Maastritchian Limestones of Feriana Mountain used in White CementProduction (Central West Tunisia)

Tahar Aloui,w Anouar Ounis, and Fredj Chaabani

Laboratory of Mineral Resources and Environment, Department of Geology, Faculty of Mathematical, Physical andNatural Sciences, University Campus, 1060 Tunis, Tunisia

The Campanian to early Maastrichtian period is marked byimportant deposits of limestones in most parts of Tunisia andAlgeria. These limestones form the so-called ‘‘Abiod forma-tion’’. The present paper focuses on the ability of limestonesof Feriana Mountain (Jebel Feriana), Central West part ofTunisia, to produce high-quality white cement clinker. Fromdetailed experimental and analytical techniques’ data, the lime-stones of Abiod formation are particularly characterized by ahigh purity degree and whiteness index. They have a bright whitecolor with a slight visible tendency toward yellow-red. Based onBogue calculation, X-ray diffraction, and microscopical point-count methods, these particular limestones can convenientlyform a white Portland cement when mixed with B12.5% ofNeogene sands of Maamoura syncline and 7–10% by weight ofcommon Mediterranean kaolins.

I. Introduction

THE Feriana Mountain is situated in the Central TunisianAtlas, close to the Algerian border (Fig. 1). Its outcrops

emerged during the Santonian and Coniacian ages, whichare (from oldest to youngest): (1) The shale of Aleg formation(Santonian to Coniacian), which is poorly exposed along theChoubet Ali and Choubet Ettaref; (2) the chalk of Abiodformation (Campanian to early Maastrichtian), which hastypically 150–200 m thickness; it is subdivided into threemembers: lower and upper layers of chalks separated by amiddle shale, which is missing at Feriana Mountain1–7; and(3) the transgressive siliciclastic series, which are present mainlyin the west–east direction, in Maamoura and Bouhaya synclines(Fig. 1). They are composed of coarse whitish quartz sand, clay,gray to brown siltstone, and gypsum. According to Robinsonand Wiman,8 these series include the Messiouta formation(Aquitanian), which is underlain by the Abiod formation, theMahmoud continental formation (Burdigalian-Langhian),the Beglia formation (Serravallian-Tortonian), and the Seguiformation (Tortonian-Quaternary). Over these siliciclasticsediments, there are Quaternary alluvium and recent soilsassociated with coarse conglomerates, encrustations, yellow-colored sands, and brown clays.2,5,9

From the beginning of the 1980s, many investigations andvalorization of these geological series were undertaken byTrabelssi,10 Aloui,5 and Aloui and Chaabani.6,7,9 Only Maast-richtian limestones are valuable because of their high-puritydegree and whiteness index and can be used in several industrialproducts, such as paper, white cement, tiling, dimension stone,glass manufacture, painting materials, and pharmaceuticalproducts.

The present work uses a multidisciplinary approach toevaluate the ability of Maastrichtian limestones of FerianaMountain to supply a second line of production of whitecement, implanted at B4 km west from Feriana town (Fig. 1).The alumina should be provided by a clay extremely poor incoloring oxides, particularly, Fe2O3, Cr2O3, Mn2O3, and TiO2.

10

The literature on clay rocks from various scientific surveyshighlights the occurrence of kaolin deposits in Aın Khmoudavillage located at about 40 km North East of FerianaMountain.Unfortunately, this material cannot be used to produce largerquantities and this is the why several mineral industries need toimport kaolin from European providers. The deficiency in silicais compensated by controlled addition of Neogene sands fromMaamoura syncline (Fig. 1).

II. Experimental Procedure

Seven cores (SC01–SC07) were drilled to a depth of approxi-mately 70 m at Feriana Mountain (Jebel Feriana) to valorizethe Maastrichtian limestones and to evaluate the exploitablereserves (Fig. 2). The step of the sampling through thewhole lithology depends on homogeneity and thickness. Ifthe sample thickness is o2 m, one sample is taken from itsmiddle. If the sample thickness exceeds this limit, one sampleis taken every 2 m.

The contents of alumina oxide (Al2O3), calcium oxide (CaO),chrome oxide (Cr2O3), phosphorus pentoxide (P2O5), ferric ox-ide (Fe2O3), magnesium oxide (MgO), dimanganese trioxide(Mn2O3), titan dioxide (TiO2), and silicon dioxide (SiO2) fromthe raw material were determined by X-ray fluorescence (XRF)analysis on a Philips PW 1606 spectrometer (France) withautomated sample feed, reverse potential end window withRhodium anode and operated at 50 kV, 40 mA. Beads wereprepared by fusing mixtures of 0.7 g of powdered sample with 6g of lithium tetraborate (LiB4O7).

