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Influence of cement type and admixtures on rheological properties of cement paste/Cheminiu imaisu poveikis reologinems cemento teslos savybems.

Introduction

The new generation of concrete is very sensitive to production conditions: ambient temperature, mixing parameters, water quality and others. Sometimes, efforts to produce a high quality product result in failure. For this reason, it is important to ensure the stability and characteristics of the mixture: to assess the effects of admixtures on the rheological properties of cement paste, select the composition of mixtures, which would assuredly regulate paste rheology control at nanostructural level and the formation of the initial cement hydration period. Using various modifiers, it is possible to achieve the desired characteristics of cement pastes (Ragaisyte et al. 2012).

Cement pastes are complex dispersion systems having considerable specific surfaces where complex time-related hydration reactions take place. The structure of such a system mainly depends on the water-to-cement ratio, ranging from 0.3 to 1.0, depending on the literature source (Gonet et al. 2004).

Cement paste is not a homogeneous fluid and is itself composed of particles (cement grains) in a liquid (water).

Because cement paste on a macroscopic scale flows as a liquid, equation as for liquid is applicable.

If a shear force is applied to a liquid, a velocity gradient is induced in the liquid. The proportionality factor between the force and the gradient is called viscosity.

Pastes rheological properties are influenced by the free water content in them (chemically or physically bound water is not affected). Over time, the water in the bound form is changing. The mineral matrix hydration leads to increase chemically and physically bound water content and a proportional decrease in the quantity of free water (Skripkiunas 2007).

At the beginning of the hydration process of cement paste and before the induction period (duration of the period amounts to 15-20 min), the cement particles are unchanged. At this early period of the solution saturated with [Na.sup.+], [K.sup.+], [Ca.sup.2+], O[H.sup.-], S[O.sub.2.sup.2-] ions, reactions between formed hydrates bear cement particles. Once the induction period starts, it lasts for several hours. In the supersaturated solution, portlandite (Ca[(OH).sub.2]) crystallizes and interaction between S[O.sub.4.sup.2-] ions and [C.sub.3]A as well as formed ettringite crystal whiskers film which slows the rapid coagulation of [C.sub.3]A structure formation and allows cement to bind at the right speed (>60 min). After the induction period, the crystallisation of calcium hydrate and accelerated hydration of alite results in a considerable growth of viscosity of the paste. The rheological properties of the cement paste gradually change with time (Eisinas, Baltakys 2009).

In recent years, the new generation of plasti-cizer admixtures--dispersants- deflocculant (polycar-boxylate esters PCE) are widely used to regulate the rheological properties of paste. As new deflocculant manufacturers and researchers (Hommer, Wutz 2005) explain PCE deflocculant, the polymer backbone and side chain lengths depends on the nano scale and size 3-20 nm (main chain) and 3-40 nm (side chains). In the system of water and cement they case a double effect of dispersion--the spatial and electrostatic (Fig. 1). Their use prevents the cement particles from sticking together, even when exposed to the original cement hydrates.

[FIGURE 1 OMITTED]

Polycarboxylate esters not only disperse the material, but also active in the cement hydration process--the first two periods of hydration of the cement paste remain plastic and buried, might be regulated by chemical and mineral admixtures (Puertas et al. 2005; Hanehara, Yamada 1999).

PCE was studied in two flocculants, possessing different structure (different lengths of the side chains), the effect of cement hydration process. Comparative cement paste deflocculant studies show (Hommer, Wutz 2005), that suspension without deflocculant hy-dration induction period lasts about 30 minutes (later to begin a massive hydrate deposition), and the suspensions deflocculant induction period lasts about 2-3 hours, depending on the side chain length. Some authors state that the cement hydration process depends of deflocculant side chains length--the longer are side chains, the shorter is time of cement hydration and the higher is early compressive strength (Hommer, Wutz 2005; Puertas et al. 2005).

Numerous methodologies can be used to determine rheological properties of cementitious paste. For this purpose, various viscometers could be used, which vary according to the mode of operation (Saak et al. 2001; Ferraris, Gaidis 1992). One of the most widespread cement paste rheological characterization techniques is based on the use of a rotational viscometer with coaxial cylinders.

Comparison of results obtained using different geometric parameters of rotational viscometer with coaxial cylinders indicated that geometric parameters of the viscometer affect the results on rheological properties of the cement paste that can be directly and quantitatively compared not by the plastic viscosity but by the relative viscosity of the plastic (Lapasin et al. 1983; Banfill 2003; Nehdi, Rahman 2004).

This work aims to investigate the effects of chemical admixtures on rheological properties of Portland cement paste and determine their impact on the effectiveness of hydration during induction period.

