH-
TABLE 2 C o m p a r i s o n of s e t t i n g fraction.
S=
Cations
C03 =
Br"
Setting
time/s
times
at 0.01% m a s s
CI-
NO3 =
SO Z
Li
300
325
370
305
360
440
560
Na
5140
5620
6300
8940
9720
6480
7800
K
7200
7400
7980
10120
10200
7920
8100
Rb
9140
9260
10930
10680
9360
9300
Cs
iiii0
11990
11200
11400
11480
11630
- dash
llne
indicates
The d i f f e r e n t l i t h i u m s h o w n in the T a b l e 3.
that the c h e m i c a l salts
have
been
was
not a v a i l a b l e
tested
and the
results
are
Discussion
T h e r e s u l t s of the r e s e a r c h i n d i c a t e that a l k a l i m e t a l s a l t s are set a c c e l e r a t o r s of HAC. The d a t a in T a b l e 1 d e m o n s t r a t e t h a t L i N O 3 a c c e l e r a t e s the s e t t i n g time of HAC e v e n at the m a s s f r a c t i o n of
T. Mamsinovic and N. Vrbos
180
Lithium
salts:
Lithium
VoL 23. No. 1
TABLE 3 C o m p a r i s o n of s e t t i n g times and pH of 0.01% l i t h i u m salts in m i x i n g water.
salt
pH values
Setting
LiOH
12.3
300
Li~S
11.8
325
Li2CO ~
11.2
370
LiBO 2
10.4
390
Li2SO 4
6.4
560
LiNO~
5.9
440
LiCI
5.6
360
LiBr
5.4
305
TABLE 4 F l e x u r a l s t r e n g t h s of HAC m o r t a r s and HAC m o r t a r s alkali metal salts. Time/ days
Flexural HAC + LiNO I
HAC + NaNO~
time/s
made with
0.01%
strength/MPa
HAC + KNO~
HAC + RbNO~
HAC + CsNO~
HAC
1
7.32
7.44
7.68
7.92
8.14
8.62
3
7.92
8.30
8.15
8.35
8.72
8.95
7
8.99
9.88
10.12
10.30
10.67
11.10
28
9.65
10.12
10.51
10.72
10.94
11.20
90
10.68
10.77
10.91
11.03
11.25
11.36
C o m p r e s s i v e s t r e n g t h s of 0.01% alkali metal salts.
TABLE 5 mortars
Compressive
Time/ days
HAC
HAC + LiNO~
HAC + NaNO~
1
49.18
52.09
3
61.87
7
HAC + KNO~
and
HAC
mortars
made
with
strength/MPa HAC + RbNO~
HAC + CsNO~
HAC
53.62
55.42
56.45
58.70
62.12
63.78
64.95
66.35
67.97
70.10
73.71
75.05
79.55
82.66
84.50
28
76.25
79.85
82.29
86.90
88.75
92.60
90
82.08
85.73
88.75
91.15
93.12
96.25
Vol. 23, No. 1
SET ACCELERATORS,AI.,KALIMETAL SALTS, ALUMINATECEMENT
181
TABLE 6 C o m p r e s s i v e and flexural strengths of HAC mortars and HAC mortars made w i t h 0.05% Li2CO3. Time/h
C o m p r e s s i v e strength/MPa HAC
HAC+ Li~CO 3
Flexural s t r e n g t h / M P A HAC
HAC+ Li2CO 3
0.5
X
1.82
X
X
1.0
X
3.86
X
X
1.5
X
4.89
X
X
2.0
X
5.93
X
1.42
2.5
X
8.96
X
2.44
3.0
X
12.60
X
3.11
3.5
X
13.12
X
3.93
X
4.21
4.0
2.65
18.33
4.5
8.80
20.02
2.19
4.37
5.0
24.58
21.25
2.64
4.56
6.0
36.65
23.87
3.34
4.96
i0.0
43.83
30.62
4.61
6.48
15.0
46.77
32.16
6.95
6.88
20.0
48.12
36.56
7.22
7.15
x - test could not be p e r f o r m e d because specimens were too soft to be removed from the mold 5xi0-4%. With increasing the fraction of LiNO~, the setting time decreases. With the fraction of 0.1% setting occurs i m m e d i a t e l y by a d d i n g of LiNO~. The principal hydraulic constituent in HAC is CaAl204 (CA). The h y d r a t i o n process of CA is generally believed to occur through initial dissolution, formation of a metastable gel and s u b s e q u e n t p r e c i p i t a t i o n p r i n c i p a l l y CaAI204xlOH20 (CAHI0), but also Ca2Al2OsxSH20 (C2AHB), and their c o n v e r s i o n to Ca3A1206x6H20 (C3AH6) (12). The c o m p o s i t i o n of the hydration products shows a t i m e - t e m p e r a t u r e dependency: the l o w - t e m p e r a t u r e hydration products (CAHI0) is t h e r m o d y n a m i c a l l y unstable e s p e c i a l l y in w a r m and humid storage c o n d i t i o n w h e n a more stable compound, C~AH6, is formed. L a b o r a t o r y and field experience with HAC concretes show that on p r o l o n g e d storage the hexagonal CAHI0 and C2AH 8 phases tend to convert to the cubic C3AH 6 (13). After d i s s o c i a t i o n of CA, the formed m e t a s t a b l e gel will acquire stability by c o n d e n s a t i o n of m o n o c o o r d i n a t e d OH groups linked to A1 to form oxobridges b e t w e e n
182
T. Matusinovic imdN. Vrbos
Vol. 23, No. 1
two A1 c e n t e r s l e a d i n g to the c r y s t a l l i n e CAHI0 (6). To produce such an o x o b r i d g e s condensation structure it is n e c e s s a r y to b r i n g the OH g r o u p in a p o s i t i o n that a lone p a i r on the o x y g e n can o v e r l a p w i t h a d o r b i t a l of AI, r e s u l t i n g in the f o r m a t i o n of an o x o b r i d g e and a m o l e c u l e of w a t e r w h i c h w o u l d r e m a i n h y d r o g e n b o n d e d to the o x y g e n atom. S o l i d - s t a t e N M R d a t a i n d i c a t e that a l u m i n i u m in CA is e n t i r e l y 4c o o r d i n a t e d but the p r i n c i p a l h y d r a t i o n p r o d u c t s of CA, CAHI0, C2AHs, AH~ and C3AH 6 c o n t a i n 6 - c o o r d i n a t e d a l u m i n i u m . The 27AI N M R w o r k shows that the h y d r a t i o n of c a l c i u m a l u m i n a t e c e m e n t s p r o c e e d s as a c o n v e r s i o n of 4- to 6- f o l d - c o o r d i n a t e d a l u m i n i u m (14). In situ 2VAl N M R s t u d i e s of the h y d r a t i o n p r o c e s s w e r e c a r r i e d out on c e m e n t s a m p l e s h y d r a t e d w i t h d e m i n e r a l i z e d w a t e r and w i t h a s o l u t i o n of Li2CO 3 in d e m i n e r a l i z e d w a t e r (8). W i t h o u t any a d d i t i v e , the A1 c o n v e r s i o n s t a r t s o n l y a f t e r a p p r o x i m a t e l y 3-4 h i n d u c t i o n p e r i o d and a p p e a r s to end a f t e r 18-20 h. At a w/c r a t i o of 0.5 the f r a c t i o n of 4 - c o o r d i n a t e d a l u m i n i u m in the final p r o d u c t a m o u n t s to approximately 30% to 40% of the e n t i r e A1 content. The d a t a o b t a i n e d w i t h the a d d i t i v e are in s h a r p c o n t r a s t to the h y d r a t i o n w i t h d e m i n e r a l i z e d water, the c o n v e r s i o n of AI(4) to AI(6) s t a r t s i m m e d i a t e l y a f t e r mixing, if f r a c t i o n of 0.5% a q u e o u s l i t h i u m c a r b o n a t e s o l u t i o n is u s e d as the h y d r a t i o n medium. H o w e v e r , the rate constant of the a l u m i n i u m conversion process is w i t h i n e x p e r i m e n t a l error, i d e n t i c a l to that