11–13 This step ofpre-preparation of the sample leads to a more homogeneousmaterial and, consequently, has the advantage of obtaining amore accurate XRF analysis. The contents of potassium oxide(K2O) and sodium oxide (Na2O) were obtained by atomicabsorption spectra. The determination of the content of sulfurtrioxide (SO3) was carried out by a gravimetric technique. Themethods used in the analysis of composition of phase include thetheoretical approach via Bogue calculation, the microscopicalpoint-count procedure, and X-ray diffraction (XRD). XRDanalyses were carried out using a Philips PANalytical X’PertPRO X-ray diffractometer with an automatic divergence slit, aspinner, an X’celator, and CuKa radiation at a scan speed of0.011 2y/s. The acceleration power applied was 40 kV, with acurrent of 40 mA. The difference between the experimental andthe theoretical peaks of Si (111) was within 2y5 0.0021 andthe diffraction data were evaluated by X’pert HightScoreplus

s

program. The percentages of the different mineral phases werecalculated using data obtained by XRD and Rietveld refine-ment. The global parameters of refinement control were basedon the scale factor and unit cell of each phase (alite, belite,aluminate, ferrite, free lime, and periclase).

P. Brown—contributing editor

wAuthor to whom correspondence should be addressed. e-mail: tahar.aloui@edunet.tnManuscript No. 23900. Received October 25, 2007; approved August 18, 2008.

Journal

J. Am. Ceram. Soc., 91 [11] 3704–3713 (2008)

DOI: 10.1111/j.1551-2916.2008.02725.x

r 2008 The American Ceramic Society

3704

For optical characterization, samples were dried systemati-cally, ground to a surface Blaine of 3000 cm2/g, and analyzed forcolor according to the International Commission on Illumina-tion CIEz 1976 L�a�b� color system.14 In this system, the colormeasurement is based on three distinct values: L� indicates thefactor of lightness or luminescence (white–black reading), a�

(red–green reading), and b� (blue–yellow reading).Additionally, three samples of kaolin and several clinker

specimens were collected from three Mediterranean countries(Spain, Turkey, and Egypt) and subjected to the same previousanalyses as limestones and sandstones.

To determine which of the chemical and optical variables con-tributed most to the variation in the entire data set, a multivariateordination technique, called principal components analysis(PCA), was performed using Systat and XLStat-pro softwares.

III. Results and Discussion

(1) Raw Materials’ Characterization

(A) Maastrichtian Limestones: One hundred and forty-four samples of the seven cores obtained from the Abiodformation have been analyzed for major and minor oxides(Table I). For the study area, the CaO content varies from55.17% (core SC02) to 55.55% (core SC05) with an average of55.32%, which proves the lateral regularity of the material.Compared with the pure calcite (CaO, CO2), limestones ofFeriana Mountain are characterized by a very high degree ofpurity (99.21%). Although the Abiod formation in the studyarea is lithologically homogeneous and typically constituted ofchalky limestones, the Fe2O3 content is relatively low and vari-able for each core. This is due to the state of bedrock, which isdeeply fractured and locally affected by karst corrosion, espe-cially near bedding planes and tectonic discontinuity. Themorphology and porosity of the sediment can also accentuatethe karstification in the area.7 Furthermore, the extremely lowcontent of MgO, o0.20%, indicates the weak dolomitizationprocess of the bedrock. As the table below demonstrates(Table I), the sum of the contents of Al2O3, coloring oxides(Cr2O3, Fe2O3, Mn2O3, and TiO2), and volatiles (K2O, Na2O,and SO3) varies between 0.25% and 0.54%, respectively, forSC05 and SC01 cores, which indicates the rarity of clays, sulfidesand sulfates in the sediment.

The observed data are constituted of p5 15 variables. Eachvariable is regarded as constituting a different dimension, in ap-dimensional hyperspace. To reduce the dimensionality of thedata set and extract the smallest number of components p0

(p0 rp) that account for most of the variation in the originaldata, a PCA was implemented.

PCA described here is achieved without axes rotation andstructured in, seven observations or cores (SC01–SC07) for 15variables analyzed, which include 11 chemical parameters(Al2O3, CaO, Cr2O3, Fe2O3, K2O1Na2O, MgO, Mn2O3, SO3,SiO2, and TiO2) and four optical parameters (whiteness (b), L�,a�, and b�). Because the original variables are equal in impor-tance, standard variates and correlation matrix are used asstated by Chatfield and Collins.15,16 The Pearson correlationcoefficient, which corresponds to the classical correlation coeffi-cient, was commonly used during compilations. It demonstratesa redundancy relatively high in the original data particularlybetween CaO and Fe2O3 (r5�0.965), CaO and SiO2

(r5�0.994), and L� and b (r5 0.96). Therefore, some ofthese variables can be removed without a significant effect onthe interpretation.

The quality of the projection from the p-dimensional initialtable (p5 15) to a lower number of dimensions (p0) is deducedfrom an eigenvalues matrix. Nine trivial eigenvalues were re-moved and only six uncorrelated PCs were extracted in a de-creasing order of importance. An eigenvalue higher than 1indicates that PCs account for more variance than accountedfor by one of the original variables in standardized data. This isused as a cutoff point for which PCs are retained. This procedureallows to reduce the dimensionality and fixing, subjectively, thefirst two components that account for a large proportion of thetotal data. The percentage of variability represented by the firsttwo factors (F1 and F2) is relatively low (67.421%), ensuringthat the maps based on F1 and F2 do not have a good quality ofprojection from the initial multidimensional table. Thus, it isnecessary to complement the results with a third factor.

