Embed Size (px)
Citation preview
This article was downloaded by: [Universite De Paris 1]On: 28 August 2013, At: 23:36Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
International Journal of ConstructionEducation and ResearchPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/uice20
Evaluation of the Environmental andEconomic Impacts of Warm-Mix AsphaltUsing Life-Cycle AssessmentMarwa Hassan Ph.D. aa Louisiana State University, Baton Rouge, LouisianaPublished online: 08 Sep 2010.
To cite this article: Marwa Hassan Ph.D. (2010) Evaluation of the Environmental and EconomicImpacts of Warm-Mix Asphalt Using Life-Cycle Assessment, International Journal of ConstructionEducation and Research, 6:3, 238-250, DOI: 10.1080/15578771.2010.507619
To link to this article: http://dx.doi.org/10.1080/15578771.2010.507619
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.
This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions
Evaluation of the Environmental and EconomicImpacts of Warm-Mix Asphalt Using
Life-Cycle Assessment
MARWA HASSAN, PH.D.
Louisiana State University, Baton Rouge, Louisiana
The use of warm-mix asphalt (WMA) has received considerable attention in recentyears to reduce energy consumption and air emissions. Despite these promising ben-efits, the promotion of WMA based on a single factor such as reduced energy con-sumption or reduced emissions does not provide a complete evaluation of thistechnology and may omit critical environmental factors that should be consideredin the decision-making process. The objective of this paper was to conduct a life-cycle assessment of WMA technology as compared with a conventional hot-mixasphalt mixture. To achieve this objective, a life-cycle inventory (LCI) that quanti-fies the energy, material inputs, and emission during aggregate extraction, asphaltbinder production, and hot-mix asphalt production and placement, was developed.Based on this inventory, life-cycle impact assessment of WMA technology was con-ducted. Based on this analysis, it was determined that WMA provides a reduction of24% on the air pollution impact of hot-mix asphalt (HMA) and a reduction of 18%on fossil fuel consumption. Overall, the use of WMA is estimated to provide areduction of 15% on the environment impacts of HMA.
Keywords life-cycle assessment, life-cycle inventory, sustainable construction,warm-mix asphalt
Introduction
In the past few years, many state agencies experienced a significant increase inconstruction bid prices. One major reason for this sharp increase in constructionprices is the rise in energy costs and the price of liquid asphalt, a petroleum product.Recent estimates predict that the current energy crisis will only worsen, as thecontinuous growth in the world’s population will result in an increase in energyconsumption. While many affected industries have taken a positive initiative to seekalternative sources of energy, the transportation industry have mainly been forced tocut back on needed roads to address rises in asphalt and energy prices. As no slow-down in freight transportation growth is in sight in the near future, it is imperativethat innovative technologies that can improve the energy efficiency of pavement con-struction operations be introduced to ensure continuous growth of the economy.
In 1997, European countries started experimenting with a new mix technologyknown as warm mix asphalt (WMA). The concept of warm mix asphalt is that
Address correspondence to Marwa Hassan, Louisiana State University, CMIE, 3128 PFTHall, Baton Rouge, LA 70803. E-mail: [email protected]
International Journal of Construction Education and Research, 6:238–250, 2010Copyright # Taylor & Francis Group, LLCISSN: 1557-8771 print=1550-3984 onlineDOI: 10.1080/15578771.2010.507619
238
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
substantial energy is spent to heat hot-mix asphalt (HMA) to temperatures in excessof 150�C during production and compaction (Johnston et al., 2006). By reducing theheating temperature during production by 16 to 55�C lower than with typical HMA,warm mix asphalt may provide significant energy savings to the asphalt industry(Newcomb, 2005). Warm mix asphalt uses specific mechanical and chemical meansto reduce the shear resistance of the mixture, which allows to process and compactthe mat at lower temperatures. Warm-mix asphalt also reduces emissions at theplant, widens the winter paving season, and reduces mixture aging (Hurley et al.,2006). By reducing emissions at the plant, WMA would also reduce health problems,complaints of odor, and fumes near all paving workers.
