Construction products and life-cycle thinking

Notes1. Adriaanse, A. et al. (1997) Resource Flows: TheMaterial Basis of Industrial Economies. WorldResource Institute Washington, D.C.2. Schmidt-Bleek. F. (1993) Wieviel Umweltbraucht der Mensch? MIPS – Das Mass für oekolo-gisches Wirtschaften, Birkhaeuser (English transla-tion: The Fossil Makers – Factor 10 and More).Birkhäuser Verlag, Berlin, Basel and Boston. Alsosee F. Schmidt-Bleek (1995) Increasing resourceproductivity on the way to sustainability, Industryand Environment, Vol. 18, No. 4, pp. 8-12.

3. Ritthoff, M., H. Rohn and C. Liedtke (2002)MIPS berechnen: Ressourcenproduktivität von Pro-dukten und Dienstleistungen. Wuppertal Spezial 27(downloadable at www.wupperinst. org). Englishtranslation will soon be available.4. Bringezu, S. (2001) Construction ecology andmetabolism: re-materialization and de-materializa-tion. In: Construction Ecology and Metabolism:Nature as the Basis for the Built Environment, C.Kibert, J. Sendzimir, G. Guy (eds.), Spon, London.5. Kuhndt, M. and C. Liedtke (1999) COMPASS– Die Methodik. Wuppertal Institute.

6. At first, social criteria were deliberately kept inthe background, mainly because at this point thediscussion of social indicators on both the nation-al and international level has not yet reached a levelequal to that of the development of environmentaland economic indicators.7. Buerkin, C. (2003) Multi-Stakeholder-Prozesseals Chance für nachhaltiges Wirtschaften: eine kri-tische Betrachtung am Beispiel des Bausektors. The-sis, University of Passau/Wuppertal Institute.

◆

Sustainable building and construction

Construction products and life-cyclethinking

Suzy Edwards, Principal Consultant, Centre for Sustainable Construction, BRE, Garston, Herts WD25 9XX, UK ([email protected])

Philip Bennett, Secretary General, Council of European Producers of Materials for Construction, Gulledelle 98 Box 7, 1200 Brussels, Belgium ([email protected])

SummaryLife-cycle concepts, in the context of the building and construction sector, are particularly suit-ed to analysis of building products. Such products play an essential role in increasing the ener-gy efficiency of buildings and contributing to economic prosperity. It has been estimated thatthe construction sector is responsible for up to half of material resources taken from natureand of total waste generation. To manage and minimize the impacts of construction prod-ucts, the impacts have to be measured using a life-cycle approach. This article reviews life-cycle concepts and considers recent developments. Materials and sustainable construction,environmental product declarations, embodied energy and differences encountered in theassessment of construction products in the North and South are among the topics addressed.

RésuméDans le contexte du bâtiment, les concepts fondés sur le cycle de vie se prêtent particulière-ment bien à l’analyse des produits de construction, lesquels jouent un rôle essentiel dansl’amélioration de l’efficacité énergétique des bâtiments et la prospérité économique. On estimeque le secteur du bâtiment est responsable de près de la moitié des ressources naturelles con-sommées et du volume total de déchets produits. Pour gérer et limiter le plus possible lesimpacts des produits de construction, il faut pouvoir les mesurer selon une méthode fondée surle cycle de vie. L’article fait le point sur les concepts liés au cycle de vie et sur les tendancesrécentes dans ce domaine. Matériaux et techniques de construction durables, déclarations deproduits respectueux de l’environnement, contenu énergétique et différences entre le Nord etle Sud dans la façon d’évaluer les produits de construction figurent parmi les sujets abordés.

ResumenLos conceptos de ciclo de vida, en el contexto del sector de la construcción y edificios, resultanparticularmente apropiados para los productos de construcción. Estos productos desempeñanun papel capital para el aumento de la eficiencia energética de los edificios y el desarrollo de laprosperidad económica. Según estimados, el sector de la construcción utiliza la mitad de losrecursos materiales provenientes de la naturaleza y es responsable de la mitad de todos losdesechos generados. Para poder administrar y minimizar el impacto de los productos de con-strucción, es necesario medir dicho impacto utilizando criterios de ciclo de vida. Los autoresexaminan conceptos de ciclo de vida y analizan la evolución reciente. Algunos de los temastratados son: materiales y construcción sostenible, declaraciones de productos ambientales,energía incorporada y diferencias en la evaluación de productos de construcción en el Norte yel Sur.

Construction materials and products areessential to life as we know it – with respectto both buildings and infrastructure.

Humans spend around 80% of their time (onaverage) in some type of building or on roads.Construction products play a major role inimproving the energy efficiency of buildings andcontributing to economic prosperity.

On the other hand, construction products alsohave a considerable impact on the environment.According to one source, the construction sector isresponsible for 50% of the material resources takenfrom nature and 50% of total waste generated.1

The impact of construction products relative tothe overall lifetime impact of a building is cur-rently 10-20%. For infrastructure this value is sig-nificantly higher, greater than 80% in some cases.As buildings become more energy efficient, theimpact of construction products will make up anincreasingly significant proportion. This hasalready been seen in recent entrants for the GreenBuilding Challenge, where construction productscontributed up to 50% of the impacts of some ofthe buildings (www.buildingsgroup.nrcan.gc.ca/projects/gbc_e.html).