found in the a b s e n c e of the l i t h i u m a d d i t i v e . Thus, the a c t i o n of l i t h i u m - c o n t a i n i n g s e t t i n g a c c e l e r a t o r s is b a s e d on a s h o r t e n i n g of the i n d u c t i o n p e r i o d w h i l e h a v i n g no e f f e c t on the rate of the p h a s e t r a n s f o r m a t i o n p r o c e s s . The i n d u c t i o n p e r i o d d u r i n g the p r e c i p i t a t i o n of CAHI0 and C2AH 8 from a s u p e r s a t u r a t e d s o l u t i o n is a r e f l e c t i o n of the n u c l e a t i o n b a r r i e r to the f o r m a t i o n of t h e s e c o m p o u n d s . D o u b l e et al. (5) a t t r i b u t e the a c c e l e r a t i n g e f f e c t of l i t h i u m salts to a r e m o v a l of this n u c l e a t i o n b a r r i e r , c a u s e d by an i n i t i a l l y fast p r e c i p i t a t i o n of l i t h i u m h y d r o m e t a a l u m i n a t e . This c o m p o u n d is t h e n t h o u g h t to act as a h e t e r o g e n e o u s nucleation substrate, thus e l i m i n a t i n g the i n d u c t i o n period. This v i e w is e n t i r e l y c o m p a t i b l e w i t h N M R r e s u l t s p r e s e n t e d by N o v i n s o n (8), w h i c h i n d i c a t e that the a c c e l e r a t o r a f f e c t s o n l y the i n d u c t i o n but not the rate of p h a s e c o n v e r s i o n once the n u c l e a t i o n b a r r i e r has b e e n broken. The N M R r e s u l t s s u g g e s t f u r t h e r that the m e a s u r e m e n t s of s e t t i n g time a p p e a r s to be m o s t c l o s e l y r e l a t e d to the end of the i n d u c t i o n period, at w h i c h p o i n t the A I ( 4 ) - to -AI(6) c o n v e r s i o n is a b o u t to begin. The r e s u l t s of such a m e a s u r e m e n t in the p r e s e n t s t u d y p r o v e it. The o x o b r i d g e s c o n d e n s a t i o n s t r u c t u r e s w i l l be a f f e c t e d by a l k a l i m e t a l c a t i o n s f o r m i n g c o - o r d i n a t i o n l i n k a g e w i t h the h y d r o x y l groups. Of the ions studied, Li* s h o u l d be d i f f e r e n t in b e h a v i o u r from the o t h e r c a t i o n s b e c a u s e of the a b i l i t y to form t e t r a h e d r a l symmetry w i t h OH groups, w h i l e Na ÷, K ÷, Rb ÷, and Cs ÷ w i l l f o r m the o c t a h e d r a l type (15). This is p r o v e d by our e x p e r i m e n t a l r e s u l t s
Vol. 23, No. 1
SET ACCELERATORS, AIJfAIJ METAL SALTS, ALUMINATE CEMENT
183
(Tables 2 and 3), l i t h i u m h a v i n g a d r a s t i c effect, but d i f f e r e n c e s b e t w e e n the o t h e r c a t i o n s are not g r e a t and e x h i b i t a d e f i n i t i v e trend. T h e s e t t i n g t i m e of HAC w i t h the d e c r e a s e s in the f o l l o w i n g order: Cs
>
Rb
>
K
>
same
Na
salts
>>
data
on the a l k a l i
Parameter Crystal
radii/nm
Hydrated Hydration
radii/nm number
-AHh/kJ mol -l
TABLE metal
7 cations
Na
K
Li
alkali
metal
Li
The s e q u e n c e f o l l o w s the t r e n d of c r y s t a l radii, and e n t h a l p i e s of h y d r a t i o n .