In spite of these promising findings, the promotion of warm-mix asphalt basedon a single factor such as reduced energy consumption during production does notprovide a realistic and complete evaluation of this technology and may omit criticalenvironmental factors that should be considered. This single-factor selectionapproach has long been used in the transportation industry to select products basedon minimum initial cost or minimum life-cycle economic analysis. However, with thecurrent trend towards sustainable construction, the deficiencies of conventionaleconomic approaches became apparent. This has led to the introduction of multi-dimensional life-cycle approaches to measure and compare the environmentalimpacts of human activities. Multi-dimensional life-cycle approaches such as life-cycle assessment (LCA) consider economic and environmental factors in the decision-making process by determining an overall performance measure that quantifies boththe environmental and economic impacts of a given technology (Heijungs, 2002).
The objective of this paper is to conduct the life-cycle assessment of warm-mixasphalt technology as compared to a conventional hot-mix asphalt mixture. Toachieve this objective, a life-cycle inventory (LCI) that quantifies the energy, materialinputs, and emission during aggregate extraction, asphalt binder production, andhot-mix asphalt production and placement, was developed. Based on this inventory,impact assessment of the technology on the environment was determined using theBuilding for Environmental and Economic Sustainability (BEES) model, whichwas developed for life-cycle assessment of sustainable construction alternatives inthe United States (Lippiat, 2007).
Background
Life-Cycle Assessment
Life-cycle assessment (LCA), also known as cradle-to-grave analysis, is a methodo-logical framework for quantifying the impacts of a product across its entire servicelife on the environment including climate change, fossil fuel depletion, human health,and acidification potential (Rebitzer et al., 2007). Though LCA is still an evolvingmethodology, it has found widespread applications in many areas such as auto-manufacturing, cleaning products, communication tools, and sustainable construc-tion. As defined by the international organization for standardization (ISO) 14040series, life-cycle assessment consists of four major steps (ISO, 1997):
. Goal and scope definition, which provides a description of the system in terms of itsboundaries and selection of a functional unit. The functional unit provides thebasis of comparison between alternative products. In this study, the functionalunit was selected as one metric ton of delivered and installed HMA.
Evaluation of the Environmental and Economic Impacts 239
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
. Life cycle inventory (LCI), which estimates the consumption of resources and thequantities of waste and emission associated with the production of hot-mixasphalt and its different components.
. Life-cycle impact assessment (LCIA), which evaluates the impact of the productlife cycle in terms of selected impact categories. This may include factors suchas global warming potential, fossil fuel depletion, impact on human health, andsmog potential.
. Life cycle interpretation, which evaluates the results of LCIA by comparing theperformance scores for all impact categories. In this study, interpretation was con-ducted based on a combined environmental and economic performance approach.
Life-cycle assessment is usually conducted using a dedicated softwarepackage.How-ever, since this is one of the first attempts to apply this methodology to asphalt concreteconstruction, assumptions underlying available software packages were not directlyapplicable to hot-mix asphalt. Therefore, compilation of the required raw data was con-ducted manually and impact assessment was conducted based on the BEES 4.0 model.
The BEES 4.0 Model
The Building for Environmental and Economic Sustainability (BEES) model, whichwas introduced in the late 1990s by the National Institute of Standard and Tech-nology, provides a systematic methodology to select sustainable construction alterna-tives that balance environmental and economic performances (Lippiat, 2007). Sinceenvironmental factors such as global warming potential and impacts on humanhealth cannot be assessed using a regular monetary scale, the BEES model computesa single index for each considered factor in order to quantify the impact of a producton the environment. For instance, global warming potential is expressed in grams ofcarbon dioxide produced per functional unit of a product. The global warming indexis then calculated based on the following relation:
global warming index ¼X
i
mi �GWPi ð1Þ
where mi¼mass (in grams) of harmful emission i per functional unit; GWPi¼ conver-conversion factor from one gram of harmful emission i to its equivalent of carbondioxide. Equivalency factors are provided by the BEES model based on research con-ducted by the U.S. Environmental Protection Agency. A similar approach is adoptedfor each environmental factor considered in the assessment process. Mode detailsabout this method have been presented elsewhere (Lippiat, 2007). In all, the BEESmodel considers 12 factors in its assessment of the net environmental benefits of aconstruction alternative (see Table 1). Out of these 12 factors, two impacts werenot considered in the assessment of hot-mix asphalt: Indoor Air Quality and HabitatAlteration. The reason for omitting the assessment of Indoor Air Quality is evident asit is not applicable to outdoor construction activities. Habitat Alteration measures thepotential for land use by humans to affect endangered species. It is mainly applied toassess the contribution of a product to landfills throughout its service life. Since HMAis regularly recycled and since the two considered construction alternatives (i.e., con-ventional hot-mix asphalt and warmmix asphalt) were compared relatively, there wasno need to assume that one alternative would be more damaging to endangeredspecies than would the other.
