FHWA’s Mobile Asphalt LaboratoryBrings Technical Assistance Close to Home

FHWA’s Mobile Asphalt Mixture Labora-tory (more commonly known as “the

asphalt trailer”) brings technical assistance

on-site to contractors and State highwayagencies across the country. Since 1993, themobile laboratory has traveled to 45 States in

every region of the UnitedStates to assist State high-way agencies and asphaltcontractors in implement-ing the Superpave mix de-sign system. Equipped withSuperpave mixture testingequipment and staffed bytechnicians with expertknowledge of the Superpavetesting protocols, the mobilelaboratory helped introduce

C O N T E N T S

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Continued on page 3

I M P L E M E N T A T I O N U P D A T EI M P L E M E N T A T I O N U P D A T E

1TECHNICAL NEWS

4RESEARCH NEWS

7IMPLEMENTATION

NEWS

9IMPLEMENTATION

RESOURCES &NOTES

11EDITORIAL

12SUPERPAVECALENDAR

AA

SH

TO

F H W

A

SUPERPAVE 2000★ ★INDUSTRY

★

Low Temperature Binder Specification to be Revisedby Dr. Robert Q. Kluttz

T here has been a long-standing per-ception that the current Superpave

Performance-Graded Binder Specification(AASHTO MP-1) does not adequately cap-ture the low-temperature performance ofbinders that are produced using specialrefining techniques, certain crude slates,and/or chemical and physical modifiers.This is an especially critical observation aslow-temperature cracking is far more de-pendent on the characteristics of the binderand far less dependent on overall mix char-acteristics than other distresses addressedby Superpave. For this reason, the FHWASuperpave Binder Expert Task Group as-signed a working group to address this prob-lem and develop a more fundamentally

sound approach to model thermal cracking.This low-temperature working group alsovigorously pursued improvement of the Di-rect Tension Test (DTT) device and evalu-ated its possible utility in meeting this need.

After years of work, the working grouppresented the first major revision of theSuperpave binder specification, a new low-temperature specification. The basis of thisspecification is a comprehensive model thatincorporates rheological information fromthe Bending Beam Rheometer (BBR) andfailure stress from the DTT to determine acritical cracking temperature. For purchasespecification purposes the thermal stress issimply compared with the failure stress.

FALL/WINTER 2000Superpaveuperpave

Continued on next page

2 Superpave Implementation Update ◆ Fall/Winter 2000

Superpave to many States in its earlyyears, and later helped “troubleshoot”Superpave projects on site. In recentyears, the mobile laboratory’s prin-ciple mission has been to assist withtest validation by “shadow testing”(duplicating) mix design tests con-ducted by contractors and State high-way agencies in their own labs.

Even States that are moving moreincrementally toward Superpaveimplementation have found the sup-port provided by the mobile labora-tory helpful. Alaska, for example, hasadopted the performance-gradedbinder classification system, but ismoving more slowly in mix designdue to concerns such as maintaininghigh asphalt content in order to re-duce damage from studded tires, andthe difficulties of optimizing grada-tions given the need to turn aroundmix designs quickly because of theshort construction season.

“We found it very valuable to beable to walk in and talk to the experts,right here,” said Newton Bingham ofthe Alaska Department of Transporta-tion. “It increased our confidence,

and as a result we may now transitionfrom Marshall to the gyratory compac-tor. For example, the trailer techni-cians tested a Superpave designagainst our current mix, and the as-phalt content was just one-tenth less,which helped decrease our concernsabout the asphalt content ofSuperpave mixes.”

The mobile laboratory visitedWilder Construction in Anchorage,Alaska in July 1999. “It represented asignificant effort for FHWA to bringthe trailer here, and we appreciate it,”Bingham said.

When the mobile laboratory visitedRieth-Riley Construction Company inTraverse City, Michigan in the sum-mer on 1999, “they helped confirmour thoughts and gave us more confi-dence,” said Marc Beyer, StatewideMixture Specialist for the MichiganDepartment of Transportation. “Wehave been doing Superpave for awhile, and we had concluded that thelocation of sampling was important.We thought we wanted to move to-ward sampling behind the paver.They helped us do that, and then theydid shadow testing of our design, and

showed us that we were indeed mov-ing in the right direction. It was alearning curve for both the contrac-tors and the State. It was helpful foran experienced, unbiased party tocome in. They provided us with awritten summary of the test resultsalong with their opinions—a verywell packaged report. They also pro-vided training for some of our newerMDOT people, and for some contrac-tors located in less populated partsof the State who have been a littleslower to move toward Superpave.“

When Los Angeles County chooseto use a Superpave mix for portionsof the Alameda Corridor, the supportprovided by the FHWA mobile as-phalt laboratory was crucial, accord-ing to Bob Humer, Senior District En-gineer for the Asphalt Institute.

The design of the Alameda Corri-dor project is under the control of LosAngeles County, although the Califor-nia Department of Transportation(CalTrans) is providing funding andwill take over maintenance when theproject is complete. CalTrans has notyet built any Superpave projects.

“The backing by the federal gov-ernment helped,” Humer said. “Itgave people assurance that theSuperpave system would be a worth-while thing. The trailer did shadowtesting, which helped increase confi-dence on everyone’s part. The factthat the FHWA engineers were in-volved helped to get the project ap-proved for Superpave; otherwise itwouldn’t have happened.”

In addition to traveling to approxi-mately six States each year to provideon-site support to contractors andStates, the mobile asphalt laboratoryis involved in conducting testing re-lated to final development of thesimple performance test, and contrib-utes strongly to refinement of specifi-cations, test protocols, and QC/QAprocedures.

