hidden ecoligical potentials in the production of materials for swiss road pavement

Hidden Ecological Potentials in the Production of Materials for Swiss Road PavementsFlorian Gschösser1; Holger Wallbaum, Ph.D.2; and Michael E. Boesch, Ph.D.3Downloaded from by SOUTH CHINA UNIVERSITY OF on 07/10/13. Copyright ASCE. For personal use only; all rights reserved.Abstract: Sustainability has become a major concern in the field of civil infrastructures in recent years. Developing road construction projects with lower ecological impacts over a project’s entire life cycle can help in making road infrastructure contribute to sustainable development. This study focuses on the ecological potentials in the production of road materials used in Swiss road pavements. The environmental assessment was performed using a cradle-to-gate life-cycle assessment (LCA) approach in which all processes from the raw material extraction to the finished product were considered. The comparison of the results of the best-case asphalt pavement and the standard asphalt pavement for Swiss highway construction shows ecological potentials of up to 55%. Use of the best-case concrete pavement lowers the environmental impact by up to 53% in comparison to the worst-case concrete pavement for Swiss highways. Concerning composite pavements, the best-case variant offers an ecological potential 38% higher than the standard pavement. DOI: 10.1061/(ASCE)ME .1943-5479.0000077. © 2012 American Society of Civil Engineers. CE Database subject headings: Life cycles; Pavements; Sustainable development; Switzerland; Ecosystems; Construction materials. Author keywords: Life cycles; Pavements; Sustainable development; Switzerland.IntroductionThe reduction of overall environmental pollution is one of the main aims of sustainable development. Therefore, the European Union aspires to reduce emissions, for example, reducing CO2 emissions by 20% by 2020 in comparison to the emissions of 1990. In 2006, transport caused (without taking the infrastructure into account) 24.6% of the carbon emissions of the EU-27 countries (European Commission 2009), with fuel consumption encompassing the biggest part of the transport emissions. Therefore, sustainability research largely focuses on energy-efficient transport vehicles. However, optimizing road infrastructure in regard to the environmental impact over the road’s whole life cycle (production, construction, use, maintenance) contributes to sustainable development. Several life-cycle assessments (LCAs), conducted in the first decade of this millennium, demonstrated the ecological usability and properties of the paving materials, asphalt and concrete, or of pavements using the two materials as a wearing course (Mroueh et al. 2000; Stripple 2001; Park et al. 2003; Treloar et al. 2004; Gambatese and Rajendran 2005; Zapata and Gambatese 2005;Ph.D. Candidate, Chair of Sustainable Construction, Institute of Construction and Infrastructure Management , Dept. Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich 8093, Switzerland (corresponding author). E-mail: gschoesser@ibi.baug.ethz.ch 2 Assistant Professor, Chair of Sustainable Construction, Institute of Construction and Infrastructure Management, Dept. Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich 8093, Switzerland. E-mail: wallbaum@ibi.baug.ethz.ch 3 Research Associate, Chair of Ecological Systems Design, Institute of Environmental Engineering, Dept. Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich 8093, Switzerland. E-mail: michael .boesch@ifu.baug.ethz.ch Note. This manuscript was submitted on October 29, 2010; approved on June 8, 2011; published online on June 10, 2011. Discussion period open until June 1, 2012; separate discussions must be submitted for individual papers. This paper is part of the Journal of Management in Engineering, Vol. 28, No. 1, January 1, 2012. ©ASCE, ISSN 0742-597X/2012/1-13–21/ $25.00.1Rajendran and Gambatese 2007; Zhang et al. 2009; Cass and Mukherjee 2010; Zhang et al. 2010). These LCAs can analyze different road construction types or road materials and can consider either the whole life cycle or only single life-cycle phases of the materials. The aim of these studies was to analyze the standard procedures for the processes of the different life-cycle phases without taking a deeper look into the processes of the production, construction, maintenance, and use phases and the ecological potentials they offer. This paper analyzes the production processes for the materials used in representative Swiss road pavements at the national level (highways—traffic-load class T6) and for cantonal roads (traffic-load classes T5 and T4) to quantify ecological improvement potentials by conducting cradle-to-gate life-cycle assessments. The impact categories examined in the LCA studies are climate change [global warming potential (GWP), GWP 100], cumulative energy demand (CED); (primary energy consumption from nonrenewable resources), and the method of ecological scarcity 2006. The system boundaries of an LCA study define the processes and products that are included in the analysis. This study analyzes the production of all materials needed for 1 m2 of road pavement, which is the functional unit of this LCA study (Fig. 1). The present cradle-to-gate LCA study (Fig. 2) combines the respective data according to the amount of materials needed for 1 m2 of road pavement. The aim of this paper is to identify the ecological potentials given by the production processes of road materials for road pavements. It does not nominate the “most ecological” pavement type for each road category.Road PavementsRoad pavements can be grouped into three main categories: asphalt pavements, concrete pavements, and composite pavements. The characteristics of the respective pavement types are explained in this section and are shown in Fig. 3.JOURNAL OF MANAGEMENT IN ENGINEERING © ASCE / JANUARY 2012 / 13J. Manage. Eng. 2012.28:13-21.Functional Unit: 1 m2 of Road Pavementplates. To avoid material shifting in the subbase layer, modern concrete paving layers are placed on an interlayer of hot mix asphalt (Werner 2004; Holcim Schweiz AG 2008). The concrete paving and the interlayer are set atop a subbase layer, which can consist of different materials. Composite PavementsFig. 1. Functional unit and analyzed pavement constructionDownloaded from by SOUTH CHINA UNIVERSITY OF on 07/10/13. Copyright ASCE. For personal use only; all rights reserved.Composite pavement consists of an asphalt wearing course placed on a concrete layer. The concrete layer is continuously reinforced and features an increased thickness compared to the pure concrete pavement. As for concrete pavements, an interlayer and a subbase support the underlay for the composite layers. Subbases Subbase layers form the foundation of all three pavement types. The material and the thickness of the subbase layer generally depend on the pavement type, the traffic-load class of the road, and the wearing capacity of the subgrade on which the road pavement is placed (VSS 1997). According to the current practice defined by the Swiss Federal Roads Office (ASTRA), road pavements of the traffic-load class T6 can only be placed on subgrades offering a high wearing capacity (wearing-capacity classes S3 and S4) (VSS 1997). Similarly, because all 26 Swiss cantons have different standards and rules concerning the construction of cantonal roads, only pavements placed on subgrades of the S3 and S4 wearing-capacity classes were analyzed. National roads with concrete or composite pavements use round or crushed gravel and hydraulically stabilized mixtures, as subbase materials (VSS 1997). Subbases of cantonal roads with concrete pavement consist of either round or crushed gravel. Asphalt pavements of all three categories contain either hot or cold asphaltic mixture subbases (cold bituminous bound mixture), hydraulically stabilized mixtures, and crushed or round gravel. Analyzed PavementsFig. 