Pavement Type Selection July 2010

7/30/2019 Pavement Type Selection July 2010

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PAVEMENTTYPE

SELECTION

AMERICA RIDES ON US

A POSITION PAPER BY

THE ASPHALT PAVEMENT ALLIANCE


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CONTENTSPreface 3

Introduction 4

Principal Factors 4 Trafc 4

Asphalt Pavements Can Handle Heavy Loads 4

Asphalt Oers Flexibility in Construction, Maintenance, andRehabilitation 5

Asphalt Provides or Easy Maintenance and Rehabilitation 5

Asphalt Pavements Last and Stay Smooth 5

Soil Characteristics 6

Asphalt Is Used on All Types o Soils 6

Weather 7

Asphalt Pavements Can Be Designed or Any Weather 7

Construction Considerations 7Asphalt Allows Staging Options 8

Asphalt Pavements Can Be Built Fast 8

Asphalt Construction Timing Is a Matter o Flexibility 8

Recycling 8

Asphalt Is Americas Most Recycled Material 8

Other Reused Materials Can Enhance Asphalt Perormance 9

Cost Comparison 9

Lie-cycle Cost Analysis Is Important 9

Initial Cost 10

Staging Costs 10Predicted Perormance Lie 10

Maintenance Costs 11

Salvage Value 11

Discount Rate 12

Asphalt Pavements Cost Less 12

Other Considerations 13

Sustainability 13

Noise 13

Roughness 14

Saety 14

Summary 15

References 16

Appendix A: Summary of Life-cycle Cost Inputs from Various States 17

Appendix B: Pavement Type Selection Checklist 19


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Preface

In general, there are no greater investmentsmade by a transportation agency than theconstruction or reconstruction o pavements. Thenancial and highway user impacts are great andar-reaching. Pavement type selection deservesanalysis commensurate with such investment.Pavement selection involves many actors, asyou will learn rom this synthesis. One thought,however, must always take precedence: that is,

pavements are intended to serve highway users.To the extent that the pavement selection servesusers, by ensuring that they travel on pavementsthat are sae, smooth, quiet, durable, economical,and constructed o sustainable materials,the designer has succeeded in meeting thisimportant objective.

Pavement type selection processes areuniversally utilized by state departments otransportation and other agencies responsible or

roadway construction to identiy and select themost durable, cost-eective, highest-perormingpavement structure or a new roadway. Theseprocesses are intended to be ree o bias andprovide an analytical review o environmental andperormance actors such as soil type, climate,trac volume, lie cycle, constructability, andcost. All these actors are weighted in a uniorm,repeatable process with the singular goal oselecting the best pavement type at the greatestoverall value to the taxpayer and with a service

lie which provides the maximum return on thepublics investment.

In addition to technical and perormance actors,roadway owners have been conronted with theneed to consider secondary qualitative actorswhile selecting a pavement material type. Theseactors include consideration o such issues

as tire-pavement noise generation, suracesmoothness, and environmental sustainability.Asphalt pavements meet these needs andstudies have conclusively shown asphaltpavements provide the smoothest, quietestride with the greatest overall satisaction orthe motoring public. Asphalt is both a recyclableand a reusable resource. Innovations suchas warm-mix asphalt and use o reclaimedasphalt pavement (RAP) have placed theindustry as a leader in improving air emissionsand in conserving virgin aggregates andnatural resources.

This document was prepared by the AsphaltPavement Alliance to provide a synthesis o theprimary items or consideration when selectinga pavement type and to present the advantageso asphalt pavement in their conormance tothese criteria. It is based on the AmericanAssociation o State Highway and TransportationOcials (AASHTO) 1993 Guide or the Design

o Pavement Structures and the newAASHTOGuide or Mechanistic-Empirical Design o Newand Rehabilitated Pavement Structures. Asphaltpavements have a proven record o long-lieperormance or all levels o trac, dierentsubgrade types, and all types o climates. Theyhave a history o economy, speed o construction,and fexibility o construction scheduling. Finally,asphalt pavements are sustainable structuresdue to their recyclability, low greenhouse gasgeneration, and long lie. Asphalt pavement

should be considered in any pavement typeselection process.

PAVEMENT TYPESELECTION

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IntroductionPavement type selection is a process used bya pavement authority such as a state highwayagency to identiy the most benecial type opavement structure or a given set o trac,soils, climate, and other actors. It is sometimes

as simple as speciying a certain type opavement on the basis o trac level, or it may beas complicated as assigning weighting actors tomore than a dozen characteristics and evaluatingthe outcome through a scoring system. Whateverprocess is used, it should be a rational andexplainable methodology in which the eectso dierent variables on decision making maybe determined. Inormation used to develop theprocess should refect documented historicalperormance and cost records.

Although the method or selecting a type opavement varies greatly rom agency to agency,the American Association o State Highwayand Transportation Ocials (AASHTO) providesbroad guidance. The 1993 AASHTO Guide orthe Design o Pavement Structures outlines theconsiderations or pavement type selection in itsAppendix B. The primary actors to be consideredinclude trac, soils characteristics, weather,construction considerations, recycling, and cost

comparison. The secondary actors includeperormance o similar pavements in the area,adjacent existing pavements, conservation omaterials and energy, and availability o localmaterials, among other issues. Appendix B othe new AASHTO Guide or Mechanistic-EmpiricalDesign o New and Rehabilitated PavementStructures (AASHTO M-E PDG) lists actorsencompassing considerations or engineering,trac, environmental, construction, economic,and other actors. Fundamentally, although

there is a dierence in the presentation othe actors between the old and new AASHTOGuides, there are no real dierences in the basicconsiderations.This position paper was preparedin order to discuss the primary considerationsin pavement type selection as presented in thetwo AASHTO Guides in detail, and to present the

advantages available rom asphalt pavements ineach o these. Other considerations include theissues o tire-pavement noise generation, ridequality, and saety, and the advantage asphalt hasin these characteristics.