For more information about the mo-bile asphalt laboratory, contact JohnD’Angelo at (202) 366-0121.

MOBILE LAB / from page 1

States Served By FHWA Mobile Asphalt Laboratory 1993–2000

AsphaltTrailerVisited

Superpave Implementation Update ◆ Fall/Winter 2000 3

FHWA Research, Partnerships Pay OffThe development of the new specification and test procedures to assurelow-temperature performance illustrates how FHWA laboratory re-searchers work with their partners in State highway departments andindustry to solve practical problems.

The FHWA’s Turner Fairbank bituminous mixture lab worked closelywith the binder expert task group to make improvements to the directtension tester (DTT), which is used in combination with the bendingbeam rheometer to predict low-temperature cracking. FHWA thenpartnered with the States to further develop the DTT equipment andtest methods through practical application.

“We were one of the first States to obtain a DTT, because we wereconcerned about low-temperature cracking and that some of our PGgrades didn’t perform,” said Cameron Petersen of the Utah Departmentof Transportation. “Utah is a modified binder State, and we needed allthe tools we could obtain at our disposal just to assure ourselves that weweren’t overlooking cold-temperature cracking. We got our unit in 1997,and we were baptized in fire...all of the bugs hadn’t been worked out,and we learned as we went.

“We worked in the results from the DTT with the bending beam rhe-ometer, in the same test method that has been recommended by TRB toAASHTO as a modification of AASHTO MP1. The DTT parameter hasalways been in the binder specification, but we never have had a goodDTT machine. Finally, now, we have a horizontal bath machine. Wehave modified our specification to require the DTT and bending beamrheometer test criteria to be met, and it has worked quite well for us.”

FHWA currently is assisting States in obtaining the DTT equipmentthrough pooled fund purchases. Equipment training is being conductedby an FHWA contractor.

Whenever the failure stress exceedsthe thermal stress at the specificationtemperature the binder is considereda “pass.” S(60) and m(60) will nolonger be used.

The model was calibrated using thebinders and the extensive data sets thatwere available from the Lamont TestRoad in Alberta. Further validation wasobtained from the analysis of the Penn-sylvania Test Road and, for two poly-mer-modified asphalts, with extensiveperformance information. A detailedreport was provided to the BinderExpert Task Group for their approval.

How does it work?

Although the calculations are quitecomplex, actual practical applicationof the specification is very simple. Acomputer program calculates thecritical cracking temperature just asa computer program now calculatesS(60) and m(60) from BBR data. Theraw data (all six stiffness measure-ments) from BBR runs at two tem-peratures is plugged into the program.From this data, the program calculatesthe thermal stress in the pavement asa function of temperature.

The DTT determines the failurestress of the binder. With DTT data atone temperature, the program willcompare the thermal stress with thefailure stress and give a “pass” or “fail”for the binder at that particular low-temperature grade. With DTT data attwo or more temperatures, the pro-gram will interpolate between a “pass”temperature and a “fail” temperatureto calculate the critical cracking tem-perature of the binder. This procedureis the same as “absolute grading” thatis now done using BBR alone.

Why do we now need BBR data attwo temperatures?

Recall that the Dynamic Shear Rhe-ometer (DSR) G*/sin d and G*·sin dare measured at the actual tempera-tures where the distresses (perma-nent deformation and fatigue crack-

ing) are anticipated to occur. The low-temperature tests, however, are con-ducted 10°C higher than the antici-pated low pavement temperature.With the old specification, this wasdone using the assumption that a testconducted at 60 seconds at, e.g., –24°Cwould give the same results as thetest performed at two hours at –34°C.This is the principle of time-tempera-ture superposition that is the basis formuch of rheology.

Over the last few years, however,researchers have learned that this10°C offset is not constant. While10°C is a reasonable average, it canvary from 8 to 14° C. With BBR data attwo temperatures, the program can

estimate much more accurately, pro-viding the offset giving a significantimprovement in the reliability of thecalculated critical cracking temperature.

What is happening now?

The Binder Expert Task Group,now under the auspices of TRB, hasunanimously endorsed the revisionto the low-temperature specification.The intention is to ballot it atAASHTO as an “alternative” MP1 andit will likely be called something likeMP1A. The only difference betweenMP1 and MP1A will be that MP1 hasS £ 300 and m ≥ 0.30 at the low tem-

BINDER / from page 1

Continued on page 10

4 Superpave Implementation Update ◆ Fall/Winter 2000

R E S E A R C H N E W SR E S E A R C H N E W S...........................................................................................................................................................................................

Turner-Fairbank BituminousMixtures Lab Focuses OnInnovative Equipment

Development of easy-to-use, practi-cal equipment to help users imple-ment Superpave and other advancedasphalt technologies is a current em-phasis at the FHWA’s Turner FairbankBituminous Mixtures Laboratory(operated by the FHWA’s Office ofInfrastructure Research and Develop-ment), and at the FHWA’s Office ofInfrastructure’s mobile binderlaboratory, also located at the TurnerFairbank facility in McLean, Virginia.Three innovative devices that FHWAresearchers are currently evaluatingare described below.

The InstroTechTM CoreLokTM: TheCoreLokTM is a system for sealing as-phalt cores and Superpave gyratoryspecimens so the densities may bemeasured by water displacementmethods. Cores for laboratory and fieldsampling are automatically sealed inspecially designed puncture-resistantpolymer bags. The CoreLokTM in-cludes a fully automatic sealing pro-cess and a large vacuum chamber.The FHWA Office of Engineering has

initiated a National Pooled Fund studyto investigate the accuracy and re-peatability of specific gravity mea-surements taken using the CoreLokTM.The FHWA Office of InfrastructureR&D will be investigating the differ-ences in density measurements usingconventional and cutting-edge tech-nology. This will include use of theFHWA state-of-the-art X-ray tomogra-phy system. The National Center forAsphalt Technology (NCAT) will becoordinating the round-robin portionof the study. For more information onthe pooled fund study, contact JasonHarrington (202) 366-1576 or e-mailK.Jason.Harrington@fhwa.dot.gov.

