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    Green Highwaysconcrete pavement research and technologyspecial repor

    Contents

    1 Introduction

    2 Longevity

    3 ReducedVehicleFuelConsumptionandEmissions

    4 LowerConstructionFuelDemand

    5 UseoIndustrialByproducts

    5 Recyclability/Reusability

    6 ReducedUseoNaturalResources

    7 Light-ColoredandCool

    ReducedLightingRequirementHeatIslandMitigationSmogReduction

    9 LowerEnergyFootprint

    9 ImprovedWaterQuality

    10 QuietSuraceTextures

    11Conclusions

    12Reerences

    American ConcretePavement Association

    October 2007

    Introduction

    The concepts o sustainability and

    sustainable development are receiving

    much attention as the causes o global

    warming and climate change are debated.

    The World Commission on Environment

    and Development has dened sustainable

    development as meet[ing] the needs o

    the present without compromising theability o uture generations to meet their

    own needs (report to the United Nations

    General Assembly, August 1987).

    In 2005, the U.S. Environmental Protection

    Agency (EPA) started the Green Highways

    Initiative as an instrument or coordinat-

    ing transportation and environmentalism.

    According to this initiative, green high-

    ways are those that are environmentally

    responsible and sustainable in all aspects,

    including design, construction, and

    maintenance.

    A major ocus o the initiative is to demon-

    strate and ensure that sustainable prac-

    tices in pavements can go hand in hand

    with economic success. This is indeed true

    o concrete pavements.

    Particularly because o its long lie, con-

    crete is an economical, cost-eective

    pavement solution that consumes minimal

    materials, energy, and other resources or

    construction, maintenance, and rehabili-

    tation activities over its lietime. Beyond

    longevity, other eatures o concrete pave-

    ment urther enhance its sustainability:

    Properly constructed and textured

    concrete pavements have reduced

    pavement defection, which results in

    reduced vehicle uel consumption.

    The construction o concrete pavements

    consumes less uel (particularly diesel)

    during materials production, transporta-

    tion, and placement than the construc-

    tion o asphalt pavements.

    Concrete pavement mixtures incorpo-

    rate industrial byproducts (i.e., fy ash

    and slag cement), which lowers the

    disposal needs, reduces the demand on

    virgin materials, and conserves naturalresources.

    Concrete pavement itsel is renewable

    and 100% recyclable.

    Concrete pavement requires less sub-

    base aggregate materials or structural

    support than asphalt pavements.

    Concrete pavements lighter color and

    increased refectivity improve nighttime

    visibility, reduce the amount o power

    needed to illuminate roads at night,

    and help mitigate urban heat island and

    smog generation.

    Concrete pavements exhibit a lower

    energy ootprint associated with their

    production, delivery, and maintenance

    than asphalt pavements do over a pre-

    determined time period.

    Concrete pavements designed with

    pervious concrete shoulders minimize

    surace-water discharge and help replen

    ish groundwater aquiers.Optimized concrete pavement surace

    textures produce quieter pavements

    over longer periods o time, reducing

    noise pollution.

    Although cement is a relatively energy-

    intensive and carbon dioxide (CO2)-

    intensive material to manuacture, it

    is important to recognize that cement

    manuacturing accounts or only 1.5% o

    Environmentally and Economically Sustainable Concrete Pavements

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    Concrete Pavement Research and Technology Special Report

    U.S. CO2emissions; the balance o emissions comes rom

    sources such as electricity production (40%), transportation

    (33%), residential heating (6%), and various other commer-

    cial and industrial processes (DOE 2006).

    Furthermore, it is critical to recognize that cement is only

    one o the materials that make up the nal productcon-crete. Figure 1 illustrates how 92% o the volume o typical

    paving concrete is comprised o materials that require very

    little energy to obtain and have a low CO2ootprint, includ-

    ing sand, gravel, water, air, and industrial byproducts.

    In addition, the cement industry has taken dramatic steps

    to reduce any environmental impact o the manuacturing

    process, reducing the amount o energy to make a ton o

    product by more than 33% since 1972. The Cement Manu-

    acturing Sustainability (CMS) Program continues this

    success with a national pledge to reduce CO2

    emissions by

    an additional 10% per ton o product by 2020, rom a 1990

    baseline.The overall positive eects o reducing energy use and

    minimizing the environmental ootprint o development

    through ecient and sustainable use o concrete dramati-

    cally outweigh the impact o the cement manuacturing

    process (Carter 2006). Put another way, concrete is one

    o the worlds most CO2-ecient and sustainable building

    materials.

    The rest o this report provides more inormation about

    the eatures o concrete pavements that contribute to their

    legacy as a cost-ecient, sustainable, and green choice or

    highway pavements.

    Longevity

    The longevity o concrete pavements is well documented.

    Numerous concrete highways in North America have lasted

    50 years or more, supporting trac volumes much greater

    than originally anticipated. Such long-lasting concrete

    pavements are not conned to one region o North Amer-

    ica, nor to a specic type o environment or climate. A ew

    notable U.S. examples are provided here:

    Interstate 10 in the San Bernardino Valley in Caliornia

    was originally constructed in 1946 as part o Route 66.Portions o this concrete highway are still carrying trac

    today at an impressive volume o more than 200,000

    vehicles per day. Ater being renewed three times by

    surace grinding during its more than 60-year lie, this

    highway is a true testament to concrete pavements sus-

    tainability (ACPA 2006).

    US 52 in Charleston, South Carolina, which local resi-

    dents call Rivers Avenue, has provided Charleston resi-

    dents with uninterrupted service or more than 50 years.