1. Materials used for research

The studies used cements produced the cement factory that meet the requirements of LST EN 197-1:2011, the characteristics given in Table 1.

Characteristics of MC-Bauchemie (Germany) chemical admixtures are shown in Table 2.

2. Research methodology

Portland cement paste was mixed according to LST EN 196-1:2005 requirements for dosing by weight of cement, and water and chemical admixtures by volume. Chemical admixtures, plasticizer and superplas-ticizer content in paste was constant--0.75% of the cement weight.

Normal consistency of Portland cement paste was determined by Vicat apparatus with the plunger according to LST EN 196-3.

Suttard viscometer was used to study the effect of plasticizer and superplasticizer on water and cement (W/C) ratio and their flow characteristics of Portland cement paste. Paste dispersion was measured in two perpendicular directions and the average measure was determined.

Investigate changes in viscosity of the same water-cement ratio (W/C = 0.33 to 0.34) of Portland cement paste with and without chemical admixtures. Paste viscosity was measured in 5 min, 15 min, 30 min, 45 min, 60 min, 90 min, 120 min since cement was mixed with water for 30 s at a constant velocity gradient (149 [s.sup.-1]). Experimental studies were carried out using a rotary viscometer Rheotest NH 4.1 with coaxial cylinders (Fig. 2).

[FIGURE 2 OMITTED]

3. Test results and discussion

3.1. Testing the plastification of Portland cement paste

The compositions of Portland cement pastes, used for investigation (amount per 1 [m.sup.3] of paste) are given in Table 3.

Compositions of paste with chemical admixtures and W/C ratio equal to spread- flow are given in Table0. 4 for pastes. The water content reduction due to the effect of the chemical admixtures in the identical spread-flow cement pastes (130 [+ or -] 10 mm) shown in Figure 3.

Figure 3 shows that the chemical admixtures in Portland cement paste can reduce required amount of water: plasticizer--5-6%, superplasticizer--24-30%. Comparing the influence of different chemical admixtures on Portland cement paste and paste flow characteristics, it was found that effective plasticizer Portland limestone CLN is more efficient than Portland cement paste CN or CR. Superplasticizer is effective for Portland cement paste CN and CR than for limestone Portland cement CNL.

3.2. Portland cement paste viscosity studies

Changes in viscosity of Portland cement paste describe changes in rheological properties of Portland paste -technological nature of deterioration during the hydra-tion process and the formation of hydration products.

Results of the impact on viscosity of chemical admixtures to Portland pastes CN, CR and CNL (in 5 min from the start of mixing the paste) are presented in Figure 4. It appears that initial viscosity values of the Portland cement paste without chemical admixtures are similar as well as the water-cement ratio (W/C = 0.33 to 0.34).

Viscosity of all Portland cement pastes with plas-ticisers CNP, CRP, CNLP decreases. Comparing the impact on the dynamic viscosity of Portland cement paste, the plasticiser reduces the viscosity by about 33% in CN and CR, CNL-- 17%. Thus, the plasticizer in Portland cement paste CN, CR reduces the viscosity by 50% more efficiently than the limestone Portland (CNL) paste.

Portland cement pastes with superplasticizer CNSP, CRSP and CNLSP demonstrated uniform viscosity reduction--viscosity of superplasticizer Portland cement paste CN, CR and CNL had greater efficiency of approx. 67-50% compared to a plasticizer such as Portland cement paste compositions.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

Viscosity results of Portland cement paste were statistically processed by a computer program Statistica. Statistical correlation and trends are evident by drawing the shape variables versus time scale used to assess the strength of the connection correlation coefficients (R) and coefficients of determination (R2).

Figures 5-7 are presented in a scatter plot, which shows the evolution of Portland cement paste with chemical admixtures and without viscosity over time.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

Figure 8. The chemical admixtures of Portland cement paste impact the effectiveness of the induction hydration period. It appears that effectiveness of some chemical admixtures is limited in duration.

Multiple regression analysis led to an equation of dependable variables, where x is time in minutes, correlation and determination coefficients (Table 5, Equations 1-3). Dependent variables in the equation can be used to calculate the viscosity of Portland cement paste with and without admixtures in known time.

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

Conclusions

1. Chemical admixtures enable the reduction in the amount of water needed for preparation of Portland cement pastes: respectively, plasticizer Centrament N3-- 5-6%, superplasticizer PowerFlow 3140-2430%, for pastes with the same flow.

2. Comparison of the impact on flow characteristics of chemical admixtures in Portland cement paste revealed that the plasticizer Centrament N3 is more efficient for limestone Portland cement (CLN) than CN or CR portlandcement pastes. Superplasticizer PowerFlow 3140 is more effective for Portland cement pastes CN and CR, than limestone Portland (CNL).

