Hydration products of calcium aluminoferrite in the presence of gypsum

CEMENT and CONCRETE RESEARCH. Vol. 24, pp. 150-158, 1994. Printed in the USA. 0008-8846/94. $6.00+00. Copyright © 1993 Pergamon Press Ltd.

H Y D R A T I O N P R O D U C T S O F CAIA2IUM A L U M I N O F E R R I T E IN T H E P R E S E N C E OF GYPSUM Tong Liang and Yang Nanru Dtrpartment of Silicate Engineering Nanjing Institute of Chemical Technology, Nanjing 210009, China (Refereed) (Received Oct. 28, 1992; in f'mal form Sept. 10, 1993)

ABSTRACT Hydration products of C6AzF, C4AF and C6AF2 in the presence of gypsum were studied by DTA, XRD, EDAX and IR techniques. An iron-rich phase, containing tittle calcimn, was found in their hydrates. DTA proved to bc an effeclivc method to detect this phase if it was enriched. Good linear relationships wcrc obtained between optical densities and Fo/(Fe+AI) ratios in AFm phases when infi,ared absorption bands between 1200-960 cm -I were fitted by Gaussian-line-shal~ era'yes. The correlations suggested that the intensity of the absorption of v3-SO42- could quantify the amount of Fe(]II) in AFm phases. A possible explanation of this rcsuR was tentatively proposed as well. INTRODUCTION The investigation of the product and the count of the reaction are the main points in the study of mechanism of cement hydration. It is well known that calcium aluminoferrite involves a series of solid solutions (CeAxFI. x with 0
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from 0 to 1 by different authors [7]. Although Kuzel [8] ostimatcd the possibility of solid solutions between C4ASH12 and CaFSHI2 by XRD study, the relationships between Fe/Fe+Ai ratios in AFm phases and in anhydrous ferrite phase and that in hydrates are not clearly established. The present paper investigated the hydration products of the t~rite phase in the presence of gypsum using XRD, DTA, IR and EDAX techniques, and attempted to correlate Fe/(Fe+AI) ratios in AFm phases and in calcium aluminoferritc. MATERIALS CtA2F, C4AF and CtAF 2 were synthesized from chemicals CaCO~, AI203 and Fe203. The stoiehiometric mixtures were pressed and burned at 1320°C for 4 hours. The products involved no other minerals as checked by XRD. In all samples, the ¢ontents of fire. lime were less than 0.2%. The burning would be repeated until pure calcium aluminoferrite was obtained. The prepared calcium aluminoferrite was mixed with 15% gypsum and CO2-fre¢ water with w/c--0.35 respectively. The hydration was carded out at 20°C for 0.3, 1, 3, 7 and 28 days in sealed plastic containers, and the reaction was stopped by acetone at the appointed period for later analysis. RESULTS AND DISCUSSIONS Evidence o f Fe(Otl)~ =el existence

The hydration courses of CoAzF, C4AF and C+AF2 in the presence of gypsum were followed by X-ray diffraction analysis, differential thermal analysis and by observing under optical microscope in water-sealed thin sections. There were some similarities to the literature [9-11]. From XRD and DTA results, the first hydration product was AFt phases. A little before gypsum was consumed, AFt phases began to convert into AFro phases. After 28 days' hydration, the products were AFro and C2(A,F)H8 or C4(A,F)H13. Amorphous hydration product seemed to be FH 3 gel (274-293°(2) checked by DTA and its amount increased when hydration proceeded. A typical DTA curve was shown in Fig. 3(c). The hydration process seemed to have little difference between CtAzF , C+AF and CtAF2 except for CtAF 2 hydrating faster.

