or limestone filler using Mixture Design of Experiments

Construction and Building Materials 143 (2017) 92–103

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Rheological study of cement paste with metakaolin and/or limestone filler using Mixture Design of Experiments Fabiano Nazário Santos a, Sara Raquel Gomes de Sousa b, Antonio José Faria Bombard b,⇑, Sheila Lopes Vieira c a

Natural Resources Institute (Instituto de Recursos Naturais – IRN), Federal University of Itajubá (Universidade Federal de Itajubá – UNIFEI), Itajubá, MG, Brazil Physics and Chemistry Institute (Instituto de Física e Química – IFQ), Federal University of Itajubá (Universidade Federal de Itajubá – UNIFEI), Itajubá, MG, Brazil c Durham, NC, USA b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Metakaolin acts as a thixotropic

additive when a superplasticizer is used in cement paste.
Limestone filler does not interfere with the viscosity or plasticity of the paste with superplasticizer admixture.
The ideal metakaolin content depends on the paste desired viscosity, thixotropy and workability.
The use of up to 5–10% metakaolin improve the compressive strength after 7 days.

a r t i c l e

i n f o

Article history: Received 27 October 2016 Received in revised form 27 February 2017 Accepted 1 March 2017

Keywords: Rheology Cement paste Metakaolin Limestone filler Mixture design

a b s t r a c t Several cement pastes with different amounts of metakaolin (MK) and/or limestone filler (LF) were prepared. The water/cementitious materials ratio was maintained constant at 0.3, with addition of 0.5% wt/ wt of poly-carboxylate ether (PCE) superplasticizer admixture. The following parameters of the fresh cement pastes were evaluated: the slump and spread, the Marsh funnel time, the plastic viscosity, yield stress, viscoelastic properties and thixotropy. After the curing of 7 day old pastes, compressive strength tests were performed according to the Brazilian standard using 50  100 mm cylinder specimens. We conclude that LF alone is not able to avoid segregation or bleeding, and there is no difference between cement pastes mixed with LF and pure OPC pastes, in terms of rheology. On the other hand, if one needs low slump and low spread, the use of MK is recommended because this material creates a strong, thixotropic interconnected net inside of the paste, increasing the yield stress and the thixotropy of the cement paste. By adding 5–10% wt/wt MK, the average increase of compressive strength is approximately 45% at 7 days, compared to the control (only OPC, water and PCE). The maximum recommended amount of LF or MK substitution in our case was 10% wt. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction The use of superplasticizer (SP) additives (also known as water reducers) in civil construction has increased in recent years, ⇑ Corresponding author. E-mail address: [email protected] (A. José Faria Bombard). http://dx.doi.org/10.1016/j.conbuildmat.2017.03.001 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

especially in large-sized works or the ones that require the use of special concretes, such as self-compacting concrete or high performance concrete, among others [1,2]. Poly-carboxylate ether (PCE) is among the additives that has superior performance in terms of viscosity reduction compared to common plasticizers, such as lignosulfonates and naphthalenesulfonates [3]. On the other hand, if poly-carboxylate ether is very effective in reducing cement paste

F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103

viscosity, extra caution with additive overdose is a must. For instance, a dose of 1 wt.% of water reducing admixture to the cement leads to cement particle segregation, with cement powder settling very fast and causing phase separation with a layer containing Portland cement (precipitate) at the bottom of the recipient and a supernatant containing a lot of water and finer cement particles. Another negative effect of poly-carboxylate ether overdose is the loss of thixotropy (and consequently the workability) of the paste. Siddique & Khan [4], describe that the use of supplementary cementitious materials (SCM), such as blast furnace slag, fly ashes, microsilica, metakaolin, limestone filler, rice husk ashes, among others, is increasingly growing. The use of such materials may be advantageous not only by the reduction of economic and environmental costs of Portland cement manufacturing but also because it can greatly increase the final performance of structures, such as compressive strength. In addition, some materials may help solving issues of segregation and workability loss caused by superplasticizers overdose. Martins & Bombard [5], showed that the use of nanosilica in combination with adequate doses of polycarboxylate ether allows the acquisition of a relatively low apparent (plastic) viscosity without workability loss (it maintains the yield stress and thixotropy of the paste). Pera [6], reports that the first documented use of metakaolin in a large-scale work was in the construction of the Jupiá Dam in 1962. Antoni et al. [7], assessed the replacement of part of a Portland cement segment with a combination of metakaolin and limestone filler, resulting in ‘‘45% of substitution by 30% of metakaolin and 15% of limestone gives better mechanical properties than 100% OPC”. In addition to that, they argue that ‘‘stoichiometric formation of monocarboaluminate hydrate (MC). . . corresponds to an addition with a weight ratio of 2:1 metakaolin:limestone.” But the authors did not study the rheology of mixtures. A partial literature revision about rheological aspects of cement pastes with supplementary cementitious materials follows. Cyr et al. [8], investigated the shear thickening effect of superplasticizers on the rheological behavior of cement pastes containing or not mineral additives. They compare the effect of: metakaolin (MK), quartz (Qtz), fly ash (MFA) or silica fumes (SF). Their superplasticizers (SP) included five different types, but without any detail about the chemistry of each SP. These authors studied three substitution amounts of Portland cement by the four supplementary cementitious materials (SCM) above: 0% (only cement), 10% or 25%.They concluded that in terms of shear thickening effect ‘‘can be amplified (metakaolin), unchanged (quartz, fly ashes) or reduced (silica fumes)”. Provis et al. [9], studied ‘‘the role of particle shape” (morphology) of some SCM: ‘‘spherical particles of fly ash”, ‘‘platy particles of metakaolin”, and the ‘‘angular particles of blast furnace slag”, ‘‘both in the context of its effect on paste rheology and on water demand”. The authors focused their report on particle shape effects in fresh pastes, particle packing and mix design in geopolymer pastes and geopolymer concretes. However, they did not mention any water reducer, plastifier or superplastifier. Banfill and Frias studied the rheology of blends cement with metakaolin or cement with paper sludge wastes, calcined at 700 °C by 2 h [10]. The authors employed a sulfonated naphthalene formaldehyde condensate as superplasticizer. They concluded that ‘‘the use of low concentrations of calcined paper sludge as a supplementary cementitious material. . . offers a route for utilising this waste material, as an alternative to the. . . environmental burden associated with the production of metakaolin from natural kaolinite resources.” Moulin, et al. reported about the effects of ‘‘OPC blended with 30% (by weight of blend) calcined clay and its rheology. However, they also did not use any superplasticizer [11]. Poulesquen et al. studied the rheology of geopolymers prepared with metakaolin, fumed silice and ‘‘Waterglass activating solutions”,

