TRB Superpave Mixture and Aggregate Expert Task Group
Meeting Minutes
Washington, DC

Cover Letter
List of Post Meeting Action Items

The meeting was convened on September 21, 1999 by Chairman Ron Sines of the New York State Department of Transportation.

Those members attending were:
Ron Sines, New York State DOT (Chair)	Frank Fee, Citgo (Vice-Chair)
John R. Bukowski, FHWA (Secretary)
Tim Aschenbrener, Colorado DOT	Lon S. Ingram, Kansas DOT
John Cheever, CAMAS Inc	Larry Michael, Maryland DOT
Ervin L. Dukatz, Mathy Construction Co	Julie Nodes, Arizona DOT
Kevin Hall, University of Arkansas	Richard Stewart, South Carolina DOT
Ron Heckel, Lafarge Constr Materials Group	Randy West, APAC Inc.
Gerry Huber, Heritage Research
Mike Anderson, Asphalt Institute (liaison Asphalt Institute)
F. M. Rick Harvey, Wyoming DOT (liaison AASHTO SOM)
Charles Marek, Vulcan Materials Co. (liaison National Stone Association)
Gale Page, Florida DOT (liaison TRB Superpave Committee)
Haleem Tahir, AASHTO (liaison AASHTO)
John D'Angelo, FHWA (Support Staff)	Tom Harman, FHWA (Support Staff)
Ted Ferragut, TDC Partners (Support Staff)	Neil F. Hawks, TRB (Support Staff)
Edward Harrigan, TRB (Support Staff)
Those friends of the ETG attending were:
Frank Dalton, Pine Instrument Co.	Rebecca McDaniels, NCSC
Dale Decker, Old Castle Construction	Chuck Paugh, FHWA-GPI
Lee Gallivan, FHWA-Indiana	Pedro Romero, FHWA-SaLUT
David Jahn, Martin Marietta	Naga Shashidhar, FHWA-SaLUT
Brian Killingsworth, Fugro, BRE	Aroon Shenoy, FHWA-NRC
Bernie McCarthy, Asphalt Institute	R. Chris Williams, FHWA

Call to Order (Sines)
Chairman Sines welcomed the group. He extended his thanks to the past chairmen and members of the former Mixture Expert Task Group. The Chairman reviewed the agenda (Attachment A), and asked the attendees for self introductions.

AASHTO, TRB, & FHWA Superpave Management (Hawks/Ferragut)
Mr. Hawks extended a welcome on behalf of TRB. He discussed the impacts of TEA21 - primarily the loss of federal funding to support many Superpave activities such as the ETGs. While some residual FHWA funds are still being utilized, AASHTO adopted resolution 5-98, "Conduct of Highway Research Under TEA 21," to provide funding for critical programs. TRB was directed to assist in external management of Superpave implementation, coordinate Superpave activities of NCHRP and FHWA, and provide oversight. TRB established the TRB Superpave Committee (created in April 1999 to replace the FHWA's asphalt technical working group) to provide this function. The purpose of these activities are to maintain focus for the Superpave program. A key task of the TRB Superpave Committee is to develop a long-range plan for Superpave's continued development and to provide recommendations for the program. While having a more formal relationship, the mission of the "parent" TRB Superpave Committee and the Mixture/Aggregate and Binder Expert Task Groups remains very similar.

The TRB Superpave Committee and ETGs must comply with the Federal Advisory Committee Act. This has resulted in a prescribed member appointment process and a more formal distinction between members and observers (friends of the ETG). Meetings still remain open to maintain a dialog between members and guest/observers. The importance of maintaining the liaison with others involved in Superpave development and implementation was also recognized, in particular with user producer groups, lead states, and the Superpave centers.

Additionally, a formal review system is now in place. A requirement of this system is at the end of each meeting, an executive session of the members and liaisons will be held. This session will be used to determine if an issue addressed in meeting had a consensus opinion and if action by the ETG is necessary. No new materials will be raised during this session.

A "Statement of Task" (Attachment B) reflecting the new ETG's mission and objectives was distributed.

John Bukowski, of the FHWA, will serve as the ETG Secretary and maintain a "friends of the ETG" mailing list. Over the next few weeks a summary of the meeting activities will be compiled. Once approved by the Chair they will be distributed to members and friends of the ETG. It is planned that ETG minutes/activities will also be posted on the TRB web site. Additionally, John Bukowski along with Tom Harman and John D'Angelo will form the FHWA representation to the DC support staff for the Superpave program.

Members Perspective of Superpave and Role of ETG (Sines)
The specific role of the ETG was further discussed. Overall the ETG will continue to identify needed improvements to the Superpave system and to assess future Superpave technology developments.

