Filler cement: The effect of the secondary component on the hydration of Portland cement

CEMENT and CONCRETE RESEARCH, VoL 20, pp. 853-861, 1990. Printed in the USA. 0008-8846/90. $3.00+00. Copyright (c) 1990 Pergamon Press plc.

FILLER CEMENT: THE EFFECT OF THE SECONOARY COMPONENT ON THE HYDRATION OF PORTLAND CEMENT Part 2: Fine hydraulic binders

Walter.A.Gutteridge & John.A.Dalziel British Cement Association, Slough,UK. (Communicatext by P.L. Pratt) (Received March 12, 1990)

ABSTRACT

In Part 1 of this paper, it was shown that enhanced hydration was achieved by blending a fine non-hydraulic filler into an ordinary Portland cement. This enhancement was considered to be a particle size effect and associated with the presence of fine particles of filler which provided the additional nucleation sites. The filler, rutile, had a variable cement equivalence and reached a maximum value of 0.9kg/kg after hydration had proceeded for three days. In this second part, the same Portland cement was blended separately with latent hydraulic binders (two puivedzed fuel ashes and a ground granulated blastfurnace slag, a Lurgi slag and a volatilized silica). The apparent overall reactivity of these binders was seen to have two components, the first being the particle size effect with its influence on the hydration of the Portland cement and the second the inherent hydraulicity of the secondary material.

Introduction The filler used in Part 1(1) was non-hydraulic in itself but nevertheless promoted enhanced hydration. It is recognized that there may be practical limitations imposed when utilising the enhancing effects of very fine materials as cement extenders, for instance both the water demand and setting time will be increased. Factors such as these warrant further consideration and additional research needs to be undertaken. In this, the second part of the investigation, the fine inert filler was replaced by a series of secondary hydraulic binders and their influence on the hydration of the ordinary Portland cement studied. Relationships between combined water, caicium hydroxide and the degree of hydration of the cement were established.

Materials The same ordinary Portland cement as used in the first Part(l) was used to produce a further six series of blends as follows :1. CP-serles Seven parts by mass of the ordinary Portland cement and three parts by mass Of a pulverized fuel ash (pfa) which had been designated P. (Referred to here as 30% replacement). 2. CW-series replacement)

Seven pans by mass of the OPC and three parts by mass of a pfa designated W. (30% 853

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W.A. Gutteridge and J.A. Dalzie|

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3. CG-series One part by mass of the OPC and one part by mass of a Lurgi process gas slag designated G. (50%replacement). 4. CS-series One part by mass of the OPC and one part by mass of a ground granulated blast furnace slag designated S. (50% replacement). 5. CV-series Four parts by mass of the OPC and one part by mass of volatilized silica designated (20% replacement). No superplasticizer was used to reduce the water demand of the silica.

V.

6. CV2-series Nineteen parts by mass of the OPC and one part by mass of volatilized silica (V). (5%replacement). Again no superplasticizer was used. Analyses for each of the secondary binders are given below:-

Material and designation

Pfa *

P

Pfa * W

Slag G

Slag # S Volatilzed silica V

SiO 2 (mass%)

47

48

33

34

96

AlsO3

25

26

23

15

0.28

Fe203

14

9

15

0.23

0.05

CaO

4.1

1.7

25

MgO

0.95

1.3

SO3

1.3

1.0

0.8

1.0 99

39

0.06

8.7

0.28

0.11

--

96

--

"Glassy material" (mass%)

79

83

45 micron residue (mass%)

8

7

Specifoc surface m2/kg

330

375

180

330

--

Density kg/m 3

2310

2400

2720

2860

--

.

.

.

.

.

.

Footnote: * Complied with BS 3892,Part 1 # Complied with BS 6699

Method Pastes having a water to solids ratio of 0.71 were prepared as described in Part 1. At each specified age the hydration was stopped using methanol exchange(2) and the hydrated paste dried over silica gel (previously conditioned at 105° C) until constant weight was achieved. Combined water content was then determined using thermogravimetric analysis (TGA). The amount of calcium hydroxide produced during hydration and the quantity of each cement phase which remained unreacted was obtained using quantitative x-ray powder diffraction analysis (QXDA)(3).

