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Comparisons of distress measurements for companion virgin and RAP sections were evaluated using pairedt-tests. Results are shown in Table 1.Table 1. Comparison of distress measurements for companion virgin and RAP sectionsDistress ParameterVirginPerformedSignificantlyBetter thanRAP(percentage)RAPPerformedSignificantlyBetter thanVirgin(percentage)InsignificantDifferenceBetweenVirgin andRAP(percentage)RAPPerformedBetter Than orEqual toVirgin(percentage)IRI 42 39 19 58Rutting 33 29 38 67Fatigue Cracking 29 10 61 71Longitudinal Cracking 15 10 75 85Transverse Cracking 32 15 53 68Block Cracking 3 1 96 97Raveling 7 15 78 93These statistical analyses showed that RAP mixes performed better than or equal to virgin mixes for theJerry Chris Jones! 9/3/09 10:57 AMDeleted: one-samplemilled sections was less than one millimeter.Milling did not have a significantimpact on longitudinal cracking,block cracking or raveling. Accordingto the ANOVA analysis, mix type (virginversus RAP mixes) was only significantfor fatigue cracking, longitudinalcracking and transverse cracking, withthe virgin mixes performing betterthan the RAP mixes.Comparisons of distress measurementsfor companion virgin andRAP sections were evaluated usingpaired t-tests. Results are shown inTable 1.These statistical analyses showed that RAP mixes performedbetter than or equal to virgin mixes for the majority of the dataobtained. It can be concluded that in most cases, using at least 30percent recycled material in an asphalt pavement can provide thesame overall performance as a virgin pavement.Paving the Way to a More Sustainable FutureThe asphalt pavement industry is a leader in the area of sustainabledesign. Sustainability encompasses a wide range of interconnectedconcepts, including environmental stewardship andresource conservation.Consider these facts:• Asphalt pavement is America’s most recycled material, savingtaxpayers more than $300 million per year.• Total emissions from hot mix asphalt plants decreased by 97percent from 1970 to 1999. During that time, production increasedby 250 percent.• Producing and constructing asphalt pavements consumesapproximately 20 percent less energy than other pavementtypes.Building upon its proven track record, the asphalt industry continuesto provide sustainable solutions, including:• Warm mix asphalt (WMA): WMA technologies significantlyreduce the temperatures at which asphalt mixes are producedand placed, thus reducing energy consumption by an averageof 20 percent and further reducing emissions. WMA trials havebeen so successful that a number of states have adopted permissivespecifications allowing WMA use at the contractor’soption.• Increased use of recycled asphalt pavement (RAP): Stateagencies typically allow mixes containing 15-20 percent RAPin surface mixes. Results from the NCAT Test Track haveshown that mixes with higher percentages of RAP (up to 45percent) can perform successfully. Increasing recycling notonly conserves natural resources but is also economically sustainable.• Porous pavement: This innovative storm water managementtool can dramatically improve water quality. Porous pavement2majority of the data obtained. It can be concluded that in most cases, using at least 30 percent recycled125 material mm in overlays an asphalt performed pavement better can provide than the the thinner same overall overlays performance as a virgin pavement.all distress types except rutting. Milling prior to rehabilitation significantlydecreased IRI, fatigue cracking and transverse crackingbut significantly increased rut depths. From a practical standpoint,however, the average difference in rutting for the milled and nonsystemshave an open-graded asphalt surface course that allowsstormwater to flow into an underlying stone rechargebed. Storm water is stored within the recharge bed until itinfiltrates into the ground. Porous pavement systems have beenused successfully for more than 30 years, primarily in parking lots.• Perpetual pavements: Perpetual pavements are designed tolast indefinitely. Distresses are confined to the surface layer,which can be removed, recycled and replaced as necessary.Perpetual pavements conserve natural resources while alsoreducing life-cycle costs.Awareness of sustainability issues is being raised by efforts suchas the Green Highways Partnership (www.greenhighways.org), apublic and private initiative that seeks to incorporate environmentalstewardship in highway planning, design and construction. TheAASHTO Center for Environmental Excellence (www.environment.transportation.org) also promotes environmental awareness andprovides technical resources for transportation professionals. Anotherresource is Greenroads (www.greenroads.us), a performancemetric that provides a quantifiable means of assessing sustainabilitygoals on a project-by-project basis.As stated by Mike Acott, President of the National AsphaltPavement Association (NAPA), “The asphalt industry is committedto providing the best possible transportation facilities for America,with the least possible impact on the environment.” Sustainabilityis more than just a driving force in the asphalt pavement industry;asphalt is the sustainable pavement.Asphalt Technology News
