Arab J Sci Eng (2014) 39:4485–4506DOI 10.1007/s13369-014-1035-5

RESEARCH ARTICLE - CIVIL ENGINEERING

Evaluation of Kuwaiti Argillaceous Materials as a Replacementof Sand for Clinker Production

Suad Kh. Al-Bahar · Tilak V. Bogahawatta · Abdullah Kh. Al-Enezi ·Sadikah Gh. Ali · Hasan Kh. Kamal · Sharifa B. Al-Fadala ·Amani A. Al-Othman · Montaha H. Bahbahani · Abdul Salam Al-Hazza

Received: 18 October 2012 / Accepted: 31 January 2013 / Published online: 1 May 2014© King Fahd University of Petroleum and Minerals 2014

Abstract The clay materials from the investigated Bahraarea were studied under laboratory conditions for its suitabil-ity to replace sand and compensate for some of the bauxiteand the iron ore used in the raw mixes for the manufactureof ordinary Portland cement (OPC) and sulphate-resistantcement (SRC). The testing program was based mostly onthe two fundamental parameters: the grindability and burn-ability. Results have shown that the raw mixes with Bahraclay required less energy for grinding to attain the criticalfineness. Also, it was evident from the grindability tests thatBahra clay matches the same grindability of the limestone,while the sand requires much longer time to attain the samefineness. Results of the burnability tests showed that addingBahra clay to the raw mixes has solved the technical problemsof fusing and cracking during burning. Results of burnabilitytests were very encouraging for SRC raw mixes with Bahraclay as the quality of clinker was similar to that of the SRC.

Keywords Grindability · Burnability · Bahra clay ·Volatility · Free lime

S. Kh. Al-Bahar (B) · T. V. Bogahawatta · A. Kh. Al-Enezi ·S. Gh. Ali · H. Kh. Kamal · S. B. Al-Fadala · A. A. Al-Othman ·M. H. Bahbahani · A. S. Al-HazzaKuwait Institute for Scientific Research,P.O. Box 24885,13109 Safat, Kuwaite-mail: sbahar@kisr.edu.kw

1 Introduction

Continuous attempts have been made in the cement industryto use alternative raw materials and modified manufactur-ing processes to reduce the cost of production of cement, to

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enhance the quality of cement and to protect the environ-ment [1–5]. One of the methods to achieve the above targetis to use the locally available raw materials for clinker pro-duction. However, the suitability of the alternative materialas a replacement of conventional material requires a deepunderstanding on the basic properties of the material.

A joint project was undertaken between Kuwait CementCompany (KCC) and Kuwait Institute for Scientific Research(KISR) to evaluate the suitability of local raw materials forthe production of Portland cement and surface and subsurfaceexplorations were carried out in various areas of Kuwait [6,7]. Based on the outcome of the preliminary investigation,three exploratory sites were recommended and selected fordetailed subsurface exploration.

These areas are Al-Ahmadi quarry, Had Al-Himarah andAl-Khairan as potential locations for limestone and Bahraarea as potential location for clay and partially for sand ofbetter quality. Forty-seven boreholes were drilled at a totaldepth of 1,000 m, and 850 samples were prepared for chem-ical analysis. The map in Fig. 1 shows the locations of theexploratory boreholes drilled in various sites in Kuwait.

Ghar formation of the Kuwait geological group andDammam formation was recognized from the drilled bore-holes in Al-Ahmadi quarry. Dammam formation, which liesbelow the Ghar formation, is composed of chertified dolomi-crite and chalky dolomicrite. In addition, the limestone isoften found intermingled with hard cherty rock layers whichare difficult to be separated. Results of limestone analyses ofAl-Ahmadi quarry found to be discouraging because of thehigh percentage of dolomite as in MgCO3 and MgO [8–10].

Clay sources were found in a 1.5-square-kilometres area inBahra. The muddy sand stratum has maximum clay contentof 10–36 %. Selective mining of productive layers in Bahrayielded lean clay, which can be used in raw mix composi-tions to partially or completely substitute bauxite (aluminiumoxide) and sand. The total volume of clay content in the Bahraarea under investigation is roughly estimated to be 18 millioncubic metres, equivalent to 45 million tons which is enoughto use for practically 20 years [8–10].

Cement companies encounters several problems such ashigh wear and tear of rotary kiln lining and dusty nature ofclinkers due to the use of sand as a raw mix constituent. Also,sand reacts slowly in clinkering when compared to clay andthis necessitates fine grinding of sand to improve the sin-tering, which is not economical. Breaking of Si-O latticestructure in silica for clinker reactions is more energy inten-sive than that for alumino silicates (clay). Based on results ofexploratory drilling program and chemical analyses carriedout in investigations, Bahra area was approved to be as a loca-tion for suitable clay. Therefore, it was agreed to utilize theBahra clay to completely replace sand and also to partiallycompensate for some of the bauxite and iron ore contents inthe raw mix. Introduction of Bahra clay was considered to be

useful to solve the technical problems and also to have lessdependence on imported raw materials.

Several raw mixes were designed to incorporate Bahraclay by completely replacing the sand and decreasing the per-centage of bauxite and iron ore based on ordinary Portlandcement (OPC) and sulphate-resistant cement (SRC) mixes.The testing program was based mostly on two fundamen-tal tests, the grindability and burnability tests. Comparisonswere drawn between the different raw mixes and laboratory-prepared clinkers to assess their qualities when Bahra clayreplaces the sand.

2 Experimental Procedure

The methodology and experimental procedure adopted in thepresent study are given below:

2.1 Reactivity of the Kiln Feed

The reactivity is the overall rate of chemical reactions bet-ween the constituents of the raw mix in burning. The com-pound composition of raw materials, the chemical/granulome-tric properties, and the chemical process of clinker formationinfluence the reactivity. Reactivity is a function of silica mod-ulus (SM) and alumina modulus (AM). Low reactive mixesrequire higher sintering temperatures and/or long burningperiods and increased fuel consumption [11].