Tim Aschenbrener presented the state DOT perspective regarding the future role of the Mixture/Aggregate ETG. A survey of 25 states currently or previously involved with the old Mixture ETG was conducted. A total of 17 responses were received. A copy of survey and results (Attachment C) were distributed. The survey posed 28 issues and asked the DOTs to prioritize the issues and determine whether they were being adequately addressed or needed improvement. The following were identified as the very high priority issues (listed in priority order):

• Construction issues (tenderness, segregation, permeability)
• Mixture strength test
• VMA criteria and effects with different gradation
• Moisture damage test
• Field verification guidelines
• N-design refinement/validation

While not listed as a very high priority issue, aggregate issues were also identified as still being a concern.

Lon Ingram commented that a particular states' priority listing was influenced based on where state is in the Superpave adoption/implementation process. Ron Heckel commented that this was a good survey and all states should have an opportunity to participate.

Frank Fee presented the industry perspective regarding the future role of the Mixture/Aggregate ETG. Many issues were the same as those identified in the state DOT survey. These included the need for: the ability to predict if a mixture will have construction problems (tenderness, joint segregation, permeability), a mix characterization/strength test, better methods to determine mixing and compaction temperature.

Additionally, a NAPA survey of 25 contractors raised these issues:

• Percentage of binder in mix some said higher, some said lower
• Aggregates need to be more clean/less fines
• Restricted zone issues - can mixes through or above the restricted zone make good mixes
• How much gradation control is appropriate
• Constructibility is an issue - harder to get good joints
• Compaction issues - need increased passes, compaction is different/unpredictable (it was noted the contractor's ability to achieve compaction improved with experience)

The role of Mix ETG in the industry's view was similar to the state survey comments (focal point to compile information on the Superpave system, decision making on what issues go forward, clarify and refine). Industry recognized an authoritative body is needed, however, any specification revision recommendations must go forward through AASHTO to insure uniformity.

John Bukowski presented the FHWA's perspective regarding the future role of the Mixture/Aggregate ETG. The priorities of FHWA Superpave efforts are very much the same as the priorities identified by the states and industry. They fall into three major categories:

• Refine Mixture Specification
  • Aggregate test refinement
  • Refine volumetric properties (air voids, VMA, VFA)
  • Continued validation SGC gyration levels
• Develop Performance Tester
  • Identify a strength tester
  • Equipment development
  • Validate results
• Construction Issues
  • Resolve compaction tenderness issues
  • Develop quick construction tests (density, permeability, specific gravity)
  • Utilization of performance related specifications
  • Modeling of Mixture Performance
  • Identify key material characteristics
  • Model characteristics for pavement performance
  • Tie to pavement design

The Mixture/Aggregate ETG should continue to have a pro-active role by identifying problems within the Superpave system, refining the technology, and communicating changes/recommendations to the users of the system. Active participation by members and friends of the ETG needs to continue.

Group Discussion
Randy West commented implementation has been positive, and the ETG has recommended positive changes to the provisional standards. Now the ETG needs to focus on the key issues identified. It is still uncertain if these mixes will perform better in all aspects, not just rutting.

Gale Page commented the states will be challenged to answer why they are implementing Superpave. Are these changes for the better? Is there uncontested proof these mixes are performing better? Implementation of Superpave has opened up to scrutiny a lot of old practices, which were not challenged in the past. Performance information is needed.

John D'Angelo commented users were not satisfied with Marshal or Hveem systems, that is why Superpave came about. Mixes were not performing in the past. We learned to place mixes but we never really maximized their performance. Need for a performance tester didn't come about just because of Superpave. We are all trying to improve overall performance of HMA pavements. Don't fall into a trap and compare Superpave with old practices.

Erv Dukatz commented communication between the states and industry is essential. Another issue to consider is things we know work previously should not be forgotten. Remember the Superpave system while encompassing a lot is not the only factor. Pavement thickness is an issue that also impacts permeability, constructibility, etc. Need appropriate mat thickness for nominal aggregate size.

Dale Decker commented implementation is going well. But remember the ETG members are far above learning curve. Things can get misinterpreted when they get to the field. For instance, there have been some issues on permeability, but don't over react some are related to lift thickness, and other factors. This is not just a Superpave issue.

The need for test procedure standardization was discussed. One way this happens is to ensure that AASHTO specifications are the focal point. We need to get away from thinking each state will have its own methods/procedures. Criteria may vary for some states, but at a minimum states need to perform test procedure in same way. Superpave gives us the opportunity to do this. Larry Michael responded it is an absolute necessity test procedures are performed the same way.