93

but they did not employ Portland cement, neither any superplasticizer [12]. Janotka et al., investigated in deep the rheology, compressive strength, isothermal calorimetry and setting time of mixtures of Portland cement with ‘‘metakaolin sands”, a type of SCM that was not pure metakaolin [13]. Their water/cement ratio was 0.5, without addition of any water reducer plasticizer. They concluded: ‘‘. . .the presence of the metakaolin sands reduces the heat released during the hydration process with respect to non-blendedcement pastes. The incorporation of metakaolin sand induces a decrease of the mechanical strength, with the decrease being higher as the metakaolin sand content increases even though they also produce a refinement in the pore structure and a decrease of the permeability”. Sonebi et al. made an ‘‘Optimization of rheological parameters and mechanical properties of superplasticized cement grouts containing metakaolin and viscosity modifying admixture”, employing ‘‘Central composite experimental design (CCED)”, a statistical tool. They employed the same type of superplasticizer we are studying, PCE. However, they stated: ‘‘The viscosity of cement grout was determined using a coaxial rotating cylinder viscometer Fann (smooth cylinders, no serration).” Therefore, slippage could have occurred during their measurements [14]. Vance et al. published a paper with the exact same materials that we are studying. The title of their paper is: ‘‘The rheological properties of ternary binders containing Portland cement, limestone, and metakaolin or fly ash” [15]. However, different from us, they also did not employ any water reducer admixture. Besides this, in their study, the water-to-solid ratio (w/s) mass/mass were 0.40 and/or 0.45. In our study, with the use of PCE SP, we prepared pastes with fixed water/solids (w/s) ratio = 0.30. Favier et al., compared the rheological properties of a geopolymer paste prepared mixing metakaolin with sodium silicate solution (water glass) versus cement paste. But not blends of OPC + MK [16]. More recently, Vance et al. compared the rheology of suspensions (pastes) prepared with ‘‘interground Portland limestone cements”  ‘‘three blended limestone cements” They described a ratio w/s = 0.45 and again, without any superplasticizer [17]. Shahriar and Nehdi reported blends of special cement (oil well API Class G OWC) mixed with four types of SCMs: MK, SF, (rice husk ashes) RHA, and low calcium FA, with replacement ranging from 5 to 15%. They also employed a polycarboxylate-based high-range water reducing admixture, but with water-to-binder mass ratio (w/b) of 0.44, which is the usual w/b recommended for oil well cement formulations. In their study, they used Design of Experiments too. [18]. For the reader interested in reviewing the significant literature on the rheology of cement pastes, as well as hundreds of scientific papers published after 2001, the classical books by Tattersal [19] and Banfill [20] are advised. Metakaolin is a material with high pozzolanic activity. In addition to being advantageous economically and environmentally, it has the effect of improving mechanical resistance, as compressive strength, since keeping low amount substitution of OPC by MK (10%) by such way the hydration heat is similar to 100% OPC [21]. Limestone filler addition to cement accelerates hydration of Portland clinker grains at early ages, improves the particle packing, can increase the hydration rate from 1 day to 3 months and produces the formation of calcium carbo-aluminates (hemicarboaluminate or monocarboaluminate), as a result of the reaction between CaCO3 and C3A of Portland clinker or metakaolin (in case of ternary blends) [22]. However, if partial substitution of OPC by LF can be advantageous (same reasons as MK: economic and environmental aspects), the formation of carbo-aluminates is a drawback, in the case of a sulfate and chloride environment. [23]. Around one hundred papers can be found reporting mixtures of ‘‘limestone AND cement AND metakaolin”. However, very few [15,17,22,24–27], focus on the rheological properties of ternary blends of these three cementitious materials. Most of these works,

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the authors focused on self-compacted concrete. This motivated us to study the rheology of cement pastes (Portland cement containing blast furnace slag) blended with metakaolin and/or limestone filler as additive, using experiment designs for mixtures. The pastes were prepared with different amounts of metakaolin and/or limestone filler so that the water/cementitious materials ratio was maintained constant and equal to 0.3 and 0.5 wt.% superplasticizer (poly-carboxylate ether type) added to all the pastes. The statistical approach of using experiment design is a powerful tool in the optimization of mixtures when dealing with multivariables. In the present study, we choose to use the design of experiment with mixtures [28,29].

H n O

H

-

O + Na

O O

O p

H

m

Fig. 1. Chemical structure of poly(sodium carboxylate)-graft-poly(oxy-ethylene) – PCE – hyper-plasticizer or ‘‘high range water reducer”.