2.2 Raw Mix Preparation

The experimental investigations of clinker produced withBahra clay by complete replacement of sand were conductedwith three basic OPC raw mixes and two basic SRC rawmixes (with six of their modifications). The mixes weredesigned based on chemical analysis of raw materials, andthe raw mix designs used by the KCC for the production ofOPC and SRC clinkers, as presented in Tables 1 and 2 alongwith the chemical composition of sand and Bahra clay.

The mineralogical composition of Bahra clay and sand iscompared, and the diffractogram of Bahra clay indicates thatkaolinite, quartz (silica) and haematite are the predominantminerals present. The accessory minerals included feldsparsand calcite. The approximate amounts obtained for kaolinite,quartz, haematite, feldspars and calcite in a selected sampleof good quality of Bahra clay are 24, 25, 21, 8 and 22 %,respectively. The mineralogical composition of sand indi-cates Quartz (silica) as the major mineral with an approxi-mate amount of 50.1 %. Calcite and albite are present in com-paratively low percentages. Traces of dolomite and micro-cline intermediate are also present in the tested sand.

The mixes differed with respect to SM, AM, hydraulicmodulus (HM), Lime saturation factor (LSF), C/S ratio and

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Fig. 1 Locations of theexploratory boreholes in Kuwait

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Table 1 Chemical analyses of commercial, theoretical and laboratory-prepared raw mixes

Parameter OPC-hard burning Kilnfeed (commercial)a

Proposed raw mixes(theoretical)b

Raw mixes (laboratoryprepared)b

Sand Bahra clay

XRF analysis Calculated composition XRF analysis XRF analysis XRF analysis

Mix I Mix II Mix I Mix II

SiO2 14.43 14.12 14.11 13.19 12.58 89.31 73.72

Al2O3 3.63 3.37 3.41 3.6 3.51 2.54 8.41

Fe2O3 2.93 2.82 2.42 2.82 2.37 1.15 1.11

CaO 41.88 42.41 42.63 42.4 42.9 2.38 5.24

MgO 0.66 0.73 0.74 0.79 0.82 0.50 1.46

K2O 0.21 0.33 0.33 0.36 0.36 0.60 0.95

Na2O 0.03 0.11 0.11 0.11 0.12 0.28 0.66

SO3 0.141 0.12 0.13 0.107 0.109 0.45 0.26

Cl− 0.013 0.02 0.021 0.025 0.026 0.06 0.10

LOI 33.64 35.23 35.39 35.51 35.84 2.54 7.26

Total 97.56 99.24 99.27 98.912 98.635 99.81 99.17

L.S.F 89.87 93.53 94.51 98.57 104.87 − −S.M 2.2 2.28 2.42 2.05 2.14 − −A.M 1.24 1.2 1.41 1.28 1.48 − −C3S 31.82 38.33 39.57 43.84 51.76 − −C2S 17.36 11.57 10.61 4.75 2.89 − −C3A 4.66 4.16 4.95 4.77 5.29 − −C4AF 8.92 8.58 7.36 8.58 7.71 − −a Raw materials ratios: limestone = 79.6 %, sand = 12.3 %, bauxite = 5.3 %, iron ore = 2.8 %, OPC raw mix residue on 170 mesh = 8 %b Raw materials ratios: Bahra clay = 16.1 %, limestone = 78 %, bauxite = 3.7 %, iron Ore = 2.2 %, mix I and II raw mix residue on 170 mesh = 8 %

Table 2 Chemical analyses of commercial, theoretical and laboratory-prepared raw mixes

Parameter SRC Kiln feed(commercial)a

Proposed raw mix III(theoretical)b

Raw mix III (laboratoryprepared)b

SRC Kiln feed (commercial6 % residue)

XRF analysis Calculated composition XRF analysis XRF analysis

SiO2 15.12 14.73 13.9 14.29

Al2O3 2.67 2.53 2.78 2.69

Fe2O3 3.72 3.52 3.38 3.66

CaO 42.27 42.35 42.16 41.86

MgO 0.65 0.74 0.85 0.77

K2O 0.22 0.35 0.38 0.24

Na2O 0.04 0.12 0.11 0.09

SO3 0.089 0.12 0.125 0.188

Cl− 0.01 0.021 0.027 0.015

LOI 33.93 34.8 35.11 35

Total 98.72 99.25 98.82 98.803

L.S.F 88.24 91.04 94.96 91.58

S.M 2.36 2.44 2.26 8.97

A.M 0.72 0.72 0.82 0.73

C3S 33.66 38.1 42.13 37.97

C2S 17.96 13.49 8.07 12.32

C3A 0.79 0.75 1.65 0.94

C4AF 11.32 10.71 10.28 11.14

a Raw materials ratios: limestone = 79.6 %, sand = 13.45 %, bauxite = 3.05 %, iron ore = 3.9 %, SRC raw mix residue on 170 mesh = 8.9 %b Raw materials ratios: limestone = 77.8 %, Bahra clay = 17 %, bauxite = 2.1 %, iron ore = 3.1 %, mix II raw mix residue on 170 mesh = 8.9 %

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Table 3 Mix designations of the different raw mix samples under inves-tigations

Raw mix Raw mix fineness as percentage residue on 170 mesh (%)

