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Journal of Cleaner Production 17 (2009) 283–296

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Development of a life cycle assessment tool for construction and maintenanceof asphalt pavements

Yue Huang a,*, Roger Bird b, Oliver Heidrich c

a Scott Wilson Ltd., 12 Regan Way, Chetwynd Business Park, Nottingham NG9 6RZ, UKb School of Civil Engineering and Geosciences, Newcastle University, Cassie Building, Claremont Road, Newcastle upon Tyne NE1 7RU, UKc Safety, Environment and Quality Management Ltd., Ouseburn Building, Albion Row, Newcastle upon Tyne NE6 1LL, UK

a r t i c l e i n f o

Article history:Received 29 October 2007Received in revised form 14 May 2008Accepted 19 June 2008Available online 8 August 2008

Keywords:Asphalt pavementsLife cycle assessmentRecyclingSustainable construction

* Corresponding author. Tel.: þ44 (0) 115 907 7000E-mail address: yue.huang@scottwilson.com (Y. H

0959-6526/$ – see front matter � 2008 Elsevier Ltd.doi:10.1016/j.jclepro.2008.06.005

a b s t r a c t

The increasing use of recycled materials in asphalt pavements calls for environmental assessment ofsuch impacts as the energy input and CO2 footprint. Life cycle assessment (LCA) is being accepted by theroad industry for such purpose. It aims to quantify and collate all the environmental impacts fromthe life time of the product or process. This paper reviews relevant LCA resources worldwide, identifiesthe knowledge gap for the road industry, and describes the development of an LCA model for pave-ment construction and maintenance that accommodates recycling and up-to-date research findings.Details are provided of both the methodology and data acquisition. This is followed by a discussion ofthe challenges of applying LCA to the pavement construction practice, and recommendations for fur-ther work. In the case study, the model is applied to an asphalt paving project at London HeathrowTerminal-5 (LHR), in which natural aggregates were replaced with waste glass, incinerator bottom ash(IBA) and recycled asphalt pavements (RAP). Production of hot mix asphalt and bitumen was found torepresent the energy intensive processes. This is followed by data analysis and sensitivity check. Fur-ther development of the model includes expanding the database to accommodate the recycling andmaintenance practice in the UK, and taking into account the effect that roadwork has on trafficemissions. The LCA model can be further tested and calibrated as a decision support tool for sustainableconstruction in the road industry.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Recycled and secondary materials are increasingly used in as-phalt pavements, in terms of tonnage and the variety [1]. The dualbenefits of saving landfill space and reducing quarry demand,however, have not come without a cost. Simply diverting the wastefrom other industries to aggregates supply has already beenquestioned for its energy and CO2 footprint, waste glass for exam-ple. The scepticism comes from a mixture of academia, researchconsultancy and government organisation, as previous studies haveindicated that using waste glass for construction aggregates overallconsumes more energy and releases more CO2 than sending themto landfill [2–4]. Recycling or reuse of asphalt materials needs up-to-date studies on the associated environmental impacts includingenergy use, emissions, leaching, etc. A life cycle approach is gainingground in meeting the needs of sustainable construction [5].Accredited by a number of industries already, life cycle assessment

; fax: þ44 (0) 115 907 7001.uang).

All rights reserved.

(LCA) is being accepted and applied by the road industry, to mea-sure and compare the key life-time environmental impacts of as-phalt products and laying processes [6].

The life cycle assessment starts with a definition of the aim andscope of the study. Its main work resides in the development of aninventory (LCI), in which all the significant environmental burdensfrom the life time of the product or process will be quantified andcompiled. This is followed by an impact assessment (LCIA) calcu-lating and presenting the result in a predefined way that supportscomparison or further analysis. The concept and working phases ofLCA are described in the ISO14040 [7].

The application of LCA in civil engineering, initially as a tool forassessing solid waste management options, has started only in thelast decade. Relevant practice in roads and asphalt pavements,notably where recycled and secondary materials are involved, islimited. Besides giving the knowledge of products’ environmentalperformance, LCA results are also able to support marketing orenvironmental labelling. For instance, the ISO14025 Type III Envi-ronmental Product Declaration (EPD), which enables the informedcomparison between products that fulfil the same function, re-quires quantified environmental information based on in-dependently verified LCA results [8].

Transport Transport

Production of secondary aggregates

Transport

Transport

Production of bitumen

Transport

Transport

Transport

Transport Transport

Transport

Transport

Production of cold mix asphalt

Production of natural aggregates (crushed rocks for example)

Production of hot mix asphalt

Excavator/Wheel loader operation

Crusher/Screening machine operation

Drying and heating

Mixing

Mixing

Surface planing Asphalt paving

Asphalt rolling

Production of emulsifier

Waste collection

Plant recycling

Production of emulsion

Application of tack coat

Crude oil extraction

Oil refining

Bitumen storage

Petroleum products

Transport

Pavement recycling

Transport

Transport

Pavement Life Expectancy

Fig. 1. Unit processes in asphalt pavement construction.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296284

2. LCA resources for the asphalt industry

In recent years, highway authorities in the UK have preferredmaintenance and rehabilitation over new road construction. Theconcept by UK Transport Research Laboratory (TRL) of design forlong-life pavements in light of resource efficiency (materials, en-ergy, etc.) and the requirement for speed repair would confinea roadwork in the future to the top few layers of the pavement only[9]. A working LCA model shall therefore duly reflect the mainte-nance and recycling in roadwork; and data specific to UK road in-dustry are preferred. Specifically, it should be:

Internationally recognised, including the methodology andsupporting database;Populated with current and relevant data;Having as many as possible variables represented in the roadpractice;Forward compatible for data update or formulas revision.

2.1. Existing and developing LCA tools

The US Environmental Protection Agency (EPA) is hosting anindex of LCA resources worldwide including books and journals,conference proceedings, websites, software and databases, andcase studies since 1998 [10]. European LCA Hub contains similarresources of LCA tools, services and data [11]. EPA’s pilot study in

the late 1990’s demonstrated that LCA can help select the envi-ronmentally preferable method for asphalt pavement treatment[12]. A hybrid I–O (input–output) model was used in Japan lookingat the life cycle emissions of CO2 from a motorway covering boththe construction and operation stage [13]. According to the WorldBusiness Council for Sustainable Development (WBCSD), the po-tential values of ‘generic data sets’, ‘technology assessment’ and‘marketing’ are viewed by the cement industry as ‘high’ or ‘mid-high’ in using LCA [14]. These works, as they built up the frameworkof LCA model and database, paved the way for introducing andapplying LCA to the road sector, based on which the following LCAtools for roads were developed.

(1) In 1993–1995, Swedish Environmental Research Institute (IVL)developed the first of its kind life cycle inventory (LCI) model ofroad construction and maintenance for Swedish National RoadAdministration. The 2nd version was released in 2001 [15].

(2) An LCI study focused on the asphalt including the use ofrecycled asphalt pavements (RAP) was initiated in 1998 by theEuropean Asphalt Pavement Association (EAPA) and Euro-bitume. IVL was commissioned to carry out the project. The 3rddraft was released in 2005 [16].

(3) In 1997–1999, Eurobitume conducted a partial LCI study onbitumen (straight run, paving grade 50/70), covering the lifecycle from crude oil extraction to refinery deposit [17].

