Flow behaviour of modified cement pastes

CEMENT and CONCRETE RESEARCH. Vol. 23, pp. 803-810, 1993. Printed in the USA. 0008-8846/93. $6.00+00. Copyright © 1993 Pergamon Press Ltd.

FLOW

BEHAVIOUR

OF MODIFIED

CEMENT

PASTES

Ya. P. I v a n o v a n d T. Tz. R o s h a v e l o v Central Laboratory of Phisico-Chemical Mechanics B u l g a r i a n A c a d e m y o f Sciences, Sofia, B u l g a r i a (Refereed) (Received May 29, 1992)

ABSTRACT Rheological behaviour of modified cement pastes has been investigated by means of a planned experiment. The regressive models of paste are obtained in the form of six-factor equations. The relative influence of each factor (component) is critically analyzed. The most significant, from a rheologicai point of view, ingredients of cement paste, as well as their influence are presented.

Introduction The complex influence of a number of modifying additives upon rheological behaviour of cement pastes, has been broadly investigated during the last few decades. One of the most frequently used approach is based on mathematical theory of planned experiment. That method allows study of the individual influence and links among great number of independent components and affords an opportunity to optimize the composition of a paste or a mortar. A priori information from scientific literature shows the form of advisable function : k

k

v -- bo + E

+ E b jX Xj + E

i=l

i
i=l

21

(1)

The preliminary idea of recent paper was to reveal the complex interdependence among the components of modified with condensed silica fume (CSF) cement pastes. The effect of CSF upon paste's rheology is well established. However, in deep study of the rheological behaviour of cement composites and optimization of the composition of that material is not available in the literature. In the paper, we describe the results of rheological study of flow of cement pastes, modified with CSF, superplastisizer (SP) and wateremulgatory epoxy resin (WER).

Materials and Methods The investigation on the rheological behaviour of pastes was subordinated to the principles of mathematical theory of planed experiment. Most appropriate matrix turned out to be the information matrix of CH4 plan (1) - modified saturated plan shown in Table 1. 803

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Ya.P. Ivanov and T.Tz. Roshavelov

Vol. 23, No. 4

Table 1 M a t r i x o f C H 4 P l a n a n d M e a n Results o f E x p e r i m e n t s N°' 1: 2' 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Se2

X1 W/C 1 1.25 -1 -1 -1 -1 -1 -0.75 -0.75 -0.75 -0.75 -0.75 1 1 1, 1~ 11 1 11 1 1 1 -1.25! 0 0 0 0 0 0 0 0

X2 SP 1 -1 1.25 -1 -1 -1 -1 -0.75 1 1 1 1 -0.75 -0.75 -0.75 -0.75! 1! 1! 11 1 1 11 0! -1.251 01 01 0 0 0 0t 0

X3 CSF

X4 StA

X5 SO~

X6 WER

1 -1 -1 1.25 -1 -1 -1

1 -1 -1 -1 1.25 -1 -1

1 -1 -1 -1 -1 1.25 -1

1 -1 -1 -1 -1 -1 1.25

-0.75' 1 1 1 -0.75 1 1 1 -0.75 -0.75 -0.75 1 1 1 0 0 -1.25 0 0 0 0 0 0

1 -0.75 1 1 1 -0.75 1 1 -0.75 1 1 -0.75 -0.75 1 0 0 0 -1.25 0 0 0 0 0

1 1 -0.75 1 1 1 -0.75 1 1 -0.75 1 -0.75 1 -0.75 0 0 0 0 -1.25 0 0 0 0

1 1 1 -0.75 1 1 1 -0.75 1 1 -0.75 1 -0.75 -0.75 0 0 0 0 0 -1.25 0 0 0

flap. p mPas 24.0 57.7 45.0 2848.4 319.1 204.4 309.1 1536.1 115.7 166.4 200.0 291.1 85.4 293.1 314.1 215.4 56.7 48.0 8.3 29.0 21.7 21.7 241.1 454.1 17.7 30.3 31.3 27.0 30.4 31.7 30.6 1.49

l~ o, p Pa 0.0 6.6 0.7 194.4 8.5 7.0 6.9 36.5 0.5 0.9 2.2 1.3 4.0 26.4 20.8 13.0 1.3 1.2 0.0 0.5 0.5 0.5 1.4 4.2 0.5 0.5 0.3 0.5 0.2 0.5 0.5 0.34

In accordance with the aims of the work, investigated factors (components) were as follows: 1)Water-to-cement ratio,w/e (X1) - varying on 6 levels in the limits 0.45:0.55; 2)Superplastisizer content, SP (in mass % of cement) (X2) - varying from 0:2%;

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FLOW,MODIFIEDCEMENTPASTES

805

3)CSF additive (in mass % of cement) (X3) - from 0% to 10%; 4)C3A content in the clinker, %

(X4)

-

varying in 6 levels from 1.43% to 9.30%;

5)SO3 content in the clinker, % ( X s ) - varying in 6 levels from 2 to 4%; 6)WER, Araldit PY 340 and hardener HZ-340 (X6). Mixing p r o p o r t i o n was kept at 100:120. The quantity varied from 0:2%. The characteristics of all materials and methods applied, except for factor X6 ( W E R ) are given elsewhere (2). The clinching argument for using WER, as a modifier of the pastes is the following: our preliminary study (1) showed a greater influence of the superplastisizer on the value of a p p a r e n t viscosity than on yield value.

