Pavements and the Environment

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Pavements and the Environment

• Nicholas Santero, Ph.D.
• Postdoctoral Scholar
• Civil and Environmental Engineering
• University of California, Berkeley

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The Pavement System
Expansive
8 million lane-miles in place in the United States
Resource Intensive
Requires 350 million tons of materials annually
Vital Infrastructure
Supports over 3 trillion vehicle-miles annually
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Life-Cycle Assessment (LCA)

• Used to quantify cradle-to-grave environmental
  impacts of a system
• Begins with upstream supply chain and ends with
  ultimate decommissioning
• Measures inputs and outputs over the life cycle
• Example inputs energy, water, resources
• Example outputs air emissions, water emissions
• General standards set by ISO 14040 series
• Provides general LCA guidance, but lacks detailed
  information for individual processes

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The Pavement Life Cycle
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The Pavement Life Cycle
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Focus of Existing LCA Research
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Traffic Delay

• Caused by construction activities
• Idling and stop-and-go traffic reduce
• fuel economy
• Occurs during initial construction and
• maintenance phases
• Impact is related to project details, e.g.,
• Traffic level
• Time of day
• Closure configuration
• Software available to estimate traffic delay
• Primarily for LCCA purposes, but can be adapted
  for environmental assessments
• e.g., CA4PRS, RealCost

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Carbonation

• Natural carbon cycle
• CO2 released during
• calcination of limestone
• is recaptured over time
• Time for appreciable sequestration is often long
• Measured in decades, centuries, or even millennia
• Sequestration rate can be expedited through
  strategic design and management techniques
• Concrete properties affect carbonation rate
• Crushing and exposing concrete to the atmosphere
  can quickly recapture large amounts of carbon

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Lighting

• Lighting provides necessary illumination for
  certain roadways
• Requirements vary by pavement classification
• Pavement surface characteristics can affect the
  light needed for proper illumination
• In general, darker pavements require more
  lighting than do lighter pavements, resulting in
  higher electricity demand
• More efficient lighting technologies (e.g., LEDs)
  will reduce the energy disparity between light
  and dark pavements

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AlbedoUrban Heat Island

• Pavements absorb incomingradiation and release
  as heat
• Result is a rise in urban temperatures, resulting
  in increased electricity demand via air
  conditioning
• Location specific effect
• Dense urban environments
• High-temperature cities
• Incremental effects not well studied
• Current research focuses on large metropolitan
  areas
• What is the marginal effect of a single unit of
  pavement?

image source adapted from adaptation.nrcan.gc.ca/
perspective/images/figure2_urbanheat.jpg
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AlbedoDirect Radiative Forcing

• Pavements directly affect the earths energy
  balance
• Higher albedo pavements reflect more radiation
  back into space
• Reflected radiation can be measured in CO2
  equivalent (CO2e) units
• Very little research on this topic
• Primarily studied by researchers at Lawrence
  Berkeley National Laboratory
• Exact numerical relationship between albedo and
  CO2e not well defined

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Fuel ConsumptionPavement Roughness

• Pavement roughness is linkedto fuel consumption
• Multiple studies have confirmed the relationship,
  but a definitive numerical model is unavailable
• Current roughness metrics (e.g., IRI) may not be
  best indicators of fuel consumption
• Ideal stopping distance and rolling resistance
  properties can be achieved simultaneously
• Texture wavelengths responsible for rolling
  resistance are separate from those providing
  friction

image sources www.topnotchcoatings.com/index/Orig
inal/9.jpg www.tc.gc.ca/civilaviation/internation
al/technical/images/pcc_spall_high.jpg
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Fuel ConsumptionPavement Structure

• Structural properties influencefuel consumption
• High stiffness pavements offer better fuel
  economy, but exact relationship is unknown
• Probably more significant for heavy vehicles
• Not necessarily a concrete versus asphalt issue
• Structures built with thick asphalt and stiff
  base layers offer similar deflection
  characteristics to concrete
• Assessments should be based on the entire
  structure, not just the surface material

image source pavementinteractive.org/images/8/82/
Hma.jpg
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Leachate

• Pavements contain heavy metals and PAHs
• In general, the literature refutes that pavement
  materials pose a significant water quality
  problem
• Much of the runoff quality issues stem from
  traffic-based pollutants, such as vehicle
  exhaust, lubrication oils, fuels, and tire
  particles
• Specialty applications present higher risks
• Recycled pavements contain high concentrations of
  traffic-based pollutants
• Asphalt sealcoats have been shown to produce high
  levels of PAHs, especially after the first
  flush

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Global Warming PotentialRanges of Impact for
Life-Cycle Components
Data source Santero and Horvath (2009) Global
Warming Potential of Pavements. Environmental
Research Letters. 4(3), 034011.
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Reducing Carbon Footprints

• Multiple ways to reduce carbon emissions
• Most effective solutions not necessarily the most
  obvious
• e.g., focusing on materials production is often
  not the most efficient method of improvement
• Different pavement locations, characteristics,
  and other details govern best-practices
• No one-size fits all solution

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Global Warming PotentialHigh- versus Low-Traffic
Scenarios
Data source Santero and Horvath (2009) Global
Warming Potential of Pavements. Environmental
Research Letters. 4(3), 034011.
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Measuring PerformanceEnvironmental Inventories
in Existing LCAs

• Pavements are commonly compared by their energy
  consumption
• However, no consistency regarding the inclusion
  of asphalts feedstock energy
• Air emissions (CO2, NOX, etc.) captured by
  roughly half of the studies
• Other environmental metrics not well inventoried,
  e.g.,
• water consumption
• water releases
• toxic releases

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Measuring PerformanceImpact Assessment

• Impact assessment improves understanding of
  inventory results
• Categories include human health, ecotoxicity,
  acidification, ozone depletion, and others
• Most pavement LCA rely on inventory results for
  conclusions
• Often not appropriate to aggregate impacts into a
  single score
• Weighting of impacts requires value choices,
  which change based on agency objectives and
  project scenarios

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Policymaking

• No silver bullet
• Each pavement presents its own unique challenges
  are opportunities for environmental improvement
• The most cost effective solutions will not be
  same for each pavement
• Focus on efficient reduction schemes
• Small changes in high-impact components will have
  a greater effect then large changes in low-impact
  components
• Identify which environmental metric(s) are
  important to the agency or institution
• Policy decisions may improve certain metrics
  while degrading others

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Next Steps

• Address research gaps in life cycle
• The use phase is particularly unexplored
• Efforts underway to develop more precise models
  (e.g., MIRIAM Project)
• Expand scope to include alternative metrics
• Energy and global warming are relatively well
  studied
• Water consumption, toxicity, and other impact
  areas deserve more attention
• Develop environmental policy based on LCA
  research
• Existing knowledge is sufficient to create
  general policies and roadmaps for improving
  environmental performance

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Acknowledgments