240 M. Hassan
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
In the interpretation phase, calculated impact performance measures are nor-malized with respect to fixed U.S. scale impact values. Normalized performancemeasures are then synthesized based on a set of weights reflecting the importanceof each environmental factor as perceived by the user. In this study, weightsdeveloped by the 2006 BEES Stakeholder Panel were modified to reflect that thecategories, Indoor Air Quality and Habitat Alteration, were not considered in ourevaluation of hot-mix asphalt. These modified weights, which are presented inTable 1, reflect the importance of fossil fuel depletion, criteria air pollutants, impactson human health, and global warming in asphalt pavement construction. Applyingthese weights provides a single performance score for the environmental impacts of agiven product. A lower score indicates a technology that is more sustainable andenvironmentally friendly.
Economic performance is assessed by determining the costs for purchase, instal-lation, maintenance, and replacement. All future costs are discounted to theirequivalent present values. Similar to environment performance, a lower score indi-cates a technology that is more cost-effective and economic. For the purpose of thisanalysis and as suggested by recent studies, the costs of replacement and
Table 1. Environmental impact factors considered in the BEES model
IDEnvironmental
impactReferencesubstance Description
Weights(%)
1 Global warming Carbon dioxide Increase in temperaturedue to greenhousegases
30
2 Acidification Hydrogen ions Affects all ecosystems 33 Eutrophication Nitrogen Undesirable shifts in
ecosystems6
4 Fossil fueldepletion
Surplus MegaJoule (MJ)
Depletion of fossil fuelextraction
15
5 Indoor air quality Not considered6 Habitat alteration Not considered7 Water Intake Water Water intake during
production and service8
8 Criteria airpollutants
Years of life lost Particles leading torespiratory diseases
10
9-1 Human health(noncancerous)
Toluene Noncancerous healthconcerns
6
9-2 Human health(cancerous)
Benzene Cancerous healthconcerns
9
10 Smog formation Nitrogen oxide Harmful effects onhuman health andvegetation
4
11 Ozone depletion CFC-11 Thinning of the ozonelayer
2
12 Ecological toxicity 2,4-D Harm terrestrial andaquatic ecosystems
7
Evaluation of the Environmental and Economic Impacts 241
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
maintenance for a conventional hot-mix asphalt and warm-mix asphalt wereassumed to be equal (Prowell et al., 2007). This assumption implies that the increasedcost due to the use of warm-mix asphalt is mainly associated with equipment modi-fication, cost of chemicals, and royalty fees. Environmental and economic scores arethen combined into a single score based on a Multi-attribute Decision Analysis(MADA) technique as developed by ASTM E1765-02. The combined score isobtained by first dividing each individual score (environmental and economic) bythe sum of corresponding scores across all alternatives (conventional HMA andwarm-mix asphalt) under analysis. Each performance score is scaled in terms ofits share of all scores to yield a relative score ranging from zero to 100. Thetwo-scaled scores are then combined into a single overall score by weighting environ-mental and economic performances with respect to their relative importance to thedecision-maker. In this study, a 50% weight was assigned to each of the environmen-tal and economic performance score.
Warm Mix Asphalt
Warm mix asphalt is an emerging class of asphalt mixture that reduces heatingrequirement during production and compaction by using a number of chemicaland organic additives. While heat is used to reduce asphalt viscosity and to dryaggregate during mixing of conventional asphalt mixtures, WMA reduces asphaltviscosity by either using water or some forms of organic additives or wax. Thereduction in viscosity still allows asphalt binder to coat adequately the aggregatesduring mixing. The reduction in mixture viscosity also improves its workabilityand allows for mix compaction at lower temperatures. FHWA has indentified fourmain additives that may be used in the production of WMA in the United States(D’Angelo et al., 2008):
. Aspha-min1, which is a manufactured synthetic zeolite with an internal content ofwater. During mixing, water is released and creates asphalt foam that improvesthe mix workability at lower temperatures.
. WAM-foam1, which consists of adding first a soft binder to the aggregate toallow for asphalt coating and then adding a hard binder in foam form by injectingcold water. During mixing, both binder grades combine to provide an asphalt bin-der with the desired rheological properties. Measurements of energy requirementsand air emission associated with WAM-foam have been conducted and were usedin this study (Lecomte et al., 2007).