The correlation circle on F1 and F2 axes shows that the con-tents of Na2O1K2O, SO3, and Mn2O3 are the nearest variableto the center (Figs. 3 and4); therefore, they are not highlycorrelated with the rest of the variables as shown previouslyby a correlation matrix. The F1 axis seems to be a factor of lightminerals. It is defined by lightness, whiteness, CaO, Fe2O3, andSiO2, whereas the chromaticity coordinates (a�, b�) and mostpart of the volatiles (Na2O, K2O, and SO3) define the F2 axis.Cr2O3 and TiO2 have the weakest squared cosines along F1

Fig. 1. Situation plan and geological draft of Feriana Mountain.

zCommission Internationale de l’Eclairage.

November 2008 Maastritchian Limestones of Feriana Mountain 3705

and F2 axes (o0.022); however, they increase considering the F3axis (0.898 and 0.531, respectively, for Cr2O3 and TiO2). Conse-quently, the F3 axis probably constitutes a factor of trace ele-ments with a high coloring effect as chrome and titanium (Fig. 4).

Fe2O3 and Al2O3 are moderately correlated (r5 0.499), whichindicates that the sources of contamination in iron are deliverednot only from karsts, which are often filled with reddish residualclay or other erosional or weathering materials (Table II), butalso from the transitional zone between the Maastrichtian lime-stones and the Santonian-Coniacian marls.5

For all cores, Fe2O3, SiO2, Al2O3, and SiO2 are two by twopositively correlated, which confirms their association in thenetwork of clayey minerals. The convergence between Al2O3 andFe2O3 described above indicates that the iron maybe emerging, in part, from illitic clay minerals. Additionally,the similar evolution of the SiO2 and Al2O3 couple leads to theassumption that the major part of silica belongs to the illite.5,6,9

However, we did not find any statistically significant correlationbetween Na2O1K2O and Fe2O3, Al2O3, and SiO2 for all cores.

From the colorimetric point of view (Table III), the lime-stones are characterized by a high whiteness index (b5 86.28)with a global tendency toward the yellow–red color (a�40 andb�40). Therefore, they can be used theoretically in totality toadjust the CaCO3 deficiency in the raw mix properly. The SC01and SC07 cores have a relatively low whiteness index (bo85),and it can be explained by the presence of reddish clay in karsticcavities.7 The core SC04 has a high whiteness (b5 87.71) and alow chromaticity value (a�5 1.06 and b�5 5.77). Therefore, itcan be used to correct the lime deficiency of the raw meal.

Based on the optical results (Figs. 5 and 6), the north flanktypically has high whiteness values (SC01, SC02, SC03, andSC06 cores), whereas the south one (SC04, SC05, and SC07cores) is much darker.

Vertically, as demonstrated by the whiteness profiles (Fig. 7),a clear correlation exists between the measured whiteness andthe depth for the cores, except for SC03 core. The whitenessvalues become larger with an increase in the content of lightminerals like carbonate and quartz and these values decrease asthe content of dark minerals, especially iron oxide and clay min-erals, increases in the sediment. To determine the cause of thecolor changes, Fe2O3 has also been plotted against depth. Theresulting profile seems to be symmetrical to whitenessone (Fig. 7). Therefore, the iron oxides are the primary factorresponsible for color changes of the sediment. The red reading(a�) is higher than zero for all samples, which ensures that theother types of oxides have a secondary effect on the whitenessvariation when compared with the iron. On the other hand, theyellow reading (b�) is characteristically higher than a�, whichsuggests, theoretically, a light yellow hue of the sediment. Visu-ally, the limestones have a light reddish hue due to hematite(Fe2O3), which masks the yellow color from goethite(FeO(OH)).

The SC04 core displays a clear positive convergence betweenwhiteness and depth (Fig. 7), which could be explained bythe presence of reddish residual clay in the fissured and karsticsector.7 However, the correlation between Fe2O3 and whitenessobserved in cores SC05 and SC06 is due to the vertical passageof the Maastrichtian-santonian marly Aleg formation.5

Fig. 2. Location map of cores drilled in the Maastrichtian limestones.