Different contexts for consideringconstruction products: North and SouthWhen considering differences related to con-struction products in the North and South, it isimportant to make a distinction between “global”and “local” construction. At the most simplisticlevel, this can be considered as a split between city-based commercial buildings and dwellings, andrural dwellings and public buildings. The distinc-tion can also be applied to products required to

UNEP Industry and Environment April – September 2003 ◆ 57

58 ◆ UNEP Industry and Environment April – September 2003


create the buildings. There are inherent differ-ences in the nature of materials, the technologiesused in extraction and manufacture, and healthand safety issues for workers involved in con-struction product manufacture and constructionactivities. Global construction products (whetherglobally traded or locally produced) includecement, steel, aluminium, glass and timber. Localproducts might include local fired/unfired block,

rammed earth, local timber, bamboo, and otherrenewable products.

Modern building materials can also have a placein local dwellings. The balance must be madebetween the desirable qualities of indigenous, tra-ditional materials in terms of internal comfort andrelatively benign environmental impacts, and thesocial need for providing quickly constructed,affordable housing solutions on a mass scale. The

decision to use different materials will be influ-enced by a number of factors; for example, Mbatu(corrugated sheet) roofs are now commonly usedacross Africa despite the fact that they offer lessprotection against extreme temperatures than tra-ditional thatch. To illustrate the complexity of thesituation, one of the reasons for this choice is thathouse owners do not have land rights to grow thethatch material. Clearly the most pressing concernin Southern countries must be the achievement ofbetter living conditions. However, an increasingnumber of solutions for affordable housing arebeing imported to the South, often with interna-tional funding. Work is urgently needed to under-stand the social, economic and environmentalimplications of different products and buildingsolutions. The findings should be fed into nation-al housing strategies and those of the lenders andaid providers, in order to plan ahead and ensurethat the best overall solutions are provided.

This article focuses on initiatives related to“global” construction products, as defined above,because this is the area in which the most work hasbeen carried out to date. However, life-cyclethinking has a role in construction at every level.For this reason, many of the concepts discussedare also of relevance to local construction tech-niques in Southern countries.

Another aspect of international relationships,often overlooked, is information transfer fromSouth to North. Plenty of products with betterthan average sustainability credentials are alreadyavailable in the North but remain marginalized:clay reed boards, unfired blocks, hemp lime blocks,and straw or earth buildings to name but a few. Aresearch project on “unburnt clay building prod-ucts” estimated that these products (bricks, tiles,blocks, boards and plasters) have less than half theenvironmental impacts of traditional products.2

An increase in the use of these products requiresinvestment in research to devise appropriate teststo ensure that they do offer lifetime benefits, aswell as a number of significant changes in thetightly defined building regulations, insuranceand standards. Influencing these processes isbeyond the budgets of most small and medium-sized companies manufacturing these products,which therefore remain outside the mainstream.Occasionally they make a breakthrough. Forexample, prefabricated straw bale panels were usedin a new building for the UK’s Bristol University.

Driving demand: sustainableconstruction Careful selection of construction products is a fea-ture of national green building labels such asBREEAM in the UK and LEED in the US. Theselabels provide an easy way for clients to demandmore sustainable construction. Using such meth-ods, construction products are treated as more orless important with respect to issues such as energyand water consumption, health considerations,opportunities to use public transport, and facilitiesfor recycling. In turn, they are part of the widerconcept of environmental procurement. TheInternational Council for Local EnvironmentalInitiatives (ICLEI) recently published The World

Figure 1Application of LCA to construction products

Productionof fuels Production

of materials

Manufacturingof products

Constructionand rebuilding

Wastemanagement

Use and maintenanceof buildings

Demolition Deposition

Productionof electricity

Watersupply

Productionby-products

Emissionsto air

Inventory

Emissionsto water

Emissionsto land

Energy resources

Materialresources

Waterresources

Building

Functional unit

Inputs Upstream Product system Downstream Outputs

Boundarykey

Table 1LCA programmes for construction products worldwide3

Country Programme organizer LCA schemes for materials and buildings Year

CH SIA (Swiss Society of Engineers SIA declaration matrix 1994and Architects)

D Stuttgart University Ganzheitliche Bilanzierung von Baustoffe und Gebäude 2000(LCA of building materials and buildings)

D AUB (Arbeitsgemeinschafft Umweltdeklarationen (environmental declarations) 2002/2003?Umweltverträgliches Bauproducte) (under development)

DK SBI (Danish Building and MVDB (Environmental Product Declaration for 2002 (?)Urban Research) Building Products) (under development)

F AIMCC (French Construction Experimental standards - Information concerning the 2001Products Association) based on environmental characteristics of construction products:AFNOR (French standardization • XP P 01-010-1: Methodology and model of data declarationorganization) standards • XP P 01-010-2: Guidelines for the application of

environmental characteristics to given construction work

FIN RTS (Building Information Environmental Product Declaration for building 2001Foundation) products

N NBI (Norwegian Building Environmental Declaration of building products 1999Research Institute)

NL NVTB (Dutch Construction MRPI (Environmentally Relevant Product Information) 2000Products Association)

NL NEN (Dutch standardization MEPB (Material Based Environmental Profile for Building) 2002/2003?organization) (in development)

N Byggforsk (Norwegian Building EcoDec (Miljødeklarasjoner - Environmental Declaration) 1999Research Institute)

S Ecocycle Council for the BVD (Building Product Declarations) 1997Building Sector

S Swedish Environmental Environmental Product Declaration 1997Management Council (Svenska Miljöstyrningsrådet)

UK BRE (Building Research Environmental Profiles of Construction Materials, 1999Establishment) Components and Buildings

US NIST BEES Building for Environmental and Economic 2002Sustainability



Buys Green, an international survey ofnational green procurement practices(www.iclei.org).