    A two-mile (3 km) section o this eastwest thoroughare

    was paved with concrete in the early 1950s and has re-

    quired little in terms o maintenance since.

    Belknap Place, one o the rst concrete streets in San

    Antonio, Texas, was paved with concrete in 1914. It is still

    perorming well today, 92 years ater it was constructed

    (Taubert 2006).

    Route 23 through Kanabec County, Minnesota, was

    originally paved with concrete in 1948. According to a

    Minnesota Department o Transportation (DOT) pavement

    condition survey conducted in 2000, the 52-year old con-

    crete pavement still has a present serviceability rating

    (PSR) o 4.1 (Very Good).

    More than hal o the concrete pavements older than 50

    years remaining in Minnesota have a PSR greater than

    3.1 (corresponding to ratings o Good or Very Good)

    (Wathne and Smith 2006).

    Such long-lived concrete pavements have demonstrated

    economic advantages in terms o lie-cycle costs. In addi-

    tion, they contribute directly to the systems sustainability

    in several important ways.

    A long-lasting concrete pavement does not require rehabil-

    itation or reconstruction as oten, and thereore consumesless raw materials in the long run. This longevity impacts

    our environment in other ways as well. Energy savings are

    realized, since rehabilitation and reconstruction eorts con-

    sume energy. Also, congestion is reduced (with accompa-

    nying energy savings and reduction in vehicle pollutants)

    by employing long-lasting concrete pavements because o

    ewer construction zones impeding trac fow.

    Figure1.Concreteconstituents

    The PSR is an index o pavement roughness measured on a scale

    rom 0.05.0, where a higher value corresponds to a better pave-

    ment condition.

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    Green Highways

    Because o this longevity, concrete pavements have the

    potential to help society address the challenges o sustain-

    able development in numerous ways. Ultimately, all these

    environmental and social benets add up to greater long-

    term economic benets to the public.

    Reduced Vehicle Fuel Consumption

    and Emissions

    Prole stability is a term used to describe the ability o

    a pavement surace to resist deormation and defection

    caused by sustained and repeated loading. Unlike asphalt

    pavement, which is viscoelastic and thereore sensitive

    to both temperature and loading, concrete pavements

    rigid surace does not deorm under heavy vehicle loading

    and thereore defects less. This not only makes concrete

    pavement less susceptible to the ormation o heavy-

    vehicle wheel ruts and the associated increased hydro-

    planing potential, it also positively impacts vehicle uel

    consumption.

    Fuel consumption is partly a unction o the degree to

    which a pavement defects in response to the load applied

    as the wheels o heavy vehicles traverse the surace. Any

    defection absorbs some o the energy that would other-

    wise be available to propel the vehicle orward.

    Several studies to date suggest that the resistance (amount

    o defection) encountered by heavy-vehicle wheels on

    asphalt pavements is measurably greater than resistance

    on concrete pavements (Figure 2). Thus, more energy and

    more uel are required to move heavy vehicles on fexiblepavements (Taylor Consulting 2002).

    The most in-depth studies into this phenomenon were

    conducted in several phases over multiple years by the

    National Research Council o Canada (NRC). The nal study

    included collaboration between Natural Resources Canada

    (NRCan) and the Cement Association o Canada, with input

    rom various departments o transportation. The studies

    concluded that tractor-trailers traveling on concrete pave-

    ments have statistically signicant lower uel consumption

    than those traveling on asphalt pavements throughout the

    summer to winter temperature range or ully loaded trucks

    operating on smooth pavements [IRI < 120 in./mi (1,900

    mm/km)].

    The ndings rom these studies (Taylor Consulting 2002;

    Taylor and Patten 2006) are illustrated in Figure 3 and

    Tables 1 and 2. Figure 3 shows that uel consumptionor two common truck typestractor tanker semi-trailer

    and tractor van semi-trailercan be reduced an average

    o about 1% to 6% when traveling on concrete versus

    asphalt pavement, depending on truck type and vehicle

    speed. These savings were used to calculate the potential

    economic and environmental benets rom tractor-trailers

    traveling on concrete pavement compared to asphalt pave-

    ment, as shown in Tables 1 and 2.

    Table 1 identies the potential yearly savings or the maxi-

    mum, minimum, and average percent diesel uel saved in

    dollars, carbon dioxide, nitrogen oxides, and sulur dioxide

    i one tractor-trailer unit traveled 100,000 miles (160,000km) in a year. For the calculations, it is assumed that the

    tractor-trailer unit has an average engine uel consumption

    o 5.5 miles per gallon (43 liters per 100 km) and that diesel

    uel costs $2.99 per gallon ($0.79 per liter).

    Table 2 identies the potential yearly savings or a major

    arterial highway that is 62 miles (100 km) long and car-

    Concrete PavementAsphalt Pavement

    Figure2.Exaggerateddepictionoatrucktirerollingonasphalt(let)andconcrete(right)

    Figure3.Fuelsavingswithconcreteversusasphaltpavement

    0%

    1%

    2%

    3%

    4%5%

    6%

    7%

    8%

    Tanker37 mph (60 km/h)

    Tanker62 m ph (100 km/h)

    V an37 mph (60 km/h)

    V an62 m ph (100 km/h)

    Semi-Tractor Type and Speed

    FuelSavings

    Range

    Midrange

    Assumptions:- Equivalent roadway design- IRI < 120 in./mi (1,900 mm/km)

    Ada pt ed fro m Ta ylo r a nd Pa tte n, 20 06

    Table1.Yearlypotentialsavingsincost,CO2,NOX,andSO2

    pertractortrailer

    Fuel

    Savings

    (%)

    Minimum: 0.80

    Average: .85

    Maximum: 6.90

    FuelCost

    Saved

    (dollars)

    $45

    $,100

    $,760

    CO2

    [tons

    (metrictons)]

    1.66 (1.50)

    8.06 (7.1)

    14.4 (1.0)

    Note: CO

    = carbon dioxide equivalent (includes carbon dioxide, methane, and

    nitrous oxide), NOx = nitrogen oxides, SO = sulur dioxide.