Table I. Chemical Composition of the Maastrichtian Limestones

Cores Number of samples Al2O3 CaO Cr2O3 Fe2O3 K2O1Na2O MgO Mn2O3 SO3 SiO2 TiO2 LOI

SC01 24 0.31 55.36 0.01 0.10 0.07 0.00 0.01 0.03 0.44 0.02 43.65SC02 12 0.19 55.35 0.01 0.16 0.04 0.20 0.01 0.05 0.55 0.02 43.42SC03 24 0.19 55.61 0.01 0.08 0.07 0.01 0.01 0.03 0.37 0.01 43.61SC04 24 0.18 55.61 0.02 0.06 0.06 0.00 0.01 0.03 0.31 0.03 43.69SC05 20 0.11 55.65 0.01 0.05 0.05 0.00 0.00 0.03 0.23 0.01 43.87SC06 15 0.12 55.72 0.00 0.04 0.05 0.00 0.01 0.06 0.23 0.01 43.76SC07 25 0.23 55.64 0.01 0.09 0.06 0.00 0.01 0.02 0.32 0.02 43.60

LOI, loss on ignition.

3706 Journal of the American Ceramic Society—Aloui et al. Vol. 91, No. 11

For SC01, SC02, and SC07 cores, their profiles display aslightly divergent behavior between whiteness and depth. At thislevel, the ground water system is highly dynamic; the water hashad a small time of contact with limestone bedrock and, there-fore, the dissolution is attenuated easily.7 This could be ex-plained in part by the presence of a fluid circulation patternparticularly through faults and nodulous passages.

Apart from the hinge zone of the anticline and the transitionzone between the formations Abiod and Aleg as the SC03 core,it was noticed that there was no significant correlation betweenthe two parameters. The absence of the upper part of limestoneand the morphology, which is favorable for fast water drainagetoward the downstream, could also be behind the indepen-dence.5

According to the variability of limestones, we can deducethree main groups shown by the diagram of observations(Fig. 8), which are:

(1) dark-colored limestones, which are represented by SC01and SC07 cores,

(2) dark and less colored limestones, which concern only theSC02 core; and

(3) light limestones, which group SC03, SC05, SC04, andSC06 cores.

(B) Neogene Sands: The sands used are sourced fromthe Beglia formation.2,5,8,9 It is comprised of mega sequences ofcross-stratified sand and whitish sand with decimetric intercala-tions of grayish to greenish clay and small ferruginousmulticolored dragee of quartz locally rusty weathering.Toward the top, plant debris, silicified wood paleoflora, dissem-inated vertebrate elements (teeth, bones, phalanges y), andtraces of burrow structures are occasionally presentspecifically in lenticular clay. The good classification of thisdetrital sediment indicates that the Beglia formation would beset up, probably, on a high river bottom by a water currentwith decreasing transport capacity.5–7,16 The detailed chemicalcomposition of a representative sample of sands is reported(Table IV).

The fine fraction is yellow (b�4a�) in most due to claylikeminerals on the grain surface; whereas the coarse one is rela-tively red due to the mineral fillers in large pores that accentuatethe overall appearance of the grain.

(C) Mediterranean Kaolins: Three Mediterraneankaolins, arbitrarily named A, B, and C, were collected andthen subjected to the same analyses as Maastrichtian limestonesand Neogene sands. In comparison with kaolinite, which iscomposed of 39.48% Al2O3 and of 46.54% SiO2, the kaolins Aand C are relatively saturated in alumina (Table IV). The kaolin

Na2O

Fig. 3. Correlation circle of variables on F1 and F2 axes.

Fig. 4. Correlation circle of variables on F2 and F3 axes.

Table II. Chemical Composition of Reddish Residual Clay

Al2O3 CaO Cr2O3 Fe2O3 K2O1Na2O MgO Mn2O3 SO3 SiO2 TiO2 LOI

4.741 30.429 0.000 3.922 0.020 8.623 0.222 0.243 14.274 0.061 37.465

Table III. CIE L�a�b� and b Parameters of MaastrichtianLimestones of Feriana Mountain

Core b L� a� b�

SC01 84.91 93.34 1.74 6.35SC02 85.84 93.78 0.96 5.84SC03 86.57 94.18 1.28 6.06SC04 87.71 94.74 1.06 5.77SC05 87.26 94.54 1.2 6.44SC06 86.76 94.28 1.25 6.24SC07 84.93 93.39 1.91 7.36

CIE, Commission Internationale de l’Eclairage.

Fig. 5. 2D distribution of cores according to L� and a� chromaticitycoordinates.

November 2008 Maastritchian Limestones of Feriana Mountain 3707

B is rich in SiO2 (61.07%) and poor in Al2O3 (26.54%). Theexcess of silica is present in the form of quartz. This naturalmixture would facilitate the homogenization of the raw flourand would minimize the contribution in coloring oxides duringthe grinding stage.5

The content of volatile components (K2O, Na2O, and SO3)varies between 0.33% (kaolin C) and 1.02% (kaolin A). As aresult, the mix probably will not have a meaningful effect on thefinal quality of the product or on the line process. Moreover,even if we suppose that all aluminum oxide is originated entirelyfrom the kaolin, these samples cannot provide a significant pos-sibility to substitute partially the Tunisian sedimentary clays,which are often rich in iron oxides.