. Sasobit1 is a wax-type product of coal gasification that dissolves in asphalt binderat high temperatures and results in a reduction in its viscosity during mixing. Thischemical process was reported to reduce mixing temperature by 10 to 30�C.
. Evotherm1 creates an asphalt emulsion when combined with the binder and isthen mixed with the aggregates at a reduced mixing temperature. A reductionin energy requirements associated with the production of this mixture of up to55% has been reported (Kristjansdottir et al., 2007).
While the long-term performance of warm-mix asphalt is still under evaluation,recent measurements at the National Center for Asphalt Technology (NCAT)showed that the rutting performance of warm-mix asphalt is comparable to hot-mixasphalt (Prowell et al., 2007). Volumetric properties did not appear to be affected bythe use of the aforementioned additives (D’Angelo et al., 2008). However, there is
242 M. Hassan
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
greater potential for moisture susceptibility due to lower mixing and compactiontemperature (Prowell et al., 2007). While field performance of WMA is a critical fac-tor that should receive careful consideration, the focus of this paper is given to theenvironmental and economic aspects of this technology. Based on the aforemen-tioned findings, the presented analysis assumes that WMA will perform comparablyto HMA.
Problem Formulation
As previously mentioned, a life-cycle inventory (LCI) was developed for a conven-tional asphalt mixture to provide a compilation of the energy requirements, materialinputs, and the emissions associated with its production and installation. Prior todevelop the LCI, one needs to define the system boundary, which defines the limitsof the life-cycle inventory. Figure 1 presents the system boundary for the developedlife-cycle inventory. As shown in this figure, the developed LCI considers energyand emissions associated with the manufacturing of asphalt binder, production ofaggregate, plant operations, and HMA placement (including compaction, HMAtransport to the site, milled asphalt transport, and site worker transport). However,the developed LCI does not consider energy, materials, and emissions associatedwith the manufacturing of equipment such as paver, refineries, and plant compo-nents. Energy and emissions associated with the production of fuels, known aspre-combustion, were also not included in the developed LCI. It is also noted thatthe presented LCIA neglected the environmental impacts of the WMA additivesgiven their small masses as compared to the functional unit considered in the analy-sis. For the purpose of this analysis, a typical surface mixture consisting of 5.2%asphalt binder, 61.6% coarse aggregate, and 33.2% fine aggregate, was assumed.
Data Sources
A wide range of published reports and databases were reviewed to identify energyand emission data for each process and activity defined as part of the system
Figure 1. Hot-mix asphalt system boundary.
Evaluation of the Environmental and Economic Impacts 243
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
boundary. Table 2 presents the general sources of data for each main process ident-ified in the life-cycle inventory. The U.S. EPA Fire Database compiles many emis-sion and energy data sources including the EPA’s AP 42, Section 11. As reportedby the EPA, emissions data for hot-mix asphalt were good to fair. The precisionwas higher for the main pollutants (i.e., CO, CO2, SO2, and NOx) than for the otherstreams. Energy consumption data were in agreement with other published sources(Zapata et al., 2005; Marceau et al. 2007).
Aggregate production was divided into two main categories: natural andcrushed aggregates. Manufacturing processes considered in natural aggregate pro-duction included excavation, crushing, screening, conveyor transfer, and storagepiles. On the other hand, production processes considered for crushed aggregatesincluded blasting, primary, secondary, and tertiary crushing, screening, conveyortransfer, and storage operations. Recorded measurements indicate that emissionfrom limestone and granite-processing operations are similar (Green Fuels, 2007).Therefore, emission data are applicable to both limestone and granite crushed aggre-gates. Adopted data were valid for uncontrolled processes in which wet suppressingtechnologies are not entirely used.
The production of asphalt binder is part of the petroleum refining process, ahigh energy-intensive manufacturing process (Zapata et al., 2005). Energy consump-tion during production is used in the extraction, hauling, heating, distillation, cool-ing, and final processing. During production of HMA, energy is used for heating ofasphalt binder, drying of aggregates, heating of the mixture, and transportation tothe construction site. Hot-mix asphalt requires a very high temperature during pro-duction (in excess of 150�C). Manufacturing processes considered in the productionof HMA included heating, drying, mixing, storage, and handling. This analysisassumed that a continuous drum mix plant with a natural gas-fired dryer is to beused. The most significant source of emission in the production of HMA is the rotarydrum dryer, which produces particle matters (PM), carbon monoxide, and a varietyof organic compounds. It is worth noting that energy consumption was divided interms of the type of fossil fuel used (i.e., natural gas, fuel, and coal) since the rateof fuel depletion differs in the BEES model from one type to the other.