Frank Fee commented a problem with AASHTO standard development is it has no formal mechanism for needed industry input. In reply, Richard Stewart commented that the Subcommittee on Materials (SOM) is now open to industry and input from industry is welcome. Rick Harvey sees the ETG as being a focal group for input to AASHTO on the Superpave standards. In the past SOM has asked ETG to address a number of issues.

Richard Stewart commented as newly adopted procedures get into use the identified problems need to get back to the SOM so they can be addressed. Often we have a problem with test method but don't share information. Technical certification will move us to better standardization.

Gerry Huber commented industry should get copies of ballots prior to vote and offer comments, even if they can't vote, this is important. It was requested that the SOM provide a copy of ballots to the ETG for review and comment.

In summary it was concluded that many similar priority issues have been raised. The ETG needs to focus on technical improvements in these priority areas.

NCHRP Superpave Projects Update (Harrigan)
Edward Harrigan presented an update of the NCHRP Superpave related projects. NCHRP's focus has traditionally been an individual project driven effort. However, the additional research needed to fully develop LTPP and Superpave is changing the NCHRP research activities to a "program" focused effort.

The NCHRP projects were selected to fill gaps in research or enhance what already exists. A summary of the projects and their objectives are detailed below:

9-9(1) "Verification of Gyrations Levels in the N_design Table" This project will verify the N_design values are correct or make changes. Will end mid- 2002 and needs to coordinate with 9-24.

9-10 "Superpave Protocols for Modified Asphalt Binders" This project is complete. Results will be released in the form of a practice for advanced binder characterization, and determination of temperatures for mixing and compaction.

9-12 "Incorporation of RAP in the Superpave Systems" This project will be complete in December 1999 and forwarded to the ETG for review in the first half of 2000. The recommended practice builds on previous ETG guidance.

9-13 "Evaluation of Mixture Sensitivity Tests" This project recommended changes to T-283. The AASHTO Technical Section responsible for this standard has reviewed the proposed changes and determined additional revisions were necessary. Another AASHTO ballot is anticipated.

9-14 "Investigation of the Restricted Zone in the Superpave Aggregate Gradation Specification" This project will evaluate the need for the restricted zone and will be complete in July 2000. The results will be forwarded to the ETG for review once the NCHRP panel has completed their review.

9-16 "Relationship Between Superpave Gyration Compaction Properties and Permanent Deformation of Pavement in Service" This project will determine if properties measurable by the SGC can be related to permanent deformation. This project will coordinate data and material with 9-19. Completion date in May, 2001.

9-17 "Accelerated Laboratory Rutting Tests: Asphalt Pavement Analyzer" This project will determine if the Asphalt Pavement Analyzer is a suitable test method to identify a mixtures rutting potential and if it can be adapted for quality control operations. Completion date in 2001. Results will be supplied to 9-19 Tack C.

9-18 "Field Shear Test for Hot Mix Asphalt" This project will determine if the Field Shear Tester developed under 9-7 can it be adapted for use with Superpave quality control. Completion date in December, 2001.

9-19 "Superpave Support and Performance Models Management" This project will develop three products of interest to ETG: (1) software for mix design version 2.0, (2) simple performance test for rutting and possibly fatigue - finish March 2000 and ETG consideration in first half of 2000, and (3) mechanistic characterization of critical mixture properties that can be related to performance. Completion date in 2001.

9-20 "Performance-Related Specifications for HMA Construction" This is the completion of the FHWA's WesTrack project. Deliverables include (1) performance-related specifications for asphalt mixtures/pavements, software and a guide specification (2) performance prediction models for rutting and fatigue, and (3) analysis of Superpave WesTrack sections performance. Completion in January 2000. The results will be forwarded to the ETG for review once the NCHRP panel has completed their review in the first half of 2000.

9-22 "Beta Testing and Validation of HMA Performance Related Specification" This project will start in 2000.

9-24 "Validation of a Simple Performance Test Device" This project will start in 2000.

Other NCHRP related projects include:

9-11 "Segregation in HMA Pavements" This project is complete. The objective of this project was to identify a rapid construction test to detect segregation in HMA mixtures before the pavement is completely constructed. Infra-red temperature determination shows promise. Practices based on this research will be produced.

4-19(2) "Validation of Performance Related Tests of Aggregate for Use in HMA Pavements" This project will look at aggregate properties in HMA. Once underway information/updates will be forwarded to the ETG for review.