The TransTech Pavement QualityIndicator (PQI): The PQI is anon-nuclear method of measuringin-place pavement density duringconstruction. The device uses capaci-tance technology to rapidly ascertainchanges in mat density.

The New York State Department ofTransportation requested the FHWAOffice of Infrastructure R&D to evalu-ate the PQI in September of 1998.Based on the favorable laboratory re-sults, the Maryland State HighwayAgency (MD SHA) initiated a RegionalPooled Fund Study to evaluate thegauge. On April 19, 2000 representa-

tives of the six States participat-ing in the pooled fund studymet in Baltimore to discuss labo-ratory and field trials of the de-vice. The participating States areMaryland, New York, Connecti-cut, Minnesota, Oregon andPennsylvania.

Throughout the summer 2000construction session the Stateshave been collecting data.FHWA will analyze the data.Currently the jury is still out onthe effectiveness of the

device. Look for a final report on thisstudy in the spring of 2001.

For more information, contactFHWA’s Tom Harman (202) 493-3072or e-mail tom.harman@fhwa.dot.gov.

The FHWA Superpave Angle Vali-dation Kit (“The Kit”): Currentlythere is no independent way to vali-date the angle calibration of theSuperpave gyratory compactors madeby various manufacturers. The FHWAOffice of Infrastructure R&D has de-veloped a device to measure and vali-date the angle of gyration. The Kit isdesigned to fit inside the mold of anySuperpave gyratory. Hot-mix asphaltis placed in the mold with the Kit andduring the compaction process the Kitmeasures and logs the angle.

Preliminary laboratory and fieldtrials of the Kit look very promising.FHWA planned to host a manufac-turers’ meeting on August 31, 2000to discuss the impacts and role of theKit in the design and construction ofasphalt pavements. The TRB Mixture/Aggregate Expert Task Group will pro-vide FHWA with further recommen-dations on the Kit in September.

For more information, contactTom Harman (202) 493-3072,tom.harman@fhwa.dot.gov.

Corelok™

Pavement Quality Indicator

Superpave Implementation Update ◆ Fall/Winter 2000 5

NCHRP RESEARCH UPDATE...........................................

Trucks Begin TraffickingNCAT Test Track

Trafficking of the new pavementtest track at the National Center forAsphalt Technology (NCAT) in Au-burn, Alabama was scheduled to be-gin in September 2000. Trucks withtriple trailers bearing 10-ton axle loadswill be driven around the track, allow-ing researchers to compare the perfor-mance of the pavement test sectionsover time under uniform loading con-ditions, in order to verify the accuracyof laboratory mix performance tests.Initial test track results are expectedto be available in about two years.

The National Asphalt PavementAssociation (NAPA), nine State high-

way departments, the Federal High-way Administration (FHWA), equip-ment manufacturers, and materialssuppliers are partnering to supportthe test track.

Forty-six test track sections havebeen constructed using a variety ofSuperpave and other mixes—fine-graded, course-graded, using differentaggregates (some of which passthrough the restricted zone, and somethat do not), and both modified andunmodified binders. Results fromlaboratory tests—such as rut tests,creep tests, and gyratory compactormeasurements—will be comparedwith the test track results.

“There is a need for test tracks as away to collect pavement performancedata other than using in-service high-

Restricted Zone:It’s Guidance!

When a mix satisfies the Superpavevolumetric and fine aggregate angu-larity (FAA) criteria, the restrictedzone criteria appear to be redundantas a requirement to assure adequaterut resistance, according to tentativeconclusions from NCHRP Project 9-14,“Investigation of Restricted Zone inthe Superpave Aggregate GradationSpecification.” The findings appear tobear out the contention of some high-way agencies and suppliers who sayit is possible to produce paving mixesthat perform well with aggregategradations that fall within the re-stricted zone.

Intended to help reduce the inci-dence of tender, or rutting-pronemixes, the Superpave mix design sys-tem includes a recommended guide-line addressing aggregate properties.The guidelines suggest that mix gra-dations avoid passing through a “re-stricted zone.” The restricted zone liesalong the maximum density gradation

between the intermediate size (either4.75 or 2.36 mm, depending on thenominal size of the aggregate) and the0.3 mm size.

“There’s nothing wrong with usingthe restricted zone as a guide,” saidE. Ray Brown, director of the NationalCenter for Asphalt Technology(NCAT), where the NCHRP study wasconducted. “But just staying outsidethe restricted zone doesn’t ensure agood mix, and being inside doesn’t en-sure a bad mix either. My feeling isthe restricted zone was originally in-tended as guidance, and not as aspecification, and it is its use as aspecification that has been the prob-lem. Because it is difficult to getpeople to pay attention to guidance,many States have incorporated the re-stricted zone criteria into their specifi-cations. The final result of our studywill be better, clearer guidance onwhether you should or shouldn’t payattention to the restricted zone crite-ria in given circumstances. I think asa result of our study some of theStates may loosen their requirements.”