From the colorimetric point of view (Table V), all kaolinsamples draw a� toward red values and b� toward yellow values.The kaolin A is less colored and lighter than the other twosamples. In the a�b� color space, kaolin B and kaolin C plot inthe yellow domain. No significant difference in was foundchrome the values between the kaolin B and C.

IV. Clinker Characterization

(1) Phase Composition

(A) By Bogue Calculation: The chemical composition ofthe raw mix corresponds to the quality requirements expressedby the silica ratio (SR), the Lafarge specific lime standard (Dbc),and the potential clinker phase tricalcium aluminate (C3A):

(1) The SR SR ¼ SiO2

Al2O3þFe2O3

� �describes the relationship

between the silicate of calcium (C2S1C3S) and the melt formedby C4AF and C3A,17 where C stands for calcium oxide, S forsilica, A for alumina, and F for iron oxide.

(2) Delta of raw is a specific notion of the Lafarge Groupthat estimates the lime quantity that is not fixed by SiO2, Al2O3,and Fe2O3; it is expressed under relation to the same oxides inthe standard kiln conditions of burning and cooling. Lowvalues may result in lower strength cement and high values

Fig. 6. 2D distribution of cores according to b� and a� chromaticitycoordinates.

Fig. 7. Lithology logs showing Fe2O3 and whiteness vertical profiles.

Fig. 8. Distribution of cores according to F1 and F2 axes.

3708 Journal of the American Ceramic Society—Aloui et al. Vol. 91, No. 11

usually indicate mixes that are difficult to burn.

Dbc ¼ 2:8SiO2 þ 1:65Al2O3 þ 0:35Fe2O2 � CaO

SiO2 þAl2O3 þ Fe2O3 þ CaO

� �

(3) Tricalcium aluminate,18 which is calculated according tothe formula: C3A5 2.650Al2O3–1.692Fe2O3.

Other criteria including fineness of the raw materials, insol-uble residue, and free lime (FL) are given in Table VI.

To calculate the optimal feed ratios of the raw materialsdespite disturbances, any ingredients in trace amounts areneglected. Only Maastrichtian limestones, Neogene sands, andMediterranean kaolin were considered. The final results on thebasis of the above criteria and analysis are presented inTable VII.

The potential chemical composition of the clinker resultingfrom the previous feed ratios is described in the Table VIII.

From the elemental composition of the clinker, it is possible topredict, in an approximate manner, the major respectivedistributions of the four main phases formed in the kiln basedon CaO, SiO2, Al2O3, and Fe2O3 percentages.14,15,19,20 Thissimplified theoretical process shows that the clinker is made up,essentially, of three main phases: tricalcium silicate C3S (72.436–73.255%), dicalcium silicate C2S (14.707–15.108%), and tricalci-um aluminate C3A (10.06–10.735%). The amount of tetra-cal-cium aluminoferrite C4AF is extremely low (o1% for all samplesof kaolin used).

The clinker has a higher final strength, better grindability (C3S450%) and lower gypsum consumption in the final grindingstage. The low contents of magnesia (o0.15%) and FLindicate the low risk of volume expansion after setting. Further-more, a clinker with a C3A amount higher than 10.06% (kaolinC) would enhance the workability of the mortar. However, due tothe low C4AF contents (o0.84%), C3A considerably aids kilnburning because of the unique flux that aids in reactions of theother phases. If we disregard the influence of the manufacturingprocess on the total alkali content as Na2O and K2O, the cementwill have a low alkali aggregate reactivity and lower possibility ofvolume change at a later age.21,22 It is important to note here thatthe Bogue equation does not fully predict the result of clinkerformation. This is mainly because it does not take into accountthe effects below:

(1) Minor oxides, which are always present in incompletefusion or remain uncombined within the clinker;

(2) Coarse grains, which hardly combine; and(3) Cooling very fast, where some quantities of vitreous

material can remain unchanged in the clinker.(B) By XRD: Because the Bogue equations predict

only a bulk average composition and cannot be used to predictlocalized concentration variations occurring within the clin-ker,23,24 the major mineral phases identified were confirmed bythe XRD method according to the ASTM C 1365-98 norm.13

The mineralogical patterns (Fig. 9) confirm that all the resultingclinkers were found to have a similar composition. However, theclinker based on kaolin A shows a slightly low C4AF and highC3A contents compared with the other two clinkers. Theoverall amount of phase mineral is essentially composed ofalite (71.7–72.25%), belite (13.18–14.65%), and aluminate(10.82–11.93%). Additionally, a small quantity of aluminofer-rite (o0.89%) was observed in all samples (Table IX).

Most part of C2S is bC2S (larnite), characterizing a rapidcooling process of the clinker. Small portions of b form (o2%)undergo a phase transformation to gC2S. This phenomenonseems to be associated with dusting and cracking that may resultin disintegration of the clinker during test. FL and periclase(MgO) were in trace amounts, characterizing an efficient clinke-ring process and low concrete expansion after a late age assignaled previously by the chemical composition of kiln feedmaterials.

