Life cycle assessment of pavement: Methodology and case study

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  • Civil and Environmental Engineering, University of South Florida, 4202 E. Fowler Avenue, Tampa, FL 33620, United States

    especially for the pavement structure effect.

    1. Introduction

    Life-cycle analysis (LCA) in pavement aaterit incresud thaen fong et

    candidates of a LCA model. For pavement, this means that they should serve the same trafc over the same analysis spanwith the same performance. To assess the environmental impacts of pavement, a system of LCA model is developed, asshown in Fig. 1. The LCA functionality is fullled by six components, including material module, distribution module, con-struction module, congestion module, usage module, and EOL module, with various supplementary models attached to thecorresponding modules.

    1361-9209/$ - see front matter 2012 Elsevier Ltd. All rights reserved.

    Corresponding author.E-mail address: yubin@mail.usf.edu (B. Yu).

    Transportation Research Part D 17 (2012) 380388

    Contents lists available at SciVerse ScienceDirect

    Transportation Research Part Dhttp://dx.doi.org/10.1016/j.trd.2012.03.004not complete; third, the EOL phase is simply taken as landll while practically, most hot mixture asphalt (HMA) is recycledand old Portland cement concrete (PCC) is crushed to substitute base course aggregates.

    2. Methodology

    We begin by dening a functional unit needed to build the LCA model framework. A functional unit quanties a standardamount to be compared between alternatives that serve this function. Equivalent functionality shall be maintained for allsists of the following components: mHowever, most of the work does nomodels, usage and trafc congestionplexity. Huang et al. (2009) suggesteroadwork periods are signicant. Evimprove (Keoleian et al., 2005; Zha 2012 Elsevier Ltd. All rights reserved.

    ssessment is still at an immature stage. Typically, a LCA model of pavement con-al, construction, use, maintenance and rehabilitation (M&R), and end of life (EOL).orporate all the components (Chan, 2007). Two most important elements in LCAlted from construction and M&R activities are typically ignored due to great com-t additional fuel consumptions and pollutant emissions due to trafc delay duringr studies that incorporate the use and congestion phases, there is still room toal., 2010): rst, data in some studies are outdated; second, the usage phase isa r t i c l e i n f o

    Keywords:Pavement designInfrastructure life cycle assessmentPavement overlay systems

    a b s t r a c t

    A life cycle assessment model is built to estimate the environmental implications ofpavements using material, distribution, construction, congestion, usage, and end of lifemodules. A case study of three overlay systems, Portland cement concrete overlay, hotmixture asphalt overlay, and crack, seat, and overlay, is presented. The case leads to thefollowing conclusions. It is reasonable to expect less environmental burdens from thePortland cement concrete and crack, seat, and overlay options as opposed to hot mixtureasphalt while although the results have a high degree uncertainties. The material,congestion, and particularly usage modules contribute most to energy consumption andair pollutant. Trafc related energy consumption and greenhouse gases are sensitive totrafc growth and fuel economy improvement. Uncertainties exist in the usage module,Life cycle assessment of pavement: Methodology and case study

    Bin Yu , Qing Lu

    journal homepage: www.elsevier .com/ locate / t rd

  • (CH4),

    B. Yu, Q. Lu / Transportation Research Part D 17 (2012) 380388 381The distribution module is closely linked to the material module and the EOL module. All materials, equipment, andwastes are transported by a combination of road, rail, and waterway. Greenhouse Gases, Regulated Emissions, and EnergyUse in Transportation (2010) is used to model greenhouse gas emissions and energy embracing a data for fuel and electricityproduction, truck transportation, tie and dowel bar production, and natural gas burned that may be used during the pave-ment life time. Emission data for all non-road construction and vehicular equipment are obtained from the US Environmen-tal Protection Agencys (EPA) NONROAD 2008 model for construction and maintenance activities. For each piece ofconstruction equipment, an estimate of the engine horsepower is made on the basis of one or two typical machines.NONROAD2008 model provides emission factors for various ranges of horsepower.

    Most prior work has not included a EOL module because the pavement structure is assume to have an indenite life. It isdesired to investigate the role of EOL module on the LCA model. Environmental burdens to dismantle and transport the oldpavement, the environmental savings due to the reuse of old pavement materials, and the potential additional energy con-sumption to process the old pavement materials before they can be used, need to be identied. They can be modeled in asimilar fashion as the way of material, distribution, and construction modules.