6–8 8–10 10–12 12–14

OPC I IS2 IS3 IS4 IS5

OPC II IIS2 IIS3 IIS4 IIS5

SRC III IIIS2 IIIS3 IIIS4 IIIS5

OPC IVa IVS2 – – –

SRC Vb VS2 – – –

OPC VIc VIS2 – – –

SRC VIId VIIS2 – – –

a Based on OPC, with Bahra clay (3–20 m), raw materials mixed andground togetherb Based on SRC, with Bahra clay (3–20 m), raw materials mixed andground togetherc Based on OPC, with Bahra clay (3–20 m), raw materials separatelyground then mixed togetherd Based on SRC, with Bahra clay (3–20 m), raw materials separatelyground then mixed together

Table 4 Raw mix compositions

Raw mix designation Raw materials proportions (%)

Limestone Sand Bahra clay Bauxite Iron ore

OPC (hard burning) 79.6 12.3 – 5.3 2.8

SRC (commercial) 79.6 13.45 – 3.05 3.9

OPC I 78 – 16.1 3.7 2.2

OPC II 78.4 – 16.1 3.75 1.75

SRC III 77.8 – 17 2.1 3.1

OPC IV 78.5 – 17.75 2 1.8

SRC V 78.6 – 18.3 0.65 3

cement constituents. It can be observed that laboratory-prepared raw mixes (Mix I, II and III) have higher C3S andlower C2S compared to commercial and theoretical mixes.C3A and C4AF are comparable for different mixes. Mixdesignations of the different raw mix samples are given inTable 3, while the raw mix compositions are given in Table 4.

2.3 Grindability Assessment of Raw Materials

The grindability of raw materials and raw mixes has beenevaluated in this paper on relative basis with respect to bothpower consumption and time to attain different levels of fine-ness (measured in terms of the residue on 170 meshes). Theburnability and grindability depend on the chemical compo-sition of kiln feed, and it is necessary to control the chemicalcomposition of the kiln feed and the amount of the liquidphase in the clinker to obtain economical burning and grind-ing process [1,11]. Also, the clinker hardness and surfacearea are considered to be the most important characteristics

for controlling the power consumption during the produc-tion of cement. The power consumption increases with theincrease in hardness and surface area. Silica ratio is anotherimportant factor influencing the clinker grindability, and asthe silica ratio increases the grindability decreases [11,12].The higher the HM, the easier the grindability. The grindabil-ity also depends on the density of the clinker. It is easy to grinda porous clinker than dense clinker [11]. Larger amounts ofK2O and MgO result in saving of energy [5,12].

Practical end limits of fineness of 8 and 12 % were chosenfor comparison. Grindability tests were performed at KCCplant using 0.2 m3 capacity ball mills fitted with a kWh metre.The efficiency of the ball mill was optimized prior to carry-ing out the grindability tests. Grindability of each raw mixcontaining Bahra clay with respect to the time to attain fourdifferent levels of fineness and respective power consump-tion was assessed and compared with the data for OPC andSRC raw mixes which contain sand. Individual raw materials,150 g of each material was ground in a laboratory planetaryball mill for 15 min using the same grinding media chargeand sieved through 170 mesh to obtain the residue for com-parative assessment.

2.4 Burnability Assessment of Clinker Samples

Burnability is the ease with which the raw materials are trans-formed into the desired clinker phases and is commonly mea-sured by the amount of free (un-reacted) lime remaining inthe clinker [13]. The burnability of a raw mix is determined byits chemical composition, the mineralogy of its componentmaterials and its fineness (percentage of quartz and mineralscoarser than 45µm and percentage of calcite grains coarserthan 125µm). In order to investigate the variation of mineral-ogy in burnability brought about by the introduction of Bahraclay, the three components of SRC Mix III (limestone, ironore and bauxite) was first ground to the desired fineness (6 %residue on 170 mesh), and then Bahra clay was groundedseparately to four levels of fineness (6, 8, 10 and 12 %) tobe added in the correct proportion and mixed to form fourcomplete raw mixes of which the burnability was determined.

The tests were designed, so for each prepared mix of cer-tain fineness (four levels of fineness), four sets of samplesof each mix were first calcined in 950 ◦C furnace for 1 h and45 min to dissociate all CO2, then samples were transferredto another furnace of which the temperature was maintainedat 1,425 ◦C and then withdrawn at time intervals of 10, 20, 30and 60 min. Laboratory-prepared clinker at each withdrawaltime was tested for free lime, sulphate and alkalis contents.The latter two constituents were determined to evaluate theirvolatility. The influence of specific factors such as finenesson the burnability is given greater emphasis and the variationin burnability of the proposed mixes, Mix I, Mix II and MixIII were assessed during the burnability testing programme.

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For this purpose, four levels of fineness (6–8, 8–10, 10–12and 12–14 %) measured in terms of residue on 170 mesheswere used in the grinding of raw mixes.

2.5 Chemical, Mineralogical and Microstructural Analysisof Laboratory-Prepared Clinkers

Samples of laboratory-prepared clinker were chemicallyanalysed for their oxide constituents. Particular emphasiswas given for free lime and free silica contents. QualitativeXRD analysis was performed on each sample of laboratory-prepared clinker, to identify cement constituents, free silicaand free lime. SEM of clinker specimens to elucidate boththeir general and special features was carried out.

2.6 Free Lime Content

Free lime content in experimental clinkers was determinedby Franke Test Method as per ASTM C 114 using ethyleneglycol as the solvent. Accordingly, free CaO content wascalculated to the nearest 0.1 %. Free lime is indicative of theburnability of the raw mix.

2.7 Volatility Test

The nature of raw materials and the phases in which alkalisare formed affect the volatility. The degree of volatilizationof Na2O, K2O, SO3 and chlorides were determined by wetanalysis of laboratory-prepared clinker.

