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University of California BerkeleyInstitute of Transportation Studies

Technology Transfer ProgramTECHNICAL TOPICS

Introduction

The existing Aged Residue (AR) gradingsystem for asphalt cements currentlyspecified by the California Departmentof Transportation (Caltrans) will bereplaced with the Performance Graded(PG) system. The implementation dateis January 1, 2006, at which timeCalifornia will join the other 49 statesthat have adopted some version of thePG system over the past 10 to 12 years.

Historical Perspective

Prior to the early 1970s, Californiarelied on the Penetration grading sys-tem to grade paving asphalts. This sys-tem is based on the amount of penetra-tion into an asphalt sample achieved bya standard needle at a given tempera-ture (25ºC) with a standard weight (100grams) for a fixed time (5 seconds).Based on Caltrans involvement with thePacific Coast Conference on AsphaltSpecifications (PCCAS), Californiaadopted 5 penetration grades in the late1950s: 40-50, 60-70, 85-100, 120-150,and 200-300 penetration. The primarypenetration grades used in Californiawere the 60-70 and 85-100 grades,with occasional use of the softer grades

(120-150 and 200-300) in colder cli-mates and the harder grade (40-50) inthe desert environment. Other tests,such as flash point, solubility, andductility on the original asphalt pluspenetration and ductility after Thin FilmOven aging, were also used to charac-terize the asphalt.

Under the Penetration gradingsystem, the consistency of the asphaltbinder at high service temperaturescould vary widely, especially inasphalts produced from a wide range ofcrude sources. As a result of this vari-ability, many states encountered “ten-der” mixes, a construction problemwhere the asphalt mix shoves exces-sively during compaction and oftenremains tender or soft for extendedperiods of time after construction. Forthese reasons, by the early 1970s moststates had switched from thePenetration grading system to aViscosity grading system, in an effort tocontrol the asphalt consistency(viscosity of the binder) at higherpavement service temperatures.

Most states adopted a Viscositygrading system that focused on themeasured viscosity of the originalasphalt at 60ºC. For example, an AC 20asphalt has a viscosity of 2,000 poise(+ 20%) at 60ºC. However, Caltrans

PERFORMANCE GRADED (PG) ASPHALTSIN CALIFORNIA

By Larry Santucci, PE, California LTAP Field Engineer, Technology Transfer Program,and Pavement Specialist, Pavement Research CenterInstitute of Transportation Studies, University of California Berkeley

The Technology Transfer Program is

a unit of the Institute of

Transportation Studies, University

of California Berkeley. Our mission

is to bridge research and trans-

portation practice by facilitating

and supporting the planning,

design, construction, operation and

maintenance of efficient and effec-

tive state-of-the-art transportation

systems. The Technology Transfer

Program provides professional train-

ing, workshops, conferences,

technical assistance and informa-

tion resources in the areas of

planning and policy, engineering,

project development, infrastructure

design and maintenance, safety,

and environmental issues for

motorized and non-motorized

roadway traffic, aviation and rail.

The Technology Transfer Program

is the California Local Technical

Assistance Program (LTAP) Center,

providing free services, technical

assistance and resources to

California’s public-sector trans-

portation agencies.

Technology Transfer Program

Institute of Transportation Studies

University of California Berkeley

1301 S 46th Street, Building 155

Richmond CA 94804

PHONE 510-665-3410

FAX 510-665-3454

E-MAIL [email protected]

WEB www.techtransfer.berkeley.edu

NO. 6

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was more interested in the consistencyof the asphalt binder as it was beingplaced on the roadway, than the consis-tency when it was produced. Therefore,through the PCCAS, Caltrans proposedan AR grading system that was basedon the viscosity of the asphalt binder at60ºC after it had gone through a labora-tory aging process to simulate the agingof the asphalt in a hot mix batch plant.Under this AR grading system, an AR4000 asphalt has a viscosity of 4,000poise (+ 25%) at 60ºC after aging. TheAR system has been in place inCalifornia since 1974. A rough compar-ison between penetration and viscosity(AC and AR) asphalt grades is shown inFigure 1.