Results and Discussion Using results given in Table 1, following adequate polynomial regression equations were obtained: - for In r / : In r] = 3.532 - 0.879X1 - 1.028X2 + 0.670X3 + 0.151X4 +0.081X5 + 0.310X60.103X1X2 - 0.265X1X3 - 0.207X1X4 - 0.122X1X5 +0.183XIX6 - 0.389X2X3 + 0.059X2X6 +0.101X3X4 +0.068X3X5- 0.318X3X6- 0.154X4X5- 0.064X4X6 + 0.55X12 +0.834X22 +0.113X32 +0.1X62 (2) - for In r 0In r 0 = -1.315 - 0.357X1 - 1.565X2 0.179X1X2 - 0.412X1X3 - 0.332X1X4 0.115X2X4 - 0.2402X5 - 0.028X2X6 0.034X4X6- 0.081XsX6 + 0.77X12 0.033Xs 2 + 0.514X62

+ 0.612X3 - 0.049X4 - 0.051X5 + 0.145X6- 0.087X1X5 + 0.106X1X6 - 0.617X2X3 + + 0.071X3X4 - 0.447X3X6 - 0.339X4X5 + 0.508X22 + 0.888X32 + 0.359X42 + (3)

Obtained models (Eqs. 2 and 3) allow to make some comparisons and draw up some conclusions concerning the results. In the models, describing the relationships of the basic rheological characteristics r]ap and r 0 as a function of considered factors (components), the greatest positiv values of the linear coefficients bi are those in front of factor X3 (CSF). That means, the factor X3 is a dominant role with regard to their increase and its influence is strengthened with quadratic effect in the two models (plus sign in front of b33 ). The greater quantity of CSFadditive in cement mix, logically leads to sharp increase of mix's specific surface and respectively to higher values of the rheological characteristics. Illustration of that effect is given on Fig.1. In the models (2) and (3), greatest absolute values of bi are those in front of X2 (SP content). That's quite normal in the light of the role which the additive of SP plays on the drop of rheological characteristics (3,4). We will only mention, that the presence of a quadratic effect with positive sign ahead of b22 confirms the existence of optimal concentration of SP from rheological point of view, over which its influence starts to decrease.

806

Ya.P. Ivanov mid T.Tz. Roshavelov

Vol. 23. No. 4

,Pa 12o

-

lOO

-

24

1'

80

60 40 20 I

20

I

40

I

60

I

80

I

100

I

120

D,s

It -1

FIG. 1 Flow curves of cement pastes containing 5% CSF (curvesl' and 2') and 0% CSF (curves 1 and 2), w = 0.4 The existence of significant coefficients of interaction bij in both equations (2) and (3) shows that the power of the influence of CSF content (X3) on rheological characteristics of pastes depends on the quantity of SP (X2). The mutual influence of the above two factors shows, that the decrease of the value of rheological characteristics, can be realized by combination of a high content of CSF and SP and vice versa. Above mentioned is true for coefficients b12, b13 and b36 also. That means, analogous decrease in rheological characteristics can be reached by combining high content of CSF and water or CSF and WER. The absolute value of b36 is also high, which shows, that WER exerts a positive influence on rIap and r 0, in presence of CSF in cement mix, but we will see further clown that the mentioned effect is too weak. Increasing gypsum content (X5) and that of C3A (X4) in the composition of cement results in decrease of r 0 till reaching certain limit, over which an increase in the value o r 0 is observed (coefficients " + b44" and " + b55"). That is due to the presence of indigent gypsum and its independent crystallization. However, influence of the both factors X4 and X5 is too weak and doesn't permit determination of more explicit quantitative dependence. From the carried out factor analysis concerning the effects of separate factors on the basic characteristics r/ and r 0 of cement pastes, quazimonofactoral relationships has been obtained. The maximal influences of the factors are shown on Fig.2 and 3, as well as diagrams of the influence of w/c ratio (X1), SP content (X2) and CSF concentration (X3), together with the range of their influence. In Table 2, separate factors are compared by the power of their influence using the method described in reference (1). The analysis of Fig.2 and 3 and Table 2 show the following : -the character of the influence of the investigated factors is very similar for both rheological characteristics;

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FLOW, MODIFIED CEMENT PASTES

807

a) 7.4 X2 X3

/

2.7

:,o~

~

Xi

0.37 I

A~

0

-

I

b) SP,%

W

1.0

,

1.0

tL.,

]

2,3.4 S'-'

0.4

0.4

0.12

0.12

0.05

Cx'.~.4.s-]l x6.-z

0.05

,

0.02

7} 0.35

0.45

0

0.55

1

1.21

n.Ta 2

CSF,%

20.1

L Xl.2,6.-1

7.4 2.7 1.0 0.4 0,12

(,,,.-,) 111,2 6 - I

0.03

~7

i

0

5

10

FIG. 2 a) Maximum factoral influences and b) Zones of the effect of the factors X1, X2 and X3 on viscossity r/.

