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Pozzolanic activity of metakaolins by the French standard of the modified Chapelle test: a direct methodology.

1. INTRODUCTION

Pozzolan is a fine inorganic material composed mainly by rich siliceous or silico-aluminous amorphous phases, which itself possess lower or no binder properties, but in the presence of water, at ordinary temperature and pressure, will chemically react with calcium hydroxide to produce compounds with binder properties.

Pozzolans are raw materials available worldwide and used for the production of blended system composites, as partial replacement of binder (cement or lime) in mortars and in concrete. These materials can be exploited like a georesource (natural source) or obtained from an industrial process (artificial source), usually from a by-product.

The ancient mortars from historic periods were based on the use of lime and in many of them pozzolans, namely natural siliceous volcanic material, were incorporated. In the ancient construction systems of the Mediterranean, since 1500 BC, Greeks used a siliceous volcanic material from Santorini (Moropoulou et al., 2004) and Romans, since the II century BC, used pozzolans extensively (Lancaster, 2005). Vitruvius (c. 16-27 BC) and Seneca (c. 62-65 AC), reported empirically that pozzolan provides hydraulicity to lime mortar in wet conditions or underwater, and Pliny (c. 77-79 AC) wrote that pozzolans increase the durability of lime mortar. Until the end of the XVIII century, the Italian architects (XV to XVIII centuries) have generally used the Vitruvius's empirical knowledge, without significantly developments about the formulation of mortars with pozzolans and the research of their behaviour. The applied research concerning these subjects got an expressive increment since the end of XVIII century to the first half of XIX century (Sala et al., 2008).

A wide range of test methods to assess the pozzolanic activity of materials have been developed. According to Donatello et al. (2010), these methods can be categorized as either direct or indirect. The first evaluate the presence of Ca(OH)2, using analytical methods such as X-ray diffraction (XRD), thermogravimetric analysis (TGA) or classical chemical titration. The second ones measure a physico-mechanical property on a probe that indicates the extent of pozzolanic activity. This may involve measurement of properties such as mechanical strength, electrical conductivity or heat evolution by conduction calorimetry.

Fratini (1950) pioneered in the development of a laboratorial methodology for the assessment of pozzolanic activity, based on the evaluation of the O[H.sup.-]and [Ca.sup.2+] concentrations presented in a mixture of Portland cement and pozzolan. The "Fratini test" is the basis of the actual EN 196-5 standard. In opposition to Fratini methodology, Chapelle (1958) developed a pseudo-dynamic test to evaluate the activity of a pozzolanic material, based on the consumption of Ca[(OH).sub.2] in a saturated water medium. Benoit (1967) improved the Chapelle methodology, particularly in terms of temperature (90[degrees]C) and duration (16 h) of the test, using 1 g of pozzolan, 1 g of calcium oxide and 100 ml of destiled water and gave the denomination "Chapelle test" to this methodology. Largent (1978) criticizing the "Fratini test", because the system does not reach equilibrium and is performed in a static environment, introduced modifications to the Chapelle test, namely the continuous stirring during the duration of the test, and renamed the methodology to "modified Chapelle test".

One of the most worldwide used pozzolanic material is the calcined kaolin (metakaolin), namely used as supplementary cimentitious material. Mitra and Bhattacherjee (1969), Slade et al. (1992), Bellotto et al. (1995), Salvador (1995), He et al. (1995), Pera and Amrouz (1998), Morsy et al. (1998), Kakali et al. (2001), Dion et al. (1998), Chandrasekhar and Ramaswamy (2002), Shvarzman et al. (2003), Souza and Molin (2005), Badogiannis et al. (2005), Bich et al. (2009), Gutierrez et al. (2008), Velosa et al. (2009), Ilic et al. (2010), Vizcayno et al. (2010), Tironi et al. (2012) and Fabbri et al. (2013) reported the influence of mineralogy, particle size distribution, moisture of the raw material, temperature and time of calcination, technique of calcination and the origin of the raw material (natural kaolinitic clay or industrial kaolinitic by-product) in order to obtain metakaolinized materials.