Energy and Emission Data for Warm-Mix Asphalt
A review of the literature was conducted to quantify the energy and emission benefitsof WMA. Measurements of emission were recently conducted for a plant producing
Table 2. Sources for energy and emission data
Process Data type Source
Aggregate production Energy U.S. Census BureauAggregate production Emission U.S. EPA Fire DatabaseAsphalt manufacture Energy Blomberg et al.Asphalt manufacture Emission Blomberg et al.Asphalt production andinstallation
Energy Canadian Industry Programfor Energy Conservation
Asphalt production Emission U.S. EPA Fire Database
244 M. Hassan
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
warm-mix asphalt (WAM1-foam) and a conventional asphalt mixture in Italy(Lecomte et al., 2007). This was one of the first attempts to quantify energy andemissions benefits associated with WMA. This process required a wide array of mea-surements at different locations in the plant and using fume collection devices duringplacement and compaction. Energy consumption was also monitored for the twomixture types. Results of this study showed that energy consumption was reducedby 35% due to the use of WMA. This is in agreement with the findings of otherresearchers (Kristjansdottir et al., 2007). This energy reduction was associated withlowering the mixing temperature from 180�C for hot-mix asphalt production to125�C for warm-mix asphalt. Measurements showed that CO and NOx emissionswere reduced by 8% and 60%, respectively. While CO2 and SO2 emissions werereduced by 35% and 25%, respectively, dust emission was reduced by 25% to 30%.Benzene soluble components were up to 200 times higher for the conventionalasphalt mixture than WMA while volatile fractions were up to 6 times higher forHMA than for WMA. These findings were incorporated into a life-cycle inventorythat describes energy and emissions associated with WMA.
Cost Data
As previously mentioned, economic performance was established based on the initialcost associated with the production of one ton of conventional HMA and one ton ofWMA. As shown in Table 3, increase in cost due to the use of WMA relates to thecost of royalties ($15,000 for the first year, $5,000 per plant per year, and $0.33 permetric ton), and plant modifications ($50,000 for plant modification and instal-lation). These costs were distributed over a 20-year production period and overthe annual asphalt concrete plant production, which was assumed 127,000 metricton per year based on published data (Kristjansdottir et al., 2007).
Results and Analysis
Environmental Impacts
Figure 2 presents the normalized weighted impact factors for the conventional HMAand WMA. As previously indicated, a lower score indicates a more sustainable alter-native. As shown in this figure, HMA production has a pronounced effect on globalwarming due to the emission of carbon dioxide; criteria air pollutants due to theemission of particle matters; fossil fuel depletion due to the consumption of a large
Table 3. Cost data for conventional and warm-mix asphalt
Cost source Value per metric ton
Cost of conventional HMA $90.00Royalties fee and equipmentmodifications�
$0.41
WMA technology WAM foamTotal cost of WMA $90.41
�(Kristjansdottir et al., 2007).
Evaluation of the Environmental and Economic Impacts 245
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
amount of energy; smog formation due to the emission of nitrogen oxide and particlematters; and ecological toxicity due to the emission of carbon monoxide and nitrogenoxide. The ozone depletion index for HMA production was zero since this industrywas not found to release harmful chemicals to the ozone layer. As expected, WMAimproved the environmental performance of HMA in all these categories. However,it is worth noting that indicated indices relate to the total environmental impacts ofthe product (i.e., aggregate production, asphalt production, hot-mix asphalt pro-duction and placement, and transportation). While WMA is expected to improvethe HMA production category, it will not have a direct effect on the other processes.