Principal FactorsTrafcThe AASHTO Guides point out that tracorecasts have been notoriously inaccurate in thepast, despite the best eorts to accommodatechanges in land-use planning. The changes intrac patterns brought about by the constructiono new roadways and the decline in rail reightservice are mentioned as contributing actorsin the underestimation o trac. The Guides

also suggest that increased truck loads maybecome a reality as uel costs increase. The1993 Guide states that a margin o saety shouldbe employed when designing pavements toaccount or the uncertainty in trac projections.AASHTO encourages comparisons o alternatestrategies including initial design, rehabilitation,and maintenance which can be evaluated toprovide or equivalent service over a given periodo time. Finally, the need or long pavement liewith minimal trac disruption is paramount on

congested roadways. In the new AASHTO Guide,the roadway geometrics and roadway eaturesare mentioned specically as having a potentialimpact on the speed and channelization o trac.The concerns expressed include the possibilityor increased repetitions o loading over a givenpoint in the pavement and the potential orlarger deormations under slower loads.

ASPHALT PAVEMENTS CAN HANDLEHEAVY LOADSAsphalt pavements have demonstratedoutstanding perormance across the spectrumo trac loadings and conditions. Asphalt isby ar the most popular pavement materialor low- and medium-trac roadways, andhas proven itsel over time under heavy trucktrac in urban and rural settings. Even under

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heavy, static, and channelized loadings suchas those at port acilities and commercialairports, asphalt pavements have providedexcellent service.

In heavy-duty highway pavements, asphalt isoten the pavement o choice such as I-695,

the Baltimore Beltway, which has an annualaverage daily trac (AADT) o 215,000 vehicles.The Washington D.C. Beltway (I-495), AtlantasI-285, San Antonios loop I-410, and I-80in Oakland are all examples o high-tracroadways where asphalt was selected asthe pavement type o choice. The Baltimore-Washington International (BWI) Airport, thePort o Seattle, and the Port o Portland,Oregon are examples o heavy-duty asphaltpavements subjected to extreme loads. It

should be noted that the BWI Airport waspresented with a Perpetual Pavement Awardrom the Asphalt Pavement Alliance in 2002 ortwo long-lie asphalt runways that are now (in2010) over 60 years old.

Many technological improvements in asphaltpavements have been made in order to handleincreased loads. These improvements haveincluded the introduction o polymer-modiedbinders, the development o Superpave

binders and mix design, and the introductiono stone-matrix asphalt (SMA) as a premiumsurace material.

ASPHALT OFFERS FLEXIBILITY INCONSTRUCTION, MAINTENANCE,AND REHABILITATION

One o asphalts primary advantages isthat it allows or a number o constructionscenarios. Staged construction allows apavement structure to be built up over

time, meaning that expenditures or a roadtake place gradually when total undingmay not be available all in one year, or i itis anticipated that trac will be graduallyadded to the road because o circumstancessuch as the completion o bridges. Becauseasphalt can be constructed during o-peaktrac times, the stages o construction can be

accomplished with minimal trac disruption.When comparing the impact o o-peak tracconstruction to a 24-hour lane shutdown, theuser-delay costs can be as much as three orderso magnitude lower with the o-peak-hour optionthan with the ull-day closure option.

ASPHALT PROVIDES FOR EASYMAINTENANCE AND REHABILITATION

Asphalt provides unequaled ease omaintenance and rehabilitation. The mostpopular option or surace renewal o asphaltpavements is the mill and ll process, whichallows close-coupling milling and pavingoperations, and this minimizes the area o laneclosure. As with staged construction, the abilityto perorm these operations during periods obelow-peak trac provides a great benet to

road users. Using echelon paving, as well asnight and weekend scheduling o work, meansminimal inconvenience to trac. The road canbe opened to trac in a matter o hours, ratherthan days or weeks. Again, the user-delaycosts associated with the shorter work timemeans a tremendous saving or the travelingpublic and shipping businesses. Shorter laneclosures also mean greater saety or vehiclestraversing the work zone.

ASPHALT PAVEMENTS LASTAND STAY SMOOTH

Asphalt has a proven track record when itcomes to long lie and smoothness. A study oasphalt pavements on interstate highways inOregon and Washington State shows that theaverage age o the asphalt pavements on thesesystems is about the same as or greater thanthe concrete pavements (Figure 1). A graphshowing the smoothness o interstate highwaysin Washington is presented in Figure 2. Here the

International Roughness Index (IRI) versus thenumber o kilometers or asphalt and concreteroads illustrates that asphalt pavements aregenerally smoother than concrete pavements(Mahoney et al., 2007). In other words, asphaltpavements have lower IRI values. Similarresults were reported in an FHWA publication(2002) where it was reported that 80 percent o

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the asphalt pavements had an IRI o less than1.5 m/km whereas 80 percent o the concretepavements had an IRI o less than 2.0 m/km.This type o asphalt pavement perormance oninterstate highways has also been documentedin Connecticut, Kansas, Minnesota, New Jersey,and Ohio. All o these studies have shown that

well-designed and well-built asphalt pavementstructures can remain in place with onlyinrequent resuracing.

FIGURE 1: AGE DISTRIBUTION FOR INTERSTATE PAVEMENTS

IN WASHINGTON STATE.

FIGURE 2: INTERNATIONAL ROUGHNESS INDEX FOR INTERSTATE

PAVEMENTS IN WASHINGTON STATE.

To highlight the perormance o properlydesigned asphalt pavements, the AsphaltPavement Alliance has presented thePerpetual Pavement Award to agencies withpavements that are at least 35 years old, withintervals between overlays o no less than13 years on average and with no structural

ailures. Between 2001 and 2010, 69 highwayand aireld pavements have received thisaward, and there are many more that have yetto be nominated. The ability to provide longservice lie while avoiding the need or costlyand time-consuming reconstruction is thehallmark o a Perpetual Pavement.

