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Environmental assessment of road construction and maintenance policies using LCA
Transportation Research Part D 29 (2014) 56–65
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Transportation Research Part D journal homepage: www.elsevier.com/locate/trd
Environmental assessment of road construction and maintenance policies using LCA A. Jullien, M. Dauvergne, V. Cerezo ⇑ LUNAM Université, Ifsttar, AME-EASE, Route de Bouaye, CS4, F-44341 Bouguenais, EU, France
a r t i c l e
i n f o
Keywords: Roads Pavements LCA Environment Maintenance strategy
a b s t r a c t This paper proposes an evaluation of pavement maintenance policies relative to their initial construction, through a Life Cycle Assessment (LCA) and in accordance with the framework established by the Society of Environmental Toxicology and Chemistry as well as in the ISO 14040 Standard. The respective influence of initial construction and maintenance operations is investigated for both asphalt concrete and cement concrete pavement structures. Several case studies are analysed using a specific method and tool, called ECORCE (French acronym for ‘‘ECO-comparator applied to Road Construction and Maintenance’’), dedicated to road pavement LCA. ECORCE takes into account the materials production, mixing and laying processes, in addition to their transport between the production site and the jobsite. This environmental assessment is based on the principles underlying the life cycle assessment methodology. The chosen Functional Unit only considers the service to road users; heavily-trafficked French motorway structures are thus described over a 30year service period. A set of overall indicators, consisting of raw material and energy consumption, global warming potential and eutrophication potential, is then calculated for two case studies. These environmental indicators highlight the ability to assess pavement designs along with two maintenance policies considered for each case studied. Results are thus able to expose the relative influence of maintenance (1/3 of the entire life cycle). In conclusion, environmental design principles to achieve a reduction in environmental loads are discussed in considering the entire road life cycle. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Over the last several decades, a considerable amount of research has been aimed at improving the mechanical characteristics of materials and road pavements, in taking into account traffic requirements and service times for the initial construction. Moreover, road-related environmental impacts have been traditionally linked to their territories and investigated using Environmental Impact Assessment (EIA) techniques, in accordance with the 1976 French law No. 76-663. Until the recent past, these environmental constraints had been widespread in regulations, with an emphasis on discharges into watercourses. Nowadays, environmental impact assessments are expected to be quantified so as to improve facility owners’ decision-making. EU countries have also decided to significantly decrease greenhouse gas emissions. In France, a 2007 public debate, known as the ‘‘Grenelle roundtable’’, was held on national environmental issues. The EIA protocol was revised in 2010 by law (No. 2010-788), requiring energy consumption and impacts of road construction to be assessed at the project level. As ⇑ Corresponding author. Tel.: +33 240845937. E-mail address: [email protected] (V. Cerezo). http://dx.doi.org/10.1016/j.trd.2014.03.006 1361-9209/Ó 2014 Elsevier Ltd. All rights reserved.
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regards public works, this revision has gradually led to the inclusion of environmental criteria in public-sector calls for tender, thus increasing recycling and the use of material production/laying techniques featuring energy consumption mitigation. In this context, a methodology that takes into account within the same framework both the roads code of practice and LCA (Life Cycle Assessment) has been developed; hence, environmental criteria are being introduced to select the technical solutions described in bids. The ECORCE tool, initially released in 2008, has been available since 2013 for guests interested in such an approach (http://ecorce2.ifsttar.fr). At first, this tool was devoted to LCA for roads and only considered construction and maintenance. Though not necessarily negligible in all situations, congestion impacts during road works were estimated to be small for 22-lane configurations handling traffic volumes of 10,000 vehicles/day (in assuming all traffic remained on the same road but with a reduced number of lanes available and travelling at slower speeds), as witnessed in investigated case studies (accounting for less than 1% of the impacts generated by the initial road construction). Moreover, according to the French code of practice, road works are usually performed at night in order to avoid congestion. Both the construction and maintenance strategies have thus been integrated into a functional unit called ‘‘construction and maintenance policy’’, which allows investigating various materials with LCA. Maintenance policies are compared to highlight possible impact mitigation strategies. A series of environmental indicators will be presented and discussed for two typical highway life cycle scenarios. Since some of the recent published LCA findings (Yu and Lu, 2012) include not only construction and maintenance, but also the operations phase thanks to several models of consumption and congestion effects, the hypotheses adopted as regards the ECORCE tool and the results provided in this paper for highways will be discussed at the international level.
2. Background 2.1. Road maintenance policy as the basis for testing scenarios In France, heavily-trafficked roads are typically designed for a 30-year service life. Road layer materials and structural design are specified in official French guidelines (SETRA-LCPC, 1998). For initial construction, each layer thickness is determined according to expected cumulative traffic, while the lower layer is optimised using specific software, such as Alizé Win (developed by LCPC in 1998). The optimal thickness of both the base and subbase courses is obtained from calculations under hypotheses of a linear elastic mechanical behaviour. Fatigue with typical material layer properties and the probability of rupture after several years are taken into consideration as well. The traffic is assumed to increase at a given annual rate for the purpose of initial layer thickness design and calculation. The upper layers, which undergo wear and surface damage, are regularly removed and rebuilt with the requisite change in thickness, in accordance with maintenance operations that are established through systematic distress monitoring programs and condition indicator measurements, including: sideways force coefficient (SFC), macrotexture (MPD), transverse unevenness, rutting, and cracking. The road network is divided into homogeneous sections defined both by geometric characteristics (slope, curvature) and by road network characteristics (urban vs. rural area, primary vs. secondary road, pavement surface type, pavement structure, etc.). On each section, the data from routine monitoring are analysed to check for consistency with the expected road behaviour on the basis of design calculations and previous measurements. This step serves to confirm the mechanical behaviour of the road section as well as anticipate the appearance of disorders. Road managers are thus able to perform a diagnosis of their facilities and schedule maintenance operations. In addition, the input data from routine monitoring are used to calculate quality indices, with threshold values to trigger maintenance operations. As an example, a methodology called ‘‘Quality Image of the National Road network’’ (IQRN), which includes a triennial survey of various distresses via the calculation of a total index, is used in France. Pavement condition measurements are input to calculate the three following indices: structural condition index Np, focusing on the state of repair of road infrastructure; surface index Ns, related to skid resistance, rut depth and pavement distress; overall index Ng, which provides a synthesis of the two previous indices and equals the minimum value of Ns and Np. The benefit of this method lies in the fact that the type of maintenance operations required to reach an initial level of service are directly correlated with their cost. Equivalent methods are applied in other European countries (COST, 1997). In Austria for example, systematic road measurements are transformed into dimensionless indices with a scale ranging from X (optimal) to Y (worst state). Depending on the index values, catalogues of maintenance measures are available for consultation. The obvious aim here is to achieve an acceptable level of service. Other countries have decided to base maintenance strategies directly on input data from routine monitoring of parameters like skid resistance or cracking. When measured values reach a threshold, maintenance operations are triggered. In the UK, for example, the structural condition of the road network is quite good, and maintenance operations mainly concern surface defects such as insufficient friction. In Sweden, parts of roads that need to be maintained are selected thanks to an IRI calculation determined by means of road data collection. The maintenance strategy in Germany is based on both surface characteristics (friction, texture) and structural defects (cracking, rutting, etc.). These countries make use of