Degree of hydration The percentage degree of hydration (DOH) of the Portland cement in each blend as a function of the time of hydration could be described either by equations of the Avrami type(I),(3),(4) or by the following :CG-series :DOH = -1.06 A 2 + 22.12 A -24.02 CP-series :DOH = -1.467 A 2 + 28.88 A -34.38 CS-series :DOH = -1.42 A 2 + 26.32 A -28.28 CV-series :DOH = -1.10 A z + 23.47 A -33.93 CV2-series :DOH = -0.936 A z + 21.21 A -22.7 CW-series :DOH = -1.05 A 2 + 20.93 A -15.66

FILLER CEMENT, HYDRATION EFFECT,REACTIVE FILLERS

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---

+/ d

855

m'll..p p+ll-W

~1101

where A = In(time(hours)) TIME(DAYS)

FIG. l(a) Comparing the difference in the degree of hydration of pastes containing an OPC and a pfa with that of a paste containing only OPC. 10, .... --, • .,,.,

Slag-G Slag-S

...... // _/

/ 0.10.3

/

1 3 10 30 100 TIME (DAYS)

FIG. l(b) Comparing the difference in degree of hydration of pastes containing an OPC and a slag with that of a paste containing only OPC. J

=e

0!

20% Fume ...................................... ~..................•

5% Fume

~

(5)

/

(10) !

I 0.10.3

3 10 30 100 TIME (DAYS)

FIG. 1(c) Comparing the difference in the degree of hydration of pastes containing an OPC and a volatilized silica with that containing only OPC.

Figure 1 shows the effect on hydration produced by secondary material. The ordinate represents the numerical difference between the DOH of the Portland cement in blended and unblended pastes. A positive value indicates that the DOH of the Portland cement had been enhanced by the presence of the secondary material. A negative value that the DOH of the Portland cement had been reduced. Figure 1(a) shows the effects induced by pfa. The presence of pfa W (which had a specific surface of 375 mZ/kg) had enhanced the DOH of the Portland cement in the CW-series after approximately six hours hydration. The amount of this enhancement increased gradually, reached a maximum at approximately seven clays and then diminished. At fifty six days there was no difference between the DOH of the Portland cement in either the CW- or C-series. In contrast pfa P (which had a smaller specific surface area of 330 m2/kg) did not induce enhancement until hydration has proceeded for three days after which time enhancement increased gradually, reached a maximum after approximately fourteen days of continuous hydration. It then gradually diminished and at 112 days there was no difference between the DOH of the Portland cement in either the CP- or C-sedes. There is a similar disparity in the effects induced by the slags G and S (Figure 1(b)). Slag G which had a low specific surface of only 180 m2/kg did not induce any significant enhancement in the DOH of the Portland cement whereas with slag S (specific surface of 330m2/kg) it was induced after approximately twelve hours. Volatilized silica at the five percent replacement level induced a small and not very significant enhancement Figure 1(c) whilst at the twenty percent replacement no enhancement was induced throughout the one hundred and twelve days continuous hydration. This may in itself have been the direct result of the lack of dispersion of the particles of volatilized silica particularly as no superplasticizer was used in these mixes. Figure 2 compares the DOH for three of the four cement phases Alite, Belite and C3A ) in the ordinary Portland cement with blends containing pfa. After twenty eight days of continuous hydration the presence of pfa can be seen to have increased the DOH of the Alita phase (Figure 2(a)); had little effect on the belite phase (Figure 2(b)) and increased the DOH of the C3A phase. Although it has been reported that pfa

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W.A. Gu-¢ridg¢and J.A. Dalziel

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retards the hydration of pure C3A(5 ) it has been found that in factory made cement the hydration of the C3A phase is accelerated(3,6). The reason for this is that some of the calcium sulphate is absorbed on the surface of the pfa and reduces its retarding influence(7).