The aim of this study was to assess the pozzolanic activity of commercial and experimental metakaolins through the French standard for the modified Chapelle test (NF P18-513). This direct methodology performed in a aqueous lime-metakaolin system, during 16 hours at 90[degrees]C with continuous stirring, allows the quantification of portlandite fixed by the metakaolin.

2. MATERIALS AND METHODS

The materials used in this study are presented in Table 1. The kaolin raw material (referred as "Kaolin") use in the production of the experimental metakaolins was provided from an industrial Portuguese sand wash plant. Six commercial metakaolins were taken in consideration to compare and serve as reference to the parameters evaluated in this study. Seven experimental metakaolins (referred as "MK") were produced from 750[degrees]C to 940[degrees]C (referred as "MK-750" to "MK-940"). The experimental metakaolin produced at 800[degrees]C (MK800) was intentionally subjected to a grinding process to obtain a ground metakaolin (referred as "MK-800M"). Overall, one kaolin raw material, six commercial metakaolins, seven experimental metakaolins and one milled (ground) experimental metakaolin were considered for analysis.

The kaolin was subjected to mineralogical, chemical, particle size and thermal characterization.

The mineralogical analysis, carried out on non-oriented powder sample, was performed on a Philips X'Pert PRO MPD diffractometer using the X-ray diffraction (XRD) technique, operating with CuKa radiation at 50 kV and 30 mA. The intensity was determined by counting with a scan rate 0.02 [theta]/s in the range 4-60 2[theta]. The identification of the crystalline phases was made by comparison with the Powder Diffraction Files (PDF) from the International Centre for Diffraction Data (iCdD) files.

[FIGURE 1 OMITTED]

Chemical analysis of the major elements was determined by X-ray fluorescence (XRF) spectrometry using a PANalytical equipment PW 4400/40 Axios, with CrK[alpha] radiation at 50 kV and 20 mA. A fused pearl with ratio 1 sample / 9 flux (Spectromelt A12) was performed. The loss on ignition was determined by gravimetric analysis, calcinating the sample in a Carbolite CSF 1200 electric furnace at 1000[degrees]C during 3 hours at maximum temperature in oxidizing ambient atmosphere.

Particle size analysis (PSA) was evaluated by sedimentation and absorption of X-rays in a Micromeritics Sedigraph 5100 apparatus, according to BS 3406-2 standard. The determination was performed on the 0.1 and 63.0 pm size range.

Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed using the simultaneous thermal analysis (STA) on a Netzsch Jupiter STA 449 apparatus, with oxidizing atmosphere, between 20[degrees]C and 1000[degrees]C and heating rate of 10[degrees]C/min, according to DIN 51006 and DIN 51007 standards.

The calcination of kaolin was performed on a 2.5 m scale prototype rotary kiln.

The characterization of the obtained experimental metakaolinized samples (MK-750 to MK940) includes mineralogical, chemical and particle size analysis in accordance with the methodology described for kaolin raw material.

The pozzolanic activity of metakaolins was assessed with the modified Chapelle test according to NF P18-513 standard (annex a). This test allows the quantification of Ca[(OH).sub.2] fixed (consumed) by 1 g of metakaolin when mixed with 2 g of CaO and 250 ml of distilled C[O.sub.2] free water. The suspension was boiled at 90[degrees]C during 16 h with continuously stirring in a stainless steel 500 ml Erlenmeyer (Figure 1).

