- Email: [email protected]
Influence of CaSO4·2H2O, CaSO4·12H2O and CaSO4 on the initial hydration of clinker having different burning degree
CEMENT and CONCRETE RESEARCH. Vol. 14, pp. 645-656, 1984. Printed in the USA. 0008-8846/84 $3.00+00. Pergamon Press, Ltd.
INFLUENCE OF CaSO4.2H20, CaSO4.½H20 AND CaSO4 ON THE INITIAL HYDRATION OF CLINKER HAVING DIFFERENT BURNING DEGREE
Hiroshi UCHIKAWA, Shunichiro UCHIDA, Kenji OGAWA and Shunsuke HANEHARA Central Research Laboratory, Onoda Cement Co., Ltd. I - I - 7 Toyosu Koto-ku, Tokyo Japan
(Communicated by D.M. Roy) (Received Aug. 8, 1983) ABSTRACT Relation between early hydration process and properties of fresh cement until setting was studied by using nine kinds of cements prepared from three commercial clinkers with various buring degree and three kinds of calcium sulfates, that i s , natural gypsum, ~-hemihydrate and anhydrite Ca(OH)9 and CaSO4 saturation ratio in l i q u i d phase influenced remarkably on the'early hydration process of cement paste rather than the hydraulic r e a c t i v i t y of clinker minerals themselves. Setting time well corresponded to the period of maximum Ca(OH)2 saturation r a t i o in l i q u i d phase which coincided also with the period of v i v i d hydration of a l i t e . Soft burning of clinker so as to remain a l i t t l e amount (0.5% level) of free lime was effective for shortening the setting time but strength at longer age was s l i g h t l y i n f e r i o r to that of cement from well burnt clinker. Though the setting time was shortened in the order of natural gypsum, 8-hemihydrate and anhydrite ~ in cement from well burnt clinker, no remarkable influence of the kind of calcium sulfate was recognized in cement from poorly burnt clinker.
. -t ~ :., ~ o . ~ v ~ ( ! / ~ ) ~ Z . i ~ . . : . ~ ,
%,
i,,~[]:~© Ca(OH" 2 ~ b~ CaS04
6"0 Ca(OH) 2 ~"1;~9<':0.
t- ~
:
:='~[!~::-':<'~i: ~:
~" ,!.-~-~:-:~i < ,~ ~ ~, ~..~..
~ ~, ~ ,~ ~! ~,~9- ;~ ~-~~! :. - - ~ - ~ - ;~.
645
-~ ~, y
6L6
Vol. i~;, !~o. I,. '_~chikav,,a, et al. INTRODUCT!ON
Properties of mortar and concrete developed in the early stage of h y d ~ t i o n of cement such as f l u i d i t y , bleeding, s e t t i n g time, change of w o r k a b i l i t y ~ t h time and e a r l y strength e s p e c i a l l y in case of using admixture became very important f a c t o r in the q u a l i t y of concrete as energy-saving and automatic placing technology of concrete developed. Therefore, i t is necessary not only to select appropriate a d d i t i v e and admixture, but also to make clear the characters of cement and admixture which influence on the properties of cement paste, mortar and concrete during the e a r l y hydration. There are two main factors which influence on the reaction during the early hydration of cement ( I ) ( 2 ) ( 3 ) . F i r s t f a c t o r is the rate of d i s s o l u t i o n of calcium s u l f a t e , that i s , gypsum, hemihydrate and anhydrite. Second one is r e a c t i v i t y of c l i n k e r minerals, e s p e c i a l l y a l i t e , C3A and C4AF. The r e a c t i v i t y of c l i n k e r minerals is considered to be s t r o n g l y influenced by burning degree of c l i n k e r . From these standpoints, the authors studied the influence of various kinds of calcium s u l f a t e on the i n i t i a l hydration of cements prepared from c l i n k e r s with various burning degree. SAMPLE Clinker Character of c l i n k e r P r a c t i c a l l y , c l i n k e r mineral formation proceeds above a l i t e formation temperature and reaction rate is e x p o n e n t i a l l y proportional to the difference between maximum (T) and c r i t i c a l (To=1250°C) temperature. Therefore, burning degree F can be expressed as f o l l o w i n g equation. F=at'exptb.(T-To)]
. . . . . I)
Where a and b are constant and t is r e t e n t i o n time to keep c l i n k e r above To. Retention time and temperature d i f f e r e n c e mentioned above in equation I) have close r e l a t i o n with size of b e l i t e and b i r e f r i n g e n c e of a l i t e (4). Chemical compositions of three c l i n k e r s from same r o t a r y cement k i l n used in t h i s experiment are shown in Table I. Content of free CaO and l i t e r weight of c l i n k e r s , b i r e f r i n g e n c e and size of a l i t e and b e l i t e , and burning c o n d i t i o n of c l i n k e r s estimated by microscopic observation are shown in Table 2. Twenty eight-day compressive strength (JIS) of cement mortar prepared from c l i n k e r W, A and P was 43.1, 39.2 and 35.3 MPa, r e s p e c t i v e l y . Mineralogical compositions of c l i n k e r s calculated by modified Bogue's equation and measured by chemical separation method are also shown in Table 2. There was small d i f f e r e n c e between them except for the amount of C3A phase. Chemical composition of a l i t e and aluminate phase measured by EPMA and separated f e r r i t e phase determined by chemical analysis was shown in Table 3. I t was proved that the amount of MgO, A1203 and Fe203 was increased and b i r e f r i n g e n c e of a l i t e was decreased when the burning degree was lowered. Table I Sample
Chemical composition of each c l i n k e r and natural gypsum
ig. i n - SiO 2 AI203 Fe203 CaO MgO Na20 K20 loss sol
C l i n k e r W 0.2 0.2 22.9 Clinker A 0.2 0.2 22.3 Clinker P 0.2 0.3 22.5 Gypsum 20.3 0.9 W: well burnt c l i n k e r
5.1 5.2 4.9 0.2
3.4 3.1 3.3 0.1
64.8 64.8 63.8 32.7
P205 TiO2
SO3 Total (~)
1.4 0.26 0.68 0.13 0.29 0.62 1.4 0.28 0.81 0.15 0.29 0.67 1.4 0.29 1.12 0.14 0.28 1.33 0.5 - 44.8
A: averagely burnt c l i n k e r
99.9 99.4 99.6 99.5
P: poorly burnt c l i n k e r
Vol. 14, No. 5
647 GYPSUM, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE
Table 2 Mineralogical composition, water soluble component and burning condition of each clinker Clinker
Mineralogical composition (~) Water soluble (%) C~S C2S C~S+C2S C3A C4AF K2S04 Na2S04 F.CaO Total Na20 K20 S03 56.2 23.2 56.5 21.2 49.7 26.8
79.4 81.5 77.7 79.0 76.5 78.4
8.410.3 6.210.9 9.4 9.4 6.6 11.3 8.3 9.9 8.3 8.8
1.3 0.7 1.5 0.9 2.1 1.6
A P
Note:
1.25 1.15 1.10
0.17 1.11 1.64
0.2 0.7 0.4
0.17 0.17 1.11 1.11 1.64 1.64
99.7* 99.7** 0.08 0.39 0.18 99.1 99.1 0.10 0.49 0.36 99.1 99.1 0.16 0.87 0.55
Estimated burning condition**** Heating Maximum Retention Cooling rate temperature time*** rate
Liter Free Alite Belite weight CaO size bf. size bf. ( k g / l ) (%) (~m) (~m) W
0.1 0.2
40 0.007 30 0.012 30 0.006 20 0.015 20 0.004 10 0.018
+ ++ +++
+++ ++ +
++++ +++ +
: Calculated from Bogue's equation ** : Measured by chemical analysis of separated phase b f . : B i r e f r i n g e n c e , ***" Retention time above c r i t i c a l * * * * " Estimated by microscopic method ++++: E x c e l l e n t , +++: Good, ++: Average, +: Poor
++++ +++ +
*
temperature
Table 3 Chemical composition and crystallographic data of each clinker mineral Clinker CaO (%)
Alite phase SiO2 MgO Al203 Fe203 Crystal Lattice constant system a (~) b c (a/b)2
W A P
71.54 25.10 0.65 0.75 71.37 24.97 0.74 0.87 70.82 24.88 0.79 0.99
0.53 0.75 0.88
W A P
Aluminate phase CaO Si02 MgO A1203 Fe203 Na20 K20 (%) 54.57 5.45 0.94 29.66 4 . 4 7 1.95 1.48 54.36 4.98 1.05 30.34 4.71 1.78 1.06 56.38 5.06 0.91 31.32 3 . 2 3 1.25 0.82
Mm 12.254 7.054 24.98 3.018 90.03 Mm 12.239 7.054 24.99 3.010 90.01 MI~12 241 7.053 25.00 3.012 89.99
Ferrite phase CaO SiO2 MgO Al203 Fe203 Crystal (%) system 46.91 3.28 3.12 23.09 19.64 46.91 3.50 3.22 23.02 19.64 47.89 2.90 3.22 23.69 19.64
Z~
Orthorhombic Orthorhombic Orthorhombic
Crystal system Cubic, Orthorhombic Cubic, Orthorhombic Cubic Lattice constant (~) a b c 5.32 14.50 5.54 5.32 14.49 5.53 5.32 14.48 5.53
Note: Chemical composition of a l i t e and aluminate phase obtained by EPMA Pure f e r r i t e phase was obtained by dissolving the residue of salicylic acid-methanol treatment (5), with 2% HNO3-methanol treatment (6). Though there was no remarkable difference of composition for ferrite phases in three clinkers, the quantity of Si02 was increased slightly and alkali was decreased with burning degree. Estimated compositions of f e r r i t e phase calculated by both powder x-ray diffraction and wet analysis were approximately C6A2F (7).