Figure 1 Mierograph of the small isolropic particales in water-sealed thin seotion

Figure 2 Micrograph of the same isotropic particles in the hydrated paste

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However, during observation in the miorosoope, an interesting phenomena aroused our attention. Little amounts of isotropic particles, about several microns in size, appeared soon after the hydration began, and then reached the largest amount ff AFt phases converted into AFm phases after gypsum were consumed. Their amount seemed not to change in the later hydration (Fig 1). When XRD showed the main hydration product was AFro phases, the hydrated samples of CsA2F, C4AF and C6AF2 were crushed into small pieces and some water added, brown-red suspended solutiom could bc available. The suspensions were then observed under a microscope. The same small particles were found (Fig.2). After separating the solid from the suspensions and dried in 60oc for 24 hours, one could get a brown- red powder. The DTA curve of the powder (Fig.3) showed that, beside the endotherm produced by AFm (182-200°C), AFt (105-143oc),

fJ

C2(A,F)I-Is or C4(A,F)H13 (213°C) and AH~ (290°C),ther¢ was an ex_othermic effect at 360°C. This is a oharaoterisfic of Fo(OH)3 gel prepared by different methods [11], and no other possible hydrates in the system have this effect. The powder was also studied by SEM and the small partioles observed under optical microscope were also be found. Analyzed by EDAX, the particles were confirmed as an iron-rich phase (Fig.3).

The above results confirmed the existence of the ferrihydrite in calcium aluminoferdte hydration in the presence of gypsum. The t~ ferrihydritc had the globe shape with the composition rich in iron, a little amount of calcium and a trace of aluminum and could not Ca be detected by XRD. DTA proved to be a good detective method when the ferrihydrite was en18.80 riched. The s'anilar thermal behavior and extremely low solubility in water [12] suggested Figure 3 that there were some shnilarity to Fo(OH)3 gel. (a) SEM miorograph of the ion-rich hydrate The fact that it contained a little oaloium also 0a) EDAX of the ion-rich hydrate proved the assmnption made by Brown [7], who (c) (1) A typical DTA ¢urve of the hydrated calculated the mass equation of the hydration paste process. That the ferr~drite deposited mainly (2) DTA curve of the brown-red powder when AFt phase converted into AFm phases seemed that the Fe/(Fe+A1) ratio was higher in AFt than in AFm phases. The further EDAX study proved this assmnption (Table. 1).

FeOIl) in AFm phases Butide Fc(OH)3 gel, AFm phase was the other stable hydration produot of calcium aluminoferrite in the presence of 15% gypsum. To establish a clear relationship between crystal structure of AFro phases and Fe,/(Fe+AI) in AFm phases or that in C2AxF1.x series, more detailed XRD and IR studies on AFro phases were carried out. Under the same instrumental conditions, XRD data of hydrated samples were colleoted by X-ray ditfiactometer (D-MAX r-B). Using the same index and twenty diffraction lines, crystal

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Tabl¢.l F¢/(Fo+AI) of AFt and AFm phases and ao and oo of AFm crystals 0

1

2

3

0 0 0.5812 2.6836

0.2041 0.0884 0.5910 2.6834

0.2356 0.1148 0.5962 2.6838

0.2523 0.1185 0.5997 2.6839

Sample No. AFt AFm a~(nm) ca(m)

Fe/(F¢+ AI) AFm No. 0:

C12AT+20%CSH2hydra~dfor7dayswithw/c=l

No. 1-3: C6A2F, C4AF and C6AF2 added 15% C§H2 hydrated for 28 days with w/c=0.3 parameters of AFt and AFm phases could be calculated by the method of the least-squares. Fc/(Fe+AI) ratios were the mean values of ten different AFt or AFro cts~ab calculated from EDAX. The results were listed in Tablel. It seemed that co had a very slight chang© with the

6.00-

tO l ll

5.95 ¢

i

l t I f #

g

t

5.90

I ¢ I t" t

il

/ t

5.~

t / /

I

t

I /t

5.~

I

i

i

I

0.024 0.048 0.672 0.096 0.12 Fe,"Fe+AI

Figure 4 correlation between ao and Fe/(Fe+AI) in AFm phases

~2oo

~ooo

aoo

6o0

400

2oo

,~E ,[mER (c=-]) Figure 5 Infrared spcctraof AFro phases A F r o (0): C12A7+20°~ C S H 2 hydrated for 7 days with w/c=1 AFro(I)-(3): C~A2F,C4AF and C6AF2 added 15% CSH2 hydrated for 28 days with W/C=0.3

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Table 2 The results oflR absorption bands fired by Gaussian-line-shap curves Peak NO.