After finished the test time, the Erlenmeyer was cooled to ambient temperature with tap water. The portlandite content that was not consumed (free in solution) was determined by sucrose extraction and acid titration. For that, 250 ml of fresh sucrose solution (0.7 M) were added to the solution, which was stirred with the magnetic bar during 15 min. 200 ml of the final solution were filtrated and taken 25 ml to titrate with HCl 0.1 N with 2-3 drops of phenolphthalein (0.1 w/v% in ethanol 50 v/v%). The titration reactions are: CaO + 2HCl [right arrow] Ca[Cl.sub.2] + [H.sub.2]O and Ca[(OH).sub.2] + 2HCl [right arrow] Ca[Cl.sub.2] + 2[H.sub.2]O. The pozzolanic activity of metakaolin is calculated according the formula:

PAM = 2 [V.sub.1] - [V.sub.2]/[V.sub.1] 74/56 1000

PAM--pozzolanic activity of metakaolin, expressed in mg Ca(OH)2 fixed / g metakaolin;

[V.sub.1]--volume of HCl 0.1 N, expressed in ml, necessary for titrate 25 ml of the final solution obtained without metakaolin (blank test);

[V.sub.2]--volume of HCl 0.1 N, expressed in ml, necessary for titrate 25 ml of the final solution obtained with metakaolin.

The blank test (without metakaolin) must verify

[V.sub.1] 56/2 < 1000 and the repeatability of the modified Chapelle test is 10 % for 1100 mg Ca[(OH).sub.2] fixed/g metakaolin.

[FIGURE 2 OMITTED]

Specific surface area of the metakaolins was determined in a Micromeritics Gemini 2.0 instrument, using the BET method (Brunauer et al., 1938). Samples were pre-treated at 200[degrees]C under a nitrogen flow before measurements were made.

The cation exchange capacity (CEC) of the metakaolins was evaluated by the classic ammonium acetate saturation method following the procedure of Cowan and White (1958) and the calculations of Chapman (1965).

The morphology of the particles was observed by scanning electron microscopy (SEM) using a Hitachi S4100 electron microscope. The samples were previously subjected to coated carbon deposition carried out on an Emitech K950X equipment.

A soft disaggregation carried out with an alumina ball mill (Gabbrielli Fast Mill) during 5 minutes on aggregate experimental metakaolins was accomplished. The milling of one experimental metakaolin was accomplished in a vibratory agate disc mill (Retsch RS1) during 20 minutes at 700 rpm.

The properties of the experimental metakaolin samples were compared with the commercial metakaolins.

3. RESULTS AND DISCUSSION

3.1. KAOLIN

Mineralogical analysis of the kaolin is presented in Figure 2. As expected, quartz and kaolinite are present as major minerals. As accessory minerals muscovite (mica), microcline (alkali feldspar) and albite (plagioclase) were identified.

The chemical composition (Table 2) of the kaolin shows higher values for silicon oxide (56.8 %) and aluminium oxide (30.7 %) which are mainly related with quartz and kaolinite minerals. The high value for potassium oxide (1.5 %) is connected with the occurrence of microcline and muscovite. The non quantification content of sodium oxide below the quantification limit of the XRF technique could reflects the vestigial amount of plagioclase discriminated on XRD pattern. Values for iron (0.9 %), magnesium (0.2 %) and titanium (0.3 %) oxides are connected with the exchanged cations presented in kaolinite crystallochemical structure, as well as to the presence of muscovite (iron and magnesium) as a penalizing mineral. The loss on ignition value (9.9 %) corroborates the presence of kaolinite (Figure 2) as main clay mineral.

Particle size distribution for kaolin present very fine particle size (d50=1.5 pm) which results from the origin of the material (industrial sand washing) and BET specific surface area of 19.0 [m.sup.2]/g.

The thermogravimetric behaviour of the kaolin presented two weight losses, the first (0.6 %) at 80[degrees]C attributed to the remove of moisture, and the second loss (10 %) that occurred between 400[degrees]C and 950[degrees]C due to the dehydroxylation of the clay minerals (kaolinite and mica). The weight loss of 10 % corroborates the value of 9.9 % obtained for the loss on ignition (Table 2).