    Fuel

    Saved

    [gal(l)]

    145 (549)

    700 (,650)

    1,50 (4,70)

    NOx

    [lb(kg)]

    7. (16.9)

    18 (8.6)

    7 (148)

    SO2

    [lb(kg)]

    4.80 (.18)

    .0 (10.4)

    41. (18.7)

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    Concrete Pavement Research and Technology Special Report4

    ries 20,000 vehicles per day with 15% trucks. Calculations

    assume the same tractor-trailer unit average engine diesel

    uel consumption and diesel uel cost used in Table 1.

    The dierence in uel consumption as a unction o pave-

    ment type should be an important consideration or

    government agencies when analyzing potential pavement

    structures or new or reconstructed pavements. Signicant

    greenhouse gas and cost savings can be realized whenoperating tractor-trailers on concrete pavements versus

    asphalt pavements.

    These environmental and economic savings can have

    signicant down-stream implications to the public. They

    also play an important role in government goals to lower

    dependence on oreign oil and oster environmental stew-

    ardship. The emission reductions result in a direct public

    health benet. The cost o consumer goods likely will be

    aected as well because lower uel consumption decreases

    transportation expenses, which, on average, comprise

    nearly one-th o the cost o a typical consumer item.

    In the context o overall transportation sustainability, these

    uel savings and pollutant reductions are enormous. In the

    case o greenhouse gases (CO2) alone, the average sav-

    ings realized by the 62-mile (100-km) long major arterial

    highway in Table 2 over its 30-year design lie [165,000 tons

    (150,000 metric tons)] are more than three times greater

    than the CO2

    emitted during the manuacture o cement

    used or the construction o the concrete pavement [52,800

    tons (48,000 metric tons)].

    Put another way, all o the CO2

    emitted during the manu-

    acture o cement used to construct a concrete highway

    pavement is compensated or during the rst nine years oservice by virtue o the reduced pavement defection and

    improved truck uel eciency. The remaining 22 years o

    service and the proportionate CO2

    savings are a urther

    testament to the sustainability o concrete pavements.

    Lower Construction Fuel Demand

    The construction o highway pavements requires a lot o

    energy. The production o paving materials, the transporta-

    tion o these materials to the site, and their actual place-

    ment consume signicant amounts o uel, mostly diesel.

    The Federal Highway Administration (FHWA) reports on

    uel usage or various elements o construction, includinghighway paving, in its Technical Advisory T 5080.3 on Price

    Adjustment Contract Provisions (FHWA 1980). Attachment

    1 o this Technical Advisory shows that the uel usage actor

    or asphalt pavements is 2.90 gallons per ton (12 liters per

    metric ton), and or concrete pavements is 0.98 gallons per

    cubic yard (4.9 liters per cubic meter). However, as these

    uel usage actors are reported in dierent units, it is some-

    what dicult to make a direct comparison (FHWA 1980).

    Table 3 converts these construction uel usage actors to

    uel required per mile o roadway constructed or asphalt

    and concrete. Though equivalently designed concrete

    pavement thicknesses are typically between two and threeinches thinner than an asphalt pavement designed or the

    same scenario, this example conservatively assumes that

    the pavements have the same thickness. This example also

    ignores the act that asphalt pavements typically require

    more layers o base granular material at a greater thickness

    when compared to an equivalent concrete pavement.

    The table shows that the amount o uel used per lane-mile

    (lane-km) o concrete roadway constructed is less than

    one-th o the uel used to construct the same lane-mile

    (lane-km) o asphalt.

    This means that i concrete pavements were placed instead

    o the roughly 500 million tons (450 million metric tons)

    o asphalt placed each year (FHWA 2007), the savings in

    diesel uel rom construction alone would amount to nearly

    1.2 billion gallons (4.5 billion liters).

    Table2.Yearlypotentialsavingsincost,CO2,NOx,andSO2oratypicalmajorarterialhighway

    FuelSaved

    [gal(l)]

    99,500 (77,000)

    479,000 (1,810,000)

    858,000 (,50,000)

    FuelCostSaved

    (dollars)

    $98,000

    $1,40,000

    $,570,000

    CO2

    [tons(metrictons)]

    1,150 (1,040)

    5,510 (5,000)

    9,880 (8,960)

    Note: CO = carbon dioxide equivalent (includes carbon dioxide, methane, and nitrous oxide), NOx = nitrogen oxides, SO = sulur dioxide.

    NOX

    [lb(kg)]

    5,900 (11,700)

    15,000 (56,700)

    4,000 (10,000)

    ,80 (1,490)

    15,800 (7,170)

    8,00 (1,800)

    SO2

    [lb(kg)]

    FuelSavings

    (%)

    Minimum: 0.80

    Average: .85

    Maximum: 6.90

    Sample calculation or CO2

    emitted during the manuacture o cement used in the construction o a concrete highway segment:

    Highway: 62 mi (100 km) long, 2 lanes wide [8 yd (7 m) total], 10 in. (250 mm) thick

    Cement content in concrete mixture: 480 lb cement per cubic yard (285 kg per cubic meter)

    Cement used in the concrete highway segment:

    62 mi (100 km) x 1760 yd/mi (1,000 m/km) x 8 yd (7 m) x 0.28 yd (0.26 m) x 480 lb/yd3 (285 kg/m3)