Minerels

v3 (cm -I)

(I)

AFm(O) ~'m(1)

1167.0 1158.o 1156.8 1157.0 1114.0 1111.0 1107.5 1106.0 1022.O 1029.0 1032.0

~m(2) ,,tFm(3) AFm(O) AFm(1) AFm(2) AFm(3)

(2)

A~m(O) Arm(l) (3)

AFm(2) AFm(3)

50

H

(~)

sw (=m -1)

11.75 17,oo 19.25 22.20 30.25 26.95 25.15 19.80 6.50 12.85 21.75 22.70

1033.0

44.0 62.0 67.0 70.0 66.0 57.6 58.0 62.0 31.O 83.0 BS.O 94.0

50

AFro (0) INE

4O

SS

ig SS

2.74

55O 1122 1373 , 1654

3.05 3.14 3.22 3.33 3.22

i 2125 1652 1553 I 1307

3.19

3.12 2.33

214 1135 2037

3.51

2271

3.36

3.o6

AFm (I)

4O A

z O

3o

3O

nO

N 2o <

10

10 0

I

I

I

.3

12 11 10 --9 13 WAVE NUMBER xlO0(cm 1)

50

I

I

I

12

11

10

9

WAVE NUMBER x100(cmt)

50

AFm (2)

AFM (3)

,.~,40

40 ~4

v

Z

z o

30

0 DO

20 10

10 0

1.3

I

I

I

12

11

10

9

WAVE NUMBER xlOO(cm"1) Figure 6

.3

I

I

I

12

11

10

9

WAVE NUMBER xl00(¢m t )

Absorbance selected from spectrograms and the assumed baseline ( . . . s e l ~ t e d points)

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amount of Fe(Iff) in AFro phases. However, there were some correlations, not very good linearly, between ao and Fe/(Fe+AI) in AFro phases (Fig.4). It was suggested that Fe(IR) was incorporated in the AFm structure. The infrared spectra of the hydrated samples, having dried at 60°C for 24 hours, were recorded on a Perckin-Elmcr 983 spectrometer. The specimens were prepared by KBr pellet. Infrared spectra are shown in Fig. 5. Because of the complexity of H20 forms in hydrates, there was a strong absorption between 3700 cm "1 and 3000 cm "1. The band at 3630 cm"I was due to OH" vibration. The evidence of the stretching vibration of v-HzO at 3420 om"1 moving to 3460 cm "1 showed that AFt phases had converted to AFro phases [ 14]. This observation agreed with the XRD results.

40-

40

AFro (0)

~ 50-

3O

!'i,1

o_

z

~ 20tT-

~I0-

/ O~____J+

900

,..%

~.......

40 ¸ _ _

,.,j 21y1 /3\,. ,,.

,l~,.

1000 1100 1200 1300

900

WAVE NUMBER ( cm "1 )

1000 1100 1200 1300 WAVE NUMBER ( cm'l )

40

AFm (2)

3O

AFm (3)

30

z

20, tr"

°i

20

~ 10

10o 1000 1100 1200 1.300

ol 9o~

WAVE NUMBER ( cm-I )

Figure 7

(I)

AFm

1000 1100 1200 1300 WAVE NUMBER ( cm'l )

Computer caloulated infrared spectra of AFm phases by curve fitting tochniqu¢ Calculated

.......

Observed

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If Fe(ifl) in AFm phases mainly replaced tho AI ion sites, both F¢ and AI ions were in octahodral sites. However, the characteristic absorption changed greatly in different crystal structures, and littlo IR data wore obtained of AFm phases containing Fc(III).Thcrefore, tho following assignment of the bands wore only a tontative explanation. 500-600 cm-land 280-360 cm "] wore the mixed vibration modes of [AIO6] and [FeO6] octahedral. The bands became wide and weak when AFm phases contain more Fe(RI).Thc highly splitted bands showed Fo(m) had inoorporated in the AFm phases structuro. Tho bands at 472 om" and 780 cm "1 would bo assigned for the a b s o ~ l i o n o f [FoO6] and [A10+] octahedral respectively. Their changc in strength correlated with the amount of Fc and AI atoms. The band at 420 cm -I could be the Ca-O vibrational absorption. The bands between 960-1200 cm -1 wcr¢ due to v3-SO4 2- absorption. Tho intensity increased with the amount of Fc(]]]) in AFm phases and the wave number had a slight shift to the higher frequencies. In order to quantify the I R data. curve fitting techniques were dcvisod to decompose the high ovor-lapped bands between 1200 ¢m-1. Readings of absorbance on the spectrogram were 3.4