Combined water 0.10.3

1 3 10 30 100 TME (DAYSI

FIG. 2(a) Degree of hydration of the Al~e phase in the OPC and OPC / Pfa pastes. 80 . . . . .

CP-~EFaES

iow--

Some of the combined water associated with the formation of new hydrates comes from the reaction with calcium hydroxide. In order to make a comparison between the blends and the ordinary Portland cement, the combined water given in F'~jure 3 excludes that in the calcium hydroxide. The effects shown for each of the secondary binders reflect the extent of further hydration as it is compared directly with the amount of combined water in the Portland cement fraction. It would appear that with the exception of blends containing volatilized silica, the presence of secondary hydraulic material induced additional combined water (per unit mass of blended cement) at any given degree of hydration. The relation between the combined water (COMW) per 100g of blended cement and degree of hydration (D) could be described as :COMW = A0 + A1 (D) + A2 (Oz) + A3 (D 3) + A4 (D 4) The coefficients for which are given below :-

A0 0.10.3

1 3 10 30 100 TIME (DAYS)

A1

A2

A3

A4

CG

- 0.333 .093

CP

1.705

-.0.072 6.513 10 .3

-9.606 10-s 5.410 10.7

Degree of hydration of the Belite phase CS in the OPC / Pfa pastes. CV

2.481

-0,087

2.089 10 .3

0.915 10"s -0.913 10.7

0.477

0.172

-0.487 10 .3

FIG. 2(b)

100 ~ - - - -

8O ~ cw..,~4~lE$

©

0.1625 10 .3 -2.915 10 -s 4.235 10.7

CV2

0.516

0.073

1.533 10 .3

CW

0.157

0.066

0.433 10 -3

C CT

& 0.055

0.t41

-3.32 0 10.3 8.398 10-s -5.059 10.7

0.035 10"s 0,6681 10.7

4,& 0.10.3

3 10 30 100 T~E (DAYS)

FIG. 2(c) Degree of hydration of the C3A phase in the OPC / Pfa pastes.

Calcium hydroxide The amount of calcium hydroxide (CH) in grams, produced per 100 g of blended material at a particular degree of hydration (D) could be described as CH = B0 + BI(D) + B2(D 2) + B3(D 3) + B4(D 4) The appropriate coefficients for which are listed below:-

Vol. 20, No. 6

FILLERCEMENT,HYDRATIONEFFECT,REACTIVEFILLERS

857

2O I

I

.

°

i If:

r,"

./

6

-

/

20

40

80

80-

j

!

0 20 40 B0 80 0EG~EE 0F HY10RATION"~

FIG. 3(a)

FIG. 3(b)

The combined water at different degrees of hydration for pastes containing Pfa compared with that for the OPC fraction.

The combined water at different degrees of hydration for pastes containing slag compared with that for the OPC fraction.

2O I

i

COC ~ l . v

I

__ J

15

i ~&S'~FU~

i

)-"~

=

10

/

/ 0

0 2O 4O 6O 8O DEGREE OF HYORA'RC~

FIG. 3 (c)

20 40 60 80 DEGREE OF HYDRATION %

FIG. 3(d)

The combined water at different degrees of hydration for pastes containing a 20 % replacement of volatilized silica compared with that for the OPC fraction.

The combined water at different degrees of hydration for pastes containing a 5 % replacement of volatilized silica compared with that for the OPC fraction.

OP¢ ,rRACI"~N

i

15

t"* ¢" ""

~o

~

i

I

~5

--.

: 0

A 2O

4O

60

130

• CW-~$

8O

FIG. 4(a) Comparing the crystalline calcium hydroxide in pastes containing Pfa with that which would be derived from the OPC fraction.

B1

B2

B3

B4

CG-

-2.2

0.3308

-3.062 10.3 9.317 10-s -9.042 10.7

CP-

1.705

1.342

-45.38 10.3 79.66 10.5 -48.30 10.7 -20.89 10.3 28.81 10"s -15.46 10.7

CS-

2.481 0.9244

CV-

0.4768 0.4326

-3.196 10.3

CV2-

0.5157 0.3442

-1.719 10.3

CW-

0.1572 -0.0822 -1.695 10.3 24.99 10.5 -24.08 10.7.