When do construction productscontribute to more sustainableconstruction?It is important to consider context: manyproducts which are not in themselvesparticularly “environmentally friendly”could be exactly the right products forreducing a building’s environmentalimpact. A particular window may nothave a lower environmental impact, butthe way it is used could maximize collec-tion of low winter sunlight and block thesummer sun. Creating a low environ-mental impact building means matchingproducts to the specific design and site inorder to optimize overall environmentalimpact.

We should not allow ourselves to bewooed by the idea of “green material” asthe only solution to sustainability. Afterall, timber accredited by the Forest Stew-ardship Council produces just as muchmethane in landfills as uncertified timber. The keyto greener material use is to use the material in away that changes the “one-way trip” mentalityinherent in so many applications of constructionproducts.

The challenge is how best to measure and tomanage the impact of construction products.

By evaluating the performance of productsagainst specific environmental parameters, it is pos-sible for the specifier to select products and com-ponents on the basis of personal, organizational orindependently chosen preferences or priorities.

A common approach to measuring the envi-ronmental impact of construction products is life-cycle assessment. How this can be applied toconstruction products is described below, togeth-er with a closer look at some of the most prevalentindicators currently measured – embodied ener-gy and “recyclability”.

What is clear from taking a life-cycle thinkingapproach is that it is not only the type of productused that is important, but also how it is produced(with clear links to environmental managementsystems) and even more importantly how it is used(and treated when its first life is over). As well asthe tools described below, this leads to conceptslike “design for adaptability” and “design fordeconstruction”. In the modern city environment,where building functions and fashions change sooften, it may also challenge the assumption thatdurability and sustainability always go hand inhand.

Life-cycle assessment The data needed to measure the lifetime environ-mental impacts of any product or system, includ-ing construction products, can be generated usinglife-cycle assessment (LCA). LCA is a method forevaluating the environmental impacts of a systemby taking into account its full life cycle from cra-dle to grave. This means consideration of all the

impacts associated with production and use of asystem, from the first time man has an impact onthe environment till the last. This concept isexpressed in Figure 1.

If we take the manufacture and use of a brickwall as an example, then using LCA we would typ-ically consider the environmental impacts associ-ated with:◆ extraction and transport of clay to the brick-works;◆ manufacture and transport of ancillary materi-als;◆ extraction and distribution of natural gas for thebrick kiln;◆ mining and transport of fuels to generate elec-tricity for use in the factory;◆ production and transport of raw materials forpackaging;◆ manufacture and transport of packaging forbricks; ◆ manufacture of brick in the brickworks;

◆ transport of bricks to the buildingsite;◆ extraction of sand and production ofcement for the mortar;◆ building of the brick wall;◆ maintenance of the wall, such aspainting or repointing;◆ demolition of the wall;◆ the fate of the products after demoli-tion.

LCA must be carried out in accor-dance with a detailed LCA methodol-ogy (in other words, a description ofrules that need to be followed). Thisensures that the LCA is fair and that theresults can be used comparatively. ISOstandards 14040 to 14043 have beendeveloped to standardize and define themanner in which LCAs should beundertaken. However, more preciserules are required to enable like-with-like comparisons using an LCA. ManyLCA programmes have been developedto create environmental product decla-ration (EPD) schemes, and a numberof national approaches for construction

products currently exist (Table 1). There is no sin-gle harmonized approach (see below).

Making fair comparisons One of the most important aspects of an LCA is toensure that comparisons are made on a like-for-like basis. For example, let us say we wanted tocompare the environmental impacts of two inter-nal walls for a building – one made of aeratedblockwork and one of timber studwork with tim-ber panelling. We might well find a database thatcould provide us with the environmental impactsassociated with production of a tonne of aeratedblockwork and a tonne of kiln dried softwood.However, the comparison of the two internal wallscannot be made immediately on the basis of thesetwo profiles. A tonne of each product would pro-duce very different areas of wall. Instead, we needto define a “functional unit” that will enable us tocompare the two internal walls.

A typical functional unit would be one squaremetre of internal wall over a particular buildinglife of, say, 60 years. Included would be assump-tions about repair and maintenance over the 60-year life, and about the dismantling/demolitionof the wall at the end of its life.

For an external wall or roof, the functional unitalso takes into account the thermal resistance ofthe construction to ensure that all the specifica-tions are compared on a like-for-like basis. Somespecifications may use less insulation product (andtherefore have a lower initial environmentalimpact). However, they will also allow muchgreater heat loss (i.e. operational environmentalimpact) over the building’s lifetime.

LCA design tools for buildingsThis interaction between the environmentalimpact of the products and the overall impact ofthe building has prompted the development ofintegrated environmental design tools for build-

Figure 2Relative contribution of different construction elements to impacts of a typical office building

Source: J. Anderson and D. Shiers, The Green Guide to Specification, Blackwells, Oxford, 2002

Ceiling finishes

Internal walls

Superstructure

Windows

Ground floor

Roof

External walls

Floor surfacing

Substructure

Upper floors

Floor finishes

Figure 3Relationship between LCA and EPD

Product basedenvironmental information

systems

Product basedexternal

communicationto stakeholders



ing. These tools allow trade-offs between higherembodied impact and lower operational impactto be evaluated. Again, tools are now available inseveral countries (Table 2). Environmentalimpacts are compared in different ways within thetools, from a simple single environmental score tofull environmental profiles.

Though not an easy task, modelling environ-mental impacts at building level is important sincereal answers concerning the environmentalimpact of building products are found when thewhole building is considered. For example, com-paring floor-covering materials with one anothermay not be fair if one product requires a moresubstantial substrate. Similarly, comparing woodand steel as light-gauge framing materials onlyworks if insulation is included in the steel assem-bly to provide comparable thermal performance.