(4) Technical Research Centre of Finland (VTT) published in 1996a comparative LCA study on environmental impacts of asphalt

Cold in-situ recycling

Hot in-situ recycling Remix

Overlay

Ex-situ recycling

Mix the old materials with new and paving

Compaction Applying tack coat

Transportto disposal

Cold planing

Paving newmaterials

Transport toasphalt plant

Production of asphalt (including RAP)

Transport and paving

Heat and scarify

Repave

Mix and lay the old materials

Applystabilising agent

Recycler operation

2-Mixing 1-Milling

3-Paving 4-Grading

Cement Lime

Emulsion Foam bitumen

Fig. 2. Treatment of pavement surface and placement of asphalt.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296 285

and concrete pavements [18]. Later in 2001, an LCA model wasdeveloped by VTT for Finnish National Road Administrationaddressing the use of industrial by-products (coal fly ash, blastfurnace slag, etc.) in roads [19].

(5) In 2005, an LCA model of road construction using municipalsolid waste incineration (MSWI) bottom ash was developed bythe Technical University of Denmark (DTU) [20].

(6) In the UK, the Built Research Establishment (BRE) published the‘Environmental Profiles’ in 1998 providing a database on

Table 1Worksheets in the LCA model

Worksheet Description

Process parameters Data on transport distance and fuel efficiency, energy ca pavement project

Pavement parameters Data on pavement dimension and materials recipe, deta pavement project

Unit inventory Inventory figures for unit operation of transport, materconstruction

Project inventory Unit inventory data are aggregated into the unit of the

Characterisation results Inventory results are assigned to defined impact categoand presented by category indicators

environmental performance of building materials and prod-ucts, as well as the methodology for applying LCA to the con-struction sector [21].

2.2. Need for a new LCA model

There are important findings from previous LCA studies,which can be taken as a starting point for further applying LCA to

Sub-worksheet

onsumption of unit processes in ‘Energy in transport’‘Energy in materials production’‘Energy in pavement construction’

ermine the materials tonnage in ‘Pavement dimension’‘Materials recipe’‘Pavement life time’

ials production and pavement ‘Energy production’‘Combustion of fossil fuel’‘Transport vehicle operation’‘Construction vehicle operation’

pavement project ‘Production process’‘Transport process’‘Construction process’

ries, characterised by selected models ‘Global warming’‘Acidification’‘Photo-oxidant formation’‘Human toxicity’‘Eco-toxicity’‘Eutrophication’

Spreadsheets in LCA Model

Process Parameters (WS1)

Data Input Progress

Data collection andvalidation

Pavement Parameters (WS2)

Unit Inventory (WS3)

Project Inventory (WS4)

Characterisation Results (WS5)

Relating data to unitprocess

Relating data tofunctional unit

Data aggregation

Refining systemboundary

Energyconsumption

Transportdistance

Pavementdimension

Materialsrecipe

Energyproduction&combustion

Transportvehicle operation

Characterisation model

Constructionvehicleoperation

Life Cycle ImpactAssessment

Goal & ScopeDefinition

Materialsproduction

Pavementconstruction

Transport

Life C

ycle Inventory Analysis

Fig. 3. Structure of the LCA model and procedures for inventory analysis.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296286

the road and asphalt industry. Nevertheless, the problems ofsimply applying one of those LCA models described above to theUK road sector are stated below [22]. The barriers can be groupedinto 5 categories.

Category 1: relevanceLow relevance to the road and asphalt industry, such as theBRE’s model;Data from non-UK sources may not represent the UK’s in-dustry average. This is of particularly a concern when ap-plying the model to real case studies;

Category 2: adaptabilitySome data are quite old, or the underlying assumptions andcalculation formulas unknown, such as Eurobitume’s LCIresults;Some data are drawn on a fixed material recipe, haulagedistance, production process or machinery that cannot begeneralised for use in other studies;

Category 3: complianceModel or database developed before the ISO14040 wasissued (in 1997) and revised (in 2006) may not be able tofully comply with it;

Table 2Conversion factors and calorific values of fossil fuels [24]

Electricity Diesel Burning oil

Unit MJ/kWh MJ/kg MJ/kgValue 3.6 45.7 46.2

a When extracted.

Category 4: scopeThe models above are generally focused on one or a fewenvironmental impacts, such as energy and air emissions inthe VTT’s model, and leaching in the DTU’s model;The inclusion of recycled materials is varied, but generallylimited, such as RAP in the IVL’s model, MSWI bottom ashin the DTU’s model;

Category 5: availabilityPractical models are not accessible, due to commercialrestriction.

The fact that there is nothing quite right available on the markethas generated the need for developing a new LCA model on top ofexisting resources that can enhance the level of acceptance of theresults in the UK.

3. Unit process definition and inventory development

A flowchart of the unit processes in asphalt pavement con-struction is illustrated in Fig. 1.

The flowchart outlines the main phases of the constructionprocess. At the same time, it is a brief description which does not

LPG (liquefied petroleum gas) Natural gas Coal

MJ/kg MJ/m3 MJ/kg49.5 39.6a 25.6

QU

AR

RY

SIT

E

ASP

HA

LT

PL

AN

T

RO

AD

SIT

E

CR

UD

E O

ILSO

UR

CE

BIT

UM

EN

EM

UL

SIO

N P

LA

NT

EM

UL

SIF

IER

PR

OD

UC

TIO

N

Bitumen

Asphalt

Emulsifier

Hotmix process

Cold mix process

Surface dressing

RAP(ex-situ)

Emulsion

Aggregates

Fig. 4. Transport in asphalt pavement construction.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296 287

tell details of the process or what machinery is used. For instance,the treatment of old pavement surface and placement of fresh as-phalt may take a number of different forms including ex situ (plant)recycling, hot in situ (place) recycling, cold in situ (place) recycling,overlay, etc. (see Fig. 2).

Based on the guidelines in the ISO14044 [23], the constructionprocess needs to be defined on a level that data for unit processesare: (1) specific to a pavement project therefore the assumptionsmade can be minimal and (2) easy to collect and aggregate. Theexperiences of obtaining data and establishing the inventory indeveloping this LCA model include:

Identify the appropriate data source; data should be up-to-date, recognised and the reference accessible;The boundary of data and any assumptions made should beunambiguously stated. Pay extra attention when data requiredin a process come from more than one place, as the databoundary and underlying assumptions in there may bedifferent;In the case that alternative data exist, state which one will beused in the model and justify the selection. It is advisable torun the model later using the ’defeated’ data as well, for sen-sitivity check and data review;Present the data alongside their sources in both the manu-script and computing tool.

This model, during its development, has been applied to, andtested by, 3 real case studies of asphalt paving projects in the UK,which in return build up the scope and adaptability of the

Table 3Emission standards for combustion of fossil fuels

Machinery in pavement project Reporting detail

Materials plant Combustion of LPG/burning oil for asphalt/cemeTransport vehicles Heavy-duty (>3.5 t) diesel trucksConstruction vehicles Diesel engines in crushing equipment, paver, rol

a Group 3: ‘combustion in manufacturing industry’.b Group 7: ‘road transport’.c Group 8: ‘other mobile sources and machinery’.

computing tool. An example is given for the London HeathrowTerminal-5 (LHR) case study in Section 5.

Case study 1 (April–November 2005): asphalt in-lay at ChapelAsh, Wolverhampton, alternative asphalt recipe and layerthickness;Case study 2 (January–February 2007): asphalt paving on anaccess road, London Heathrow Terminal-5, use of glass, IBAand RAP in base and binder course;Case study 3 (May–July 2007): rehabilitation of A34, Stoke-on-Trent, effect of speed delivery of the roadwork on reducing thetraffic emissions.