Concerning the thermodifferential behaviour, there was one endothermic peak at [approximately equal to] 72[degrees]C, which is due to the release of moisture and another endothermic peak at [approximately equal to] 536[degrees]C, which represents the maximum temperature of dehydroxylation. There is also an exothermic peak at [approximately equal to] 996[degrees]C due to the formation of primary mullite. In summary, it can be noted that the process of dehydroxylation of the kaolinite, which leads to the transformation into metakaolinite, occurs at a wide temperature range from 400[degrees]C to 950[degrees]C.

3.2. COMMERCIAL METAKAOLINS

The mineralogical analysis of commercial metakaolins (Figure 2) present penalizing minerals, such as, muscovite, quartz and feldspar that can be observed on M1200S, M1000 and BZ metakaolins. Also is evident in all metakaolins (except BZ) the presence of anatase (Ti[O.sub.2]). The HP metakaolin presents a rest of non calcined kaolinite. The Optipozz metakaolin denotes the presence of mullite, indicating that this material was calcined at a temperature near the uppermost limit ([approximately equal to] 1000[degrees]C). In all metakaolins, a wide convexity with low intensity, developed between [approximately equal to] 15-3[theta] degrees ([degrees]20) is noticeable, attributed to the discrimination of the amorphous phase (metakaolinite).

HP (19.1 pm), BZ (11.5 [micro]m) and M1000 (8.2 [micro]m) metakaolins show coarser d50 grain distribution when compared with the remnant studied metakaolins. The Optipozz, PoleStar 450 and M1200S metakaolins presents fine grain distribution, with d50 range between 1.1 and 1.8 pm (Table 3).

The chemical elemental analysis of commercial metakaolins is shown in Table 2. No significant differences between commercial metakaolins were found, but some facts must be evidenced: i) relatively high content of titanium oxide related with the presence of anatase; ii) the potassium oxide content of 1.0 % (M1200S) and 0.8 % (BZ) is related with the alkali feldspar presented in both metakaolins; iii) the calcium oxide content (0.9%) observed in the BZ metakaolin is due to the presence of plagioclase; iv) both BZ and HP metakaolins presented the highest iron oxide values, 4.5% and 2.2%, respectively, which can be related with iron oxide minerals as contaminants; v) the loss on ignition values of 5.0 % (M1000), 3.4 % (HP), 1.9 % (M1200S) and 1.3 % (BZ) are related with the muscovite and for HP also with the remaining kaolinite that was not transformed into metakaolinite (Figure 2); vi) the values observed for silicon and aluminium oxides are mainly correlated with the metakaolinite content and with mullite in Optipozz material.

According to the modified Chapelle test (Table 3), the Optipozz and PoleStar 450 metakaolins exhibit higher pozzolanic activity values, 1560 and 1550 mg Ca[(OH).sub.2]/g metakaolin, respectively. The BZ metakaolin showed the lowest value (920 mg Ca[(OH).sub.2] /g metakaolin). Optipozz metakaolin present the higher value of modified Chapelle pozzolanic activity. This material is classified as "high reactive metakaolin" in cimentitious systems (Antoni et al., 2012). The NF P 18-513 standard defines that the pozzolanic activity of a metakaolin should not be less than 700 mg Ca[(OH).sub.2]/g metakaolin.

The morphology of the particles presented in the commercial metakaolins can be observed in Figure 3. The calcined kaolinite particles in the Optipozz metakaolin (highest pozzolanic activity material) preserves the pseudo-hexagonal shape of the original kaolinite morphology with pseudo regular shape and pseudo angular borders (Figure 3a) by opposition to the BZ metakaolin (lowest pozzolanic activity material) that present roundness and smoothing particles (Figure 3b). In this sense, the shape of the calcined kaolinite particle can have some influence in the pozzolanic activity of the commercial metakaolins.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The d50 particle size values for the commercial metakaolins denounce an interesting correlation with the modified Chapelle results expressed by an inverse linear trend (modified Chapelle = -32.032 x d50 + 1505.700, [R.sup.2] = 0.8551). The d50 results for M1200S (1.1 [micro]m), PoleStar 450 (1.2 pm) and Optipozz (1.8 [micro]m) presents the lowest values for the studied metakaolins. This allows to infer that at least these commercial metakaolins are subjected to an intense milling stage.