The incorporation of restrictedzone criteria into agency specifica-

tions has been particularly controver-sial in localities where the local aggre-gates fall inside the restricted zone. “Ifhighly angular aggregates are used inthe mix it is likely that the mix willnot exhibit any tenderness duringconstruction and will be rut-resistantunder traffic, although its gradationmay pass through the restricted zone.The Georgia Department of Transpor-tation has used such mixes success-fully for many years,” said Prithvi(Ken) Kandhal, principal investigatorfor the NCHRP 9-14 project.

The study and its findings

In the NCHRP 9-14 study, NCATresearchers compared five 9.5 mmnominal maximum aggregate size(NMAS) gradations. Three of the gra-dations violated the restricted zone,and the two control gradations felloutside of the restricted zone.

The performance of the mixes withvarious factor-level combinationsmeeting all volumetric requirementswas evaluated on the basis of perfor-mance-related mechanical tests. Sincethe primary purpose of the restricted

ways. Test tracks are safer and protectthe public, and in some States, it isthe only way tests can possibly beconducted,” said NCAT Director E.Ray Brown.

The only other pavement testtrack currently in operation in theUnited States is MinnRoad, operatedby the Minnesota Department ofTransportation.

Aerial view, NCAT Test Track

6 Superpave Implementation Update ◆ Fall/Winter 2000

zone is to avoid rut-prone mixes, themixes in the study were evaluated fortheir rutting potential. This was ac-complished by two different types oftests: empirical and fundamental. Forthe empirical test, the Asphalt Pave-ment Analyzer (APA) was used. TheSuperpave shear test (SST) and thedynamic confined creep (DCC) testwere used as fundamental tests. Part 1of the study tested the performance ofthe 9.5 mm mix and one compactiveeffort (Ndesign = 100 gyrations). Part 2involved the same 9.5 mm NMAS mixbut two additional compactive efforts(Ndesign = 75 and Ndesign = 125 gyra-tions).

Parts 1 and 2 have been completed,and results of the three mechanicaltests used for evaluation showed simi-lar trends in terms of permanent de-formation. In these tests, the grada-tions violating the restricted zone didnot necessarily result in higher rutdepths compared to the gradationscomplying with the restricted zone.Part 3 of the project is currently un-der way. It involves a 19.0 mm NMASmix and two compaction levels(Ndesign = 75 and 100 gyrations).

“It is expected that Part 3 mostlikely also will indicate the redun-dancy of the restricted zone as seenin Parts 1 and 2,” Kandahl said. Theentire project is scheduled forcompletion by March 31, 2001.

For more information, contact Prithvi(Ken) Kandhal at the National Centerfor Asphalt Technology (334) 844-6242.

Three Rut and Crack TestsWill be Validated on Real Roads

In July an NCHRP panel recom-mended that three potential “simpleperformance tests” for rut and crackresistance undergo field validation:(1) the stiffness test using the dy-namic complex modulus procedure;(2) the tertiary flow or static creeptest, measuring flow time; and (3) thetriaxial repeated load test, measuring

flow number.The three tests

were selected basedon results of NCHRPProject 9-19, conduc-ted by the Universityof Maryland under thedirection of PrincipalInvestigator MatthewWitczak of the Univer-sity of Arizona. Witczak’s researchteam correlated laboratory test re-sults, using nine different candidatetests and various testing parameters,for a variety of mixes with the perfor-mance of the mixes at three pave-ment test tracks (MnRoad, WesTrack,and ALF).

The three tests selected for furtherstudy all showed very high correlationswith pavement performance. “Theyall had correlations with r-squaredvalues of .9 or better, which is veryunusual,” said NCHRP Project Direc-tor Ed Harrigan. “In some ways wehave an embarrassment of riches withthe laboratory results. The next hurdlewill be to see whether the correlationshold up on real roads.”

In-service pavement test sectionsconstructed for the Strategic HighwayResearch Program’s Long Term Pave-ment Performance SPS Studies, alongwith those built by State DOTs andother accelerated pavement tests, willbe used for the field validation stud-ies, to be conducted by the Universityof Maryland research team in the nextphase of Task C under NCHRP Project9-19.

“The objective for the field valida-tion studies will be to see whetherone of the tests stands out as clearlysuperior, and whether the test condi-tions proposed by the research teamare the best ones to use,” Harrigansaid. The tests can be conducted onequipment that many agencies andcontractors already own, and it ispossible that one piece of equipmentmay be able to do all three tests. Noneof the proposed tests is new, and theresearch is more about test conditions

and parameters than the tests.In the end, more than one test may

be recommended. “They each havetheir advantages,” Harrigan said. “Dy-namic modulus is the same test thatwill be used as an asphalt characteris-tics test in AASHTO’s 2002 DesignGuide. Tertiary flow is a good simpletest for field verification.”

Final results from the field valida-tion studies are expected in late 2001.

For more information, contactEd Harrigan at 202-334-3232.

RAP Technicians’ Manual,Guidelines Available

The results of NCHRP Project 9-12,“Incorporation of Reclaimed AsphaltPavement in the Superpave System,”provide new information on how Re-claimed Asphalt Pavement (RAP) in-teracts with binders in Superpavemixes. Based on laboratory and fieldtests, a North Central Superpave Cen-ter/Purdue University research teamheaded by Rebecca McDaniel has pro-duced new guidelines for incorporat-ing RAP in the Superpave system, anda manual for laboratory and fieldtechnicians that provides a step-by-step procedure.

The findings of NCHRP Project9-12 support the guidelines previouslydeveloped by the Superpave Mixtureand Aggregate Expert Task Group.The new guidelines expand upon theexisting ETG guidance, providingmore detail.

To obtain copies of the guidelinesand manual, contact Ed Harrigan atNCHRP, (202) 334-3232.