4. LCA model description

Microsoft’s spreadsheet, Excel, is selected for calculation andgraphical presentation of inventory results in this LCA model. Themodel consists of 5 worksheets (WS): process parameters, pave-ment parameters, unit inventory, project inventory and character-isation results. Data in worksheet ‘process parameters’ and‘pavement parameters’ are specific to a project. Worksheet ‘unitinventory’ is made of calculating formulas and the life cycle in-ventory of unit processes. Inventory results in the unit of thatpavement project are presented in the ‘project inventory’ work-sheet. The inventory loadings are characterised for impact assess-ment; the characterisation models and factors can be found in the‘characterisation results’ worksheet. Data in these worksheets arelinked by calculation formulas. For instance, when energy data on

Name of CORINAIR activity Chapter

nt production Cement/asphalt concrete plant Group 3a: B331Road transport Group 7b: B710

ler, etc. Other mobile sources and machinery Group 8c: B810

Table 4EU emission standard (Euro IV) for heavy-duty diesel engines

Tier Test Emission (g/kWh)

Euro IV ESC&ELRa CO HC NOx PM Smoke (m�1)1.5 0.46 3.5 0.02 0.5

a ESC: European Stationary Cycle; ELR: European Load Response.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296288

a pavement process are altered, the project inventory and charac-terisation results will change accordingly. The structure of the LCAmodel and relations between worksheets in it are designed to thefeatures of a road project, and follow the ISO14040 norms (see inTable 1 and Fig. 3).

4.1. Process parameters

The ‘process parameters’ worksheet includes data on transportdistance (km), fuel efficiency of transport vehicles (litre/km or litre/km� t) and energy consumption per unit of materials production(MJ/t) and pavement construction (MJ/m2) in a pavement project.Data on energy consumption include both the amount and energytype. The calorific value (see Table 2) defined by UK Department ofTrade and Industry (DTI) is used in this model to convert the vol-ume of combusted fossil fuels into the universal energy unit (MJ). Itis noted that the selection of use of an energy type is often limitedin a specific industry, and the upstream emission loadings for theseenergy types are different. Parameters can be grouped into ‘energyin materials production’, ‘energy in transport’ and ‘energy inpavement construction’.

This model uses data from UK plants and contractors, as well asother European studies reviewed above. Details can be found inPhD thesis at Newcastle University, UK [25]. Data on energy con-sumption are also available from other sources including US De-partment of Energy, National Crushed Stone Association (NCSA),Canadian National Research Council (NRC), etc. [26]. One of themain elements of LCA is transparency, in that, a user or reviewer ofthe model should be able to tell where the data in the model camefrom, and what assumptions were used in making calculations. Thisis duly followed in the development of this model. Data analysisincluding sensitivity check on data sources can be carried out, asshown later in the case study.

The mileage and vehicles for transport depend on the construc-tion process and materials in use (see Fig. 4), so does the fuel effi-ciency. When calculating the diesel consumption, transport vehiclesare normally assumed to run at ‘full load’ and ‘empty on return’. Fuelconsumption in these cases needs to be differentiated. A key featureof the computing tool is the adaptability. Assumptions made likeabove can be changed to reflect the particulars in a project. Cargoship and rail locomotive may be employed for long-distance, heavy-load haulage, depending on the availability and economics.

In asphalt laying assembly, the roller will pass up and down overthe freshly paved material for a certain number of passes as spec-ified for that material. It must roll before the temperature drops toomuch, so it can never get too far behind the paver, or too close

Table 5EU emission standard for stage III controlled (20 kW< P< 560 kW) diesel engines

Engine power (kW) Emission (g/kWh)

NOx N2O CH4 CO

0–20 14.1 0.35 0.05 8.320–37 6.40 0.35 0.05 5.537–75 4.00 0.35 0.05 5.075–130 3.50 0.35 0.05 5.0130–560 3.50 0.35 0.05 3.5>560 14.4 0.35 0.05 3.0

a FC: fuel consumption.

where the material is still too soft. Therefore the working speed ofpaver and roller in a pavement project is restrained by each other;the selected figure for LCA calculation must refer to the manage-ment of that laying assembly [27].

4.2. Pavement parameters

The ‘pavement parameters’ worksheet includes data on pave-ment dimensions (surface area, layer thickness) and materialsrecipe (ratio of coarse and fine aggregates, filler, bitumen, etc.). Theinformation it has on materials tonnage, together with data in‘process parameters’, will determine the workloads in a pavementproject for inventory calculation. Parameters can be grouped into‘pavement dimension’, ‘materials recipe’ and ‘pavement life time’.

Data on asphalt tonnage in a project are normally available frommaterial supplier. This spreadsheet is using ‘conditional formatting’which is able to warn the user of any illogical data input, for ex-ample, the sum of components tonnage (or percentage) does notequal to the total weight (or 100%). Bitumen emulsion is seen intack coat, chip seal (surface dressing) or cold mix asphalt. Both thebitumen and emulsifier contents are varied between these appli-cations. Emulsion usage in tack coat and chip seal is measured inthe unit of ‘kg/m2’, whilst in cold mix asphalt, by weight ratio.Different service life should be applied to the asphalt layers in thepavement structure, for example, 12 years for surface course, 15years for binder course, etc. Pavement life expectancy is an im-portant factor affecting the inventory results, for it effectively in-fluences the definition of system boundary and functional unit inthe LCA study.

4.3. Unit inventory

In the ‘unit inventory’ worksheet, an environmental input andoutput inventory is built up for the unit processes in a pavementproject. Available inventory data for some ‘primary’ processes (e.g.energy production, vehicle engine operation) are presented first,followed by progressive calculations to get the inventory data onother processes in the pavement project. Emissions from a processhave two aspects. One is the process itself (e.g. diesel engine oper-ation, gas oil combustion); the other is the production of energyconsumed in that process. Figures on energy consumption of vehi-cles and equipments come from the ‘process parameters’ worksheet.This worksheet can be grouped into ‘energy production’, ‘combus-tion of fossil fuel’, ‘transport vehicle operation’ and ‘constructionvehicle operation’, which is described in more detail below.

4.3.1. Energy productionData on production of electric power come from the Union of

the Electricity Industry (EURELECTRIC), using the industry averageof 15 European countries [28]. A later version of 2005 is available,only to EURELECTRIC members. The breakdown of fuel used inelectricity generation in the UK is available since 2002 [24], yet theemissions (complete inventory) from the generation process are

FCa (g/kWh)

NMVOC PM NH3

8 3.82 2.22 0.002 2710 1.10 0.60 0.002 2690 0.70 0.40 0.002 2650 0.50 0.30 0.002 2600 0.50 0.20 0.002 2540 1.30 1.10 0.002 254

Table 6Classification and characterisation (selected)a

Impact category Inventory loading Unit of characterisation factor Value of characterisation factor Source

Depletion of minerals Aggregates tonne minerals 1Bitumen 1

Depletion of fossil fuels Energy (MJ) MJb 1 BRE [21]

Global warming CO2 kg CO2-eq. (100 years) 1 IPCC [38]CH4 23N2O 296

Stratospheric ozone depletion kg CFC11-eq. WMO [39]

Acidification SO2 kg SO2-eq. 1 IIASA [40]NOx 0.7c

NH3 1.88

Photo oxidant (ground-level ozone, or fog)formation

SO2 kg C2H4-eq. 0.048 CML [41]NOx 0.028c

CO 0.027CH4 0.006NMVOC 1.0

Human toxicity Emission to air SO2 kg 1,4-dichlorobenzene-eq. 0.096 CML [41]NOx 1.2CO 2.4HCd 5.7Eþ05NMVOC 0.64PM10 0.82NH3 0.1Heavy metalse 5.1Eþ05