2.8 Mineralogy of Laboratory-Prepared Clinkers

X-ray diffraction (XRD) analyses were used to identify theclinker minerals formed by burning the raw mixes under vari-able time and temperature conditions. The presence of freelime and free silica remaining in clinker due to the low reac-tivity of mix can be detected. A highly reactive mix will becharacterized by comparatively intense signals for clinkerminerals, weak free lime peak and absence of free silica.

2.9 Thermal Analyses of Selected Raw Mixes

The most promising raw mixes, which were identified fromthe investigation based on the burnability, microstructure andother data, were subjected to differential thermal analysiscoupled with thermo gravimetric analysis. The analyses wereperformed to estimate the relative differential heat contentthat accompany the changes in raw mix, which may havean effect on sintering temperature and therefore on the fuelconsumption.

3 Results and Discussion

3.1 Grindability

The grindability of raw materials and raw mixes has beenevaluated on relative basis with respect to both power con-sumption and time to attain different levels of fineness (mea-sured in terms of the residue on 170 meshes). If the practicalend limits of fineness of 8 and 12 % are chosen for compari-son, it appears that the relative ease of grinding is the highestfor the OPC Mix I with respect to both criteria. This may bedue to the slight increase in SiO2 content of OPC Mix II. SRCMix III shows almost the same ease of grinding as the OPCMix I with respect to time, but indicates slightly higher powerconsumption rates. The lowest ease of grinding is associatedwith the OPC Mix II, as presented in Tables 5, 6 and 7.

Table 5 Comparative results of power consumption for attaining dif-ferent residue on 170 meshes for raw mix 1

Sampleno.

Residue on170 mesh %

Total time requiredto attain requiredfineness (min)

Power consumption(kWh)

S2 8.00 31 0.5

S3 12.00 29 0.48

S4 13.80 28 0.46

S5 15.40 25 0.41

OPC 8.00 120 1.995

Table 6 Comparative results of power consumption for attaining dif-ferent residue on 170 mesh for raw mix II

Sampleno.

Residue on170 mesh %

Total time requiredto attain requiredfineness (min)

Power consumption(kWh)

S2 8.00 42 0.72

S3 12.00 37 0.63

S4 14.00 34 0.59

S5 16.00 28 0.48

OPC 8.00 120 1.995

Table 7 Comparative results of power consumption for attaining dif-ferent residue on 170 mesh for raw mix III

Sampleno.

Residue on170 mesh %

Total time requiredto attain requiredfineness (min)

Power consumption(kWh)

S2 8.00 31 0.56

S3 11.20 29 0.52

S4 13.00 28 0.50

S5 15.00 25 0.45

SRC 8.30 120 2.06

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Table 8 Comparative grindability assessment of raw materials

Raw material Weightretained on170 mesh (g)

Percentage oftotal weightretaineda (%)

Limestone (RAK) 26 17.33

Limestone (IRAN) 23 15.33

Bauxite 34 22.67

Iron ore 39 26

Sand (Wafra quarry) 38 25.33

Bahra clay 27 18

Each material pulverized for 15 mina Starting weight of each material is 150 g

The grindability of individual raw materials is presentedin Table 8 which indicates that limestone has the same orderof grindability as Bahra clay (17.33 and 18 %, respectively),whereas sand has a relatively high grindability (25.33 %) withrespect to the residue on 170 mesh sieve, showing an increasein energy demand for the sand grinding.

3.2 Burnability Assessment of the Raw Mixes

It has to be noted that conditions of clinker preparation in thelaboratory furnace differ to great extent from the rotary kilnatmosphere. Besides, evolved gases are trapped and absorbedin the furnace, while gases in the kiln atmosphere are directedto escape. That is to a great extent affects the formationsof the clinker compounds and their crystallization, whichhas great impact on clinker composition especially at thecooling stage. In addition, the rate of clinker cooling greatlyaffects the properties of cement. Therefore, the properties oflaboratory-prepared clinker cannot be precisely comparableto those of commercial clinker. Nevertheless, a comparisoncan be drawn taking into account the different conditionsbetween laboratory-prepared clinker with sand and that pre-pared with Bahra clay reducing the amount of Bauxite andIron ore. The comparative study of burnability of differentmixes showed that in the case of OPC mixes, Mix I and MixII are equally good with respect to the burnability thoughmarginally low free lime content at each level of fineness isassociated with the Mix II. Furthermore, the burnability ofthe raw Mix II at 8.85 % residue (IIS3) is excellent. Therefore,it appears that the OPC Mix II is superior to the Mix I. SRCMix III containing Bahra clay needs to be prepared coarserto nearly 12 % residue to obtain acceptable burnability. Also,grinding of raw materials separately and then mixing is detri-mental, and marginal change in free lime content at differentlevels of fineness indicates that grinding Bahra clay coarserto 10–12 % residue seems adequate. This shows that the per-formance of mixes is affected by the oxide composition ofthe raw materials, fineness and mode of preparation of the

raw mix. Although oxide contents of the laboratory-preparedclinkers with Bahra clay are within acceptable limits for OPC,the main clinker compounds are not, when evaluated sepa-rately. This is attributed to the heat treatment of the furnaceenvironment, the mode of burning and the amount of heatavailable at the time.

3.3 Free Lime Content

The reference OPC mix (reconstructed in the laboratory) ofresidue 8 % showed a free lime content of 0.35 % (at time ofwithdrawal 60 min) as shown in Figs. 2 and 3. The experi-mental OPC mix, as anticipated, showed gradually decreas-ing free lime contents from 0.43 to 0.40 % when the mixwas made finer from 13.03 to 9.21 % residue. However, thefiner most mix IS2 (6.9 % residue) showed anomalous results;it exhibited the highest free lime content of all the mixes(0.50 %) at 60-min withdrawal time as presented in Figs. 2and 3. Nevertheless, the overall decrease in free lime contentof 0.03 % from 13.03 to 9.21 % residue is marginal, and it iswithin the range of experimental errors. This indicates thateven at the coarser most end (13.03 % residue), the burnabil-ity is good (i.e. of the order 0.40 % free lime) for the threecoarser mixes when compared with the reference OPC mix.The finer most mix has moderate burnability. Differencesin the mineralogy of mix components leading to differencesin grindability resulting in variation in the chemical com-position of the different size fractions of the raw mix mayhave contributed to the irregular behaviour of the finer mostmix.