648
Vol. 14, Ho. 5 H. Uchikawa, et el.
The amount of water soluble Na20, K20 and S03 was large in poorly burnt c l i n k e r as shown in Table 2. Large d i f f e r e n c e of water soluble Na20 in spite of same Na20 level i n d i c a t e s the existence of Na20 bearing s o l i d solution. L a t t i c e constants of a l i t e calculated a f t e r Yamaguchi and Miyabe (8) and f e r r i t e phase were shown in Table 3. Clinker P contains M~and MI m o d i f i c a t i o n of a l i t e . X-ray d i f f r a c t i o n peaks of separated i n t e r s t i t i a l phase in Fig. I show the existence of small amount of orthorhombic C3A in c l i n k e r W and A i n d i c a t i n g the formation of a l k a l i s o l i d s o l u t i o n by rapid cooling of molten phase (9). Though d i f f e r e n c e was observed in the i n t e n s i t y of C3A and C4AF s o l i d s o l u t i o n , no d i f f e r e n c e could be observed in l a t t i c e constants of f e r r i t e phase among three c l i n k e r s .
ill~
,l.i
32 33 34 3
32 33 34 35
32 33 34 35
Cu K(~ 2~ clinker W •
clinker A
orthrh~ic
clinker P
C3A (400,040)
Fig. I X-ray diffraction profile
of interstitial phase gypsum
hemihydrate
anhydrite
6
Calcium s u l f a t e
5
10
4
9
3
8
Character of calcium s u l f a t e B-hemihydrate and anhydrite ~ was 7 prepared by heating natural gypsum at 120°C for 12hrs. and at 800°C for 2hrs. 1 6 r e s p e c t i v e l y . They were i d e n t i f i e d by XRD and TG-DSC. Chemical composition 5 6 of natural gypsum is shown in Table I . 0 6 6 12 C r y s t a l l ~ t e size of anhydrite reached Time (rain.) to 2000 A and was almost corresponded i pure water • Ca(OH)2 saturated soln. 10.25% Na2CO3 soln., • pH with that of natural a n h y d r i t e . The amount of S042- dissolved and Fig. 2 The amount of S042- dissolved pH value of l i q u i d phase of w a t e r - s o l i d and pH of liquid phase for each mixture f o r each calcium s u l f a t e are shown in Fig. 2. In gypsum, the amount calcium s u l f a t e - w a t e r suspension of S042- dissolved into pure water reached maximum value of 1.63 S042g/l immediately a f t e r mixing. In hemihydrate, i t was three times as large as that of gypsum but the amount of S042- in l i q u i d was decreased by the p r e c i p i t a t i o n of secondary gypsum. In a n h y d r i t e , i t was about four f i f t h s as large as t h a t of gypsum and the amount of S042- in l i q u i d increased with time. Amounts of S042- from dissolved calcium s u l f a t e was rised in a l k a l i s o l u t i o n such as Na2CO3 and i t was lowered in the Ca(OH)2 saturated s o l u t i o n . The pH value at 20°C of 4 g/l water s o l u t i o n of a n h y d r i t e , hemihydrate and gypsum was 10.2, 7.2 and 6.6, r e s p e c t i v e l y . Preparation of cement J
0
1
[
,
1
,
I
l
I
I
L
L
J
l
I
Cements were prepared from c l i n k e r W, A and P by adding natural gypsum hemihydrate and anhydrite u n t i l t o t a l SO~ in cement attained to 1.9%. Each mixture wa~ interground and adjusted u n t l l Blaine s p e c i f i c surface area reached 3200:100cmL/g.
Vol. 14, No. 5
649 GYPSUM, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE
EXPERIMENT Preparation of hydrated sample Each cement was hydrated at IO°C, 20cC and 30cC with the water cement ratio of 0.3. After determined curing time, hydration was stopped by dispersing the sample in acetone. Hydrated sample was dried by two methods, that is, D-drying and drying under CO2 free air of which relative humidity is 15% (RH 15% drying).
Determination of ionic concentration in l i q u i d phase Liquid phase of suspension (W/C=4.0) was obtained b% the f i l t e r a t i o n a f t e r determined curing time and the concentration of Caz+, Na+, K+, OH- and S042- in l i q u i d phase was measured. Measurement of heat evolution in hydration Heat evolution of each cement paste was measured by conduction calorimetry at I0°C, 20~C and 30°C with the water cement r a t i o of 0.4. Quantitative analysis of Ca(OH)2 and e t t r i n g i t e The amount of Ca(OH)2 and e t t r i n g i t e in the hydrated sample dried in a i r of RH 15% was determined by modified TG-DSC method (10). Measurement of specific surface area and observation of morphology of hydrates Specific surface area of D-dryed hydrated sample was measured by BET method. Microstructure of hydrated sample was observed by scanning electron microscopy. Measurement of settin 9 time Setting time of cement was measured under JIS R5201. Flow curve measurement with rotational viscometer Each cement was mixed with water at W/C=O.3 for 210 seconds by hand. Flow curve of the paste was obtained by coaxial rotational viscometer with double cylinders RV 12 (HAAKE Co., Ltd.) using the sensor system of MVIP(11). Paste was dispersed homogeneously on the surface of sensor system by rotating the rotor at 512 rpm for 30 seconds. The measurement was continued u n t i l noize caused by the setting of paste was observed. RESULT AND DISCUSSION Early hydration process Time dependency of ionic concentration and Ca(OH)2 and CaSO4 saturation ratio of l i q u i d phase Fig. 3 shows the time dependency of concentration of ions in l i q u i d phase of cement-water suspension. Concentration of CaL+, Na+, K÷ and OH- showed high level in poorly burnt clinker which contained much free CaO and alkali sulfate as shown in Fig. 3 (a)(d)(e). CaL+ and S042- concentration was remarkably changed by the kind of calcium sulfate added with time but this change of OHconcentration was not so large. This result coincided with the tendency shown in Fig. 2. Fig. 4 shows the time dependency of Ca(OH)2 and CaSO4 saturation ratio calculated from concentration of each ion after Fujii and Kondo (12)(13). Ca(OH)2 saturation ratio increased rapidly and reached the peak at an early age in cement from poorly burnt clinker. Influence of the kind of calcium sulfate was not so clear except for e a r l i e r appearence of peak in cements
650
Vol. 14, ~,o. 5 F: Lichikawa, et al.
containing hemihydrate, which is deduced to r e l a t e to the increase of Ca2+ i o n i c concentration. CaS04 s a t u r a t i o n r a t i o was large in the order of a n h y d r i t e , gypsum and hemihydrate added cement. I n i t i a l CaS04 s a t u r a t i o n r a t i o was l a r g e s t when
10°C
20°C
30 C
A 8o
[ ~//F
r
II
(Ca~';'~O'-I 2
1
..
•
_~'"
§2o v --
t .... 0 0
I .... 2
40
2
I .... 40
2
. 4 n
Ti,'r~ ,ih~. : 0
2
40
2
40
2
40
2
4C
2
4~
Time ( h r . ) W-g: c l i n k e r W - gypsum W-h: c l i n k e r W - hemihydrate W-a: c l i n k e r W - anhydrite
A-g: c l i n k e r A - gypsum P-g: c l i n k e r P - gypsum
Fig. 3 Change of ionic concentration in liquid phase of cementwater suspension
[CaE+l "[ OH-J7
I g
.ia
I •
•
(CaE+~'IS04 E'! J ":
I i:!:i ,
•
~ j ~
Ag!~g i
Fig. 4 Change of [Ca2+].[OH-] 2 and [Ca2+].[S042-] in l i q u i d phase of cement-water suspension ( s a t u r a t i o n level=1.0)
hemihydrate was used but i t was decreased r a p i d l y by the p r e c i p i t a t i o n of secondary gypsum. CaS04 s a t u r a t i o n r a t i o was decreased in the cement from poorly burnt c l i n k e r and the d i f f e r e n c e among three calcium s u l f a t e s was small. Much soluble a l k a l i s u l f a t e s in poorly burned c l i n k e r are considered to be responsible to the decrease of CaSO4 s a t u r a t i o n r a t i o . At high curing temperature, Ca(0H) 2 s a t u r a t i o n r a t i o was lowered and peak appeared e a r l i e r , while CaS04 s a t u r a t i o n r a t i o rised. The e f f e c t of the kind of calcium s u l f a t e and burning degree of c l i n k e r on both Ca(OH)2 and CaSO4 s a t u r a t i o n r a t i o was unchanged with temperature. Heat e v o l u t i o n rate Heat e v o l u t i o n curves of each cement at various curing temperature are shown in Fig. 5. The p o s i t i o n and height of the second peak which corresponded to hydration of a l i t e were remarkably influenced by the burning degree of c l i n k e r . The second peak appeared e a r l i e r in the cement from poorly burnt c l i n k e r . The i n f l u e n c e of the kind of added calcium s u l f a t e on the p o s i t i o n of second peak was small but i t appeared e a r l i e r when hemihydrate was added. The p o s i t i o n of second peak was c l o s e l y related to the peak p o s i t i o n of Ca(0H) 2 saturation ratio. This r e s u l t i n d i c a t e s the v i v i d hydration of a l i t e a f t e r i n d u c t i o n period begins when Ca(OH)2 s a t u r a t i o n r a t i o a t t a i n s to maximum value. The period of v i v i d hydration of a l i t e is accelerated in cement manufactured by the i n t e r g r i n d i n g of c l i n k e r , gypsum and lime (14). Therefore, i t is considered t h a t v i v i d hydration of a l i t e is s t r o n g l y c o n t r o l l e d by Ca(OH)2 satur a t i o n r a t i o of l i q u i d phase r a t h e r than the d i f f e r e n c e of hydraulic r e a c t i v i t y of a l i t e mainly depended on c r y s t a l s t r u c t u r e and minor c o n s t i t u e n t s .