3. Viscosity of Portland cement paste can be controlled by chemical admixtures during all hydration induction period.

4. The equations obtained by regression analysis of the dependent variables can be used in the calculation of Portland cement paste viscosity, known as the time variable.

Caption: Fig. 1. Dual dispersion mechanism by PCE: electrostatic + steric repulsion = electrosteric repulsion (Hommer, Wutz 2005)

Caption: Fig. 2. Illustration of the rheometer used (shown with coaxial cylinders)

Caption: Fig. 3. The water content reduction due to the effect of the chemical admixtures in the identical spread-flow cement pastes (130 [+ or -] 10 mm)

Caption: Fig. 4. The impact of chemical admixtures on initial viscosity of Portland cement pastes

Caption: Fig. 5. Viscosity of common cement pastes without admixtures

Caption: Fig. 6. Change in viscosity of common cement pastes with plasticizer

Caption: Fig. 7. Change in viscosity of common cement pastes with superplasticizer

Caption: Fig. 8. The changes of effectiveness of chemical admixtures in cement pastes within the time span of two hours

http://dx.doi.org/ 10.3846/2029882X.2014.912431

Received 14 September 2013; accepted 19 December 2013

References

Banfill, P. F. G. 2003. The rheology of fresh cement and concrete--a review, in Proc 11th International Cement Chemistry Congress, May 2003, Durban, 1-13 p.

Eisinas, A.; Baltakys, K. 2009. Portlandito kiekio hidratuota-me portlandcemesntyje nustatymas vienalaikes termines analizes metodu, Chemine Technologija 1(50): 18-23.

Ferraris, Ch. F.; Gaidis, J. M. 1992. Connection between the rheology of concrete and rheology of cement paste, ACI Materials Journal 88(4): 388-393.

Gonet, A.; Stryczek, S.; Pinka, J. 2004. Analysis of rheological models of selected cement slurries, Acta Montanistica Slovaca 9(1): 16-20.

Hanehara, S.; Yamada K. 1999. Interaction between cement and chemical admixture from the point of cement hydration, absorption behavior of admixture, and paste rheology, Cement and Concrete Research 29(8): 1159-1165. http://dx.doi.org/10.1016/S0008-8846(99)00004-6

Hommer, H.; Wutz, K. 2005. Recent developments in deflocculats for castables, in 9th Biennial Worldwide Congress on Refractories, 8-11 November, 2005, Orlando, Florida, USA, 2-6.

Lapasin, R.; Papo, A.; Rajgelj, S. 1983. Flow behavior of fresh cement pastes. A comparison of different rheological instruments and techniques, Cement and Concrete Research 13(3): 349-356. http://dx.doi.org/10.1016/0008-8846(83)90034-0

Nehdi, M.; Rahman, M. A. 2004. Estimating rheological properties of cement pastes using various rheological models for different test geometry, gap and surface friction, Cement and Concrete Research 34(11): 1993-2007. http://dx.doi.org/10.1016/j.cemconres.2004.02.020

Puertas, F.; Santos, H.; Palacios, M.; Martinez-Ramirez, S. 2005. Polycarboxylate superplasticizer admixtures: effect on hydration, microstructure and rheological behaviour in cement pastes, Advances in Cement Research 17(2 (April)): 77-89. http://dx.doi.org/10.1680/adcr.2005.17.2.77

Ragaisyte, I.; Dauksys, M.; Klovas, A. 2012. Cheminiu priedu silanu pagrindu itaka cementinio akmens savybems, Statybines Konstrukcijos ir Technologijos-- Engineering Structures and Technologies 4(1): 29-36.

Saak, A. W.; Jennings, H. M.; Shah, S. P. 2001. The influence of wall slip on yield stress and viscoelastic measurements of cement paste, Cement and Concrete Research 31(2): 205-212. http://dx.doi.org/10.1016/S0008-8846(00)00440-3

Skripkiunas, G. 2007. Statybiniu konglomeratu struktura ir savybes. Kaunas: Vitae Litera. 334 p.

LST EN 196-1: 2005. Cemento bandymu metodai. 1 dalis. Stiprio nustatymas.

LST EN 197-1: 2011. Cementas. 1 dalis. Iprastiniu cementu sudetis, techniniai reikalavimai ir atitikties kriterijai.

LST EN 196-3: 2005. Cemento bandymu metodai. 3 dalis. Risi-mosi trukmiu ir turio pastovumo nustatymas.