3.4 Volatilized Alkalis and Sulphates in Raw Mixes

The percentages of volatilized total alkalis and sulphates indifferent raw mixes are shown in Figs. 4, 5, 6, 7 and 8. In OPCraw Mix II, the condensation of sulphates was observed forIIS4, as shown in Fig. 4. In general, the amounts volatilizedfor both sulphates and chlorides are below for the OPC mix.SRC Mix III, however, exhibited anomalous characteristics.Sulphate volatilization exceeds that of the reference SRCmix for the raw mixes Mix IIIS5 and Mix III S4, as shownin Fig. 5. Condensation was evident in the other two rawmixes (Mix IIIS3 and Mix IIIS2), though Mix IIIS3 showedexcessive volatilization at both 10 and 60 min withdrawaltimes.

In OPC Mix IV and Mix VI, the sulphate volatilizationwas far below that for the reference mix OPC. However, totalalkalis in the mix made by grinding constituents togetherexceeded those of reference mix OPC, though marginally, asshown in Fig. 6.

In SRC Mix V and Mix VII, both sulphates and total alka-lis volatilized exceeded those of reference mix SRC mix,whereas sulphate volatilization of Mix VIIS2 was below that

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Fig. 2 Comparison of residual free lime content for different mixes

Fig. 3 Comparison of residual free lime content for different mixes

of reference mix SRC mix, as shown in Fig. 7. In MixesVIII, IX, X and XI (Refer Fig. 8), sulphate volatilization islower for Mix IX, marginally higher for Mix X and slightlyexceeded for Mix VIII and Mix XI. Total alkalis are farbelow (of the order of 0.11 %) when compared with thosefor the reference SRC (0.52 %) for all the four mixes. The

volatilization of alkali sulphates and its circulation plays arole in notarization, which may provide reasons for someof the dusty clinker problems. The melting of sulphates canalso aid in C2S formation and limestone calcinations, andtherefore, SRC Mix V and Mix VII may lead to dusty clinkerproblems.

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Fig. 4 Comparison of volatilized sulphate content for different mixes

Fig. 5 Comparison of volatilized sulphate content for different mixes

3.5 Mineralogy Assessment of Clinker Samples

3.5.1 Mineralogy Assessment of Clinker Samples of OPCMix I and Mix II

The XRD patterns of OPC clinker of Mix I, (Refer Fig. 9),show the presence of the four main clinker constituents (C2S,C3S, C3A and C4AF) and free lime. Free silica cannot be

detected. The same conditions exist for the set of XRD pat-terns of OPC clinker of Mix II. Also, the proportion of C2S/-C3S in OPC clinker of Mix I is higher than that of the Mix 2,and the difference is marginal. The presence of same clinkerconstituents for both mixes shows that the reactivity of bothmixes are same. The presence of free lime in both cases showslightly low reactivity of the mix.

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Fig. 6 Comparison of volatilized total alkalies for different mixes

Fig. 7 Comparison of volatilized sulphates for different mixes

3.5.2 Mineralogy Assessment of Clinker Samples of SRCMix III

The reflections for the four main clinker constituents ((C2S,C3S, C3A and C4AF) were present in the clinker samplesof SRC Mix III along with the signal for free lime in thediffractogram as in the case of OPC Mix I. There were no

major changes in composition with changes in fineness of thesource mix. However, differences for the SRC laboratory-prepared clinker made from the kiln feed and those for thetrial mixes III S2—III S5 (made under different levels offineness), were that the relative proportion of C2S/C3S issubstantially low in the clinker made from the kiln feed andC3A cannot be detected in this clinker. The lower proportion

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Fig. 8 Comparison of volatilized sulphates and alkalies for differentmixes

of C2S/C3S and the absence of C3A indicate that the earlystrength development will be lower for the clinker made fromkiln feed.

3.5.3 Mineralogy Assessment of Clinker Samples of OPCMix IV and Mix VI

Comparison of the X-ray diffractograms presented in Fig.10a–c, of Mix IV and Mix VI indicate that the clinker result-ing from raw materials ground separately and mixed (MixVI) had a relatively high free lime content associated withit. This is substantiated by actual analytical data. Further-more, the relative proportion of C2S/C3S in this mix is evi-dently low. The increased intensities of peaks in high 2θ

region is indicative of unreacted minerals present in thisclinker. The diffractogram for the clinker of Mix IV showsthe presence of four clinker constituents and free lime. Thehigh free lime content of the Mix IV and Mix VI repre-sents the low reactivity of the mix and less developmentof C2S.

3.5.4 Mineralogy Assessment of Clinker Samples of SRCMix V and Mix VII

The diffractograms presented in Fig. 11a–c are representativeof SRC Mix V and Mix VII; One by grinding raw materi-als together (clinker Mix V) and the other by grinding rawmaterial individually and mixing (clinker Mix VII). The dif-

fractogram for clinker Mix V shows relatively low free limecontent in contrast to clinker Mix VII, substantiated by theanalytical results for free lime. The relative intensities of thepeaks of clinker constituents and C2S/C3S proportion appearto be of the same order and both diffractograms show the pres-ence of the clinker constituents. This shows that in the casesof both OPC and SRC, the grinding of raw materials togetherleads to better reactivity. The diffractogram of the reconsti-tuted laboratory-prepared SRC clinker presented in Fig. 11exhibits a faint C3A reflection and relatively high C2S/C3Sproportion. A higher free lime content than that present inclinker Mix V was evident.