C & CT 0.0542 0.0996

6.485 10.3

-5.719 10-5 0.4775 10.7

The amount of calcium hydroxide produced per 100g of blend is shown in F',gure 4 as a function of the degree of hydration of the Portland cement. The thin continuous line in this

858

W.A. Gutteridge and J.A. Dalziel

I

I

Vol. 20, No. 6

20

__

.

.

.

.

coc F~J,cr~x~

15 !/..

i

i

4/ 10

;¢ 0

__ 20

40

80

80

0 20 40 80 80 {~EG4~EEOF HyI3~RAT1ON

~GI~-~ OF HYORATI()N %

FIG. 4(b)

FIG. 4(c)

Comparing the crystalline calcium hydroxide in pastes containing slag with that which would be derived from the OPC fraction.

Comparing the crystalline calcium hydroxide in pastes containing 20% volatilized silica with that which would be derived from the OPC fraction.

Figure represents the quantity of calcium hydroxide which could be produced by an equivalent mass of ordinary Portland cement in the absence of a secondary material. Any difference between this quantity and that produced by the blended cement is due to reaction of secondary material with calcium hydroxide in the pore solution. There is always sufficient calcium hydroxide present in the hydrated paste to keep the pore solution in a saturated condition and the effect of the pozzolanic reaction is seen (in these experiments) as a depletion of crystalline calcium hydroxide. Figure 4(a) shows a good example of this where once the degree of hydration has reached seventy percent both pfa-P and pfa-W remove the same quantity of calcium hydroxide. These fuel ashes are therefore ( as far as these experimental conditions are concerned) equally 20 - - 7 . - - ~ & 5,L t~jMI[ Pfa-P reactive as a pozzolan differing Pfa-W only in their effect / on the hydration of the Portland cement.

/.

jr

-

DE(~fflEE OFHYDRATION%

FIG. 4(d) Comparing the crystalline calcium hydroxide in pastes containing 5% volatilized silica with that which would be derived from the OPC fraction.

0.1

0.3

1 3 10 TiME (DAYS)

30

100

FIG. 5(a) Cementing equivalence factor for the pulverized fuel ashes.

Cement eauivalence factor (fine powder effect/ As was shown in Part 1 of this paper, the enhancement induced by a finely powdered material can be expressed a s a cement equivalence factor. Values for this factor were obtained for each secondary material used here and are shown in Figure 5 as a function of the time of hydration. The two fuel ashes

FILLER CEMENT, HYDRATIONEFFECT. REACTIVE Frl U=RS

Vol. 20, No. 6

02-

- - - -

F~

j. Slag-S__

!

i ~

~

0.1

0.~

0.103

3

10 3O

_ 100

TIdE (DAYS)

FIG. 5(b) Cementing equivalence factor for the slags.

859

1,4

and the ground granulated blastfurnace slag have values which are approximately 0.15 kg/kg and only at the five percent replacement level with volatilized silica is the cement equivalence factor greater than this.

~.2 g o sl ~ os i o,= 02 o o I0 3

i I I ........

, i

i

3 10 3(} 100 T~ME(DAYS)

FIG. 5(c) Cementing equivalence factor for the volatilized silicas.