In the early 1990s, Caltrans partici-pated in a PCCAS study group thatexamined a new approach to asphaltspecifications called Performance BasedAsphalts (PBA). The study groupfocused on the temperature susceptibili-ty of the asphalt binder, reasoning thatclimate conditions play a major role inbinder selection. Both conventional andpolymer modified asphalts are a part of

the PBA system. Initially, conventionaltests such as penetration, viscosity, andductility were used to characterize PBAasphalts. Later, more sophisticated rhe-ological tests were incorporated into

the PBA specifications. PBA binders arestill specified in California although thepredominant grades have become thepolymer modified asphalts identified asPBA 6a, PBA 6b, PBA 7, and PBA 6a*,which has a higher polymer loadingthan PBA 6a. The concepts generatedfrom the development of the PBAgrading system had a significant impacton the development of the PG gradingsystem.

What is PG?

The PG asphalt binder grading systemwas developed as part of the $150 mil-lion, 5-year Strategic Highway ResearchProgram (SHRP) conducted from 1987to 1992. The PG system addressesmany of the limitations of thePenetration and Viscosity grading sys-tems by focusing on the three specificpavement distress modes: permanentdeformation (rutting), fatigue cracking,and low temperature cracking. The cli-mate conditions (primarily temperature)to which pavements are exposed is a

F I G U R E 1

Comparison of Penetration and Viscosity Asphalt Grades

F I G U R E 2

PG Asphalt Binders Suggested for California Climate Conditions

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key element of the PG system. Forexample, PG 64-16 asphalt is intendedto provide:

� enough stiffness at 64ºC pavementtemperature to help the mix resistpermanent deformation or rutting,

� enough elasticity at -16ºC pavementtemperature to prevent low tempera-ture thermal cracking, and

� enough flexibility at intermediatetemperatures to minimize fatigue-cracking.

Number of PG Asphalts inCalifornia

The big question becomes “how manyPG asphalts are needed in California tocover the wide range of climate condi-tions existing in the state?” An analysisof temperature data gathered from 308weather stations in California suggests20 different PG asphalt binders wouldbe required (see Figure 2). Obviously,this is not practical from an asphalt

supplier, hot mix producer, or highwayagency standpoint. Like other statesfaced with similar decisions, Caltransneeded to decide on a workable num-ber of PG asphalts to cover the state’smany and varied climate regions. Inpartnership with industry, Caltrans hasselected four PG grades: 64-10, 64-16,64-28, and 70-10. These four gradescover 279 of the 308 California weath-er stations analyzed (see Figure 3). Themap in Figure 4 and the data in Table 1show the PG grades of choice for thevarious climate regions of California.

In addition, Caltrans believes that ahigher temperature PG grade (namely,PG 70-10) will be needed for certaindesignated routes that experienceextremely heavy traffic and for specialsituations such as on/off ramps, inter-sections, or standing/slow moving loadapplications in the Central Coast,Inland Valley, and South Coast regions.Caltrans also believes that polymermodified PBA asphalts should be anoption for designated routes and specialsituations throughout the state.

PG Tests and Specifications

Most of the tests and specificationsused to characterize PG asphalts arevery different from those that we wereaccustomed to under the Penetrationand Viscosity grading systems. Sinceasphalt is a visco-elastic material, theSHRP binder research team drew fromthe polymer industry to introduce a testto measure the relative contributions ofthe viscous and elastic components ofthe asphalt binder. The Dynamic ShearRheometer (DSR) is used to measurethese properties at intermediate temper-atures. The Bending Beam Rheometer(BBR) and Direct Tension Test (DTT)were developed to measure low tem-perature properties of the asphalt whilethe Rotational Viscometer (RV) wasselected to measure the flow propertiesof the asphalt at high temperatures formixing and compaction.

An important feature of the PGgrading system is that it measuresasphalt properties over a much broaderrange of aging conditions than previousgrading systems. Short term aging to

Asphalt Grade California Climate Regions

PG 64-10 Central Coast,Inland Valley,South Coast

PG 64-16 North Coast,Low Mountain, South Mountain

PG 64-28 High Desert, High Mountain

PG 70-10 Desert

F I G U R E 3

Four PG Binders Cover Over 90% of California Climate Conditions

TA B L E 1

PG Asphalt Gradesfor California

PG Binder

Loca

tion

s

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simulate hot mix hardening in the mixplant is accomplished with the RollingThin Film Oven (RTFO) test, which wasadopted from the AR grading system. Anew aging test, the Pressure AgingVessel (PAV), was developed to simu-late long-term aging in the field.