3.5.5 Mineralogy Assessment of Clinker Samples of SRCMixes VIII, IX, X and XI

The mineralogy assessment of clinker Samples of SRC MixesVIII, IX, X and XI also indicate the presence of four clinkerconstituents (C2S, C3S, C3A and C4AF) in each clinker andsmall amount of free lime.

3.6 Microstructural Study of Clinker Samples

3.6.1 Evaluation of the Scanning Electron Microscopy(SEM) of Laboratory-Prepared Clinkers

The clinker structure with alite and belite crystals is shownin the micrographs of the commercial clinker of OPC andSRC (Refer Fig. 12); no or minimum free lime is observed.This includes the use of appropriate raw mixes and improvedburnability. It is also important to ensure formation of well-nodulized clinker.

3.6.2 Evaluation of SEM of Clinker Samples of LaboratoryOPC Mix I

Photomicrographs presented in Fig. 13a, b show the microstruc-ture of clinker samples of laboratory-prepared OPC Mix I.The general microstructure is indicative of a clinker of lowreactivity mix consisting of ill-defined rounded grains ofbelite, interstitial material and lime. Hexagonal alite grainscould hardly be seen in the microstructure. Interstitial mate-rials are not completely reacted.

The general microstructure of IS2 (6–8 %), IS3 (8–10 %),IS4 (10–12 %) and IS5 (12–14 %) clinkers obtained fromfine to coarse raw mixes is presented in the photomicro-graphs (Refer Fig. 13). The average grain size of alite repre-senting the coarsest mix (12–14 % residue) is about 15µm,whereas that representing the finest mix (6–8 % residue) isabout 45µm. This is true for belite grains also and the aver-age size varying from 10 to 15µm from coarse to fine mixrespectively. Interstitial material is abundant but not uni-formly distributed in IS5 clinker. It becomes fairly uniformly

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Fig. 9 XRD patterns of OPCclinker of mix 1

Fig. 10 a–c XRD patterns of OPC clinker of Mix IV and VI

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Fig. 11 a–c XRD patterns of SRC clinker of Mix V and VII

distributed in IS4 and IS3 until it depletes in the clinker madefrom finer most mix IS2, which in addition shows poros-ity. IS2 produced a microstructure, which shows the onset offormation of alite crystals, though not still fully grown onprolonged burning (120 min). Clusters of formation of alitegrains by the reaction of belite are observable. The num-bers of grains has reduced, and in IS5, the interstitial mater-ial occurs predominantly between grains and rarely betweenbelite grains. It is expected that such clinkers made fromcoarse raw mixes will be slightly harder to grind, due to highliquid content.

In general, the microstructure of IS4 with randomly dis-tributed and well-developed alite and belite grains embeddedin interstitial materials can be considered good.

3.6.3 Evaluation of SEM of Clinker Samples of LaboratoryOPC Mix II

Photomicrographs IIS2 (6–8 %), IIS3 (8–10 %), IIS4 (10–12 %) and IIS5 (12–14 %) presented in Fig. 14a, b representclinkers obtained from fine to coarse raw mixes of OPC MixII. In contrast to the previous series of clinkers (OPC Mix I),this series shows much even granulometry (with change infineness of mix) with larger alite (25–30µm) and belite crys-tals (15–20µm) may be due to higher burnability of the MixII; the largest alite grains reach up to 40µm. The microstruc-ture of clinker made from raw mix of residue 8.85 % (IIS3)

shows a well-developed and well-packed array of alite andbelite grains. In general, the micrographs represent clinkers

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Fig. 12 SEM of Commercial OPC and SRC

of high reactivity raw mixes. The presence of more interstitialphases in IIS2 due to prolonged firing indicates the difficultyin grinding this clinker.

3.6.4 Evaluation of SEM of Clinker Samples of LaboratorySRC Mix III

Photomicrographs IIIS2 (6–8 %), IIIS3 (8–10 %), IIIS4 (10–12 %) and IIIS5 (12–14 %) presented in Fig. 15a, b representclinkers obtained from fine to coarse raw mixes of SRC MixIII. The microstructure of clinkers SIII5, SIII3 and SIII2 ischaracterized by well-developed alite (20–35µm) and belite(10–20µm) and the presence of interstitial materials to alesser extent.

Prolonged firing of the clinker made from finer most rawmix SIII2 produced a microstructure with increasing sizeand abundance of belite crystals. The clinker made fromthe coarsest raw mix (SIII5) vividly exhibits an array of

dense-packed alite and belite crystals indicating that the rawmix is reactive even when it is coarsely ground (12–14 %residue).

3.6.5 Evaluation of SEM of Clinker Samples of LaboratoryOPC Mix IV and Mix VI

The microstructure of Mix IV clinker as shown in Fig. 16has improved to some extent when the source raw mix ofthe clinker was prepared by grinding raw materials together.More abundant C2S grains (12µm), a few longitudinal C3Sgrains along with some interstitial materials are present. Theamount of unreacted lime has reduced. However, both typesof grains of which belite is predominant are still poorly defined,and the microstructure indicates low reactivity of themix.

The analysis of microstructural features of Mix VI (ReferFig. 16) shows large irregular grains of unreacted lime andabundance of C2S grains. The microstructure reflects poorburnability of the source raw mix and the detrimental effectof grinding each raw material separately and mixing themfor burnability assessment, which is in accordance with thechemical analysis of the clinker showing excess freelime.

