ALTERNATIVE FUELS IN CEMENT

MANUFACTURETECHNICAL

AND ENVIRONMENTAL REVIEW

AssociationEuropéennedu CimentThe EuropeanCementAssociation

CEMBUREAU – the European Cement Association, based in Brussels, isthe representative organisation for the cement industry in Europe. Its FullMembers are the national cement industry associations and cement com-panies of the European Union and the European Economic Area countriesplus Switzerland and Turkey. Associate Members include the national ce-ment associations of the Czech and Slovak Republics, Hungary and Poland.

The Association acts as spokesman for the cement sector towards the Euro-pean Union institutions and other authorities, and communicates the in-dustry’s views on all issues and policy developments likely to have an effecton the cement market in the technical, environmental, energy and promotionareas. Permanent dialogue is maintained with the European and interna-tional authorities and with other International Associations as appropriate.

Serviced by a multi-national staff in Brussels, Standing Committees andissue-related Project Groups, established as required, enable CEMBUREAUto keep abreast of all developments affecting the industry.

CEMBUREAU also plays a significant role in the world-wide promotion ofcement and concrete in co-operation with member associations, and theready-mix and precast concrete industries. The Association regularly co-hostsconferences on specific issues aimed at improving the image of concrete andpromoting the use of cement and concrete products.

Since its foundation in 1947, CEMBUREAU has developed into the majorcentre for the dissemination of technical data, statistics and general infor-mation on the cement industry world-wide. Its publications serve as the prin-cipal source of information on the cement industry throughout the world. Itis the editor of the “World Cement Directory” providing data on cementcompanies and works based in some 150 countries.

CEMBUREAU PRESENTATION

Rue d’Arlon 55 – B-1040 BrusselsTel.: (32-2) 234 10 11 – Fax: (32-2) 230 47 20E-mail: cembureau@infoboard.be

ALTERNATIVE FUELS IN CEMENT MANUFACTURETECHNICAL AND ENVIRONMENTAL REVIEW

2

CONTENTS

Executive summary

Introduction

Background

• The European cement industry

• Responsible environmental management by the cement industry

Regulatory framework

How cement is made

• The process

Environmental aspects of cement manufacture

• Raw materials

• Energy

• Emissions

The use of alternative fuels

• The benefits of using alternative fuels

• Safe valorisation in cement kilns

Environmental performance of concrete

Literature references

3

The use of cement has long been thebasis for development of society and forthe welfare of the people. Forgenerations concrete, which is madefrom cement, has been the ultimatematerial for construction of harbours,roads, bridges, dams, houses, schools,hospitals.

The cement industry in the EuropeanUnion produces about 170 milliontonnes of cement each year. Itcontributes significantly to local andregional economies through more than300 plants spread all over Europe andoften in rural areas.

The cement industry recognises itsresponsibility to manage theenvironmental impact associated withthe manufacture of its products. Overthe past 20 years specific energyconsumption has been reduced by about30%, equivalent to approximately 11million tonnes of coal per year. Dustemissions have been reduced by 90% asthe industry has invested heavily invarious emission abatement techniques.

Cement is produced in accordance withEuropean and national legislation as wellas internal procedures. Strict regulationsare applied and plants are operated onthe basis of permits from nationalauthorities. Emissions are regularlychecked by the authorities.

The cement industry is able to use wasteas alternative fuels and raw materials toreinforce its competitiveness and at thesame time contribute to solutions tosome of society’s waste problems in away which valorises the waste and isbeneficial to the environment. The use ofalternative fuels today substitutes

approximately 2.5 million tonnes of coalevery year.

The use of waste as alternative fuels inthe cement industry has numerousenvironmental benefits such as:• The use of waste as alternative fuels

reduces the use of non-renewablefossil fuels such as coal as well as theenvironmental impacts associatedwith coal mining.

• The use of waste as alternative fuelsalso contributes towards a lowering ofemissions such as greenhouse gasesby replacing the use of fossil fuelswith materials that would otherwisehave to be incinerated withcorresponding emissions and finalresidues.

• The use of alternative fuels in cementkilns maximises the recovery ofenergy from waste. All the energy isused directly in the kiln for clinkerproduction. It also maximises therecovery of the non-combustible partof the waste and eliminates the needfor disposal of slag or ash, as theinorganic part substitutes rawmaterial in the cement.