(C) By Microscopical Analysis: Microscopic analysiswas used as an accurate tool to qualify and to quantify themajor phases of the clinker based on kaolin A, B, and Csamples. The counting of 2000 point results according to theASTM C 1356M-96 norm,13 shown in Table X, confirmed anormal formation and distribution of the major phases ofalite (72.21–73.05%), belite (14.58–14.83%), aluminate(10.73–11.43%), and aluminoferrite phases (0.37–0.78%). In

Table IV. Average Chemical Composition of Neogene Sands of Maamoura Syncline and Kaolin A, B, and C

Al2O3 CaO Cr2O3 Fe2O3 K2O1Na2O MgO Mn2O3 SO3 SiO2 TiO2 LOI

Neogene sands 3.23 0.00 0.01 0.46 1.11 0.45 0.01 0.16 92.74 0.19 1.64Kaolin A 32.44 — 0.008 0.235 1.02 — 0.001 — 52.70 0.64 12.95Kaolin B 26.54 0.27 — 0.637 0.03 0.20 — 0.141 61.07 0.43 10.66Kaolin C 34.02 0.47 0.004 1.250 0.15 0.16 0.001 0.028 48.27 2.42 13.26

LOI, loss on ignition.

Table V. CIE L�a�b� and b Parameters of the Used Kaolins

b L� a� b�

Kaolin A 74.93 88.90 5.46 17.49Kaolin B 68.25 85.87 9.53 28.39Kaolin C 69.25 86.32 9.53 28.39

Table VI. Main Criteria used to Adjust the Feed Materials

SM Dbc C3A

Limestone and

kaolin fineness

Sand

fineness

Insoluble

residue

Free

lime

5–5.6 4.5–5 10–11% 10%(100 mm)

0%(100 mm)

0.15% 2.5%

Table VII. Theoretical Feed Rate of Raw Materials

Kaolin (%) Limestone (%) Sand (%)

Kaolin A 6.37 80.81 12.82Kaolin B 7.89 80.83 11.28Kaolin C 5.88 80.70 13.42

Table VIII. Potential Chemical Composition of the Studied Clinkers

Al2O3 CaO Cr2O3 Fe2O3 Na2O1K2O MgO Mn2O3 SO3 SiO2 TiO2

Clinker based on kaolin A 4.14 70.49 0.02 0.22 0.40 0.13 0.01 0.08 24.38 0.13Clinker based on kaolin B 4.06 69.83 0.01 0.26 0.27 0.14 0.01 0.10 24.19 0.11Clinker based on kaolin C 4.06 70.35 0.02 0.31 0.32 0.15 0.01 0.09 24.41 0.29

November 2008 Maastritchian Limestones of Feriana Mountain 3709

general, the results demonstrate a reasonable agreement amongBogue calculation, XRD, and optical data for the silicatesand the total interstitial phases. The slight increase observed insilicates, by microscopy, is due to the incorrect identification ofother phases that are limited by homogeneity and crystal size asaluminate, ferrite, FL, and periclase in the specimen. The ferritephase is in traces for all clinkers. This may result from itsfine crystal size (fine grained to extremely fine grained), whichmade it difficult to see this phase and to distinguish visually fromthe aluminate.

The EDAX spectrum according to the method withoutstandards (Fig. 10) shows the presence of low amounts ofmanganese in the clinkers which result probably from themanganese dendrites observed in the Maastrichtian limestones.

V. Clinker Morphology

The clinker has a crystal with an intermediate size and exhibits arelatively homogeneous phase distribution (Fig. 11). Aliteappears as crystals of subhedral to anhedral forms, rangingapproximately from 30 to 40 mm in size, and it forms the bulk ofthe clinker. Very small inclusions of FL and periclase on thesurface are also noticed. Several pores sometimes have alkalis

and sulfates. Belite occurs as rounded crystals about 15 mm indiameter, which often exhibits the internal lamellar structure.Aluminate displays 4 mm cubic or orthorhombic crystals,exhibiting an irregular to a lath-like habit, filling the areabetween the alite and the belite crystals. The relatively smallsize of C3A implies that they are highly reactive with water. Theferrite crystals may be microscopically difficult to distinguishfrom aluminate in the matrix because of the fine texture of thealuminate and lack of iron in the raw materials.

VI. Prediction of the Burnability

The readiness with which the raw mix is transformed into alite,belite, and aluminate during the high-temperature treatment isdetermined by their chemical (balance of alkalies and sulfur),mineralogical and granular composition, or a combination ofthese parameters.19 Generally speaking, the burnability ofthe raw mix in the kiln can, to a large degree, be predicted asdescribed in Table XI.

As mentioned previously, taking into consideration the lowvalue of FL in the clinker and the high aluminoferric module(MAF5 17), the high minimal burning temperature of raw meal(15801C) is certainly due to the low iron content in the raw

Fig. 9. X-ray diffraction (XRD) patterns of clinker based on kaolin A.