Vol. 14, No. 5
651
GYPSUI~, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE The amount of hydration products and time dependency of BET specific surface area of each cement paste E t t r i n g i t e , Ca(OH)2 and C-S-H were main hydration products during i n i t i a l few hours. F~g. 6 shows the change of the amount of e t t r i n g i t e and Ca(OH)2 formed and the change of BET specific surface area of paste with
I0~C w
8, 6-
4. 3-
30"C
20:C T
|
W -
. .
2.
I
4. I 3.
i
4 i
4
W
1
W
•
A
-P I
/
3
3
-
2
-
u~ 8£
'
"
-
'4
3,~
-
.
3 ~3
2.i ~ .
i
a
i
I
0
calcium i
0
I
2
10
20
;
2
;0
2F~
2
I;
2;
T~me ( h r . ) • gypsum
• hemihydrate
i
i
i
~
.
0~0 1 2 3 0 1 2 3 0 ~ ~ 3 4 Ti~ (hr.) • gypsum • hemihydrate •anhydrite
• annydr;te
Fig. 6 Change of amount of hydrates formed and BET s p e c i f i c surface area of paste
Fig. 5 Heat evolution curves of each cement at different curing temperature (same notation as in Fig. 3)
W,'S=I.0
p•n•e20-C,
sample s~ze; 11.67g 120- 3 ~ i ~ "time. The influence of kind of calcium 80(I) Inters~tla~ sulfate on the amount of e t t r i n g i t e formed was changed with burning degree 40of clinker. The amount of e t t r i n g i t e formed is considered to be influenced by o: 0 I l Ca(OH)2 and CaSO4 saturation ratio in 80(2) Interst}tlal phase liquid-phase as well as hydraulic CaSOa.2H20 60r e a c t i v i t y of i n t e r s t i t i a l phase i t s e l f . ~ w - w ~ (~IA'F:O,5,~: S03) Heat evolution curves of inter40s t i t i a l phase of each clinker separated by s a l i c y l i c acid-methanol method are 20shown in Fig. 7. As f e r r i t e phase had ! l i t t l e compositional and structural 0 0 5 10 15 difference with the difference of burning Time ( h r . ) degree, hydraulic r e a c t i v i t y of inter• cllnker W • clinker A Pcllnker P s t i t i a l phase seemed to depend mainly on the quantity, crystal structure and Fig. 7 Heat evolution curves of minor constituents of CsA solid solution. i n t e r s t i t i a l phase Clinker P has i n t e r s t i t i a l phase of the highest r e a c t i v i t y . I n t e r s t i t i a l phase of clinker W is more reactive than that of clinker A from the data in Fig. 7 The difference of hydraulic r e a c t i v i t y of C3A solid solution in each E
652
Vol. ia, '~o. 5 F. -:ci~ikav.a, et al.
c l i n k e r could be explained by the character of C3A such as difference of m o d i f i c a t i o n of C3A as reported by Regourd (15) and the amount of K20 as impurity of C3A s o l i d s o l u t i o n ( I ) . The amount of e t t r i n g i t e formed in the cement paste from c l i n k e r P was small in spite of highest r e a c t i v i t y of i n t e r s t i t i a l phase. High Ca(OH)2 s a t u r a t i o n r a t i o in l i q u i d phase under the presence of calcium s u l f a t e depressed the hydration of i n t e r s t i t i a l phase. In the cement from well burnt c l i n k e r , amount of e t t r i n g i t e formed in the e a r l y hydration was large in the order of hemihydrate, gypsum and annydrite added cement corresponding to CaSO4 s a t u r a t i o n r a t i o in l i q u i d phase. This difference became small or the trend turned opposite in cements from c l i n k e r A and P. Depressed d i s s o l u t i o n of calcium s u l f a t e , p r e c i p i t a t i o n of small e t t r i n g i t e and the formation of dense layer of e t t r i n g i t e on the surface of unhydrated grain in high Ca(OH)2 satur a t i o n r a t i o in the l i q u i d phase might be one of the reasons of the abovementioned phenomenon observed in the cements from c l i n k e r A and P. This r e s u l t suggests that the amount of e t t r i n g i t e formed was influenced by Ca(OH)2 satur a t i o n r a t i o in l i q u i d phase which has close r e l a t i o n to free CaO in c l i n k e r and CaSO4 s a t u r a t i o n r a t i o in l i q u i d phase which is affected by the kind of added calcium s u l f a t e r a t h e r than hydraulic r e a c t i v i t y of i n t e r s t i t i a l phase i t s e l f . The amount of existed Ca(OH)2, that is the d i f f e r e n c e between sum of formed Ca(OH)2 by the hydration of calcium s i l i c a t e s and free lime and consumed Ca(OH) 2, measured by TG-DSC method was ranged from 0.3 to 1.1% a f t e r 4 hour hydration. Therefore, the amount of existed Ca(OH)2 is not always represented the rate of hydration of a l i t e in cement. On the c o n t r a r y , the change of BET s p e c i f i c surface area with time shown in Fig. 6 corresponds to the rate of hydration of a l i t e at the i n i t i a l stage (16). Increase in BET s p e c i f i c surface area of cement from c l i n k e r P at an e a r l i e r age showed good correspondence to the second peak p o s i t i o n in heat e v o l u t i o n curve. Morphology of hydrate Scanning electron micrographs of hydrated cement paste are shown in F i g . 8 . E t t r i n g i t e formed p a r t l y on the surface of cement p a r t i c l e s and i t remained almost same size. Morphology of e t t r i n g i t e became short prismatic at high Ca(OH)2 s a t u r a t i o n r a t i o and became small i r r e g u l a r rod and equidimentional shape at high CaS04 s a t u r a t i o n r a t i o . This e f f e c t was much more remarkable in Ca(OH)2 than in CaS04 s a t u r a t i o n r a t i o . The morphology of e t t r i n g i t e formed did not change at the i n i t i a l stage w i t h i n 4 hours. Precipit a t i o n of large gypsum c r y s t a l could be observed in hemihydrate added cement paste. With the descending of burning degree of c l i n k e r , the size of p r e c i p i tated gypsum turned small due to the increase of Ca(OH)2 and the decrease of CaSO4 s a t u r a t i o n r a t i o . Small hexagonal plate l i k e Ca(OH)2 was observed in cement r i c h in free CaO. The reason why c l i n k e r P has a large BET s p e c i f i c surface area at I hour in s p i t e of less e t t r i n g i t e formation is considered that small Ca(OH)2 by the hydration of free CaO and small e t t r i n g i t e c r y s t a l are formed under high Ca(OH)2 s a t u r a t i o n r a t i o . In cement paste containing a n h y d r i t e , calcium aluminate hydrate and monosulfate hydrate could not be observed in the e a r l y hydration. A f t e r 2 hours, a c i c u l a r C-S-H p r e c i p i t a t e widely around cement p a r t i c l e s and i t s morphology was not changed by CaSO4 and Ca(OH)2 s a t u r a t i o n r a t i o . Properties of cement paste during e a r l y hydration Setting time I n i t i a l and f i n a l s e t t i n g time of cement at each curing temperature are shown in Fig. 9. Setting time was shortened with lowering of burning degree and with r i s i n g of curing temperature. The d i f f e r e n c e of s e t t i n g time with d i f f e r e n t kind of calcium s u l f a t e was recognized c l e a r l y in well burnt c l i n k e r
[
H~r,-.
.d,,
r,,-. z
I
I[
Clinker W - anhydrite
,
+
~
,
Clinker W - hemihydrate
Clinker W - gypsum
.
-.~
4
I ,;m
Clinker A - anhyd~ite
Clinker A - gypsum
Clinker A - hemihydrate
Fig. 8 Scanning el~ctron mic,'ograph c ~ hydrated cement (age 30 min.,a: 2~ C. cured ~C It,... temperature. The setting zit,- ~.~a~ ",÷ c,.-der of gyp'.-..'. , c . hydFat~ ano ar, hjd,-ite c o n t a i n i n § ceE+~:,- . ~ . ; long s.~e. S~_:tin; of cement paste is co,re.:gc~ceo to. the [."ocess of s t r , ' - . . : : formation whet. colloidal solution de,;ec.:~ gel properties a,;d i t is c . ~ e : ~.' the adhesiveness of water film aroun~ ce-:er,t and hydrate par+:.;le_- ~ ' : ,+.~ cohesive force between hydrates. Therefore. the in:t-ease of specific s,,:'~..E area and contact points of hydrates g,-owr, to needle !i~:e shape contribute.: to setting of cement paste. Generally, no,-mal setting of cement paste is brought by the hydration of a l i t e (17)(i~',. But Locher et a: (I': have r~?'.tL5 that normal setting occurs upDr the recrystallizatior, o~ ~it,!r,.*;t-'. ,-ath.:. than by the formation of new hydration p-oducts ( f a ] i t e . . , c , r v.~ . ti::~ As before mentione~, the second pea,. positic, r. c,f heat evol ..... curve and r i s i n g position of BET specific surface a~ea vs. ti~.-~ cu,-;.~ cc.i,-cidc with the i n i t i a l s e t t i r g time, therefore, setting, time is ce,'tair.ly ,'e]ateC~ closely to the beginrir, g of vivid hydra.tic: cf a~ite, The diffe,-ence of setting time by the kind of calcium su]'.'a -~_ :'.~v b~. caused D) the diffe,'e,ncE of amount and morphology of e t t r i n g i t ~ dE:;÷r~£J Q"+ rF~inly CaC0h)2 a~:d CaSD, saturation ratio i,; l i q u i d ph~.~e. In the cement fron, poorly bj.-n • Ll;ni~", ~'~, iC h)dratior, of a l i t ¢ a,formation of C-S-H having large specific s~,'fa-e area at the i n i t i a l stage n'u:n contribute to the setting time of ceme,:-, pa~:,.,, as the ~.,,,=~,~r+,. and sha:÷, of e t t r i n g i t e formed are small. Or. the c,tr, er ha,'c;, im the cement froF. well bu:-nt c l i n k e r , as e t t r i n g i t e formed has much a.~.2~rI ant large acicular shape, hydration of i n t e r s t i t i a l phase mDre cor','+but'.-.~ :c the setting time st tr,~the effect o¢ the k.nd of calc<...~ .:~ . . . . . . . . + ,
654
Vol. ,4, ?qo. 5 H. Cchikawa, et al.