    2,000 lb/ton (1,000 kg/metric ton)

    CO2

    emitted: 58,700 tons (53,300 metric tons) x 0.9 tons o CO2

    per ton o cement manuactured = 52,800 tons ( 48,000 metric tons)

    58,700 tons ( 53,300 metric tons)=

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    Green Highways 5

    Table3.Constructionueldemandorasphaltversusconcretepavement

    Pavementtype Thickness ConstructionFuelDemand

    Asphalt 10 in. (50 mm) 10,718 gal (40,57 l)

    Concrete 10 in. (50 mm) 1,916 gal (7,5 l)

    Assumptions: Asphalt density = 140 lb/yd (8 kg/m). Fuel usage actors:

    Asphalt .90 gal/ton (1 l /metric ton), Concrete 0.98 gal/cy (4.9 l/m) rom

    FHWA T 5080., Attachment 1.

    In addition to the obvious economic benets, there are

    enormous environmental advantages. The savings in

    diesel uel eliminates the emission o approximately 13.3

    million tons (12.1 million metric tons) o CO2

    into our atmo-

    sphere each year. To put this into perspective, the average

    passenger car emits about ve tons (4.5 metric tons) o CO2

    annually (EPA 1997). The CO2

    savings realized by construct-

    ing concrete pavements instead o the 500 million tons(450 million metric tons) o asphalt placed annually would

    be equivalent to taking 2.7 million cars o the road.

    Use of Industrial Byproducts

    In most concrete used or highways in North America,

    some o the portland cement is replaced or supplemented

    with one or more industrial byproducts. These byproducts

    are oten reerred to as supplementary cementitious mate-

    rials (SCMs). The three most commonly used SCMs are fy

    ash (byproduct o coal burning), slag cement or ground

    granulated blast urnace slag (byproduct o iron produc-tion), and silica ume (byproduct o silicon or errosilicon

    alloy manuacturing).

    Using SCMs in concrete pavement has several environ-

    mental benets. First, recovering industrial byproducts

    avoids the use o virgin materials needed or cement man-

    uacturing. Additionally, benecial utilization reduces the

    amount disposed in landlls. More importantly, however,

    are the greenhouse gas and energy reductions achievable

    by using SCMs to replace a portion o portland cement.

    CO2

    and energy savings are related to the percentage o

    SCM used in the concrete mixture design. Many state

    highway agencies allow up to 25% o portland cement tobe replaced with fy ash and 50% to be replaced with slag

    cement; some states even allow higher SCM replacement

    levels.

    While portland cement is an essential ingredient in con-

    crete, its production requires signicant energy use and

    generates greenhouse gases. The cement industry in North

    America has made signicant strides in reducing energy

    and emissions associated with cement manuacturing.

    Beyond these production technology improvements, the

    environmental impact o portland cement can be urther

    reduced through partial replacement o cement with SCMs.

    One study (Marceau and VanGeem 2005) showed that,

    or a typical Maryland DOT concrete pavement mixture,

    a replacement o 50% o the portland cement with slag

    cement resulted in a 35% reduction in embodied primaryenergy and a 45% reduction in embodied greenhouse gas

    per cubic yard (cubic meter) o concrete. This calculation

    includes all the energy utilized and emissions generated in

    mining, manuacturing and transporting concretes con-

    stituent materials, as well as the manuacturing processes

    involved with producing concrete.

    The EPA also recognizes the importance o SCMs in

    disposal, energy, and greenhouse gas reduction. Their

    Comprehensive Procurement Guidelines require that slag

    cement, fy ash, and silica ume be included in all construc-

    tion project specications utilizing ederal unding (greater

    than $10,000), unless a valid technical or market reason ornot using them can be documented.

    Besides these environmental benets, SCMs can enhance

    concrete properties when used in appropriate quantities.

    For example, they can improve workability o the mixture,

    decrease concrete permeability, improve durability, and

    enhance strength. Cost savings may also result in markets

    where SCMs are less expensive than portland cement,

    or where mixture optimization can provide engineering

    properties (e.g., strength or durability) that would be more

    expensive to achieve without SCMs.

    Details on several U.S. and Canadian DOTs allowances or

    the use o SCMs can be ound in A Synthesis of Data onthe Use of Supplementary Cementing Materials in Con-

    crete Pavement Applications Exposed to Freeze/Thaw and

    Deicing Chemicals (Cement Association o Canada 2005),

    as well as in ACPAs State Practices database, accessible

    online at www.pavement.com.

    Recyclability/Reusability

    At the end o its useul lie, a concrete pavement surace

    can be renewed via concrete pavement restoration (CPR)

    activities, such as ull/partial depth repairs, dowel-bar retro

    tting, and grinding. Diamond grinding is a particularlyuseul technique used to restore pavements and improve

    ride quality, noise, and surace texture. Studies reported

    by the Caliornia Department o Transportation (Caltrans)

    suggest that the average time beore additional rehabilita-

    tion is needed or a diamond ground pavement is approxi-

    mately 17 years (Stubstad et al. 2005).

    Experience tells us that grinding a pavement as many as

    three times is possible without compromising its atigue

    lie. An excellent example o this is a section o I-10 (San

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    Concrete Pavement Research and Technology Special Report6

    tional global warming benets resulting rom a process

    called carbon sequestering.

    Approximately 60% o the CO2

    emitted during the manu-

    acture o portland cement results rom a process known as

    calcination, a chemical reaction among the raw materials

    in the cement kiln. When cement is subsequently used toproduce concrete, another chemical reaction, called hydra-

    tion, occurs that allows the cement to orm compounds

    that bind the aggregates together. Later, when hardened

    concrete is exposed to air, the calcination reaction reverses

    in a process called carbonation.