Table IX. Quantitative Phase Analysis of the Clinker usingXRD Method

Phases

Content (%)

Kaolin A Kaolin B Kaolin C

C3S 72.2572.5 72.1372.5 71.772.5b-C2S 12.6970.5 13.4570.5 12.9270.5g-C2S 1.0970.2 1.2770.2 1.2970.2C3A 11.9370.2 10.8270.2 11.3670.2C4AF 0.4270.3 0.5970.3 0.8970.4

Table X. Crystallographic Composition of Clinkers byPoint-Counting (at 96% Confidence Level)

Phases

Content (%)

Kaolin A Kaolin B Kaolin C

C3S 73.0572 72.8372 72.2172C2S 14.5871.6 14.8371.6 14.6271.6C3A 11.4371.5 10.7371.4 11.2971.4C4AF 0.3770.3 0.5970.3 0.7870.4

3710 Journal of the American Ceramic Society—Aloui et al. Vol. 91, No. 11

mix that forms the matrix. Besides, the lack of iron makescombination with the clinker minerals more difficult andrequires more thermal energy.23,24 Consequently, the viscosityof the clinker would be important and the diffusion in themelted matter would be decelerated. The contribution ofmineralizers as CaF2 reinforces the calcination process, adjuststhe quality of the clinker, and decreases the energy consumptionin the kiln.10,25,26 Furthermore, this process reduces the eventualemission of nitrogen oxides (NOX) considerably.

27

The high SR of 5.6 decreases not only the tendency to burn,but also its tendency toward for granulation in the clinkeringreaction zone. It results in a dusty clinker with fine grains re-sponsible for the gC2S polymorph phase, accompanied by aweak thermal efficiency during, cooling, which would result in aslow hardening of the clinker and a fast attack of refractorybricks which is a relatively frequent problem in white cementline production. Moreover, the significant content of C3S (72%)implies the possibility to generate a cement of a high initial setand final strength with developed resistance to sulfur attack.

VII. Comparison with Mediterranean White Clinkers

Compared with other Mediterranean clinkers (Table XII), thepresent clinker has less coloring oxides, expressed essentially byFe2O3 that have a tendency to redden the cement with time dueto sunlight exposure. The content of hazardous oxides, MgO,SO3, and total alkali (K2O1Na2O), is low too; these alkaliescan inevitably enter the kiln system with the raw mix and,

eventually, the fuel. On reaching the kiln burning zone, somevolatile components evaporate and are carried with the kiln gasto the preheater, where they condense. A higher concentrationof volatile matter increases dust stickiness, which in turn causescoating formation and cyclone blockages.28

With an average whiteness and brightness of 86% and 94%,respectively, the clinker has an excellent quality. Its brightnessand whiteness are superior to those of Mediterranean clinkers.The chromaticity analysis shows that the Mediterraneansamples tend toward yellow or gray colors, while the presentclinker tends toward green, which is due to the higher Cr2O3

content of magnesia-chrome refractory bricks. These resultsprove that every clinker has its own color tendency thatdepends on the quality of the raw materials, the kiln anddiscolorator atmospheres, and the conditions of storage and use.

VIII. Optimization of the Optical Characteristics

(1) Selection of Raw Materials

The whiteness and brightness of white cement are the result ofthe discriminating choice of raw materials on the basis of theclinker. The limestone must have a very high degree of purity.The required alumina (Al2O3) and silica (SiO2) oxides areprovided, preferably, by the kaolin. The deficiency of silicawould be adjusted by adding sand with a high purity. Althoughthe samples of limestones and sands used in this study meet therequirements of white cement clinker, the propositions below(Table XIII) could significantly enhance the optical consistencyof the end product when adopted appropriately.

(2) Process and Production Line

During kiln burning, particles furnished by the erosion ofthe refractory bricks, which are generally rich in Cr2O3, canpass to the melt and give the clinker its green hue. Thiscontamination can be remedied by the use of magnesia-based refractory.11 The coloring effect of transitional metallicions in cement clinker is dependent on the individual metalion, in the presence of other metal ions, and their relativemetal ion-oxygen bond strengths. The ions with the highestbond strength to oxygen occupy tetrahedral coordinationsites in the clinker crystal structure.29 In order to reducethe iron coloring effect, the pyroprocess should be modifiedto form octahedral ions rather than tetrahedral ones by inducinga reducing atmosphere in the kiln that leads the ions to takeup the (1II) oxidation state rather than the (1III) oxidationstate.

The burning of the clinker in a reducing environment shiftsthe composition of the C4AF solid solution series toward theC6AF2 composition. This approach releases more alumina toform C3A, which is a colorless mineral, and promotes whiteness

Fig. 10. EDAX spectrum of the clinker based on kaolin A.

phase (i) which is composed essentially by aluminate

Fig. 11. Overall view on the microstructure of clinker A.

November 2008 Maastritchian Limestones of Feriana Mountain 3711

in the clinker.30 To preserve the whiteness of these minerals, theymust be cooled rapidly to avoid all reoxidation of the clinker.