!000
;
.
_w
6
.
k
500~ A P
~
'
:.
final
set
-
a
~ "~"
i
• g.Yps~m A A hglthydrate 0
_p
30
' 0
2
10 20
30
I0
20
30
10 20
Inhydrt te
O •
so
3
20 40
'
'
'
'
0 20 40 0 20 40 60 80 Time (min.)
~
"
120
•
'
160
ZOO
Fig. II The time dependency of y i e l d value of fresh cement paste (W/C:O.30, 20°C)
30
Temperature (:C) • gypsum •hemihydrate
cement from varlously burnt cllnker and ~psum
•anhydrite
Fig. 9 Setting time of each cement at different curing temperature
_ d
/!
initial setting level (ISL) b m
m
~
w
~ i
/
,s,
r
-
i I
/
final setting le~e~ ~ F ~ L ] _
L m su
~ ~,,,,,,=~,~L,f
•
I
-
I
inters~al phase
~
x11
initial set ~
|
I l
Oil W-g ¢)0 A-g
II I II I
initial set al set c ~ n t from well burnt clinker and different kind of calcium sulfate
I
L h
~/./i~'
I~ - -
-
~
~lll II
of a11~ _
I g~
II t II oo W-g I al W-h
~,~
i;
initial set ~ f i n a l
final set
set
Setting time
Fig. I0 Schematic explanation of relationship between index of hydration for each c l i n k e r mineral and setting time (same notation as in Fig. 3) Time dependency of the degree of hydration for each c l i n k e r mineral u n t i l setting time was schematically explained in Fig. 10. Setting of cement paste is expressed as the summed results of hydration of calcium s i l i c a t e and i n t e r s t i t i a l phase and s e t t i n g occurs when the index of hydration which includes the kind, size, morphology and amount of hydrates reaches a certain level. Change of the y i e l d value of cement paste with time The increase of y i e l d value shown in Fig. 11 during i n i t i d l two hours was mainly caused by c r y s t a l l i z a t i o n of gypsum from hem•hydrate and increase
Vol. 14, No. 5
655
GYPSUM, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE of specific surface area by the formation oF e t ~ r i n g i t e . Vivid hydration of a l i t e was responsible at the most part a f t e r t h i s period. Generally, y i e l d value was increased more rapidly with poorly burnt c l i n k e r corresponding to i t s increase in specific surface area except for the cement containing hemihydrate. increase in y i e l d value of hemihydrate added c l i n k e r W t i l l one hour may be caused by the c r y s t a l l i z a t i o n of large crystal of gypsum by the hydration of hemihydrate. This result shows that influence of calcium sulfates on the f l u i d i t y of fresh cement paste at early stage is closely related to burning degree of c l i n k e r . CONCLUSION Following results were obtained by using the cements prepared from variously burnt clinkers with same k i l n and natural gypsum, B-hemihydrate and anhydrite ~ obtained by heating natural gypsum. I . Burning degree of c l i n k e r defined as the function of temperature and retention time at burning zone shows good correspondence to the amount of free CaO and l i t e r weight measured by conventional method, and the optical properties of c l i n k e r measured by microscopic observation. A l i t e in well burnt c l i n k e r belonged to M~ modification. In poorly burnt c l i n k e r , MI modification of a l i t e was recognized and the amount of impurities such as MgO, AI203 and Fe203 in a l i t e increased and birefringence of a l i t e lowered. The amount of water soluble Na20, K20 and SO3 was small in well burnt clinker. Orthorhombic C3A solid soluton containing much amount of Na20 and K20 was observed in rapidly cooled c l i n k e r . In the cement prepared from well burnt c l i n k e r and gypsum, the best 28-day compressive strength of mortar was obtained. 2. Ca(OH)? and CaSO4 saturation r a t i o in l i q u i d phase were more i n f l u e n t i a l factors on ~he early hydration process of a l i t e and i n t e r s t i t i a l phase than t h e i r hydraulic r e a c t i v i t y . 3. CaS04 saturation r a t i o in l i q u i d phase of cement-water suspension was i n i t i a l l y high in the order of anhydrite, gypsum and hemihydrate added cement from same c l i n k e r but i t decreased remarkably with time in hemihydrate added cement because of the p r e c i p i t a t i o n of gypsum. The difference was large in low Ca(OH)2 and small in case of high Ca(OH)2 saturation r a t i o . 4. Maximum value of Ca(OH)p saturation r a t i o in l i q u i d phase of cement-water suspension was attained quicRly in poorly burnt c l i n k e r and slowly in well burnt c l i n k e r regardless of the kind of added calcium sulfates. The difference was caused by the quantity of free CaO and water soluble a l k a l i sulfate and i t was reduced with the rise of curing temperature. 5. The amount of e t t r i n g i t e formed was roughly inversely proportional to the amount of Ca(OH)2 existed in paste and a l k a l i sulfate in cement, that i s , less in the cement from poorly burnt c l i n k e r and much in the cement from well burnt clinker. In case of low Ca(OH)2 saturation r a t i o , the amount of e t t r i n g i t e formed was increased with the decrease of CaS04 saturation r a t i o . But the influence of CaSO4 saturation r a t i o on the amount of e t t r i n g i t e formed was reduced in high Ca(OH)2 saturation r a t i o . The morphology of e t t r i n g i t e formed in high Ca(OH)2 saturation r a t i o became short and prismatic. Small i r r e g u l a r rod and equ~dimentional shaped e t t r i n g i t e was formed in high CaSO4 saturation r a t i o . Acicular C-S-H precipitated around the cement p a r t i c l e a f t e r 2 hours but i t s morphology was not changed by Ca(OH)2 and CaSO4 saturation r a t i o . 6. S t i f f e n i n g of paste w i t h i n 2 hours at 20°C is mainly caused by the c r y s t a l l i z a t i o n of gypsum from hemihydrate (so-called plaster set) and extraordinary increase of specific surface area of e t t r i n g i t e . The former occurs in case of cement from well burnt c l i n k e r and hemihydrate, the l a t t e r occurs in case of cement from poorly burnt c l i n k e r and anhydrite or gypsum.
656
Vol. 14, No. 5 H. Uchikawa, et al.
I t is recognizable q u a n t i t a t i v e l y by the yield value of paste measured by viscometry. 7. Normal setting time is closely related to the period of the i n i t i a t i o n of the v i v i d hydration of a l i t e which corresponds to the maximum value of Ca(OH)2 saturation r a t i o in l i q u i d phase of cement-water suspension and is easily observable by the peak of heat evolution curve in conduction calorimetry and the increasing point of BET specific surface area. 8. The difference of setting time with kind of calcium sulfate was recognized c l e a r l y in well burnt c l i n k e r cured at low temperature. The phenomenon was caused mainly by the difference of amount and morphology of e t t r i n g i t e formed. REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9. I0. II. 12. 13. 14. 15. 16. 17. 18.
F.W. Locher, W. Richartz and S. Sprung, Zement-Kalk-Gips 2_99, 435-442 (1976); 3__33, 271-277 (1980);35, 669-676 (1982). L. Odler and R. Wonneman, 7th International Congress on the Chemistry of Cement (Paris), IV, 510-513 (1980). J.P. Skalny and J.P. Young, 7th International Congress on the Chemistry of Cement (Paris), ~, II I / 3 - I / 4 5 (1980). Y. Ono, 7th International Congress on the Chemistry of Cement (Paris) LI, 1206-211 (1980). S. Takashima and F. Amano, Sement G i j i t s u Nenpo, 13, 50-54 (1959). S. Sato, Y. Tamura, K. Takahashi and H. Muto, Semento G i j i t s u Nenpo, 24, 24-26 (1970). E. Woermann, Th. Hahn and W. Eysel, Amer. Ceram. Soc., Bull. 44, 299 (1965). G. Yamaguchi and H. Miyabe, J. Amer. Ceram. Soc. 43, 219-224 ~ 9 6 0 ) . K.S. Han and F.P. Glasser, Cement and Concrete Research I0, 483-489 (1980). H. Uchikawa, S. Uchida and Y. Mihara, Sement G i j i t s u Nen~ 3_44, 58-66 (1980). H. Uchikawa, K. Ogawa and S. Uchida, Proc. Ann. Mtg. of Materials Research Society, r14, 4, Boston (1982). W. Kondo and K. F u j i i , J. Cer. Assoc. of Japan, 82(6), 333-336 (1974). K. F u j i i , Proc. Cement and Concrete Seminar ( P r i ~ t e meeting). H. Uchikawa, S. Uchida and K. Ogawa, in preparation. M. Regourd, i l Cemento, 75, 323-336 (1978). R. Kondo, 5th International Symposium on the Chemistry of Cement (Tokyo), I I , 203-248 (1968). J. Gebauer, Zement-Kalk-Gips, 3__II, 302-304 (1978). L.D. Adams, Cement and Concrete Research 6, 293-307 (1976).