Concerning SSA and CEC results obtained on commercial metakaolins, it was not found mathematical correlations to modified Chapelle pozzolanic activity.

3.3. EXPERIMENTAL METAKAOLINS

The parameters for the production of experimental metakaolins are shown in Table 4. The experimental calcination temperatures established in the rotary kiln were restricted between 750[degrees]C and 940[degrees]C, since according the STA analysis, the dehydroxilation of the kaolinite occurs from 400[degrees]C to 900[degrees]C Due to the formation of particle aggregates during the calcination process, some of the calcinated materials (MK-830, MK-850, MK-900 and MK-940) were submitted to a soft mechanical disaggregation (Table 4). In order to evaluate the effect of particle size reduction in the modified Chapelle pozzolanic activity of the experimental metakaolins, the metakaolin produced at 800[degrees]C (MK-800) was milled to obtain one ground metakaolin (MK-800-M).

The mineralogical analysis of the seven experimental metakaolins is discriminated in Figure 4. In addition to the initial penalizing minerals (muscovite, quartz and feldspars) presented in the kaolin, the presence of kaolinite that has not been fully calcinated (metakaolinized) was identified in the MK-750 metakaolin, due to the calcination at the lowest temperature (750[degrees]C). The limit for calcination temperature was not reached, since the presence of mullite in MK-940 metakaolin was not identified (Figure 4). However at this temperature, it is possible the formation of vestigial cubic, spinel or gammaalumina phase undetected in XDR pattern.

All the experimental metakaolins presented a narrow particle size range, except for MK-800-M metakaolin that was submitted to a purposeful comminution process. There were no significant differences in d50 between samples that did not undergo disaggregation after calcination (MK-750, MK-800 and MK-840) (Tables 3 and 4). As referred, the MK-800-M sample was submitted to a particle size reduction and by this way present the finest particle size of the experimental samples (d50=2.2 [micro]m). The disaggregated samples MK-850 and MK-940 presents lower particle size with d50=4.5 [micro]m and d50=3.5 [micro]m, respectively.

For an efficient calcination of the kaolinite material, the d50 of the calcinated material is a crucial parameter for a better pozzolanic behaviour. The influence of particle size in the reactivity of metakaolins is reported by Oliveira et al. (2005).

The physicochemical parameters evaluated in the experimental metakaolins are presented in Table 3. The increase of calcination temperature from MK-750 to MK-940 metakaolin (except for MK-900) was responsible for the increase of the modified Chapelle pozzolanic activity.

When compared with MK-850 metakaolin, the decrease in modified Chapelle pozzolanic activity on MK-900 could be related with the increase in d50, the decrease of CEC and higher duration of calcination.

The effect of particle size reduction in the calcinated product is a key factor for the increase of the modified Chapelle pozzolanic activity, as can be observed from MK-800 to MK-800-M samples. The MK-800 sample was submitted to a grinding process, which has resulted in a consequent reduction ([approximately equal to] 4x less) of the particle size from 8.4 [micro]m to 2.2 [micro]m (Table 3) and a consequent increase in the specific surface. With this additional process a relative gain of 21 % in the modified Chapelle pozzolanic activity was obtained. This fact is directly related with the comminution of metakaolins, which promotes a surface particle with less nanorough and increase the Lewis basic properties of the surface on the ground metakaolinitic particles (Gamelas et al., 2014).