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programming tools that select the candidate maintenance strategies by inspecting routine measurements and identifying where the data indicate road degradation. Depending on the type of distress, maintenance solutions are then proposed. Regardless of the country, data concerns remain the same: the only approach to establishing an efficient maintenance policy is to collect accurate data through routine measurements, without which maintenance planning would be impossible. This statement means that countries must use calibrated monitoring devices able to provide high-quality data. 2.2. Road LCA as a framework for impact calculations With respect to the above context, it seems impossible at the beginning of this study, given the non-homogeneous nature of in situ maintenance data in France, to define a meaningful functional unit (FU) based on a single local instance of timedependent road damage. The FU for a pavement LCA intended to assess ‘‘maintenance policies’’ thus only considers generic maintenance operations (SETRA-LCPC, 1998; Laurent, 2004). On the other hand, roads cannot be considered as standard products assessed by means of a generic approach. The chosen structures, materials and corresponding processes to be included or not in the system are expected to directly influence the total LCI and impacts over the entire life cycle. Before and after working on a dedicated tool for road LCA, a literature review was conducted. During the initial survey, the studies dealing with the LCA of roads often focused on road material comparisons (Lundström, 1998; Mroueh et al., 2000, 2001; Stripple, 2001; Athena, 1999; Peuportier, 2003) and provided general information (Pontarollo and Smith, 2001). Instead of comparing materials however, the authors compared pavement structures. Given the broad range of countries concerned, it also appears that many parameters vary with road location, available materials, transport distances and maintenance practices. Only a few studies included traffic. Comparisons between these literature results was not so straightforward as regards the selected FU and materials by the various authors. A subsequent survey with more recent references (Chester and Horvath, 2010; Santero et al., 2011a; Santero et al., 2011b) has indicated that the FUs in the literature are not necessarily devoted to investigating maintenance policies and often incorporate the end of life of the road into current LCA practice along with congestion effects. In sum, the road LCA practice in including the ECORCE tool indicates that various FUs can be selected as follows: 1 ton or 1 m3 of a material or any total mass or volume of the component raw materials or road materials studied; 1 km with a defined width and length for each case study or any multiple of these; a single operation or several operations defined by the user as a combination of material production, road works incorporating or not dismantling, road construction, road maintenance once the unit of length and number of lanes (width) have been chosen; one road section for a number of years with a given traffic volume motivating the selection of defined road structures. The present study therefore focuses on assessing policies linked to standard code of practice techniques that provide and maintain the road level of service and do not include end of life as a parameter. Depending on the materials considered, the processes may be international or national, whereas energy supply is solely based on the French energy mix. 3. Presentation of the two studied maintenance policies using LCA 3.1. Case studies Table 1 summarises the characteristics of the cases studied (C1 to C4). The first structure considered (cases C1 and C3) is a continuously reinforced concrete (CRC) structure, while the second one (cases C2 and C4) is a bituminous asphalt concrete (BBGA3) structure. In all cases, the pavement surface is a super thick asphalt concrete (STAC). Policies C1 through C4, as presented in Table 1, are therefore compared according to LCA for each technical class of solution, i.e. C1 with C3 and C2 with C4. Fig. 1 (CRC pavement) and Fig. 2 (bituminous pavement) detail the initial pavement construction and maintenance policies for the upper layers on a heavily-trafficked TC6 highway over 30 years, the equivalent of 25 106 trucks/year/lane – 20% heavy vehicles and 80% passenger cars. The structural design was performed by considering a heavy vehicle traffic (weight >30 kN) of 2000 vehicles/day/direction/slow lane. The traffic level was assumed to increase at an annual rate of 5% during the considered period. Figs. 1 and 2 display the operations for each case: two maintenance policies, labelled MP98 (SETRA-LCPC, 1998) and MP04 (Laurent, 2004), are studied. MP98 considers a partial renewal of surface layers every 3–5 years, whereas MP04 is based on a
Table 1 Type of structure versus maintenance policy. Case
C1
C2
C3
C4
Type of structure Pavement type Maintenance policy
CRC STAC MP98
BBGA3 STAC MP98
CRC STAC MP04
BBGA3 STAC MP04
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Fig. 1. Description of two maintenance policies for a continuously reinforced concrete pavement structure (C1, C3).
Fig. 2. Description of two maintenance policies for a bituminous pavement structure (C2, C4).
more intensive works program, with total surface layer renewal every 11 years. The latter (MP04) constitutes an alternative policy of the former (MP98). 3.2. Environmental assessment The methodology and tool used plus their contents are explained in detail at: http://ecorce2.ifsttar.fr.
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Typical raw material and road material production as well as road work processes are taken into consideration for LCA in ECORCE; moreover, they have been combined into the generic environmental system. The systems of each scenario C1/C3 and C2/C4 are the same (see Fig. 3), while the FU is defined as the level of service for ‘‘a traffic of 25 106 trucks/year/lane for a 1-km, 2-lane road offering the same level of service for 30 years’’. In the present study, interactions between the desired level of service and the level of use provided relative to traffic variations over the 30 years have not been addressed. This system takes into account: inbound flows, such as non-renewable resources (materials) and energy consumption; outbound flows, such as products, atmospheric emissions, water emissions and waste. The various layers are assessed through LCA by describing the processes involved: (i) for raw component material extraction for road layers (aggregates, excavated earth, water); (ii) for the production of finished materials (refineries for bitumen, cement plants for cements, steel plants for steel); (iii) for mixed materials, hot mix plants or concrete mix plants. Performing a life cycle inventory (LCI) of roads implies collecting many parameters, including a soil type, road design, road works for initial construction and maintenance, and service conditions. Data corresponding to processes for material production and non-road equipment use for road laying are collected before implementation of the tool to select input data that describe the construction and maintenance operations. The ECORCE database (LCIs) has been extensively utilised and provides 37 LCIs of materials used in road construction, transport modes and non-road vehicles. In the present study, LCIs (Fig. 3) are drawn from ATILH (2009), Capony (2013), FD P01015 (2006), Eurobitume (2011), Jullien et al. (2010), Jullien et al. (2012), IISI (2002) and Stripple (2001). The ECORCE tool seeks to calculate material consumption, energy consumption correlated with each process for each level, and all environmental impacts from the individual processes as follows: raw material manufacturing, road works equipment use during pavement construction and maintenance, and equipment transport according to the steps shown in Fig. 4. Based on road design knowledge, the masses of the various manufactured materials can be determined along with their relationship to material masses. Equipment operating periods throughout the duration of road works are also collected; both are considered as input data for impact calculations, as will be explained below. For road works, equipment correlated with type of material enters into the assessment. All LCIs, which are correlated with the total amount of material masses and equipment operations, are combined into a common framework, called ‘‘processes’’, which involves unit flow data. The description of the principles and equations involved in process assessment is given below. The mass of manufactured materials at the output of process k is denoted Qk. Each manufacturing or road equipment process is tied to a specific LCI in the database containing unit flows. The LCI was created using environmental data obtained from several sources drawn from the literature and internal Ifsttar data. The LCI publication year differs substantially from one reference to the next. No feedstock energy, which is the energy potentially released by ignition, was considered for the studied materials, including those containing bitumen. ! For process number k, the unit flow vector FðkÞ is defined; it contains some 300 lines, each of which is matched either to chemical elements considered in the environmental release (CO2, SO2, CO, etc.) or to water and energy consumption. These elements can be discharged into air, water or soil in impacting one or several media, or be waste with the potential for transformation into new resources entering a second life (e.g. Reclaimed Asphalt Pavement or RAP). For a given process, known flow values are expressed in mg/kg or mg/m3. A 0 value is assigned to those lines whose element is not involved in the process. An empty line corresponds to an element involved in an environmental assessment yet whose value is not available and has only been estimated.