3.5

R--0.992 .J'""

3.2 69

,,-.1

3.25

• ..,

3¸

~

.J"

¸ --

I

0.58

3.5

3.4:

0.59 a o (nm)

0.6

.... ..°.....--

0

0.59

0.6

o.-.'" •

3

R=0.937

..... ._...~. -..

3

t

0

0.03

PEAK (2) I I 0.06 0.09 Fe/(Fe+AI)

0.

R=0.999

q

...J'"~

. .f""

~a

y..."

. ..,-"

...,'"

0.12

3.5 ¸

..y

F~--=0.980

•,~ 2.5

I

0,06 0.09 FeI(Fo+AI)

3.1

PEAK (2)

/..

I

0.03

._~ 3 . 2

...... .e -'-,...,..,.

ao (nm) ¸

J

3.3: ""-t-... .

,-~ 3.23 0.58

PEAK (1)

3.4-

-,-...,.

3.1

2.5

3.5

R=0.983

3.3-

3.5

.......... ....--""

2.75PEAK (1)

(,D

..... if. ..''''~qi'

3.

.y

"~2.8 2.6

¸

..r ,..'"

,y"

-~2.5

/"

/''t

2

0.58

PEAK (3) I

I

0.59 a o (nm)

0.6

0

PEAK (3) I

I

0.03 0.06 0.09 0.12

Fe/(RH-AI)

Figure 8 Correlation betwocn intc~itie.s of the infTarvd absorption bands anda o , Fe/(Fo+AI) of AFro phases

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corrected for baseline (Fig. 6). Based on the three normal modes of V3-8042", i.e., using threepeak fitfin~ th© curves were fired by Gausian-line-shaped ourvcs. The best fitting curves are shown in Fig, 7, and the parameters [Frequenoy v3 (om-l), half-width HW (ore'l), height of peaks H (%), and area of the peaks SS and lg SS] are listed in Table 2. Relationships between lg SS and ao, lg SS and Fe(Fe+AI) in AFm phases detected by EDAX, are plotted in Fig.8.

"

"""

"~

"

"" "';"

.'"

"" -7",

(s)

', i'i ,,I

H/ ii

....

O OH /~

• cB

• A1

a possible site which SO 2could occup/{

(b)

Figure 9 (a) Schematic normal modes of v~-S04-2 (b) Crystal structure of AFm phase ( only half of a ceil)

Both a o and Fe/(Fe+AI) in AFro had an very good linear correlation with the intensities 0g SS) of the three peaks. The intensities of peak 1 and peak 3 were increased with ao and Fe/(Fe+AI) while the wave number (v3) of the highest point of peak 3 s h i f ~ to the higher frequencies. The position of peak 1 seemed to be insensitive to the amount of Fe(RI) in AFm. Peak 2, on the contrary, had decreased its intensity and the wave number (v3) with the increasing of a o and Fe/(Fe+A1) in AFro phases. From the structural point of views, the above results could be understood. The vibration of v3-SO4z- had three forms of normal modes [15] (Fig.9). Due to its Td symmetry , the three forms of vibration are the same. However, when SO42- ions were incorporated into the interlayers of AFro crystals to balance the charge, they would interact with the unsymmetrical crystal field and cause the splitting of the triple degeneration. AFm phase had the layer structure derived from that of Ca(OH) z by the ordered replacement of one Ca 2+ ion in three by AP + ion [1,6](Fig.9). SO42- ions, which batanoed the charge, must be atWaoted by Ca2+ and AP+. Through polarization, in sulphate for example, the intensity and the wave number of v3-SO,2- could be influenced by cations which S O 4Z- conRoctod to. Tho higher the

eleotronegatha'ties

of

cations are, the greater the force constants and the dipole moments of S-O bonds. These effects finally resulted when the absorption bands (v3-SO42-) shiecA to the higher wave numbers and got more intensive absorption when SO+2- incorporated the cations of greater elec~oneg~ties.