    In essence, carbonation recaptures CO2. Carbonation

    occurs naturally in all concrete, albeit at very slow rates

    due primarily to the low permeability o concrete. How-

    ever, exposing a large surace area o concrete to the atmo-

    sphere, typically through crushing, dramatically accelerates

    the carbonation process. Eventually, such exposure may

    allow or the recapture o all the CO2 originally evolvedrom the cement raw materials during calcination (RMRC

    2005).

    Reduced Use of Natural Resources

    Another consideration is the volume o granular base/sub-

    base materials needed to provide structural support or

    pavement. Because o concretes rigidity and stiness, the

    slab itsel supplies a major portion o its structural capacity

    and distributes heavy vehicle loads over a relatively wide

    area o subgrade. An asphalt pavement is not as rigid and

    does not spread loads as widely. Thereore, asphalt pave-

    ments usually require more layers o base granular mate-

    rial at a greater thickness when compared to an equivalent

    concrete pavement design (ACPA 2007).

    Based on an analysis perormed on equivalent pavement

    designs or asphalt and concrete pavements or an arterial

    Bernardino Freeway) just east o Los Angeles. It was

    originally constructed in 1946 as part o Route 66. In 1965,

    it was ground to correct the considerable amounts o joint

    spalling and aulting that had developed during its more

    than 20 years o service.

    This rst ever continuous grinding project in North Amer-ica provided 19 years o additional service. In 1984, this

    pavement got a third lease on lie when Caltrans decided

    to restore the pavement again using diamond grinding. In

    1997, the 51-year old pavement was ground or a third time.

    Ater more than 60 years o service, the concrete pave-

    ment is currently carrying more than 200,000 vehicles each

    day, a true testament to concrete pavements sustainability

    (ACPA 2006).

    Concrete pavement is a 100% recyclable material as well.

    At the ultimate end o its atigue lie, concrete pavement

    can be crushed and reused in many ways, or example,

    as granular ll, subbase material, or base course or newpavement. A 2005 study conducted by the Construction

    Materials Recycling Association revealed that about 130

    million to 140 million tons (118 million to 127 million metric

    tons) o concrete were crushed and recycled in 2004.

    Recycled concrete pavement can also be used as an aggre-

    gate or new concrete pavement. Some state DOTs allow

    up to 100% o coarse aggregate in concrete mixtures to be

    recycled concrete aggregate. This leads to reduced demand

    on nonrenewable natural resources. In addition, the short

    hauling distance or recycled concrete aggregate can, in

    some cases, reduce the cost o providing aggregate or

    the project. Figure 4 shows an on-site concrete pavementrecycling operation.

    Using recycled concrete pavement, particularly in applica-

    tions that expose it to the atmosphere (e.g., embankment

    ll, gravel roads, roo ballast, and railroad ballast) has addi-

    Figure4.Paradigmin-placeconcreterecyclingequipmentinoperationinOklahoma(photocourtesyoDuitConstruction)

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    Green Highways 7

    road on a low-strength subgrade, approximately twice as

    much granular material is needed or an asphalt pavement

    structure than or a concrete structure (ARA 2003). The

    environmental eect o this increased demand on granular

    material may be amplied i suitable aggregate sources

    are not locally available. Longer haul distances result in

    aggregate haul trucks consuming more uel and emitting

    more CO2.

    Light-Colored and Cool

    Concrete suraces readily refect light. This characteristic

    o concrete, generally reerred to as albedo, is advanta-

    geous or several reasons. It can signicantly improve

    both pedestrian and vehicular saety by enhancing night-

    time visibility on and along concrete roadways. It reduces

    the amount o energy needed or articial roadway illu-

    mination during the night. It also reduces the amount o

    energy needed to cool urban environments, and reducesthe potential or smog ormation. These eects are urther

    discussed in the ollowing sections.

    Reduced Lighting Requirement

    Lighting xtures are important elements o most urban

    highway acilities. Enhanced nighttime visibility is intui-

    tively related to improved trac saety. Figure 5, which

    shows highway Castello Branco in Sao Paulo state, Brazil,

    at night, clearly illustrates how visibility is improved in

    the lanes paved with concrete (ABCP 2005). In addition,

    because o the more refective nature o concrete pave-

    ments, a specied luminance level can be achieved withewer high-output lighting xtures and standards. Ulti-

    mately, this translates to lower costs and lower energy

    consumption over time.

    A report comparing the environmental impacts o concrete

    pavements to asphalt pavements indicates that asphalt

    pavements require more lights per unit length to achieve

    the same illumination as concrete pavements (Gajda and

    VanGeem 1997). The results suggest cost savings o as

    much as 31% in initial energy and maintenance costs

    or lighting concrete pavements versus lighting asphalt

    pavements. Similar results are shown in Figure 6, where

    energy costs required to illuminate an asphalt roadway are

    estimated to exceed the costs o illuminating a concrete

    roadway by 33%.