Hydration
of
hydration numbers
(16).
Rb
Cs
0.068
0.098
0.133
0.148
0.167
0.340
0.276
0.232
0.228
0.228
25
16
10
-
10
530
420
340
315
280
T h e c o m p r e s s i v e s t r e n g t h of HAC m o r t a r s c o u l d not be m e a s u r e d w i t h i n 4 h o u r s b e c a u s e the s p e c i m e n s w e r e too soft to be r e m o v e d from the mold. A f t e r 4 h, w h e n the p e r i o d of i n d u c t i o n time e n d e d the s p e c i m e n s had the m i n i m a l c o m p r e s s i v e s t r e n g t h of 2.65 MPa. It can be s e e n from t a b l e 6 that t h e r e is a s u d d e n i n c r e a s e in s t r e n g t h for HAC m o r t a r s up to the age of 4 h. A f t e r 20 h HAC m o r t a r h a d a c o m p r e s s i v e s t r e n g t h of 48.12 MPa, a p p r o x i m a t e l y 50% v a l u e s of the i n f i n i t i v e c o m p r e s s i v e s t r e n g t h . HAC m o r t a r s w i t h l i t h i u m c a r b o n a t e s h o w e d a f t e r 30 m i n a c o m p r e s s i v e s t r e n g t h of 1.82 M P a and i n c r e a s e s r a p i d l y w i t h aging. T h e s e r e s u l t s s u p p o r t the r e s u l t s of r e s e a r c h m a d e by D o u b l e (5) as w e l l as N o v i n s o n (8). The results of the m e a s u r e m e n t s of c o m p r e s s i v e and flexural s t r e n g t h of a l k a l i m e t a l n i t r a t e s (Tables 4 and 5) s h o w t h a t a l k a l i m e t a l s a l t s d e c r e a s e the s t r e n g t h of HAC. It is a p p a r e n t that the s t r e n g t h i n c r e a s e s w i t h an i n c r e a s e in age of H A C m o r t a r s as w e l l as HAC m o r t a r s w i t h a l k a l i m e t a l salts. T h e i n v e s t i g a t e d l i t h i u m salts can be c l a s s i f i e d in t w o g r o u p s , a l k a l i n e l i t h i u m salts, from l i t h i u m h y d r o x i d e and v e r y w e a k a c i d s (K^ ~ i0 -7 mol dm -3) and a c i d l i t h i u m salts d e r i v e d f r o m s t r o n g and v e r y s t r o n g a c i d s (K A ~ 10 -2 mol dm -3) (17). The d a t a w e r e p l o t t e d as s e t t i n g times v_ss. pH of the s o l u t i o n . Figs. 1 a n d 2 i l l u s t r a t e the r e l a t i o n s h i p b e t w e e n s e t t i n g t i m e and pH for a l k a l i n e salts and a c i d salts. Alkaline lithium salts, salts (hydroxide, carbonate, sulfide
of and
weak and very weak metaborate) have a
acids linear
184
VoL 23,No. 1
T. Matusinovlc and N. Vrbos
E 0 u3
r-
I;3t) 0 v
400
SETTING TIME 1 -O.059pH + 3.2116 t=lO I00 I
I
I0
II
pilaf
I
12
0.001°/o tithium salt in mixing water
FIG. 1 Setting times of paste v_ss. pH for alkaline lithium salts.
u') QU,
E
A
.,,.,
or) r-.