Similarly when Fc ~+replaced some AP ÷ ions in AFm phases, the vibration of SO 42- must be influenced. Due to the greater electronegativity of Fe 3+ than AP +, Fe 3+ could affect the electron distribution and the force constant of the S-O bond in spite of relalively slight because of Ca 2. ions existing between them_ In crystal cells of AFn~ ions are unevenly distributed. Two extreme cases

of the ion-connecting mode could be considered. One is SO42-....Ca2+....Fc3+ connecting mode. i.e., Fc -~ ions were closed to SO, 24, for example, Fe 3÷ ions are in the site "a" in Fig. 9. Peak 3 mainly showed this kind of mode. With the F¢(BI) amount inoroasing in AFro phases, the intensity of peak 3 increased obviously and the absorption band s ~ slightly to the high frequencies. The other case is SO4Z...Ca2÷...AP+ connecting mode. Fe 3+ions are relatively far away from SO42- and do not show in the Fig. 9. Peak 2 seemed to exhibit this original (no Fe(flI) replacement) case and was slightly infhenoed by Fe(III) in AFm phases. As for peak 1, it probably suggested the transition form of the two extreme cases.

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L. TongandN. Yang

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The previous cxplmmtion showed that 1~ak 3 was sensitive to F¢(IH) contained in AFro phases. Based on the good linear ~rr¢lation betw~n Ig SS and F¢/(Fv+AI), one c~mld estimate the amount of Fe(III) in AFro phases by analyzing infrared spectra.

CONCLUSIONS 1. Fe(OH)3 gel was one of the hydration prodtmts of calcium aluminoferrite hydrated in the presence of gypsum, while the hydration also produced AFt, AFm, C2(A,F)H8 or C4(A,F)Ht3 and AI(OH)3 gel. 2. F~IlI) was inde.~d incorporated in AFro crystals. F¢/(Fc+AI) ratio in AFro phase in~rcascd with that in anhydrous calcium aluminoferrite. 3. The absorption band between 1200-960 cm-1 could quantify the amount of Fe(III) in AFro phases. REFERENCE [1] H.F.W.Taylor, Cement Chemistry, Academic Press Limited, London (1990) [2] F.D.Tam~ and Vertcs, Cement and Concrete Research, 3, 515 (1973) [3] K.S.Harchand, Visgwamit~ar and K.Chandra, ibit, 10, 243 (1980) [4] K.S.Harchand, R.Kumar and K.Chandra, ibit, 14, 170 (1984) [5] 1VLFukuhara, S.Goto and K.Asagc ct al, ibit, I_L1407 (1981) [6] J.M.Fortune, ibit, 13, 696 (1983) [7] P.W.Brown, J. Am. Ceramic Sot., 70, 493 (1987)

[8] H.-J.Kuz¢I, Zement-Kalk-Gips, 21, 493 (1968) [9] I.Jawed, S.Goto and R.Kondo, Cement and Concrete Research, _6, 441 (1976) [10] V.S.Ramachandran and J.J.Beaudoin, 7th International Congress on the Chemistry of Cement, Vol. I111-25 (1980) [11] M.Collepardi, S.Moss and G.Morioni, Cement and Concrete Research, _9, 431

(1979)

[12] Huang Boling, Handbook of Differential Thermal Analysis of Minerals. (in Chinese) (1997) [13] Tong Liang and Yang Nanru, Bulletin of the Chinese Ceramic Society 10(2), 34 (1990) [14] Yang Nanru, Testing Methods of Inotgatfic Nonmctalic Materials, (in Chinese) (1990) [15] E.G.Brame Jr and J.G.Graaselli, Infrared and Raman Spectroscopy, Part A Marcel Dekker, INC. New York (]976) [16] S.J.Ahmed and H.F.Taylor, Nature, 215, 622 (1967)