The PG grading system specifica-tion limits are indicators of the contri-bution of the asphalt binder to the

pavement distress conditions of perma-nent deformation (rutting), fatiguecracking, and low temperature crack-ing. Since rutting occurs early in apavement’s life, DSR measurementsnear the highest anticipated servicetemperature should be obtained froman unaged asphalt sample and com-pared against DSR measurementsobtained from an RTFO aged sample.

On the other hand, fatigue crackingand low temperature cracking generallyoccur later in a pavement’s life. DSRmeasurements on an RTFO and PAVaged sample at an intermediate temper-ature are used to predict fatigue crack-ing. BBR and DTT results on an RTFOand PAV aged sample at the lowestanticipated pavement surfacetemperature are used to predict low

F I G U R E 4

PG Binder Map for California

Asphalt Grade California Climate Regions

PG 64-10 Central Coast, Inland Valley,South Coast

PG 64-16 North Coast,Low Mountain, South Mountain

PG 64-28 High Desert, High Mountain

PG 70-10 Desert

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temperature cracking. The relationshipbetween PG tests, test temperatures,aging conditions, and pavement perfor-mance/ construction properties isshown in Figure 5.

Several other states have adoptedthe standard PG specifications con-tained in AASHTO M320-04. However,some of those other states have modi-fied these requirements based on theirexperience with PG asphalts and/orasphalt supply considerations specificto their area. Caltrans has adoptedAASHTO M320-04 with the followingexceptions and options:� The DSR maximum limit on RTFO

and PAV aged asphalt may beexceeded by some major asphaltsources in California. If so, the sam-ple may be tested at a 3ºC highertemperature than the specified test

temperature and will be accepted ifit satisfies the specified maximumlimit.

� A ductility limit of 75 cm at 25ºC onthe RTFO sample is included.

� The option allowed under M320-04for a PAV aging temperature of110ºC has been selected for the PG70-10 asphalt grade.

Polymer Modified Asphalts

The four PG grades selected by Caltransdo not require polymer modification. Itis likely that most of these grades willbe supplied from the same asphaltsources currently used to supply ARasphalts with some possible modifica-tions in manufacturing procedures. Oneexception is the PG 64-28 asphaltrequired for the High Mountain and

F I G U R E 5

PG Graded Asphalt Performance Criteria, Required Tests, Temperatures and Aging Conditions

High Desert climate regions. Somesuppliers may find it necessary to poly-mer modify their asphalt to meet therequirements for this grade.

Polymer modified asphalts aregrowing in popularity in California.They are often preferred in someextreme climates such as the HighMountain or Desert regions or underheavy loading conditions such as veryhigh traffic, intersections, port installa-tions, etc. To meet this need, Caltranshas elected to retain four PBA gradesthat are polymer modified, namelyPBA 6a, 6a*, 6b, and 7. It is likely thesePBA grades will be replaced by poly-mer modified PG grades by January2007. A Caltrans-industry task force isdetermining which PG grades could besubstituted for the polymer modifiedPBA grades. The polymer modified

PerformanceCriteria

Test

Temperature

AgingCondition

Low Temperature Cracking

Direct Tension Test

DDT

Minimum Pavement Surface Temperature

Short Term Aging (RTFO) plus Long Term Aging (PAV)

Intermediate PavementTemperature

Average 7-dayMaximum Pavement

Temperature

No Aging andShort Term Aging

(RTFO)

No Aging

Mixing/CompactionTemperature

Bending BeamRheometer Test

BBR

Dynamic ShearRheometer Test

DSR

Dynamic ShearRheometer Test

DSR

RotationalViscometer Test

Fatigue Cracking Rutting Pumpability

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binders will probably require a “PGPlus” specification to assure the pres-ence of a certain level of polymer inthe binder.

Asphalt Rubber Binders

There is also a great deal of interest inthe use of asphalt rubber mixes inCalifornia. These are primarily used inopen graded or gap graded surfacemixes. A Caltrans-industry task forcewas formed to decide which baseasphalts under the PG system would berequired to satisfy the needs of theseasphalt rubber mixes. The task forcefound that a PG 64-16 asphalt could beused as the base asphalt in most asphaltrubber applications, except in coldclimate regions, where a PG 58-22asphalt would be required. Therefore,one additional PG grade, beyond thefour already identified, will be part ofthe asphalt supply picture.

