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J. Aust. Ceram. Soc. 44 [1] (2008) 23-30 23

A Preliminary Research On The Properties of Lightweight Expanded Clay

Aggregate

O. ARIOZ1*, K.KILINC1, B. KARASU2, G. KAYA2, G. ARSLAN1, M. TUNCAN1,A. TUNCAN1, M. KORKUT1and S. KIVRAK1

1Anadolu University, Faculty of Engineering and Architecture, Department of Civil Engineering,

Iki Eylul Campus, 26555 Eskisehir,Turkey.2Anadolu University, Faculty of Engineering and Architecture, Department of Material Science and

Engineering, Iki Eylul Campus, 26555 Eskisehir, Turkey.

*email: [email protected]

ABSTRACT

In the present study, lightweight expanded clay aggregates were produced from clay, waste brick powders, albitefloatation waste, and coal at various temperatures ranged from 900 C to 1250 C. After the production, thephysical and microstructural properties of the aggregates were determined. The effect of clay type, treatment(firing) temperature, amount and type of a pore forming agent on the water absorption, specific gravity, porestructure, and surface texture of the expanded granules were examined. Test results showed that lightweight

aggregates with almost 0 % water absorption can be produced from clay by utilising albite floatation waste as apore forming agent. The effects of type of raw material and treatment temperature on the properties of theaggregates were found to be significant. This was proved by microstructure and surface properties obtained bymeans of optical microscope. The results also revealed that the waste brick powders can also be used in theproduction of lightweight expanded granules. However, the specific gravity and water absorption values of theaggregates produced from clay were found to be generally lower than those produced from brick powders.

KEYWORDS: Lightweight aggregate, clay, heat treatment, albite floatation waste utilisation, microstructure

INTRODUCTION

The use of lightweight aggregate (LWA) inconstruction industry will increase in near futuresince it offers functional and economical

advantages to the house building projectsparticularly. The voids and pores in theseaggregates improve the thermal and acousticalinsulating properties [1]. Moreover, low densityproducts reduce self weight, foundation size, andconstruction costs [2]. There are different types ofLWA suitable for construction purposes. They varyin their composition, density, surface texture,porosity and water absorption capacity [3]. SomeLWAs occur naturally; others are manufacturedfrom natural materials or from industrial by-products. Because they are found only in someparts of the world, natural LWAs are not

extensively used [4]. Furthermore, the physical andmicrostructural properties of artificial LWAs can beperfectly controlled since they are produced bysome treatments. The most widely used artificialLWAs are expanded clay, expanded glass, perlite,expanded vermiculite and sintered ash [3]. Theproduction of lightweight expanded clay aggregate(LECA) becomes more popular since the rawmaterial is clay which is abundant all over theworld. LECA is named as Brazilian lightweightaggregate [5] and Azerit [6] in Brazil andAzerbaijan, respectively.The production and use of LECA is not wide in

Turkey partly because the natural lightweightaggregate sources are available and partly because

the use of lightweight structural elements inconstructions is not common. Expanded clay isproduced by firing natural clay, which swells at

1000-1200 C due to the action of the gasesgenerated inside the mass [3, 7]. The lightweight ofthis product is largely attributed to a relatively highproportion of semi-closed pores which can accountfor up to 90 % of the particle volume. LECAs aretypically manufactured from bloating clays which,upon firing, expand or bloat into a frothy mass witha high proportion of semi-closed pores. The porousstructure of loose expanded clay granulates iscomposite and formed by the voids betweenindividual grains and by the air-filled opening in thegrain base [8].The expansion occurring in the ceramic body is

caused by steam and gases, forming at differenttemperatures, which for various reasons are unableto escape from the body. This can be achieved byorganic components of the clay, water vapour, andsteam developments [9]. The admixture ofexpanded glass granules is one of the most widelyused agents in pore-forming process of expandedclay material. Pore-forming by means of expandedglass granules can be combined with the admixtureof combustible additives. This is generally applieddue to the economic reasons in order to limit theproduction costs. They may reduce the productioncosts of LECA [10]. On the other hand, the use of

combustible pore-forming agents can cause theemission of harmful gases and increase in costs

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O. Arioz, K. Kilinci, B. Karasu, G. Kaya, G. Arslan, M. Tuncan, A. Tuncan,