Superpave Implementation Update ◆ Fall/Winter 2000 7

...........................................................................................................................................................................................I M P L E M E N T A T I O N N E W SI M P L E M E N T A T I O N N E W S

State Implementation Status UpdateForty-seven States and

the District of Columbianow have implemented theSuperpave binder specifica-tion, according to the mostrecent survey by AASHTO’sSuperpave Lead States.Oregon and Puerto Rico haveadopted plans to implementthe binder specification inthe near future. California

and Nevada are the onlystates with undeterminedplans for Superpave binderspecification implementa-tion. (Figure 1)

For Superpave mixtures,Figure 2 shows that 24States and the District ofColumbia already haveachieved full implementa-tion. Fourteen states and Puerto Rico plan to im-

plement the Superpavemixture specification inthe near future. The plansof the remaining 12 Statesfor Superpave mixtureimplementation are

undetermined.Figure 3 shows annual

increases in Superpave ton-nage versus conventionalhot mix asphalt (HMA), andfuture projections in termsof yearly market trends.

Pacific Coast ConferenceAdopts Superpave Binder Specification

Figure 1: Superpave Binder Implementation

By 2000After 2000Undetermined

Figure 2: Superpave Mixture Implementation

By 2000After 2000Undetermined

Figure 3: Projected Superpave Market Share

1996 1997 1998 1999 2000 2001

Metri

c Ton

s (mi

llions

)

160–

120–

80–

40–

0–

–100%

–75

–50

–25

–0

Percent Total HMA Tonnage

| | | | | |

Awarded Planned Projected

134 M Tons (83%)

The Pacific Coast Confer-ence on Asphalt Specifica-tions (PCCAS)—known backEast as the West Coast User-Producer Group—voted atits May 2000 meeting to rec-ommend that its membersadopt the current Superpavebinder specification as writ-ten. The user agency mem-bers—including Arizona,Alaska, California, Hawaii,Nevada, Oregon, and Wash-ington—voted unanimously“to adopt the PG specifica-tion (using the most currentAASHTO MP-1 specifica-tion), as written. The pro-ducer agency conferencemembers then unani-mously agreed to supplythe user agencies with the

specified material.”“By adopting the specifi-

cation, it doesn’t mean thatthey are agreeingto use it exclusively, rightaway,” said PCCAS Secre-tary Lisa Economy. “Theyare agreeing to actively pur-sue with industry theimplementation of thespecifications. They intendto analyze the successes andfailures of Superpave in eachState, so that industry andgovernment can work to-gether to analytically deter-mine how to move forward.”

Arizona and Washingtoncurrently are currentlyimplementing Superpave.Most of the other western

PCCAS / continued on page 11

8 Superpave Implementation Update ◆ Fall/Winter 2000

Table 1: Asphalt Binder Correlation (A, B)Penetration Viscosity Performance Grade [C] Grade [C] Grade [D]

60-70 - PG64-22 - - -60-70 - - PG64-28 - -60-70 - - - PG70-22 -

- AC-20 PG64-22 - - -- AC-20 - PG64-28 - -- AC-20 - - PG70-22 -

- - PG64-22 PG64-28 - -- - PG64-22 - PG70-22 -

- - - - PG70-22 PG76-28- - - - - PG76-28

The City of Albuquer-que, one of the first localurban highway agencies tobuild Superpave projects, iscurrently in the midst of atransition to full Superpaveimplementation, targetedfor mid-2001. The City’s ap-proach to working with sup-pliers and with the State tosolve “binder proliferation”problems during their tran-sition to Superpave may behelpful in other localities.

“Binder proliferation” re-fers to the problems that as-phalt suppliers and asphaltconcrete producers facewhen they are required tosupply numerous Superpaveperformance-graded as-phalts as well as traditionalAC binders in the same geo-graphic market. They face

additional capital costs forstorage tanks, driving upcosts for everyone.

Suppliers in the Albu-querque area were facingmajor challenges last yearin supplying both City andState projects. The City ofAlbuquerque specifies twoPG grades (PG64-22 for low-volume streets, and PG76-28 for high- volume streets,collectors, arterials, andcontrolled access streets)as well as traditional ACgrades. The State selectsbinders based on theunique requirements ofeach project.

When the binder prolif-eration problem surfacedin the Fall of 1999, City ofAlbuquerque officials metwith State officials, metro

area asphalt concrete sup-pliers, contractor associa-tion representatives, andother specifying agencies toaddress the differences indesign/specification poli-cies. The solution to theproliferation problem wasfor the City to adopt amechanism for the metroarea asphalt concrete pro-ducers to program theirbinder requirements tomeet both City and Statespecifying agencies’ re-quirements in the Albu-querque area, recognizingwhere asphalt binders areequivalent or substitutablefor PG binders. The City re-vised its asphalt binderspecification to provide forsubstitution of equal or bet-ter binders, without com-

promise of itsspecificationrequirements.(See Table 1.)

“At a fol-low-up meet-ing with sup-pliers, thesuppliers vis-ibly relaxedwhen wepassed aroundthe substitu-tion table,”said MartinBarker, PE,Pavement andMaterials En-gineer for theDesign/Con-struction Divi-sion of theCity’s PublicWorks Depart-ment. “It was

A. GRADE CORRELATION: A binder grade to the right of a respective bindergrade in the same row may be substituted.

B. Binder substitution in an authorized job mix formula shall not be allowed.C. Marshall analysis/designD. Gyratory analysis/design

a tremendous relief to them.”Barker said the City’s

Superpave mixes typicallyused fine-side aggregate gra-dations for all streets, whichinitially conflicted with theState’s approach. “In the lastrevision of their specs, theState became less rigid intheir gradations, ‘S-curvecoarse side gradations,’ andbegan to recognize the needfor fine-side aggregate grada-tion designs for low-volumetraffic roads,” Barker said.

