Brick Clay

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J Pak Mater Soc 2008; 2 (1)

33

Phase and Microstructure of Brick-Clay Soil and Fired Clay-BricksFrom Some Areas in Peshawar Pakistan

Safeer Ahmad

1

, Yaseen Iqbal

2

, Fazal Ghani

3

1. Department of Physics, Islamia College University, Peshawar Pakistan2. Department of Physics, University of Peshawar, Pakistan3. Department of Prosthodontics, Khyber College of Dentistry, Peshawar (Pakistan).

Corresponding Author: Safeer Ahmad, Lecturer, Department of Physics, Islamia College University, Peshawar (Pakistan).Tel: 0092 – (091) 9216513 Cell: 0092 0 (0333) 9119526 Email: [email protected]

ABSTRACTObjectives: Bricks being the most frequently used product in the local construction industry. However,there has been very little or no relevant information about the manufacturing standards and quality of locally-made bricks as compared to that in developed countries. It is the aim of this study to provide someinformation about the local raw brick-materials as well as of the bricks manufactured from these.

Materials and Methods: Samples of soil and bricks were collected from two representative kilns of district Peshawar (Pakistan). Fine powders of both of these were obtained by manual triturating in a

pestle and mortar system. XRD was performed for phase analysis using powder X Ray Diffractometry (JEOL, JDX 3500) system. SEM studies for micro-structural analysis of brick samples (4x4x4 mm

3 ) were

also carried out using a JSM-5910 JEOL SEM. For SEM, samples were fine polished with a twin prep 3TM

grinding polishing machine. The smooth polished surfaces were chemically etched with 5% HF solutionfor one minute. Finally, the samples were mounted onto stubs with silver paint and gold coated in order toavoid charging in the SEM.Results: X-ray diffraction revealed that raw brick soils in use by the local brick-industry comprised

predominantly of quartz, albite and chlorite along-with illite, melilite, calcite and orthoclase. In the processed brick-samples, mullite and cristobalite were not observed in SEM indicating the use of a low-firing temperature (~1000

oC) and absence of kaolinite in raw materials. Consequently, the local brick

specimens were expected to be more porous and mechanically weak as compared to those from

advanced countries. The direct naked eye examination of the sample brick had non-uniform colour and the presence of pebbles a further indication of non-professional processing of initial raw ingredients.Cracks seen in the fired brick samples were seen as further indication of improper heat-treatment and

processing. SEM EDS of brick-samples showing the presence of iron was seen as the cause of red colour in the brick.Conclusions: The use of low-temperature firing cycle, rapid cooling, and absence of kaolinite in raw materials were seen as the main factors leading to bricks with compromised quality.

INTRODUCTIONBrick is a ceramic material mainly used inconstruction industry. Its production processinvolves forming of clay into rectangular blocksof standard size, followed by firing totemperatures ranging from 900 to 1200°C

1. It is

made of clay or shale and when given desiredshape is dried and fired into a durable ceramicproduct. Brick is one of the most importantbuilding material. Energy consumption andpollution are the two important environmentaland cost concerns related to brick industry. Areport, in 1993, showed some more than 3000brick kilns in operation in the country with anannual growth of 3 percent

2. Old rubber, low-

quality coal, wood and used-oil were reported asfuel in most brick kilns. Consumption of thesefuels, combined with inefficient combustion

process produces large quantity of hazardousgases that threaten the environment as well asthose working in brick kilns. Since long, in fact,the brick-industry in the country has remainedmostly traditional with no importance toenhancement or standardization of physicalproperties of the final product at all. Among theproblems faced by the industry, the first andprobably the most important is the supply of reasonably priced fuel in the form of fuel woodas well as coal. A second major problem is thatthe industry is not well organized and technicallyill-prepared with very little know-how about it andfew engineers and scientists having takeninterest in this industry

2.

The history of brick industry is very old and canbe traced back to about 5000 years old

Safeer Ahmad, Yaseen Iqbal, Fazal Ghani: Phase and Microstructure of Brick-Clay Soil…….

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Mohinjodaro civilization in Sindh (Pakistan)where fired brick had been used probably for thefirst time in human history. Despite being

amongst the oldest crafts, the quality of brickshas deteriorated over the centuries3-4

. In spite of the technological revolutions, today’s brick isweaker and more porous than it had been in thepast in the country. This could be certainlysurprising to many in the event that in the pastseveral decades, significant advances inscientific and technological research have beenregistered, particularly in the developedcountries, with respect to low-cost constructiontechniques and building materials

5. Bricks can

be divided into various groups on the basis of mineralogy namely, silica bricks, zirconia bricks,alumina bricks, mullite bricks, magnesite bricksand dolomite bricks8-9. In bricks, a balancedproportion of crystalline phases and a glassphase help in binding the whole structuretogether with the ratio of cristobalite to quartzregarded as a reliable predictor of bricksdurability

6.