The use of waste as alternative fuels is asafe way of valorising waste. The organicconstituents are completely destroyeddue to the high temperatures, longresidence time and oxidising conditionsin a cement kiln. The inorganicconstituents combine with the rawmaterials in the kiln and leave the processas part of the cement. Heavy metals inthe cement end up bound in the concrete.Concrete made from cementmanufactured using alternative fuels hasthe same construction and environmentalproperties as concrete made from cementmanufactured using fossil fuels.

EXECUTIVE SUMMARY

4

This publication was prepared byCEMBUREAU with the assistance ofERM (Environmental ResourcesManagement) to provide information onthe usage of selected waste materials inthe European cement industry and inparticular the usage of organic materialsas substitutes for fossil fuels.

The primary objective of a cementcompany is to produce and sell highquality cement. Whilst respecting thispurpose, the use of waste materials can

bring a number of benefits both to thecement industry and to society ingeneral. This publication givesbackground information concerning themanufacture of cement and theregulatory framework, and describes thespecial characteristics of cement plantswhich provide for the safe and effectiveuse of alternative fuels. Competitivenesscan be reinforced and at the same timesome of society’s waste problems can besolved in a way which valorises the wasteand is beneficial to the environment.

INTRODUCTION

The primary

objective of

a cement company

is to produce and

sell high quality

cement.

Valorisation

of waste provides

environmental

benefits and

reinforces the

competitiveness

of the cement

industry.

Bernburg plant -

5000 t/day capacity

5

BACKGROUND

The European cement industry

Cement has played a key role as aconstruction material throughout thehistory of civilisation. In Europe the useof cement and concrete in large civic

works can be traced from antiquitythrough modern times. Portland

cement was patented in 1824 and bythe end of the 19th centuryconcrete, based on Portlandcement, had become a highly

appreciated construction materialthroughout Europe.

Cement manufacturing is a major mineralcommodity industry. In 1995 the worldproduction of cement was 1420 milliontonnes. In the European Union cement isproduced in more than 300 plants. Thetotal cement production in the EuropeanUnion amounted to 172 million tonnes in1995 and the consumption was 168million tonnes. The cement consumptionper capita was 450 kg.

6

From water supply to waste watersystems, from roads and bridges to airtransport infrastructure and harbours,from residential houses to commercialand industrial structures, from schoolsto hospitals, concrete is the essentialmaterial in providing for developmentof man’s activities.

The cement industry is a highly capitalintensive industry, with yearly capitalinvestments in CEMBUREAU membercountries in the order of ECU 1 billion.

The use of cement has contributed

to the welfare of society

for generations.

The cement industry

contributes significantly to local

and regional economies.

Number of cement plants

in 1995

Full Members

Associate Members

14(Benelux)

43

93

13

11

66

24

2

1

2

3

208

75

42

7

51

1

8

7

World cement production 1995

Rest of Asia 23 %

China 30 %

Japan 7 %

Oceania 1 %

CEMBUREAU countries 15 %

Other Europe 3 %

Former USSR 4 %

USA 5 %

Other America 8 %

Africa 4 %

The huge investments and long pay-back periods for process modificationsmake the cement industry very carefulin selecting and developing newtechnologies.

The use of cement has contributed tothe welfare of society for generations.The cement industry significantlycontributes to local and regionaleconomies through the wide geographicspread of its plants which are mainlylocated in rural areas.

2

8

Responsible environmentalmanagement by the cementindustry

The cement industry recognises itsresponsibility to manage theenvironmental impact associated withthe manufacture of its products. Overthe past few decades the Europeancement industry has demonstrated animpressive record in continualenvironmental improvement within thecontext of the sustainable manufactureand use of cement. A few examples ofthese achievements and their resultingbenefits to the wider environment areas follows:

• Dust emissions have been reduced by90% over the last 20 years, as aresult of refinements in theproduction process and substantialinvestment in modern producthandling methods and air pollutioncontrol equipment.

• The industry has been at the forefrontof developing and applying quarryrestoration methods to returndepleted quarries to productive,scenic or recreational use.