“The City’s philosophyhas been to work with sup-pliers to establish a manu-facturing specification for aspecific set of products, au-thorized on an annual ba-sis,” Barker said. “But theState designs and specifiesuniquely for each project.”

Albuquerque was argu-ably the first agency in thenation to specify a PG76-28binder, a very high-perfor-mance PG binder. “We be-gan specifying it for specificprojects in 1994, selectingbased on environmentrequirements for typicalurban traffic movements,deceleration, acceleration,slow moving and turningtraffic,” Barker said. “It ishighly modified, and it in-creased our asphalt con-crete costs significantly,but we were having perfor-mance problems and werewilling to do what it wouldtake to get the performancewe needed. We have con-cluded that the improvedperformance and projectedincrease in life more than

City of Albuquerque Tackles Binder Proliferation During Transition to SuperpaveSUPERPAVE AND LOCAL ROADS..............................................

ALBUQUERQUE / see page 11

Superpave Implementation Update ◆ Fall/Winter 2000 9

...........................................................................................................................................................................................I M P L E M E N T A T I O N R E S O U R C E S & N O T E SI M P L E M E N T A T I O N R E S O U R C E S & N O T E S

Plan Now to Attend AsphaltTechnology Conferencein Austin

Plan now to attend Asphalt Tech-nology 2000: Sharing Technologies inthe 21st Century at the RenaissanceAustin Hotel in Austin, Texas,December 10–14, 2000.

The conference will provide anextensive program of interactive dis-cussions and will benefit public worksofficials, consultants, engineers, man-agers, and contractors. The objectiveof the conference is to create a forumto effectively solve asphalt pavementproblems. Topics of discussion willinclude specifications, innovationsin pavement maintenance, surfacing,and new asphalt technologies.

The Asphalt Technology 2000 con-ference builds on similar conferencesheld in Austin in 1998 and 1996, andhas an international flavor, involvinga number of participants and exhibi-tors from Latin America as well as theUnited States.

The University of Texas at AustinCollege of Engineering is sponsoringthe conference, in cooperation withthe Pan American Institute of High-ways, the Federal Highway Adminis-tration, the Asphalt Institute, and anumber of industry partners.

For more information, go toHTTP://lifelong.engr.utexas.edu/conferences.html, call Sharon Camposat (512) 232-5168, or e-mailscampos@mail.utexas.edu.

New NHI Superpave CourseA new one-day course on “Superpave

Fundamentals” incorporating thelatest modifications to the Superpavesystem is now available through the

Michael Anderson. We would getideas for projects to pursue based onour contacts in the industry, and theyknew what the users were looking for.We were able to work together to keepthings moving forward.”

Listed below are reports available:

Education◆ Superpave Asphalt Mixture

Analysis Text

◆ Observations of Field Experiencewith Superpave Projects Con-structed in 1996

◆ Superpave Asphalt Binder Equip-ment Operations Manual: CannonBending Beam Rheometer; AppliedTest Systems Binding BeamRheometer; Bohlin Dynamic ShearRheometer; TA InstrumentsDynamic Shear Rheometer

Test Procedures◆ Ruggedness Evaluation of AASHTO

TP7 and TP9, Phase I: SimpleShear Test at Constant Height(TP7); Indirect Tensile StrengthTest (TP9)

◆ Ruggedness Evaluation of AASHTOTP7 and TP9, Phase I: SimpleShear Test at Constant Height(TP7) Executive Summary

◆ Ruggedness Evaluation of AASHTOTP7 and TP9, Phase I: IndirectTensile Strength Test (TP9)Executive Summary

◆ Ruggedness Evaluation of AASHTOTP4: Superpave Gyratory Compac-tion Procedure

◆ Statistical Evaluation of SuperpaveGyratory Compaction Data forEffects of Short-Term Oven Aging

State/Federal Assistance◆ Asphalt Mixture Performance Testing

and Analysis: South Carolina

FHWA’s Na-tional High-way Institute(NHI). Thecourse is taught by subject-matterexperts from the Regional SuperpaveCenters.

Course content focuses on imple-mentation strategies for transporta-tion agencies and describes how to in-corporate this evolving technologyinto paving programs. Upon comple-tion of the course, participants will beable to (among other things) discussthe basic functions of testing proce-dures and equipment operation; inter-pret the data obtained from testingprocedures; and apply test results toselect materials for high-quality mixdesign and performance.

The course is intended forengineers and technicians who areresponsible for road repair and main-tenance.

For course scheduling information,contact Lynn Cadarr at (703) 235-0528or e-mail lynn.cadarr@fhwa.dot.gov.

Superpave Reports AvailableFrom The Asphalt Institute

In a productive partnership thatbegan in 1993, the FHWA and theAsphalt Institute have worked to-gether to train the first generation ofSuperpave technicians and to furtherdevelop and promote the Superpavesystem. Although the partnership iscurrently winding down due to fund-ing scarcity, a number of Superpavereports produced jointly by FHWAand the Asphalt Institute are stillavailable.