Soil CharacteristicsThe AASHTO Guides emphasize the importanceo the underlying soil characteristics topavement perormance. Both geographicalvariability and seasonal variability are mentionedas being primary concerns in the design o thepavement structure. The Guides also statethat the nature o the soil in a given area maydictate the economic viability o a pavementtype. As an example, they mention the use ostaged construction to achieve satisactoryride quality over a soil subject to volumechange. The importance o the oundationin terms o construction and perormanceo the pavement cannot be overemphasized.The stiness o the working platorm must besucient to allow compaction o the overlyingpavement structure in order to obtain adequatedensity in the granular and asphalt layers toensure perormance.

ASPHALT IS USED ON ALL TYPES OF SOILSAsphalt pavements have been successullyemployed over any type o soil on which apavement may be constructed, rom gravelto peat. The type o soil will dictate what typeo treatment might be employed to obtainthe desired perormance regardless o whattype o pavement is to be built. For instance,because o long-term settlement concerns,a lightweight ll may be used over peatormations prior to constructing an asphalt

pavement. Lime treatment o expansive claysis oten used to minimize volume change incertain areas. A combination o undercuttingand mechanical stabilization is sometimesused in areas with rost heave. There arenumerous techniques that can be used toimprove subgrade behavior in all types opavements. Asphalt provides an additional

1000

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HMA (Lane Miles)

PCCP (Lane Miles)

0 - 10 11 - 20 21 - 30 31 - 40 41 - 50 51 - 60 61 or More

LaneMiles

Age (Years)

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600

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0

HMA (Lane Miles)

PCCP (Lane Miles)

0.0-0.5 0.5-1.0 1.0-1.5 1.5-2.0 2.0-2.5 2.5-3.0 3.0-3.5 3.5-4.0 4.0-4.5 4.5-5.0 5.0 orMore

LaneMiles

IRI (m/km)

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advantage in being able to accommodate acertain amount o settlement or displacementin the underlying soil without a signicantloss in serviceability.

WeatherAASHTO discusses the eects o weather on

both the subgrade and the wearing course o thepavement. In the new AASHTO M-E PDG, theseare reerred to as environmental considerations.Precipitation in the orm o snow, ice, and rainallaects the strength o soils on a seasonalbasis. Likewise, moisture and temperature, interms o reezing and thawing, have an impacton the road surace. The ability o the suraceto acilitate snow clearing operations throughsolar absorption and its resistance to wear romclearing equipment can both actor into thetype o surace selected.

ASPHALT PAVEMENTS CAN BEDESIGNED FOR ANY WEATHER

In climates ranging rom the cold o Alaskato the warmth o Florida, asphalt has beenspecied or the vast majority o pavements.Seasonal weakening in subgrade soilscan best be handled through a thicknessdesign procedure that will provide enoughstress reduction on the subgrade to prevent

permanent deormation in the soil or basematerials during critical periods. In the past,CBR (Caliornia bearing ratio) and R-valuetests were used to obtain subgrade strengthmeasurements in a saturated condition,which insured that the pavement thicknessdetermination was conservative. With theAASHTO M-E PDG, thickness design ocuseson the soil resilient modulus as the measureo pavement bearing capacity. The advantageo using resilient modulus is that the value

may be adjusted according to season to bettercharacterize a pavements responses to loadsthroughout its lie.

As or surace characteristics, asphaltprovides a variety o eective options tohandle warm climates. Rut-resistant SMA

and Superpave suraces have perormed verywell in warm weather, as evidenced by therutting perormance o asphalt mixtures at theNational Center or Asphalt Technology (NCAT)Test Track in Alabama. Over the course o 10million equivalent single axle loads, the rutdepth o all the mixtures came out to be less

than 0.3 in., with the average o rutting in allthe test sections being slightly more than 0.1in. (Brown et al., 2002).

While rutting resistance is also a characteristico open-graded riction courses (OGFCs),the main advantage o OGFCs is the ability todrain water rom the road surace, increasingthe skid resistance and reducing the splashand spray. This type o surace should beconsidered an elective, lie-saving saety

eature to be used whenever easible onhigh-speed roadways. OGFCs have been usedon reeways in cold-weather states such asMassachusetts, New Jersey, and Wyoming, andin warmer climates such as Arizona, Caliornia,Florida, Georgia, North Carolina, and Texas.

A study o the Long-Term PavementPerormance Programs SPS-9 testsections showed that the relatively new PG(perormance-graded) asphalts have resulted

in improved thermal cracking resistanceo asphalt pavements in cold weather(Kavanaugh, 2004). As or snow removal,asphalt pavements continuously prove theirability to resist the wear o snowplow blades,and asphalts dark color promotes earliermelting o ice and snow.

Construction ConsiderationsThe 1993 AASHTO Guide states that the optiono staged construction may dictate the type o

pavement chosen in a given situation. Otheractors such as speed o construction, accessto businesses, maintenance o trac duringconstruction, saety, ease o placement,accommodation o uture widening, and timing oconstruction during the year are also importantin the selection o pavement type.

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ASPHALT ALLOWS STAGING OPTIONSAsphalt pavements allow or fexibility inconstruction, both in the ability to stage theconstruction sequence and in the ability tominimize the time or lane closures. Stagingconstruction is oten advantageous whenunding levels or weather do not allow or aacility to be completed in a single year. Theability to build a substantial portion o thestructure and then to nish it later helpsagencies stretch budgets to take care o moreprojects in tight times. Also, i constructionhappens to start later in the year, andnishing it would push the schedule into coldweather, then letting trac use the road overthe winter and waiting or the next season toput on the wearing course allows maximumuse o the acility.