2. Cradle-to-gate approachAsphalt Pavements Standard asphalt pavement consists of an asphalt concrete wearing course, base course, and road base [Swiss Association of Road and Transportation Experts (VSS) 2008]. These three asphalt layers are placed on a subbase layer, which can consist of different materials. Concrete Pavements In standard road construction applied in Switzerland, a concrete paving layer consists of 5 × 5 m unreinforced plates connected to each other by anchors every 50 cm on all sides. Waterproof joint compounds fill the appearing joints between the plates (Holcim Schweiz AG 2008). In Switzerland, it has become state of the art to apply an exposed aggregate layer atop the bottom concreteThe pavement types analyzed in this study are shown in Fig. 4. The pavement and material combinations were selected on the basis of expert opinions, standards, and guidelines of the Swiss Federal Roads Office (2007) and standards of two selected cantonal civil engineering offices (Canton Aargau 2008; Canton Zurich 2008). The analyzed pavements and materials were selected to be representative for the Swiss national and cantonal road network.Wearing Course Base Course Road BaseAsphalt Concrete Wearing Course Asphalt Concrete Base Course Asphalt Concrete Road Base Asphalt Concrete Subbase Cold Mixture Asphalt Subbase Hydraulically Bound Subbase Unbound SubbaseWearing CourseExposed Aggregate Concrete (Top Concrete Layer) Bottom Concrete Layer Asphalt Concrete Road Base Asphalt Concrete SubbaseWearing CourseAsphalt Concrete Wearing CourseConcrete LayerConcrete LayerContinuously Reinforced Concrete LayerInterlayerInterlayerSubbaseAsphalt Concrete Road Base Asphalt Concrete SubbaseSubbaseHydraulically Bound Subbase Unbound SubbaseSubbaseHydraulically Bound Subbase Unbound Subbase(a)(b)(c)Fig. 3. General structure of Swiss road pavements: (a) asphalt pavement for Swiss cantonal and national roads; (b) concrete pavement for Swiss cantonal and national roads; (c) composite pavement for Swiss national roads14 / JOURNAL OF MANAGEMENT IN ENGINEERING © ASCE / JANUARY 2012J. Manage. Eng. 2012.28:13-21.Asphalt Pavements T6 Wearing Course: 30 mm AC 8 H or 30 mm AC MR 8 ASTRA T5 Wearing Course: 30 mm AC 8 S or 30 mm AC MR 8 T4 Wearing Course: 30 mm AC 8 S or 30 mm AC MR 8 T6 Wearing Course: 50 mm EA ConcreteConcrete Pavements T5 Wearing Course: 50 mm EA Concrete T4 Wearing Course: 50 mm EA ConcreteComposite Pavements T6 Wearing Course: 30 mm AC 8 H or 30 mm AC MR 8 ASTRABase Course & Road Base: 70 mm AC B 22 H 80 mm AC T 22 H or 80 mm AC EME 22 C1Base Course & Road Base: 60 mm AC B 16 S 60 mm AC T 22 SRoad Base: 90 mm AC T 22 SConcrete Layer: 190 mm Bottom Conc.Concrete Layer: 150 mm Bottom Conc.Concrete Layer: 120 mm Bottom Conc.Concrete Layer: 240 mm Bottom Conc.Interlayer: 80 mm AC T 22 N or 100 mm AC F 22Interlayer: 80 mm AC T 22 N or 100 mm AC F 22Interlayer: 80 mm AC T 22 N or 100 mm AC F 22Interlayer: 80 mm AC T 22 N or 100 mm AC F 22Downloaded from by SOUTH CHINA UNIVERSITY OF on 07/10/13. Copyright ASCE. For personal use only; all rights reserved.80 mm AC EME 22 C2Subbase: S3: 110 mm AC F 22 200 mm Round Gravel or 160 mm Crushed Gravel or 160 mm AC F 22 or 132 mm BSB 200 mm Round Gravel or 160 mm Crushed Gravel or 192 mm BSB or 160 mm Hydr. Bound Mixture 150 mm Round Gravel or 120 mm Crushed Gravel or 160 mm Hydr. Bound Mixture S4: 110 mm AC F 22 or 132 mm BSB or 160 mm Hydr. Bound MixtureSubbase: S3: 90 mm AC F 32 200 mm Round Gravel or 160 mm Crushed Gravel or 140 mm AC F 32 or 108 mm BSB 200 mm Round Gravel or 160 mm Crushed Gravel or 168 mm BSB or 160 mm Hydr. Bound Mixture 150 mm Round Gravel or 120 mm Crushed Gravel or 200 mm Hydr. Bound Mixture S4: 90 mm AC F 32 or 108 mm BSB or 160 mm Hydr. Bound MixtureSubbase: S3: 70 mm AC F 32 200 mm Round Gravel or 160 mm Crushed Gravel or 120 mm AC F 32 or 84 mm BSB 200 mm Round Gravel or 160 