Emission to fresh water HCd 2.8Eþ05Heavy metalse 950.6 (As)

22.9 (Cd)12.3 (Pb)1426.0 (Hg)

Eco-toxicity f Emission to air NMVOC kg 1,4-dichlorobenzene-eq. 3.2E�11 CML [41]HCd 1480Heavy metals e 7.8Eþ04 (As)

3.7Eþ05 (Cd)2.4Eþ03 (Pb)4.1Eþ05 (Hg)

Emission to fresh water HCd 1.1Eþ04Heavy metalse 4.0Eþ04 (As)

7.4Eþ04 (Cd)3.7Eþ02 (Pb)7.2Eþ04 (Hg)

Eutrophication NOx kg PO4-eq. 0.13c CML [41]NH3 0.35COD 0.022Phosphate 1Nitrate 0.1

Noise Noise/1000 vehicle� km DALY 1.3(26)E�03g SAEFL [42]

Depletion of landfill space Solid waste m3 landfill space

a IPCC: Intergovernmental Panel on Climate Change; WMO: World Meteorological Organisation; IIASA: International Institute of Applied System Analysis; CML: Institute ofEnvironmental Sciences, Leiden University; EMEP: Convention on Long-range Transboundary air pollution; SAFEL: Swiss Agency for the Environment, Forests and Landscape;DALY: Disability Affected Life Years.

b In normalisation phase (see Table 7), tonne of oil equivalent (TOE, 1TOE¼ 41,868 MJ) is used, to be consistent in the unit with other environmental loadings, such as thequarry depletion and emissions.

c Figure for NO2.d Figure for carcinogenic PAH (polycyclic aromatic hydrocarbons).e Figure for the total of Arsenic (As), Cadmium (Cd), Mercury (Hg) and Lead (Pb).f Figures in Eco-toxicity are the mean characterisation factor of ‘fresh water aquatic eco-toxicity’, ‘marine aquatic eco-toxicity’ and ‘terrestrial eco-toxicity’.g Figure in the bracket is for night-time (22pm–6am) journey (sleep disturbance); figure outside is for daytime (6am–22pm) journey (communication disturbance). As for

comparison, the DALY of truck emissions (CO, NOx, HC and PM10) per 1000 vehicle kilometre is 1.14E�03. If the time of the day of the transport is unknown, a day/night-timesplit of 95:5 is assumed. If the road traffic data are provided in the unit of tonne� kilometre, the following loading factors are assumed for conversion: 3.8 t for a 16 t truck, 7.0 tfor a 26 t truck and 10.8 t for a 40 t truck [43].

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296 289

not known. Data on production of diesel are taken from the IVL’sstudy covering the life stage of crude oil extraction, refining andtransport to the consumer [16]. The inventory loadings for pro-duction of burning oil and LPG are assumed to be the same asdiesel. Alternative sources of inventory data on energy production(electric power, natural gas and petroleum oil) may include theNational Atmospheric Emissions Inventory (NAEI) report [29], andthe BUWAL250 (database in SimaPro7).

4.3.2. Combustion of fossil fuelNatural gas and petroleum oil (burning oil, LPG, etc.) are com-

busted in plants (for asphalt, emulsion, etc.) and construction ve-hicles (paver, remixer, etc.) for heating purpose. Diesel is consumedby engines in transport vehicles (truck, locomotive, etc.) and con-struction vehicles (paver, roller, etc.). Emission limits on these fossilfuel combustion processes are specified in the European Environ-ment Agency’s (EEA’s) EMEP/CORINAIR Emission Inventory

Table 7Normalisation factors

Impact category Characterisation result UK total Year Data source

Depletion of minerals Aggregates 214 Mt 2004 QPA [45]Depletion of fossil fuels TOE 243,963Eþ 03 2005 DTI [24]Global warming CO2 559.223 Mt 2004 NAEI [46]Stratospheric ozone depletion CFC11 88,000 ta 2003 WMO [39]Acidification SO2 979 t 2003 NAEI [25]Photo oxidant (ground-level ozone, or fog) formation NMVOC (replace C2H4)b 1089 t 2003 NAEI [25]Human toxicity NH3 (replace 1,4-Dichlorobenzene)b 300 t 2003 NAEI [25]Eco-toxicity Heavy metals (replace 1,4-dichlorobenzene)b 339.479 t c 2001 Environment Agency [47]Eutrophication NOx (replace PO4)b 1570 t 2003 NAEI [25]Noise DALY 499.4 billion vehicle� km 2005 Department for Transport [48]Depletion of landfill space Landfill disposal 75 Mtd 2002 Environment Agency [49]UK population 60,209,500 2005 Office of National Statistics [50]

a Global figure.b Data on UK total emissions of C2H4 and PO4 are difficult to obtain. Therefore in the normalisation phase, NMVOC and NOx are appointed instead as the indicator for ‘ground-

level ozone formation’ and ‘eutrophication’, respectively. Characterised results presented as C2H4-equivalent and PO4-equivalent are then converted, using the characterisationfactor in that impact category, into NMVOC-equivalent and NOx-equivalent, respectively. For the same reason, NH3 and Heavy metals are used in the LCA study to replace 1,4-Dichlorobenzene as the indicator for ‘human toxicity’ and ‘eco-toxicity’, respectively.

c Same as in Table 6, data on heavy metals refer to the total of Arsenic (As), Cadmium (Cd), Mercury (Hg) and Lead (Pb). The normalisation factors for each are presented inTable 8.

d Total tonnage of waste sent to landfill.

Hig

h

Priority

Fossil fuel

Global warming

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296290

Guidebook [30]. It has 11 groups in it addressing the combustionprocess in different industries. Those relevant to this LCA study areshown in Table 3.

To avoid confidentiality restrictions and the differences betweenmachine manufacturers, these emission limits, if available, are usedin this LCA model as the inventory loadings of fossil fuel consump-tion. Alternative emission limits on diesel engines (including CO2,CO, HC, NOx and particulates) are defined by European AutomobileManufacturers Association (ACEA) and United Nations EconomicCommissions for Europe (UNECE), in the unit of ‘g/km’ [31,32].

4.3.3. Transport/construction vehicle operationA number of vehicle features (fuel type, age, mileage, etc.), op-

erational conditions (load, road layout, speed, acceleration, trafficflow, etc.) as well as environmental factors (altitude, ambienttemperature, etc.) have an effect on the vehicle’s exhaust emissionslevel; there is a lack of relevant model or database that measuresuch emissions from heavy-duty trucks [33]. EU emission limits(see Table 4, effective from October 2005) on heavy-duty dieselengines are used in this LCA model as the inventory for diesel en-gine operation of transport vehicles [34]. The limits (see Table 5,effective from January 2006) on stage III controlled diesel enginesare used as the inventory for diesel engine operation of construc-tion vehicles [30]. Missing data (e.g. SO2) are supplemented by thedata from the IVL’s study [16].

Transport and construction vehicles are assumed in the LCAstudy to run at their ‘operating capacity’ as specified by contractors.Transport vehicles for example, the unit inventory loadings oftransport vehicles operation (g/km) can be calculated by multi-plying the fuel consumption (MJ/km) by the sum of engine oper-ation (g/MJ) and fuel production (g/MJ [16]).