FHWA Update (D'Angelo/Harman/Bukowski)
AASHTO through TRB wanted to continue a number of existing FHWA activities and provided funding in FY1999/2000 to the FHWA for these efforts.

A summary of the projects and their objectives are is detailed below:

90-01 "Demonstration Project 90: Advanced Asphalt Mix Design and Field Quality Control" This project is a continuation of the FHWA's mobile testing laboratory which provides data for equipment validation and field control. This effort has previously produced considerable data for the ETG's consideration/recommendations. The simple performance tester, PRS specification, etc. will be validated as part of this project. Additionally, 9-7 recommendations for tolerance limits will be refined and specifications developed for DOTs as result of current trailer efforts.

90-03 "Superpave Mix Tenderness" This project will investigate tenderness of mixtures during compaction. Project to be completed by end of 2000.

90-05 "Fine Aggregate Specific Gravity Test" This project will attempt to develop a simple, repeatable test for the determination of fine aggregate specific gravity. The production model work should begin by end of 1999 and all work completed by end of 2000.

90-06 "Ruggedness Testing of Superpave Shear Tester and Indirect Tensile Tester" Ruggedness testing of the Superpave shear tester (SST) and indirect tensile tester (IDT) is currently being conducted in accordance with established ASTM procedures by the Superpave Regional Centers and FHWA's Turner-Fairbank Highway Research Center (TFHRC) with the assistance of the Asphalt Institute. When this program is completed guidance will be provided on promising tests for predicting pavement performance. This project will be complete by the end of 2000.

90-07 "Update of Binder and Mix Specifications" This is an extension of TFHRC's polymer asphalt program (mix and binder specification development). Determine if the specification is blind to source of asphalt and/or method of modification. Look to ETG for input on direction/results of ALF effort.

90-08 "National Superpave Conference (Forum 2000)" A national Superpave conference to be held in Denver, Colorado in April 2000.

An additional project to the above list will be proposed for FY2001 to validate the simple performance tester and facilitate delivery of equipment to industry.

TRB is looking to the ETG for an independent assessment of the FHWA activities. In executive session the ETG formed teams to provide technical monitoring of the FHWA Superpave mixture and aggregate related activities. Each team will act in a similar manner to an NCHRP Project Panel by: reviewing and commenting on the scope of work, providing technical input for FHWA consideration, coordinating presentation of deliverables to the ETG for deliberation and make recommendations to the ETG on necessary action. Three teams are being formed as follows:

Team 1 90-01, 90-03, and 90-05 FHWA Lead - John D'Angelo, ETG Team - Tim Aschenbrener (Lead), Ron Sines, John Cheever, and Kevin Hall.

Team 2 90-07 FHWA Lead - Tom Harman, ETG Team - Larry Michael (Lead), Rebecca McDaniel, Mike Anderson, Lon Ingram, and Richard Stuart.

Team 3 90-06, 90-08, and Simple Performance Testers (develop prototype and commercialize, ruggedness, validation) FHWA Lead - John Bukowski, ETG Team - Julie Nodes (Lead), Gerry Huber, Erv Dukatz, and Frank Fee.

This work could be handled by mail, but a once a year supplemental meeting of team may be needed. The possibility of having a meeting of these teams at annual TRB meeting is at discretion of each team. At the next ETG meeting the Team Lead will report to the ETG on activity of their group. Copies of problem statements and progress will be provided to the teams by the FHWA Lead.

Mix ETG - Processing Past Guidelines (Bukowski)
John Bukowski reviewed a list of past ETG accomplishments, recommendations, and guidelines (Attachment D). These included:

• Evaluation of SGC mold size
• SGC equipment modifications
• SGC procedural ruggedness
• Initial revisions of TP4, MP2, and PP28
• Recommendations for mixes in restricted zone formed the basis for NCHRP 9-14
• Superpave moisture sensitivity considerations formed the basis for NCHRP 9-13
• RAP usage in Superpave formed the basis for NCHRP 9-12
• Recommendations of 2 hours versus 4 hours short term aging
• Sampling study of criteria for fine aggregate angularity
• Summary of 1996 construction experiences
• Development of an SST "lab standard" specimen
• Development of an IDT "lab standard" specimen
• Initial SST & IDT procedural changes to AASHTO TP7 and TP9
• Developed a Loaded Wheel Testers advisory
• Developed a Mixture Solid Additives Evaluation Procedure
• Developed a procedure for the Evaluation of New SGC's - AASHTO PP35
• Validation studies of N-design
• Revised N-design table
• Current revisions to TP4, MP2, PP2, and PP28
• Practice to compare within procedure differences in SGC results

ETG recommendations are not part of the specifications until adopted by AASHTO. When AASHTO adopts specification revisions there are delays in getting the revised specification into use. Ultimately it is up to individual states to adopt and incorporate the revised specifications into their system. It is hoped the formal relationship between the ETGs and AASHTO will eliminate some of the delays and uncertainties to full adoption.