2. Experiment 2.1. Materials For this study, ordinary Portland cement class CP II E 32, limestone filler (LF) of 97.6% calcium carbonate (CaCO3) purity, metakaolin (MK) and tap water (w) were used. The chemical composition and other properties of all the cementitious components used can be seen in Table 1. Hyper-plasticizer (SP) (poly-carboxylate ether, provided by BASF, Fig. 1) is differentiated from conventional superplasticizer in that it is based in a unique carboxylate co-polymer with long lateral (graft) poly(ethylene-oxide) chains. This greatly improves cement dispersion [2,3]. 2.1.1. Material characterization The materials were characterized to confirm the composition, structure and size of the particles. A FTIR spectrophotometer Perkin Elmer, model Spectrum 100 was used to confirm the composition and structure of the superplasticizer (poly-carboxylate ether – PCE) and results can be seen in Fig. 2. The spectrum (as well as their peak assignment) is in qualitative agreement with the reported by Andersson et al. [30]. The average molecular masses were measured by Gel Permeation Chromatography (GPC Shimadzu, model Prominence, equipped with refractive index differential detector RID-10A, columns Phenogel 5l 10,000–1,000,000). The GPC was calibrated with PEO polymer standards of molar mass known. The sample of PCE was diluted in distilled water. We obtained Mn = 18,831 and Mw = 40,052 g/mol. These values are in reasonable qualitative agreement with the literature (Mn = 12,148 and Mw = 22,174 g/mol). [30]. Table 1 Chemical analysis of Portland cement type II (OPC), metakaolin (MK) and limestone filler (LF) Analysis

OPC

MK

LF

SiO2 (wt.%) CaO (wt.%)

23.52 56.54

1.6 53

Fe2O3 (wt.%) Al2O3 (wt.%( Na2O Alkaline equivalent (wt.%) MgO (wt.%) SO3 (wt.%) TiO2 (wt.%) P2O5 (wt.%) Mn2O3 (wt.%) Loss on ignition (wt.%) Specific gravity S.S. Blaine BET Area (m2/g) Pozzolanic activity (Chapelle test) Residue # 200 (wt.%)

3.84 6.52 0.70 1.56 1.68 – 0.29 0.80 5.10 3.09 3820 cm2/g – – 3.4

57 <0.1 (CaO + MgO) 2 34 <1.5 <0.1 <0.1 1.5 – – 3 2.56 – 23 0.88 g Ca(OH)2 /g 1.2

<0.1 1.4 0.19 0.43 <0.1 – – – 44 2.60 – – – <1

Fig. 3 shows the particle size distribution (PSD) cumulative plots of PC, MK and LF particles. Measurements of each powder dispersed in Isopropyl alcohol as liquid carriers were made in Malvern Mastersizer 2000 using laser DLS, according Ferraris et al. [31]. The refraction indices nD of the materials are: LF = 1.60; PC = 1.73 and MK = 1.62. 2.2. Mixtures All blends were prepared in the same manner, following the recommendations of the standard API 10B (American Petroleum Institute), Appendix A [32]. For the production of all cement paste mixtures, varying the proportions of limestone and metakaolin (0%–20%), the mixture proportions is shown in Table 2. Ratio water/cementitious materials was kept fixed = 0.3 and the amount of SP (0.5% wt./wt.) was also the same all blends. The motivation for the choice of the mix proportions using metakaolin was selected based on works by three different groups: a) A study by Ambroise, Maximilien and Pera. The authors studied mixes prepared with only Portland cement and metakaolin, without any limestone, with MK contents: 0, 10, 20, 30, 40 and 50% replacement. They did not report the use of any water reducer admixture to prepare their pastes. Additionally, ‘‘the water:solid ratio (W:S) was not constant; the water added was adjusted to a constant consistency.” They concluded: ‘‘At up to 30% replacement, MK acts as an accelerating agent, the pore size distribution is displaced toward small values, the CH (calcium hydroxide) content is considerably reduced, and compressive strengths are not affected.” However, they showed in their paper, that maximum compressive strength was obtained with 10% MK replacement. There was an improvement in strength, compared to control (100% OPC), with 10% MK. With 20% MK replacement, the compressive is practically the same of pre OPC. With 30% MK and above, the strength was reduced compared to control, decreasing the strength with MK replacement. Therefore, we chose to test 20% MK (or LF) maximum replacement [33]. b) Helal (2002) studied five cement–limestone blends, using 0%, 5%, 10%, 15%, and 20% of limestone as a partial substituent of Portland cement, and the cement pastes were prepared using the standard water of consistency of 0.255, 0.255, 0.258, 0.261, and 0.263, respectively. There was no significant gain in compressive strength compared to 100% OPC [34]. c) Antoni et al. (2012) studied ‘‘Cement substitution by a combination of metakaolin and limestone” and they concluded: ‘‘TGA (Thermogravimetric Analysis) shows that the reactions

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100

T (%)

1572

60

1466

3410

80

2881

961

40

20

841,9

1342,8

FTIR with ATR of PCE admixture 1101,7

(sample dried vacuum oven 80°C)

4000

3500

3000

2500

2000

wavenumber

1500

1000

500

(cm-1)

Fig. 2. FTIR spectrum of hyper-plasticizer poly-carboxylate ether.

Fig. 3. Cumulative size distribution of Portland cement powder, metakaolin and limestone filler, measured by laser Dynamic Light Scattering, employing isopropyl alcohol as carrier liquid.

of metakaolin and limestone consume calcium hydroxide, which may be completely absent in blends with high levels of substitution at late ages. The metakaolin appears to react faster in the system with limestone than in the binary metakaolin/Portland cement blend. Also, the limestone reacts faster in the system with metakaolin than in the binary limestone/Portland cement blend. These results point to strong synergistic effects with coupled substitutions of this type. Of course the consumption of calcium hydroxide could mean that the high substitution level blends may carbonate more rapidly. This and other aspects of durability are currently being studied.” [7]. Therefore, based on these previous studies, we choose, with help of Mixture Design of Experiments [28,29], to investigate

blends binary or ternary with OPC, MK and LF, with maximum 20% replacement SCM. 2.3. Methods The flow time of each fresh paste was measured with the Marsh funnel making it possible to measure the viscosity following the ASTM D6910 [35,36]. Part of the paste was separated (400 ml) to perform the rheological measurements using stress-controlled rheometer (Physica MCR-301, Anton Paar, Germany) equipped with the measuring system (a stirrer with two hollow vanes, model ST59-2V-44.3/120). The measuring rotor dimensions are: outer diameter 59.00 mm, and length 44.3 mm. The cup of the rheometer have inner diameter 70 mm, and a basket inset cage with serrations inside which prevents wall slippage. Fig. 4 shows the stirrer.