INFLUENCE OF CaSO4.2H20, CaSO4.½H20 AND CaSO4 ON THE INITIAL HYDRATION OF CLINKER HAVING DIFFERENT BURNING DEGREE
Hiroshi UCHIKAWA, Shunichiro UCHIDA, Kenji OGAWA and Shunsuke HANEHARA Central Research Laboratory, Onoda Cement Co., Ltd. I - I - 7 Toyosu Koto-ku, Tokyo Japan
(Communicated by D.M. Roy) (Received Aug. 8, 1983) ABSTRACT Relation between early hydration process and properties of fresh cement until setting was studied by using nine kinds of cements prepared from three commercial clinkers with various buring degree and three kinds of calcium sulfates, that i s , natural gypsum, ~-hemihydrate and anhydrite Ca(OH)9 and CaSO4 saturation ratio in l i q u i d phase influenced remarkably on the'early hydration process of cement paste rather than the hydraulic r e a c t i v i t y of clinker minerals themselves. Setting time well corresponded to the period of maximum Ca(OH)2 saturation r a t i o in l i q u i d phase which coincided also with the period of v i v i d hydration of a l i t e . Soft burning of clinker so as to remain a l i t t l e amount (0.5% level) of free lime was effective for shortening the setting time but strength at longer age was s l i g h t l y i n f e r i o r to that of cement from well burnt clinker. Though the setting time was shortened in the order of natural gypsum, 8-hemihydrate and anhydrite ~ in cement from well burnt clinker, no remarkable influence of the kind of calcium sulfate was recognized in cement from poorly burnt clinker.
. -t ~ :., ~ o . ~ v ~ ( ! / ~ ) ~ Z . i ~ . . : . ~ ,
%,
i,,~[]:~© Ca(OH" 2 ~ b~ CaS04
6"0 Ca(OH) 2 ~"1;~9<':0.
t- ~
:
:='~[!~::-':<'~i: ~:
~" ,!.-~-~:-:~i < ,~ ~ ~, ~..~..
~ ~, ~ ,~ ~! ~,~9- ;~ ~-~~! :. - - ~ - ~ - ;~.
645
-~ ~, y
6L6
Vol. i~;, !~o. I,. '_~chikav,,a, et al. INTRODUCT!ON
Properties of mortar and concrete developed in the early stage of h y d ~ t i o n of cement such as f l u i d i t y , bleeding, s e t t i n g time, change of w o r k a b i l i t y ~ t h time and e a r l y strength e s p e c i a l l y in case of using admixture became very important f a c t o r in the q u a l i t y of concrete as energy-saving and automatic placing technology of concrete developed. Therefore, i t is necessary not only to select appropriate a d d i t i v e and admixture, but also to make clear the characters of cement and admixture which influence on the properties of cement paste, mortar and concrete during the e a r l y hydration. There are two main factors which influence on the reaction during the early hydration of cement ( I ) ( 2 ) ( 3 ) . F i r s t f a c t o r is the rate of d i s s o l u t i o n of calcium s u l f a t e , that i s , gypsum, hemihydrate and anhydrite. Second one is r e a c t i v i t y of c l i n k e r minerals, e s p e c i a l l y a l i t e , C3A and C4AF. The r e a c t i v i t y of c l i n k e r minerals is considered to be s t r o n g l y influenced by burning degree of c l i n k e r . From these standpoints, the authors studied the influence of various kinds of calcium s u l f a t e on the i n i t i a l hydration of cements prepared from c l i n k e r s with various burning degree. SAMPLE Clinker Character of c l i n k e r P r a c t i c a l l y , c l i n k e r mineral formation proceeds above a l i t e formation temperature and reaction rate is e x p o n e n t i a l l y proportional to the difference between maximum (T) and c r i t i c a l (To=1250°C) temperature. Therefore, burning degree F can be expressed as f o l l o w i n g equation. F=at'exptb.(T-To)]
. . . . . I)
Where a and b are constant and t is r e t e n t i o n time to keep c l i n k e r above To. Retention time and temperature d i f f e r e n c e mentioned above in equation I) have close r e l a t i o n with size of b e l i t e and b i r e f r i n g e n c e of a l i t e (4). Chemical compositions of three c l i n k e r s from same r o t a r y cement k i l n used in t h i s experiment are shown in Table I. Content of free CaO and l i t e r weight of c l i n k e r s , b i r e f r i n g e n c e and size of a l i t e and b e l i t e , and burning c o n d i t i o n of c l i n k e r s estimated by microscopic observation are shown in Table 2. Twenty eight-day compressive strength (JIS) of cement mortar prepared from c l i n k e r W, A and P was 43.1, 39.2 and 35.3 MPa, r e s p e c t i v e l y . Mineralogical compositions of c l i n k e r s calculated by modified Bogue's equation and measured by chemical separation method are also shown in Table 2. There was small d i f f e r e n c e between them except for the amount of C3A phase. Chemical composition of a l i t e and aluminate phase measured by EPMA and separated f e r r i t e phase determined by chemical analysis was shown in Table 3. I t was proved that the amount of MgO, A1203 and Fe203 was increased and b i r e f r i n g e n c e of a l i t e was decreased when the burning degree was lowered. Table I Sample
Chemical composition of each c l i n k e r and natural gypsum
ig. i n - SiO 2 AI203 Fe203 CaO MgO Na20 K20 loss sol
C l i n k e r W 0.2 0.2 22.9 Clinker A 0.2 0.2 22.3 Clinker P 0.2 0.3 22.5 Gypsum 20.3 0.9 W: well burnt c l i n k e r
5.1 5.2 4.9 0.2
3.4 3.1 3.3 0.1
64.8 64.8 63.8 32.7
P205 TiO2
SO3 Total (~)
1.4 0.26 0.68 0.13 0.29 0.62 1.4 0.28 0.81 0.15 0.29 0.67 1.4 0.29 1.12 0.14 0.28 1.33 0.5 - 44.8
A: averagely burnt c l i n k e r
99.9 99.4 99.6 99.5
P: poorly burnt c l i n k e r
Vol. 14, No. 5
647 GYPSUM, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE
Table 2 Mineralogical composition, water soluble component and burning condition of each clinker Clinker
Mineralogical composition (~) Water soluble (%) C~S C2S C~S+C2S C3A C4AF K2S04 Na2S04 F.CaO Total Na20 K20 S03 56.2 23.2 56.5 21.2 49.7 26.8
79.4 81.5 77.7 79.0 76.5 78.4
8.410.3 6.210.9 9.4 9.4 6.6 11.3 8.3 9.9 8.3 8.8
1.3 0.7 1.5 0.9 2.1 1.6
A P
Note:
1.25 1.15 1.10
0.17 1.11 1.64
0.2 0.7 0.4
0.17 0.17 1.11 1.11 1.64 1.64
99.7* 99.7** 0.08 0.39 0.18 99.1 99.1 0.10 0.49 0.36 99.1 99.1 0.16 0.87 0.55
Estimated burning condition**** Heating Maximum Retention Cooling rate temperature time*** rate
Liter Free Alite Belite weight CaO size bf. size bf. ( k g / l ) (%) (~m) (~m) W
0.1 0.2
40 0.007 30 0.012 30 0.006 20 0.015 20 0.004 10 0.018
+ ++ +++
+++ ++ +
++++ +++ +
: Calculated from Bogue's equation ** : Measured by chemical analysis of separated phase b f . : B i r e f r i n g e n c e , ***" Retention time above c r i t i c a l * * * * " Estimated by microscopic method ++++: E x c e l l e n t , +++: Good, ++: Average, +: Poor
++++ +++ +
*
temperature
Table 3 Chemical composition and crystallographic data of each clinker mineral Clinker CaO (%)
Alite phase SiO2 MgO Al203 Fe203 Crystal Lattice constant system a (~) b c (a/b)2
W A P
71.54 25.10 0.65 0.75 71.37 24.97 0.74 0.87 70.82 24.88 0.79 0.99
0.53 0.75 0.88
W A P
Aluminate phase CaO Si02 MgO A1203 Fe203 Na20 K20 (%) 54.57 5.45 0.94 29.66 4 . 4 7 1.95 1.48 54.36 4.98 1.05 30.34 4.71 1.78 1.06 56.38 5.06 0.91 31.32 3 . 2 3 1.25 0.82
Mm 12.254 7.054 24.98 3.018 90.03 Mm 12.239 7.054 24.99 3.010 90.01 MI~12 241 7.053 25.00 3.012 89.99
Ferrite phase CaO SiO2 MgO Al203 Fe203 Crystal (%) system 46.91 3.28 3.12 23.09 19.64 46.91 3.50 3.22 23.02 19.64 47.89 2.90 3.22 23.69 19.64
Z~
Orthorhombic Orthorhombic Orthorhombic
Crystal system Cubic, Orthorhombic Cubic, Orthorhombic Cubic Lattice constant (~) a b c 5.32 14.50 5.54 5.32 14.49 5.53 5.32 14.48 5.53
Note: Chemical composition of a l i t e and aluminate phase obtained by EPMA Pure f e r r i t e phase was obtained by dissolving the residue of salicylic acid-methanol treatment (5), with 2% HNO3-methanol treatment (6). Though there was no remarkable difference of composition for ferrite phases in three clinkers, the quantity of Si02 was increased slightly and alkali was decreased with burning degree. Estimated compositions of f e r r i t e phase calculated by both powder x-ray diffraction and wet analysis were approximately C6A2F (7).
648
Vol. 14, Ho. 5 H. Uchikawa, et el.