These calculation tools can demonstrate thevery significant trade-offs between materials andspecification choices and the operational perfor-mance of buildings. This is important; the mostsignificant decisions about a new design are madeat the very beginning of the design process, soimmediate feedback on energy use and materialchoice is crucial. Comparison of the various toolsis currently underway in the PRESCO (PracticalRecommendations for Sustainable Construction)project (www.etn-presco.net).

Embodied energyEmbodied energy is the most frequently citedmeasure of the environmental impact of buildingproducts. Embodied energy is measured usingLCA principles, collating information on totalenergy used in extraction, manufacture, transport,maintenance and disposal. It is normally mea-sured in “primary” rather than delivered terms.This means it includes the energy used to producethe energy delivered to the point of use (e.g. theenergy used to generate electricity or the energyused to mine for coal, as well as the energy in thefuel or power source itself ).

If a whole range of processes all use the same sort

of energy (e.g. coal), the embodied energy for eachof these processes provides a good proxy for theamount of climate change or acid rain that eachprocess would cause. However, different processeswill use different mixes of fuel and electricity, andmany fuels or energy sources can be used to gener-ate electricity. Embodied energy figures can there-fore be misleading. This will apply in particular torenewable energy sources. The other difficultywith using embodied energy as a proxy for all envi-ronmental impacts is that many products requireonly low amounts of energy but still have consid-erable impacts on the environment (e.g. throughminerals extraction, waste generation and waterusage). The range of issues commonly covered inan LCA give a more holistic and accurate picture ofoverall environmental impact.

Recycling and construction productsLCA can take account of both actual levels of recy-cled input and the current fate of products at theend of their life cycle, due to the way they are gen-erated. A masonry product made using recycledinput, for example, will have a reduced mineralextraction impact; products such as primary steelwhich are recycled are sometimes calculated tohave lower impact if the LCA methodology usedpasses some of the environmental impacts associ-ated with primary manufacture on to future recy-cled phases of the product’s life.

The merits of recycling should be judged on acase-by-case basis. However, it is important thatwe do not choose products that may potentially berecycled tomorrow at the expense of recycledproducts that are available today. Passing theresponsibility to future generations does notreflect the spirit of sustainable development.

Ensuring that buildings are designed so thatproducts can be either reused (as a preference) orrecycled is very much the responsibility of today’sdesigner and is embraced by the concept “Designfor Deconstruction”. This is the subject of aninternational task group (CIB TG 39, “Decon-struction”, www.cibworld.nl ).

The importance of different elementsBRE calculated the embodied environmentalimpacts relating to a typical UK office buildingand broke them down into constituent elements.The contribution of each building element isshown in Figure 2. This includes all the elementsof the building, including substructure and super-structure, and covers the maintenance andreplacement of elements over the 60-year life.

Floor finishes contribute the largest impactbecause they are typically fossil fuel intensive andreplaced frequently. Choosing lower impact prod-ucts can significantly reduce a building’s overalllifetime impact. In addition, raised access floorsoffer flexibility while floor surfaces contribute thethird most significant embodied impact.

Of the major design elements, windows havethe lowest impact (only 3% of the building total).For a building with higher glazing ratios, theimpact of windows will increase as the impact ofthe external walls reduces.

The choice of structure makes very little differ-ence to the overall impacts of the building sinceboth cement and steel account for around 2% ofthe total.

Green procurementTwo important decisions affect procurement ofbuilding products and its impact on the environ-ment: what to buy (i.e. the product type) and fromwhom to buy it.

General LCA information provides assistanceto specifiers on what to buy. Deciding from whomto buy can be determined in a variety of ways.Clients might use certification to ISO14001 or anEMAS environmental management system as anindicator of good performance by a supplier.Alternatively, specific measures such as use of localor low-impact raw materials or low-emission tech-nologies may also be useful.

Neither an Environmental Management Sys-tem nor evidence of a “single issue” approach toenvironmental impact help clients to decide howa particular manufacturer’s product compares tothe typical product across the wide range of issuesthat need to be considered. Many manufacturersare therefore now turning to LCA in the form ofenvironmental product declarations (EPDs) tocommunicate their own environmental perfor-mance to their customers.

The ISO 14025 Technical Report: Environ-mental Labels and Declarations – Type III Envi-ronmental Declarations gives guidance on how aproducer can provide quantified environmentallife-cycle product information. The informationis presented across a range of indices relevant tothe product category. The objective of such a dec-laration is “to encourage the demand for, and sup-ply of, those products and services that cause lessstress on the environment, thereby stimulating thepotential for market driven continuous environ-mental improvement” (ISO 14020). The rela-tionship between LCA and EPDs is illustrated inFigure 3.

Specifiers can ask their suppliers for environ-mental product declarations to satisfy themselvesthat the company they are using takes a responsi-

Table 2Calculation tools for environmental impact assessment of buildings4

Country Model owner Model Further information

Canada Athena Sustainable Athena www.athenasmi.caMaterials Institute

Germany IKP – Stuttgart University Build-It

Denmark SBI (Danish Building Building Environmental www.by-og-byg.dk/english/research/and Urban Research) Assessment Tool 2000 environmental-impacts-from-buildings/

(BEAT) index.html

France CSTB Escale www.cstb.fr

Finland VTT LCA House www.vtt.fi/rte/esitteet/ymparisto/lcahouse.html

Norway NBI (Norwegian Building Ecoprofile www.byggforsk.no/oekoprofil/default.Research Institute) html

Netherlands SBR Eco-Quantum www.ecoquantum.nl

Stichting SUREAC Greencalc www.dgmr.nl/new/software/software_gc.html

Sweden KTH Infrastructure Eco-effect hwww.infra.kth.se/bba/bbasvenska/& Planning forsning/miljoweb/miljovardering/

nysammanft.pdf

UK BRE (Building Research Envest: environmental www.bre.co.uk/sustainable/envest.htmlEstablishment) impact estimating software

Life-cycle thinking made simple: The Green Guide to Specification



ble attitude to management of their environmen-tal performance. Choosing lower lifetime envi-ronmental impact solutions often goes hand inhand with lower whole-life cost solutions, creat-ing a double business benefit.