Chairman Sines discussed when the ETG puts forth specification revisions or other guidelines, it should follow up on how they are utilized, ensure users receive the information, and if appropriate ensure AASHTO considers proposed revisions. Some members asked to obtain copies of past guidelines. A package of key guidelines and recommendations will be sent to all ETG members.

Aggregate Mix Design Issues (Marek)
Chuck Marek, a member of the TRB Superpave Committee, was asked to frame the issues currently facing the aggregate industry relative to Superpave which need to be resolved. The following areas of concern were identified:

• Aggregate test procedures standards and definitions are not being applied uniformly. For example differences exist in how states implement Flat and Elongated (F&E) and Fine Aggregate Angularity (FAA) test procedures, use of the restricted zone varies, and where to draw the maximum density line and control points. The concept of promoting the use of variable criteria among the states, while still utilizing the same procedures, needs to be explored.
• The aggregate industry is concerned with potential problems with the Superpave criteria regarding the restricted zone, FAA, dust to binder ratio, degradation, VMA (specific gravity values are critical to VMA), tighter grading control (variability in grading control), limited use of natural sands. Aggregate producers need to develop a lot more test data for each aggregate product. Also of concern is the competence and understanding of the technicians running these tests.
• Improvements in the test procedure used to determine FAA are needed. There is a significant source of variability in test results.
• Excess crusher fine material is being generated and there are less places in SMA and coarse graded Superpave to use these materials.
• Many in the aggregate industry cannot manufacture aggregate to the specific sizes needed in Superpave. Changes in aggregate production requirements include fractionalization of coarse aggregate to meet gradation, more aggregate breakdown, more wear and tear on plants, and reduced production rates.
• Approximately 25% of HMA plants are over 30 years old, and another 25% are 20 to 30 years old. These facilities may have problems with tight aggregate control. This will impact on areas of production. Availability of material depends on the producer and location. The aggregate industry wants good performance, but at reasonable economics.

Available materials must be used widely. The aggregate industry wants to ensure good materials are used and bad materials are rejected. Valid performance measures need to be developed, the economic impacts of requirements fully understood, and aggregate research continued.

John Cheever reminded the ETG the aggregate industry is not just producing aggregates for asphalt mixtures. A lot of issues raised are not just Superpave. The aggregate industry should be surveyed to get their opinions on need and priority.

Ron Heckel commented the aggregate industry recognizes capital expenditures may be needed to meet the new requirements. In his opinion there is a lack of "hard" evidence on FAA or F&E as being the best properties to describe an aggregate's quality. The aggregate industry doesn't want to spend a lot of money to meet the current criteria and then have criteria changed.

Based on this discussion, ETG members associated with the aggregate industry summarized the key aggregate issues to be addressed as:

• Test procedure standardization among states (allow variable criteria)
• VMA (need different requirements for fine and coarse gradations)
• Restricted zone (eliminate term "restricted zone" and rename "caution zone" to prevent the hump in the fine aggregate gradation, advise agency this is not mandatory)
• Conduct ruggedness of consensus aggregate criteria and promote standard procedures between states
• Fine graded mixes that work well need to be utilized
• FAA test procedure issues (bulk specific gravity, sample gradation, recommended test blends/acceptance criteria)
• F&E criteria

Chairman Sines asked Chuck Marek to coordinate the development of a paper intended to identify on-going aggregate research, areas where additional research is needed, and identify activities the ETG could undertake to address areas of concern to the aggregate industry. Mr. Marek was asked to provide this paper by March 1, 2000 so that it may be sent to the ETG members before the next meeting.

Superpave Gyratory Compactor Comparisons (Harman)
AASHTO currently maintains two specifications related to the use of Superpave Gyratory Compactors (SGC) PP35 "Standard Practice for Revaluation of Superpave Gyratory Compactors" and TP-4 "Standard Method for Preparing and Determining the Density of HMA Specimens by Means of the SHRP Gyratory Compactor." A new AASHTO standard has been proposed to establish a procedure to evaluate a situation where SGCs meet all the specifications but during field testing results differ between two or more SGCs. This standard is being evaluated by the SOM. The ETG will provide further information on user variability related to this standard.