The photomicrograph shown in Fig. 16, which pertainsto the microstructure of reference laboratory-prepared OPC6 %, shows that it is composed mainly of belite grains, whichhave grown in size to 20–30µm. The general microstructureis that of a low reactivity raw mix consisting of ill-definedcalcium silicate grains (mainly belite) and low interstitialmaterial. The less quantity of interstitial material in this mixhelps to grind it easily.

3.6.6 Evaluation of SEM of Clinker Samples of LaboratorySRC Mix V and Mix VII

It can be observed that the microstructure of the laboratory-prepared clinker of SRC Mix V made by grinding raw mate-rials together and is shown in the photomicrograph (ReferFig. 17). The defined grains, which are mainly belite (25µm)with a high amount of interstitial materials. The micrographof laboratory-prepared clinker of SRC Mix VII shows smallerbelite grains (20µm) in a very high amount of interstitialmaterials. In general, the microstructure of this clinker isless favourable when compared with the clinker of SRCMix V.

The photomicrograph of the reference SRC 6 % clinker(Refer Fig. 17) shows that the belite grains grew in size toabout 30µm; a few alite grains of size 20–30µm are alsopresent and most of the interstitial materials are reacted. Thismicrostructure appears to be better than that of Mix V clinker.

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Fig. 13 a SEM of Laboratory OPC Mix I. b SEM Laboratory OPC Mix I

3.6.7 Evaluation of SEM of Clinker Samples of LaboratorySRC Mixes VIII, IX, X and XI

The micrographs of the clinkers of Mix VIII, Mix IX, Mix Xand Mix XI are represented in Fig. 18. Comparative analysesof the microstructural features indicate that well-developedhexagonal, quadrangular and polygonal alite crystals of dif-ferent sizes are present embedded in interstitial materials inall the clinkers. However, regular structures of alite crystalsare more apparent in the clinkers of Mix VIII, Mix IX andMix X. In addition, interstitial materials are relatively welldefined in the clinker of Mix VIII, which indicates a betterstructure in this clinker. Belite crystals appeared in relativelylow proportions in the microstructures and are smaller (ofaverage size 10µm) than the alite crystals (15–30µm). Freelime cannot be detected in any of the microstructures, show-ing high reactivity of the raw mix.

3.7 Volatility Test Results

The volatilizations of alkalis are important from the view-point of their condensation causing clogging in pre-heatersystem. It is also believed that the circulation of volatile alkalisulphates plays a role in notarization, which may provide rea-sons for some of the dusty clinker problems. Alkali sulphatemelts between 700 and 1,050 ◦C into a chloride-containing

eutectic of Na2SO4, K2SO4 and CaSO4 and vaporized alkaliscondense on incoming raw meal. This sulphate melt causesearly nodule formation. It can also aid C2S formation andlimestone calcinations. These latter effects are important bec-ause they increase the time that belite and free lime crystalscan grow. Thus, when the material gets to the nodulizationzone within the kiln, it is coarser crystalline, and less wellsuited for nodulization. The crystals of belite, and the alitecrystals obtained from these belites, are too large for facilenodulization, resulting in dustier clinker.

3.8 Results of Differential Thermal Analyses (DTA)

The thermal analysis of raw mixes was carried out to anend limit of 1,000 ◦C since this experimental temperaturerange covers the major thermal reactions of dissociation oflimestone, dehydroxylation of clay minerals, rearrangementof crystal lattices etc., which are endothermic and requirethe bulk heat input in firing giving a comparison of majorenergy input required during the manufacturing clinker fromdifferent mixes.

Comparison of DTA charts for the raw mix IIS3 and refer-ence OPC raw are presented in Fig. 19a–c. They indicate thatthe heat content (external heat input) required for firing thedesigned mix up to a temperature of 1,000 ◦C (72.30 cal/g) ishigher than that for the reference OPC raw mix (68.17 cal/g)

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Fig. 14 a SEM of LaboratoryOPC Mix II. b SEM of clinkersamples of Laboratory OPCMix I

by 6.0 %. However, this additional heat input is reduced to4.9 % when the raw mix is ground finer as is evident fromthe heat content associated with the raw mix IIS2 (71.5 cal/g)presented in Fig. 19.

In contrast, the designed SRC raw mix IIIS5 with an asso-ciated heat content of 65.30 cal/g, presented in Fig. 20a–cshows an advantage over the reference SRC raw mix (6 %residue) which has a heat content of 67.73 cal/g, in view ofthe reduction of external heat input by 3.6 %. In relation toa coarser ground (8.9 % residue) reference SRC kiln feedwith a heat content of 74.69 cal/g, the reduction in heat con-tent is 12.60 %. Thus, it is anticipated that the designed SRC

raw mix IIIS5 is more favourable than the current SRC kilnfeed in terms of the energy requirement to clinker the kilnfeed.

4 Conclusions and Recommendations

The suitability of locally available clay for the production ofPortland cement as well as the quality of clinker producedfrom them is studied in this work. The grindability and burn-ability of different mixes are analysed, and the conclusionsare derived as follows.

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Fig. 15 a SEM of Clinker Samples of Laboratory SRC Mix III. b SEM Laboratory SRC Mix III

Fig. 16 SEM of ClinkerSamples of Laboratory OPCMix IV and Mix VI

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Fig. 17 SEM of Clinker Samples of Laboratory SRC Mix V and MixVII

1. Suitable OPC and SRC raw mix compositions in whichsand (presently used by the KCC as an integral rawmix constituent) completely replaced by Bahra clay havebeen evolved for the production of clinkers for Type I andType V ordinary Portland cements, respectively. Com-patible optimum fineness for each raw mix in terms ofthe residues on 170 and 70 meshes were also established.The raw mix compositions (wt.%) and levels of finenessfor the most promising trial mixes—OPC IIS3 and SRCIIIS5 are given below representing good reactivity andburnability for both raw mixes.