• The specific energy consumption forthe production of cement clinker hasbeen reduced by approximately 30%since the 1970s. This reduction inprimary energy requirements isequivalent to approximately 11million tonnes of coal per year withcorresponding benefits in reductionof CO2 emissions.

• Research into improved cementproducts has resulted in increased

1950 1960 1970

Dust Emission

Reduction of dust emission

Dus

t em

issi

on in

% o

f the

pro

duct

ion

1980 1990 95

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5 1960 1965 1970 1975 1980 1985 1990

Reduction of specific energyDevelopment of the specific fuel energy consumption in CEMBUREAU countries since 1960

Fuel

ene

rgy

in k

J/kg

clin

ker

3500

4000

4500

5000

5500

6000

9

strength performance and moreefficient use of cement.

• Conservation of natural non-renewable resources has beenobtained through the valorisation ofwastes as raw materials for clinkerproduction and as alternative fuels.Through this valorisation the cementindustry contributes to solvingsociety’s waste problems by reducingthe amount of waste to be disposed

of (with additional benefits inemission of CO2).

• The use of blended cements in whichblastfurnace slag, power station flyash, natural pozzolana or limestone isused together with cement clinker iscontributing further to theconservation of primary naturalmineral resources and fossil fuels,and to the reduction of atmosphericemissions, especially of CO2.

Old quarries

used for

recreational

leisure time

10

The cement industry, likeother industrial sectors, isstrictly regulated vianational and internationallegislation regardingenvironmental protection,

health and safety and quality ofproducts.

The manufacture of cement is a matureindustrial activity and the emissioncontrol regulations currently applied tothe industry are the result of extensivereview and refinement over a numberof years. Legislation regardingemissions from cement plants exists inall EU countries and the cement plantsmeasure emissions under the control ofregulatory authorities. These nationalsystems have proved effective inregulating the use of ordinary fuels aswell as alternative fuels in cement kilnsto the overall benefit of theenvironment.

The rules for national regulation ofcement plants are laid down atEuropean level in the EuropeanCommunity Directive on the combatingof air pollution from industrial plants(84/360/EEC). These rules are beingreplaced by those in the new Directiveon Integrated Pollution Prevention andControl (96/61/EC) – the “IPPC”Directive. This new importantenvironmental legislation aims atachieving a high level of protection forthe environment as a whole by meansof measures “designed to prevent or,where that is not practicable, to reduceemissions” to air, water and land.

The use of hazardous waste as analternative fuel in cement kilns isregulated at EU level by Directive

94/67/EC. While the Directive sets outrules for the burning of hazardouswastes in dedicated plants forincineration of waste, it also recognisesand provides for the procedure of co-combustion or co-incineration, that isthe burning of wastes in industrialfurnaces (such as cement kilns) notexclusively designed for such purposes.The Directive also accepts the need totake account of emissions from rawmaterials and fuels other thanhazardous fuels in setting emissioncontrols on exhaust gases from cementkilns.

The same strict standards that areapplied to dedicated hazardous wasteincinerators are also applied in cement

REGULATORY FRAMEWORK

The cement industry, like

other industrial sectors,

is strictly regulated.

IPPC Directive covers

procedures for

granting operation

permits. Permits shall

include emission limits for

dust, SOx, NOx, heavy

metals and organic

compounds.

These limits shall be set by

national Authorities based

on “Best

Available Techniques”.

11

kilns to the emissions whichresult from the combustionof hazardous waste.

The European Commission,the Parliament and theCouncil have recentlypublished their reviews ofthe Community Strategy forWaste Managementoriginally established in

1989. All three documents have acertain flexibility regarding theapplication of the waste managementhierarchy. The utilisation of alternativefuels in the cement industry issupported by the general principles ofwaste management at both EuropeanUnion and national levels.

National permit systems

effectively control the use of

ordinary fuels as well as

alternative fuels to the

benefit of the environment.