Unit inventory ðg=kmÞ ¼FC ðMJ=kmÞ � ½engine ðg=MJÞ þ fuel production ðg=MJÞ�

Table 8UK total of heavy metals to air and water [47] (Unit:tonne)

Arsenic Cadmium Mercury Lead Total

Emission to air N/A 5.070 8.820 194.000 207.89Release to water 110.560 1.074 19.710 0.245 131.589

Total 110.560 6.144 28.530 194.245 339.479

FC (MJ/km): fuel consumption, the amount of fuel added tothe engine, using lower heating value (Table 2), convertedfrom l/km;Engine (g/MJ): emissions from engine operation, g emissionsper MJ work energy output from the shaft of the engine,converted from g/kWh, Table 4 for transport vehicles andTable 5 for other construction vehicles.

4.4. Project inventory

In the ‘project inventory’ worksheet, unit inventory data formaterials production, transport and pavement construction areaggregated into the unit of the pavement project, based on theworkloads calculated from ‘pavement parameters’ (for materialstonnage and pavement area) and ‘process parameters’ (for trans-port distance). The results can be grouped into ‘materials pro-duction’, ‘transport’ and ‘materials placement’. At the end of theworksheet is the total of each environmental input (e.g. energy,aggregates) and output (e.g. CO2, PM) for that pavement project.The percentage that each process accounts for the total is alsoavailable.

4.5. Characterisation results

A consensus has been formed on 6 ‘key’ impact areas by the UKasphalt industry, after a review workshop set up by the RefinedBitumen Association (RBA), Quarry Products Association (QPA) andthe Highways Agency, and published by UK TRL [35]. This modelalso refers to the review of existing LCIA methods [36], and the

Impact Area NoiseLow

Global Regional Local & Site

Minerals

AcidificationLandfill

Eutroph.

Ozone depletionHuman-tox.

Eco-tox,Fog

Fig. 5. Grouping and weighting of environmental impact categories.

Production ofaggregates

Production ofbitumen

Production ofasphalt

Placement of asphalt

Production ofemulsion

Planing of oldasphalt surface

Placement oftack coat

Glassrecycling

System Boundary Inci

nera

tion

Landfill

Indicates alternativepractice for comparison

Production ofemulsifier

Glasscollection

Indicates transport

Indicates omission

Fig. 6. System boundary of LHR terminal-5 project.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296 291

methods recommended by UK BRE and the ISO14047 [21,37]. Basedon the findings from above studies, 11 impact categories are se-lected for use in this model (see Table 6), also presented in the‘characterisation results’ worksheet are the selected assessmentmethod (characterisation model and characterisation factor). Al-ternative models for some impact categories are identified in thethesis [25].

Inventory loadings in this model are allocated in their fullamount to relevant categories as if they all go through the ‘serial’processes [37]. The characterised result for an impact category isthe total of all the individually characterised loadings in that cat-egory (see equation below). There are LCI loadings that have notbeen assigned to, and characterised in, any of the impact categories.Impact assessment of these loadings is expected in light of on-goingdevelopment of the environmental assessment (LCIA) method. Anumber of emissions to water (e.g. BOD, Chloride) apply to thiscase.

Characterisation result ¼X

i

Inventory loadingi � Characterisation factori

4.6. Optional phases after characterisation

Depending on the scope of an LCA study, the characterisationresults can be further divided by a reference value (normalisation),which in this LCA study is the characterisation factor per UK capita.The latest figures from the literature are presented in Table 7. This

Fig. 7. Pavement structure in

LCA study proposes a grouping and weighting method, in accor-dance with the ‘Eco-points’ (see Fig. 5) developed by UK BRE for theconstruction industry [44]. It is specified in the ISO14044 thatweighting is not recommended for use in comparative LCA study[23]. Identification of significant areas based on the inventoryloadings, and data analysis (including completeness check, sensi-tivity check and consistency check) also can be carried out fora pavement project, as shown later in the case study.

5. Case study: asphalt paving at London Heathrow (LHR)Terminal-5

5.1. Project background, goal and scope definition

Previous LCA studies have questioned the environmental ben-efits of using waste glass for construction aggregates in terms ofcarbon footprint [3], especially when the recycling involvesa transportation of waste glass of more than 30–40 km [51]. Thiscase study investigated the life cycle environmental impacts ofasphalt paving at LHR Terminal-5 access road in which naturalaggregates were partially replaced with waste glass, incineratorbottom ash (IBA) and reclaimed asphalt pavement (RAP), andcompared the results to the pavement of the same size and functionbut made using virgin aggregates only. This is followed by a dis-cussion and data analysis referring to the most significant variablesin this project. This case study is to test and calibrate the LCA modeldescribed above. The findings, presented as inventory loadings(LCI), can be beneficial to road engineers or researchers dealingwith recycling in roads.

LHR terminal-5 project.

Table 9Materials in LHR termianl-5 project (unit: tonne)

Natural aggregates Glassc IBA RAP Primary bitumen

Coarse Fine Filler Total

New proposal Surface course 1379.7 283.5 113.4 1776.6 113.4Tack coat 7.2a

Binder course 2402.6 1394 123 2530.2 139.4 240.3 1025b 165.2Tack coat 7.2a

Base 7490.7 4391.1 516.6 8021.8 439.1 749.1 3228.8b 476.2Total 12328.6 578.5 989.3 4253.8 769.2

Conventional proposal Total 18094.6 824.8

a Specific density of bitumen and emulsion is assumed to be 1 kg/litre.b US National Cooperative Highway Research Program (NCHRP) research indicated that residue binder in the RAP might need to be counted as ‘active’ binder when the

replacement rate of RAP exceeds 20% [53]. UK TRL suggested a 50% recovery rate of the binder in porous asphalt that is recycled into thin surfacing accounting for up to 30% ofthe new mixture [54]. In this case study, 50% residue binder in the RAP is assumed to be recovered in the new asphalt mixture. The rest 50% is counted as hardened ‘black rock’,the aggregates portion of the new mixture.

c Fuel consumption for collection of waste glass is 0.4 MJ/t [55]. The processes (crushing, screening, etc.) and energy input for making glass aggregates are assumed the sameas for making natural aggregates.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296292

5.1.1. Data source, quality and allocationData needed for this LCA study are obtained primarily from

materials suppliers and contractors, Aggregate Industries UK Ltd.(AI) in the project. The missing data come from those justified foruse in the model described above, which are a combination of lit-erature and other European LCA results. Quality of these data isanalysed later in the ‘interpretation’ phase. As the inherent prop-erties of glass have not been changed by recycling, waste glass inputin this LCA study is counted the same way as stone aggregates.Embedded energy in glass manufacture is therefore not included inthis LCA study.

5.1.2. System boundaryProduct systems are defined as the asphalt layers (surface

course, binder course and base) in the LHR Terminal-5 projectconstructed partially using glass, IBA and RAP (referred as ‘newproposal’), compared to the asphalt layers of the same size andfunction but containing virgin aggregates and binder only (referredas ‘conventional proposal’): this is a comparative LCA study. It isassumed that using those recycled materials has no measurableeffects on the asphalt layers’ life expectancy or technical constraintson reuse or recycling when these layers are replaced.

The upstream boundary for recycled materials is set at the col-lection point: bottle banks for glass, incinerators for IBA and roadsite of the old asphalt pavement for RAP. Alternative ways of dis-posal include transport of those materials to landfill (see Fig. 6).Boundaries, assumptions and data options made for conventionalmaterials are described above in the model. The transport of bi-tumen and emulsifier to emulsion plant is not included in thisstudy, for data are not available.