    Heat Island Mitigation

    The energy o sunlight that is not refected o pavement

    suraces is converted into thermal energy that increases

    the pavements temperature. This, in turn, increases the

    Figure5.Brazilroadwayillustratingconcrete(let)vs.asphaltalbedo

    Figure6.Theneedoradditionallightfxturesleadstohigherannualenergycostsorroadspavedwithasphalt

    InitialCost

    forPoles

    Annual

    EnergyCost

    $126,000

    $155,000

    $4,560

    $5,630

    Cost ($) per mile of pavement

    Assumes: Initial cost = $5,000/pole; Maintenance cost = $100/pole/year;Energy cost = $0.0814/kwh; Operating time = 4,000 hours/pole/year

    Conc

    rete

    Aspha

    lt

    Asphalt requires 24% more poles

    Initial costs, maintenance costs, and energy costs

    are all 24% higher

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    Concrete Pavement Research and Technology Special Report8

    temperature o the air around the pavement. In urban

    areas, the higher air temperature that occurs as a result

    o pavements and other suraces absorbing the suns heat

    is known as the heat island eect. According to some

    researchers, downtown areas o North American cities are

    up to 9F (5C) warmer than surrounding suburban and

    rural areas, where natural vegetation cools the air throughevapotranspiration (Granitto 2000). Figure 7 shows an EPA

    illustration representing the urban heat island prole.

    The heat island eect can contribute signicantly to energy

    consumption or air conditioning to cool urban buildings.

    This not only consumes energy and costs money, it also

    leads to higher emissions rom power plants. One esti-

    mate is that the increase in temperature due to heat island

    eects accounts or 510% o peak urban electric demand

    or air conditioning use (Akbari 2005).

    Paving urban roadways with concrete is an eective strat-

    egy to help mitigate urban heat island eects. With theirhigher albedo, concrete pavements refect signicantly

    more sunlight and are cooler than asphalt pavements.

    Research conducted at the Lawrence Berkeley National

    Laboratory suggests that, when exposed to sunlight,

    lighter-colored concrete pavements typically have surace

    temperatures approximately 21F (12C) lower than darker-

    colored asphalt pavements (Pomerantz et al. 2000).

    Figure 8, a thermal image o the ramp to State Road 202 in

    Mesa, Arizona, taken in August 2007, shows that the reduc-

    tion in heat retention and emittance can be signicant or

    brighter and more refective concrete pavements. The ther-

    mal image illustrates the temperature dierence betweenconcrete pavement (oreground) and asphalt pavement

    (background) in the same ambient conditions. The picture

    was taken at approximately 5:00 pm during partly cloudy

    conditions, and the temperature dierence between the

    two pavement suraces was approximately 20F (11C).

    One estimate puts the cooling energy savings rom cool

    suraces and shade trees, when ully implemented, at $5

    billion per year in the United States alone (Akbari 2005).

    A 1997 report suggests that increasing the albedo o 775

    miles (1,250 km) o pavement in Los Angeles (L.A.) by 0.25

    (i.e., converting asphalt to concrete) would save $15 million

    in cooling energy each year (Pomerantz et al. 1997).

    Smog Reduction

    The exact eect o pavement type on heat retention and

    resulting air quality issues, such as smog ormation, is

    complicated and somewhat poorly understood. However, it

    is clear that the process o smog ormation is very sensitive

    to temperature.

    Automobile exhaust and industrial emissions are respon-

    sible or the release o a amily o NOx

    (nitrogen oxide)

    gases and other volatile organic compounds (VOCs) as

    byproducts o burning gasoline and coal. On warm sunny

    days, these NOx

    and VOCs can combine with oxygen to

    orm ozone. Higher temperatures result in increased smog

    ormation. Typically, at temperatures below 70F (21C),

    smog concentrations are not signicant. However, at tem-

    peratures o 95F (35C) and above, the presence o smog

    is very likely. Cooling a city by only 5F (3C) can have a

    dramatic impact on smog concentration (Lawrence Berke-

    ley Laboratories 2004).

    Use o lighter-colored concrete pavements can help in this

    regard. Computer simulations or L.A. show that resurac-

    ing about two-thirds o the pavements and rootops with

    more refective suraces and planting three trees per house

    can lower temperatures by as much as 5F (3C) and can

    thereore signicantly reduce the potential or smog orma-

    tion (Akbari 2005).

    Figure8.ThermalimageoapavementinMesa,Arizona(notethetemperaturedierencebetweentheconcretepavement(oreground)andtheasphaltpavement(background))

    Figure7.EPAillustrationoanurbanheat-islandprofle

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    Green Highways 9

    The previously mentioned Pomerantz study also ound that

    switching the surace o 775 miles (1,250 km) o pavement

    in L.A. rom asphalt to concrete would reduce smog-related

    medical and lost-work expenses by $76 million per year.

    Lower Energy FootprintEmbodied primary energy is a measure o all energy use

    associated with the production, delivery, and maintenance

    o a acility over a predetermined time period. It includes

    both eedstock energy (the gross combustion heat value

    o any ossil hydrocarbon that is part o the pavement, but

    is not used as an energy source; e.g., bitumen) as well as

    primary energy (ossil uel required by system processes

    including upstream energy use).

    An embodied primary energy analysis in this context

    accounts or the energy needed to extract materials rom

    the ground (e.g., aggregates, raw materials or cement

    production, oil or asphalt, etc.), process these materials,produce the paving mixtures, construct the roadway, main-

    tain it, and rehabilitate it over a predetermined time period.

    This approach is an eective means to evaluate the energy

    ootprint a acility makes during its lietime.

    A recent study conducted by the Athena Institute presents

    embodied primary energy and global warming estimates

    or the construction and maintenance o equivalent con-

    crete and asphalt pavement structures or several dier-

    ent road types in various geographic regions in Canada

    (Athena Institute 2006). The study period was 50 years, a

    period that takes into account original road construction

    and all maintenance and rehabilitation activities or bothpavement alternatives.