Mindaugas Macijauskas, Albinas Gailius

Vilnius Gediminas Technical University, Sauletekio al. 11, 10223 Vilnius,

Lithuania

Corresponding author: A. Gailius E-mail: albinas.gailius@vgtu.lt

Mindaugas MACIJAUSKAS. MSc Student at the Department of Building Materials, Faculty of Civil Engineering, Vilnius Gediminas Technical University (VGTU), Lithuania. Research interests include theoretical and experimental investigations of structure and properties of building materials (binders, concrete, dry mixtures), durability, rheological properties, renewable resources in production of building materials in the context of sustainable development.

Albinas GAILIUS. Dr Prof. at the Department of Building Materials, Faculty of Civil Engineering, Vilnius Gediminas Technical University (VGTU), Lithuania. Research interests include materials science, theoretical and experimental investigations of structure and properties of building materials (binders, concrete, dry mixtures, heat insulation and acoustical materials), durability, rheological properties, quality assurance and control of composite materials, recycling and reuse of wastes, renewable resources in production of building materials in sustainable development context, modernization of buildings.
Table 1. Technical information on cements types
(AB "Akmen?s cementas")

Type of cement   Mark of   Compressive    The         Amount of
                 cement    strength       initial     [H.sub.2]O
                           after 7 and    and final   for
                           28 days, MPa   setting     normal
                                          time of     consistency
                                          cement      of cement
                                          paste,      paste, %
                                          min

CEM I 42,5 N     CN        25.5   55.0    120   175   25.9
CEM I 42,5 R     CR        28.9   54.6    150   200   26.0
CEM II/A-LL      CLN       23.7   51.1    190   285   25.4
  42,5 N

Type of cement   Fineness                   Loss on       Insoluble
                 Blaine,      >90           ignition, %   residue, %
                 [m.sup.2]/   [micro[m, %
                 kg

CEM I 42,5 N     327          2.7           1.32          0.29
CEM I 42,5 R     356          1.1           1.43          0.22
CEM II/A-LL      408          4.3           5.79          -
  42,5 N

Type of cement   S[O.sub.3],
                 %

CEM I 42,5 N     2.74
CEM I 42,5 R     3.10
CEM II/A-LL      2.69
  42,5 N

Table 2. Technical information on chemical admixtures

Name of the          Centrament N3       PowerFlow 3140
admixture

Type of the          Plasticizer         Superplasticizer
  admixture            on a basis of       on a basis of
                       lignosulphonate     polycarboxylate
                                           ester (PCE)
Mark of the                  P                  SP
  admixture
pH (20 [degrees]C)          6.0                 5-7
Density,                   1,17                1.07
  kg/[dm.sup.3]
Max. amount                <0.10               <0.10
  of chlorides, %
Conc. of                    50                  30
  active
  material
  in
  solution, %

Table 3. Compositions of cement pastes, kg/[m.sup.3]

Mark of the cement paste   CN                 CR

Mark of the admixtures     ---    P      SP   ---    P      SP
Cement, kg                 485       485      485       485
Watter, kg                 166       166      166       166
Chemical admixtures, kg    ---       3.64     ---      3.64
W/C                        0.34               0.34

Mark of the cement paste   CNL

Mark of the admixtures     ---    P      SP
Cement, kg                 493       493
Watter, kg                 164       164
Chemical admixtures, kg    ---      3.70
W/C                        0.33

Table 4. The influence of cement type and chemical admixtures on
W/C ratio in the identical spread-flow cement pastes

Mark of the    CN     CNP    CNSP   CR     CRP    CRSP   CLN
  specimen *

W/C            0.34   0.32   0.24   0.34   0.33   0.24   0.33
Flow, mm       130 [+ or -] 10

Mark of the    CLNP   CLNSP
  specimen *

W/C            0.31   0.25
Flow, mm       130 [+ or -] 10

* Mark of the specimen consists of mark of cement paste and of
admixture.

Table 5. Empirical equations and coefficients of correlation and
determination on cement pastes with and without chemical admixture

Pastes\           Without           With              With
Parameters        chemical          plasticizer       superplasticizer
                  admixtures
                  1                 2                 3

Empirical         y = 1.1926-exp    y = 1.0198-exp    y = 0.365-exp
  equations         (0,0085-x)        (0,0109-x)        (0,0129-x)
  (where
  x--time in
  minutes;
  y--viscosity)
Coefficients of   0.986             0.995             0.93
  correlation
Coefficients of   0.9725            0.9901            0.8649
  determination
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Author:Macijauskas, Mindaugas; Gailius, Albinas
Publication:Engineering Structures and Technologies
Article Type:Report
Date:Dec 1, 2013
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