Our understanding of the brick microstructure asinfluenced by the range of temperature duringfiring cycle has been enhanced by theexperimental work in this area. For example,McConvile et al

12 investigated the micro-

structural evolution of various clays using XRD

and TEM. They observed that the pseudo-hexagonal morphology of the kaolinite changedto pseudo-hexagonal meta-kaolin at around

550°C with meta-kaolin broken down at

temperatures >900°C to γ-alumina-type spinaland a silica-rich phase. The spinal type phase

started to transform into mullite at >1000°C. At

1300°C, mullite increased in size to ~1µm and insome regions, cristobalite formed from the silica-rich matrix

12-15. XRD, TGA/DTA and EF-TEM

studies of clay have revealed that meta-kaolin

partially transforms to γ-alumina at 920°C16

. Onfurther increase in the firing temperature to

>940°C, the crystallization of Al2O3-rich mullitebegan and excess amorphous silica wasdiscarded into the matrix

16. Mullite begins to

crystallize at 1050°C and its crystal sizeincreases with increase in firing temperature

12. A

number of phases are usually present in firedbricks. Quartz is observed in all samples, usuallyless abundant in the brick than in the rawmaterial. Hematite is also present in all sampleswhich impart the red colour to bricks. Even inyellow bricks, the presence of Hematite isobserved though in smaller amounts

7. In

addition to quartz, a number of other alkalisilicate phases survive the firing cycle. In under-fired bricks, illite is the most persistent of the

clay minerals

17-18

. Calcite is also foundoccasionally, but it has been thought to resultfrom the re-carbonation of lime. Cristobalite hasbeen noted as the most commonly occurringhigh temperature silica phase by some studies

19.

MATERIALS AND METHODSRaw brick material as soil and processed brickswere collected from various places of Peshawar,Pakistan. Fine powders of the brick sampleswere obtained by triturating them in a pestle andmortar system. XRD was performed for phaseanalysis using powder X-ray Diffractometer (JEOL, JDX 3500). For micro-structural study,scanning electron microscopy (SEM) wasperformed using a JSM-5910 JEOL machine.SEM samples were prepared by cutting smallpieces (4x4x4 mm

3). Samples were fine polished

with a twin prep 3TM

grinding polishing machine.The smooth polished surfaces were chemicallyetched with 5% HF solution for one minute.Finally, the samples were mounted onto stubswith silver paint and gold coated in order toavoid charging in the SEM. The experimentalwork was carried out using the equipments atthe Materials Research Laboratory and at theCentralized Resource Laboratory at the

Department of Physics, University of Peshawar.

RESULTS AND DISCUSSION

XRD AnalysesX-ray diffraction patterns of clay soil and firedbricks are shown in Figures 1-4. The inter-planar spacing corresponding to XRD peaks observedfor clay soil samples from Khazana Villagematched with ICDD card# 50490 for quartz,ICDD card# 240027 for calcite, ICDD card#199749 for clinochlore and ICDD card# 90462for orthoclase (Figure 1). The inter-planar

spacing corresponding to XRD peaks from thefired brick from the same region (Figure 3)matched with the ICDD card# 50449 for quartz,ICDD card# 20023 for chlorite and ICDD card#42136 for moissonite.

Similarly the inter-planar spacing correspondingto the XRD peaks observed for raw clay soilfrom village Bahadar Kalay as shown in Figure 2matched with ICDD card# 30444 for quartz,ICDD card# 90466 for albite, ICDD card#430697 for calcite and ICDD card# 90462 for orthoclase. For fired brick the inter-planar


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spacing corresponding to the XRD peaks fromVillage Bahadar Kalay as shown in Figure 4matched with ICDD card# 50490 for quartz,

ICDD card# 90466 for albite and ICDD card#20023 for chlorite. In general, the phasecomposition of raw brick clays and fired bricks

are complex due to use of highly impure soil,however, the major phases found in the raw soilmaterials included quartz, calcite, chlorite, and

albite which again varied from region to regionwithin the same district.