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F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103

Table 2 Proportions of Portland cement, limestone and metakaolin. Portlant cement (%)

Metakaolin (%)

Limestone (%)

100 90 90 95 95 90 93.33 96.66 91.66 91.66 93.33 93.33 93.33 93.33 80 80 80 86.66 96.66

0 10 0 5 0 5 3.33 1.67 6.67 1.67 3.33 3.33 3.33 3.33 20 0 10 6.67 1.67

0 0 10 0 5 5 3.33 1.67 1.67 6.67 3.33 3.33 3.33 3.33 0 20 10 6.67 1.67

All the rheological parameters, and their units followed the recommendations of standard ASTM C1749-12: ‘‘Standard guide for measurement of the rheological properties of hydraulic cementitious paste using a rotational rheometer” [37]. With this, the following rheological tests were possible: Flow curve (up-hold-down 3 intervals), with temperature kept constant at 25 °C. 1st interval: up-ramp of shear rate c_ initial 0.01–100 s1, during 205 s. 2nd interval: hold shear rate c_ constant of 100 s1 during 50 s. 3rd interval: down-ramp of shear rate c_ initial 100–0.01 s1, during 205 s. Thixotropy (three interval time test) [38] – performed at constant temperature 25 °C. First, using shear rate c_ constant of 0.1 s1 during 60 s Then, shear rate c_ constant of 100 s1 during 50 s Finally, shear rate c_ constant of 0.1 s1 during 250 s

Amplitude sweep ramp of strain c from 0.01% to 100% with slope 6pt./dec, oscillation frequency 10 rad/s and temperature = 25 °C. Frequency sweep (keeping the strain c = 0.02% constant and ramp angular frequency from 500 rad/s to 0.05 rad/s with slope 5pt./decade, and temperature 25 °C. The rheological measurements were performed satisfactorily during all of the tests and samples did not present any segregation or slippage of the pastes, due to the use of the appropriate method and equipment (cup with inner serrated cage and two vane rotor). The deformation capacity of the cement paste was verified from the slump flow type test, modified according Roussel and Coussot [39]. The slump flow test was performed using a square glass plate with an 80 cm edge. A mold was placed in the center of the glass plate, then added to the paste inside the cylindrical mold with dimensions ø 96.8 mm  100.8 mm. Thereafter, the mold was lifted vertically so that the cement paste flowed until it reached an equilibrium. After that, the cement paste spreading value was measured, using the average of two perpendicular diameters. At the same time, we obtained the slump values (when no spreading occurs), taking into account the other authors’ essay [39]. For the compression test, sample test specimens were produced following the Brazilian standard NBR 7215 [40]. This standard describes the method for the determination of the compressive strength of cylindrical specimens measuring 50 mm in diameter and 100 mm in height. When demolded, the specimens were placed in a tank containing water saturated with lime for the cure until the date of its rupture, at 7 days (or 28 days). At the date of their rupture, the specimens were removed from the tank and capped with a thin layer of cement paste in order to regularize their surfaces. The ruptures were made in a press with capacity for 100 metric tons, from the manufacturer TIME Testing Machines, model WAW – 1000 C (China). This press is controlled by computer and is of the universal type, with control Servo electrohydraulic. For the rupture of the ø 50 mm  100 mm specimens, a ‘‘RILEM” device (an adapter of the testing compression machine, equipped with two steel bearing blocks with hardened faces, used to better centralize the specimens and distribute equally the force applied, according note 3 of the ASTM C39/C39-14), was employed [41].

Compressive strength 7 days (MPa)

70

LF MK

60 50 40 30 20 10 0 0

5

10

15

20

25

SCM substitution (%)

Fig. 4. Stirrer with two hollow vanes, model ST59-2V-44.3/120 (Anton Paar, Germany).

Fig. 5. Compressive strength after 7 days for binary blends of Portland cement with supplementary cementitious materials: OPC + MK or OPC + LF. Columns heights are the average value for 3 test specimens rupture. Error bars are the standard deviation.

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F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103 Table 3 Compressive strength after 7-day cure. CP (%)

MK (%)

FC (%)

R1 (MPa)

R2 (MPa)

R3 (MPa)

Mean (MPa)

Std Dev

100.000 96.667 95.000 95.000 93.333 91.667 91.667 90.000 90.000 90.000 93.333 93.333 93.333 93.333 96.667 80.000 80.000 80.000 86.667 90.000 90.000

0.0000 1.6667 5.0000 0.0000 3.3333 6.6667 1.6667 10.0000 0.0000 5.0000 3.3333 3.3333 3.3333 3.3333 1.6667 20.0000 0.0000 10.0000 6.6667 0.0000 10.0000

0.0000 1.6667 0.0000 5.0000 3.3333 1.6667 6.6667 0.0000 10.0000 5.0000 3.3333 3.3333 3.3333 3.3333 1.6667 0.0000 20.0000 10.0000 6.6667 10.0000 0.0000

33.14 61.00 56.27 36.53 40.60 40.75 54.92 56.00 51.38 56.00 41.44 43.76 38.00 41.95 38.44 39.28 48.17 47.00 45.00 52.00 58.41

30.79 49.00 51.00 53.87 40.65 40.75 42.83 50.00 40.90 46.00 42.30 42.43 40.57 39.76 38.66 44.09 43.53 46.89 43.00 50.99 53.44

50.40 54.00 59.00 44.91 40.45 40.47 27.63 48.00 43.00 61.00 40.00 41.00 41.00 39.02 42.53 35.00 40.35 46.00 33.00 39.00 57.84