    For all six pavement structural design comparisons, the

    concrete pavement alternatives clearly require signicantly

    less energy than their asphalt pavement counterparts rom

    a lie-cycle perspective. Results show that asphalt pave-

    ments require two to ve times more energy than equiva-

    lent concrete pavement alternatives. As an example, Figure

    9 shows the comparative embodied primary energy or

    the high-volume highway pavement structures analyzed

    (with 0% recycled asphalt pavement (RAP) included in the

    nal pavements). As this gure illustrates, the embodied

    primary energy associated with concrete pavement alterna-

    tives is only about 33% o the embodied primary energy

    associated with asphalt pavement alternatives.

    Also evident rom Figure 9 is that the eedstock energy

    component is the largest contributor to total energy or

    the asphalt pavements. However, even when eedstock

    energy is excluded rom the analysis, concrete pavements

    still present a signicant energy advantage over their

    asphalt counterparts or all pavement structures analyzed.

    Even with the inclusion o 20% RAP in the asphalt pave-

    ment alternatives, the energy advantage o the concrete

    pavement counterparts is still signicant, especially at theembodied energy level (Athena Institute 2006).

    This study refects the embodied energy and greenhouse

    gas emissions related only to production, transportation,

    and placement o materials or initial construction, mainte-

    nance, and rehabilitation. Operational considerations, such

    as truck uel savings by operating on dierent pavement

    types (see Reduced Vehicle Fuel Consumption and Emis-

    sions on page 3) and energy savings due to the dierent

    light refectance properties o the pavement types (see

    Reduced Lighting Requirement on page 7), are not consid-

    ered. The report does suggest that uel savings and urban

    heat island eects should be taken into account in any decisions predicated on lie-cycle environmental analyses.

    Improved Water Quality

    Stormwater quality can be improved through the innova-

    tive use o pervious concrete pavements. Pervious con-

    crete pavements are comprised o specially graded coarse

    aggregates, cementitious materials, admixtures, water, and

    little or no nes. Mixing these products in a careully con-

    trolled process creates a paste that orms a thick coating

    around aggregate particles and creates a pavement with

    interconnected voids on the order o 12 to 35%. This results

    in a pavement that is highly permeable, with drainage rates

    in the range o 2.5 to 18 gallons per minute per square oot

    (100 to 730 liters per minute per square meter) (Brown

    2003).

    Pervious concrete has the potential to provide an envi-

    ronmentally sensitive product or specic applications.

    Currently, the most common uses o pervious concrete are

    parking lots (Figure 10), low trac pavements, and pedes-

    trian walkways. However, interest in its use or highway

    pavements and shoulders is increasing.

    Figure9.Comparisonoembodiedprimaryenergyorhigh-volumeroadways(0%RAP)

    0 (0)

    5 (5)

    10 (11)

    15 (16)

    20 (21)

    25 (26)

    30 (32)

    35 (37)

    As ph al t ( CB R= 3) Co nc re te (C BR =3 ) As ph alt (C BR =8 ) Co nc re te (C BR =8 )

    Pavement Structure

    Feedstock Energy

    Primary Energy

    Energy[B

    TU(

    kJ)]

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    Concrete Pavement Research and Technology Special Report10

    Pervious concrete pavements reduce stormwater runo

    and help recharge groundwater aquiers. They also reduce

    the amount o pollutants, such as car oil, anti-reeze, and

    other automobile fuids, contained in non-runo stormwa-

    ter. By allowing some rainall to percolate into the ground,

    pervious concrete promotes natural ltration and treat-

    ment o rainwater via soil chemistry and microbial activity

    (Brown 2003).

    Experience with pervious concrete pavements has been

    promising, particularly in warmer southern climates.

    Research in progress is addressing the reeze-thaw dura-

    bility o pervious concrete to establish parameters or its

    durability and application as shoulders in colder climates.

    One research project at the National Concrete Pavement

    Technology Center at Iowa State University in Ames,

    Iowa, suggests that, with a properly proportioned mixture,

    reeze-thaw perormance can be excellent (Kevern et al.

    2005; Schaeer et al. 2006).

    Clogging o pores within the concrete matrix has also been

    noted as a challenge o pervious paving materials. Even

    with signicant deposition o nes within the pore struc-

    ture o pervious concrete, however, the drainage rate is still

    sucient to maintain fow during the majority o signicant

    rainall events. Routine sweeping or vacuuming o the

    pavement surace will remove any deposited material and

    restore the porosity o clogged pervious concrete to nearly

    new conditions.

    Quiet Surface Textures

    Noise pollution is a growing concern in North America.

    The surace texture o a highway pavement controls many

    important actors, including trac noise. Noise generated

    at the tirepavement interace is oten the most dominant

    at highway speeds (TCPSC 2005).

    One o the advantages o concrete pavements is that virtu-

    ally any texture can be created during nishing operations,

    including textures that minimize tirepavement noise while

    maintaining wet- and dry-weather riction or the lie o the

    pavement.

    Research by the concrete paving industry is currently

    underway to identiy optimal textures or low noise generation at the tirepavement interace in a variety o circum-

    stances. In North America, a signicant amount o noise

    issues are related to existing transversely-tined concrete

    pavements. Consequently, some o the ongoing research

    is ocused on identiying diamond grinding techniques

    or retexturing pavement to produce the quietest sur-

    ace textures. Research currently underway at Purdue

    Universitys Institute or Sae, Quiet, and Durable Highways

    is evaluating the eect o grinder blade widths and blade

    spacing on noise perormance.

    Research by the National Concrete Pavement Technology

    Center is looking at conventional textures in order to deneconstruction variability (in terms o depth, width, spacing,

    etc.) and to develop an understanding o the relationship

    between three-dimensional (3D) surace texture and noise.

    The 3D texture is measured using a new, lightweight,

    remote-controlled, line-laser measurement device that pro-

    vides real-time graphic displays o both micro- and macro-

    texture (Cackler et al. 2006).