IX. Conclusion

From the results presented and discussed above, we highlight acertain number of inferences that we judge useful to underline:

(1) Maastrichtian chalks of FerianaMountain are very purelimestones that are characterized by a high CaO content(98.79%) and a high whiteness degree (b5 86.28). In the CIE

L�a�b� space, they have a bright white color (L�5 94.04) with aslight visible tendency toward yellow–red (a�5 1.34; b�5 6.29).

(2) Based on the Bogue calculation and the XRD technique,it can be inferred that the limestones studied, under the optimumconditions of SR, Dbc, and C3A phase, can conveniently form ahigh-quality white cement clinker when mixed with 7–10%by weight of common Mediterranean kaolins. The deficiencyof silica in the raw meal can easily be adjusted by adding anadequate quantity of Neogene sands from Maamoura syncline(B12.5%).

Table XI. Burnability of the Raw Mix

Formula Kaolin A Kaolin B Kaolin C

Minimal burning temperature (1C) 130014.51C3S�3.74C3A�12.64C4AF 1582 1578 1578Liquid phase (%) MAF 40.64 at 14501C 3.0Al2O312.25Fe2O31MgO1K2O1NaO21SO3 13.5 13.2 13.4

Kuhl burnability index C3SC3AþC4AF

6.5 6.5 6.5

Burnability factor LSF110.MS13(MgO1K2O1NaO2) 153 153 153

Table XII. Comparison of the Studied Clinker with Mediterranean Ones

Other Mediterranean clinkers Present clinker

Min Max Average Kaolin A Kaolin B Kaolin C

Chemical composition (%)Al2O3 2.18 4.61 3.39 4.14 4.06 4.06CaO 66.83 68.87 67.85 70.49 69.83 70.35Fe2O3 0.26 0.27 0.26 0.22 0.26 0.31K2O1Na2O 0.24 0.46 0.35 0.40 0.27 0.32MgO 0.61 2.67 1.64 0.13 0.14 0.15SO3 2.24 2.67 2.45 0.08 0.10 0.09SiO2 22.7 23.23 22.96 24.38 24.19 24.41

Optic characteristicsL� 72.79 93.66 83.22 94.57 94.30 93.61a� �1.67 �1.50 �1.58 �2.17 �2.62 �2.73b� 130.83 15.37 18.10 13.23 13.90 14.19b 83.79 88.03 85.91 86.52 86.12 86.02Tendency Yellowish to grayish Greenish Greenish Yellowish to grayish

L� indicates the factor of lightness or luminescence white–black reading. a� indicates the factor of lightness or luminescence red–green reading. b� indicates the factor oflightness or luminescence blue–yellow reading.

Table XIII. Main Possibilities to Reduce the Clayey Fraction in Raw Materials

Propositions Observations

Limestone Preserve the limestone of good quality by adequatemixture of materials sourced from many quarry faces

Use a selective exploitation;Employ large quarry faces with 12 m high benches7

Sand Separate fine and coarse fractions by sifting andhydrocycloning methods

Decreases the service life of the sand grinder withmore maintenance programs;Difficulty in store unused materials;Expensive project

From well logs and outcrop data, materials nearSS02 core seem to be of good quality

The sand is characterized by a suitably low levels ofcoloring oxides;Difficult access to the sand quarry particularly in rainyweather;Risk of modification of the hydrographic network

Partial substitution of neogene sands bythose of Sidi Aıch formation located roughly17 km south of Feriana town

This sand is characterized by9:SiO2 498%Fe2O3 o0.05%98% of grain size are o400 mm

Kaolin Use a kaolin richer in alumina and poorerin transitional metals and total alkalis

Optimize the fine grinding of kaolin by adding anadequate quantity of local sand;A detailed investigation to partially substitute theMediterranean kaolins by Tunisian clay must be takeninto consideration

3712 Journal of the American Ceramic Society—Aloui et al. Vol. 91, No. 11

(3) The overall amount of phase mineral in the resultingclinker is essentially composed of alite (B72%), belite (B14%),and aluminate (B11.5%). Additionally, a small quantity offerrite is noted in all samples (o1%).

(4) Even with fixed SR, Dbc, and C3A, considerabledifferences can occur in the clinker due to alkali, sulfur, andmagnesium raw mix grade variations. This composition reflectsmainly the effects of kiln temperatures, residence time, quench-ing, oxygen, and methane availability.

Acknowledgments

The authors gratefully acknowledge the comments and suggestions of thereviewers. This study could not have been completed without the dedicated effortsof the Tunisian-Andalusian White Cement Company (SOTACIB). Theauthors thank Miss Rawdha Brini (Laboratory of Photovoltaic Materials andSemiconductors (LPMS-ENIT)) for her skillful assistance with the acquisition ofphotographic material. The authors would also like to thank Besma Zouabi Aloui,Samia Zouabi, Moncef Allala, Zouhair Boukari, and Karen Goraieb (Universi-dade Estadual de Campinas, Instituto de Quımica, Brazil) for their contributionsin this work.

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