38.11 54.67 55.42 45.10 40.57 40.66 41.79 51.33 45.09 54.33 41.25 42.40 39.86 40.24 39.88 39.46 44.02 46.63 40.33 47.33 56.56

10.71 6.03 4.07 8.67 0.10 0.16 13.67 4.16 5.54 7.64 1.16 1.38 1.62 1.54 2.30 4.55 3.93 0.55 6.43 7.23 2.72

3. Results and discussion

3.2. Slump, spreading and Marsh funnel time

3.1. Compressive strength after one week

The spreading and the slump of each paste was measured in the same test. Next, the time flow of each paste was measured using the Marsh funnel. Table 4 summarizes the results for all tested pastes. In some cases, it was not possible to measure all of these 3 responses. Fig. 6 shows the effect of the increase of metakaolin content as a function of the spreading (left axis) and the funnel time (right axis). The dotted line in Fig. 6 at 100 mm represents the spreading threshold because this value is the internal diameter of modified frustum. Therefore, spreadings smaller than 100 mm do not make sense in the test. The curves are only a guideline for the eyes. The paste with 10% of metakaolin (or more) does not flow inside the Marsh funnel.

As our focus was on the rheology of the fresh mixtures, compressive strength was only measured with 7 days curing time. Fig. 5 shows the results for binary blends. The results for all of the mixtures are in Table 3. One can see in Fig. 5 that the maximum strength in our formulations seems to be around 5% wt. substitution of Portland cement. Above 10% wt. MK, the strength start decreases. Besides, the paste with 20% wt. substitution OPC by MK, was impossible to measure in the rheometer, because the maximum torque limit of the instrument. In other words: the paste OPC:MK 80:20 was so plastic that its workability is bad. Even mixing this particular blend was difficult. Therefore, we focused the study on involving mixtures and statistical analysis in the range 0–10% wt. substitution OPC by SCM. The compressive strength of the pastes did not present great changes compared to the control paste (only cement). However, in the case that cement was replaced with 5% of metakaolin, the compressive strength had a 45% average increase.

3.3. Yield stress measured by means of oscillatory amplitude sweep The yield stress can be experimentally measured in different ways. However, the result strongly depends on the measurement technique. One of them is the strain amplitude sweep test,

Table 4 Slump, spreading and Marsh funnel time for the tested pastes.

*

Portland cement (%)

Metakaolin (%)

Limestone filler (%)

Slump (mm)

Spreading (mm)

Marsh Funnel (seconds)

100 90 90 95 95 90 93.33 96.66 91.66 91.66 93.33 93.33 93.33 93.33 80 80 80 86.66 96.66

0 10 0 5 0 5 3.33 1.66 6.66 1.66 3.33 3.33 3.33 3.33 20 0 10 6.66 1.66

0 0 10 0 5 5 3.33 1.66 1.66 6.66 3.33 3.33 3.33 3.33 0 20 10 6.66 1.66

*

602

31.41

35

*

*

*

615 405 604 415 462 530 324 575 491 540 511 526

44.78 112.54 45.53 77.35 58.44 51.03 139.56 45.16 48.03 47.38 49.63 48.37

Asterisk indicates that it was not possible to measure slump/spreading/time.

* * * * * * * * * * *

11

*

*

*

538

71.76

20 50

*

*

*

*

*

562

42.88

F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103

700

160

600

140

500

120

400

100

300

80

200

60

Marsh Funnel Time (sec)

Spread (mm)

98

40

100 Spread >/= 100 mm

20

0 0

2

4

6

8

10

Metakaolin amount (%) Fig. 6. Effect of metakaolin content on the spreading of the pastes (left axis) and on the Marsh funnel time (right axis).

performed in a controlled-stress (or strain) oscillatory rheometer. In this case, an increasing logarithmic strain ramp is applied to the sample to be analyzed. Although the strain, which varied from 0.01 to 100%, is in fact the independent variable, a plot of the elastic modulus (or complex viscosity) can be built as a function of the applied shear stress. It is considered that the sample underwent plastic deformation (it flowed) where the function G0 = f (r) has a point of inflection. Thus, the yield stress can be easily obtained for each paste if the necessary torque is not greater than the maximum torque of the rheometer, which is 200 mN-m. As an example, Fig. 7 shows G0 (elastic modulus) curves as a function of the applied shear stress for the control paste (Portland cement, water and PCE) and the other pastes. More details explaining how the yield stress and complex viscosity values were measured can be found in reference [5]. Fig. 7 shows that increasing the metakaolin content will considerably increase the pastes’ yield stress and the G0 value. For example, the yield stress is approximately 1 Pa for pastes with 10% filler

Fig. 8. Mixture contour plot (component amounts) of yield stress measured in oscillatory mode. PC = Portland Cement, MK = Metakaolin, LF = limestone filler.

and for the control. As metakaolin is added to the sample, the yield stress shows values of 3 Pa for the sample containing 5% metakaolin, and values between 20 and 30 Pa for the sample containing 10% filler. On the other hand, the use of limestone filler (at least up to 10%) does not change the yield stress considerably when compared to the control. The yield stress results for mixtures with maximum 10 wt% substitution were analyzed with help of Minitab software (DOE Mixtures) considering pseudo-components instead component amounts. The results were fitted with a Full Cubic Model, excluding those terms, which inflate the variance. Fig. 8 shows the contour plot of the full cubic model for the yield stress, which was obtained using mixture design data analysis. Tables 5 and 6 resumes the Regression analysis for yield stress of the mixtures: Yield VA versus PC; MK; LF. The metakaolin coefficient value of 28.93 in Table 5 confirms that this additive contributes to the increase of the yield stress much more than the cement itself or the limestone filler. A full cubic model (R2 adj. = 99.55%), is much more complex than other, simpler multilinear regression models (linear, quadratic, special cubic), that were also tested. But the best fitting, with acceptable ‘‘lack-of-fit” value was reached only with a full cubic model. For the linear model, standard errors were larger than corresponding coefficient’s. Quadratic or special cubic models works better than linear model. However, these models resulted with lack-of-fit, and thus, we choose the full cubic model for yield stress.