808

Ya.P. Ivanov and T.Tz. Roshavelov

+

Vol. 23, No. 4

a)

54.6 X2

20.1

X3 ]

7.4 2.7 1.0

~'-

x6

~~____~

Xi

0 ,3 7 0 .1 2

0.05

A'Co b) W 1,0

7,4

tx6.1

2.7 1.0

0.4

) 0.4 0.12 0.03 0.02

0,12

SP,%

~

...,o.°.,l

x2'3'4"'1 100.00 1

0.03

,

.0 5

x6.-i

0.02

C,,.3.,.°.°-,I

J

0.35 o.41

0.45

0'530.55

'7" ~o

1.3

0

I

2

CSF,%

148.4 54.6 20.1 7.4 2.7 1.0 0.4 0.12 0.03

J X4-1

J

Xx,~:._)~.,-, 7.1

0

5

0

FIG. 3 a) Maximum factoral influences and b) Zones of the effect of the factors X1, X2 and X3 on yield value r 0.

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FLOW, MODIFIED CEMENT PASTES

809

Table 2 Influence of Factors Xi on the Rheological Characteristics Factors

Xl

X2

X3

X4

X5

X6

3.76 1.73

3.48 3.23

2.80 2.56

1.55 1.17

1.00 1.01

2.09 1.00

Model Ln r/ Lnr0

-increase of w/c ratio and SP content in the paste results in a parabolic decrease of both rheological characteristics with a maximum around the upper limit of their content. The above is well illustrated about factor X2 on Fig.2 and 3; -the greatest influence upon the value of r/and r 0 inserts w/c ratio (X1) - In r/=3.76 and SP additive (X2) - In r 0 = 3.23, respectively; -SP additive has the greatest plasticizing effect in combination with high w/c ratio and high concentration of CSF. That is probably due to its relatively weaker effect on cement grains as dispersing agent as that on CSF particles; -maximal increase of the rheological characteristics has been observed with minimal w/c ratio and SP content. That's why for reaching an optimal fluidity of silicate disperse cement composites, modified with CSF a higher w/c ratio is required with combination of a superplastisizer; -the factor analysis confirmed the preliminary results showing the greatest influence of SCF for the increase of the value of r 0 than that of ~]ap; -the increase of CSF content in the system results in a parabolic decrease of the yield value with reaching of a minimum (optimum) within the experiment's boundaries; -factors X4 and X5 (C3A content, in % and SO3 , in %) on the rheological characteristics of examined composites;

have

the weakest effect

-WER additive (X6) has the weakest effect on the value of r 0 • The result shows that its use as a mean of reducing the yield value, is ineffective compared to the use of SP; -the optimal intervals of the factor's levels, for yielding of a maximal plasticizing effect are as follows: for In r/

~ w/c (X1) E [0.45+0.55] SP (X2) E [1.21+1.781%

for In r 0 ~, w/c (X1) E [0.41+0.53] SP (X2) ~ [1.3+2.01% CSF(X3) C [0+7.11%

810

Ya.P. Ivanov and T.Tz. Roshavelov

Vol. 23, No. 4

Conclusions The following conclusions has been drawn out from the results of the experiments:

1)Cement pastes, modified with CSF and SP display all known types of flow - from typical Bingham to defined pseudoplastic with a vivid yield value. It is shown that the great variety of flow curves is due to the specific role, which CSF plays on the formation of the primary aggregate structure of such systems. Characteristic feature of that system is its well defined tyxotropic behaviour in contrast to traditional cement pastes. 2)The rheological behaviour of cement pastes, modified with CSF and polymer additives depends on the investigated factors in the following succession: -for the yield value r 0 - X2 > X3 > X1 > X4 > X5 > X6 -for the apparent viscosity r/- X1 > X2 > X3 > X6 > X4 > X5 3)It is shown that the use of CSF is more efficient when using greater w/c ratios. 4)The efficiency of application of a superplastisizer has been demonstrated in every case when SCF is applied. Optimal dosages are also obtained. References 1. T.T.Roshavelov, Rheology and technological problems of modified cement composites, PhD Thesis, Bulg. Acad. of Scienses, Sofia, 1991,(in Bulgarian).

2. Ya.Ivanov and T.Roshavelov, The effect of condensed silica fume on the rheological behaviour of cement paste, In :Rheology of fresh cement and concrete, Edited by P.F.G.Banfill, Liverpool, 1990. 3. Ya.Ivanov and T.Roshavelov, Properties of disperse cement based systems, modified with polymer and active mineral additives. I. Influence of the components., Mag. ,,Technical thought", BAS, (1), 1992, (in Bulgarian). 4. K.Asaga and D.M.Roy, Rheological properties of cement mixes: IV.Effect of super plastisizer on viscosity and yield stress, Cem. Concr. Res., Vol.10, 2, 1980.