The amount of water soluble Na20, K20 and S03 was large in poorly burnt c l i n k e r as shown in Table 2. Large d i f f e r e n c e of water soluble Na20 in spite of same Na20 level i n d i c a t e s the existence of Na20 bearing s o l i d solution. L a t t i c e constants of a l i t e calculated a f t e r Yamaguchi and Miyabe (8) and f e r r i t e phase were shown in Table 3. Clinker P contains M~and MI m o d i f i c a t i o n of a l i t e . X-ray d i f f r a c t i o n peaks of separated i n t e r s t i t i a l phase in Fig. I show the existence of small amount of orthorhombic C3A in c l i n k e r W and A i n d i c a t i n g the formation of a l k a l i s o l i d s o l u t i o n by rapid cooling of molten phase (9). Though d i f f e r e n c e was observed in the i n t e n s i t y of C3A and C4AF s o l i d s o l u t i o n , no d i f f e r e n c e could be observed in l a t t i c e constants of f e r r i t e phase among three c l i n k e r s .
ill~
,l.i
32 33 34 3
32 33 34 35
32 33 34 35
Cu K(~ 2~ clinker W •
clinker A
orthrh~ic
clinker P
C3A (400,040)
Fig. I X-ray diffraction profile
of interstitial phase gypsum
hemihydrate
anhydrite
6
Calcium s u l f a t e
5
10
4
9
3
8
Character of calcium s u l f a t e B-hemihydrate and anhydrite ~ was 7 prepared by heating natural gypsum at 120°C for 12hrs. and at 800°C for 2hrs. 1 6 r e s p e c t i v e l y . They were i d e n t i f i e d by XRD and TG-DSC. Chemical composition 5 6 of natural gypsum is shown in Table I . 0 6 6 12 C r y s t a l l ~ t e size of anhydrite reached Time (rain.) to 2000 A and was almost corresponded i pure water • Ca(OH)2 saturated soln. 10.25% Na2CO3 soln., • pH with that of natural a n h y d r i t e . The amount of S042- dissolved and Fig. 2 The amount of S042- dissolved pH value of l i q u i d phase of w a t e r - s o l i d and pH of liquid phase for each mixture f o r each calcium s u l f a t e are shown in Fig. 2. In gypsum, the amount calcium s u l f a t e - w a t e r suspension of S042- dissolved into pure water reached maximum value of 1.63 S042g/l immediately a f t e r mixing. In hemihydrate, i t was three times as large as that of gypsum but the amount of S042- in l i q u i d was decreased by the p r e c i p i t a t i o n of secondary gypsum. In a n h y d r i t e , i t was about four f i f t h s as large as t h a t of gypsum and the amount of S042- in l i q u i d increased with time. Amounts of S042- from dissolved calcium s u l f a t e was rised in a l k a l i s o l u t i o n such as Na2CO3 and i t was lowered in the Ca(OH)2 saturated s o l u t i o n . The pH value at 20°C of 4 g/l water s o l u t i o n of a n h y d r i t e , hemihydrate and gypsum was 10.2, 7.2 and 6.6, r e s p e c t i v e l y . Preparation of cement J
0
1
[
,
1
,
I
l
I
I
L
L
J
l
I
Cements were prepared from c l i n k e r W, A and P by adding natural gypsum hemihydrate and anhydrite u n t i l t o t a l SO~ in cement attained to 1.9%. Each mixture wa~ interground and adjusted u n t l l Blaine s p e c i f i c surface area reached 3200:100cmL/g.
Vol. 14, No. 5
649 GYPSUM, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE
EXPERIMENT Preparation of hydrated sample Each cement was hydrated at IO°C, 20cC and 30cC with the water cement ratio of 0.3. After determined curing time, hydration was stopped by dispersing the sample in acetone. Hydrated sample was dried by two methods, that is, D-drying and drying under CO2 free air of which relative humidity is 15% (RH 15% drying).
Determination of ionic concentration in l i q u i d phase Liquid phase of suspension (W/C=4.0) was obtained b% the f i l t e r a t i o n a f t e r determined curing time and the concentration of Caz+, Na+, K+, OH- and S042- in l i q u i d phase was measured. Measurement of heat evolution in hydration Heat evolution of each cement paste was measured by conduction calorimetry at I0°C, 20~C and 30°C with the water cement r a t i o of 0.4. Quantitative analysis of Ca(OH)2 and e t t r i n g i t e The amount of Ca(OH)2 and e t t r i n g i t e in the hydrated sample dried in a i r of RH 15% was determined by modified TG-DSC method (10). Measurement of specific surface area and observation of morphology of hydrates Specific surface area of D-dryed hydrated sample was measured by BET method. Microstructure of hydrated sample was observed by scanning electron microscopy. Measurement of settin 9 time Setting time of cement was measured under JIS R5201. Flow curve measurement with rotational viscometer Each cement was mixed with water at W/C=O.3 for 210 seconds by hand. Flow curve of the paste was obtained by coaxial rotational viscometer with double cylinders RV 12 (HAAKE Co., Ltd.) using the sensor system of MVIP(11). Paste was dispersed homogeneously on the surface of sensor system by rotating the rotor at 512 rpm for 30 seconds. The measurement was continued u n t i l noize caused by the setting of paste was observed. RESULT AND DISCUSSION Early hydration process Time dependency of ionic concentration and Ca(OH)2 and CaSO4 saturation ratio of l i q u i d phase Fig. 3 shows the time dependency of concentration of ions in l i q u i d phase of cement-water suspension. Concentration of CaL+, Na+, K÷ and OH- showed high level in poorly burnt clinker which contained much free CaO and alkali sulfate as shown in Fig. 3 (a)(d)(e). CaL+ and S042- concentration was remarkably changed by the kind of calcium sulfate added with time but this change of OHconcentration was not so large. This result coincided with the tendency shown in Fig. 2. Fig. 4 shows the time dependency of Ca(OH)2 and CaSO4 saturation ratio calculated from concentration of each ion after Fujii and Kondo (12)(13). Ca(OH)2 saturation ratio increased rapidly and reached the peak at an early age in cement from poorly burnt clinker. Influence of the kind of calcium sulfate was not so clear except for e a r l i e r appearence of peak in cements
650
Vol. 14, ~,o. 5 F: Lichikawa, et al.
containing hemihydrate, which is deduced to r e l a t e to the increase of Ca2+ i o n i c concentration. CaS04 s a t u r a t i o n r a t i o was large in the order of a n h y d r i t e , gypsum and hemihydrate added cement. I n i t i a l CaS04 s a t u r a t i o n r a t i o was l a r g e s t when
10°C
20°C
30 C
A 8o
[ ~//F
r
II
(Ca~';'~O'-I 2
1
..
•
_~'"
§2o v --
t .... 0 0
I .... 2
40
2
I .... 40
2
. 4 n
Ti,'r~ ,ih~. : 0
2
40
2
40
2
40
2
4C
2
4~
Time ( h r . ) W-g: c l i n k e r W - gypsum W-h: c l i n k e r W - hemihydrate W-a: c l i n k e r W - anhydrite
A-g: c l i n k e r A - gypsum P-g: c l i n k e r P - gypsum
Fig. 3 Change of ionic concentration in liquid phase of cementwater suspension
[CaE+l "[ OH-J7
I g
.ia
I •
•
(CaE+~'IS04 E'! J ":
I i:!:i ,
•
~ j ~
Ag!~g i
Fig. 4 Change of [Ca2+].[OH-] 2 and [Ca2+].[S042-] in l i q u i d phase of cement-water suspension ( s a t u r a t i o n level=1.0)
hemihydrate was used but i t was decreased r a p i d l y by the p r e c i p i t a t i o n of secondary gypsum. CaS04 s a t u r a t i o n r a t i o was decreased in the cement from poorly burnt c l i n k e r and the d i f f e r e n c e among three calcium s u l f a t e s was small. Much soluble a l k a l i s u l f a t e s in poorly burned c l i n k e r are considered to be responsible to the decrease of CaSO4 s a t u r a t i o n r a t i o . At high curing temperature, Ca(0H) 2 s a t u r a t i o n r a t i o was lowered and peak appeared e a r l i e r , while CaS04 s a t u r a t i o n r a t i o rised. The e f f e c t of the kind of calcium s u l f a t e and burning degree of c l i n k e r on both Ca(OH)2 and CaSO4 s a t u r a t i o n r a t i o was unchanged with temperature. Heat e v o l u t i o n rate Heat e v o l u t i o n curves of each cement at various curing temperature are shown in Fig. 5. The p o s i t i o n and height of the second peak which corresponded to hydration of a l i t e were remarkably influenced by the burning degree of c l i n k e r . The second peak appeared e a r l i e r in the cement from poorly burnt c l i n k e r . The i n f l u e n c e of the kind of added calcium s u l f a t e on the p o s i t i o n of second peak was small but i t appeared e a r l i e r when hemihydrate was added. The p o s i t i o n of second peak was c l o s e l y related to the peak p o s i t i o n of Ca(0H) 2 saturation ratio. This r e s u l t i n d i c a t e s the v i v i d hydration of a l i t e a f t e r i n d u c t i o n period begins when Ca(OH)2 s a t u r a t i o n r a t i o a t t a i n s to maximum value. The period of v i v i d hydration of a l i t e is accelerated in cement manufactured by the i n t e r g r i n d i n g of c l i n k e r , gypsum and lime (14). Therefore, i t is considered t h a t v i v i d hydration of a l i t e is s t r o n g l y c o n t r o l l e d by Ca(OH)2 satur a t i o n r a t i o of l i q u i d phase r a t h e r than the d i f f e r e n c e of hydraulic r e a c t i v i t y of a l i t e mainly depended on c r y s t a l s t r u c t u r e and minor c o n s t i t u e n t s .