Fig. 3. Environmental system and processes considered for case studies C1 to C4.
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Pavement studied case
Operations (construction and maintenance)
Pavement layers
Deconstruction
Materials composition
Paving and rolling
Calculations
Life Cycle Inventory
Environmental indicators Fig. 4. Principle behind the ECORCE tool used.
! Environmental index number j is calculated by employing an extraction vector IðjÞ composed of 0s and 1s. The 1 values ! are placed on the lines corresponding to the chemical elements of FðkÞ included in the index calculations. These lines are thus linked to the known and measured pollutant emissions. The calculation principle for an index that combines several chemical elements therefore supposes that these elements are chemically equivalent. In LCA, coefficients aj are defined to express each indicator in an equivalent unit, with j being the number of the element under consideration. As an example, GWP is expressed in ‘‘kg eq. CO2’’, which means that the whole elements included in the calculations are transformed into ‘‘CO2’’. ! The 1 values of extraction vector IðjÞ are thus replaced by the equivalence coefficients aj. Lastly, the environmental indicator Fj is calculated as follows:
! ! F j ¼ Q k FðkÞ IðjÞ
ð1Þ
with Qk: final mass of materials produced at the output of process k. Material transport from the processing site to the road worksite is also considered. For the transport parameter, the single trip number is denoted STk. For each trip, if the vehicle is either full or partially loaded (0.8), then the mass considered is equal to the maximum load, in which case STk is derived as follows:
STk ¼
Qk ck
ð2Þ
with ck: mass transported during one trip for a given process k. By considering both a real value of (2) and the consumption relative to the return trip with an empty truck, the total number of trips Nk is set equal to:
Nk ¼ E
Qk 1:8 ck
ð3Þ
with E: integer part; 1.8: coefficient to account for the return trip with empty trucks (80% of a single trip for the return). In considering vehicle emissions, both road (trucks) or non-road vehicles are taken into account separately. For the former, truck emissions are estimated by considering both time and distances travelled. A wide range of data are available for ! heavy-duty vehicles given the overall importance ascribed to these vehicles. A flow vector K trucks ðkÞ is determined for trucks in the same manner as for environmental emissions during the manufacturing process. In the latter case, operating periods of non-road vehicles are determined and correlated with engine consumption. The choice of equipment is governed by pavement geometry. For each equipment in operation, the analysis starts by identifying the pavement parameters. A flow vector ! K non-road engine ðkÞ can then be defined. A limited set of values is available for these vehicles, considering the fact that only road builders are interested in collecting such data. Moreover, the effect of trucks or non-road vehicles is estimated by calculating the environmental index Kj with Eq. (1). As a minimum, the overall environmental index Ij equals the sum of the effects of material manufacturing flows or road equipment process and transport flows, i.e.:
Ij ¼ F j þ K j
ð4Þ
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with j: varying from 1 to the total number of processes considered (i.e. the number of final masses produced). Once the pavement case study and its operations have been validated (according to Fig. 4), results are submitted to a panel of ten available indicators. An Excel spreadsheet can also be generated as part of the post-treatment of results. 4. Results The total masses of materials and mixed materials are presented in Fig. 5. For both types of structures, material consumption is higher during construction than over the entire maintenance period. Mass consumption values (aggregates + binders) do not differ much between the two types of structures. During maintenance, the MP04 policy generates less consumption than MP98 for both the cement and bituminous structures. The total energy consumed by each type of pavement for an FU with the two maintenance policies can then be estimated (Fig. 6). Total energy consumption ranges from 5000 to 11,000 GJ, respectively, for concrete and bituminous asphalt concrete structures, which amounts to a large difference in LCA terms. For the initial construction, Fig. 6 shows a marked difference between the bituminous asphalt structure (3500 GJ) and the concrete structure (6000 GJ). This figure also serves to compare MP04 and MP98 maintenance policies. For the reinforced concrete pavement structure, the MP98 policy imposes more frequent maintenance operations than MP04, which explains why its energy consumption is three times higher. For the bituminous pavement structure, the gain is approx. 15% between the two policies. The energy consumed for pavement construction is greater than for maintenance, as shown in Fig. 6 for the selected FU. These observations are only logical when considering the maintenance operations proposed for the two policies (Figs. 1 and 2). Fig. 7 presents the Global Warming Potential (GWP) expressed in kg equivalent CO2 for the two policies applied to both types of structures. In considering GWP, similar results to those observed with energy are obtained, yet with the following values: 750,000 for CRC structures, and 200,000 kg eq. CO2 for BBGA structures. On the one hand, GWP is reduced by a factor of 6 for the BBGA3 structure, like for the energy level, with respect to the chosen maintenance policy, while on the other hand, GWP decreases by 15% for BBGA3. Beyond the amount of GWP, which differs from one technology to the other, a drastic improvement offered by the MP04 policy is clearly seen. Let’s note that the decrease in GWP between the two maintenance policies exceeds the decrease in energy consumption. This outcome is mainly due to the type of materials used. Steel and cement represent 12% of the mass of materials yet account for 86% of the energy consumed. Between MP98 and MP04, a 48% decrease in the mass of materials can be observed, which in turn induces an 86% energy decrease. Fig. 8 completes the above trends by presenting the level of potential eutrophication, as expressed in kg equivalent PO4, associated with each construction and maintenance policy and both solutions. This figure shows that maintenance policy MP04 lowers by a factor of 3.5 the eutrophication indices for the CRC structure and yields a 10% decrease for the BBGA3 structure. It must be emphasised that prior to the study this indicator was expected to differ markedly in terms of variations. Moreover, the overall downward trend produced by the change in maintenance policy is similar for all LCA indicators provided by ECORCE. Figs. 6–8 indicate that for CRC concrete structures with the same initial energy consumption, the maintenance component differs substantially between MP98 and MP04, which clearly demonstrates the benefit of optimising maintenance. As regards bituminous structures (BBGA3), which basically require the same initial energy as the concrete structure, the studied maintenance scenario also improves environmental effects but to a lesser extent. Once again, the benefit of LCA is displayed for maintenance optimisation in terms of raw material consumption effects.
Mass of materials (ton)
14000 12000 10000 8000 6000 4000 2000 0 CRC + MP98
CRC + MP04 BBGA + MP98 BBGA + MP04 Maintenance during 30 years Initial Construction
Fig. 5. Mass of materials - ratio of initial construction to maintenance (in tons) per FU.
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12 000 000 Maintenance during 30 years
10 000 000
Energy (MJ)
Initial Construction
8 000 000 6 000 000 4 000 000 2 000 000 0 CRC + MP98
CRC + MP04
BBGA +MP98
BBGA + MP04
Fig. 6. Energy consumption associated with two maintenance policies applied to two pavement structures per FU.
1 400 000 Maintenance during 30 years
GWP (kg eq. CO2)
1 200 000
Initial Construction
1 000 000 800 000 600 000 400 000 200 000 0 CRC + MP98
CRC + MP04
BBGA +MP98
BBGA + MP04
Fig. 7. Global warming potential (GWP) of two maintenance policies applied to two pavement structures per FU.