The FHWA is developing a device to measure the SGC angle of compaction to aid in checking SGCs compliance and to provide an additional tool to determine why different SGCs give different results. The SGC criteria are angle, speed, and pressure. Because of the unique manner each SGC induces angle differences exist between compactors in how the angle is measured. In most cases angle measurement is difficult. The angle can change due to wear, accidents, etc. This device will provide a way to check the compactor angle during compaction under load, using the same method for all SGCs. The FHWA will develop a draft specification for this device, then obtain multiple manufacturers. The device will be supplied to the FHWA mobile labs as soon as possible. A ruggedness study conducted in association with several state will be conducted. Device cost is projected to be under $5000. It is envisioned a pooled fund would obtain initial devices for each state DOT.

Currently, AASHTO TP-4 only requires a static measurement of angle. Concern exists if a device is produced to measure SGC angle dynamically a conflict with existing SGCs could arise. If angle differences are seen but mixes produced result in the same air void content, the angle tolerance when measured dynamically could be increase over the current static measurement tolerance.

It was noted a difference of .01 in specific gravity will result from a 0.1 degree difference in angle. A much larger difference in pressure (60 Kpascals) would be required to create a similar difference. This device will focus on angle differences which could be the source of large differences in measured mixture properties between different SGCs.

The ETG members are supportive of the development this device. The FHWA will develop a prototype over the next several months and work with the ETG in completing its evaluation.

Aggregate Blend Optimizations (Huber)
Aggregate gradation is a key to high performance pavement. Evaluating the impact changes in aggregate gradation have on a mixture, by plotting the compaction curve data, was made possible by the SGC. The Superpave mixture design process requires the development and evaluation of three aggregate blends through a trial and error process. The Superpave system does not currently include a rational basis for selecting trial or alternate gradations.

What type of aggregate structure is needed for performance? To be rut resistance a mixture should have a coarse aggregate skeleton locked together with a strong fine aggregate and high stiffness binder. For fatigue resistance a mixture should have sufficient asphalt binder in thick stiff layers. For durability the mixture should have low in-place air voids to ensure a moisture resistant mix. Only when a mixture's aggregate structure allows each of the conditions described above is the aggregate structure optimized. The concept of aggregate packing can be utilized to help optimize an mixture's aggregate structure.

The concept of aggregate packing is not new. NCHRP project 9-8 investigated the idea of coarse aggregate packing. How much aggregate can be fitted into a particular volume depends on the aggregate and how much energy is put into system. The process being proposed is relatively simple. Coarse aggregate is placed loosely into a known volume to determine its loose unit weight (the point when the coarse aggregate are just touching). Then coarse aggregate is rodded into the same volume to determine its maximum coarse aggregate unit weight (the point when the aggregates are packed as tightly as possible).

If the mixture is designed near the dry rodded unit weight limit it will be difficult to obtain compaction in-place. This is a very basic overview of a concept for coarse aggregate packing that could be put into practice to provide guidance on the selection of aggregate gradation as part of the mixture design process. The full procedure includes analysis of the fine aggregate as well.

Gale Page commented not all mixes need to be designed at this level and fine graded mixes should not be excluded from use. Further, we need to be careful not to add to much new criteria to the Superpave system.

This presentation is further discussed in Attachment E. Gerry Huber will prepare expanded information by March 1, 2000 on this procedure for the ETG's evaluation.

Simple Performance Tester (Killingsworth)
An objective of NCHRP project 9-19 is to identify a strength test for use with the Superpave system. Brian Killingsworth presented a summary of these activities (Attachment F).

N-Design, Phase II (Anderson)
Initial N_design work performed as part of SHRP was based on a limited number of pavements (17 test sites). Concern as to whether this was a sufficient basis for N_design and the desire to more fully validate N_design exists. The Asphalt Institute, with FHWA guidance and funding, started the initial phase of the effort to validate N_design using in-service pavements. The Asphalt Institute team include representatives from industry and Academia and former SHRP researchers. However, the initial N_design work could not be validated with the field data available.

Phase II of this experiment was divided into two groups. Group 1, included the conventional approach which looked at two issues. First are mixes densifying to 4% air voids in-place, and second, how sensitive are mixture designs changes to N_design (this work was performed under NCHRP 9-9). In Group 2, a laboratory measured performance property was attempted to be related to the field performance of a mixture. WesTrack specimens were investigated, using frequency sweep (G*) and repeated shear (permanent shear strain) tests to determine what change in design gyrations was needed to have a substantial effect on the measured properties. While not identical the Group 1 (NCHRP 9-9 results) and Group 2 results matched well. This work along with NCHRP 9-9 formed the basis for changes by AASHTO to the N_design table in TP-4. Copies of the final report were distributed.

