Hydration of cement paste and concrete from raw mix containing metallic particles

Pergamon

Cemmtand ConcreteResearch.Vol.24, No. 8, pp. 1549-1557.1994 Copyright© 1994ElsevierScienceLtd Printedin the USA. All rightsreserved 0008-8846/94 $6.00+00

0008-8846(94)00100-6

HYDRATION OF CEMENT PASTE AND CONCRETE FROM RAW MIX CONTAINING METALLIC PARTICLES

J.O. Odigure Federal University of Technology, Chemical Engineering Department P.M.B. 65, Minna, Niger State, Nigeria

(ReceivedFebruary(Refereed) 3; in finalformJuly22, 1994)

i

Abstract

A comparative analysis of the hydration kinetics of cement paste and mortar from raw mix containing f'mely dispersed metallic particles and of natural origin was perfo~,ned using the most ;:;ii~~::~: rational methods of investigation. These methods include the differential thermal, X-ray, IR-spectroscopy, chemical and electrochemical analyses. Results of the different analyses showed that the kinetics of chemical reaction in hardening cement mortars produced from raw mix containing metallic panicles differ from those of ordinary Portland cement of natural origin. The increased presence of Fe203 in the clinker minerals to a great extent negatively influenced their solubility, thus increasing the induction, setting and hardening periods. This research also to some extent revealed the effect of wearing of grinding balls and metallic lining surfaces of grinding mills (especially during preparation of raw mix), on the chemical-mechanicalproperties of cement of natural origin.

Introduction One of the main problems encountered during choice of cement for construction work is knowing the phase content of the hardened cement mortar and the hydrates formed. Identification and quantification of the hydrate phase, especially the calcium silicate hydrates, arc difficult to perform since they are poorly crystallized and in most cases in the amorphous statc.(l, 2) Quantitative analyses of cement mortar do not often reveal the exact amount of Ca(OH)2 produced during hydration, because of poor selectivity of the available method.O) X-ray analyses are hampered by the amorphous state of the hydrates and so no exact information can be derived.(4) Therefore the most rational methods of investigating the hydration properties of cement arc those involving differential thermal (DTA), X-ray, IR-spectroscopy, electrochemical and chemical analyses. This research is aimed at performing comparative analyses of the hydrating properties of cement paste and mortars from raw mix containing metallic particles and those of natural origin.

Experiment Experiments were conducted on cement samples produced using chalk, open-hearth slag, abrasive slurry, tripoli (sand) and ordinary cement raw mix of industrial origin. Raw mix was

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Vol. 24, No. 8

thoroughly mixed, ground in a vibromill, granulated at a moisture content of 30% and burnt at 1400." C, with a holding time of 30 min. in an electric furnace using silicon carbide heaters. At the maximum temperature the clinkers were removed from the furnace and allowed to cool to ambient temperature and ground in the vibromill. The chemical constituents of the raw materials and the cement raw mix compositions are presented in Tables 1 and 2. TABLE 1 Chemical compositions of raw materials Materials Chalk

Loss on Ignition 39.9

Open-hearth slag Abrasive slurry Tripoli

5.6

SiO2

A1203

Fe

Fe203

7.7

1.1

0.6

49.6

0.4

37.2

11.1

14.6

26.7

2.3

3.6

9.3

3.1

27.0

0.8

0.1

1.8

0.7

76.7

6.6

6.6

1.2

54.0

4.3

FeO

CaO MgO C r 2 0 3

6.7

2.8

MnO

TABLE 2 Composition of raw mix No.

Chalk

Tripoli

Open-hearth slag

1

80.33

9.00

7.33

2

81.00

9.00

6.67

3

72.00

Abrasive slurry

Abrasive slurry burnt at 600o C

Clay

Iron pyrite

3.34 3.33 26.00

74.30

8.40

6.30

5

80.00

9.00

8.00

3.00

5

79.53

9.00

7.80

3.67

7

82.00

13.00

2.00 11.10

5.0

To investigate the hydration mechanism of the produced cement at the early stage, the electrochemical(5) and chemical analyses (6) of pastes were used. The electroconductivities of cement pastes N 1 to 4 (Table 2) with and without gypsum at a water/cement ratio of 0.35 were measured using kiloohmeter L 6-5 (manuracture calibration error 0.3 + 1%). The major problem encountered was the need to maintain effective contact between the electrodes and cement pastes, since with time, the effective contact was reduced due to the continuous rise in temperature and water evaporation. Investigation of the liquid phase chemical content of cement paste from sam01es N 1 to 4 using water/cement ration of 10, was performed using the method explained in Baev.(6)"

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HYDRATION KINETICS, METAL PARTICLES, MORTARS, CHARACTERIZATION

1551

7 "~ !