Design Considerations

Selection of an asphalt grade under thePG/PBA system is fairly straight forward(see Table 2). First, the designer or engi-neer determines what climate regionthe project in (see Figure 4). Then, thePG grade for that region is determined.If the designer feels special circum-stances, such as heavy or unusual traf-fic, warrant classification under the“designated route” category, a highertemperature PG grade or polymer mod-ified asphalt might be selected. Forexample, a PG 64-10 is the PG grade ofchoice for the Inland Valley. However,in the “designated route” category, aPG 70-10 or PBA 6a* might be justifiedfor certain applications. For the Desertregion, PG 70-10 is the primary choicewith a “designated route” option ofPBA 6a* or PBA 7.

Data extracted from a survey by theAsphalt Institute shows how a limitednumber of AR asphalts used on actual

projects in California would grade outunder the PG system (see Table 3). Ingeneral, AR 4000 asphalts tend to gradeout as PG 64-10 asphalts with a fewPG 64-16 examples, while the AR 8000asphalts tend to grade out as PG 64-16asphalts with some PG 64-28 exam-ples. Asphalt source will continue toplay a role in the grade supplied asit did under the AR system. For orienta-tion to the PG system, the AR viscosityat 60ºC of conventional (unmodified)asphalts produced in California andneighboring states is compared tovarious PG graded materials in Table 4.

Mix design is not expected to be anissue with this change to PG grading.

The same dense graded, open graded,and gap graded mixes used currentlywill continue to be used under thePG system. Caltrans is not changingmix types at this time. Since many ofthe same asphalts supplied under theAR system will be supplied under thePG system, changes in mix designare not anticipated. One possibleexception may be the use of a some-what harder binder (PG 70-10) in theDesert region. No doubt, contractorswill check their mix designs during thetransition to the PG system to be cer-tain asphalt contents are not changingsignificantly.

TA B L E 2

Asphalt Grade Selection under the PG System in California

Binder forClimate Region PG Grade Designated Route

Central Coast, PG 64-10 PG 70-10 or PBA 6a*Inland Valley,South Coast

North Coast, PG 64-16 PBA 6a*Low Mountain,South Mountain

High Desert, PG 64-28 PBA 6a or PBA 6bHigh Mountain

Desert PG 70-10 PBA 6a* or PBA 7

NOTES: PBA 6a* is a modified version of PBA 6a.

For Open Graded Asphalt Concrete (OGAC) statewide, use the PG grade for theappropriate climate region above or PBA 6a for low temperature placementconditions.

For Rubberized Asphalt, the base stock will be PG 64-16 for all climate regionsexcept the High Desert and High Mountain regions where the base stock will bePG 58-22.

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Construction Issues

With any change of this magnitudefrom the familiar to the unfamiliar, con-struction concerns are bound to sur-face. Will mixes made with PG 64-10asphalt behave differently under theroller during compaction from the AR4000 mixes used previously? Will theuse of PG 70-10 asphalt change mixplant operations or laydown proce-dures? Will tender mix issues complete-ly disappear once the PG grading sys-tem is in place? The answers are “prob-ably not” to each of these questions,but there will, without a doubt, be alearning period as contractors makeadjustments to the new PG system.Fortunately, 49 other states have madethis transition without major disruptionsand, in many of those states, mix typeswere also changed.

Caltrans Construction is workingclosely with industry to make the transi-tion from the AR grading system to thePG system as seamless as possible.Projects that are awarded in 2005 andextend into 2006 may involve anasphalt binder change. Caltrans willallow the contractor to use the AR grad-ed asphalt specified for the job until theproject is completed, even if the projectextends beyond the January 2006implementation date. Alternatively, thecontractor will be allowed to switch tothe equivalent PG grade during theproject if the AR asphalt is no longeravailable from the supplier.

Caltrans’ Implementation Plan

In summary, the Caltrans implementa-tion plan includes the followingelements:

� Replace the AR grading system withfour PG grades, each associatedwith specific climate regions inCalifornia, by January 2006.

� Provide training to Caltrans, localagencies, and private industry atseveral locations throughoutCalifornia in late 2005.

Local Agency Impact

This change in asphalt specifications byCaltrans will, of course, impact localagencies. AR graded asphalts will nolonger be available in California shortlyafter the January 2006 implementationdate. Engineers or consultants for localagencies will need to select appropriatePG or PBA asphalts to replace whatthey are currently using. The guidanceprovided by this article is a startingpoint. Pavement Associations, theAsphalt Institute, hot mix contractors,and asphalt suppliers can also provideassistance. Although the binder

� Permit the use of a higher tempera-ture PG grade and four PBA polymermodified asphalts for designatedroutes or special situations.