ASPHALT PAVEMENTS CAN BEBUILT FAST

Speed o construction is one o asphaltsprimary advantages. Asphalt does not need acure time o days or weeks, it merely needs tocool to a temperature that allows it to supportloads, usually only a matter o hours ater nalcompaction. There are numerous exampleso reeway and airport pavement projectswhere asphalt pavements were completed in

a matter o weekends with minimal disruptiono trac. This minimizes the cost o delays topavement users, whether they are highwaydrivers and passengers, reight truckers, orairlines and airline passengers. It also helpsto minimize the amount o emissions thatresult rom trac delays on highways due toidling engines. Thirty-two lane-miles o I-285in Atlanta were constructed with asphalt usingull shutdown or 56-hour work windows onweekends over a period o 22 weeks (PublicWorks, 2002). A similar strategy was employedin the rehabilitation o the I-710 reeway nearLong Beach, Caliornia in 2003. In this case,weekend shutdowns were used to crack andseat the existing concrete pavement, whichwas then overlaid with asphalt. The trac onI-710 at that time consisted o about 150,000

vehicles per day with 15 percent trucks. Thisproject is notable because I-710 is the maincorridor between the Port o Long Beach andthe main railhead to transport goods acrossthe country.

Warm-mix asphalt technology was used

to reconstruct the main runway at theinternational airport in Frankurt, Germany,which is the tenth largest air cargo hub inthe world. This involved the mobilization oequipment late each night, removal o a portiono the concrete pavement, the placement andcompaction o the warm mix, and having thepavement ready or air trac by 6:00 a.m.every day.

ASPHALT CONSTRUCTION TIMING

IS A MATTER OF FLEXIBILITYBecause asphalt does not need to cure,trac can be allowed during peak hours andconstruction can take place during o-peakperiods. As with the examples in Atlanta andLong Beach, a series o complete weekendclosures allows lanes to be available duringweekday trac, or i trac dictates, thepavement can be closed and work can beaccomplished during the night and reopenedor trac during the day as was done at the

Frankurt International Airport. A detailedtrac study, including hourly volumes andalternate routes, and a public inormationcampaign will help to minimize user costand inconvenience. In any case, long, user-expensive shutdowns are not needed toconstruct asphalt pavements.

RecyclingAccording to the 1993 AASHTO Guide, the optiono recycling the existing pavement or material

rom other sources may be a reason to selecta particular type o pavement. Future recyclingopportunities may also actor into the decision.

ASPHALT IS AMERICAS MOSTRECYCLED MATERIAL

Asphalt is unique in composite constructionmaterials in that when it is recycled back into

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a new asphalt mix, the binder is reused aswell as the aggregate. Reclaimed asphaltpavement (RAP) saves on the amount o newbinder needed in an asphalt mixture becausethe RAP binder still unctions to coat theRAP aggregate and when it bonds to thenew asphalt, it helps create the needed

cohesion. This saves the need or both newasphalt and new aggregate, creating a moresustainable product.

About 90 percent o the asphalt pavement thatis removed is recycled back into pavement. Thisamounts to about 100 million tons o materialannually that is saved rom landlls. Recyclingsaves resources in terms o virgin asphalt andaggregate, resulting in simultaneous savings inenergy and cost. The mill and ll operation,

requently used in the surace renewal process,allows properly sized recycled material tobe taken rom the roadway and placed in astockpile ready or use.

OTHER REUSED MATERIALS CANENHANCE ASPHALT PERFORMANCE

There is a variety o by-products rom otherindustries that can serve useul unctionsin asphalt pavements. For instance, roongshingles provide asphalt, ne aggregate, and

bers. The asphalt binder available in roongshingles has been especially crucial in certainareas in reducing the demand or new asphalt.Adding as little as 5 percent waste roongshingles to an asphalt mixture can save asmuch as 20 percent o the total binder neededin the mix. Also, steel slag has been used ormany years as a hard, durable aggregate inasphalt pavements. Rubber rom waste tiresis being successully used in asphalt mixturesin a number o states, most notably Arizona,

Caliornia, Florida, and Texas. Sand romoundry castings can be used as a portion othe ne aggregate in the mix.

Simply viewing asphalt mixes as adepository or waste materials is not thegoal the industry is striving to achieve. Aslong as waste materials provide improved

economy, environmental riendliness, utureopportunities or asphalt recycling, andengineering perormance, their use in asphaltmixes should be encouraged. Each o theseconsiderations should be weighed beoreintroducing them.

Cost ComparisonThe AASHTO Guide states that cost comparisoncan be used to aid in decision making whenseveral pavement types could perorm welland there are no other dominant actors.

The Guide acknowledges there are instanceswhen initial cost may preclude other costconsiderations, but it encourages lie-cycle costanalysis. Initial costs, the cost o staging, thepredicted perormance lie, maintenance costs,

and salvage value are mentioned as actors inthe Guide. It also states that user delay costscan be actored into the decision process. Thelength o the analysis should be long enough toincorporate a representative rehabilitation orreconstruction or each alternative.

LIFE-CYCLE COST ANALYSIS IS IMPORTANT

The Asphalt Pavement Alliance supports thedetermination o lie-cycle costs o alternativepavement types as part o a rational means

or decision making. An appropriate andnon-biased method or lie-cycle costanalysis is promoted by the Federal HighwayAdministration (FHWA) in DemonstrationProject No. 115 (FHWA, 1998). It uses thenet present value approach or determiningthe costs o several alternatives. Using thisprocedure, all o the considerations in theAASHTO Guide, including user delay cost, canbe accommodated. The APA has developedsotware capable o perorming lie-cycle

cost analysis using the FHWA procedure. Thissotware can be downloaded or ree romhttp://www.asphaltroads.org/why-asphalt/

economics.html.

A simplied sketch o how the net presentvalue method o lie-cycle cost analysis worksis shown in Figure 3. The initial cost, the

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rehabilitation costs, and salvage value are allentered according to what their values wouldbe in terms o the present value o money. Thena discount rate is applied to account or thetime value o money and the anticipated rateo infation, and the uture rehabilitation costsand salvage value are discounted back to the

present. The lie-cycle cost is the sum o theinitial costs and discounted uture costs andsalvage value.