    Results rom research conducted to date indicate that or

    ordinary concrete pavements, longitudinal textures

    including tining, grooving, and grindingare particularly

    avorable in terms o low noise generation (Ardani and

    Outcalt 2005). Some o the quietest concrete pavementsmeasured in North America are longitudinally-ground

    pavements, oten called whisper ground.

    Whisper grinding reers to the practice o grinding con-

    crete pavement specically or improving its noise prole,

    as opposed to grinding or smoothness and ride. Blade

    width, blade spacing, and grinding depth are selected with

    noise mitigation in mind.

    FHWA, in its recent Technical Advisory on Surace Texture

    or Asphalt and Concrete Pavements, includes longitudinal

    tining, grooving, and grinding as recommended practices

    to provide the desired texture over the perormance lie othe pavement and minimize objectionable levels o tire

    pavement noise (FHWA 2005). Figure 11 depicts one o the

    quietest concrete pavement textures measured in North

    America (Section o I-94 along the MNRoad test acility).

    Ongoing research is also looking at other innovative tex-

    tures that may provide desired environmentally sensitive

    surace characteristics. Although experience with exposed

    aggregate textures is very avorable in Europe, in terms o

    both noise mitigation and cost eectiveness, there is very

    Figure10.PerviousconcretepavementparkingareainNormal,Illinois

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    Green Highways 1

    little experience and only a ew installations with exposed

    aggregate textures in North America.

    When ongoing research on optimal surace textures or

    noise is completed, public highway agencies and the pav-

    ing industry will have even better guidelines or construct-

    ing concrete pavements that generate minimal noise at the

    tirepavement interace, while still meeting or exceeding

    dry- and wet-weather riction requirements.

    Another consideration when evaluating any pavements

    perormance in terms o noise is acoustic durability, or how

    tirepavement noise changes over time as the pavement

    surace wears.

    A pavements noise prole must be considered not only

    immediately ater construction but over the lie o the

    pavement. Concrete pavements inherently rigid structure

    reduces the potential or erosion o the desirable sur-

    ace texture eatures under trac loading. Unlike asphalt

    pavements, which are viscoelastic and thereore sensitive

    to both temperature and sustained or repetitive loading,

    concrete pavements much more readily retain their initial

    surace textures and the associated noise characteristics or

    the lie o the pavement. As detailed in previous sections,

    this characteristic o concrete pavements also positively

    impacts both truck uel economy and saety.

    Conclusions

    Concrete pavement has long been considered an environ-

    mentally and economically sustainable pavement choice

    or its longevity. This hallmark o concrete pavements

    ensures that the desirable perormance characteristics o

    the pavement remain essentially intact or several decades.

    In addition, long-lasting concrete pavements do not require

    rehabilitation or reconstruction as oten and, thereore,

    consume ewer raw materials over time. Energy savings

    also are realized, since rehabilitation and reconstruction

    eorts consume energy. Even more importantly, conges-

    tion is reduced by using long-lasting concrete pavements

    because o less requent construction zones that impedetrac fow. Ultimately, all o these benets add up to

    greater long-term economic and social benets to the

    public.

    However, there are many other eatures o concrete pave-

    ments that also support the case or concrete pavements

    sustainability. As mentioned beore, these eatures all con-

    tribute to making concrete pavements an environmentally

    sensitive pavement choice:

    The rigidity o concrete pavement means lower vehicle

    uel consumption and emissions.

    Less uel-intensive construction operations or concretepavement result in enormous economic and CO

    2sav-

    ings.

    Using industrial byproducts in concrete improves pave-

    ment longevity, saves money, reduces the need or

    disposal in landlls, and greatly reduces both energy use

    and generation o greenhouse gases.

    Concrete pavements renewability and 100% recyclability

    lead to improved longevity and reduced demand on non-

    renewable resources.

    The strength and rigidity o concrete means ewer andthinner required layers o subbase materials.

    The light-colored and cool surace o concrete pavement

    leads to improved visibility, reduced lighting require-

    ment, and reduced heat island eects.

    Concrete pavements overall lower energy ootprint

    means tremendous savings in energy over the lie o the

    pavement acility.

    Pervious concrete pavements capture and lter pave-

    ment runo and help improve stormwater quality.

    Optimized surace textures can be imparted on concretepavements that result in long-lasting, quiet pavements.

    These benets result in greater long-term cost-eective-

    ness to the public. As such, concrete pavements are the

    clear choice or environmentally sensitive and economi-

    cally sustainable roadwaystruly green highways, in more

    ways than one.

    1.

    2.

    3.

    4.

    5.

    6.

    7.

    8.

    9.

    Figure11.Quiet,longitudinallygroovedconcretepavement(photocourtesyoDiamondSurace,Inc.)

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    AmericanConcretePavementAssociation

    5420OldOrchardRoadSuiteA100Skokie,IL60077

    phone:847.966.2272ax:847.966.9970www.pavement.com

    PublicationNo.SR385P

    The American Concrete Pavement Association (ACPA) is the premier national association representing concrete pavement contractors, cement companies,

    equipment and materials manuacturers and suppliers. We are organized to address common needs, solve other problems, and accomplish goals related to

    research, promotion, and advancing best practices or design and construction o concrete pavements.

    The opinions, ndings, and conclusions expressed in this special report are based on the acts, tests, and authorities stated herein. This publication is intended

    or the use o proessional personnel competent to evaluate the applicability and limitations o the reported ndings and who will accept responsibility or the

    application o the material contained herein. The ACPA and its partners disclaim any liability or the application o the inormation contained in this document an

    cannot be held responsible or the accuracy o any o the sources other than work developed by the association.