Waste Management

Hierarchy

• prevention

• recovery

• disposal

CO2

SO2

NOx

Fossil Fuels(Coal, Fuel Oil, Natural Gas)

Fossil Fuels(Coal, Fuel Oil, Natural Gas)

Waste usedas

Alternative Fuels

Waste

CEMENTPLANT

CO-COMBUSTIONIN CEMENT PLANT

INCINERATIONPLANT

CO2

SO2

NOx

CO2

SO2

NOx

Waste recovery by the cement industry reduces emissions

+

+

The wastes used as alternative fuels incement kilns would alternatively eitherhave been landfilled or destroyed indedicated incinerators with additionalemissions as a consequence. Their usein cement kilns replaces fossil fuels andmaximises the recovery of energy.

Employing alternative fuels in cementplants is an important element of asound waste management policy. Thispractice promotes a vigorous andthriving materials recovery andrecycling industry, in line with theessential principles of the EU’s wastemanagement hierarchy.

12

HOW CEMENT IS MADE

The process

Cement production involves theheating, calcining and sintering ofblended and ground raw materials,typically limestone and clay or shale andother materials to form clinker. Thisclinker burning takes place at a materialtemperature of 1450 °C in kilns, whichare inclined rotating cylinders lined withheat-resistant bricks. Afterwards, theclinker is ground with a small amountof gypsum to give Portland cement,which is the most common variety ofcement manufactured in Europe. Inaddition, blended cements are producedby intergrinding cement clinker, smallamounts of gypsum as well as materialslike fly ash, granulated blast furnaceslag, limestone, natural or artificialpozzolanas.

Portland 43 %

Portland composite 44 %

Blastfurnace slag 7 %

Composite + other 1 %

Pozzolanic 5 %

Deliveries of cement typesin EU and EFTA

DRY PROCESS

� Quarries (limestone, clay)

� Drill

� Dumper

� Crushing

� Prehomogenization

� Grinding

� Filter

Preheating

Rotary Kiln

� Cooler

� Clinker storage

Additions

� Cement grinding

� Cement silos, dispatching

WET PROCESS

� Wet grinding

� Homogenization

� Filter

� Rotary kiln

WET PROCESS

DRY PROCESS

13

Large cement plants produce of theorder of 4,000 tonnes of cement perday.

Depending on how the raw material ishandled before being fed to the kiln,basically three different types ofprocesses can be distinguished: the dry,semi-dry/semi-wet and wet process.The technology applied depends on theorigin of the raw materials. Theorigin/type of limestone/clay and thewater content (ranging from 3% forhard limestone to above 20% forchalk), are particularly important.

In the dry process the feed materialenters the kiln in a dry, powdered form.The kiln systems comprise a tower ofheat exchange cyclones in which thedry feed is preheated (“preheater kiln”)by the rotary kiln’s hot exit gases priorto entering the actual kiln. Thecalcination process can almost becompleted before the raw materialenters the kiln if part of the fuel isadded in a special combustion chamber(“precalciner kiln”).

In the wet process, which is often usedfor raw materials with a high moisturecontent, the feed material is made bywet grinding and the resulting slurry,which contains typically 30-40% water,is fed directly into the upper end of theinclined kiln.

In the semi-dry or semi-wet process 10-20% water is either added to theground dry feed material or removedfrom a slurry for instance by filterpresses resulting in a feed materialcontaining about 15-20% moisture.Pellets of feed material are loaded ontoa travelling grate where they are

preheated by the rotary kiln’s hot exitgases. By the time the feed materialreaches the kiln entrance the water hasevaporated and calcination has begun.

Over the past few decades theEuropean cement industry has investedheavily in a planned move from the wetprocess to the more energy-efficient dryprocess, where the raw materials allow.Presently, about 78% of Europe’scement production is from dry processkilns, a further 16% of production isaccounted for by semi-dry and semi-wetprocess kilns, and about 6% ofEuropean production now comes fromwet process kilns due to lack of suitableraw materials for other processes.

Dry 78 %

Wet 6 %

Semi-dry + Semi-wet 16 %

Cement is produced by three processes

14

ENVIRONMENTAL ASPECTS OF CEMENT MANUFACTURE

Raw materialsIn the cement kiln new minerals areformed giving cement its specificproperties. The main components arethe oxides of calcium, silicon,aluminium and iron.

Calcium is provided mainlyby raw materials such aslimestone, marl or chalk. Thesilicon, aluminium and ironcomponents as well as otherelements are provided byclay, shale and othermaterials. All the naturalmaterials mentioned alsocontain a wide variety ofother elements in smallquantities.