8

!

7

~ 6 0 0 ~.}

~5

,--I

.~t '..M .~t

• 4

I:~ e~

2 + 3~ g y p s u m [

HI

•

ill

.

100

200

Time

mln

o

FIG. 1 Specific electroconductivity of cement paste versus time relationship

::¸:¸:¸:¸:¸:¸:¸:¸:¸:¸:¸:¸:

TABLE 3 Kinetics of Chemical reactions in hydrating cement paste Hydrating time, hr.

Ca2+ content in liquid phas~ of samples, mg -/m3

2

75.9

36.1

58.2

29.0

8

75.4

32.2

49.1

27.0

12

60.3

35.1

40.1

47.0

16

56.0

34.0

20.0

24.0

24

23.0

27.'0

17.0

21.0

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The hydration mechanism of the cement paste after 3, 7, 90 and 180 days was investigated using IR-spectroscopy, X-ray diffraction and differential thermal analyses. Weight loss of hydrated cement mortars was calculated using the TG curves up to 1000°C. Results and Discussion

Figure 1 showed the specific electroconductivity (x) versus time relationship of cement pastes with and without gypsum. For cement samples N 1 and 3 (Table 2), the specific electroconductivity fell in the first 5 to 7 min., rapidly increased for the next 30 to 50 min. and then gradually decreased thereafter. In case of cement paste N 2 and those containing gypsum (3% by mass), the same phenomena were observed except that x has a reduced period of growth. This showed that these samples have poor electrolyte properties.

1 + 3% gypsum

+ 3% gypsum

Control

Sample

FIG. 2 IR absorption spectra of cement mortar after 3 days hydration

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HYDRATION KINETICS, METAL PARTICLES, MORTARS, CHARACTERIZATION

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On mixing, water molecules are adsorbed on clinker mineral surfaces. This increased the resistivity at the contact zone, hence the initial fall in x. This period is followed by that of chemical adsorption, dissolution of clinker minerals in the liquid medium, the hydration and hydrolysis of alite by water and the eventual release of Ca2+ and OH- to the medium. This explains the observed increase in x. In presence of gypsum in cement paste N2, the maximum x value was lower. For paste N2, the observed rapid fall in x could be associated with the low solubility of the clinker minerals, most especially those of alite present. This is reflected in the long induction period, prolonged setting time, beginning after 3 hrs. 30 min., unlike those of samples 1 and 3 with 1 hr 10 min. and 35 rain.

+ 3% gypsum

+ 3% gypsum

2 Control

FIG. 3 1R - Spectra of cement mortar after 7 days hydration

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respectively. Final setting times were 12 to 13 hrs. for sample N2, while for 1 and 3 they were 1 hr. 30 rain. and 60 min. respectively. From results of chemical analyses (Table 3), it can be said that abrasive slurry containing finely dispersed metallic particles, just like increased iron pyrite content, increased the Fe203 content in cement clinker minerals, changed both the solubility of cement in water and the kinetics of chemical reactions in hydrating cement paste. 1R - spectroscopy analyses results showed decrease in intensity of absorption bands for C3S (920, 522cm -1) after 3 days (Figure 2). The observed shift in absorption band from 920 to 970cm -1 could be linked to the presence of large quantities of Ca(OH) 2 and calcium silicate hydrates. In the presence of gypsum, the intensity of 520cm -1 was reduced and that of 644cm -1 broadened. These bands characterized the combined vibration of aluminoferrite and [SiO4]. After 7 days hydration, the absorption band of Ca(OH) 2 shifted to 985cm -1, signifying continuous changes in the morphology of calcium silicate minerals and their hydrates. The absorption band 641cm -1 was conspicuously absent in the paste containing gypsum. In all the pastes, the 849cm -1 absorption band characterizing belite was present (Figure 3). From the rate of disappearance of absorption bands 517,594, 650, 923cm -1, it can be said that clinkers containing abrasive slurry produced slow hardening cement. This could be attributed to the

o••/''•

~

~D cO

-.T

+ 3% gypsum OO

u% %O ~D

2

FIG. 4 1R -spectmofcementmortarafier90days hydration.