M. Korkut, S. Kivrak

24

related to utilisation of technical plants for theprocessing and dosing of the pore-forming agents,suction extraction units for gases, costs for thepore-forming agents [11]. Furthermore, as aconsequence of burning out pore-forming agents,the local temperature in clay body often increases

leading to a decrease in the pores with smallvolume that precisely represents the essential factorfor improving the thermal insulation [11]. In thisexperimental investigation, albite floatation wastewas used as a pore-forming agent and differentLECA granules were produced from two differentclays at different firing temperatures rangedbetween 900 to 1250 C. The effects of clayproperties, amount of pore-forming agent, and levelof firing temperature on the physical andmicrostructural properties of LECA granules wereexamined.

RESEARCH SIGNIFICANCEThe production of artificial lightweight aggregates(LWA) becomes popular due to the scarcity ofnatural sources. Among artificial LWA, the

lightweight expanded clay aggregate (LECA) ismore important since it is manufactured from awidely available material, clay. On the other hand,the properties of final product depend largely on thetype of clay, the type and amount of pore-formingagents, and the firing temperature during heat

treatment. The main objectives of this experimentalstudy is to examine the effects of the albitefloatation waste usage as a pore-forming agent onthe physical and microstructural properties ofLECA produced from different clays at differentfiring temperatures.

EXPERIMENTAL STUDY

Materials

In the current study, lightweight expanded clayaggregates (LECA) were produced from two typesof clays having different chemical compositions.

One type was obtained from a pottery productionindustry (CLAY-A) and the second one from wastebrick powder (CLAY-B). The chemicalcompositions of the clays are given in Table 1.

Table 1: Chemical compositions of raw materials

Type of Clay SiO2 Al2O3 Fe2O3 CaO MgO TiO2 Na2O K2OCLAY-A 58.0 27.0 1.0 0.2 0.4 1.3 0.3 2.3CLAY-B 51.8 15.6 13.0 9.3 6.1 1.7 1.2 1.3

Albite floatation waste, which is obtained from orepreparation process of albite especially at the stageof quartz floatation, was also used as a pore-forming agent. Its chemical composition is given inTable 2 [12]. It is clear from the chemical analysisthat this waste consists of high amounts of fluxing

oxides such as CaO, Na2O, and P2O5. X-raydiffraction (XRD) analysis can be seen in Fig. 1which indicates that this floatation waste wascomposed of albite, rutile, and hydroxyl apatitephases [12].

Table 2: Chemical composition of albite floatation waste [12]

SiO2 Al2O3 Fe2O3 CaO MgO TiO2 Na2O K2O P2O5 L.O.I34.7 10.3 0.40 11.0 22.2 0.20 5.20 0.20 15.1 0.70

*LOI: losses on ignition.

Fig. 1: XRD pattern of albite floatation waste [12]

A: AlbiteR: RutileHa: Hydroxyapatite

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Preparation of the samples

CLAY-A and CLAY-B were mixed with albitefloatation waste in different ratios ranging from 10to 40 % and a plastic mud was prepared. In one ofthe mixtures, coal was used as a pore formingagent. The raw material was first ground in a ring

mill and then mixed homogenously in a ball mill.The prepared mud was dried in porous stone inorder to achieve proper plasticity. Finally, the mudwas rounded by shaping operation. After

preparation, the rounded mud aggregates were firstdried in an oven for 24 hours at 67 C and then, theproducts are treated for 10 minutes in differentfiring temperatures ranging from 900 to 1250 C inan electrically heated furnace. The rate oftemperature increase in furnace was kept constant

as 10 C/min. Totally 38 different recipes wereprepared and tested in the present study. Themixtures and corresponding firing temperatures arepresented in Table 3.

Table 3: Mixtures and firing temperatures of aggregates

Type ofClay

Type of Pore-forming Agent

Amount ofPore-forming

Agent (%)

Firing Temperature (C)

900 1000 1100 1125 1150 1200 1250

CLAY-AAlbite

FloatationWaste

10 + + + +

20 + + +

30 + + + +40 + + +

CLAY-B

AlbiteFloatation

Waste

10 + + + + +

20 + + Melt

30 + + + + Melt

40 + + Melt

Coal5 + + + Melt

7,5 + + + Melt

+: performed

Melt: aggregates melted during heat treatment.