Significant quantities of limestone, clayand other primary raw materials arequarried to service the demand forcement. In line with its commitment tosustainable development, the Europeancement industry has increasingly sourcedalternative materials to substitute for thetraditional natural raw materials. Theindustry currently uses large quantitiesof blast furnace slag, power station flyash, silica fume, natural pozzolanas andlimestone fines, mainly to substitute forclinker in cement. Some of these are alsoused as raw materials in the clinkerproduction process.

The use of these alternative materialshas significant positive environmentalbenefits. The need for quarrying ofprimary raw materials is reduced, energyconsumption in producing cement isreduced and overall reductions inemissions of dust, CO2 and acid gasesare attained. In some applications, theperformance of concrete can be

enhanced when Portland cement clinkeris complemented by these materials.

EnergyDepending on the raw materials and theprocess, a cement plant consumes fuelamounting to about 3200 to 5500 MJ/tclinker. Electrical energy consumption isabout 90 to 120 kWh/t cement.

Historically, the primary fuel used iscoal. A wide range of other primaryfuels are also used, including petroleumcoke, natural gas and oil. The averageEuropean energy requirement toproduce one tonne of cement isequivalent to the combustion ofapproximately 120 kg of coal.

The main constituents of fuel ash aresilica and alumina compounds whichcombine with the raw materials tobecome part of the clinker. Like othernatural products fuel ashes contain awide range of trace elements which arealso incorporated in the cement clinker.

With energy typically accounting for30-40% of the production cost ofcement, the cement industrythroughout Europe has successfullyconcentrated significant efforts onimproving energy efficiency in recentdecades. In 1993 a study by theEuropean Commission estimated thatthe real remaining potential energysaving in the cement manufacturingprocess was approximately 2.2% forthe entire sector in the European Union.

EmissionsReleases from the cement kiln comefrom the physical and chemicalreactions of the raw materials and fromthe combustion of fuels.

Natural raw materials and

coal ash used to produce

cement contain a wide range

of trace elements in addition

to calcium, silicon,

aluminium and iron.

15

The main constituents of the exit gasesfrom a cement kiln are nitrogen from thecombustion air, CO2 from calcinationand combustion, water from thecombustion process and the rawmaterials, and excess oxygen.

The exit gases also contain smallquantities of dust, chlorides, fluorides,

sulphur dioxide, NOx, carbonmonoxide, and still smaller quantities oforganic compounds and heavy metals.

Composition of exhaust gases

%N2 45-66CO2 11-29H2O 10-39O2 (stack) 3-10Remainder < 1

The exit gases from cement kilns arededusted in filters (normallyelectrostatic precipitators) and the dustis normally returned to the process.

Cement plants are usually liquideffluent-free, since any water used inthe process is evaporated within thekiln. If the air pollution control deviceuses a wet cleaning system, then theresulting effluent is generally returnedto the start of the production processfor use as makeup water, while thesludge is also returned to the kiln asfeed material.

Emissions

are controlled

16

THE USE OF ALTERNATIVE FUELS

The benefits of using alternative fuelsAnnually, the energy equivalent of about25 million tonnes of coal is required byCEMBUREAU Members to service thedemand for cement in Europe. This is asignificant use of non-renewableprimary fossil fuel, and therefore theindustry is committed to seeking outmore energy efficient ways of producingcement as well as alternative, moresustainable energy sources.

The use of alternative fuels is a wellproven and well established technologyin most of the European cementindustry and this has been the case formore than 10 years. In 1995 about10% of the thermal energyconsumption in the European cementindustry originated from alternativefuels. This is equivalent to 2.5 milliontonnes of coal. The proportion isgradually increasing and figures above50% are already achieved in certainregions.

Waste materials which the cementindustry has utilised as alternative fuelsinclude used tyres, rubber, paper waste,waste oils, waste wood, paper sludge,sewage sludge, plastics and spentsolvents.

The use of waste as alternative fuels inthe cement industry has numerousenvironmental benefits such as:

• Reduction of the use of non-renewable fossil fuels such as coal aswell as the environmental impactsassociated with coal mining.