Control

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H Y D R A T I O KINETICS, N METAL PARTICLES,MORTARS, CHARACrERI7__,ATION

1555

presence of excessive Fe203 that enhanced the formation of slow hydrating C6AF 2 and calcium silicate minerals of predominantly belite. After 3 months the extent of hydration in all cement paste observed still differed considerably. (Figure 4) Identification of hydration products using X-ray analysis is quite difficult due to the combination or merging of diffraction peaks (especially with time), and the amorphous state of the hydrates. The extent of hydration of silicate components in cement paste and mortar was monitored by observing the changes in diffraction peaks' intensities of d = 0.277, 0.260, 0.176 rim, etc. and 0.274, 0.206, 0.205 nm characterizing the alite and belite minerals respectively or by increase in intensity of d = 0.489nm for Ca(OH)2 and calcium silicate hydrates. (Figure 5 and 6)

• O~ ~ ~

0 ~

0 c~ • 0

t'~.

~

~ •

2'B

~.

oo

~ ~ ~

r ~ ~

i[iiiiiiiiiiiiiiiii~iiiii::::r

180 days

~

-

~ ~ ~

~

~.~ ,~

:::::::::::::::::::::::::

iiiiiiiii!iiiiii!iii!!iiiiii

;

d~ ~

~

~

~

~

l~.ln

:::::::::::::::::::::::: :::::::::::::::::::::::::: ::::::::::::::::::::::::::

7 days

.

i~l

I~I I ~ I' .

~~

~

I

N

I I

~ ~ ~

I~I I

s

~

~

~ ~•

o

~ ~

I day

FIG. 5 X-ray diffraction diagrams of sample 2 after 1.7 and 180 days. Key: 0 - belite; x - alite; ~ - calcium aluminoferrite; • - Ca(OH)2"

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Vol. 24, No. 8

X-ray diffraction diagrams showed that the concentration and morphology of Ca(OH) 2 and calcium silicate hydrates continued to change with time. This authenticates the fact that as a result of the large ionic radius of Ca2÷, in the tetrahedral vacancy of the Ca(OH)2 lattice, ions of smaller ionic radius such as those of AI, Si, Fe are easily lodged and the simultaneous substitution of (OH) -1 for 02- occurs with the formation of solid solutions. X-ray diffraction analyses of 3 months hydrated cement mortar, samples N 1 to 3, showed that the extent of hydration of belite (d = 0.277, 0.274 nm etc), alite (d = 0.277, 0.198 nm, etc) and calcium aluminoferrite (d = 0.265, 0.218nm) in sample 1 and 3 exceeded those of sample 2. Remarkable influence of gypsum was not observed. Differences in the extent of hydration of the various samples was further authenticated by results of weight loss computed using the TG curves. It showed that for samples 1, 5 and 6 the net weight losses were 22.0, 20.0, 19.6 % respectively, with samples containing lesser Fe20 3 having more water of crystallization in their hydrates.

O

Jj

ii

Key:

I]

Oh

cxl

J

o

-

belite

x

-

alite

-

~J

Calcium alumoferrite

0 • _

Ca(OH)2

1

J

Q 0

FIG. 6 X-ray diffraction diagrams of samples 1 to 3 after 90 days hydration.

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HYDRATION KINETICS, METAL PARTICLES, MORTARS, CHARACTERIZATION

1557

Conclusion Results of the different analyses showed that the kinetics of chemical reactions in hardening cement mortar produced from the raw mix containing metallic particles, differ from those of ordinary portland cement using raw materials of natural origin. The increased presence of Fe203 in the clinker minerals to a great extent negatively influenced their solubility, increasing the induction, setting and hardening periods.

References 1. Taylor, H.F.W.. "Hydrated Calcium Silicate Part 1: Compound Formation at Ordinary

2. Brunauer, S. and S.A. Greenberg. "The Hydration of Tricalcium Silicate and l~-Dicalcium Silicate at Room Temperature". Proc. of the IV Int. Syrup. on the Chemistry of Cement, Washington 19,,60. Washington, Vol. I, p. 135-165 (1962). ,, 3. Grudemo, A.. The Microstrueture of Hydrated Cement Paste, Proc. of the IV Int. Symp. on ............ the Chemistry of Cement, Washington 1960. Washington, Vol. II, p. 615 - 647 (1962). ::::::::::::: 4. Fujii, K., Bestimmung Von Freien, "CaO and Ca(OH)2 in Portland Klinker and Hydratisiertem Zement Mittels O-xresol", Zement-Kalk-Gips, 6, 302-305 (1972). 5. Perez-Pena, M., D.M. Roy, and F.D. Tamas. "Influence of Chemical Composition and Inorganic Admixtures on the Electrical Conductivity of Hydrating Cement Pastes", J. Mat. Res. 4 (1), 215-223 (1989). . Baev, A.K., Handbook of "Chemical Analyses of Silicate Materials." Beloru~sian Techn. Institute, Minsk, p. 38, 1983.

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