5.13. Functional unitThe function of asphalt surface is to provide a safe, comfortable,

economical and durable driving. Functional unit is defined as the30,000 m2 of the asphalt surface. This case study assumes the same

Table 10Transport parameters

Freight Origin Destination Mileage

Aggregates Bardon Hill quarry West Drayton 120 mi (193.1 km)Bitumen Southampton West Drayton 80 mi (128.7 km)Emulsionb York (to Crawley first) LHR T5 230 mi (370.1 km)Asphalt West Drayton LHR T5 4 mi (6.4 km)Glassb Brentford West Drayton 11 mi (17.7 km)IBAb Edmonton West Drayton 20 mi (32.2 km)

a Fuel consumption in empty journey is counted in the calculation of fuel efficiency.b The suppliers of emulsion, glass and IBA are Colas, Day Group Ltd. and Ballast Phoen

durability of asphalt layers between the two proposals. This isreflected in the definition of functional unit that includes elementsin only the construction stage. The pavement layers included forstudy consist of 35 mm Stone Mastic Asphalt (SMA) surface course,77 mm High Modulus Bituminous (HMB) binder course and205 mm HMB base. Quarry aggregates, bitumen and emulsion,waste glass, IBA and RAP are used (see Fig. 7). Technical assessmentof the Smatex for surface course is seen in UK TRL report [52].

5.1.4. Method of impact assessmentThe nature and amount of work in the life cycle impact assess-

ment phase have been discussed with the client when defining thescope of the study, and was considered purely an environmentalanalysis process that needs very little input from road engineersonce the life cycle inventory is complete. Based on the client’s in-struction, and the fact that most of the procedures would repeatthose described earlier in the LCA model development (Section 4.5and 4.6), this case study will proceed straight into the in-terpretation phase, from the completion of the inventory analysis.

5.2. Inventory analysis

5.2.1. Pavement parametersPavement dimension, asphalt recipe and materials tonnage are

seen in Fig. 7. It is assumed that the only difference between thetwo proposals is the use of waste glass, IBA and RAP. 10% IBA and10% glass were used to replace coarse and fine aggregates, re-spectively, in both binder course and base. 25% RAP (48% coarse,47% fine, and 5% binder) was also used in both layers. The break-down of materials usage in this project is seen in Table 9.

5.2.2. Process parametersThe transport vehicles and distance, and fuel consumption of

construction vehicles are seen in Table 10 and Table 11.

Vehicle type Fuel consumption Payload Fuel efficiency

Train 8–9 L/mi (5.0–5.6 L/km) 1729 t 0.85 L/ta

Truck Data missing, the figures for 14 t truckfrom the IVL’s study are used forcalculation

TruckTruckTruckTruck

ix Ltd., respectively.

Table 11Machinery parameters

Width ofscreed/roller (m)

Working speed(m/hr)

Fuelconsumption (L/hr)

Emulsion applier 2 220 6.0Paver 4.9 300a,b 16.87Roller 1.7 6000b 12.5

a Normally, the paver runs at a speed of 10–12 m/min on surface and bindercourse, and 8–10 m/min on the base.

b Paving and rolling is finished in 2 passes on the base.

Energy and CO2 Loadings for Comparison

363 357 365 375 371

869 853 874 900 888

0200

400600

8001000

T5 No Glass No IBA No RAP No Recycling

Energy Total (TOE) CO2 emission (t)

Fig. 8. Comparison of energy and CO2 between recycling scenarios.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296 293

5.2.3. Inventory loadings calculationEnvironmental inputs (raw materials, energy) and outputs

(emissions to air and water, solid waste) are calculated for the LHRTerminal-5 project. For comparison, the tonnage of glass, IBA andRAP in the asphalt is in turn set to zero, hypothetically (with theasphalt recipe design altered, replacing that recycled portion withvirgin aggregates), to see how the LCI loadings change as a result.Some of the inventory loadings in these scenarios are presented inTable 12. Complete inventory results are shown in the spreadsheet.It can be seen that RAP replacement has the greatest effects,compared with glass and IBA. There are two reasons for the sig-nificance: (1) its tonnage and (2) its dual effects of replacing ag-gregates and reducing the input of primary bitumen, an energyintensive product. Glass replacement causes more energy use andemissions. This is due to the high consumption rate of fuel in wasteglass collection (442 MJ/t), compared to that of 42 MJ/t for aggre-gates quarrying. Energy and CO2 loadings for these recycling sce-narios are presented in Fig. 8.

5.3. Interpretation

Not all the data required for this LCA study were available fromcontractors. Some (e.g. transport) were obtained from industryaverage not specific to this project; other data gap (e.g. glass/IBAaggregates) has affected the definition of system boundary. Dataused in this case study were of mixed age, accuracy and applica-bility. A full inventory of environmental loadings of asphalt prod-ucts and processes is welcome for LCA use; very often, however,only energy data are available.

5.3.1. Identification of significant areasIn the LHR Terminal-5 project, asphalt mixing, bitumen and

aggregates production consumed approximately 62%, 23% and 6%,respectively, of the energy total and resultantly, produced moreemissions than other processes. The use of recycled materials re-duced, by about 7%, the primary bitumen input. Another significantbenefit of the recycling was the saving of 5766 t of natural aggre-gates, and diverting 579 t and 989 t of waste glass and IBA, re-spectively, from landfill. Old asphalt planing is the desirable type ofrecycled aggregates considering quantity, transport, resource effi-ciency and recyclability of the asphalt layers. Further research isneeded to determine the recovery rate of residue binder from theRAP.

Table 12Inventory loadings of LHR terminal-5 and alternative scenarios

Scenario of using recycled materials Inventory loadings (selected)

Aggregates (t) Bitumen (t) En

Glass, IBA, RAP as in T-5 12328.6 769.2 36IBA, RAP as in T-5, no glass 12907.1 769.2 3Glass, RAP as in T-5, no IBA 13317.9 769.2 36Glass, IBA as in T-5, no RAP 16526.8 824.8 37Virgin materials only 18094.6 824.8 3

Transport of aggregates accounted for more than 61% of alldiesel use for transport. This is due to the long haulage distance(193 km) and materials tonnage. Railway locomotive with a higherfuel efficiency (0.17 MJ/t� km) than trucks (0.46–0.94 MJ/t� km)was used for aggregates transport. Glass and IBA were obtainedfrom fairly local sources; the haulage of RAP which was applied onsite was not counted in the calculation. The road site in this projectwas fairly close (6.4 km) to the hot mix asphalt plant, whichexplained the diesel use of only 17% for asphalt transport.

5.3.2. Sensitivity checkThe sensitivity check aims to determine the influence of varia-

tions in data source, methodology and assumptions on the in-ventory results. Normally it is carried out after the identification ofsignificant areas. Materials production, notably the hot mix asphalt,bitumen and aggregates, represented in the LHR Terminal-5 projectmost of the energy use and emissions. The production process wasalso found to be where more alternative data exist. Sensitivitycheck is therefore carried out, on the effect of data source on theinventory loadings of energy and CO2. A variation of 10% is con-sidered by the authors as being significant for this case study.

It can be seen from Table 13 and Table 14 that the source of dataon materials production does not have significant effects on theenergy or CO2 total in the inventory. However, the project’s energytotal would be more than halved had the aggregates and bitumen(emulsion) been mixed by the ‘cold’ method. This is of course,based on the assumption that aggregates grading and bitumencontent remain the same, and durability of the asphalt is notchanged as a result.