• Contribution towards a lowering ofemissions such as greenhouse gases

by replacing the use offossil fuels with materialsthat would otherwise haveto be incinerated withcorresponding emissionsand final residues.

• Maximisation of therecovery of energy fromwaste. All the energy isused directly in the kilnfor clinker production.

Use of waste as fuels in

cement kilns saves fossil

fuels, reduces emissions to

air and eliminates the need

for disposal of slag and ash.

17

• Maximisation of the recovery of thenon-combustible part of the wasteand elimination of the need fordisposal of slag or ash, as theinorganic part substitutes rawmaterial in the cement.

Safe valorisation in cementkilnsThe use of waste as alternative fuels istechnically sound as the organic part isdestroyed and the inorganic part,including heavy metals, is trapped andcombined in the product. Cement kilns

have a number of characteristics whichmake them ideal installations in whichalternative fuels can be valorised andburnt in safety, such as:

• High temperatures• Long residence time• Oxidising atmosphere• High thermal inertia• Alkaline environment• Ash retention in clinker• Continuous fuel supply

18

Organic constituentsNormal operation of cement kilnsprovides combustion conditions whichare more than adequate for thedestruction of even the most difficult-to-destroy organic substances. This isprimarily due to the very hightemperatures of the kiln gases (2000 °Cin the combustion gas from the mainburners and 1100 °C in the gasfrom the burners in theprecalciner). The gas residencetime at high temperature in therotary kiln is of the order of 5-10seconds and in the precalcinermore than 3 seconds.

Because a cement kiln is a largemanufacturing unit operating as acontinuous process and with a highheat capacity and thermal inertia, a

Two characteristics in

particular are of importance

for the use of waste

as alternative fuel in cement

kilns: burning

conditions (high temperature

with long residence time

and oxidising atmosphere)

and a natural alkaline

environment.

2000

1800

1600

1400

1200

1000

800

600

400

200

0

Electrofilter Rotary Kiln

Gas Retention Time

Material Retention Time

CoolerPreheater

Calciner

Gas Temperature

ca. 10 s.ca. 10 s. ca. 10 s. 3 s. ca. 1 s.

ca. 30 min.ca. 30 min.

Material Temperature

Tem

pera

ture

s (°

C)

ca. 1 min.

19

significant change in kiln temperaturein a brief period of time is not possible.The cement kiln can readily switchback to conventional

fuel. The cement kiln therefore offersan intrinsically safe thermalenvironment for the use of alternativefuels.

Complete combustion of an organiccompound composed only of carbonand hydrogen produces CO2 and water.Additionally, if the organic compound(conventional fuel or alternative fuel)contains chlorine or sulphur, then acidgases such as hydrogen chloride andsulphur dioxide are also produced.These gases are absorbed andneutralised by the freshly formed limeand other alkaline materials within thekiln.

A number of studies evaluating organicemissions from combustioninstallations have focused on the familyof chemicals known as “dioxins”.Directive 94/67/EC on the incinerationof hazardous waste stipulates anemission limit of 0.1 nanogram ofdioxins per cubic metre of gas emitted,the dioxins being measured in units of“toxic equivalents”. Cement kilns firedwith conventional fossil fuel or withalternative fuels of all types can meetthis emission limit.

20

Inorganic constituentsAlternative fuel ash can provideimportant constituents whichcontribute towards building the clinkerphases in the same way as coal ashdoes. Used tyres, for instance, provideiron which is required as a clinkerconstituent as well as energy. If thisiron is not provided by tyres, it has tobe added to the process using othermaterials.

Metals, like any other elements, are notdestroyed in an industrial furnace.Metals introduced into the cement kilnthrough the raw materials or the fuelwill be present in either the releases orin the clinker. Extensive studiesinvestigating the behaviour of metals incement kilns have shown that the vastmajority are retained in the clinker. Forexample, studies on antimony, arsenic,barium, beryllium, cadmium,chromium, copper, lead, nickel,selenium, vanadium and zinc haveestablished that near 100% of thesemetals are retained in the solids.Extremely volatile metals such asmercury and thallium are notincorporated into the clinker to thesame degree and these metals are,therefore, carefully controlled in thealternative fuel.