Contrary to the trend observed on commercial metakaolins, on experimental metakaolins the modified Chapelle results presents lower correlation with particle size (d50) results (modified Chapelle = -41.624 x d50 + 1302.500, [R.sup.2] = 0.6561). This evidence could be related to the relative proximity of the global values. Except MK-800-M, MK-850 and MK-940, the d50 values range from 6.2 to 8.4 pm, which involves less data discrimination.

As expected, the CEC values of the not ground experimental metakaolins (Table 3) are lower (6.1 to 9.9 cmolc/kg) and with the same order as reported by San Cristobal (2010) for an industrial sand wash kaolin calcined at 750[degrees]C for 3 h (2.4 [cmol.sub.c]/kg). The ground metakaolin (MK-800-M) shows the higher CEC value (38.5 [cmol.sub.c]/kg) due to the purposeful grinding stage, which increases CEC at about 400 % when compared with the MK-800 metakaolin (7.6 [cmol.sub.c]/kg). The modified Chapelle pozzolanic activity obtained on the experimental metakaolins showed a linear trend with CEC (modified Chapelle = 84.311 x cation exchange capacity + 382.490) and good correlation ([R.sup.2]=0.9219). This correlation was calculated without the ground metakaolin (MK-800M), since there is only one ground result and the obtained value is from an upper order.

For both commercial and experimental metakaolins, it was not observed any correlation to SSA data. Apparently, and contrary to what occurs to CEC, SSA do not have relation with Lewis basic properties of the surface on calcined kaolinite particles. Further studies are in progress on this subject.

The morphology of the particles for the experimental metakaolins do not present notable differences between them (Figures 3c and 3d). The experimental metakaolins with lower (MK-750) and higher modified Chapelle pozzolanic activity (MK940) presents generically roundness and smoothing calcined kaolinite particles. In fact, the modified Chapelle pozzolanic activity for MK-940 metakaolin (1240 mg Ca[(OH).sub.2]/g metakaolin) is at the same order (except BZ metakaolin) of the modified Chapelle pozzolanic activity of commercial metakaolins, putting in evidence that the increment in the modified Chapelle pozzolanic activity of the experimental metakaolins is not closely related with shape and geometry of the calcined particle.

4. CONCLUSIONS

According the goal of this study and based in the obtained results, discussion and interpretation of the data, the following remarks can be stated about the direct methodology that allows the evaluation of the pozzolanic activity of metakaolins by the French standard of the modified Chapelle test applied to commercial and experimental metakaolins:

* It is an expeditiously methodology, with simple and quick execution allowing the direct evaluation (non strength tests) of the pozzolanic activity of metakaolins;

* The modified Chapelle pozzolanic activity of commercial metakaolins presented values between 920 and 1560 mg Ca[(OH).sub.2]/g metakaolin, highlighting the significant differences in the quality of each commercial tested material;

* The values of the modified Chapelle pozzolanic activity obtained in the experimental metakaolins are above the standard limit (700 mg Ca[(OH).sub.2]/g metakaolin);

* The evaluation of the modified Chapelle pozzolanic activity on experimental metakaolins yielding an optimized material with a pozzolanic activity value of 1240 mg Ca[(OH).sub.2]/g metakaolin;

* In commercial metakaolins, the modified Chapelle results has an interesting correlation with particle size (d50);

* In experimental metakaolins, the modified Chapelle results increase with the increase of the cation exchange capacity results. The modified Chapelle pozzolanic activity is independent of the particle morphology. The grinding stage affects significantly the modified Chapelle pozzolanic activity;

* For both commercial and experimental metakaolins, it was not observed any relation either with specific surface area or calcined kaolinite morphology to modified Chapelle pozzolanic activity.