mm Crushed Gravel or 144 mm BSB or 170 mm Hydr. Bound MixtureSubbase: S3: 150 mm Hydr. Bound Mixture or 150 mm Round Gravel or 120 mm Crushed GravelSubbase: S3: 150 mm Round Gravel or 120 mm Crushed GravelSubbase: S3: 150 mm Round Gravel or 120 mm Crushed GravelSubbase: S3: 150 mm Hydr. Bound Mixture or 150 mm Round Gravel or 120 mm Crushed GravelS4: 80 mm AC F 32 or 96 mm BSB or 160 mm Hydr. Bound MixtureS4: No SubbaseS4: No SubbaseS4: No SubbaseS4: No SubbaseNote: AC = asphalt concrete, 8, 16, 22, 32, upper face value of the largest used mineral aggregate; MR = rough-textured wearing course; EA = exposed aggregate; B = base course; T = road base; F = subbase; EME = high-modulus-asphalt; C1 = very high resistance; C2 = excellent resistance; BSB = cold bituminous bound subbase; N = mixture type for normal loads; S = mixture type for strong loads; H = mixture type for high loads.Fig. 4. Analyzed road pavementsLife-Cycle AssessmentMethod A life-cycle assessment is a method used to analyze the environmental impact factors of products and services (DIN EN ISO 14040:2006 2006). This study applies a cradle-to-gate approach that comprises all environmental impacts from the primary resource extraction to the finished product. It also uses the cutoff rule concerning the allocation of recycled materials (i.e., for the analysis of the production processes, the upgrading of usable recycling materials is assumed to be part of the previous life-cycle system). Hence, the first process included in the analyzed system is the transport from the recycling pool to the place of production.Scope and Functional Unit All inputs and outputs analyzed for the evaluation of environmental impact factors are related to a functional unit (DIN EN ISO 14040:2006 2006). The functional unit chosen for the cradle-togate LCA of road pavement in this study is defined as “1 m2 of road pavement.” The analyzed products were asphalt, concrete, and composite road pavements used for road categories T4, T5, and T6. Life Cycle Inventory The life cycle inventory (LCI) quantifies relevant inputs and outputs of the analyzed product system. The LCIs for the material production itself analyzed different scenarios for the production ofJOURNAL OF MANAGEMENT IN ENGINEERING © ASCE / JANUARY 2012 / 15J. Manage. Eng. 2012.28:13-21.Asphalt Mixtures Material Options for Asphalt Layers Wearing Course (WC) (WC 1) AC 8 S (WC 2) AC 8 H (WC 3) AC MR 8 (WC 4) AC MR 8 ASTRA Base Course (BC) (BC 1) AC B 16 S (BC 2) AC B 22 H (RB 1) AC T 22 N (RB 2) AC T 22 S Road Base (RB) (RB 3) AC T 22 H (RB 4) AC EME 22 C1 (RB 5) AC EME 22 C2 Asphalt Subbase (ASB) (ASB 1) AC F 22 (ASB 2) AC F 32Production Options for Asphalt Mixtures Standard Production (ASP) Recycling Scenarios for Asphalt Mixtures No Recycling (NR) Average Recycling (AR) Maximum Recycling (MR) Optimized Production (AOP)Downloaded from by SOUTH CHINA UNIVERSITY OF on 07/10/13. Copyright ASCE. For personal use only; all rights reserved.Concrete Mixtures Cement Options for Concrete Layers Exposed Aggregate Concrete (EAC) (C1) CEM I (C2) CEM II/ A-S (C3) CEM II/ A-LL (C4) CEM II/ B-T (C1) CEM I (C2) CEM II/ A-S Bottom Concrete (BC) (C3) CEM II/ A-LL (C4) CEM II/ B-TProduction Options for Concrete Mixtures Standard Production (CSP) Recycling Scenarios for Concrete Mixtures 0 % (R0) Subbase Mixtures Material Options for Subbase Layers Unbound Subbases (USB) Production Options for HSB and BSB Central Mixing at Plant (CP) Recycling Scenarios for HSB and BSB Primary Material (PM) Secondary Material (SM) Central Mixing at Site (CS) In-Situ Mixing (IS) Hydraulically Bound Subbases (HSB) Bituminous Bound Subbases (BSB) 25 % (R25) 50 % (R50) 75 % (R75) 100 % (R100)Fig. 5. Production and recycling scenarios (ASTRA 2007; Canton Aargau 2008; Canton Zurich 2008)1 m3 of asphalt, concrete, and subbase mixtures. Gschösser et al. (2011) lists the LCI data for all road materials and their different production scenarios used in this