Fig. 8. Eutrophication of two maintenance policies applied to two pavement structures per FU.
5. Discussion of LCA pertinence for maintenance optimisation Despite standard and LCA experts underscoring that a pavement LCA model should take into account materials, construction, use, maintenance, rehabilitation and end of life, a recent review conducted by Yu and Lu (2012) led to the conclusion that pavement LCA remains in its early stages. Congestion effects due to maintenance differ significantly from one author to the next and congestion impacts depend mainly on the hypotheses adopted (with/without deviation), which exert a strong influence, as noticed by Yu and Lu (2012) and confirmed by our research. Nonetheless, major congestion effects and consumption correlated with type of pavement have not been addressed in the present study, which instead has merely focused on materials, structures and their associated maintenance policies.
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In this paper, an LCA tool for roads has been introduced to asses a FU of road service (25 106 trucks/year/lane for a 1-km section of 2-lane road), in taking into account typical cases of French pavements for a 2 2-lane configuration, namely on the national highway system. A smaller number of environmental indicators have been discussed herein, providing information about the impacts on soil (raw material consumption/energy), air quality (GWP) and water quality (eutrophication). The contribution of initial construction and maintenance has also been investigated. Results were plotted for the reduction/optimisation of technical solutions (C1 to C4) and then analysed in terms of impact mitigation. Consumption/energy resource results indicate that facility owners can help improve the entire life cycle by using LCA tools. As regards the initial objective, strong LCA trends are observed with respect to maintenance policy influence throughout the results of this study (Figs. 5–8). On the whole, let’s remark that the use of an MP04 policy vs. MP98 systematically increases the share of initial mass of raw material consumption while lowering all other environmental indicators. These result trends are the same for all calculated LCA indicators (midpoint indicators). Such a homogeneous trend is rare when performing road LCA (i.e. Jullien et al. (2006) and Ventura et al. (2008) studying RAP ratios showed other trends). These results are obviously given for the French energy mix and should be modified when introducing other LCI data and energy production assumptions. An expansion to other countries is currently underway (Tremblay and Jullien, 2013), namely through implementation of the ECORCE database. In considering that material production seems to be a central issue that needs to be addressed, this paper has shown that maintenance policies can be analysed in the aim of decreasing environmental loads regardless of the techniques involved, i.e. whether cement concrete or bituminous concrete. These results prove the benefit of considering maintenance strategy from an environmental perspective and as additional input into the roads code of practice. Moreover, future work is expected to better match the actual steps of pavement damage, instead of adopting a predefined scenario as the maintenance solution. Congestion effects must also be introduced into the case of very heavy traffic conditions. 6. Conclusion Due to the cumulative effect of traffic, pavement surface characteristics tend to deteriorate with time by means of aggregate polishing, bitumen ageing and scuffing. In the literature, instead of comparing materials, authors compare structures, which is also a general feature of what should be investigated with LCA. This paper has set hypotheses for an environmental assessment using LCA, in addition to applying LCA to several national road designs, based on the roads code of practice to evaluate construction and maintenance policies. A specific tool, called ECORCE, has been developed and applied along with its database. A small selection of impacts, i.e. material and energy consumption, global warming potential and eutrophication, which exhibit typical trends as regards both the functional unit and study objectives, aptly illustrates that all indicators are found to vary similarly and decrease sharply as material consumption decreases. The contributions of each life cycle phase (construction, structural maintenance) to environmental impacts have been detailed: approx. 2/3 of all impacts are due to initial construction, as regards the policy being considered. The ECORCE tool is well adapted to various road case studies whose characteristics depend to a great extent on the local territory; at the same time, it provides a good degree of modularity in any structural assessment. Lastly, such a tool can help identify how to better control environmental nuisances and include environmental concerns when choosing technological solutions. For other countries, such an investigation into maintenance policy effects on the environment could be performed using the same method, in adapting the ECORCE LCI database to accommodate country requirements and changes in service times and pavement design, in accordance with each nation’s applicable design rules. Acknowledgment The authors wish to gratefully acknowledge partners involved in the ECORCE tool development: C. Proust (Université d’Orléans), A. Feeser (LRPC Strasbourg) and M.-H. Tremblay (MTQ), A. Ventura (Ifsttar), P. Tamagny (Ifsttar) and M. Naullet (Ifsttar). References Athena Sustainable Materials Institute (Ed.), Canadian Portland Cement Association, 1999. Life Cycle Embodied energy and global warming emissions for concrete and asphalt roadways, John Emery Geotechnical Engineering Limited, Venta Glaser & Associates; Jan Consultants, p. 102. ATILH: Association Technique de l’industrie des Liants Hydraulique, 2009. Inventaire de cycle de vie des ciments produits en France. Capony, A., 2013. Evaluation environnementale d’un chantier de terrassement - mise au point d’un outil paramétrable de mesures d’émissions relatives aux engins de terrassement, thèse de l’Ecole Centrale de Nantes, soutenue le 10 janvier 2013. Chester, M., Horvath, A., 2010. Life-cycle assessment of high-speed rail: the case of California. Environ. Res. Lett. 5, 8pp. COST324, 1997. Long Term pavement Life – Final Report, 178 p. FD P01015, 2006. Qualité environnementale des produits de construction – Fascicule de données énergie et transport. Eurobitume, 2011. Life Cycle Inventory: Bitumen, INBS 2-930160-16-0-2011. Jullien, A., Monéron, P., Quaranta, G., Gaillard, D., 2006. A study on air emissions from pavement layings made of different reclaimed asphalt rates. Resour. Conserv. Recycl. 47, 356–374. Jullien, A., Gaudefroy, V., Ventura, A., Paranhos, R., de La Roche, C., Monéron, P., 2010. Airborne emissions assessment of hot asphalt mixing: methods and limitations. RMPD 11 (1), 149–169. Jullien, A., Proust, C., Martaud, T., Rayssac, E., Ropert, C., 2012. Environmental impacts variability of aggregates production. Resour. Conserv. Recycl. 62, 1–13. IISI: International Iron and Steel Institute, 2002. World steel life cycle inventory. 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Laurent, G., 2004. Evaluation économique des chaussées en béton et classiques sur le réseau routier national français, Ed. LCPC, Paris, 83 pages. Lundström, K., 1998. Influence des chaussées en béton et asphalte sur le milieu. In: International Symposium on Concrete Road, Lisbon (Portugal), p. 195. Mroueh, U.M., Eskola, P., Laine-Ylijoki, J., 2001. Waste Manage 21 (3), 271–277. Mroueh, U.M. Eskola, P. Laine-Ylijoki, J., 2000. Life Cycle Assessment of road Construction, Final Report, Teilatos, Finnish National Road Administration, Helsinki (Finland), p. 65. Peuportier, B., 2003. Analyse de vie d’un kilomètre de route et comparaison de six variantes, Ecole des Mines de Paris, CIM béton, Paris, p. 48. Pontarollo, G. and Smith, T., 2001. A life-Cycle Analysis Of the Environmental Impacts of Asphalt and Concrete Road, IRF World Road Congress, Paris. Santero, N., Masanet, E., Horvath, A., 2011a. Life-cycle assessment of pavements. Part I: Critical review. Resour. Conserv. Recycl. 55, 801–809. Santero, N., Masanet, E., Horvath, A., 2011b. Life-cycle assessment of pavements. Part II: Filling the Research Gaps. Resour. Conserv. Recycl. 55, 810–818. SETRA-LCPC, 1998. Catalogue des structures types de chaussées neuves, Ed. SETRA-LCPC. Stripple, H., 2001. Life cycle assessment of road. A Pilot Study for Inventory Analysis. 2nd revised Edition, Report from the IVL Swedish Environmental Research Institute, B 1210E; 97p. Tremblay, M.H., Jullien, A., 2013. Cheminement vers l’adoption de l’éco-comparateur de chaussées Écorce au MTQ-Revue route et transports de l’ATQR, vol. 42, no. 1, pp. 44–47. Ventura, A., Monéron, P., Jullien, A., 2008. Environmental impact of a binding course pavement section, with asphalt recycled at varying rates – use of life cycle methodology. J. Road Mater. Pavement Des. 9 (1), 319–338 (Special Issue EATA 2008). Yu, B., Lu, Q., 2012. Life cycle assessment of pavement: methodology and case study. Transport. Res. Part D Trans. Environ. 17 (5), 380–388.