Towards harmonizationMany companies manufacture in several coun-tries. They therefore wish to see the range ofschemes listed in Table 1 harmonized in order toallow more economic use of LCA and environ-mental product declarations across their business.

The International Organization for Standard-ization Committee on Sustainability in BuildingConstruction (ISO/TC59/SC17) is working tocreate, inter alia, an international standard for envi-ronmental declarations for building products par-allel to the more general activity on EPDs of aseparate committee (ISO/TC207/SC3/WG4).The European Commission published a compre-hensive report in 2002 which described the differ-ent schemes currently in operation and consideredopportunities for harmonization.5 SETAC (theSociety of Environmental Toxicology and Chem-istry) has produced a state of the art report that ishelpful in demonstrating the basis on which har-monization can be achieved.6

ConclusionsThe overall performance of the building is themost important consideration in achieving moresustainable construction. Construction productsmust be chosen in this context. The most success-ful approach to specification is one in whichunderlying objectives and priorities are clearlyestablished at the early stages of a project, as thiscan then help determine the appropriate balancebetween environmental and technical require-ments. Taking a life-cycle approach is a significantand very positive step in the right direction.

Notes1. Anink, D., et al. (1996) The Handbook of Sus-tainable Building: Ecological Choice of Materials inConstruction and Renovation. James and James(Science Publishers), London. 2. Targeted Research Action – Environmentally

The third edition of The Green Guide to Specification, a simple guide for design professionals, waspublished in 2002. It provides environmental impact, cost and replacement interval information fora wide range of commonly used building specifications, using simple A, B, C ratings. The GreenGuide uses a normalized and weighted approach to analyzing data, allowing environmental infor-mation to be added together. A-rated products have the lowest scores, C-rated the highest.

Element

Beam and blockwork floor with screed A A A A A A A A A A A A 47-73 60 A C C A

Hollow precast reiniforced slab and screed A A A A A A A A A A A A 47-73 60 C A C A

Hollow precast reiniforced slab with B B B A B B B B A B A B 50-80 60 C A C Astructural topping

In situ reinforced concrete slab C B B A B C B B A B A C 40-60 60 C A C A

In situ reinforced concrete trough slab B A A A A B A A A A A B 40-60 60 C A C A

In situ reinforced concrete waffle slab B A A A A B A A A A A B 40-60 60 C A C A

Lattice girder precast concrete floor B A A A B B A A A A A C 84-153 60 C A C Awith in situ concrete topping

Lattice girder precast concrete floor with B B C A A A A B A A A A 84-153 60 C B C Cpolystyrene void formers and in situ concrete topping

Profiled steel permanant steel shuttering, B B C A A B C A C A C B 55-120 60 C A A Ain situ concrete slab, steel reinforcement bars and mesh

Solid prestressed composite floor with C C C A C C C C A C A C 65-90 60 C A C Astructural topping

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Friendly Construction Technologies (www.tra-efct.com). 3. Tables 1 and 2 are adapted from DG EnterpriseEuropean Commission and Pricewaterhouse-Coopers, Comparative study of national schemesaiming to analyse the problems of LCA tools and theenvironmental aspects in harmonised standards,2002 (http://europa.eu.int/comm/enterprise/

construction/internal/essreq/environ/lcarep/lcafinrep.htm).4. See note 35. Anderson, J., and D. Shiers (2002) The GreenGuide to Specification. Blackwells, Oxford. 6. Kotaji, S., Schuurmans, A. and Edwards, S.(eds.) (June 2003) Life Cycle Assessment in Buildingand Construction. SETAC (www.setac.org). ◆



On the sustainability of concreteVanderley M. John, Escola Politécnica, University of São Paulo, Brazil, Ed. Engenharia Civil

Cidade Universitária São Paulo, 05508 900 Brazil ([email protected])

After several important technical improvements, concrete made with Port-land cement is probably the world’s most used man-made material. Glob-al cement production in 1997 was 1.57 billion tonnes (Humphreys andMahasenan, 2002). That much cement, mixed with water, gravel and othersubstances, equals some 1.05 trillion tonnes of building material to pro-duce houses, office buildings, sewage pipes, dams, concrete roads, etc.

Cement production is widespread: plants are found in 150 countries(Marland et al., 2002 ), with China being responsible for roughly one-thirdof the total. Global cement production is increasing as consumption indeveloping countries rises: between 1990 and 2000, production grew 55%in developing countries and 3% in the developed ones. Cement demand in2020 is expected to be 120-180% higher than in 1990, with most of thegrowth in developing countries (Humphreys and Mahasenan, 2002).

The basic way to make Portland cement is to heat a mixture of limestoneand clay – two largely available, natural, non-renewable materials – in akiln at about 1500°C to produce cement “clinker”. After cooling, the clink-er is finely ground and mixed with gypsum and, frequently, other finelyground materials such as fly ash and blast furnace slag to produce variouscommercial varieties of cement.