FIGURE 3: SKETCH OF NET PRESENT VALUE APPROACH TO

LIFE-CYCLE COST ANALYSIS.

A summary o dierent state practicespertaining to lie-cycle costanalysis is givenin Appendix A. Here, the times to rst, second,and third overlays are presented along withdiscount rates and total analysis periodlengths. These were based on a survey ostate asphalt pavement associations andcontractors.

In determining the lie-cycle cost o apavement, it is important to include onlythose costs which pertain to the pavement.In other words, costs such as striping, sod,guardrails, etc., should not be included unlessthe dierence in pavement type causes a costdierential in these items.

INITIAL COSTThe basis or initial cost should be unit pricesrom bid records o recent construction projects.An average price or projects constructedover the last two or three years is a airlycommon approach. Care should be taken thatonly representative prices are included. Forexample, very small projects or projects where

paving is only a minor component o the totalcost may cause unit prices to be skewed.

It is realistic to consider the initial cost both byitsel and as part o the lie-cycle cost analysis.This recognizes that the agency is constrainedby an annual budget, and needs to examine the

short-term ramications o expenditures aswell as the long-term impact o pavement typedecisions. For example, while a higher initial costoption may have a more attractive maintenanceschedule, selecting it may mean that ewerprojects get completed in a given year.

STAGING COSTS

I staged construction is to be used, then itscost should be discounted rom the plannedtime back to present in terms o the net

present value, and not included in the initialcost. In other words, the uture stages shouldbe considered as uture costs in the lie-cyclecost analysis.

PREDICTED PERFORMANCE LIFE

In putting orth a scenario or perormance lie,it is important that the agency reer to its pastexperiences with dierent pavement types.With respect to the perormance o asphaltpavements, it is recommended that at least

two categories be used: asphalt pavementsless than 8 inches thick over granular baseand asphalt pavements thicker than 8 inches.It is important to document the perormancerom the time o original construction orreconstruction until the next reconstruction.It is worth noting that simple overlaysand mill and ll operations are rehabilitationactivities and do not mark the end o thepavement lie.

The analysis period should be long enough tocapture major rehabilitation or reconstructionactivities or all pavement options. It shouldbe noted that when the Perpetual Pavementconcept is used, reconstruction occurs welloutside the normal analysis period o 30 to50 years. The Asphalt Pavement Alliancerecommends that the analysis period be noless than 40 years and that it include at least

Initial Construction

Rehabilitation

Time

Cost

Salvage

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one rehabilitation activity or each pavementoption. This complies with the FHWA-recommended minimum o 35 years. Thedata in Appendix A suggest that the averageanalysis period used is about 38 years, with themost requently used value being 40 years.

In lie-cycle cost analysis, it is veryimportant that the timing and extent o therst rehabilitation be based upon actualconstruction and pavement management datarather than memory or judgment. AppendixA shows that, on average, the time to rstoverlay is 15.1 years, according to the survey ostate practices. However, the most requentlyoccurring interval to rst overlay among statesis 20 years. The average time to the secondoverlay is 27.2 years. These gures correspond

well with an FHWA study o asphalt overlayperormance rom the Long-Term PavementPerormance Program study which showedthat most overlays lasted or over 15 yearsand many lasted or more than 20 years beoresignicant distress was noted (FHWA, 2000).

It should be noted that most o the above dataand policies refect averages, and, in somecases, engineering judgment in place o dataover a number o decades and rehabilitation

practices in dierent jurisdictions. Mostdo not account or recent improvementsin the selection o materials, mix-designprocedures, and pavement-design methods.The implementation o Superpave occurredin the mid-1990s, and SMA was adopted bya number o agencies throughout the 1990s,so the impacts o these improvements onperormance have not been ully realized.Such improvements come at higher costsor materials, so it is logical to give some

conservative credit or perormance althoughit may not be completely documented.When perorming an analysis o pavementperormance, it is important to dierentiatebetween new construction and variousrehabilitation strategies. For example, thetime to the rst overlay is oten dierent romthe time to the second overlay. Also, there

will be dierences in perormance betweenthick and thin overlays. Another actor relatingto perormance is whether the overlays areplaced on asphalt or unractured concrete. Itis advisable or an agency to conduct its ownanalysis o pavement perormance and todetermine its own strategies or lie-cycle cost

analysis. Using Perpetual Pavement concepts,it is possible or a state to go longer than60 years using only periodic overlays on anexisting structure.

MAINTENANCE COSTS

Maintenance costs are requently dicultto dene because o either a lack o recordkeeping or because o accounting practicesthat do not appropriately discriminate betweendierent types o maintenance activities

(e.g., between restoration o side slopes andshoulder sealing). Maintenance costs in alie-cycle cost analysis (LCCA) usually haveminimal impact when compared to the initialand rst rehabilitation costs. I maintenancecosts are used in an LCCA procedure, thenhistorical documentation o actual pavementactivities and expenditures should be used.As with rehabilitation, unrealistically requentor inappropriate maintenance activities canarticially increase lie-cycle cost.

SALVAGE VALUE

Because some or all o the pavement

structure continues to serve its purposesbeyond the analysis period, it is importantto account or its condition at the end o theanalysis period. Salvage value is typicallythe term used in lie-cycle cost analysis, butFHWA chooses to use the term remainingservice lie (RSL) value to distinguish theidea that the pavement will continue to serve

beyond the end o the analysis period. TheRSL value, according to the FHWA, shouldbe considered as a ratio o the period otime rom the last rehabilitation to theend o the analysis period, and rom thelast rehabilitation to the next projectedrehabilitation, times the cost o the lastrehabilitation (FHWA, 1998). Another method

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used is to consider the salvage value assome percentage o the initial pavementconstruction cost.