Figure 3 presents the contribution of each of the four main processes (i.e., aggre-gate production, asphalt refinery, HMA production, and transportation and con-struction) to the environmental impacts of HMA. These values were obtained bycalculating the environmental damage for the four main processes using Eq. (1)and similar models adopted in the BEES model for each impact category. The con-tribution of each of the four main processes was then obtained by dividing theenvironmental damage calculated for each process by the total environmental dam-age calculated for each impact category. As shown in this figure, transportation andconstruction processes are the main source of harmful pollutants causing globalwarming and ecological toxicity since they emit a large amount of carbon dioxide,carbon monoxide, and nitrogen oxide. On the other hand, HMA production is themain source of energy consumption (51%) and the main source of pollutants causingair pollution, which arise from vehicle operations, materials handling, and combus-tion operations. Air pollution accounts for years of life lost and years lived with dis-ability. HMA production and transportation and construction processes appear tocontribute equally to smog formation. Based on these results, it appears that the
Figure 2. Environmental impacts of hot-mix asphalt and warm-mix asphalt.
246 M. Hassan
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
use of WMA would mainly benefit four main categories: global warming, fossil fueldepletion, criteria air pollutants, and smog formation. The percentage improvementsdue to the use of WMA on the four main categories expected to be influenced by theuse of this technology are shown in Figure 4. Warm-mix asphalt provides areduction of 24% on the air pollution impact of HMA and a reduction of 18% onfossil fuel consumption.
Figure 3. Contribution of main processes on the environmental impacts of HMA.
Figure 4. Percentage improvements due to the use of WMA.
Evaluation of the Environmental and Economic Impacts 247
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
Overall Performance
Figure 5 presents the weighted environmental and economic scores for HMA andWMA. As shown in this figure, the economic difference between the two alternativeswas marginal (49.9 for HMA vs. 50.1 for WMA). However, warm-mix asphalt per-formed better than hot-mix asphalt with respect to the overall environmentalimpacts (54.2 for HMA vs. 45.8 for WMA). This represents a reduction of 15%on the environment impacts of HMA. Assuming a weight of 50% for economic fac-tors and 50% for environmental factors, the overall performance score of HMA was52.0 as compared with 48.0 for warm-mix asphalt; a lower overall score for WMAreflects a technology that is more environmentally friendly while being economicallycompetitive. This is considered a positive improvement and support furtherevaluation and possible adoption of this technology.
While warm-mix asphalt is expected to improve the hot-mix asphalt productioncategory, it will not have a direct effect on the other processes. In order to achievefurther improvement of the sustainability of HMA production and constructionactivities, it will be necessary to consider additional technologies that would lowerthe environmental impacts of aggregate production, asphalt refinery, and transpor-tation and construction activities. Technologies such as low-emission and fuel-efficient construction equipments and use of reclaimed asphalt pavement appearparticularly promising. For instance, hybrid technology was recently introduced topower heavy vehicles such as trucks and construction equipments. This technologyis expected to improve fuel efficiency by as much as 35% (Green Fuel, 2007). Moredetails for sustainable construction alternatives for flexible pavement constructionhave presented elsewhere (Hassan, 2008).
Summary and Conclusions
The use of WMA has received considerable attention in recent years to reduce energyconsumption during hot-mix asphalt production and to reduce air emissions. In spite
Figure 5. Environmental and economic performances of HMA and WMA.
248 M. Hassan
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
of these promising benefits, the promotion of warm-mix asphalt based on a singlefactor such as reduced energy consumption during production or reduced emissions,does not provide a realistic and complete evaluation of this technology and may omitcritical environmental factors that should be considered in the decision-making pro-cess. The objective of this paper was to determine the life-cycle assessment of WMAtechnology as compared with a conventional HMA mixture. Based on the analysisconducted, the following conclusions may be drawn:
. The use of WMA affects three main environmental factors: air pollution, fossilfuel depletion and smog formation. WMA provides a reduction of 24% on theair pollution impact of HMA and a reduction of 18% on fossil fuel consumption.It also reduces smog formation by 10%.
. The use of WMA is estimated to provide a reduction of 15% on the environmentimpacts of HMA. Assuming a weight of 50% for economic factors and 50% forenvironmental factors, the overall performance score of HMA was 52.0 ascompared to 48.0 for WMA.
. While warm-mix asphalt is expected to improve the HMA production category, itwill not have a direct effect on the other three main processes taking place duringproduction of hot-mix asphalt: aggregate production, asphalt refinery, and trans-portation and construction processes.
. The use of WMA is considered a positive improvement and support further evalu-ation and possible implementation of this technology. However, in order toachieve further improvement of the sustainability of HMA production and con-struction activities, it will be necessary to consider additional technologies suchas low-emission and fuel-efficient construction equipments and use of reclaimedasphalt pavement.