Vol. 14, No. 5
651
GYPSUI~, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE The amount of hydration products and time dependency of BET specific surface area of each cement paste E t t r i n g i t e , Ca(OH)2 and C-S-H were main hydration products during i n i t i a l few hours. F~g. 6 shows the change of the amount of e t t r i n g i t e and Ca(OH)2 formed and the change of BET specific surface area of paste with
I0~C w
8, 6-
4. 3-
30"C
20:C T
|
W -
. .
2.
I
4. I 3.
i
4 i
4
W
1
W
•
A
-P I
/
3
3
-
2
-
u~ 8£
'
"
-
'4
3,~
-
.
3 ~3
2.i ~ .
i
a
i
I
0
calcium i
0
I
2
10
20
;
2
;0
2F~
2
I;
2;
T~me ( h r . ) • gypsum
• hemihydrate
i
i
i
~
.
0~0 1 2 3 0 1 2 3 0 ~ ~ 3 4 Ti~ (hr.) • gypsum • hemihydrate •anhydrite
• annydr;te
Fig. 6 Change of amount of hydrates formed and BET s p e c i f i c surface area of paste
Fig. 5 Heat evolution curves of each cement at different curing temperature (same notation as in Fig. 3)
W,'S=I.0
p•n•e20-C,
sample s~ze; 11.67g 120- 3 ~ i ~ "time. The influence of kind of calcium 80(I) Inters~tla~ sulfate on the amount of e t t r i n g i t e formed was changed with burning degree 40of clinker. The amount of e t t r i n g i t e formed is considered to be influenced by o: 0 I l Ca(OH)2 and CaSO4 saturation ratio in 80(2) Interst}tlal phase liquid-phase as well as hydraulic CaSOa.2H20 60r e a c t i v i t y of i n t e r s t i t i a l phase i t s e l f . ~ w - w ~ (~IA'F:O,5,~: S03) Heat evolution curves of inter40s t i t i a l phase of each clinker separated by s a l i c y l i c acid-methanol method are 20shown in Fig. 7. As f e r r i t e phase had ! l i t t l e compositional and structural 0 0 5 10 15 difference with the difference of burning Time ( h r . ) degree, hydraulic r e a c t i v i t y of inter• cllnker W • clinker A Pcllnker P s t i t i a l phase seemed to depend mainly on the quantity, crystal structure and Fig. 7 Heat evolution curves of minor constituents of CsA solid solution. i n t e r s t i t i a l phase Clinker P has i n t e r s t i t i a l phase of the highest r e a c t i v i t y . I n t e r s t i t i a l phase of clinker W is more reactive than that of clinker A from the data in Fig. 7 The difference of hydraulic r e a c t i v i t y of C3A solid solution in each E
652
Vol. ia, '~o. 5 F. -:ci~ikav.a, et al.
c l i n k e r could be explained by the character of C3A such as difference of m o d i f i c a t i o n of C3A as reported by Regourd (15) and the amount of K20 as impurity of C3A s o l i d s o l u t i o n ( I ) . The amount of e t t r i n g i t e formed in the cement paste from c l i n k e r P was small in spite of highest r e a c t i v i t y of i n t e r s t i t i a l phase. High Ca(OH)2 s a t u r a t i o n r a t i o in l i q u i d phase under the presence of calcium s u l f a t e depressed the hydration of i n t e r s t i t i a l phase. In the cement from well burnt c l i n k e r , amount of e t t r i n g i t e formed in the e a r l y hydration was large in the order of hemihydrate, gypsum and annydrite added cement corresponding to CaSO4 s a t u r a t i o n r a t i o in l i q u i d phase. This difference became small or the trend turned opposite in cements from c l i n k e r A and P. Depressed d i s s o l u t i o n of calcium s u l f a t e , p r e c i p i t a t i o n of small e t t r i n g i t e and the formation of dense layer of e t t r i n g i t e on the surface of unhydrated grain in high Ca(OH)2 satur a t i o n r a t i o in the l i q u i d phase might be one of the reasons of the abovementioned phenomenon observed in the cements from c l i n k e r A and P. This r e s u l t suggests that the amount of e t t r i n g i t e formed was influenced by Ca(OH)2 satur a t i o n r a t i o in l i q u i d phase which has close r e l a t i o n to free CaO in c l i n k e r and CaSO4 s a t u r a t i o n r a t i o in l i q u i d phase which is affected by the kind of added calcium s u l f a t e r a t h e r than hydraulic r e a c t i v i t y of i n t e r s t i t i a l phase i t s e l f . The amount of existed Ca(OH)2, that is the d i f f e r e n c e between sum of formed Ca(OH)2 by the hydration of calcium s i l i c a t e s and free lime and consumed Ca(OH) 2, measured by TG-DSC method was ranged from 0.3 to 1.1% a f t e r 4 hour hydration. Therefore, the amount of existed Ca(OH)2 is not always represented the rate of hydration of a l i t e in cement. On the c o n t r a r y , the change of BET s p e c i f i c surface area with time shown in Fig. 6 corresponds to the rate of hydration of a l i t e at the i n i t i a l stage (16). Increase in BET s p e c i f i c surface area of cement from c l i n k e r P at an e a r l i e r age showed good correspondence to the second peak p o s i t i o n in heat e v o l u t i o n curve. Morphology of hydrate Scanning electron micrographs of hydrated cement paste are shown in F i g . 8 . E t t r i n g i t e formed p a r t l y on the surface of cement p a r t i c l e s and i t remained almost same size. Morphology of e t t r i n g i t e became short prismatic at high Ca(OH)2 s a t u r a t i o n r a t i o and became small i r r e g u l a r rod and equidimentional shape at high CaS04 s a t u r a t i o n r a t i o . This e f f e c t was much more remarkable in Ca(OH)2 than in CaS04 s a t u r a t i o n r a t i o . The morphology of e t t r i n g i t e formed did not change at the i n i t i a l stage w i t h i n 4 hours. Precipit a t i o n of large gypsum c r y s t a l could be observed in hemihydrate added cement paste. With the descending of burning degree of c l i n k e r , the size of p r e c i p i tated gypsum turned small due to the increase of Ca(OH)2 and the decrease of CaSO4 s a t u r a t i o n r a t i o . Small hexagonal plate l i k e Ca(OH)2 was observed in cement r i c h in free CaO. The reason why c l i n k e r P has a large BET s p e c i f i c surface area at I hour in s p i t e of less e t t r i n g i t e formation is considered that small Ca(OH)2 by the hydration of free CaO and small e t t r i n g i t e c r y s t a l are formed under high Ca(OH)2 s a t u r a t i o n r a t i o . In cement paste containing a n h y d r i t e , calcium aluminate hydrate and monosulfate hydrate could not be observed in the e a r l y hydration. A f t e r 2 hours, a c i c u l a r C-S-H p r e c i p i t a t e widely around cement p a r t i c l e s and i t s morphology was not changed by CaSO4 and Ca(OH)2 s a t u r a t i o n r a t i o . Properties of cement paste during e a r l y hydration Setting time I n i t i a l and f i n a l s e t t i n g time of cement at each curing temperature are shown in Fig. 9. Setting time was shortened with lowering of burning degree and with r i s i n g of curing temperature. The d i f f e r e n c e of s e t t i n g time with d i f f e r e n t kind of calcium s u l f a t e was recognized c l e a r l y in well burnt c l i n k e r
[
H~r,-.
.d,,
r,,-. z
I
I[
Clinker W - anhydrite
,
+
~
,
Clinker W - hemihydrate
Clinker W - gypsum
.
-.~
4
I ,;m
Clinker A - anhyd~ite
Clinker A - gypsum
Clinker A - hemihydrate
Fig. 8 Scanning el~ctron mic,'ograph c ~ hydrated cement (age 30 min.,a: 2~ C. cured ~C It,... temperature. The setting zit,- ~.~a~ ",÷ c,.-der of gyp'.-..'. , c . hydFat~ ano ar, hjd,-ite c o n t a i n i n § ceE+~:,- . ~ . ; long s.~e. S~_:tin; of cement paste is co,re.:gc~ceo to. the [."ocess of s t r , ' - . . : : formation whet. colloidal solution de,;ec.:~ gel properties a,;d i t is c . ~ e : ~.' the adhesiveness of water film aroun~ ce-:er,t and hydrate par+:.;le_- ~ ' : ,+.~ cohesive force between hydrates. Therefore. the in:t-ease of specific s,,:'~..E area and contact points of hydrates g,-owr, to needle !i~:e shape contribute.: to setting of cement paste. Generally, no,-mal setting of cement paste is brought by the hydration of a l i t e (17)(i~',. But Locher et a: (I': have r~?'.tL5 that normal setting occurs upDr the recrystallizatior, o~ ~it,!r,.*;t-'. ,-ath.:. than by the formation of new hydration p-oducts ( f a ] i t e . . , c , r v.~ . ti::~ As before mentione~, the second pea,. positic, r. c,f heat evol ..... curve and r i s i n g position of BET specific surface a~ea vs. ti~.-~ cu,-;.~ cc.i,-cidc with the i n i t i a l s e t t i r g time, therefore, setting, time is ce,'tair.ly ,'e]ateC~ closely to the beginrir, g of vivid hydra.tic: cf a~ite, The diffe,-ence of setting time by the kind of calcium su]'.'a -~_ :'.~v b~. caused D) the diffe,'e,ncE of amount and morphology of e t t r i n g i t ~ dE:;÷r~£J Q"+ rF~inly CaC0h)2 a~:d CaSD, saturation ratio i,; l i q u i d ph~.~e. In the cement fron, poorly bj.-n • Ll;ni~", ~'~, iC h)dratior, of a l i t ¢ a,formation of C-S-H having large specific s~,'fa-e area at the i n i t i a l stage n'u:n contribute to the setting time of ceme,:-, pa~:,.,, as the ~.,,,=~,~r+,. and sha:÷, of e t t r i n g i t e formed are small. Or. the c,tr, er ha,'c;, im the cement froF. well bu:-nt c l i n k e r , as e t t r i n g i t e formed has much a.~.2~rI ant large acicular shape, hydration of i n t e r s t i t i a l phase mDre cor','+but'.-.~ :c the setting time st tr,~the effect o¢ the k.nd of calc<...~ .:~ . . . . . . . . + ,
654
Vol. ,4, ?qo. 5 H. Cchikawa, et al.