500

1000

1500

2000

2500

3000

5 15 25 35 45 55 65

Q

O

Q

Ca

O

U

Ca

C

Ca

O

U

2θ

Q

O

ClU

Q------------------- Quartz Low(50490)

C------------------------Calcite(240027)

Ca--------------------------CaO(280775)

O---------------------Orthoclase(90462)

U---------------------H8Si8O20(350060)

Cl-----CLINOCHLORE-2MIIB (190749)

I n t e n

s i t y

QC

Ca

U Q

ClQ

OQ

Q

O

UC

O

U

ClCl

Figure 1: X-Ray Diffraction of Clay Soil (Village Khazana Peshawar)

500

1500

2500

3500

5 10 15 20 25 30 35 40 45 50 55 60 65 70

I n t e n s i t y

Q

IU

B

Q

M

U

A

O

A

Q---------------------Quartz (30444)

A------------ Albite,ordered(90466)

B-----------------------Biotite(20057)

I---------------------------Illite(20056)

M----------------------Melilite(40683)

u---------K C10 H19 O2 (50024)

C-----Calcite Magnesian(430697)

O-----------------Orthoclase(80048)

a-------------------Amesite(521569)

B

Q

AO

Q

IU

M

Q

M

O

A

I

M

C

B

a

B

I U

B

A

a

U

C

O

C

I

U

a

a

2θ

Figure 2: X-Ray Diffraction of local clay Soil (Village Bahadar Kalay, Peshawar)


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0

200

400

600

800

1000

1200

1400

5 15 25 35 45 55 65 75

I n t e n s i t y

Q

MF

U

C

Q-------------------------Quartz[50449]M--------------Moissanite-5H[42136]

F-------Mg3 Si2 O5 ( O H )4[60056]

U----Na0.25 K0.05 Ca0.92 Mg0.01

Al2.19Si5[491838]

C-------------Chlorite (NR) [ 20023]

F

U

M

F

C Q

M

Q

M

U

FQ

M

F

CU

C

2θ

Figure 3: X-Ray Diffraction of Brick Sample (Village Khazana Peshawar)

0

200

400

600

800

1000

1200

1400

1600

1800

5 15 25 35 45 55 65 75

I n t e n s i t y

Q

C

B

Q---------------Quartz[50490]

C---------------Chlorite[20023]

A------Albite-ordered[90466]

K---K2 A l ( Cl O4 )5[330985]

B-------- ----- -Al O C[140651]l

Q

S

Q

A

K

B

C

A

K

CC

Ca

A

S

Q

C

AA

K

Q

A

Q

C

A

Q

B

Q

C

A

K

B

B

2θ

Figure 4: X-Ray Diffraction of Brick Sample (Village Bahadar Kalay Peshawar)

Microstructure of the Bricks The SEM images of the brick samples areshown in Figures 5-8. The gross elementalweight% compositions of the brick clay sampleswere about 40% Ca, 20% Si, 12% Al, 17% Feand 5% K along with varying amounts of C andO. EDX spectrum collected from a sharp edgedgrain indicated that the grain labeled “Q” in

Figure 6a is α-quartz, while the elongated grainwas close in composition to albite as reported byBraganca and Bergmann

20. EDX spectra from

some regions/grains with bright contrastindicated the presence of calcium in highconcentration, which might be calcite or lime.XRD also revealed the presence of peaks due to


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calcite and lime (Figure 1). EDX showed that theelemental composition of the crackedregion/grain labeled as “F” in Figure 7, was

close to feldspar. The cracking observed insome regions/grains may be due to abruptchange in temperature as also suggested byGol’sova et al

10. In vitreous ceramics cracking, in

fact, was shown to occur because of thermalexpansion coefficient gradient of heterogeneously distributed constituentphases

21.

Figure 5: A general area secondary electron SEM image of brick sample

Figure 6: SEM micrograph of brick sample showing a)quartz labeled “Q”, albite labeled “A”, b) quartz, albite andclay particle labeled as “Q”, “A” and “C” respectivelyclosed to chlorite

Figure 7: SEM micrograph of brick sample showing crackingof feldspar-relict grain/region.

Researchers are in a constant search to look for compositions, processing and microstructure-

property relationship for materials, by employingmodern techniques such as x-ray diffraction andelectron microscopy. The brick vary in colour,compressive strength and water absorption.These are the characteristics which determinethe durability of a brick and are related to itsmicrostructure and mineralogy

6.

In Europe, the brick manufacturing industry hasbeen modernized and most appropriate rawmaterials (soil) are selected keeping in view thebest product, whereas, in Pakistan brick industryis still run in traditional way and the physicalproperties of the final product are not considered

in a technical manner. The net result is the morepronounced technology gap between thedeveloping and developed countries

7. Brick

making is regarded as a traditional craft, a skillthat is passed down through an internship withmoulders, kiln setters and firemen over aprolonged period. To obtain good bricks theydepend on the rate of firing, maturingtemperature and soaking time

5.