DOI: 10.13168/AGG.2015.0026

ARTICLE INFO

Article history:

Received 19 January 2015

Accepted 26 May 2015

Available online 13 July 2015

ACKNOWLEDGMENTS

This research was supported by Sistema de Incentivos a Investigacao e Desenvolvimento Tecnologico--Vale I&DT to Ceramica Condestavel, Lda (Portugal), supported by Quadro de Referencia Estrategica Nacional, Research Project METACAL Study of Lime-Metakaolin Mortars for Building Conservation (PTDC/ECM/100431/2008), Research Unit (UID/GEO/04035/2013) and Projecto Estrategico (PEst-OE/CTE/UI403 5/2014) financed by the Fundacao para a Ciencia e a Tecnologia (FCT) and COMPETE--Programa Operacional Factores de Competitividade.

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Eduardo FERRAZ (1) *, Slavka ANDREJKOVICOVA (2), Walid HAJJAJI (2), Ana Luisa VELOSA (3), Antonio Santos SILVA (4) and Fernando ROCHA (2)

(1) Polytechnic Institute of Tomar, Geobiotec Research Unit. Quinta do Contador, Estrada da Serra, PT--2300-313 Tomar, Portugal

(2) Geosciences Department, University of Aveiro, Geobiotec Research Unit. Campus Universitario de Santiago, PT--3810-193 Aveiro, Portugal

(3) Civil Engineering Department, University of Aveiro, Geobiotec Research Unit. Campus Universitario de Santiago, PT--3810-193 Aveiro, Portugal

(4) Materials Department, National Laboratory for Civil Engineering, Avenida do Brasil, 101, PT--1700-066 Lisboa, Portugal Corresponding author's e-mail: ejmoferraz@ipt.pt; ejmoferraz@gmail.com
Table 1 Materials used in this study.

Sample                                   Origin    Designation

Kaolin                                  Portugal      Kaolin

Optipozz                                  USA        Optipozz
PoleStar 450                              USA      PoleStar 450
Argical M1200S                           France       M1200S
Argical M1000                            France       M1000
HP                                       Brazil         HP
BZ                                       Brazil         BZ

Metakaolin produced at 750 [grados]C       -          MK-750
Metakaolin produced at 800 [grados]C       -          MK-800
Ground metakaolin produced                 -         MK-800-M
  at 800 [grados]C
Metakaolin produced at 830 [grados]C       -          MK-830
Metakaolin produced at 840 [grados]C       -          MK-840
Metakaolin produced at 850 [grados]C       -          MK-850
Metakaolin produced at 900 [grados]C       -          MK-900
Metakaolin produced at 940 [grados]C       -          MK-940

Sample                                        Description

Kaolin                                       Raw material

Optipozz
PoleStar 450
Argical M1200S                           Commercial metakaolin
Argical M1000
HP
BZ

Metakaolin produced at 750 [grados]C
Metakaolin produced at 800 [grados]C
Ground metakaolin produced
  at 800 [grados]C
Metakaolin produced at 830 [grados]C    Experimental metakaolin
Metakaolin produced at 840 [grados]C
Metakaolin produced at 850 [grados]C
Metakaolin produced at 900 [grados]C
Metakaolin produced at 940 [grados]C

Table 2 Chemical composition of the kaolin
raw material and commercial metakaolins.

Oxides (%)             Kaolin raw   Optipozz   PoleStar   M1200S
                        material                 450

Si[O.sub.2]              56.84       51.93      52.18     54.39
[Al.sub.2][O.sub.3]      30.70       44.94      45.48     39.36
[Fe.sub.2][O.sub.3]       0.89        0.44       0.47      1,75
MnO                       0.01         nd         nd       0.01
MgO                       0.16        0.01       0.02      0.16
CaO                       0.05        0.01       0.03      0.10
[Na.sub.2]O                nd          nd         nd        nd
[K.sub.2]O                1.53        0.14       0.09      1.03
Ti[O.sub.2]               0.27        1.39       0.97      1.55
[P.sub.2][O.sub.5]        0.04        0.12       0.08      0.06
LOI                       9.85        1.23       0.93      1.90