    Trafc delay induced by construction and rehabilitation activities has signicant inuences on energy consumption andpollutant emissions compared with those under normal vehicular operations. The changes in trafc ow, trafc delay, andqueue length are estimated using the QuickZone model. Outputs include detour rate, queue length and speed reductionwithin work zones. Once vehicle delays due to construction and maintenance events are determined, they are coupled withfuel consumption and vehicle emissions to measure their environmental impacts. CO2 is calculated by the fuel consumptions(Emission Facts, 2005). Other vehicle emissions are calculated using US EPAs MOBILE 6.2 model, which supplies the tailpipeemissions and evaporative emissions at varying trafc speeds on a per year basis through 2050.

    Fuel consumptions and environmental burdens are calculated as the differences between those of construction and reha-bilitation periods and those of normal operations:

    Ytotal VMTqueue Yqueue VMTworkzone Yworkzone VMTdet our Ydet our VMTnormal Ynormal 1where Yi is the value of different environmental indicators, such as fuel usage (L/km) or emission values (g/km), VMTi is themiles traveled by vehicles (km or mile), i is scenario index, representing the total, waiting in queue, passing through workzone, taking detour, or operating under normal conditions.Thperiod

    Throughand tr

    Incand proughsuremfrom 2lioratevehicl2

    nitrogen oxide (NOx), sulfur oxide (SOx), volatile organic compound (VOC), particulate matter (

  • 3.1. Th

    direction, the widths of the inner paved shoulder, main lanes, and outsider paved shoulder are 1.2 m, 3.6 2 m, and2.7 m

    HM

    382 B. Yu, Q. Lu / Transportation Research Part D 17 (2012) 380388and Muench, 2010). Crack, seat, and overlay (the CSOL option). Crack and seat the existing PCC pavement and then overlay with 125 mmHMA.Use the same mill-and-ll plan as the periodic rehabilitation strategy every 16 years (Weiland and Muench, 2010).

    The pavement overlay designs follow the Florida Department of Transportation (FDOT) pavement design manual as ver-ied by the Mechanistic-empirical Pavement Design Guide (MEPDG) software using Florida local weather data. Thus thefunctional unit is a one kilometer overlay system over an existing PCC pavement with four lanes in two directions that wouldprovide satisfactory performance over a 40-year period.

    For material module, cement concrete production uses data from the Portland Cement Association (Marceau et al., 2007)while HMA production uses data from the Swedish Environmental Research Institute (Stripple, 2001). Distribution and con-struction modules are estimated based on the quantities of construction and maintenance activities.

    For EOL module, reclaimed concrete material (RCM) is frequently used to substitute aggregates in base course. Reclaimedasphalt pavement (RAP) is now routinely accepted in asphalt paving mixtures with substitution rates ranging from 10% toA surface and replace the same depth of new HMA) plan every 16 years as a periodic rehabilitation strategy (Weilanda year. Three replacement options frequently adopted in Florida are considered:

    Remove and replace the 225 mm PCC pavement with 250 mm new PCC (the PCC option). Diamond grinding is frequentlyused to restore surface smoothness and reported to be viable for 1617 years (Stubstand et al., 2005) and thus is per-formed every 16 years as a periodic rehabilitation strategy.

    Remove and replace the existing pavement with 225 mm HMA (the HMA option). Use a mill-and-ll (remove 45 mm. There is an annual average daily trafc ow (AADT) of 70,000, with 8% being truck that is growing at growth of 4%For the case study we consider an old PCC pavement that is at the end of its service life and requires rehabilitation torestore the serviceability. The existing base course is assumed to perform well and can function without intensive mainte-nances. This pavement has a 225 mm PCC surface with 250 mm crushed aggregate as base course, and subgrade. In eache studyBesides the inuence on fuel economy, increase of IRI reduces the driving speed and thus leads to a reduction of highwaycapacity. The speed-reduced eet may witness signicant fuel consumption increase and pollutant emission changes.Moreover, additional roughness causes increased friction and vertical acceleration of the vehicle body, and thus leads tomore vehicle fuel consumption and pollutant emissions. How these factors contribute to the life cycle inventory will beaddressed by the case study in detail.

    Pavement structures have signicant inuence on the fuel consumptions of vehicles, especially for asphalt compared withPCC and composite pavements (Taylor et al., 2000). Taylor and Pattens (2006) study suggested that PCC and composite pave-ments have signicant fuel

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