-$
E} L) Lt} 133 0
u~
s<
600 _
4O0
cC Br~- ~ ' ~ ' ' /
j
J
r SETTING TIME L t= 100"2599pH+1,0935
200
l
55 pilaf
I
I
6 6.5 0.001°/o [ithium sort in mixing water
FIG.2 Setting times of paste v__ss, pH of acid lithium salts.
Vol. 23, No. 1
SET ACCELERATORS, ALKALI METAL SALTS. ALUMINATE CEMENT
185
e x p r e s s i o n w i t h a negative slope and follow the equation t
=
1 0 -°'°sgPs +
3.2116
w h e r e t is the setting time. The acids salts (bromide, chloride, nitrate, sulphate) follow a linear plot w l t h a positive slope and seem to obey the e q u a t i o n t
=
1 0 0"2599pH + 1.0935
The effect of hydroxyl group is greater than the effect of the other i n v e s t i g a t e d anions due to the replacement of m o l e c u l e s H20 by hydroxyl groups in the A1 environment leading to a further centre for o x o b r i d g e formation. The other investigated anions have a lesser effect w h i l e they substitute OH groups in the c o o r d i n a t i o n sphere of AI, w h i c h leads to the removal of a hydroxyl group n e c e s s a r y In the process of oxolation. Acknowledqment
The authors a c k n o w l e d g e financial support from the M i n i s t r y of science, t e c h n o l o g y and informatics of Croatia. References
I.
"Fluldizlng M o d l l n g Material for M a n u f a c t u r i n g Cores and Molds and a M e t h o d Therefor", U.S. Patent 3,600.203. 2. "Verfahren zur V e r k ~ r z u n g der A b b l n d e z e l t von T o n e r d e z e m e n t e n " R e l c h s p a t e n t a m t Patentschrlft, Deutschland, Nr. 648851. 3. "Setting and H a r d e n i n g of Alumlnous Cement", U.S. Patent 3,826.665. 4. T.W.Parker, Proc. Third Int. Symp. C h e m i s t r y of Cement, L o n d o n 1952, p512 (5), Cement and Concrete A s s o c i a t i o n (1954). 5. S . R o d g e r and D.D.Double, Cem. Concr. Res., 14, 73 (1984). 6. B.R.Currell, R.Grzeskowlak, H . G . M i d g l e y and J.R.Parsonage, Cem. Concr. Res., Z, 420 (1987). 7. T . I . N o v i n s o n and J.Crahan, Am. Concr. Inst. Mater. J., !, 12 (1988). 8. T.Luong, H.Mayer, H.Eckert and T.I.Novlnson, J. Am. Ceram. Soc., 72 (ii) 2136 (1989). 9. R.Juza and P.Laurer, Z. anorg, allgem. Chem., 275, 79 (1954). 10. R.Juza and P.Laurer, Z. anorg, allgem. Chem., 287, 113 (1956). ii. G.Brauer, H a n d b u c h der Praparatlven A n o r g a n l s c h e Chemle, F e r d i n a n d Enke Verlag, Stuttgart, (1960).
186
12. 13. 14. 15. 16. 17.
T. Matuslnovlc and N. Vrbos
Vol. 23, No. 1
F.M.Lea, The Chemisty of Cement and Concrete, Edward Arnold Ltd., London (1976). P.K.Mehta, Concrete Structure, Properties and Materials, Prentice-Hall., Engelwood Cliffs, New Jersey (1986). D.Muller, A.Rettel, W.Gessner and G.Scheler, J. Magn. Reson., 57, 152 (1984). A.F.WelIs, Structural Inorganic Chemistry, Oxford Press, London (1962). F.A.Cotton and G.Wilkinson., Advanced Inorganic Chemistry: A Comprehensive Text, Interscience Publishers, New York, (1972). J.C.Bailar, H.J.Emeleus, R.Nyholm and A.F.Trontman-Dickenson (Eds.), Comprehensive Inorganic Chemistry, Volume i, Pergamon Press, New York (1973).