Cement production and the environmentThe major global impact of cement production is global warming.Humphreys and Mahasenan (2002) estimate that the cement industry isresponsible for 3% of global anthropogenic greenhouse gas emissions and5% of global anthropogenic CO2 emissions. About half the CO2 is releasedby limestone decomposition in the kiln – “cement process CO2”(Humphreys and Mahasenan, 2002; Gale and Freund, 2000) – and theother half is due mainly to fuel burning (Figure 1).

CO2 release rates differ among countries, depending on a) productionprocess, b) clinker content, c) energy efficiency in the calcination phase,which is responsible for 90% of energy consumption (Gale and Freund,2000), and d) differences in fossil fuels’ carbon content. Old cement plantsare less energy efficient and sometimes still use the wet process, which con-sumes 20-40% more energy (Gale and Freund, 2000).

Cement production also generates emissions of NOx, SOx, dust, diox-ins, etc.

Blending materialsMixing clinker with other materials, a process called “blending”, reducesCO2 emissions and increases energy efficiency during cement production.

Table 1 presents the most common blending materials. Fly ash (includ-ing from cement-making itself ) and blast furnace slag are the types of wastemost used in blending. Their use could be greatly increased except wherelocal shortages exist.

Clinker content can range from about 95% (when only gypsum isadded) to 5%. In the mid-1990s average clinker content was 88% in theUS, 80% in Japan and 70% in Europe. The overall trend has been towardsdecreasing clinker content.

Recent research into new sources of blending materials has concentrat-ed on waste from agriculture, industry and mining, including ash fromburning lignocellulosic material (e.g. rice husk), fly ash slag from munici-pal solid waste incineration, paper mill sludge ash, colemanite waste andceramic waste.

Concrete and the environmentConcrete typically contains 8-15% cement, 2-5% water, about 80% aggre-gates (e.g. gravel, sand, limestone filler) and less than 0.1% chemicaladmixtures.

Despite its size, the 80% share of natural or recycled aggregates causesless than 3% of total emissions and energy use in concrete production(Vares and Häkkinen, 1998). Hence cement content and composition, asdetermined by engineers and architects, determine the concrete’s environ-mental load.

For a constant set of materials, the cement content is a function of thedesired mechanical strength, production variability, service life require-ment and concrete workability, along with the nature of the admixturesused.

Chemical admixtures can reduce the cement consumed for a givenstrength, or increase concrete workability, without increasing cement con-sumption. A modern concrete mix design, combining several aggregategrades with admixtures, produces a more eco-efficient concrete. Minimiz-

Figure 1CO2 released in limestone decomposition during cement production, selected regions, 1920-2020*

*Projected.

Source: Marland et al., 2002.

Far East

Africa

Latin America and Caribbean

World

USA and Canada

8

6

4

2

0

1920

CO

2 fro

m o

rdin

ary

Port

land

cem

ent (

% o

f tot

al)

1940 1960 1980 2000 2020Year

Table 1Most common blending materials used in cement

production

Material Description Nature

Blast furnace slag Pig iron by-product Waste

Fly ash Coal combustion by-product Waste

Silica fume Silicon metal/ferrosilicon alloy by-product Waste

Natural pozzolan Volcanic ash Natural

Burnt clay Pozzolan calcinated at ~700°C Industrial

Limestone filler Ground limestone Natural

Metakaolin Kaolin (a special clay) calcinated at ~700°C IndustrialSource: author



ing concrete production variability by using adequatelytrained personnel, carefully selected raw materials and moresophisticated proportioning and mixing equipment, as mostready-mix companies today can do, is also an effective way toreduce concrete’s environmental impact.

When concrete is made on site by do-it-yourself homebuilders or small contractors, the above approaches are notviable. In Brazil, for instance, 68% of the cement sold isbought by building material dealers and used with little orno controls.

A large share of concrete used worldwide is reinforcedwith steel. In Brazil most steel rebars are made by recyclingsteel scrap in electric mini-mills. In countries where the steelfor concrete reinforcement is often made from virgin pigiron, the environmental impact is higher. Steel’s contribu-tion to the environmental load of reinforced concrete isgreater than that of the aggregates but much less than that ofthe cement.

Service lifeIncreasing the service life of concrete structures is a very effi-cient way to improve the eco-efficiency of the global econo-my. Service life can be dramatically extended with little orno increase in – or even a reduction of – the environmentalload. Doubling the thickness of the concrete over the steel rebar from 10mm to 20 mm, for instance, quadruples the service life of reinforced con-crete, defined as the time it takes carbonation reach the rebar, but increas-es concrete consumption by only 5-10% (Helene, 1993). In marineenvironments, a high blast furnace slag or fly ash content can increase ser-vice life and decrease the environmental load.

At the end of its service life, most concrete can be recycled as aggregate oreven in cement production. But because natural aggregate is usually cheap,concrete is not extensively recycled except in a few European countries (e.g. theNetherlands). In Brazil, as in most developing countries, only local authoritiesrun recycling plants processing concrete and other construction and demoli-tion waste, and the resulting aggregate is generally used as road base. Addi-tional recycling opportunities for such waste need to be investigated.

Making concrete a more sustainable materialAside from some specialized applications such as the use of chalk or glue asmortar, there are currently no viable alternatives to clinker-based cementand concrete, and despite intensive research it will probably take decades todevelop any. And while the technical options mentioned above, along withother technologies, can increase the sustainability of concrete and are avail-able on markets worldwide, they are not always explored.