The use o Perpetual Pavement conceptswould allow or the maximum salvage valuein lie-cycle cost analysis. In this case, it is

suggested that the salvage value would be thevalue o the structure plus the value o theremaining pavement surace lie times thediscount rate.

DISCOUNT RATE

The 1993 AASHTO Guide does not specicallymention the issue o discount rate, butthe new M-E PDG does. The selection o adiscount rate in lie-cycle costing can becontentious because there is a great deal o

uncertainty associated with uture interestrates and infation. However, the time valueo money has been historically establishedto refect that money loses its relative valuewith time. An unreasonably low or negativediscount rate essentially means that it wouldnot matter nancially i a project were to beconstructed today or 10 years rom now andoveremphasizes the infuence o uncertainuture costs. Too high a discount rate wouldoveremphasize the importance o the initial

cost and not allow the proper infuenceo uture maintenance and rehabilitationcosts over the analysis period. FHWA (1998)recommends using a discount rate between 3and 5 percent, and the M-E PDG recommendsestablishing the discount rate according tothat set by the ederal Oce o Managementand Budget Circular A-94 which is updatedannually. This circular may be accessed onlineat http://www.whitehouse.gov/omb/rewrite/circulars/a094/a094.html.

Appendix A shows that or the states surveyed,an average discount rate o 3.8 percent is used,with a range between 2.3 and 7.1 percent. It isinteresting to note that 23 states have chosento use a discount rate o 4 percent whenperorming lie-cycle cost analysis.

ASPHALT PAVEMENTS COST LESS

The economics o pavement type selection

vary according to jurisdiction because oissues such as material availability,specication requirements, designmethodologies, etc. It is important or each

agency to conduct a realistic assessmento pavement economics in order to provideobjective input into the lie-cycle cost analysis.Examples o asphalt pavements economicadvantages are cited below.

In a comparison o costs or reconstructinghighways in Colorado (CTL Thompson, 2002),it was shown that, on the basis o initial cost,asphalt pavements were 14 percent less costlythan concrete.

A study o the cost o interstate pavementownership in Kansas (Cross, 2002) ound thatasphalt pavements were 22 percent cheaperto build and 60 percent cheaper to operate overa 40-year period.

A comparison o asphalt and concreteinterstate pavements in Ohio (Gibboney,1995) showed that asphalt pavements costless to build initially and required only smallincremental investment in the orm o overlays,

compared to the cost o reconstruction orconcrete pavements. Asphalt pavements wereup to 20 percent cheaper to build and between30 and 80 percent cheaper to maintain

At the end o a pavements service lie, thequestion arises as to whether rehabilitationor reconstruction is needed. As discussedabove, reconstruction is normally used whenthe existing pavement is concrete, and this isextraordinarily expensive when compared tothe rehabilitation processes normally usedor asphalt pavements. When the conceptso Perpetual Pavements are employed, thenthe uture rehabilitation costs are minimized,making the economics even more attractive.

Further advantages in asphalt pavementeconomics can be realized in the preservationo existing grade lines in urban areas and in

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the vicinity o overpasses. The use o mill andll rehabilitation means that the pavements onstreets with medians, curbs, and gutters can bemaintained at their current elevations withoutcomplete removal, as opposed to concretepavements that would need to be removed orundergo very expensive and time-consumingpatching operations. The mill and ll approachto rehabilitation is especially attractive underexisting overpasses where elevating the roadprole would require expensive eorts to raisethe bridges.

Other Considerations

There are considerations beyond those discussedabove that may be used in determining the type opavement appropriate or a given situation.It is important to review these in order todevelop a holistic justication or pavementtype selection decisions.

SustainabilityIt is becoming increasingly important to considerthe environmental and economic impacts opavement type selection and construction bothnow and in the uture. Many o the practices usedin the construction o asphalt pavements over thelast ew decades are recognized as sustainable.

It has been common practice to incorporaterecycled materials in asphalt mixtures since thelate 1970s. Recycling has important implicationson the consumption o raw materials and theprocessing it takes to incorporate them intothe pavement. By reusing the asphalt binder inthe RAP, it is possible to consume less virginbinder, which conserves petroleum. The reuse oaggregate allows or less mining. Currently, thereare about 18 billion tons o asphalt mixtures

in place on U.S. roadways. Virtually all o thismaterial is available or uture generations touse. Furthermore, waste materials rom otherindustries such as waste shingles, slag, oundrysand, and tire rubber can all be beneciallyincorporated into asphalt mixtures.

Emissions rom asphalt mix plants haveimproved dramatically over the years, decliningby 97 percent since 1970, while the productiono asphalt mixtures increased by 250 percent.The emissions improved to the point that theEnvironmental Protection Agency removed themrom the list o major sources o hazardous airpollution. Newly available warm-mix asphalttechnologies can reduce the temperaturesrequired to produce and place the material,reducing uel consumption as well as emissions.

The speed o construction and fexibility in timingrehabilitation also contributes to an improvedenvironment. Because roadway work on asphaltpavements is requently accomplished during o-peak trac hours, it is possible to signicantlyreduce congestion and reduce the accompanying

vehicle emissions.

The construction o Perpetual Pavements is a verysustainable practice because the design is suchthat the overall structure remains intact with onlyinrequent resuracing required. This reducesthe materials consumed over the long term andresults in a low lie-cycle cost.

Asphalt pavements have a low carbon ootprintcompared to other pavement types. Whilea certain amount o atmospheric carbon isgenerated in the production o raw materials andmix production, it is ar lower than the amountgenerated in the production o portland cementconcrete when one considers the amount ocarbon dioxide released in the manuacturingo the cement. The carbon contained in theasphalt binder is also bound in the productrather than being released to the atmospherethrough burning.