study. Fig. 5 shows all options for the materials and the production and recycling scenarios analyzed for the different road materials. Fig. 5 demonstrates that an optimized production (AOP) variant was analyzed for asphalt production in addition to standard production (ASP). Furthermore, three different recycling scenarios [no recycling (NR), average recycling (AR), and maximum recycling (MR)] were analyzed. Concrete mixtures for road pavements contained four different cement types (C1–C4). For the production of the concrete mixtures, the standard production (CSP) scenario was analyzed. Bottom concrete mixtures contained five different shares of recycled concrete reused as mineral aggregates within the mixture (R0–R100). In addition to the hot asphalt mixture subbases (ASB), unbound (USB), hydraulically bound (HSB), and bituminous bound subbase (BSB) mixtures were analyzed. The production of the bound subbases occurred centrally in a stationary plant (CP) or a mobile mixing plant on site (CS). Furthermore, the bound subbases could be produced in situ (IS; i.e., directly in place). A bound subbase layer can use either primary (PM) or secondary (recycled) aggregates (SM). These data for material production processes were combined according to the pavements listed in Fig. 4. Fig. 6 shows the main processes required for the production of ‘1 m2 of road pavement.Impact Categories The impact categories used to evaluate the environmental impact of the production of the road construction materials were the global warming potential 2007, CED, and the method of ecological scarcity 2,006. These categories are briefly described in this section. Global Warming Potential 2007 The Intergovernmental Panel on Climate Change (IPCC) GWP indicator includes all substances that contribute to climate change according to the guidelines of the IPCC (Forster et al. 2007). The atmospheric lifetime of a substance and the efficiency of the substance as a greenhouse gas are considered to determine the GWP. The GWP of a greenhouse gas is measured relative to the same mass of CO2 , yielding kg CO2 equivalents (eq). The GWPs can be determined for different time periods (20, 100, and 500 years). The 20-year period is relevant because a limitation of the gradient of change in temperature is necessary to ensure the adaptation ability of ecosystems. The 500-year period is approximately equivalent with the integration until infinity, which permits monitoring of the overall change in temperature. This study evaluates the GWP for a time span of 100 years in accordance with the requirements of the Kyoto protocol. CED The cumulative energy demand describes the consumption of fossil, nuclear, and renewable energy sources over the life cycle of a good or service. This indicator involves the direct uses and16 / JOURNAL OF MANAGEMENT IN ENGINEERING © ASCE / JANUARY 2012J. Manage. Eng. 2012.28:13-21.Resources, Material, EnergyUpstream Chain Recycled Aggregates Upstream Chain Additives / Auxiliary Supplies Upstream Chain Bitumen Binders Unbound SubbasesUpstream Chain Hydraulic BinderUpstream Chain SteelUpstream Chain Natural AggregatesWaterDownloaded from by SOUTH CHINA UNIVERSITY OF on 07/10/13. Copyright ASCE. For personal use only; all rights reserved.Concrete / Hydraulically Stabilized Mixture ProductionAsphalt / Bituminous Bound Mixture ProductionConcrete / Composite Pavements Hydraulically Stabilized SubbasesRoad ConstructionAll Pavement TypesSystem BoundaryAir, Water, Soil Emissions1 m2 of Road PavementFig. 6. Process model for the production of materials for road pavementsthe indirect or gray consumption of energy because of the use of, for example, gravel or concrete as construction or raw materials (Boustead and Hancock 1979). The CED indicator used in this study was “CED, nonrenewable [megajoule-equivalents (MJ-eq)],” which considered fossil, nuclear, and biomass energy from primary forests.Ecological Scarcity The Swiss ecological scarcity method weights environmental impact factors (i.e., pollutant emissions and resource consumption) by applying “eco-factors.” The eco-factors of a substance are derived from environmental law or corresponding political targets. The more the current level of emissions or consumption of resourcesFig. 