3.4. Complex viscosity of pastes measured using oscillatory frequency sweep test

Fig. 7. Elastic modulus (G0 ) as a function of the shear stress (r) for the following pastes: 10% of filler (blue triangles); control (black line); 5% metakaolin + 5% filler (green circles) and 10% metakaolin (red squares). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

In this case, an under fixed and constant strain value of 0.02% (within the linear viscoelastic region), a decreasing logarithmic frequency sweep from 500 to 0.08 rad/s, is applied to the samples and the following parameters are measured: viscoelastic moduli (G0 and G0 ) and complex viscosity (g⁄). Fig. 9 shows the complex viscosity obtained for some pastes and Table 7 summarizes the values obtained for G0 , G0 and g⁄ (measured using frequency sweep tests at an angular frequency of x = 5 rad/s) for all pastes.

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F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103 Table 5 Estimated regression coefficients for Yield VA (pseudo-components). Term

Coef

SE Coef

T

P

VIF

PC MK LF PC * MK MK * LF PC * MK * LF PC * MK * () MK * LF * () S = 0.498610 R-Sq = 99.79%

1.19 28.93 0.89 48.81 50.21 51.24 27.72 25.32

0.4516 0.4968 0.4516 2.4044 2.4044 10.6317 8.0912 8.0912

* * * 20.30 20.88 4.82 3.43 3.13 PRESS = 159.549

* * * 0.000 0.000 0.003 0.014 0.020

2.097 2.537 2.097 3.481 3.481 3.586 1.625 1.625

R-Sq(pred) = 77.63%

R-Sq(adj) = 99.55%

Table 6 Analysis of variance for yield VA (pseudo-components). Source

DF

Seq SS

Adj SS

Adj MS

F

P

Regression Linear Quadratic PC * MK MK * LF Special Cubic PC * MK * LF Full cubic PC * MK * () MK * LF * () Residual error Lack-of-fit Pure error Total

7 2 2 1 1 1 1 2 1 1 6 2 4 13

711.603 437.694 256.392 139.621 116.770 6.746 6.746 10.772 8.337 2.434 1.492 0.720 0.772 713.095

711.603 583.813 184.979 102.442 108.403 5.774 5.774 10.772 2.918 2.434 1.492 0.720 0.772

101.658 291.907 92.490 102.442 108.403 5.774 5.774 5.386 2.918 2.434 0.249 0.360 0.193

408.90 1174.15 372.02 412.05 436.03 23.22 23.22 21.66 11.74 9.79

0.000 0.000 0.000 0.000 0.000 0.003 0.003 0.002 0014 0020

1.86

0.268

10000

PC-MK-LF (%) 100-00-00 90-3.3-6.7 95-05-00 91.6-6.7-1.7 90-10-00

Metakaolin effect

1000

Complex viscosity (Pa.s)

100 10 1

10000

PC-MK-LF (%) 100-00-00 93-3.3-3.3 95-00-05 90-3.3-6.7 90-00-10

Filler effect

1000 100 10 1 0,1

1

10

100

1000

Angular frequency (rad/s) Fig. 9. Complex viscosity as a function of angular frequency for control pastes containing 3.3, 5, 6.7, and 10% metakaolin or limestone filler. This test was performed in oscillatory mode at constant strain of 0.02%.

Fig. 9 shows that metakaolin contents above 3.3% lead to an increase of complex viscosity throughout entire analyzed frequency range and that the pastes exhibited a pseudo plastic behavior. On the other hand, the limestone filler did not cause any change in viscosity, except for the region above 100 rad/s, where shear-thickening is observed. The shear-thickening behavior increased with filler content increase when no metakaolin was added.

All the values measured of viscoelastic moduli G0 and G00 , as well as the complex viscosity, are summarized in the Table 7. 3.5. Thixotropy of fresh pastes measured using ‘‘3 ITT” test A three-interval of time test was used to obtain and evaluate thixotropy (even if only for comparison) between the different cement pastes formulations. According to MEZGER (2011), this test

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F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103

Table 7 Elastic and viscous moduli (G0 e G00 ) and complex viscosity of pastes measured in frequency sweep tests. Metakaolin (%)

Limestone filler (%)

G’ (Pa)

G” (Pa)

g* (Pa.s)

100 90 90 95 95 90 93.33 96.66 91.66 91.66 93.33 93.33 93.33 93.33 80 80 80 86.66 96.66

0 10 0 5 0 5 3.33 1.66 6.66 1.66 3.33 3.33 3.33 3.33 20 0 10 6.66 1.66

0 0 10 0 5 5 3.33 1.66 1.66 6.66 3.33 3.33 3.33 3.33 0 20 10 6.66 1.66

36 790 47 67 33 68 64 42 122 38 35 29 38 37

7.3 83 8.8 8.3 5.8 8.2 8.0 6.6 13.6 6.4 5.5 5.6 6.2 6.8

7.3 158 9.5 13.6 6.6 13.7 12.8 8.5 24.6 7.6 7.0 6.0 7.7 7.5

*

*

*

40 1936 554 39

6.0 292 64.4 7.4

8.0 392 111.5 8.0

Asterisk indicates that was not possible to measure this paste in the rheometer, due torque limit.