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Transportation Research Part D journal homepage: www.elsevier.com/locate/trd
Environmental assessment of road construction and maintenance policies using LCA A. Jullien, M. Dauvergne, V. Cerezo ⇑ LUNAM Université, Ifsttar, AME-EASE, Route de Bouaye, CS4, F-44341 Bouguenais, EU, France
a r t i c l e
i n f o
Keywords: Roads Pavements LCA Environment Maintenance strategy
a b s t r a c t This paper proposes an evaluation of pavement maintenance policies relative to their initial construction, through a Life Cycle Assessment (LCA) and in accordance with the framework established by the Society of Environmental Toxicology and Chemistry as well as in the ISO 14040 Standard. The respective influence of initial construction and maintenance operations is investigated for both asphalt concrete and cement concrete pavement structures. Several case studies are analysed using a specific method and tool, called ECORCE (French acronym for ‘‘ECO-comparator applied to Road Construction and Maintenance’’), dedicated to road pavement LCA. ECORCE takes into account the materials production, mixing and laying processes, in addition to their transport between the production site and the jobsite. This environmental assessment is based on the principles underlying the life cycle assessment methodology. The chosen Functional Unit only considers the service to road users; heavily-trafficked French motorway structures are thus described over a 30year service period. A set of overall indicators, consisting of raw material and energy consumption, global warming potential and eutrophication potential, is then calculated for two case studies. These environmental indicators highlight the ability to assess pavement designs along with two maintenance policies considered for each case studied. Results are thus able to expose the relative influence of maintenance (1/3 of the entire life cycle). In conclusion, environmental design principles to achieve a reduction in environmental loads are discussed in considering the entire road life cycle. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Over the last several decades, a considerable amount of research has been aimed at improving the mechanical characteristics of materials and road pavements, in taking into account traffic requirements and service times for the initial construction. Moreover, road-related environmental impacts have been traditionally linked to their territories and investigated using Environmental Impact Assessment (EIA) techniques, in accordance with the 1976 French law No. 76-663. Until the recent past, these environmental constraints had been widespread in regulations, with an emphasis on discharges into watercourses. Nowadays, environmental impact assessments are expected to be quantified so as to improve facility owners’ decision-making. EU countries have also decided to significantly decrease greenhouse gas emissions. In France, a 2007 public debate, known as the ‘‘Grenelle roundtable’’, was held on national environmental issues. The EIA protocol was revised in 2010 by law (No. 2010-788), requiring energy consumption and impacts of road construction to be assessed at the project level. As ⇑ Corresponding author. Tel.: +33 240845937. E-mail address: [email protected] (V. Cerezo). http://dx.doi.org/10.1016/j.trd.2014.03.006 1361-9209/Ó 2014 Elsevier Ltd. All rights reserved.
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regards public works, this revision has gradually led to the inclusion of environmental criteria in public-sector calls for tender, thus increasing recycling and the use of material production/laying techniques featuring energy consumption mitigation. In this context, a methodology that takes into account within the same framework both the roads code of practice and LCA (Life Cycle Assessment) has been developed; hence, environmental criteria are being introduced to select the technical solutions described in bids. The ECORCE tool, initially released in 2008, has been available since 2013 for guests interested in such an approach (http://ecorce2.ifsttar.fr). At first, this tool was devoted to LCA for roads and only considered construction and maintenance. Though not necessarily negligible in all situations, congestion impacts during road works were estimated to be small for 22-lane configurations handling traffic volumes of 10,000 vehicles/day (in assuming all traffic remained on the same road but with a reduced number of lanes available and travelling at slower speeds), as witnessed in investigated case studies (accounting for less than 1% of the impacts generated by the initial road construction). Moreover, according to the French code of practice, road works are usually performed at night in order to avoid congestion. Both the construction and maintenance strategies have thus been integrated into a functional unit called ‘‘construction and maintenance policy’’, which allows investigating various materials with LCA. Maintenance policies are compared to highlight possible impact mitigation strategies. A series of environmental indicators will be presented and discussed for two typical highway life cycle scenarios. Since some of the recent published LCA findings (Yu and Lu, 2012) include not only construction and maintenance, but also the operations phase thanks to several models of consumption and congestion effects, the hypotheses adopted as regards the ECORCE tool and the results provided in this paper for highways will be discussed at the international level.