7. Normalized results of the impact assessment of T6 pavements with S3 subbases : (1) worst-case pavement; (2) standard pavement; (3) bestcase pavement in regard to the GWP indicator; (4) best-case pavement in regard to the CED and ecological scarcity indicatorJOURNAL OF MANAGEMENT IN ENGINEERING © ASCE / JANUARY 2012 / 17J. Manage. Eng. 2012.28:13-21.exceeds the environmental protection target, the higher the ecofactor becomes. The eco-factors are expressed as eco-points (eco-Pt) [or, in German, Umweltbelastungspunkte (UBP)] per functional unit (Frischknecht et al. 2009). Sensitivity Analysis To reduce the amount of different material compilations, a sensitivity analysis was performed by analyzing combinations for the three layers on top of the pavement and the subbase layers separately. Thus, on the basis of this sensitivity analysis, four different pavement samples for each pavement type, traffic-load class, and wearing-capacity class were analyzed in greater detail: worst-case pavement (1), standard pavement (2), best-case pavement in regard to the GWP indicator (3), and best-case pavement in regard to the CED and ecological scarcity indicator (4). The worst-case pavement was selected because of the highest impact regarding the ecological scarcity indicator.Downloaded from by SOUTH CHINA UNIVERSITY OF on 07/10/13. Copyright ASCE. For personal use only; all rights reserved.ResultsFig. 7 shows the normalized results for the traffic-load class T6 and the wearing-capacity class S3. Results for the pavements in category T6-S4 show a correlation to the results for the categories T6 and S3. Thus, no figure for the normalized results of T6-S4 is shown. Fig. 7 shows that regarding national roads (category T6), the production of asphalt pavements generally entails lower impactsconcerning the global warming potential and the ecological scarcity indicator than the production of concrete and composite pavements. However, the nonrenewable cumulative energy demand for the production of concrete pavements is lower than for the production of asphalt pavements (e.g., approximately 30%) when comparing standard concrete pavement [Fig. 7, Concrete Pavements, (2)] with standard asphalt pavement [Fig. 7, Asphalt Pavements, (2)]. The best-case composite pavements [Fig. 7, Composite Pavements, (3) and (4)] have a higher impact in reference to the CED nonrenewable indicator compared to the best-case asphalt pavements [Fig. 7, Asphalt Pavements, (3) and (4)]. Fig. 7 also demonstrates the influence of recycling material. Concrete and composite pavements applying recycling bottom concrete mixtures [Fig. 7, Concrete Pavements, (2) and (4); Composite Pavements (2) and (4)] have a lower impact concerning the ecological scarcity indicator and have the same impact for the CED indicator; however, they have a higher impact regarding the global warming potential indicator compared to the pavements containing primary aggregates [Fig. 7, Concrete Pavements, (1) and (3); Composite Pavements (1) and (3)]. In addition, for asphalt pavements, optimized production conditions [Fig. 7, Asphalt Pavements, (3) and (4)] lower the global warming potential by up to 50% compared to the worst-case pavement [Fig. 7, Asphalt Pavements, (1)] and by up to 40% compared to standard pavement [Fig. 7, Asphalt Pavements, (2)]. In regard to concrete and composite pavements, Fig. 7 also shows the influence of the applied cement type for the concrete mixtures. For example, the impact concerning the global warming potential indicator of pavements with concrete mixtures using CEM II/BFig. 8. Normalized results of impact assessment of T5 pavements with S4 subbases: (1) worst-case pavement; (2) standard pavement; (3) best-case pavement in regard to the GWP indicator; (4) best-case pavement in regard to the CED and ecological scarcity indicator18 / JOURNAL OF MANAGEMENT IN ENGINEERING © ASCE / JANUARY 2012J. Manage. Eng. 2012.28:13-21.Downloaded from by SOUTH CHINA UNIVERSITY OF on 07/10/13. Copyright ASCE. For personal use only; all rights reserved.