“It was a great help to us to workwith FHWA, because we had a goodtwo-way relationship,” said the As-phalt Institute’s Director of Research,

10 Superpave Implementation Update ◆ Fall/Winter 2000

◆ Evaluation of Torture and StrengthTests as an Addendum to theSuperpave Volumentric Mix DesignProcess: Missouri Case Study

◆ Verification and Performance Testingof Florida DOT Superpave Mixes

Research◆ Evaluation and Update of Design

Gyrations for the SuperpaveGyratory Compactor: Ndesign IIExperiment, Phase 2

◆ Development of Low TemperatureBlending Charts for RecycledAsphalt Binders Using theSuperpave Binder SpecificationParameters

◆ Investigation of the Superpave Gyra-tory Compactor: Angle of Gyration

◆ Investigation of the Effects ofSuperpave Gyratory compactorType and Compaction Angle onMixture Volumetric and Densifica-tion Properties

◆ Investigation of the Role of Non-Linear Viscoelastic Behavior ofAsphalt Binders in DefiningMixture Behavior: Phases I and II

◆ Parameters for Quantifying Aggre-gate Orientation in Asphalt Mixes

For ordering information contact theAsphalt Institute at (606) 288-4960.

NAPA to Publish Mix TypeSelection Guide

The FHWA and the National As-phalt Pavement Association (NAPA)plan to publish a new Mix Type Selec-tion Guide in the fall of 2000 that willprovide additional guidance for de-signers on which pavement mix typesare most appropriate for various con-ditions. The guide will cover open-graded friction courses (OFGC), stonematrix asphalt (SMA), and fine-andcoarse-graded dense mixes.

“Hot mix asphalt (HMA) industryorganizations have identified thatwhile many of these pavement mix

types have been used successfully incertain applications, some also havebeen placed in applications inappro-priate for the mix type,” the authorssay. Examples cited included placingan OGFC as in interlayer, and specify-ing high-quality aggregates wherethey are not needed, which increasescosts unnecessarily.

The information in the guide wasgathered from a combination of litera-ture reviews, current practices, andexpert opinion.

The guide includes a table showingrecommended mix types and thick-nesses for various pavement layersunder given traffic conditions. For eachtype of mix, there is a general descrip-tion, a discussion of the recommendedapplications for the mix, and guide-lines for materials specification forvarious layers and traffic conditions.

General recommendations for sur-face preparation also are provided.

For more information about theMix Type Selection Guide, includingordering information, contact DavidNewcomb at NAPA (301) 731-4748, ore-mail napa@hotmix.org.

Superpave Mixture DesignGuide Available Soon

A new Superpave Mixture DesignGuide is scheduled for publication inthe fall of 2000. The new documentprovides additional guidance for mixdesigners on how to avoid potentialproblems, and is based on the mostrecent information available, includ-ing the findings of the expert teamthat investigated the premature testsection failures at WesTrack. Accord-ing to its authors, “The guide is in-tended to serve as a bridge betweenexisting knowledge and additionaltools being developed to measure andpredict Superpave mixture perfor-mance under traffic.”

Topics covered include: compac-tion level determination; binder selec-tion; aggregate selection; mix design

considerations; mixing and compac-tion temperatures; dust-to-binder ra-tio; and performance indicator tests.The document includes a designchecklist and an appendix describingvarious types of performance tests forpredicting rutting.

“No single test is suitable currentlyas a national standard for predictingrutting,” the document states. The de-velopment of such a procedure is ur-gently needed, but a satisfactory pro-cedure may be years away. In themeantime, if an agency has extensiveexperience with a particular test overa range of materials typical of its geo-graphic area, it should consider usingthe test to predict rutting performance.Each of the devices outlined here hasdifficulty in predicting the true per-formance of an asphalt mixture andshould be used with great caution.”

For more information about theSuperpave Mixture Design Guide andordering information, contact TerryMitchell at (202) 493-3147.

perature grade +10°C and MP1A willhave “pass” at the low temperaturegrade +10°C. The Standard Practicefor performing the calculations onBBR and DTT data to determine pass/fail has also been balloted at AASHTOand will be referenced in MP1A.

The retention of two specificationswill allow states to adopt the revisedspecification at a pace that meetstheir needs and the needs of theirsuppliers. It is anticipated that even-tually MP1 will be phased out muchas conventional AC grading wasphased out during the 1990s.

The MP1A proposal is currentlyunder study by an AASHTO task group.

Dr. Robert Q. Kluttz, a member of theSuperpave Binder Expert Task Group’sLow-Temperature Working Group, is asenior research chemist for Shell Chemi-cal Company’s KRATON Polymersgroup in Houston, Texas, and may bereached at (281) 544-8184.

BINDER / from page 3

Superpave Implementation Update ◆ Fall/Winter 2000 11

E D I T O R I A L..........................................................................................................................

E D I T O R I A L

Why Do We Need Performance-Based Quality Control?Within the coming decade, the TRB Superpave Committee’s Long-Range Plan

calls for development of a performance-based quality control system, including aperformance-based specification (PBS), to complete the Superpave mix designsystem. However the need for performance-based specifications goes beyondjust the utilization of the Superpave system. Many ask, “Why do we need a PBS,and how will PBS differ from the performance-related specifications (PRS) thatwe already have?”

The current system of performance-related specifications (PRS) requires mixes tomeet certain criteria such as traffic and temperature that are related to perfor-mance. However, criteria based on actual performance requirements are abso-lutely necessary to enable agencies to contract with roadbuilders to construct apavement warranted to perform, for example, for a specified traffic loading over a10-year period. In order to respond to a PRS and provide warranties, contractorswill need to have confidence that the mixes they design will deliver predictedperformance. This is the purpose of the current research effort. Distress predic-tion models and simple, valid materials characterization tests will provide thecontractor and highway agency with the tools they will need to implement PBS.

A performance prediction system will make it possible to evaluate materialsand economic trade-offs. Most importantly, it will be possible to evaluate the per-formance of the mix in the laboratory instead of on the road.