6. Discussion

It is the case studies that built up the scope and capacity of thisLCA model during its development. The case studies show howmore details of the asphalt pavement project went into the model,how a case study learned from the previous ones and applied thefindings, and how the LCA model and case studies will benefit fromeach other’s advancement. The main improvements include thefollowing aspects. The key elements for a quality LCA study of as-phalt pavements are summarised in Fig. 9.

ergy (TOE) CO2 (t) SO2 (kg) NOx (kg) Solid waste (t)

3 869 2230 4310 �5803.357 853 2220 4260 �5224.8

5 874 2240 4400 �4813.85 900 2360 4700 �1548.3

71 888 2370 4740 19.8

Table 13Sensitivity check on data source and mixing method for asphalt production

Total energyuse (TOE)

Hot mixproduction

Cold mixproduction

Deviation(�, %)

Sensitivity

AI data 363 165 �198, �54.6% SignificantEAPA data 365IVL data 164Deviation (�, %) þ2, þ5.5% �1, �0.6%Sensitivity Insignificant Insignificant

Table 14Sensitivity check on data source for bitumen and aggregates production

Total CO2

emissions (tonne)Deviation(�, %)

Sensitivity

Bitumen production Eurobitume data VTT data869 908 þ39, þ4.3% Insignificant

Aggregates production AI data VTT data869 847 �22, �2.5% Insignificant

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296294

The communication skills with contractors, make concise andto-the-point questionnaire for project specific data;The level of details and sophistication of the model, when thecalculation process becomes swift and more adaptive at thesame time;The incorporation of up-to-date and alternative data sources,rather than rely on a low number of references which is proneto limit the scope and accuracy of any LCA study;The presentation of results, featured by graphic illustration anddata quality analysis (check for completeness, sensitivity andconsistency);The development of the LCIA phase, provide both the manda-tory and optional elements addressed in the ISO14040 series.

7. Conclusion and recommendations

Life cycle assessment makes an important part of the ‘life cycleapproach’ as a tool to support decision making. This paper in-troduced the concept of LCA; reviewed the existing LCA toolsworldwide; identified the knowledge gap for the UK road industry;and described the development of an LCA model for asphaltpavement construction. Details were provided of both the meth-odology and data sourcing. A case study of applying the LCA modelto a real asphalt paving project in the UK was provided, referring tothe most significant variables in the project. This was followed bydata analysis and sensitivity check, and a discussion of the expe-riences obtained from this and other case studies.

To duly reflect the current practice in UK road construction, theLCA model should accommodate maintenance and recycling sce-narios, with data specific to the UK road industry. The model shouldrepresent as many as possible variables in a pavement project,whilst remaining flexible for data update and formula revision. Apractical model must be populated with good quality data. It mustalso be tested and calibrated through real case studies. Data in this

Knowledge of the Industry

Presentation of LCA Results

CompliISO S

Communication

Transparency

T

Fig. 9. Elements for a successful LC

LCA model come from a mixed source of UK plants, EU standardsand relevant European LCA results.

Still there is a room for improving both the wealth and quality ofdata fed to the LCA study. Its application in road practice is rela-tively new; inventory data for some materials and processes are yetto be available. Many processes that do not have energy input werescoped out of the LCA study, simply because the required emissiondata were not documented. Company’s Integrated Pollution Pre-vention and Control (IPPC) application documents for their sites orplants could be potential sources of data for those ‘process related’emissions. On the other hand, innovative asphalt materials andlaying techniques emerge in response to the industry improve-ment, which calls for an expanding database for LCA practitionersthat can accommodate these novelties. Where the required data fora unit process come from more than one source, the compatibility(date, boundary, underlying assumptions, etc.) of the data needs tobe studied. Data acquisition for LCA is further hurdled by com-mercial restriction on some proprietary data. In summary, the mainchallenges of applying LCA to pavement construction practice in-clude the following aspects, which make the areas for further work:

Include the non-energy (process) related emissions in themodel;Look for energy or inventory data on more secondary aggre-gates in the asphalt;Predict the life expectancy, and the way of disposal, of pave-ment layers made using recycled materials;Include the effect of road maintenance works on the traffic andresultantly, the fuel use and emissions, helped by micro-sim-ulation model (e.g. VISSIM).

Despite the challenges above, LCA is being accepted by theroad industry to measure and compare the key life time environ-mental impacts of its products and construction processes, anduse the results for internal review or environmental labelling.

ance with tandards

Quality of Data

Powerful Computing Tool

Speed Quality

LCA Model Development

ARGET

A study of asphalt pavements.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296 295

Recommended applications of LCA in road paving include thecomparison of

Different asphalt composition and materials usage;Recycled materials with virgin aggregates (like the LHR Ter-minal-5 case study);Different recycled materials (glass, RAP, etc.);Different laying or recycling techniques (hot ex situ, cold insitu, etc.) and maintenance options (depth, interval, etc.);Asphalt with concrete (standard recipe for both, same functionin the pavement layer).

Despite previous LCA studies that have questioned the envi-ronmental benefits of recycling some waste (e.g. glass) for use asaggregates based on such impacts as the carbon footprint, it isadvisable to study by LCA the environmental impacts of therecycling in pavement projects. The reason is that these twotypes of LCA studies normally do not share the same functionalunit or system boundary. For instance, in LCA of glass, thefunctional unit is packaging a certain volume of liquid, while thefunctional unit in LCA of roads is the provision of a certain areaof asphalt surface on the carriageway. Therefore, the LCA resultsof the ‘close-loop’ recycling do not negate the environmentalbenefits of the ‘open-loop’ recycling that could be identifiedwhere the quarrying limits, transport scenarios, landfill re-striction, etc. are taken into account.

Acknowledgments

An earlier version of this paper was presented at the 6th In-ternational Conference on Sustainable Aggregates, Pavement En-gineering and Asphalt Technology, JMU Liverpool, UK, 21st–22ndFebruary 2007. Financial support and intellectual inputs from Ag-gregate Industries UK Ltd. are greatly appreciated. We would like tothank Dr. Paul Phillips and Bob Allen for providing technical adviceand data for case studies throughout this research.

References

[1] Greeman A. Road recycling is widespread. Road recycling – a supplement toworld highways; June 2007.

[2] Dacombe PJ, Krivtsov V, Banks CJ, Heaven S. Use of energy footprint analysisto determine the best options for management of glass from householdwaste. In: International conference on sustainable waste management andrecycling, London; 2004.

[3] Thornton Grant, Hollins Oakdene. The impact of the carbon agenda on thewaste management business; 2006.

[4] WRAP. Environmental benefits of recycling – an international review of lifecycle comparison for key materials in the UK recycling sector. The Waste andResources Action Program; 2006.

[5] WSSD. Plan of implementation. World summit on sustainable development.Johannesburg; 2002.

[6] Bird R, Clarke R, Donnelly T, Heidrich O, Huang Y. Life cycle and sustainabilityindices for road paving materials [unpublished report]. School of Civil Engi-neering and Geosciences, University of Newcastle upon Tyne; 2004.

[7] BS EN ISO14040. Environmental management - life cycle assessment - prin-ciples and framework. British Standard Institution; 2006.

[8] BS EN ISO14025. Environmental labels and declarations – type III environ-mental declarations – principles and procedures. British Standard Institution;2006.

[9] TRL. Guidance on the development, assessment and maintenance of long-lifeflexible pavements. TRL Report 639. Transport Research Laboratory; 2005.