There were few comments on the revised N_design requirements when balloted by AASHTO. However, one area of concern was the 3-10 million ESALs range and the potential loss in mixture durability resulting from designing these mixes at 100 gyrations. AASHTO PP-28 currently contains a note which allows designs prepared for this range of ESALs to be compacted to 75 gyrations at the agencies discretion. state DOTs would like to see more validation of the current N_design requirements. It is hoped that NCHRP 9-9(1) will further help to verify these criteria.

Subcommittee on Materials Issues (Harvey/Tahir)
Based on work from WesTrack, LTPP, the NCHRP 9-9 and the Asphalt Institute, and the Lead States several recommendations for revisions to the provisional standards were made by the ETG at its meeting held in September 1998 in Baltimore. The SOM balloted the recommended changes to the Superpave specifications and adopted them in the Interim Standards in May, 1999. The SOM has asked the ETG to respond to comments submitted by some states as part of the ballot. Standards involved include MP-2, PP-28, PP-2, and TP-4. Each provisional standard had 4 to 5 negatives votes and several comments or questions. AASHTO does not need a unanimous vote pass a standard revision, however, all negatives comments are attempted to be addressed.

The SOM asked ETG for review and advice on the following were the most:

• Dust-to-binder Ratio (MP2) The comments centered around the statement that if the aggregate gradation was below maximum density line consider raising limit to 1.6 . Some comments indicated no change was warranted, while another indicated they thought it should be mandatory.

  ETG Response - the dust-to-binder issue was previously assigned to an ETG task force for review, however due to ETG reorganization, this did not move forward. At this time the ETG suggests the change remain as a note. A new task force consisting of Randy West (lead), Gerry Huber, Eric Harm, Chris Williams, Mike Anderson, and Chuck Marek was formed to review the genesis of the dust-to-asphalt ratio and what impact the current note will likely have on gradation and mixture performance. The task force will report back to the ETG at the next meeting.

• Don't fix design air voids at 4%. At a high VMA air void at 4% may be acceptable, but at low VMA want some ability to change.

  ETG Response - the design air void level of 4% is based on considerable experience. During SHRP, the Asphalt Institute's MS-2 VMA requirements were reviewed and tied to 4% air voids. This has been a traditional number, and a lot of practices are based on 4% air voids. VMA and air voids are linked. This is an area where additional research is needed, and some work is already being considered. At this time the ETG does not believe there is a basis or data to warrant a change.

• 20 year ESAL prediction. Comments suggested the design ESALs should be represented as a yearly number.

  ETG Response - a 1 year cumulative ESAL could be used instead of the currently listed 20 year cumulative ESAL. However, the ETG is concerned a change to a yearly ESAL could be misperceived by some. Considerable training efforts have been implemented to accustom people to the 20 year ESAL concept. Further, Superpave Software Version 2.0 uses the 20 year ESALs throughout. In the current specifications, a description of roads for the various traffic levels was added to assist many in the selection of the proper design ESAL level. The ETG believes this is what many users will rely upon to select design ESALs. The magnitude of the effort required to change to a yearly number is not warranted.

• Recent changes require mixture designs to be developed with specimens compacted to N_design (PP-28). Comments suggested a need to review the increased variability with the more open specimens resulting from compaction to N_design. Since Superpave parameters were established by back-calculations, should the parameters be changed as a result of compaction to N_design. Also, N_max should be checked early in design phase.

  ETG Response - compaction to N_design provides more accurate volumetric data than is achieved from specimens compacted to N_max and back-calculated. The ETG agrees it is important to know if a mixture will fail N_max criteria during initial evaluation of a proposed design, however, there was disagreement whether any mixes failed this criteria. Additionally, some members felt a mix designer should be able to determine if a proposed mix will potentially fail this criteria. Current changes are also used in version 2.0 of the Superpave software. Mixes that are more open at N_design, may need to be cooled a bit longer. These are operational inconveniences but not sufficient to warrant a change back to the previous method. At this time the ETG does not believe there is a basis or data to warrant a change.

• Use of equiviscous mix and compaction temperatures should be eliminated due to variability and problems with determining these temperatures (PP-2). Additionally, a single temperature for short term conditioning should be used.

  ETG Response - research is on-going into determining mixing and compaction temperatures based on asphalt properties. When this work is completed it will be reviewed for impact on specifications. A number of members believe a single short term conditioning temperature should not be used, rather the issue is how to determine the appropriate conditioning temperature for each mix. Keeping the short term conditioning temperature based on viscosity is an attempt to equalize this effect. At this time the ETG does not believe there is a basis or data to warrant a change in the specification.