While a general framework is presented in this paper for environmental analysisof WMA using life-cycle assessment, required data are currently available from alimited number of sources. Therefore, consistency and completeness of the dataand the assumptions made throughout the LCA process need to be evaluated. Basedon the results presented in this study, further research is recommended to considerfactors omitted in the analysis such as maintenance and rehabilitation activities,end-of-life recycling options, and variation of adopted data with project size andlocation.
References
Blomberg, T. (1999). Partial life cycle inventory or ‘‘Eco-profile’’ for paving grade bitumen.Eurobitume Report 99=007.
Canadian Industry Program for Energy Conservation. (2005). Road rehabilitation energyreduction guide for Canadian road builders. Report No. TE26.R62 2005, Ottawa, ON.
D’Angelo, J., Harm, E., Bartoszek, J., Baumgardner, G., Corrigan, M., Cowset, J., Harman,T., Jamshidi, M., Jones, W., Newcomb, D., Prowell, B., Sines, R., & Yeaton, B. (2008).Warm-mix asphalt: European practice. Report No. FHWA-PL-08-007, Alexandria, VA.
Green Fuel Drives Construction. (2007). Available at http://www.volvo.com/constructione-quipment/.
Hassan, M. M. (2008). A Framework for the assessment and construction of sustainableflexible pavements. Journal of Green Building, 3(3), 1–11.
Heijungs, R. & Suh, S. (2002). The computational structure of life cycle assessment. Boston:Kluwer Academic Publishers.
Evaluation of the Environmental and Economic Impacts 249
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
Hurley, G. C. & Prowell, B. D. (2006). Evaluation of potential processes for use in warm mixasphalt. Journal of the Association of Asphalt Paving Technologists, 75, 41–90.
International Organization for Standardization. (1997). Environmental management—lifecycle assessment—principals and framework, ISO 14040.
Johnston, A., Da Silva, M., Soeymani, H., & Yeung, C. K. (2006). An early evaluation of theinitial Canadian experience with warm asphalt mix. 2006 Annual General Conference ofthe Canadian Society for Civil Engineering, Calgary, Alberta, Canada.
Kristjansdottir, O., Muench, S. T., Michael, L., & Burke, G. (2007). Assessing the potentialfor warm mix asphalt technology adoption. Transportation Research Record: Journal ofthe Transportation Research Board, 2040, 91–99.
Lecomte, M., Deygout, F., & Menetti, A. (2007, September). Emission and occupationalexposure at lower asphalt production and laying temperatures. Shell Bitumen. Presentedat the 23rd World Road Congress, Paris.
Lippiat, B. (2007). Building for Environmental and Economic Sustainability (BEES) TechnicalManual and User Guide. Wellington, ON: National Institute of Standards andTechnology.
Marceau, M. L., Nisbet, M., & Van Geem, M. (2007). Life cycle inventory of Portland cementconcrete. Report No. PCA R&D Serial 3011, Skokie, IL.
Newcomb, D. (2005). Warm mix: The wave of the Future? HMAT, 10(4), 33–36.Prowell, B. D., Hurley, G. C., & Crews, E. (2007, January). Field performance of warm-mix
asphalt at the NCAT test track. Paper No. 07-2514, Presented at the 86th TransportationResearch Board Annual Meeting, Washington, D.C.
Rebitzer, G., Ekvall, T., Frischknecht, R., Hunkler, D., Norris, T., Rydberg, W., Suh, S.,Weidema, B., & Pennington, D. (2004). Life cycle assessment, Part 1: Framework, goaland scope definition, inventory analysis, and applications. Environment International,30, 701–720.
U.S. Census Bureau. (2004). Construction sand and gravel—mining: 2002. Report No. ECO2-211-212321, U.S. Department of Commerce.
U.S. Environmental Protection Agency (EPA). (2004). Factor Information Retrieval (FIRE)Data System Version 6.25, Research Triangle Park, NC: Office of Air Quality Planningand Standards.
Zapata, P. & Gambatese, J. (2005). Energy consumption of asphalt and reinforced concretepavement materials and construction. Journal of Infrastructure Systems, ASCE, 11(1),9–19.
250 M. Hassan
Dow
nloa
ded
by [
Uni
vers
ite D
e Pa
ris
1] a
t 23:
36 2
8 A
ugus
t 201
3