NoiseNoise generation can be considered on high-speed roadways. At speeds over 50 mph, thepredominant trac noise comes rom tire-pavement interaction. Using a low-noise suracereduces trac noise at the source. Studies haveshown that dense-graded asphalt mixtures canreduce the noise level by 2 to 3 dBA compared to

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concrete pavements. A reduction o 3 dBA rom76 to 73 has the same eect as either reducingthe trac by hal or doubling the distance romthe source o the noise (Wayson,1998). A noisereduction o up to 5 dBA can be obtained by usingan SMA surace, and a reduction o up to 9 dBAcan be obtained by using an open-graded riction

course (Wayson,1998).

RoughnessAsphalt pavements are generally very smoothupon construction. I they are properly designedstructurally, they maintain their smoothnessbetter than i they are under-designed. Asphaltpavements are built in lits instead o all in onelayer like concrete pavements. Each lit providesthe opportunity to obtain a better ride quality inthe nal product. Thus, it is easier to obtain asmooth pavement with asphalt. Furthermore, anFHWA study (Perera et al.,1997) o the data romthe Long-Term Pavement Perormance Programshows that asphalt overlays provide excellentsmoothness, regardless o the pavementroughness prior to rehabilitation. Data rom theWesTrack experiment (FHWA, 2000) show thatsmoother pavements can save highway usersuel and maintenance costs. It was noted thatater rehabilitation o rough pavement sections,uel costs or the trucks used in this eld studydecreased 4.5 percent and the number ovehicle atigue ailures decreased drastically.As shown in the Washington State study (Figure2), interstate asphalt pavements are smootherthan interstate concrete pavements. Given thatthe rolling resistance o a vehicle will be primarilyaected by the pavements roughness, thesmoother pavement will promote loweruel consumption (Marks, 2009).

SaetyEach time a new asphalt surace is applied to an

existing pavement, an opportunity presents itsel to

renew the riction and water-handling characteristics

o the roadway. The use o hard, durable aggregates,

combined with technology designed to reduce rutting

and consequently reduce hydroplaning, will enhance

the skid resistance o the pavement. Furthermore,

i a new generation open-graded riction course

is applied to the surace, not only are the skid

resistance and rutting resistance improved, but

the amount o splash and spray during rainstorms

is also reduced, which improves driver visibility.

Delineation o lanes and pavement markings is

enhanced with asphalt pavements.

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Summary

In making a decision concerning the type opavement to use on a roadway, an agency isobligated to get the best value or the taxpayers.It is up to contractors to provide the pavementthat gives the best possible perormance at

the lowest possible price. Thus, pavementtype selection should be a road user-orientedprocess, not an industry-oriented process.

In order to accomplish this, the system usedto select pavement type should be:

1. Objective2. Deensible3. Understandable4. Based on historical records5. Primarily driven by economics6. Periodically reviewed

Asphalt pavements possess many advantagesin the primary actors listed in theAASHTODesign Guides.

Among these are low initial cost, lowmaintenance costs, fexibility and speed oconstruction, the ability to handle heavy loads, along lie, and complete recyclability. Furthermore,asphalt pavements allow an opportunity to reduce

trac noise at the source and improve ridequality. Asphalt pavements should be consideredin every pavement type decision. A check list isenclosed as a handy reerence when consideringthe pavement type to be selected.

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16

References

Brown, E.R., L.A. Cooley Jr, D. Hanson, C. Lynn, B. Powell,B.D. Prowell, and D. Watson. 2002. NCAT Test Track Design,Construction, and Perormance. NCAT Report No. 2002-12.National Center or Asphalt Technology. Auburn, Alabama.

Cross, Stephen A. and Robert I. Parsons. 2002. Evaluationo Expenditures on Rural Interstate Pavements in Kansas.

University o Kansas. Kansas University TransportationCenter. Lawrence, Kansas.

CTL/Thompson, Inc. October 2002. Asphalt Vs. Concrete: APavement Cost Comparison Study o Reconstructing MajorHighway Corridors in Colorado, Report Prepared or theColorado Asphalt Pavement Association, Centennial, Colorado.

ERES Consultants. November 2003. Neutral Third Party -Ohio Pavement Selection Process, Drat Final Report orOhio Department o Transportation. Columbus, Ohio.

Federal Highway Administration. 1993.A Study o the Use oRecycled Paving Materials, Report to Congress, Report No.FHWA-RD-93-147, U.S. Department o Transportation,

Federal Highway Administration, Washington, D.C.

Federal Highway Administration. 1998. Lie Cycle Cost Analysisin Pavement Design, Report No. FHWA-SA-98-079, FederalHighway Administration, Washington, D.C.

Federal Highway Administration. 2000. Perormance Trends oRehabilitated AC Pavements, Tech Brie No. FHWA-RD-00-165,Federal Highway Administration, Washington, D.C.

Federal Highway Administration. 2000. WesTrack TrackRoughness, Fuel Consumption, and Maintenance Costs, TechBrie No. FHWA-RD-00-052, Federal Highway Administration,Washington, D.C.

Federal Highway Administration. 2002. Pavement SmoothnessIndex Relationships, Final Report. Publication No. FHWA-RD-02-057. Federal Highway Administration. Oce o Research,Development, and Technology. McLean, Virginia.

Florida Department o Transportation. 2002. PavementType Selection Manual, Document No. 625-010-005-C.Tallahassee, Florida.

Gibboney, Willis B. 1995. Flexible and Rigid Pavement Costson the Ohio Interstate Highway System, Final Report, FlexiblePavements o Ohio, Columbus, Ohio.

Kavanagh, Leonin. January 2004. Nine-Year Evaluation oField Cracking and Rutting Perormance o SPS-9 SuperpaveExperiment, Submitted or Transportation Research Record,

Transportation Research Board. Washington, D.C.

Mahoney, J.P. 2001. Study o Long-Lasting Pavements inWashington State. Transportation Research Circular Number503, Perpetual Bituminous Pavements, Pp. 88-95. TransportationResearch Board. Washington, D.C.