[Fig. 7, Concrete Pavements, (3) and (4); Composite Pavements (3) and (4)] is up to 40% lower than for pavements applying mixtures with CEM I [Fig. 7, Concrete Pavements, (1) and (2); Composite Pavements (1) and (2)]. Fig. 8 shows the normalized results for the traffic-load class T5 and the wearing-capacity class S4 representatively for all cantonal road pavements (T5 and T4). The relationship among different pavement types for cantonal roads is almost identical to the relationship among the pavements for national roads. Table 1 compares the impacts of the standard and the best-case pavements in regard to the three analyzed indicators. The comparisons in Table 1 show potentials concerning the three indicators of up to 59% for asphalt pavements, 54% for concrete pavements, and 35% for composite pavements. Monte Carlo Simulation To reduce the amount of different material compilations, a sensitivity analysis was performed by analyzing combinations for theTable 1. Potentials Given for T4, T5, and T6 Road Constructions IPCC GWP 100a (kg-CO2 -eq=m2 ) CED nonrenewable (MJ-eq=m2 )three layers on top of the pavement and the subbase layers separately. Thus, on the basis of this sensitivity analysis, the analyzed pavements for the different traffic-load and wearing-capacity classes were obtained. To determine the reliability of the results in Table 1, a Monte Carlo simulation comparing the standard and the best-case asphalt, concrete, and composite pavements of the categories T6 and S3 was performed. This simulation chose a random value within the uncertainty range defined for every inventory entry (Ries 2003). For each pavement comparison, 1,000 Monte Carlo runs were performed to form a sufficient uncertainty distribution. Fig. 9 indicates the probability that the impact concerning the three indicators of the best-case pavement is lower or higher compared to the standard pavement. The comparison of the best-case variants with the standard pavements shows that the results regarding all three indicators were stable. For example, the probability that the impact regarding the GWP indicator of the standard asphalt pavement was lower than the impact of the best-case asphaltEcological scarcity (1; 000 Pt=m2 ) Asphalt pavementsIPCC GWP 100a (kg-CO2 -eq=m2 )CED nonrenewable Ecological scarcity (MJ-eq=m2 ) (1; 000 Pt=m2 )T6 Standard pavement Best case pavement Reduction potential T5 Standard pavement Best case pavement Reduction potential T4 Standard pavement Best case pavement Reduction potential 27.4 23.7 13% 37.7 30.0 20% 40.1 31.5 21%S3 1,760 784 55% S3 1,743 745 57% S3 1,204 516 57% 49,030 21,481 56% Concrete pavements 27.3 23.1 15% 62,232 29,033 53% 37.0 27.7 25% 64,442 31,304 51% 40.3 29.2 28%S4 1,225 772 37% S4 1,728 733 58% S4 1,238 513 59% 38,223 21,133 45% 52,887 27,642 48% 52,288 29,912 43%T6 Standard pavement Best case pavement Reduction potential T5 Standard pavement Best case pavement Reduction potential T4 Standard pavement Best case pavement Reduction potential 73.2 54.7 25% 82.5 62.2 25% 111.3 72.8 35%S3 1,265 599 53% S3 1,030 514 50% S3 978 470 52% 83,504 48,621 42% Composite pavements 72.6 53.8 26% 83,504 53,326 36% 81.8 61.2 25% 93,879 62,072 34% 101.8 71.7 30%S4 1,202 566 53% S4 1,016 488 52% S4 964 444 54% 66,592 40,430 39% 74,159 45,136 39% 78,874 51,833 34%T6 Standard pavement Best case pavement Reduction potential132.5 94.5 29%S3 1,755 1,090 38%123,161 91,620 26%123.0 93.4 24%S4 1,692 1,057 37%10,8155 81,382 25%JOURNAL OF MANAGEMENT IN ENGINEERING © ASCE / JANUARY 2012 / 19J. Manage. Eng. 2012.28:13-21.。