The current timetable calls for development of an asphalt pavement PBS by 2005.This will be followed by at least two years of beta testing prior to implementation.

Superpave and Low-Volume RoadsThe majority of States have already implemented the Superpave mixture

specification or currently are transitioning to Superpave. Most city and countyhighway agencies, on the other hand, are just beginning to consider Superpaveas an option for the low-volume city streets and rural roads that they administer.The Superpave system was originally developed to fill the need for high-perfor-mance pavement that could withstand heavy traffic and climate demands. Con-sequently, most of the applications built to date have been on higher volumeroads. This has caused some to wonder whether the design criteria for low-vol-ume roads (which always has been included in the Superpave system) will per-form as well as expected. Experience to date has been that the criteria for lowerESALs works well. In fact, much of the criteria formalized in Superpave for low-volume roads will allow for the use of materials similar to those that have beentraditionally used by local agencies. The key issue on many of these low-volumeroads is really an engineering-based decision as to what level of projects war-rants a mixture design. This has always been a factor; Superpave just provides amore sophisticated system and set of tools that can be selected.

—John Bukowski—John D’Angelo—Tom Harman

justifies the additional cost.”On the other hand, the PG64-22

binder that Albuquerque will specifyfor its residential and local streets isquite similar to the AC grade that theyspecified under the Marshall system.

“Since we started with Superpavein 1992, we have had a committee atthe local level—suppliers, State, fed-eral and local agencies—who workwith us to provide a better commu-nity product at a lower cost, whilerecognizing each agency’s andsupplier’s unique requirements. It’sbeen very effective,” Barker said.

Albuquerque started usingSuperpave fine-side aggregate grada-tions in 1992 (while still using theMarshall mix design method), withreview and agreement by the localasphalt concrete producers. The Cityhas found the asphalt concrete mixesusing the Superpave gradations, andresulting characteristic gradation curves,“a great improvement.” In 1997 theCity built its first full-fledgedSuperpave project, Sunport Boule-vard, a feeder road connecting the In-terstate to the airport. They have con-tinued to specify Superpave for selectprojects in the last three years, andexpect to complete the transition toSuperpave specifications for all streetprojects next year.

ALBUQUERQUE / from page 8

States have built at least some Superpaveprojects. California, which has notbuilt any Superpave projects to date(although portions of the AlamedaCorridor being designed by Los Ange-les County are Superpave) recentlyhas agreed to work with asphalt pro-ducers to conduct further researchand to evaluate the potential use ofSuperpave in that State by “puttingsome projects down,” Economy said.

For more information contact LisaEconomy at (808) 961-3196 or e-maillgeconomy@aol.com.

PCCAS / from page 7

12 Superpave Implementation Update ◆ Fall/Winter 2000

◆ September 11-12, 2000: TRB Superpave Mixture/AggregateExpert Task Group, Indianapolis, IN. For more information, contactJohn Bukowski. Phone (202) 366-1287; Fax (202) 366-9981;john.bukowski@fhwa.dot.gov.

◆ November 13-14, 2000: TRB Superpave Binder Expert TaskGroup, Tampa, FL. For more information, contact John D’Angelo.Phone (202) 366-0121; Fax (202) 366-7909; john.d’angelo@fhwa.dot.gov.

◆ November 15-17, 2000: 8th Annual U.S. Hot Mix Asphalt Confer-ence, Cincinnati, OH. For more information, contact conferencecoordinator, National Asphalt Pavement Association. Phone (888) 468-6499; Fax (301) 731-4621; www.hotmix.org.

◆ December 10-14, 2000: Asphalt Technology 2000: SharingTechnologies in the 21st Century, Renaissance Austin Hotel,Austin, TX. For more information, go to http://lifelong.engr.utexas.edu/conferences.html, or contact Sharon Campos.Phone (512) 232-5168; scampos@mail.utexas.edu.

◆ February 4-8, 2001: NAPA’s 46th Annual Convention and Worldof Asphalt Trade Show, Wyndham Palace Spa and Resort,Orlando, FL. For more information, contact conference coordinator,National Asphalt Pavement Association. Phone (888) 468-6499; Fax (301)731-4621; www.hotmix.org.

◆ March 19-21, 2001: Association of Asphalt Paving TechnologistsAnnual Meeting, Hilton Hotel, Clearwater, FL. For more informa-tion, contact AAPT office. Phone (651) 293-9188; www.asphalttechnology.org.

S U P E R P A V E C A L E N D A R.........................................................................................................................

S U P E R P A V E C A L E N D A R

U.S Departmentof Transportation

Federal HighwayAdministration

400 Seventh St., S.W.Washington, DC 20590

Official BusinessPenalty for Private Use $300

FIRST CLASS MAILPOSTAGE AND FEES PAID

FEDERAL HIGHWAYADMINISTRATIONPERMIT NO. G-66

Superpave Implementation Updateis published periodically by theU.S. Department of TransportationFederal Highway Administration’sSuperpave Technology Delivery Team.

FEDERAL HIGHWAY ADMINISTRATORKenneth R. Wykle

SUPERPAVE TECHNOLOGY DELIVERY TEAMJohn D’AngeloTom HarmanJohn Bukowski

EDITORKaren Haas MartinPhone: 301-949-8581Fax: 301-949-8582editorsink@starpower.net

FEDERAL HIGHWAY ADMINISTRATION400 Seventh Street, SWWashington, DC 20590Phone: 202-366-0121

Notice—The United States Govern-ment does not endorse products ormanufacturers. Trade or manufac-turers’ names appear herein solelybecause they are considered essen-tial to the objectives of the article.

Superpave is a registered trademark.