!000
;
.
_w
6
.
k
500~ A P
~
'
:.
final
set
-
a
~ "~"
i
• g.Yps~m A A hglthydrate 0
_p
30
' 0
2
10 20
30
I0
20
30
10 20
Inhydrt te
O •
so
3
20 40
'
'
'
'
0 20 40 0 20 40 60 80 Time (min.)
~
"
120
•
'
160
ZOO
Fig. II The time dependency of y i e l d value of fresh cement paste (W/C:O.30, 20°C)
30
Temperature (:C) • gypsum •hemihydrate
cement from varlously burnt cllnker and ~psum
•anhydrite
Fig. 9 Setting time of each cement at different curing temperature
_ d
/!
initial setting level (ISL) b m
m
~
w
~ i
/
,s,
r
-
i I
/
final setting le~e~ ~ F ~ L ] _
L m su
~ ~,,,,,,=~,~L,f
•
I
-
I
inters~al phase
~
x11
initial set ~
|
I l
Oil W-g ¢)0 A-g
II I II I
initial set al set c ~ n t from well burnt clinker and different kind of calcium sulfate
I
L h
~/./i~'
I~ - -
-
~
~lll II
of a11~ _
I g~
II t II oo W-g I al W-h
~,~
i;
initial set ~ f i n a l
final set
set
Setting time
Fig. I0 Schematic explanation of relationship between index of hydration for each c l i n k e r mineral and setting time (same notation as in Fig. 3) Time dependency of the degree of hydration for each c l i n k e r mineral u n t i l setting time was schematically explained in Fig. 10. Setting of cement paste is expressed as the summed results of hydration of calcium s i l i c a t e and i n t e r s t i t i a l phase and s e t t i n g occurs when the index of hydration which includes the kind, size, morphology and amount of hydrates reaches a certain level. Change of the y i e l d value of cement paste with time The increase of y i e l d value shown in Fig. 11 during i n i t i d l two hours was mainly caused by c r y s t a l l i z a t i o n of gypsum from hem•hydrate and increase
Vol. 14, No. 5
655
GYPSUM, HEMIHYDRATE, ANHYDRITE, CLINKER HYDRATION, RATE of specific surface area by the formation oF e t ~ r i n g i t e . Vivid hydration of a l i t e was responsible at the most part a f t e r t h i s period. Generally, y i e l d value was increased more rapidly with poorly burnt c l i n k e r corresponding to i t s increase in specific surface area except for the cement containing hemihydrate. increase in y i e l d value of hemihydrate added c l i n k e r W t i l l one hour may be caused by the c r y s t a l l i z a t i o n of large crystal of gypsum by the hydration of hemihydrate. This result shows that influence of calcium sulfates on the f l u i d i t y of fresh cement paste at early stage is closely related to burning degree of c l i n k e r . CONCLUSION Following results were obtained by using the cements prepared from variously burnt clinkers with same k i l n and natural gypsum, B-hemihydrate and anhydrite ~ obtained by heating natural gypsum. I . Burning degree of c l i n k e r defined as the function of temperature and retention time at burning zone shows good correspondence to the amount of free CaO and l i t e r weight measured by conventional method, and the optical properties of c l i n k e r measured by microscopic observation. A l i t e in well burnt c l i n k e r belonged to M~ modification. In poorly burnt c l i n k e r , MI modification of a l i t e was recognized and the amount of impurities such as MgO, AI203 and Fe203 in a l i t e increased and birefringence of a l i t e lowered. The amount of water soluble Na20, K20 and SO3 was small in well burnt clinker. Orthorhombic C3A solid soluton containing much amount of Na20 and K20 was observed in rapidly cooled c l i n k e r . In the cement prepared from well burnt c l i n k e r and gypsum, the best 28-day compressive strength of mortar was obtained. 2. Ca(OH)? and CaSO4 saturation r a t i o in l i q u i d phase were more i n f l u e n t i a l factors on ~he early hydration process of a l i t e and i n t e r s t i t i a l phase than t h e i r hydraulic r e a c t i v i t y . 3. CaS04 saturation r a t i o in l i q u i d phase of cement-water suspension was i n i t i a l l y high in the order of anhydrite, gypsum and hemihydrate added cement from same c l i n k e r but i t decreased remarkably with time in hemihydrate added cement because of the p r e c i p i t a t i o n of gypsum. The difference was large in low Ca(OH)2 and small in case of high Ca(OH)2 saturation r a t i o . 4. Maximum value of Ca(OH)p saturation r a t i o in l i q u i d phase of cement-water suspension was attained quicRly in poorly burnt c l i n k e r and slowly in well burnt c l i n k e r regardless of the kind of added calcium sulfates. The difference was caused by the quantity of free CaO and water soluble a l k a l i sulfate and i t was reduced with the rise of curing temperature. 5. The amount of e t t r i n g i t e formed was roughly inversely proportional to the amount of Ca(OH)2 existed in paste and a l k a l i sulfate in cement, that i s , less in the cement from poorly burnt c l i n k e r and much in the cement from well burnt clinker. In case of low Ca(OH)2 saturation r a t i o , the amount of e t t r i n g i t e formed was increased with the decrease of CaS04 saturation r a t i o . But the influence of CaSO4 saturation r a t i o on the amount of e t t r i n g i t e formed was reduced in high Ca(OH)2 saturation r a t i o . The morphology of e t t r i n g i t e formed in high Ca(OH)2 saturation r a t i o became short and prismatic. Small i r r e g u l a r rod and equ~dimentional shaped e t t r i n g i t e was formed in high CaSO4 saturation r a t i o . Acicular C-S-H precipitated around the cement p a r t i c l e a f t e r 2 hours but i t s morphology was not changed by Ca(OH)2 and CaSO4 saturation r a t i o . 6. S t i f f e n i n g of paste w i t h i n 2 hours at 20°C is mainly caused by the c r y s t a l l i z a t i o n of gypsum from hemihydrate (so-called plaster set) and extraordinary increase of specific surface area of e t t r i n g i t e . The former occurs in case of cement from well burnt c l i n k e r and hemihydrate, the l a t t e r occurs in case of cement from poorly burnt c l i n k e r and anhydrite or gypsum.
656
Vol. 14, No. 5 H. Uchikawa, et al.
I t is recognizable q u a n t i t a t i v e l y by the yield value of paste measured by viscometry. 7. Normal setting time is closely related to the period of the i n i t i a t i o n of the v i v i d hydration of a l i t e which corresponds to the maximum value of Ca(OH)2 saturation r a t i o in l i q u i d phase of cement-water suspension and is easily observable by the peak of heat evolution curve in conduction calorimetry and the increasing point of BET specific surface area. 8. The difference of setting time with kind of calcium sulfate was recognized c l e a r l y in well burnt c l i n k e r cured at low temperature. The phenomenon was caused mainly by the difference of amount and morphology of e t t r i n g i t e formed. REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9. I0. II. 12. 13. 14. 15. 16. 17. 18.
F.W. Locher, W. Richartz and S. Sprung, Zement-Kalk-Gips 2_99, 435-442 (1976); 3__33, 271-277 (1980);35, 669-676 (1982). L. Odler and R. Wonneman, 7th International Congress on the Chemistry of Cement (Paris), IV, 510-513 (1980). J.P. Skalny and J.P. Young, 7th International Congress on the Chemistry of Cement (Paris), ~, II I / 3 - I / 4 5 (1980). Y. Ono, 7th International Congress on the Chemistry of Cement (Paris) LI, 1206-211 (1980). S. Takashima and F. Amano, Sement G i j i t s u Nenpo, 13, 50-54 (1959). S. Sato, Y. Tamura, K. Takahashi and H. Muto, Semento G i j i t s u Nenpo, 24, 24-26 (1970). E. Woermann, Th. Hahn and W. Eysel, Amer. Ceram. Soc., Bull. 44, 299 (1965). G. Yamaguchi and H. Miyabe, J. Amer. Ceram. Soc. 43, 219-224 ~ 9 6 0 ) . K.S. Han and F.P. Glasser, Cement and Concrete Research I0, 483-489 (1980). H. Uchikawa, S. Uchida and Y. Mihara, Sement G i j i t s u Nen~ 3_44, 58-66 (1980). H. Uchikawa, K. Ogawa and S. Uchida, Proc. Ann. Mtg. of Materials Research Society, r14, 4, Boston (1982). W. Kondo and K. F u j i i , J. Cer. Assoc. of Japan, 82(6), 333-336 (1974). K. F u j i i , Proc. Cement and Concrete Seminar ( P r i ~ t e meeting). H. Uchikawa, S. Uchida and K. Ogawa, in preparation. M. Regourd, i l Cemento, 75, 323-336 (1978). R. Kondo, 5th International Symposium on the Chemistry of Cement (Tokyo), I I , 203-248 (1968). J. Gebauer, Zement-Kalk-Gips, 3__II, 302-304 (1978). L.D. Adams, Cement and Concrete Research 6, 293-307 (1976).