The produced LECA granules were illustrated inFig. 2. The diameter of the aggregates was rangedbetween 3 and 8 mm. The light coloured, red, and

black aggregates were produced from CLAY-A,CLAY-B, and CLAY-B with coal, respectively.

Fig. 2: Produced LECA granules

Tests applied to the produced aggregatesAfter production, water absorption and specificgravity tests were conducted on aggregate samples.In this experiment, the aggregates are dried to a

constant weight at 105 C and weighed. Then, theyare boiled for 5 hours and immersed in water for 24hours and then, their surfaces are dried. The waterabsorption values are calculated according tofollowing Eqn 1;

100,% xW

WWWA

dry

dryssd

= (1)

Where, WA is the water absorption of the aggregatein percent, Wssd is the weight of the aggregate insaturated-surface-dry state, and Wdry is the weightof the oven-dry aggregate.

In specific gravity test, the mass of the aggregatesample is determined in air and water. Then, thespecific gravity of the aggregate is calculated byusing the Eqn 2 below;

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sw

d

WW

WSG

= (2)

Where, SG is the bulk specific gravity of theaggregate, Wd is the weight of the dry sample, Ww

is the weight of the saturated-surface-dry testsample in air, and Wsis the weight of saturated testsample in water.

Microstructures of the lightweight aggregatesproduced at different temperatures were observedby an optical microscope.

RESULTS AND DISCUSSIONSThe water absorption properties of LECA granulesproduced in the present study are shown in Figs. 3-

5. According to the test results, the water absorptionvalues of the aggregates produced from CLAY-Areduced with increase in firing temperature. Thelowest water absorption value, 0 %, was measuredon aggregates produced at 1250 C. It seems thatthis level of temperature makes a compact and

homogenous outer glassy film on the surface of theaggregates and that makes them impervious towater. R. de Gennaro et al. found similar results onthe expanded zeolite aggregates produced at around1400 C [1]. The effect of amount of floatationwaste on the water absorption can not begeneralized for the treatment (firing) temperatureslower than 1250 C. However, the water absorptionof the granules treated at 1250 C decreased withincrease in albite floatation waste.

900 1100 1200

1250

1020

3040

0

5

10

15

20

Water

Absorption

(%)

Firing Temperature (oC)

Floatation

Waste (%)

CLAY-A

Fig. 3: Water absorption values of LECA granules produced from CLAY-A and floatation waste

900

1000

1100

1125

1150

1200

1020

3040

05

10

15

20

WaterAbsorption

(%)


FloatationWaste (%)

CLAY-B

Fig. 4: Water absorption values of LECA granules produced from CLAY-B and floatation waste

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J. Aust. Ceram. Soc. 44 [1] (2008) 23-30 27

9001000

11251150

5

7.5

0

5

10

15

20

25

30

Water

Absorption(%)


Coal (%)

CLAY-B

Fig. 5: Water absorption values of LECA granules produced from CLAY-B and coal

The effect of firing temperature on the water

absorption values of LECA granules produced fromCLAY-B can not be generalized. Even for the heattreatment at 1200 C, the water absorption valueswere found between 10 and 15 % (Fig. 4.)However, almost 0 % water absorption wasobtained at the temperature of 1125 C. It can beseen that the water absorption values of theaggregates produced from CLAY-A were found tobe generally lower than those produced fromCLAY-B.

Fig. 5 presents the water absorption values ofaggregates produced from CLAY-B with coal.

Similar to Fig.4, very low water absorption valueswere obtained at the temperatures of 1125 and 1150C. It was interesting that the water absorptionvalues of LECA granules produced at 1125 C wassignificantly lower than those produced at 1000 C.It seems that the temperatures of 1125 and 1150 Care proper to reduce the water absorption of

aggregates produced from CLAY-B, irrespective to

the pore forming agent.