Mahoney, J.P., C.L. Monismith, J. Coplantz, J. Harvey, V.Kannekanti, L. Pierce, J. Uhlmeyer, N. Sivaneswaran, and T.Hoover. 2007. Pavement Lessons Learned rom the 50-Year-Old Interstate Highway System: Caliornia, Oregon, andWashington. E-Circular No. 118, Pp. 88-103. TransportationResearch Board. Washington, D.C.

Marks, Howard, PhD. 2009. Smoothness Matters: The Infuenceo Pavement on Fuel Consumption. Hot Mix Asphalt TechnologyVol. 14, No. 6, Pp. 18-29, available at www.nxtbook.com/nxtbooks/naylor/NAPS0609/index.php#/18. National AsphaltPavement Association. Lanham, Maryland.

Perera, R.W., C. Byrum, and S.D. Kohn. 1997. Roughness Trendso Flexible Pavements, Report No. FHWA-RD-97-147, FederalHighway Administration, Washington, D.C.

Public Works Journal Corp. 2002. Asphalt Reconstruction othe Atlanta Beltway. Public Works. Vol. 133, No. 1, Pp. 24-26.Ridgewood, NJ.

Wayson, Roger L. 1998. Relationship Between Pavement SuraceTexture and Highway Trafc Noise. NCHRP Synthesis 268,Transportation Research Board. Washington, D.C.


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Appendix A

Summary o Lie-cycle Cost Inputs rom Various States

StateYear at 1st

OverlayYear at 2nd

OverlayYear at 3rd

OverlayYear at 4th

OverlayTotalYears

DiscountRate

Alabama 12.0 20.0 28.0 4.0

Alaska-North 10.0 20.0 20.0

Alaska-South 15.0 30.0 30.0

Arizona 15.0 20.0 30.0 35.0 4.0

Arkansas 12.0 20.0 30.0 3.8

Caliornia 20.0 25.0 30.0 35.0 4.0

Colorado 10.0 20.0 30.0 40.0 3.5

Connecticut 15.0

Delaware 12.0 20.0 30.0 3.0

Florida 14.0 28.0 40.0 4.0

Georgia 10.0 20.0 40.0 3.0

Hawaii 17.0 35.0 40.0 4.0

Illinois 20.0 40.0 40.0 3.0

Indiana 20.0 35.0 4.0

Iowa 20.0 40.0 40.0

Kansas 12.0 22.0 32.0 40.0 3.0

Kentucky 10.0 20.0 30.0 40.0 4.0

Louisiana 15.0 30.0 30.0 4.0

Maine 16.5 25.5 4.0

Maryland 14.8 26.6 40.0 4.0

Massachusetts 18.0 34.0 3.0

Michigan 13.0 26.0 26.0 2.8

Minn 7 MESALs* 20.0 35.0 50.0 3.5

Minn 7 MESALs* 15.0 27.0 40.0 50.0 3.5

Mississippi 12.0 22.0 30.0 40.0 4.0

Missouri 20.0 33.0 45.0 2.3

Montana 15.0 27.0 4.0

Nevada 20.0 35.0 4.0

New Hampshire 20.0 31.0 4.0

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StateYear at 1st

OverlayYear at 2nd

OverlayYear at 3rd

OverlayYear at 4th

OverlayTotalYears

DiscountRate

New Jersey 15.0 30.0 40.0 4.0

Nebraska 20.0 35.0 50.0 2.4

North Carolina 10.0 20.0 30.0 4.0

Ohio 12.0 22.0 34.0 35.0 2.8

Oklahoma 15.0 30.0 45.0

Oregon 20.0 40.0 4.0

Pennsylvania 10.0 20.0 35.0 6.0

Rhode Island 20.0 31.0 20.0 4.0

South Carolina 12.0 22.0 30.0

South Dakota 16.0 32.0 40.0 7.1

Tennessee 10.0 20.0 30.0 40.0 4.0

Texas**

Vermont 17.5 31.0 4.0

Virginia 12.0 22.0 32.0 44.0 50.0 4.0

Washington 15.0 30.0 45.0 50.0 4.0

West Virginia 22.0 26.0 50.0 50.0 3.0

Wisconsin 18.0 30.0 42.0 54.0 50.0 5.0

Wyoming 20.0 35.0 4.0

Average 15.1 27.2 35.4 42.8 37.9 3.8

Minimum 10.0 20.0 30.0 35.0 20.0 2.3

Maximum 22.0 40.0 50.0 54.0 50.0 7.1

*MESAL = MILLION EQUIVALENT SINGLE AXLE LOADS

**TEXAS INPUTS WERE UNDER REVIEW AT THE TIME OF PUBLICATION (SUMMER 2010)

18

Appendix A (continued)


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Appendix B

Pavement Type Selection Checklist

Consideration Alternate 1 Alternate 2 Alternate 3 Alternate 4

COSTS

Initial

Future

User Delay

CONSTRUCTABILITY

Speed o Construction

Timing o Work Zones

PERFORMANCE

Frequency o Rehabilitation

EASE OF REHABILITATION

NEED FOR RECONSTRUCTION

SUSTAINABILITY

Recyclability

Carbon Footprint

Conservation o Materials

OTHER

Noise

Roughness

Saety

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For More Information, Contact Us

Asphalt Pavement Alliance

5100 Forbes Boulevard2nd FloorLanham, MD 20706877.272.0077 Voice

301.731.4621 Faxwww.asphaltroads.org

For More Information AboutAsphalt Pavement and the Industry

Warm-mix asphaltwww.warmmixasphalt.com

Porous asphalt pavements

www.porouspavement.net

For members o the community to learn

about asphalt plants

www.beyondroads.com

National Center or Asphalt Technology

www.ncat.us

Increasing percentage o RAP

www.morerap.us

Jobs in the asphalt industry

www.asphaltjobs.com

Asphalt Institute

www.asphaltinstitute.org

Asphalt Pavement Alliance

www.asphaltroads.org

National Asphalt Pavement Associationwww.hotmix.org

Documents

Pavement Type Selection July 2010