2. Background 2.1. Road maintenance policy as the basis for testing scenarios In France, heavily-trafficked roads are typically designed for a 30-year service life. Road layer materials and structural design are specified in official French guidelines (SETRA-LCPC, 1998). For initial construction, each layer thickness is determined according to expected cumulative traffic, while the lower layer is optimised using specific software, such as Alizé Win (developed by LCPC in 1998). The optimal thickness of both the base and subbase courses is obtained from calculations under hypotheses of a linear elastic mechanical behaviour. Fatigue with typical material layer properties and the probability of rupture after several years are taken into consideration as well. The traffic is assumed to increase at a given annual rate for the purpose of initial layer thickness design and calculation. The upper layers, which undergo wear and surface damage, are regularly removed and rebuilt with the requisite change in thickness, in accordance with maintenance operations that are established through systematic distress monitoring programs and condition indicator measurements, including: sideways force coefficient (SFC), macrotexture (MPD), transverse unevenness, rutting, and cracking. The road network is divided into homogeneous sections defined both by geometric characteristics (slope, curvature) and by road network characteristics (urban vs. rural area, primary vs. secondary road, pavement surface type, pavement structure, etc.). On each section, the data from routine monitoring are analysed to check for consistency with the expected road behaviour on the basis of design calculations and previous measurements. This step serves to confirm the mechanical behaviour of the road section as well as anticipate the appearance of disorders. Road managers are thus able to perform a diagnosis of their facilities and schedule maintenance operations. In addition, the input data from routine monitoring are used to calculate quality indices, with threshold values to trigger maintenance operations. As an example, a methodology called ‘‘Quality Image of the National Road network’’ (IQRN), which includes a triennial survey of various distresses via the calculation of a total index, is used in France. Pavement condition measurements are input to calculate the three following indices: structural condition index Np, focusing on the state of repair of road infrastructure; surface index Ns, related to skid resistance, rut depth and pavement distress; overall index Ng, which provides a synthesis of the two previous indices and equals the minimum value of Ns and Np. The benefit of this method lies in the fact that the type of maintenance operations required to reach an initial level of service are directly correlated with their cost. Equivalent methods are applied in other European countries (COST, 1997). In Austria for example, systematic road measurements are transformed into dimensionless indices with a scale ranging from X (optimal) to Y (worst state). Depending on the index values, catalogues of maintenance measures are available for consultation. The obvious aim here is to achieve an acceptable level of service. Other countries have decided to base maintenance strategies directly on input data from routine monitoring of parameters like skid resistance or cracking. When measured values reach a threshold, maintenance operations are triggered. In the UK, for example, the structural condition of the road network is quite good, and maintenance operations mainly concern surface defects such as insufficient friction. In Sweden, parts of roads that need to be maintained are selected thanks to an IRI calculation determined by means of road data collection. The maintenance strategy in Germany is based on both surface characteristics (friction, texture) and structural defects (cracking, rutting, etc.). These countries make use of
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programming tools that select the candidate maintenance strategies by inspecting routine measurements and identifying where the data indicate road degradation. Depending on the type of distress, maintenance solutions are then proposed. Regardless of the country, data concerns remain the same: the only approach to establishing an efficient maintenance policy is to collect accurate data through routine measurements, without which maintenance planning would be impossible. This statement means that countries must use calibrated monitoring devices able to provide high-quality data. 2.2. Road LCA as a framework for impact calculations With respect to the above context, it seems impossible at the beginning of this study, given the non-homogeneous nature of in situ maintenance data in France, to define a meaningful functional unit (FU) based on a single local instance of timedependent road damage. The FU for a pavement LCA intended to assess ‘‘maintenance policies’’ thus only considers generic maintenance operations (SETRA-LCPC, 1998; Laurent, 2004). On the other hand, roads cannot be considered as standard products assessed by means of a generic approach. The chosen structures, materials and corresponding processes to be included or not in the system are expected to directly influence the total LCI and impacts over the entire life cycle. Before and after working on a dedicated tool for road LCA, a literature review was conducted. During the initial survey, the studies dealing with the LCA of roads often focused on road material comparisons (Lundström, 1998; Mroueh et al., 2000, 2001; Stripple, 2001; Athena, 1999; Peuportier, 2003) and provided general information (Pontarollo and Smith, 2001). Instead of comparing materials however, the authors compared pavement structures. Given the broad range of countries concerned, it also appears that many parameters vary with road location, available materials, transport distances and maintenance practices. Only a few studies included traffic. Comparisons between these literature results was not so straightforward as regards the selected FU and materials by the various authors. A subsequent survey with more recent references (Chester and Horvath, 2010; Santero et al., 2011a; Santero et al., 2011b) has indicated that the FUs in the literature are not necessarily devoted to investigating maintenance policies and often incorporate the end of life of the road into current LCA practice along with congestion effects. In sum, the road LCA practice in including the ECORCE tool indicates that various FUs can be selected as follows: 1 ton or 1 m3 of a material or any total mass or volume of the component raw materials or road materials studied; 1 km with a defined width and length for each case study or any multiple of these; a single operation or several operations defined by the user as a combination of material production, road works incorporating or not dismantling, road construction, road maintenance once the unit of length and number of lanes (width) have been chosen; one road section for a number of years with a given traffic volume motivating the selection of defined road structures. The present study therefore focuses on assessing policies linked to standard code of practice techniques that provide and maintain the road level of service and do not include end of life as a parameter. Depending on the materials considered, the processes may be international or national, whereas energy supply is solely based on the French energy mix. 3. Presentation of the two studied maintenance policies using LCA 3.1. Case studies Table 1 summarises the characteristics of the cases studied (C1 to C4). The first structure considered (cases C1 and C3) is a continuously reinforced concrete (CRC) structure, while the second one (cases C2 and C4) is a bituminous asphalt concrete (BBGA3) structure. In all cases, the pavement surface is a super thick asphalt concrete (STAC). Policies C1 through C4, as presented in Table 1, are therefore compared according to LCA for each technical class of solution, i.e. C1 with C3 and C2 with C4. Fig. 1 (CRC pavement) and Fig. 2 (bituminous pavement) detail the initial pavement construction and maintenance policies for the upper layers on a heavily-trafficked TC6 highway over 30 years, the equivalent of 25 106 trucks/year/lane – 20% heavy vehicles and 80% passenger cars. The structural design was performed by considering a heavy vehicle traffic (weight >30 kN) of 2000 vehicles/day/direction/slow lane. The traffic level was assumed to increase at an annual rate of 5% during the considered period. Figs. 1 and 2 display the operations for each case: two maintenance policies, labelled MP98 (SETRA-LCPC, 1998) and MP04 (Laurent, 2004), are studied. MP98 considers a partial renewal of surface layers every 3–5 years, whereas MP04 is based on a
Table 1 Type of structure versus maintenance policy. Case
C1
C2
C3
C4
Type of structure Pavement type Maintenance policy
CRC STAC MP98
BBGA3 STAC MP98
CRC STAC MP04
BBGA3 STAC MP04
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Fig. 1. Description of two maintenance policies for a continuously reinforced concrete pavement structure (C1, C3).
Fig. 2. Description of two maintenance policies for a bituminous pavement structure (C2, C4).
more intensive works program, with total surface layer renewal every 11 years. The latter (MP04) constitutes an alternative policy of the former (MP98). 3.2. Environmental assessment The methodology and tool used plus their contents are explained in detail at: http://ecorce2.ifsttar.fr.
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Typical raw material and road material production as well as road work processes are taken into consideration for LCA in ECORCE; moreover, they have been combined into the generic environmental system. The systems of each scenario C1/C3 and C2/C4 are the same (see Fig. 3), while the FU is defined as the level of service for ‘‘a traffic of 25 106 trucks/year/lane for a 1-km, 2-lane road offering the same level of service for 30 years’’. In the present study, interactions between the desired level of service and the level of use provided relative to traffic variations over the 30 years have not been addressed. This system takes into account: inbound flows, such as non-renewable resources (materials) and energy consumption; outbound flows, such as products, atmospheric emissions, water emissions and waste. The various layers are assessed through LCA by describing the processes involved: (i) for raw component material extraction for road layers (aggregates, excavated earth, water); (ii) for the production of finished materials (refineries for bitumen, cement plants for cements, steel plants for steel); (iii) for mixed materials, hot mix plants or concrete mix plants. Performing a life cycle inventory (LCI) of roads implies collecting many parameters, including a soil type, road design, road works for initial construction and maintenance, and service conditions. Data corresponding to processes for material production and non-road equipment use for road laying are collected before implementation of the tool to select input data that describe the construction and maintenance operations. The ECORCE database (LCIs) has been extensively utilised and provides 37 LCIs of materials used in road construction, transport modes and non-road vehicles. In the present study, LCIs (Fig. 3) are drawn from ATILH (2009), Capony (2013), FD P01015 (2006), Eurobitume (2011), Jullien et al. (2010), Jullien et al. (2012), IISI (2002) and Stripple (2001). The ECORCE tool seeks to calculate material consumption, energy consumption correlated with each process for each level, and all environmental impacts from the individual processes as follows: raw material manufacturing, road works equipment use during pavement construction and maintenance, and equipment transport according to the steps shown in Fig. 4. Based on road design knowledge, the masses of the various manufactured materials can be determined along with their relationship to material masses. Equipment operating periods throughout the duration of road works are also collected; both are considered as input data for impact calculations, as will be explained below. For road works, equipment correlated with type of material enters into the assessment. All LCIs, which are correlated with the total amount of material masses and equipment operations, are combined into a common framework, called ‘‘processes’’, which involves unit flow data. The description of the principles and equations involved in process assessment is given below. The mass of manufactured materials at the output of process k is denoted Qk. Each manufacturing or road equipment process is tied to a specific LCI in the database containing unit flows. The LCI was created using environmental data obtained from several sources drawn from the literature and internal Ifsttar data. The LCI publication year differs substantially from one reference to the next. No feedstock energy, which is the energy potentially released by ignition, was considered for the studied materials, including those containing bitumen. ! For process number k, the unit flow vector FðkÞ is defined; it contains some 300 lines, each of which is matched either to chemical elements considered in the environmental release (CO2, SO2, CO, etc.) or to water and energy consumption. These elements can be discharged into air, water or soil in impacting one or several media, or be waste with the potential for transformation into new resources entering a second life (e.g. Reclaimed Asphalt Pavement or RAP). For a given process, known flow values are expressed in mg/kg or mg/m3. A 0 value is assigned to those lines whose element is not involved in the process. An empty line corresponds to an element involved in an environmental assessment yet whose value is not available and has only been estimated.