� Re-examine the PBA grades andtheir uses and grade polymer modi-fied asphalt binders as “PG Plus” byJanuary 2007.

� Define PG base asphalts for asphaltrubber mixes.

� Require AMRL certification for PGtesting by asphalt laboratories byJanuary 2007.

� Adopt AASHTO M320-04 specifica-tions for PG asphalts with Californiamodifications.

TA B L E 3

PG Grade Comparisons for California AC Paving Projects

Project Nearest AR Binder Equivalent

Number City Specified PG Binder

#22 Sunol AR 4000 PG 64-10

#38 Placerville AR 4000 PG 64-16

#55 Fresno AR 4000 PG 58-28

#107 East Sacramento AR 4000 PG 64-22

#108 East Palo Alto AR 4000 PG 64-10

#110 Kettleman City AR 4000 PG 64-10

#111 Magic Mountain AR 4000 PG 64-10

#114 Oroville AR 4000 PG 64-10

#116 Fremont AR 4000 PG 64-16

#39 Sacramento AR 8000 PG 64-10

#52 Mendota AR 8000 PG 64-28

#101 Carpenteria AR 8000 PG 64-16

#102 Paso Robles AR 8000 PG 64-28

#103 Los Angeles AR 8000 PG 64-16

#105 San Luis Obispo AR 8000 PG 64-16

#113 East Barstow AR 8000 PG 64-10

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selection process based on climateregion described earlier is straightfor-ward, special situations will arise forlocal agencies which will require goodengineering judgment on the proper PGasphalt to use. For example, what PGasphalt should be used for asphalt curbconstruction or for container storagefacilities in a climate region calling forPG 64-10 for normal paving opera-tions? If an agency has, based on expe-rience, adjusted the use of AR grades tomeet its needs, what adjustments arenecessary under the PG system? These,and other questions, will be answeredas local agency pavement engineersand consultants become more familiarwith the PG grading system.

Training

Both agencies and industry agree thatproper training plays a critical role in asuccessful transition to PG grading.Caltrans and industry are jointly plan-ning training sessions for at least 12

locations throughout California duringthe fall of 2005, to disseminate moredetailed information on the subject.This training will be available to repre-sentatives of Caltrans, local agencies,the asphalt industry, and consultingfirms.

In addition, the Technology TransferProgram of the Institute ofTransportation Studies (ITS) at theUniversity of California, Berkeley isdeveloping a half-day Road Show onPG asphalts for local agencies. RoadShows are low-cost training coursesthat can be put on at a local agency’slocation by request. Road Shows aretaught by experienced instructorsretained by ITS, and are partially sup-ported by Local Technical AssistanceProgram (LTAP) funds. For moreinformation regarding this on-goingtraining option, seewww.techtransfer.berkeley.edu/roadshows, e-mail [email protected] or call 510-665-3410.

Educational material on the PG asphalt system is also available on-linefrom the Asphalt Institute atwww.asphaltinstitute.org and theNational Asphalt Pavement Associationat www.hotmix.org.

Contacts for Technical Assistance

� CaltransKee [email protected]

� The Asphalt InstituteRobert [email protected]

� Asphalt Pavement AssociationJim St. [email protected]

� Northern California AsphaltPavement AssociationBrandon [email protected]

� University of California BerkeleyPavement Research Center/ CA-LTAPLarry [email protected]

The contents of this publication do not reflect theofficial views or policies of the University ofCalifornia, the State of California, or the FederalHighway Administration, and do not constitute astandard, specification or regulation.

This publication was produced with support fromthe California Local Technical Assistance Programand may be reproduced for noncommercial pur-poses. We request notice of reprint and inclusionof the following acknowledgement: “These materials were developed by the California LTAP Center at the Institute of TransportationStudies Technology Transfer Program, Universityof California Berkeley. For more information see www.techtransfer.berkeley.edu or contact510-665-3410.”

TA B L E 4

AR Viscosities for PG Production Asphalts Used in California and Neighboring States

Asphalt AR ViscosityUsed in PG Grade @ 60ºC, Poises

California (Valley Asphalt) PG 64-10 4,889

California (Coastal Asphalt) PG 64-16 4,110

Oregon PG 64-28 6,676

Arizona PG 70-16 12,302

Arizona PG 76-16 29,765