One of the most important properties of lightweightaggregate (LWA) granules is the specific gravity.This property plays an important role on the designof concrete structures and insulation properties ofthe building members. The specific gravity (SG)values of the light weight expanded clay aggregate(LECA) granules produced in the present study aregiven in Figs.6-8. It is clear from Fig. 6 that LECAgranules with specific gravity between 1.5 and 2.0can be produced from CLAY-A at 1250 C. Theheat treatment temperatures lower than 1250 C

were not found to be sufficient to produce lightergranules. Test results revealed that SG valuesdecreased with increase in albite floatation waste.For example, the SG values were 1.55 and 1.95 forthe aggregates produced with 40 and 10 %floatation waste, respectively (Fig. 6).

900 1100 1200 1250

1020

3040

1.5

2.0

2.5

SpecificGravity


FloatationWaste (%)

CLAY-A

Fig. 6: Specific gravity values of LECA granules produced from CLAY-A and floatation waste

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900

1000

1100

1125

1150

1200

1020

3040

1.5

2.0

2.5

Specific

Gravity


Floatation

Waste (%)

CLAY-B

Fig.7: Specific gravity values of LECA granules produced from CLAY-B and floatation waste

9001000

11251150

5

7.5

1.5

2.0

2.5

Specific

Gravity


Coal (%)

CLAY-B

Fig.8: Specific gravity values of LECA granules produced from CLAY-B and coal

The SGs of LECA granules produced from CLAY-B ranged between 2.2 and 2.4 even the firingtemperature increased up to 1200 C (Fig. 7). It wasnot possible to produce LECA granules with a SGless than 2.0 with CLAY-B and floatation waste inthe present study. On the other hand, LECAgranules with SG value of less than 2.0 can beproduced at 1150 C by using coal as a pore

forming agent (Fig. 8).The pore structures and surface textures of theaggregates were illustrated in Figs. 9 and 10,respectively. It is clear that the pore structure andsurface properties of the aggregates aresignificantly affected by the type of raw materialand treatment temperature. The distribution,amount and size of the pores become very suitableas the pore forming agent is 40 % and the treatment

temperature is 1250 C with CLAY-A (Fig. 9b).The size of the pores ranged from 0.2 and 1 mmand there was no connection between the pores.This may reduce the specific gravity of theaggregate and also provide perfect insulation. It canbe seen from Fig. 6 that the smallest specificgravity value was measured in aggregates producedfrom CLAY-A with 40 % albite floatation addition

at a treatment temperature of 1250 C. This was notobtained by using CLAY-B even though the poreforming agent was 40 % and the treatmenttemperature 1200 C (Fig. 9c). The pores of theseaggregates were found to be small anddiscontinuous. It is also clear that the treatmenttemperature of 1100 C is not enough for CLAY-Ato form a suitable pore structure even the poreforming agent is 40 % (Fig. 9a).

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J. Aust. Ceram. Soc. 44 [1] (2008) 23-30 29

Fig. 9: Pore structures of the aggregates

(a) CLAY-A, 40 % albite floatation, 1100 C,

(b) CLAY-A, 40 % albite floatation, 1250 C,

(c) CLAY-B, 40 % albite floatation, 1200 C

Fig. 10: Surface textures of the aggregates

(a) CLAY-A, 40 % albite floatation, 1100 C,

(b) CLAY-A, 40 % albite floatation, 1250 C,

(c) CLAY-B, 40 % albite floatation, 1200 C

The surface properties of the aggregates are

important for water absorption capacity of theaggregates. Re. de Gennaro et al. state that theexpanded aggregates have a compact andhomogenous outer glassy film that makes themimpervious to water [1]. It was found that the heattreatment and type of clay played an important rolein the surface properties of LECA granules. Thesurface of the aggregates seemed smooth andimpervious in case of CLAY-A usage treated at1250 C (Fig. 10b). This will reduce the waterabsorption capacity of the aggregate. It can be seenfrom Fig. 3 that the smallest water absorption valuewas observed in aggregates produced from CLAY-

A with 40 % albite floatation at 1250 C. On theother hand, the surface texture was rough and

seemed to be pervious when CLAY-A was treated

at 1100 C (Fig. 10a). The surface of the aggregatesproduced from CLAY-B was rough and perviouseven though the treatment temperature increased to1200 C.

CONCLUSIONSThe following conclusions may be drawn from thisexperimental study;1. The water absorption values of aggregates

produced from pottery clay (CLAY-A) at 1250C decreased with increase in the amount offloatation waste.