Specifications and control proceduresThe European cement industry issubject to strict controls on everyaspect of its activities, from quarryingto cement production and productquality. All cement manufacturingplants have installed appropriateabatement techniques and control andmanagement systems which are subjectto regular audit and review. As a resultof this, and the inherent suitability of

cement plants to handle organic andinorganic constituents of alternativefuels, the industry is in a position toensure that there is no net increase inemissions when alternative fuels areused. Monitoring of kiln operations andof the quality of stack discharges isbecoming increasingly sophisticated.Equipment has become automated assites continue to invest in modern,upgraded systems.

The cement process is fully controlled

Control room - Bernburg plant

21

Alternative fuels

are regularly

analysed

22

Cement is used to produce concrete.Concrete is an artificial stone made ofcement, aggregates, sand and water.

Concrete is known for its highenvironmental performance. Thisperformance is not impaired whenalternative fuels are used for cementproduction. Concrete made fromcement manufactured using alternativefuels has the same properties asconcrete made from cementmanufactured using fossil fuels.

One aspect of the environmentalperformance of concrete is thebehaviour of heavy metals in concrete.These trace elements are found invarious concentrations in the materialsused for cement and concreteproduction, and ultimately determinethe respective concentration in theconcrete.

Inorganic constituents of alternativefuels like heavy metals are combined inthe cement clinker. The use ofalternative fuels for cement productionmay result in higher or lowerconcentrations of heavy metals inconcrete as compared to when ordinaryfuels are used. However, in practice theheavy metal concentrations in concreteare not significantly changed by the useof alternative fuels for cementproduction.

The heavy metals in the cement arebound in the clinker components, andthey are chemically bound in thealkaline reaction products formed whencement reacts with water to give theconcrete its strength. This fixation aswell as the high denseness and lowpermeability of concrete result in a very

ENVIRONMENTAL PERFORMANCE OF CONCRETE

Concrete looked

at through

a microscope - it is

a dense material

23

low potential for heavy metals to bereleased.

The leaching of heavy metals fromconcrete has been examined in anumber of investigations. They all showthat the release is very low,independently of the kind of fuels usedfor cement clinker production. Theleached quantities have always beenfound to be either not measurable orsignificantly below levels allowed fordrinking water.

Concrete is used for water

storage constructions

as there is no harmful leaching

from concrete

LITERATURE REFERENCES

“La produzione del cemento e il riuti-lizzo dei residui – Un contributo alla salvaguardia del-l’ambiente”, ITALCEMENTI, Bergamo,1997.

“Valorisation des résidus dans les fours de cimenterie”, Association Technique de l’Industrie des Liants Hydrauliques (ATILH), Paris, May 1995.

“Environmental Relevance of the Use of Secondary Constituents in Cement Production”,M. Schneider, K. Kuhlmann, Zement-Kalk-Gips International, N° 1/1997, p. 10-19.

“Reducing Environmental Pollution by Using Secondary Materials”, S. Sprung, Zement-Kalk-Gips, 7/1992, P. 167-173.

“Use of Non-Ferrous Slag in Cement and the Leaching Behaviour of Concrete in DrinkingWater”, CEMBUREAU, June 1995.

“Waste Recovery in the European andFrench Cement Industry”, P. Fauveau: Fifth NCB International Seminar onConcrete and Building Materials, New Delhi 26-29 November 1996.

“Environmental Compatibility of Cement and Concrete”, S. Sprung, W. Rechenberg; G. Bachmann: Environmental Aspects of Construction with WasteMaterials, ed.: J.J.J. Gourmanns et al. 1994.

IPC Guidance Note – S2 3.01 –“Processes Subject to Integrated Pollu-tion Control – Cement Manufacture, Lime Manufacture andAssociated Processes”, Environment Agency, HMSO London, September 1996.

“L’utilisation des déchets comme com-bustibles en cimenterie: une contribution positive à la protection de l’environnement”, Syndicat Français del’Industrie Cimentière (SFIC), June1996.

APRIL 1997

Lay out and Printing byWEISSENBRUCH s.a.

SINCE IN 1775

Photo cover by: Eric Halleux CCB

© Copyright: CEMBUREAUN° Editeur: D/1997/5457/April

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