The first reason seems to be lack of knowledge/awareness on the part ofprofessionals and authorities. With few exceptions, there is almost no tech-nical reason to use cement with high clinker content, but many engineersand architects still prefer it. Designing reinforced concrete structures foran extended service life is a relatively new, often unfamiliar concept thatneeds to be refined and has not yet been incorporated into concrete designcodes and standards, which sometimes set a minimum of cement con-sumption in structural concrete. Much effort is needed in the technical andenvironmental education of civil engineers and architects, and to change

design codes and create incentives to use blended cement.Other barriers are market based. Old, inefficient cement plants may still

be competitive. Advanced admixtures can be expensive. Ready-mix con-crete sometimes costs more than concrete produced at the building site, soDIY builders and small contractors often prefer the latter option. Here theneed is to balance social sustainability with environmental sustainability.

Finally, concrete’s sustainability must be judged in real situations. Ageneric life-cycle assessment approach that may work for more standardizedmaterials, like plastics and metals, will seldom be adequate to evaluate con-crete. There is a great need for more accurate and independent data aboutlife-cycle loads of cement – and other building materials – especially indeveloping countries.

ReferencesCarvalho, J. (2002) Life cycle analysis applied to building products. Case study: Com-parison among different Portland cement types. M. Eng. dissertation, University of SãoPaulo, 2002 (in Portuguese).

Gale, J. and P. Freund, papers presented at GHGT-5 Conference on work by IEAGHG (Cairns, Australia, 2000). See www.ieagreen.org.uk/ GHGT5-3.pdf.

Helene, P.R.L. (1993) Contribution to the understanding of corrosion of steel rebars inconcrete. Associate professor thesis, University of São Paulo, 1993 (in Portuguese).

Humphreys, K. and M. Mahasenan (2002) “Climate Change” in Toward a Sustain-able Cement Industry. Battelle – World Business Council for Sustainable Develop-ment.

Marland, G., T.A. Boden and R.J. Andres (2002) “Global, Regional, and NationalCO2 Emissions” in Trends: A Compendium of Data on Global Change, Carbon Diox-

ide Information Analysis Center. See http://cdiac.esd.ornl.gov/trends/emis/em_cont.htm.

Vares, S. and T. Häkkinen (1998) Environmental burdens of concrete and concrete prod-ucts. Nordic Concrete Research publication 21 1/98. June. See www.itn.is/ncr/pub-lications/doc-21-10.pdf.

Figure 2CO2 release per kg of cement produced, selected regions

Source: Humphrey and Mahasenan, 2002

Middle East

Africa

S. & L. America

Former Soviet Union

India

S.E. Asia

China

Australia & N. Zealand

Japan

W. Europe

Canada

USA

0.7 0.8 0.9 1

kg CO2 per kg cement

20001990



Bamboo in construction: status and potentialLionel Jayanetti, Head of TRADA International, and

Paul Follett, Senior Development Engineer, TRADA International, Chiltern House, Stocking Lane, Hughenden Valley,High Wycombe, Buckinghamshire HP14 4ND, UK ([email protected]; www.trada.co.uk)

Bamboo is a well established cultural feature in manyregions of the world. Its diversity and versatility arewell documented. Some 1250 species and 1500 tra-ditional applications have been identified. The mainusers are the rural poor, and it is perhaps for this rea-son that bamboo has largely been taken for grantedby the wider community. As a material resource,bamboo has not received the mainstream recognitionit deserves.

Bamboo is the fastest growing woody plant on theplanet. However, it actually belongs to the grass fam-ily. Most species produce mature fibre in about threeyears, much more rapidly than any tree species. Somespecies grow by up to one metre a day, and the major-ity reach a height of 30 metres or more.

Bamboo has exemplary “green” credentials. It isadaptable to most climatic conditions and soil types,acts as an effective carbon sink and helps counter thegreenhouse effect. It is being used increasingly in landstabilization to check erosion and conserve soil. It canbe grown quickly and easily, even on degraded land,and harvested sustainably on three- to five-year rota-tion. Bamboo is a truly renewable, environmentallyfriendly material.

The bulk of bamboo is gathered from the wild orrural environment, but in many areas bambooresources have dwindled due to overexploitation andpoor management. This issue needs to be addressed through well organizedand managed cultivation if bamboo utilization is to develop on a sustainablebasis. Plantations are already being raised in China and India to supportthe pulp and paper industry.

A billion people worldwide live in bamboo houses. For the most part theyare low-grade, impermanent buildings, belying the material properties ofbamboo and doing little to promote its image as a viable construction mate-rial. At little extra cost these buildings can be upgraded to provide safe, secureand durable shelter, benefiting the most vulnerable members of society.

Possibly the major factor contributing to the view of bamboo as a tem-porary material is its lack of natural durability. It is susceptible to attack byinsects and fungi. Its service life may be as low as one year when in groundcontact. However, the durability of bamboo can be greatly enhanced byappropriate specification and design and by careful use of safe and envi-ronmentally friendly preservatives such as boron.

The main structural advantages of bamboo – its strength and light weight– mean that properly constructed bamboo buildings are inherently resis-tant to wind and earthquake. These properties can be effectively exploitedthrough careful yet simple design and detailing.

Even when issues of durability and strength are resolved, the question ofacceptability remains. A bamboo building need not look “low-cost” or evennecessarily look like bamboo! Imaginative design and the use of other local-

ly available materials within the cultural context can make the buildingdesirable rather than just acceptable.