For ages exceeding six hours, each secondary material when blended with the Portland cement modified the way in which the cement hydrated. The hydration of the cement in pastes containing either pfa or slag was first retarded and then enhanced at some later age whereas with volatilized silica the condition depended upon the level of replacement. Superplasticizers have been shown to influence hydration of Portland cement blended with volatilized silica(8),(9) and consequently were not used in either the CV- or the CV2-series. The relationships between degree of hydration and time imply that secondary binders generally retard hydration of the Portland cement during the first few hours after they have been mixed with water. The progress of hydration is sometimes monitored using conduction calorimetry so as to obtain values relating the rate at which heat is evolved against time. Hydration of cement blended with a secondary material is often described in these terms by referring to the time at which the principal or so-called "second peak" occurs. Some authors consider that hydration has been accelerated when the second peak occurs earlier for the blended cement than for the unblended cement and likewise retarded when it appears later. Others may use either, the rate of heat evolution or the integrated value, within a specified time interval to describe the influence of the secondary material. It is not our intention to assess the validity of such descriptions but to limit confusion particularly when comparing results obtained in this present work with those reported by other authors. Secondary materials such as non-hydraulic fillers(I),(10),(11), pulverized fuel ashes(3),(12),(13),(14), slag(6),(14),(15) and silica fume(7),(16) have been shown to accelerate the rate of hydration of Portland cement. Ramachandran and Zhang(11) showed that fine Calcium Carbonate could induce a retardation (or delay) in the hydration of tricalcium silicate during the first four hours of hydration and yet produce an accelerating effect when hydration was continued beyond twenty four hours. Delays have also been associated with blends which contain pfa (7),(17),(18),(19) and to a lesser extent those containing slag(6),(20),(21). Data presented here whilst not obtained using heat evolution techniques do not conflict with these findings. According to the studies in which silica fume has been used(6),(8),(9),(22) there is no delay in the time at which the second peak occurs. Nevertheless Meland(8) using blends containing ten percent of silica fume reported that the heat output associated with the second peak was higher than when twenty percent of volatilized silica was used in the blended material. At five percent replacement level (as used in the blends of the CV2-series) volatilized silica has an equivalence factor between 1.5 and 0.5kg/kg OPC as hydration proceeded (F'~jure 5(0)). At the twenty percent replacement level the factor is negative throughout the period of hydration (112 days). The effect of a retardation at early ages of hydration followed by a pedod of accelerated or enhanced hydration is consistent with-the idea that secondary materials increase the number of nucleation sites for

860

W.A. Gutteridge and J.A. Dalzi¢l

Vol. 20, No. 6

deposition of the cement hydrates. Odler and Schi3ppstuhl(23) found that the length of the dormant period in the hydration of C3S could be changed by several means which were consistent with the theory that the dormant period ended when the C-S-H nuclei formed on the active sites of the surfaces reached a critical size. The age at which this occurs therefore will depend upon the time required to attain this critical size. The increase in the number of nucleation sites provided by the addition of the secondary material to the Portland cement will result in growth at these sites being less at a given degree of hydration. Thus the time before renewed activity occurs will be lengthened and the dormant period extended. Odler and Sehfippstuhl also showed that the length of the dormant period was influenced by a change in the composition of the liquid phase. Secondary material may affect the chemical composition of the pore solution and therefore also have an influence upon the length of the dormant period. Secondary materials form additional hydration products. This effect is shown by the additional combined water per unit mass of Portland cement in the blended mixtures (Figure 3) and by the depletion of calcium hydroxide (Figure 4). In these terms each pfa and each slag had similar reactivities. The former induced a pozzolanic reaction and produced additional hydration product which was accompanied by a small increase in combined water. The latter whilst depleting the calcium hydroxide also used it as an activator and the additional hydrate produced increased the quantity of combined water significantly. At an early age of hydration volatilized silica reacts with the calcium hydroxide (Figure 5(c)) to form C-S-H having a low calcium oxide to silica ratio(22) accompanied by an increase in the amount of water combined.

Conclusions When blended with ordinary Portland cement it was found that:1. The addition of a pulverized fuel ash enhanced the degree of hydration of the ordinary Portland cement. Ash with the larger specific surface induced enhancement at an age earlier than the ash of the smaller specific surface. Both ashes used here performed equally effectively as pozzolans when the degree of hydration of the Portland cement exceeded seventy percent. 2. Ground granulated blastfurnace slag having a specific surface of 330m2/kg induced a significantly larger enhancement in the degree of hydration than was obtained using the coarsely ground Lurgi slag of specific surface 180m2/kg. 3. At the five percent replacement level and in the absence of a superplasticizer, volatilized silica induced a small insignificant enhancement in the degree of hydration but at the twenty percent replacement level no enhancement was induced. 4. These findings are consistent with the view that the addition of fine particulate material to an ordinary Portland cement whether as a filler or a hydraulic extender will influence the degree of hydration of the cement. If such material is well dispersed and has a larger specific surface than the Portland cement it will contribute to the apparent reactivity by enhancing the hydration of the cement; the fine powder effect. It is for this reason that the so-called cement equivalence factor of such materials will depend on the fineness of the cement with which it is used.