OPC raw mix composition:

Limestone 78.40 %Bahra clay 16.10 %Bauxite 3.75 %Iron ore 1.75 %Residue 170 mesh 8.85 %; 70 mesh 0.13 %

SRC raw mix composition:

Limestone 77.80 %Bahra clay 17.00 %Bauxite 2.10 %Iron ore 3.10 %Residue 170 mesh 12.00 %; 70 mesh 0.52 %

2. Burnability data substantiated by microstructural analy-sis have consistently proven that grinding Bahra clay sep-arately to the fineness 6–12 % residue on 170 mesh andmixing with the other three raw mix constituents (lime-stone, bauxite, and iron ore) pre-ground to 6 % residuein the preparation raw mixes is more favourable than thepreparation of raw mix by grinding together all the rawmaterials to the fineness of 6 % residue. The former pro-duces a more reactive raw mix.

3. It could be expected that the fluxes present in Bahra clay(e.g. feldspars) create a highly reactive raw mix by mak-

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Fig. 18 SEM of ClinkerSamples of Laboratory SRCMixes VIII, IX, X and XI

ing liquid phase to occur earlier, thereby allowing moreC3S (alite) to form; microstructural analysis supports thisview.

4. In most of the trial mixes investigated, volatile alkalisulphate content (and chlorides) is below, if not within,acceptable limits. Since sulphate melt cause early nod-ule formation and therefore coarser-crystalline materialswhich are less well suited for nodulization and may pro-duce dustier clinker; it could be expected that the clinkersproduced from the trial raw mixes will be less prone tothe formation of dusty clinker.

5. Burnability and microstructural data suggest that finergrinding of raw mix to 6 % residue on 170 mesh has

little or no effect when compared to grinding coarser to10 % residue. More effective is grinding the Bahra clayseparately to even coarser residue (e.g. 12 % residue) andmixing with the other three pre-ground materials.

6. DTA data indicate that of the two most favourable desi-gned raw mixes, the OPC raw mix IIS3 requires a mar-ginally higher heat input to clinker the kiln feed com-pared to SRC raw mix IIIS5 with an appreciably low heatinput. Therefore, SRC raw mix IIIS5 is more favourablethan the current SRC kiln feed in terms of the energyrequirement to clinker the kiln feed.

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Fig. 19 a–c DTA of referenceOPC compared to SII-2 andSII-3

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Fig. 20 a–c DTA of SRC kilnfeed compared to raw mix SRC6 % and raw mix SIII5

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Acknowledgments The project team is grateful to Kuwait Foundationfor the Advancement of Sciences and Kuwait Cement Company, fortheir financial support for the research study, which have contributed tothe advancement of one of the leading construction industry in Kuwaitsuch as the cement manufacturing industry.

References

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2. Vangelatos, I.; Angelopoulos, G.N.; Boufounos, D.: Utilization offerro alumina as a raw material in the production of ordinary Port-land cement. J. Hazard. Mater. 168(1), 473–478 (2009)

3. Dwivedi, V.N.; Sing, N.P.; Das, S.S.; Sing, N.B.: A new pozzolanicmaterial for cement industry: bamboo leaf ash. Int. J. Phys. Sci.1(3), 106–111 (2006)

4. Shi, C.; Jimenez, A.F.; Palomo, A.: New cements for the 21st cen-tury: the pursuit of an alternative to Portland cement. Cem. Concr.Res. 41, 750–763 (2011)

5. Schneider, M.; Romer, M.; Tschudin, M.; Bolio, H.: Sustainablecement production: present and future. Cem. Concr. Res. 41, 642–650 (2011)

6. Abu-Eid, R.M.: Potential utilization of Kuwait sand in local indus-tries. In: Almond, D.C., Abu-Eid, R.; Al-Sulaimi, J. (eds.) Indus-trial Raw Materials of the Arabian Gulf and Their Utilization.Kegan Paul International Ltd., London (1994)

7. Emmanuel, A.; Al-Mutairi, N.; Al-Hamdan, H.; Zaki. I.: Utiliza-tion of Kuwait’s raw materials for production of portland cement.Kuwait Institute for Scientific Research, Proposal, KISR 5955,Kuwait (2000)

8. Al-Bahar, S.; Bogahawatta, VTL.; Missak, R.; Al-Onizi, A.; AliHussain, S.; Kamal, H.; Behbehani, M.; Al-Enezy, N.; Al-Foraih,R.; Al-Fadala, S.: Evaluation of Kuwait’s raw materials for pro-duction of portland cement: phase I—Final Report, KISR 6275(2001)

9. Al-Bahar, S.; Bogahawatta, V.T.L.; Al-Enezi, A.; Ali, S.; Kamal,H.; Al-Fadala, S.; Al-Foraih, R.: Utilization of Kuwait’s raw mate-rials for production of portland cement. Kuwait Institute for Scien-tific Research, Final Report–Phase II, KISR 6842, Kuwait (2003)

10. Al-Bahar, S.; Bogahawatta, V.T.L.; Al-Fadala, S.; Bahbahani, M.:Utilization of Kuwait’s raw materials for production of portlandcement. Kuwait Institute for Scientific Research, Final Report–Phase III, KISR 7098, Kuwait (2004)

11. Gouda, G.R.: Effect of clinker composition on grindability. Cem.Concr. Res. 9, 209–218 (1979)

12. Frigione, G.; Zenone, F.; Esposito, M.V.: The effect of chemicalcomposition on Portland cement clinker grindability. Cem. Concr.Res. 13, 483–492 (1983)

13. Christensen, N.H.; Smidth & Co, F.L.: Burnability of cement rawmixes at 1400 ◦C, I: the effect of the chemical composition. Cem.Concr. Res. 9, 219–228 (1979)

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