Bamboo: the international viewBamboo has a long history as a building material. It is widely used in con-struction throughout the world’s tropical and sub-tropical regions, with arange of applications to match or even exceed those of timber. Bamboo build-ings of every description can be found in Central and South America, fromlow-grade temporary shanties to exclusive, architect-designed mansions.

Bamboo products for use in construction are increasing in availability.They range from bamboo mat boards (flat and corrugated), to more sophis-ticated panel products such as fibreboard, “plyboo” and flooring, to largelaminated sections (now under development) for use in external joinery.Costs are currently similar to those of equivalent timber products. Bamboowill therefore find a market where timber is in short supply, or where it isspecified for architectural reasons. In Europe there is a small but flourishingmarket in bamboo for internal applications (e.g. flooring) but not as yet forstructural ones.

Bamboo use is not restricted to building. Bamboo has been used as con-crete reinforcement, and development work is continuing in this field.Bamboo is used for light traffic bridges, and the feasibility of constructinglarge span bridges carrying vehicular traffic has recently been demonstrat-

Corrugated bamboo matboard (IPIRTI, India) and laminated bamboo flooring

52 metre bamboo road bridge by Jorg Stamm (Colombia)and bamboo scaffolding (Hong Kong)



ed in Colombia. Bamboo as scaffolding is well known (40-storey con-struction is not uncommon in the Far East), and its use is set to increase asa result of the development of a design and erection guide in Hong KongKong.1

Other construction applications include ground stabilization, throughthe use of retaining walls and piling, and coastal protection (recently tri-alled in Sri Lanka).

TRADA’s experienceTRADA (the Timber Research and Development Association) is an inter-nationally renowned centre for forest product engineering and technology.Its origins can be traced to 1934. TRADA is based in the UK, with opera-tions worldwide.

TRADA has recently completed the first phase of a project in India todevelop and promote a cost-effective bamboo based building system. Thisproject is designed to provide safe, secure and durable shelter at a cost thatis within reach of even the poorest communities in developing countries. Ithas demonstrated that with careful specification, detailing and environ-ment-friendly preservation, the life of bamboo can be extended to matchthat of other building materials.

Prototype testing provided an effective visual demonstration of the per-formance and strength of components and assemblies, as well as of the resis-tance of walls and roofs to wind, earthquakes and impacts.

The building system costs around half that of traditional brick, block orreinfoced concrete construction. It is one of the cheapest permanent meth-ods of building yet developed. It is also sustainable, simple to erect, strongand durable, incorporating all the essential requirements for affordable shel-ter. Moreover, the basic system can enhanced through improved use ofshape, space and colour at little or no cost. Overall, the system effectivelydemonstrates that desirability and quality are fully compatible with afford-ability.

In its second phase (2000-05) the project will be extended to Bangladeshand Sri Lanka. The technology will be applied in the development ofdesigns for larger community buildings such as schools and health clinics.Use of bamboo for construction of footbridges in rural areas will also beinvestigated, with the development and testing of prototypes.

Bamboo’s potentialTaking into account all that bamboo has to offer, it is well placed to addressfour major global challenges:◆ shelter security through provision of safe, secure, durable, affordable hous-ing and community buildings;◆ livelihood security through generation of employment in planting, pri-mary and secondary processing, construction, furniture and manufactureof high value-added products;◆ ecological security through conservation of natural forests by substitutionof primary timber species, as an efficient carbon sink, and as an alternativeto non-biodegradable and high-embodied energy materials such as plasticsand metals;◆ sustainable food security through agro-forestry systems, by maintainingthe fertility of adjoining agricultural lands, controlling erosion. Bamboo isalso a direct food source.

The challenge now is how to share this knowledge: to bring it to the

attention of a wider audience and demonstrate that the new technologiesare equally viable in areas which have not had exposure to the “new think-ing” and, above all, to deliver the benefits it promises to the poorest mem-bers of society.

Future requirementsSustainable supplyA policy of organized planting, careful management of plantations and nat-ural stands, and appropriate regulation of supply are prerequisites for anyother interventions aimed at promoting bamboo as a building material.

StandardizationLack of guidance on use of bamboo in building has been a major obstacleto its wider adoption. Draft international standards ISO 22156 and 22157represent the first step towards addressing this problem. New or amendednational regulatory instruments such as manuals, codes of practice, speci-fications, building regulations and standards are now required.

Research and extension activitiesThe will must exist at government level to explore the potential of alterna-tive materials, and to put in place the resources and mechanisms to carryout necessary material developments and evaluations. Where this capacityalready exists, it is often necessary to reorient the approach of research insti-tutions to link them directly with the building industry, together with theirgovernment and private sector clients.

TrainingCurriculum revision is required to give greater emphasis to the new tech-nologies. This would apply to institutions training high-level artisans ortechnicians for the construction industry, as well as professionals such asarchitects, building technologists, civil, structural and mechanical engi-neers, and quantity surveyors.

Fiscal policyFinancial incentives are required in order to encourage the establishmentand support of industries involved with the new technologies. In addition,the widespread policy which limits the advance of bank loans and mort-gages on “bamboo” houses must be reviewed.

Demonstration and qualityEffective dissemination aimed at popularizing the new technologies is vital,considering the negative perceptions held by many about bamboo in build-ing. Even when issues of durability and strength are resolved, the questionof acceptability remains. Construction of model buildings is thereforeessential to overcome prejudice and boost the confidence of specifiers (e.g.architects, engineers, builders) and users. In this regard the quality must bethe highest achievable, since any shortcomings in the standard of con-struction, detailing and finish will be reflected, unfairly, on the buildingsystem as a whole.

1. Draft documents prepared by the University of Hong Kong .

Documents

Construction products and life-cycle thinking