Fourth Cycle Begins at NCAT Test TrackConstruction of 18 new and rehabilitated test sections at theNCAT Pavement Test Track was completed in August and thefourth cycle of trafficking is now underway. Originally constructedin 2000, the 1.7-mile track is divided into 200-foot test sectionsand is circled by a fleet of heavily loaded trucks 16 hours a day, fivedays a week, resulting in 10 million equivalent single axle loads(ESALs) applied over a two-year period.The 2009 research cycle consists of nine surface performancesections (4 new mill/inlay, one new surface treatment and fourtraffic continuation sections) and 16 thinner structural performancesections (10 new structures, three rehabilitated sections from the2006 cycle and three traffic continuation sections). All surface performancesections are built on perpetual foundations to ensurethat surface distresses are materials-related. The structural performancesections, however, have much thinner asphalt pavementcross sections and some also have different bases and subgrades.All sections (both structural and surface performance) contain temperatureprobes at three depths in the asphalt pavement. Structuralsections are also instrumented with stress and strain gaugesto measure pavement responses to loads and changing environmentalconditions.Structural SectionsThe six-section Group Experiment (GE) forms the core of thestructural research effort. All GE sections have a total asphalt thicknessof seven inches, with six inches of dense-graded aggregatebase and a stiff subgrade underneath. Several sustainable technologiesare being evaluated within the Group Experiment:An array of strain gauges is installed on a structural sectionat the test track.Fall 2009 • Vol. 21 • No. 2Warm Mix Asphalt (WMA): Two full-depth WMA sections wereconstructed to compare the performance of WMA technologiesto conventional HMA in the control section. One of the WMAsections used MeadWestvaco’s Evotherm DAT technology; theother used the Double-Barrel Green foaming process by Astec, Inc.High RAP Contents: Previous cycles of the track have proventhat surface mixes with moderate to high RAP contents canperform very well with regard to rutting and short-term durability.This experiment includes two sections with 50 percentRAP in each asphalt lift to compare performance to the allvirgincontrol HMA section in a thin asphalt cross-section tobetter assess fatigue performance. One of the 50 percent RAPsections also used the foaming warm mix process to see if theWMA-RAP combination affects pavement performance andstructural responses under traffic.Porous Friction Course (PFC): PFCs, also known as opengraded-frictioncourses (OGFC), have proven their value bydramatically improving safety and reducing tire-pavementnoise. This experiment will determine how PFCs contribute tothe structural response of the pavement. The PFC replaces thetop 1.25 inches of dense-graded HMA surface layer. The restof the asphalt cross-section is equivalent to the control HMAtest section. As an interesting bonus experiment, the PFC wasdesigned and built with 15 percent coarse fractionated RAP.Based on previous seven-inch structural sections on the testtrack, some bottom-up fatigue cracking is expected to occur duringthe two-year trafficking cycle. It will be interesting to see whichsections have the most cracking when the cycle is completed.Sponsors of the GE are Alabama, FHWA, Florida, North Carolina,Oklahoma, South Carolina, and Tennessee.Four, privately sponsored sections complement the Group Experiment.Those sections are:Shell Thiopave: Two sections built with mixtures containing asulfur replacement technology. One of the Thiopave sections isseven inches thick like the GE sections; the other is nine inchesthick. The Thiopave base mixtures contain 30 percent sulfurby weight of asphalt and the intermediate layers contain 40percent sulfur. The Thiopave mixtures also contain a warm mixadditive to allow for lower mixing temperatures. The surfacelayers for both Thiopave sections are a regular HMA mix.Kraton: This test section was built with HMA containing a highlypolymer modified binder in all three lifts. The binder used inthe mixes contains 7.5 percent styrene-butadiene-styrene (SBS)polymer. Theoretical pavement modeling indicates that mixeswith this level of modification will provide much greater resistanceto rutting and fatigue, so the total asphalt thickness forthis test section is 5.75 inches.Trinidad Lake Asphalt (TLA): TLA is a natural asphalt that wasused in the first asphalt pavements built in the U.S. more than100 years ago. TLA is still used today in high-stress applicationsaround the world. TLA is now produced in a pellet formto facilitate shipping and introduction into modern asphalt3
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