Oxides (%)             M1000    BZ      HP

Si[O.sub.2]            57.13   59.59   50.03
[Al.sub.2][O.sub.3]    34.20   31.39   42.62
[Fe.sub.2][O.sub.3]    1.15    4.45    2.17
MnO                    0.01    0.04    0.01
MgO                    0.23    0.45    0.18
CaO                    0.10    0.87    0.01
[Na.sub.2]O             nd     0.21     nd
[K.sub.2]O             0.49    0.82    0.53
Ti[O.sub.2]            1.91    0.67    1.39
[P.sub.2][O.sub.5]     0.04    0.23    0.04
LOI                    5.00    1.30    3.37

LOI: loss on ignition, nd: less quantification limit

Table 3 Physico-chemical properties and characteristics
of the commercial and experimental metakaolins.

                   d50       Pozzolanic activity
                ([micro]m)   (mg Ca[(OH).sub.2]/
                                g metakaolin)

Commercial metakaolin

Optipozz          1.8 *             1560
PoleStar 450       1.2              1550
M1200S             1.1              1320
M1000              8.2              1190
HP                 11.5             1120
BZ                 19.1              920

Experimental metakaolin

MK-750            8.3 *              910
MK-800             8.4               950
MK-800-M           2.2              1150
MK-830             8.7               990
MK-840            7.7 *             1030
MK-850             4.5              1180
MK-900             6.2               910
MK-940            3.5 *             1240

                 Specific surface    Cation exchange capacity
                area ([m.sup.2]/g)      ([cmol.sub.c]/kg)

Commercial metakaolin

Optipozz              17.9 *                   9.9
PoleStar 450           14.7                    3.9
M1200S                 21.7                    3.7
M1000                  14.9                    3.0
HP                     23.6                    4.1
BZ                     12.6                    7.6

Experimental metakaolin

MK-750                16.3 *                   6.1
MK-800                 9.6                     7.6
MK-800-M               11.8                    38.5
MK-830                 5.6                     6.7
MK-840                9.8 *                    7.8
MK-850                 10.9                    9.4
MK-900                 9.1                     6.3
MK-940                9.7 *                    9.9

* Gamelas et al. (2014)

Table 4 Experimental conditions for the production
of experimental metakaolins.

Sample      Input particle size          Input moisture content

MK-750             Powder             [approximately equal to] 2 %

MK-800             Powder             [approximately equal to] 2 %

MK-830    [approximately equal to]   [approximately equal to] 16 %
                   1.5 cm

MK-840             Powder             [approximately equal to] 2 %

MK-850    [approximately equal to]   [approximately equal to] 16 %
                   1.5 cm

MK-900    [approximately equal to]   [approximately equal to] 16 %
                   1.5 cm

MK-940    [approximately equal to]   [approximately equal to] 16 %
                   1.5 cm

Sample    Kiln temperature      Calcination time (h:min)
            ([degress]C)

MK-750          750          [approximately equal to] 1:05

MK-800          800          [approximately equal to] 1:30

MK-830          830          [approximately equal to] 2:25

MK-840          840          [approximately equal to] 1:05

MK-850          850          [approximately equal to] 1:05

MK-900          900          [approximately equal to] 2:25

MK-940          940          [approximately equal to] 1:05

Sample     Processing after
              calcination

MK-750             -

MK-800             -

MK-830    Soft disaggregation

MK-840             -

MK-850    Soft disaggregation

MK-900    Soft disaggregation

MK-940    Soft disaggregation
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Title Annotation:Original paper
Author:Ferraz, Eduardo; Andrejkovicova, Slavka; Hajjaji, Walid; Velosa, Ana Luisa; Silva, Antonio Santos; R
Publication:Acta Geodynamica et Geromaterialia
Article Type:Report
Geographic Code:1USA
Date:Jul 1, 2015
Words:5929
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