Acknowledeements v

The authors wish to thank Dr Christine Shepperd of the British Gas Corporation for supplying the sample of Lurgi slag used in this work and acknowledge the assistance given by Mr R T Musson and Miss D Wyndham.Birch in the preparation of samples for x-ray diffraction analysis.

1. W.A.GUTTERIDGE, and J.A.DALZIEL, (to be published) 2. R.G.PATEL, L.J.PARROI-I, J.A.MARTIN and D.C.KILLOH,, Cement and Concrete Res., 15, 343,

(1985). 3. J.A.DALZIEL and W.A.GUTI'ERIDGE, Cement and Concrete Association, Slough, Technical Report

No.560, (1986).

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FILLER CEMENT. HYDRATION EFFECT. REACTIVE FII] FRS

86 !

4. TAYLOR, H.F.W., Adv.in Cement Res., 1, No.l, 5, (1987). 5. C.PLOWMAN, and J.G.CABRERA, Proc.Symp.N Annual Meeting Mats. Res. Soc., 71, (1981). 8. H.UCHIKAWA, 8th. Internat. congress on the chemistry of cement. Rio de Janeiro, I, 2249, (1986). 7. E.RAASK, Intemat.Symp."l'he use of Pfa in concrete',Leeds,1,5, (1982). 8. I.MELAND, lsLIntemat, conference on the use of fly ash, silica fume, slag and other mineral by-products in concrete. Montebello, VII, 665, (1983). 9. Y.HALSE, D.J.GOULT, and P.I_PRATT, BdLCeram.Proc. No.35, 403, (1984). 10. H.G.ELLERBROCK, S.SPRUNG, and K.KULMANN, Zement Kalk Gips, 10, 586, (1986). 11. V.S.RAMACHANDRAN, and CHUN-MEI ZHANG, Durability of Building Materials, 4, 45, (1986). 12. H.F.W.TAYLOR, K.MOHAN, and G.K.MOIR,, J.Amer.Cerem.Soc., 68, 685, (1985). 13. W.LUKAS, Mats and Struct.: Res. and Testing,_9, 331, (1976). 14. K.TAKEMOTO, and H.UCHIKAWA,, 7th.lntemat.congress on the chemistry of cement, Paris, l, IV-2, 1, (1980). 15. Y.TOTANI, Y.SAITO, M.KAGEYAMA, and H.TANAKA, ibid, II,, 111-95,(1980). 18. D.ANDRIJA, 8th.lnternat.congress on the chemistry of cement, Rio de Janerio, 1, 279, (1986). 17. W.FAJUN, W.GRUTZECK, and D.M.ROY, Cement and Concrete Res., 15, 174, (1985). 18. A.GHOSE, and P.L_PRA'n, Proc.of the Symposium on the effects of fly-ash incorporation in cement and concrete. Mats. Soc., 82, (1981). 19. N.TENOUTASSE, and A.M.MARION, Proc. 2nd. InternaLconference ;Fly-ash, silica fume and natural pozzolans in concrete,G, 51, (1986). 20. K.OGAWA, H.UCHIKAWA, K.TAKEMOTO, and I.YASUI, Cement end Concrete Res., 10, 683, (1980). 21. X.WU, D.M.ROY, and C.A.LANGTON, Cement and Concrete Res., 13, 277, (1983). 22. CHENG-YI HUANG and R.F.FELDMAN,, Cement and Concrete Res., 15, 585, (1985). 23. I.ODLER, and J.SCHOPPSTUHL, Cement and Concrete Res.,11. 765, (1981).