1st interval

Viscosity (Pa.s)

1000

3rd interval

100

10

MK 6.6, LF 1.6% MK 5%, LF 0 MK 5%, LF 5% MK 3.3, LF 3.3% MK 0, LF 10%

1 2nd interval

0,1 0

60

120

180

240

300

360

Time (s) Fig. 10. Three-Interval thixotropy test. Viscosity as a function of time for 5 pastes with different contents of metakaolin (MK) and limestone filler (LF).

be used as a reference. In the second time interval, the rotation is suddenly increased to a value 1000 times greater and then it is maintained constant for a period of time (50 s was the time used in the present study). The high shear rate of the second time interval aims to break the sample’s entire internal structure. Finally, the rotation in the third and last time interval (immediately after the second interval) is the same as the one used in the first interval. In the third interval, the viscosity is monitored during a relatively greater time and its values are recorded every 0.5 s to verify how much of the initial viscosity is recovered and how much time does it take for this recovery. In our case, the rotation profile and the interval times used were as follows: 1st interval (0.1 rpm, 60 s, 12 data points), 2nd interval (100 rpm, 50 s, 100 data points), and 3rd interval (0.1 rpm, 250 s, 500 data points). Fig. 10 shows some of the curves obtained in the 3-ITT thixotropy tests. Fig. 10 shows that the pastes viscosity increases with metakaolin content. In addition, thixotropy (which is measured through recovery time (s) for a certain viscosity recovery level and/or viscosity recovery degree (%) after 1 min) also strongly depends on

is also called ‘‘3ITT” (three-interval of time test) [38]. In the first time interval of this thixotropy test, the sample is sheared under constant low rotation for 1 min to obtain the viscosity, which will Table 8 Thixotropy of cement-metakaolin-filler pastes Paste PC-MK-LF (%)

Thixotropic recovery (%) after 1 min

Time (s) for 63.2% recovery (1  1/e) of viscosity

91.6-6.7-1.7 95-5.0-0.0 90-5.0-5.0 93.4-3.3-3.3 90-0.0-10 90-10-0.0 96.6-1.7-1.7 91.6-1.7-6.7 95-0.0-5.0 100-0.0-0.0 93.4-3.3-3.3 93.4-3.3-3.3 93.4-3.3-3.3

66 55 57 52 43 90 45 38 48 39 50 49 53

47 105 82 99 110 14 126 158 99 143 111 123 96

(b)

(a) (c) (d)

(a,b,c,d): replicate samples.

Thixotropic Recovery after 1 min (%)

100

160

MK LF

90

140

80 70 60

120 100

Control: only Cement + water + SP

80

50

60

40

40

30

Recovery time @ 63.2% (sec)

*

Portland Cement (%)

20

MK LF

20

0 0

5

10

Suppl. Cimentitious Mat. (%) Fig. 11. Effect of metakaolin and limestone filler contents on the pastes thixotropy measured on the 3rd interval after 1 min (left axis, black) and time for the viscosity to return to 63.2% (1  1/e) of the reference value (right axis, red). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103

Fig. 12. Mixture contour plot of thixotropic recovery (%) after 1 min. PC = Portland Cement, MK = Metakaolin, LF = limestone filler.

Table 9 Estimated Regression coefficients for thixotropic recovery after 1 min (pseudo components). Term PC MK LF S = 7.36259 R-Sq = 75.17%

Coef

SE Coef

39.38 5.316 80.38 5.316 40.38 5.316 PRESS = 1094.23 R-Sq(pred) = 49.88%

T * * *

P * * *

VIF 1.274 1.274 1.274

R-Sq(adj) = 70.20%

Table 10 Analysis of variance for thixotropic recovery after 1 min (pseudo components). Source

DF

Seq SS

Adj SS

Adj MS

F

P

Regression Linear Residual error Lack-of-fit Pure error Total

2 2 10 7 3 12

1641.00 1641.00 542.08 532.08 10.00 2183.08

1641.00 1641.00 542.08 532.08 10.00

820.500 820.500 54.208 76.011 3.333

15.14 15.14

0.001 0.001

22.80

0.013

metakaolin content. Table 8 summarizes thixotropy results for the tested pastes whenever measurement was possible. Fig. 11 shows two ways of evaluating thixotropic results: percentage recovery of the viscosity after arbitrary time (we choose 1 min), and the time spent to recovery the same level of viscosity the 1st interval (commonly this level can be 63.2%). One can see in Fig. 11 that the greater the added kaolin content, the greater the thixotropy. On the other hand, this also leads to less spreading and higher Marsh funnel time. Therefore, we concluded that metakaolin increases plasticity and thixotropy of cement paste, i.e., it improves paste workability for metakaolin contents of 5 to 8% but makes workability much more difficult for contents above 10%. Fig. 12 shows the contour plot for the percentage thixotropy recovery level of the pastes after 1 min. The linear model is a good fit; and indicates how prevalent the effect of the metakaolin content over thixotropy is.

Fig. 13. Mixture contour plot (component amounts) for plastic viscosity measured in rotational mode.

Table 11 Estimated regression coefficients for viscosity plastic (pseudo-components). Term

Coef

SE Coef

PC MK LF PC * MK MK * LF S = 0.618696 R-Sq = 96.73%

1.31 11.18 1.31 15.74 18.64

0.5312 0.5893 0.5312 2.5925 2.5925

T

P

VIF

* * 1.884 * * 2.319 * * 1.884 6.07 0.000 2.628 7.19 0.000 2.628 PRESS = 38.2884 R-Sq(pred) = 63.66% R-Sq(adj) = 95.28%

Table 12 Analysis of variance for viscosity plastic (pseudo-components). Source

DF

Seq SS

Adj SS

Adj MS

F

P

Regression Linear Quadratic PC * MK MK * LF Residual error Lack-of-fit Pure error Total

4 2 2 1 1 9 5 4 13

101.925 63.523 38.402 18.612 19.790 3.445 3.374 0.071 105.370

101.9249 89.0158 38.4020 14.1184 19.7904 3.4451 3.3741 0.0709

25.4812 44.5079 19.2010 14.1184 19.7904 0.3828 0.6748 0.0177

66.57 116.27 50.16 36.88 51.70

0.000 0.000 0.000 0.000 0.000

38.06

0.002

In the case of the regression model of thixotropic recovery, the linear model was better than other, more complex models. The thixotropic recovery it is independent of the limestone filler Portland cement ratio and is a function only of the metakaolin content. Tables 9 and 10 summarize the linear regression and ANOVA for thixotropic recovery after 1 min. Fig. 13 shows the contour plot (in terms of component amounts) for plastic (or apparent) viscosity, measured in rotational mode in rheometer. The regression model here was quadratic, because linear was insufficient to explain the viscosity results. More complex models are not worth being employed, due to the ‘‘lack-of-fit” changes. The quadratic model is the simplest with acceptable R2 (adjust or predictable).