2. The water absorption values of aggregates

produced from waste brick powders (CLAY-B)were found to be almost 0 % when they are

(c)

(b)

(a)

(c)

(a)

(b)

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treated at a temperature of 1125 C irrespectiveto the type of pore forming agent.

3.The water absorption values of aggregatesproduced from CLAY-A were found to begenerally lower than those of aggregatesproduced from CLAY-B.

4.

Lightweight expanded clay aggregates withspecific gravity between 1.5 and 2.0 and almost 0% water absorption can be produced fromCLAY-B by using albite floatation wastes.Specific gravities of the aggregates generallydecreased with increase in the amount offloatation waste.

5.The waste brick powders can also be used in theproduction of LECA granules but the specificgravity values were very high even the treatment(firing) temperature increased to 1200 C whenthe pores were obtained by floatation waste. Onthe other hand, somewhat lower specific gravity

values were measured on the aggregatesproduced with the addition of coal.

6.The pore structure and surface properties of theaggregates were significantly affected by thetype of raw material and treatment temperatureapplied in the granule production.

7.The distribution, amount and size of the poresbecome very suitable as the pore forming agentis 40 % and the treatment temperature is 1250 Cwith CLAY-A.

8.The surface of the aggregates seemed smoothand impervious when CLAY-A was treated at1250 C

Conclusively, it was found that the type of clay, thetype and amount of pore forming agent, and thefiring temperature were very important for theproperties of lightweight expanded clay aggregate(LECA). The test results have revealed that it ispossible to produce LECA granules from clay byusing albite floatation waste in different amounts.Utilisation of floatation waste for pore-forming mayreduce the production costs. These wastes can beutilised properly in this sector. Since the clay islocally available material, it is possible to producelightweight aggregate with low costs. This is

advantageous for countries with low naturallightweight aggregate sources. These LECAgranules can be used to produce lightweightconcrete and lightweight blocks or isolation brickreducing the energy costs in buildings.

FURTHER RESEARCHIn the present investigation, albite floatation wasteswere used in the production of lightweightexpanded clay aggregate granules. However, it isdesirable to use different pore forming agents suchas perlit and glass. The results of such studieswould make enable to compare the effects of the

pore forming agent for different clay types.

ACKNOWLEDGEMENTS

The Authors would like to thank to The ResearchFund of Anadolu University for funding the presentstudy (Project no: 06 02 08). The Authors also verymuch appreciate to Dr. I. Tore of AnadoluUniversity for their collaboration relating to this

experimental study. The Authors also would like tothank to Professor N. Varcan for his invaluablecontributions to several aspects of the workreported in this paper.

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deGennaro, M., Dondi, M. and Langella, A.,Neapolitan Yellow Tuff as Raw Material forLightweight Aggregates in LightweightStructural Concrete Production, Applied ClayScience, Vol. [28], (2005), 309-319.

2. Alduaij, J., Alshaleh, K., Haque, M. N. andEllaithy, K., Lightweight Concrete in HotCoastal Areas, Cement and ConcreteComposites, Vol. [21], (1999), 453-458.

3. Mladenovic, A., Suput, J. S., Ducman, V. andSkapin, A. S., Alkali-Silica Reactivity of SomeFrequently Used Lightweight Aggregates,Cement and Concrete Research, Vol. [34],(2004), 1809-1816.

4. Neville, A. M., Properties of Concrete, Addison-Wesley Longman, (1995).

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8. Vasina, M., Hughes, D. C., Horoshenkov, K. V.and Lapcik, L., The Acoustical Properties ofConsolidated Expanded Clay Granulates,Applied Acoustics, (2005), Article in press.

9. Toth, M. N. and Csaky, I. B., The Role of theSmectite Group in the Bloating Process,Ziegelindustrie, Vol. [5], (1989), 246-250.

10. Bettzieche, H., Schops, W. and Hohmann, H.,Pore-Forming in Brickmaking Clay by Meansof Expanded Glass Granules, Ziegelindustrie,Vol. [5], (2000), 41-53.

11. Sveda, M., Bagel, L. and Komora, L., A NewPossibility for Pore-Forming in the Clay Body,Ziegelindustrie, Vol. [4], (1996), 240-245.

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