Fig. 3. Environmental system and processes considered for case studies C1 to C4.
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Pavement studied case
Operations (construction and maintenance)
Pavement layers
Deconstruction
Materials composition
Paving and rolling
Calculations
Life Cycle Inventory
Environmental indicators Fig. 4. Principle behind the ECORCE tool used.
! Environmental index number j is calculated by employing an extraction vector IðjÞ composed of 0s and 1s. The 1 values ! are placed on the lines corresponding to the chemical elements of FðkÞ included in the index calculations. These lines are thus linked to the known and measured pollutant emissions. The calculation principle for an index that combines several chemical elements therefore supposes that these elements are chemically equivalent. In LCA, coefficients aj are defined to express each indicator in an equivalent unit, with j being the number of the element under consideration. As an example, GWP is expressed in ‘‘kg eq. CO2’’, which means that the whole elements included in the calculations are transformed into ‘‘CO2’’. ! The 1 values of extraction vector IðjÞ are thus replaced by the equivalence coefficients aj. Lastly, the environmental indicator Fj is calculated as follows:
! ! F j ¼ Q k FðkÞ IðjÞ
ð1Þ
with Qk: final mass of materials produced at the output of process k. Material transport from the processing site to the road worksite is also considered. For the transport parameter, the single trip number is denoted STk. For each trip, if the vehicle is either full or partially loaded (0.8), then the mass considered is equal to the maximum load, in which case STk is derived as follows:
STk ¼
Qk ck
ð2Þ
with ck: mass transported during one trip for a given process k. By considering both a real value of (2) and the consumption relative to the return trip with an empty truck, the total number of trips Nk is set equal to:
Nk ¼ E
Qk 1:8 ck
ð3Þ
with E: integer part; 1.8: coefficient to account for the return trip with empty trucks (80% of a single trip for the return). In considering vehicle emissions, both road (trucks) or non-road vehicles are taken into account separately. For the former, truck emissions are estimated by considering both time and distances travelled. A wide range of data are available for ! heavy-duty vehicles given the overall importance ascribed to these vehicles. A flow vector K trucks ðkÞ is determined for trucks in the same manner as for environmental emissions during the manufacturing process. In the latter case, operating periods of non-road vehicles are determined and correlated with engine consumption. The choice of equipment is governed by pavement geometry. For each equipment in operation, the analysis starts by identifying the pavement parameters. A flow vector ! K non-road engine ðkÞ can then be defined. A limited set of values is available for these vehicles, considering the fact that only road builders are interested in collecting such data. Moreover, the effect of trucks or non-road vehicles is estimated by calculating the environmental index Kj with Eq. (1). As a minimum, the overall environmental index Ij equals the sum of the effects of material manufacturing flows or road equipment process and transport flows, i.e.:
Ij ¼ F j þ K j
ð4Þ
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with j: varying from 1 to the total number of processes considered (i.e. the number of final masses produced). Once the pavement case study and its operations have been validated (according to Fig. 4), results are submitted to a panel of ten available indicators. An Excel spreadsheet can also be generated as part of the post-treatment of results. 4. Results The total masses of materials and mixed materials are presented in Fig. 5. For both types of structures, material consumption is higher during construction than over the entire maintenance period. Mass consumption values (aggregates + binders) do not differ much between the two types of structures. During maintenance, the MP04 policy generates less consumption than MP98 for both the cement and bituminous structures. The total energy consumed by each type of pavement for an FU with the two maintenance policies can then be estimated (Fig. 6). Total energy consumption ranges from 5000 to 11,000 GJ, respectively, for concrete and bituminous asphalt concrete structures, which amounts to a large difference in LCA terms. For the initial construction, Fig. 6 shows a marked difference between the bituminous asphalt structure (3500 GJ) and the concrete structure (6000 GJ). This figure also serves to compare MP04 and MP98 maintenance policies. For the reinforced concrete pavement structure, the MP98 policy imposes more frequent maintenance operations than MP04, which explains why its energy consumption is three times higher. For the bituminous pavement structure, the gain is approx. 15% between the two policies. The energy consumed for pavement construction is greater than for maintenance, as shown in Fig. 6 for the selected FU. These observations are only logical when considering the maintenance operations proposed for the two policies (Figs. 1 and 2). Fig. 7 presents the Global Warming Potential (GWP) expressed in kg equivalent CO2 for the two policies applied to both types of structures. In considering GWP, similar results to those observed with energy are obtained, yet with the following values: 750,000 for CRC structures, and 200,000 kg eq. CO2 for BBGA structures. On the one hand, GWP is reduced by a factor of 6 for the BBGA3 structure, like for the energy level, with respect to the chosen maintenance policy, while on the other hand, GWP decreases by 15% for BBGA3. Beyond the amount of GWP, which differs from one technology to the other, a drastic improvement offered by the MP04 policy is clearly seen. Let’s note that the decrease in GWP between the two maintenance policies exceeds the decrease in energy consumption. This outcome is mainly due to the type of materials used. Steel and cement represent 12% of the mass of materials yet account for 86% of the energy consumed. Between MP98 and MP04, a 48% decrease in the mass of materials can be observed, which in turn induces an 86% energy decrease. Fig. 8 completes the above trends by presenting the level of potential eutrophication, as expressed in kg equivalent PO4, associated with each construction and maintenance policy and both solutions. This figure shows that maintenance policy MP04 lowers by a factor of 3.5 the eutrophication indices for the CRC structure and yields a 10% decrease for the BBGA3 structure. It must be emphasised that prior to the study this indicator was expected to differ markedly in terms of variations. Moreover, the overall downward trend produced by the change in maintenance policy is similar for all LCA indicators provided by ECORCE. Figs. 6–8 indicate that for CRC concrete structures with the same initial energy consumption, the maintenance component differs substantially between MP98 and MP04, which clearly demonstrates the benefit of optimising maintenance. As regards bituminous structures (BBGA3), which basically require the same initial energy as the concrete structure, the studied maintenance scenario also improves environmental effects but to a lesser extent. Once again, the benefit of LCA is displayed for maintenance optimisation in terms of raw material consumption effects.