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F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103

Fig. 15. Overlaid contour plot for yield stress and elastic modulus (oscillatory rheometry); thixotropic recovery after 1 min and plastic viscosity (rotational rheometry). Fig. 14. Mixture contour plot (component amounts) for elastic modulus (G0 ) measured in oscillatory mode, in the rheometer.

2.097 2.537 2.097 3.481 3.481 3.586 1.625 1.625

Fig. 14 clearly suggests that, if one is looking for pastes with an elastic modulus of G0 > 120 Pa in these particular blends (PC + MK + LF, w/b = 0.30 and 0.5% wt. PCE), a minimum amount of 6% wt. of MK must be present in the formulations. However, let us see other responses in combination, since the ideal outcome would be a paste with plastic viscosity as low as possible; fast thixotropic recovery; yield stress and elastic modulus as high as possible. This is not an easy task. Fig. 13 shows an overlaid plot of some of the responses. We arbitrarily chose: a) 60 < G0 < 120 Pa; b) 2 < yield stress < 10 Pa; c) 2.5 < Plastic viscosity < 3.5 Pa.s and d) 60% < thixotropic recovery after 100 < 70%. Of course, in an ‘‘perfect world”, plastic viscosity should be less than 1 Pa.s, thixotropic recovery should approaches 100% as quick as possible, and yield value or G’ should be as high as possible. The old problem of optimization of functions with maximums and minimums. . . One solution, not ideal, but real and acceptable, is displayed in Fig. 15, as an overlaid contour plot. The Fig. 15 suggests that a paste prepared with PC:MK:LF 90:5:5 must fulfill all the requirements, inside the white region delimited. 4. Conclusions

Table 13 Estimated regression coefficients for elastic modulus (pseudo-components). Term

Coef

SE Coef

PC MK LF PC * MK MK * LF PC * MK * LF PC * MK * () MK * LF * () S = 17.1235 R-Sq = 99.66%

30 787 41 1387 1405 1626 1139 995

15.51 17.06 15.51 82.57 82.57 365.12 277.87 277.87

T

P

VIF

* * * * * * 16.80 0.000 17.02 0.000 4.45 0.004 4.10 0.006 3.58 0.012 PRESS = 218,282 R-Sq(pred) = 57.66% R-Sq(adj) = 99.26%

Table 14 Analysis of variance for elastic modulus (pseudo-components). Source

DF

Seq SS

Adj SS

Adj MS

F

P

Regression Linear Quadratic PC * MK MK * LF Special cubic PC * MK * LF Full Cubic PC * MK * () MK * LF * () Residual error Lack-of-fit Pure error Total

7 2 2 1 1 1 1 2 1 1 6 2 4 13

513,764 289,295 199,969 110,229 89,740 7061 7061 17,439 13,682 3756 1759 1026 733 515,523

513,764 424,691 147,094 82,754 84,916 5814 5814 17,439 4923 3756 1759 1026 733,183

73,395 212,345 73,547 82,754 84,916 5814 5814 8719 4923 3756 293 513

250.31 724.20 250.83 282.23 289.60 19.83 19.83 29.74 16.79 12.81

0.000 0.000 0.000 0.000 0.000 0.004 0.004 0.001 0.006 0.012

2.80

0.174

Tables 11 and 12 summarizes the quadratic regression model and ANOVA for plastic viscosity. Finally, Fig. 14 shows the mixture contour plot for elastic modulus, G0 measured in oscillatory rheometer. The elastic modulus, in the same trend as yield stress value, are both related to the cohesion of the pastes, and thus, their ‘‘workability”. Table 13 and 14 resumes the full cubic regression model and ANOVA, respectively, for elastic modulus (pseudo-components).


Metakaolin acts as a thixotropic additive and a modifier of the cement paste viscosity, which did not happen in the case of limestone filler. There is an improvement of paste workability when a water reducer admixture is used.
Excess of superplasticizer (SP), such as poly-carboxylate ether, may reduce paste workability especially when contents above 0.5 wt.% SP are used (even with low water/cement ratio). The partial replacement of Portland cement with metakaolin (up to 10% wt/wt) maintains workability. On the contrary, binary blends with only cement and limestone filler was not able to maintain it.
Because limestone filler does not interfere with the viscosity or plasticity of the paste with PCE admixture, its use is preferred when fluidity is desirable. However, with only limestone filler and Portland cement, segregation can occurs, especially if higher contents of this superplasticizer is employed.
The ideal metakaolin content depends on the paste desired viscosity, thixotropy and workability. For example, the thixotropy recovery of 62.3% only takes 14 s for blend 90% cement with 10% metakaolin. The slump was of 35 mm; however, this fast recovery leads to a loss of fluidity: the paste does not flow through the Marsh funnel. This also avoids segregation.

F. Nazário Santos et al. / Construction and Building Materials 143 (2017) 92–103


The use of up to 5–10% metakaolin substitution may result in 30–45% average increase in compressive strength after 7 days.
A paste containing 90% Portland cement, blended with 5% Metakaolin and 5% limestone filler, should present good thixotropy with 60% viscosity recovery after 1 min, elastic modulus above 60 Pa, and plastic viscosity 3.5 Pa.s The compressive strength (7 days) of this blend was 54 ± 8 MPa.

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