[10] EPA. LCA resources. Available from: http://www.epa.gov/NRMRL/lcaccess/re-sources.html; 2007 [accessed 03.04.07].

[11] EUROPA. LCA resources directory. Available from: http://lca.jrc.ec.europa.eu/lcainfohub/directory.vm; 2007.

[12] Schenck R. Using LCA for procurement decisions: a case study performed forthe US environmental protection agency. Environmental Progress 2000;19(2):110–6.

[13] Inamura H. Life cycle inventory analysis of carbon dioxide for a highwayconstruction project using input–output scheme: a case study of the Tohokuexpressway construction works. Graduate School of Information Sciences,Tohoku University; 1999.

[14] WBCSD. Toward a sustainable cement industry (Substudy 6): what LCA can tellus about the cement industry. World Business Council for Sustainable De-velopment; 2002.

[15] Stripple H. Life cycle assessment of road – a pilot study for inventory analysis.2nd ed. Swedish Environmental Research Institute (IVL); 2001.

[16] Stripple H. Life cycle inventory of asphalt pavements. 3rd ed. Swedish Envi-ronmental Research Institute (IVL); 2005.

[17] Eurobitume. Partial life cycle inventory or ‘‘eco-profile’’ for paving grade bi-tumen; 1999.

[18] Hakkinen T, Makela K. Environmental adaption of concrete – environmentalimpact of concrete and asphalt pavements. Technical Research Centre of Fin-land; 1996.

[19] Mroueh U-M, Eskola P, Laine-Ylijoki. Life-cycle impacts of the use of in-dustrial by-products in road and earth construction. Waste Management2001;21:271–7.

[20] Birgisdottir H. Life cycle assessment model for road construction and use ofresidues from waste incineration. Institute of Environment & Resources,Technical University of Denmark; 2005.

[21] Howard N, Edwards S, Anderson J. BRE methodology for environmental pro-files of construction materials, components and buildings, built research es-tablishment; 1999.

[22] Huang Y, Bird R, Allen B. A life cycle assessment tool for recycling inpavement construction. In: SETAC Europe 13th LCA Case Study Sympo-sium with Focus on the Building and Construction Sector, Stuttgart,Germany; 2006.

[23] EN ISO 14044 BS. Environmental management – life cycle assessment – re-quirements and guidelines. British Standards Institution; 2006.

[24] DTI. Digest of United Kingdom energy statistics 2006. Department of Tradeand Industry; 2006.

[25] Huang, Y. Life cycle assessment of use of recycled materials in asphalt pave-ments. Ph.D. thesis, School of Civil Engineering and Geosciences, Newcastleupon Tyne, Newcastle University; 2007.

[26] Zapata P, Gambatese JA. Energy consumption of asphalt and reinforced con-crete pavement materials and construction. Journal of Infrastructure SystemsMarch 2005:9–20.

[27] Lavin P. Asphalt pavements: a practical guide to design, production andmaintenance for engineers and architects. London: Spon; 2003.

[28] EURPROG. Programmes and prospects for the european electricity sector.EURPROG Report, final version. 26th ed. Union of the Electricity Industry;1998.

[29] NAEI. UK emissions of air pollutants 1970 to 2003. National AtmosphericEmissions Inventory; 2005.

[30] EEA. EMEP/Corinair emission inventory guidebook. European EnvironmentalAgency; 2005.

[31] UNECE. Protocol to the 1979 convention on long-range transboundary airpollution to abate acidification, eutrophication and ground-level ozone. ECE/EB.AIR/72. United Nations Economic Commissions for Europe; 1999.

[32] ACEA. Reducing CO2 emissions: working together to achieve better results.Available from: http://www.acea.be/home_page; 2007 [accessed 25.06.07].

[33] TRL. A review of available road traffic emission models. TRL report 457.Transport Research Laboratory; 2000.

[34] European Union. Directive 2005/55/EC of the European Parliament and of theCouncil; 2005.

[35] TRL. A model set of asphalt sustainability indicators. TRL report 638. TransportResearch Laboratory; 2005.

[36] Pennington DW, Potting J, Finnveden G, Lindeijer E, Jolliet O, Rydberg T, et al.Life cycle assessment (Part2): current impact assessment practice. Environ-mental International 2004;30:721–39.

[37] EN ISO 14047 BS. Environmental management – life cycle impact assessment.examples of application of BS EN ISO14042. British Standards Institution;2003.

[38] IPCC. IPCC third assessment report, intergovernmental panel on climateChange; 2001.

[39] WMO. Scientific assessment of ozone depletion: 2006 [prepared by the Sci-entific Assessment Panel on the Montreal Protocol on Substances that Depletethe Ozone Layer]. World Meteorological Organisation; 2006.

[40] Huijbregts M, Krewitt W, Verkuijlen E, Reijnders L, Heijungs R. Spatially ex-plicit characterization of acidifying and eutrophying air pollution in life-cycleassessment. Journal of Industrial Ecology 2000;4(3):75–92.

[41] CML. CML impact assessment. Leiden; 2004.[42] Muller-Wenk R. Attribution to road traffic of the impact of noise on health.

Environmental Series No.339. Swiss Agency for the Environment, Forests andLandscape (SAEFL); 2002.

[43] Muller-Wenk R. Life-cycle impact assessment of road transport noise. dis-cussion Paper No.077. Institute for Economy and the Environment, Universityof St. Gallen; 1999.

[44] Dickie I, Howard N. BRE Digest446: assessing environmental impacts ofconstruction – industry consensus BREEAM and UK ecopoints. Built ResearchEstablishment; 2000.

[45] QPA. Resource conservation. Available from: http://www.qpa.org/sus_natres_cons01.htm; 2007 [accessed 04.01.07].

[46] NAEI. Greenhouse Gas Inventories for England, Scotland, Wales and NorthernIreland: 1990–2004. National Atmospheric Emissions Inventory; 2006.

[47] EA. Pollution inventory data report: trends and analysis 1998–2001. The En-vironment Agency; 2004.

Y. Huang et al. / Journal of Cleaner Production 17 (2009) 283–296296

[48] DfT. Transport statistics great Britain – 2006 Edition. Department for Trans-port; 2006.

[49] The Environment Agency. Waste management options. Available from: http://www.environment-agency.gov.uk/subjects/waste/1031954/1031960/?version¼1%26lang¼_e; 2007 [accessed 06.01.07].

[50] Office of National Statistics. Population estimates. Available from: http://www.statistics.gov.uk/CCI/nugget.asp%3FID¼6; 2007 [accessed 04..01.07].

[51] Hopkins A, Foster C. Achieving life cycle benefits through practical sustainablewaste management – opportunities, benefits and barriers associated with the useof glass waste as aggregates in coated roadstone. RMC Environment Fund; 2003.

[52] TRL. Assessment of SMATEX – a Bardon thin asphalt surface course. TRL report435. Transport Research Laboratory; 2000.

[53] NCHRP. Recommended use of reclaimed asphalt pavement in the SUPERPAVEmix design method: technician’s manual. NCHRP Project 9–12. National Co-operative Highway Research Program; 2001.

[54] TRL. Feasibility of recycling thin surfacing back into thin surfacing systems.TRL report 645. Transport Research Laboratory; 2005.

[55] Edwards DW, Schelling J. Municipal waste life cycle assessment (Part 2) –transportation analysis and glass case study. Transactions of the Institution ofChemical Engineers. 1999;77:259–74.