The durability of brick can vary significantly,depending both on the raw material itself and onthe local environment

22. The durability of the

brick, based on a visual assessment of distress,seemed related to the amount of cristobalitepresent (where cristobalite is a high temperaturepolymorph of quartz)

23. As a general rule, bricks

fired to high temperature (~1000°C), are moredurable than those fired at low temperatures

23,

which shows temperature dependence of brick’sstrength.The brick industry uses a great variety of clays,laid down at different geological periods andranging from soft, easily moulded glacial (aperiod of expansion of glacial ice) deposits tomuch older, relatively harder shale’s (Shale’sare clays that have been subjected to high

A

Qa

Q

ACb

F

F


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pressures until they have hardened almost tothe form of slate). This geological diversityreflects itself in the varied composition and

mineralogy of brick making clays

1

.The presence or absence of carbonates stronglyinfluences the porosity development andtherefore, the brick texture and physical-mechanical properties. The carbonates in theraw clay promote the formation of fissures andof pores under 1 µm in size when the bricks arefired between 800 and 1000°C

16, 24.

The phosphate-bonded products are also of lowporosity and improved dimensional stability. Theproperties of the phosphate-bonded clay bodiesare critically affected by new mineral phasesresulting from the reactions of phosphates withclay, which subsequently undergo physico-chemical changes above 550°C25. The importantqualities of standard bricks are; adequatemechanical strength, well sintered with uniformcolour, even surfaces and free of flaws or crackswith sharp and well defined edges, giving clear ringing sound when struck against each other,so hard that no impression is left whenscratched with finger nails. In addition, theyshould absorb no more than 15% of its weight of water when kept immersed in it for 24 hours andshould have a crushing strength more than55kg/cm. Upon breaking, the surface shouldshow a bright homogenous and compact surface

free from voids or grit2. A brick soaked in water for 24 hours should not show deposits of whitesalt on drying in shade

26.

The study of the temperature regime along thekiln indicates that the temperature in thepreheating zone is below the prescribed valueand in front of the firing zone it sharplyincreases, i.e., the rate of the temperature riseon this particular site exceeds the theoreticalrate and the brick is subjected to an abruptthermal shock, which impairs the quality of firingand increases the quantity of defects

10. Such

defects include; bulges, non-uniform surface tint,

metallic tarnish on bricks walls, cracks,decomposed brick or black core.The firing cycle begins with the drying to driveoff the absorbed water

11. The total time within

the kiln varies between 24 to 48 hours duringwhich the temperature gradually reachestypically to less than 1100

oC. Transformation of

clay into brick can be divided into six stages11

including; dehydration of clay minerals, gypsumand iron oxide, loss of CO2, sulphur andhydrocarbons, the alpha to beta quartztransformation, the solid-state mineral reactions,melt production and reactions upon cooling.

The clay minerals illite, montmorillonite andhalloysite also contain weakly bound water within their lattice structure, which is readily lost

at 150 to 200ºC. The chemically bound water isevolved as the clay minerals themselvesdecompose between about 400ºC and 700ºC,leaving a residue of preponderantly non-crystalline material. Pyrite loses sulphur onheating by oxidation at around 400-450ºC

3.

Kaolinite is stable below 400ºC, however, above

400°C, the de-hydroxylation of kaolinitebegins

27.

CONCLUSIONSWithin the limitations of this study, the followingconclusions may be made:1. Quartz, calcite, and albite are the major

phases present in the raw brick materialswhile quartz, albite and chlorite were themajor constituent phases found almost in allthe fired brick samples.

2. The absence of mullite or cristobalite in thepresent samples might be due to thecommonly used low firing temperature(~1000

oC).

3. The local bricks are generally more porous,and thus it could be mechanically weak ascompared to that from advanced countriesbecause of improper and non scientific localmethods of processing and heat treatment.

4. The cracking observed in some of the bricksmight be due to abrupt temperatureschanges and thermal expansion coefficientmismatch among the heterogeneouslydistributed constituent phases.

5. This preliminary work highlights tremendouslack of locally relevant research on this veryimportant construction material and the needfor tremendous scope for further research inthis field.

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work. ” Br Ceram Proceed 1999; 2: 359 -400.

5. Hasan A. The art and science of brick-making. 1

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6. Livington RA. Stutzman PE, Schumann.Conservation of historic brick structure.1998, 105 -116.

7. Amjad J. Investigation of phases in soilsused for brick-making. M.Phil Thesis, Centreof Excellence in Solid State Physics,University of Punjab, 2000, pp1 – 6.

8. Singer FF. Industrial ceramics. London,Chapman Hall, 1979; 1455.

9. Karim F. Ceramics and Plastics. 1st

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