SOM is also considering an SMA standard. Other standards being examined are large aggregate standard and revision of T-283.

Superpave 2005 - Long Range Plan (Ferragut)
Ted Ferragut detailed a long range plan for Superpave development to be completed by FY2005 currently being considered by the TRB Superpave Committee and the proposed FY2001 Superpave budget (Attachment G).

The long-range Superpave plan was favorably received by the ETG. However, the ETG members suggested aspects of the pavement structural design systems need to be integrated with the Superpave long-range plan to make a complete system. The AASHTO 2002 design guide will take states a long period of time to adopt and validate. This time line lays out the approach for but not the completion of this final integration. It is critical this activity be coordinated with pavement design community so the performance models from design, PRS and material characterization will work together. The ETG notes the best material design put into a wrong pavement design system, will have problems. This integration may be beyond 2005. The FY2005 target appears reasonable for most aspects of the Superpave long range plan. Additional comment were made that time lines themselves can be a problem. The ETG suggests the correct steps be identified and not made to fit into a time frame that is to rigorous. This usually will not work for a larger system, where essential parts may be delayed. On the other hand a time line is needed to commit enough resource to meet time goals.

The ETG notes there is not one central entity for Superpave implementation, it is hoped the TRB Superpave Committee and ETGs will provide the needed coordination and focus.

Field Aging of Mixes - Florida Study (Page)
The Florida DOT completed a study of seven mixes samples at the plant and roadway to determine if a post production conditioning period is required to have plant produced material match the laboratory design. A report of this evaluation will be sent to the ETG (Attachment H) for review. ETG members are asked to review this report so that it can be discussed at the next meeting to dettermine if changes are warranted to the Superpave specifications.

Mixing and Compaction Temperatures (Dukatz)
Mixing and compaction temperatures from the Brookfield on modified asphalt have generally been excessively high. This raises an environmental issue for HMA producers as well as concerns about additional aging of material. Erv Dukatz distributed a chart for a modified asphalt that was studied which showed the Brookfield overestimated the mixing and compaction temperature. This is also being looked at under NCHRP project 9-10. Based on a study presented by Dukatz, it is recommended that the DSR be used to generated mixing and compaction temperatures. This information will be presented to the Binder ETG for consideration.

Regular ETG meeting adjourned.

Next Mix ETG meeting will be held in Washington, DC , currently planned for two full days on March 28 and 29, 2000.

Executive Session - ETG Members

Action Items

1. The state Survey conducted by the ETG will be forwarded to the remaining states to get a clear picture of all states. Ron Sines will send survey to the other states, DC, Puerto Rico, and Canadian Province materials engineers.

2. How does industry have input into AASHTO standards? Two types of standards, full and provisional. Need full SOM 2/3 vote on ballot to get accepted, usually by November of each year. Provisional standards can come out at any time, but go through the same process. Technical Sections can also send a ballot to just those people in that tech section. Technical Section ballots do not establish standards, only a full SOM ballot can establish standards. On Technical Section ballots, Rick Harvey will include ETG in the distribution so the members will be able to input comments on the ballot. The ETG will compile its comments and forward them as a group to Rick Harvey. In normal SOM ballots Rick Harvey will provide to ETG a copy of the ballot on Superpave issues. At this point any ETG input should take the form of ETG recommendations. Neil Hawks stated that comments by ETG as a group need approval through Academy. Harvey will provide copy of a proposed procedure to Hawks and discuss at next meeting.

3. NCHRP Reports of projects for next meeting. Should get a copy of report (executive summary) before meeting. Some likely projects ready for review will be 9-12, 9-19 Task C, and 9-14. The ETG asked Ed Harrigan to use his discretion to provide these materials and additionally decide if a representative of the research team should be present at the ETG meeting, depending on the topic.

4. Request the Binder ETG allow a liaison member from the Mixture and Aggregate ETG. If approved the ETG will designate John Bukowski to be the liaison to Binder ETG. Further, the ETG asked John D=Angelo to brief on Binder ETG at next meeting.

5. John Bukowski was asked to assemble all former ETG guidelines and recommendation for mailing to members. Minutes will be sent electronically (Stewart hard copy). Also all past minutes will be sent electronically to Ingram, Marek, Hall, Cheever.

6. Additional comments on Superpave long-range plan and FY2001 projects should be sent to Ted Ferragut by end of September 1999.

7. Comments on T-283 should be sent to Ted Ferragut by end of September 1999.

In February, ETG members will be contacted for additional agenda items.

Adjourn 12:40 PM.