Mass of materials (ton)
14000 12000 10000 8000 6000 4000 2000 0 CRC + MP98
CRC + MP04 BBGA + MP98 BBGA + MP04 Maintenance during 30 years Initial Construction
Fig. 5. Mass of materials - ratio of initial construction to maintenance (in tons) per FU.
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12 000 000 Maintenance during 30 years
10 000 000
Energy (MJ)
Initial Construction
8 000 000 6 000 000 4 000 000 2 000 000 0 CRC + MP98
CRC + MP04
BBGA +MP98
BBGA + MP04
Fig. 6. Energy consumption associated with two maintenance policies applied to two pavement structures per FU.
1 400 000 Maintenance during 30 years
GWP (kg eq. CO2)
1 200 000
Initial Construction
1 000 000 800 000 600 000 400 000 200 000 0 CRC + MP98
CRC + MP04
BBGA +MP98
BBGA + MP04
Fig. 7. Global warming potential (GWP) of two maintenance policies applied to two pavement structures per FU.
Fig. 8. Eutrophication of two maintenance policies applied to two pavement structures per FU.
5. Discussion of LCA pertinence for maintenance optimisation Despite standard and LCA experts underscoring that a pavement LCA model should take into account materials, construction, use, maintenance, rehabilitation and end of life, a recent review conducted by Yu and Lu (2012) led to the conclusion that pavement LCA remains in its early stages. Congestion effects due to maintenance differ significantly from one author to the next and congestion impacts depend mainly on the hypotheses adopted (with/without deviation), which exert a strong influence, as noticed by Yu and Lu (2012) and confirmed by our research. Nonetheless, major congestion effects and consumption correlated with type of pavement have not been addressed in the present study, which instead has merely focused on materials, structures and their associated maintenance policies.
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In this paper, an LCA tool for roads has been introduced to asses a FU of road service (25 106 trucks/year/lane for a 1-km section of 2-lane road), in taking into account typical cases of French pavements for a 2 2-lane configuration, namely on the national highway system. A smaller number of environmental indicators have been discussed herein, providing information about the impacts on soil (raw material consumption/energy), air quality (GWP) and water quality (eutrophication). The contribution of initial construction and maintenance has also been investigated. Results were plotted for the reduction/optimisation of technical solutions (C1 to C4) and then analysed in terms of impact mitigation. Consumption/energy resource results indicate that facility owners can help improve the entire life cycle by using LCA tools. As regards the initial objective, strong LCA trends are observed with respect to maintenance policy influence throughout the results of this study (Figs. 5–8). On the whole, let’s remark that the use of an MP04 policy vs. MP98 systematically increases the share of initial mass of raw material consumption while lowering all other environmental indicators. These result trends are the same for all calculated LCA indicators (midpoint indicators). Such a homogeneous trend is rare when performing road LCA (i.e. Jullien et al. (2006) and Ventura et al. (2008) studying RAP ratios showed other trends). These results are obviously given for the French energy mix and should be modified when introducing other LCI data and energy production assumptions. An expansion to other countries is currently underway (Tremblay and Jullien, 2013), namely through implementation of the ECORCE database. In considering that material production seems to be a central issue that needs to be addressed, this paper has shown that maintenance policies can be analysed in the aim of decreasing environmental loads regardless of the techniques involved, i.e. whether cement concrete or bituminous concrete. These results prove the benefit of considering maintenance strategy from an environmental perspective and as additional input into the roads code of practice. Moreover, future work is expected to better match the actual steps of pavement damage, instead of adopting a predefined scenario as the maintenance solution. Congestion effects must also be introduced into the case of very heavy traffic conditions. 6. Conclusion Due to the cumulative effect of traffic, pavement surface characteristics tend to deteriorate with time by means of aggregate polishing, bitumen ageing and scuffing. In the literature, instead of comparing materials, authors compare structures, which is also a general feature of what should be investigated with LCA. This paper has set hypotheses for an environmental assessment using LCA, in addition to applying LCA to several national road designs, based on the roads code of practice to evaluate construction and maintenance policies. A specific tool, called ECORCE, has been developed and applied along with its database. A small selection of impacts, i.e. material and energy consumption, global warming potential and eutrophication, which exhibit typical trends as regards both the functional unit and study objectives, aptly illustrates that all indicators are found to vary similarly and decrease sharply as material consumption decreases. The contributions of each life cycle phase (construction, structural maintenance) to environmental impacts have been detailed: approx. 2/3 of all impacts are due to initial construction, as regards the policy being considered. The ECORCE tool is well adapted to various road case studies whose characteristics depend to a great extent on the local territory; at the same time, it provides a good degree of modularity in any structural assessment. Lastly, such a tool can help identify how to better control environmental nuisances and include environmental concerns when choosing technological solutions. For other countries, such an investigation into maintenance policy effects on the environment could be performed using the same method, in adapting the ECORCE LCI database to accommodate country requirements and changes in service times and pavement design, in accordance with each nation’s applicable design rules. Acknowledgment The authors wish to gratefully acknowledge partners involved in the ECORCE tool development: C. Proust (Université d’Orléans), A. Feeser (LRPC Strasbourg) and M.-H. Tremblay (MTQ), A. Ventura (Ifsttar), P. Tamagny (Ifsttar) and M. Naullet (Ifsttar). References Athena Sustainable Materials Institute (Ed.), Canadian Portland Cement Association, 1999. Life Cycle Embodied energy and global warming emissions for concrete and asphalt roadways, John Emery Geotechnical Engineering Limited, Venta Glaser & Associates; Jan Consultants, p. 102. ATILH: Association Technique de l’industrie des Liants Hydraulique, 2009. Inventaire de cycle de vie des ciments produits en France. Capony, A., 2013. Evaluation environnementale d’un chantier de terrassement - mise au point d’un outil paramétrable de mesures d’émissions relatives aux engins de terrassement, thèse de l’Ecole Centrale de Nantes, soutenue le 10 janvier 2013. Chester, M., Horvath, A., 2010. Life-cycle assessment of high-speed rail: the case of California. Environ. Res. Lett. 5, 8pp. COST324, 1997. Long Term pavement Life – Final Report, 178 p. FD P01015, 2006. Qualité environnementale des produits de construction – Fascicule de données énergie et transport. Eurobitume, 2011. Life Cycle Inventory: Bitumen, INBS 2-930160-16-0-2011. Jullien, A., Monéron, P., Quaranta, G., Gaillard, D., 2006. A study on air emissions from pavement layings made of different reclaimed asphalt rates. Resour. Conserv. Recycl. 47, 356–374. Jullien, A., Gaudefroy, V., Ventura, A., Paranhos, R., de La Roche, C., Monéron, P., 2010. Airborne emissions assessment of hot asphalt mixing: methods and limitations. RMPD 11 (1), 149–169. Jullien, A., Proust, C., Martaud, T., Rayssac, E., Ropert, C., 2012. Environmental impacts variability of aggregates production. Resour. Conserv. Recycl. 62, 1–13. IISI: International Iron and Steel Institute, 2002. World steel life cycle inventory. Methodology Report 1999/2000. Committee on Environmental Affairs Brussels, October, 90 p.
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