NCAT invites your comments and questions, which may be submitted to Christine Hall. Questions and responses are published with editing for consistency and space limitations.
Michael Stanford, Colorado DOT
Colorado DOT is interested in the balanced mix design concept and plans on collecting IDEAL-CT data on current HMA production samples.
Greg Sholar, Florida DOT
How is density handled for portions of intersecting side streets that may be part of the scope of work for the mainline project? Are they included in density testing or are they exempted?
The following responses have been received to questions shared in the previous issue.
Do you use the spray paver with a 4.75 dense-graded mix? Do you have concerns with the water in the emulsion being trapped between the two lifts? Do you use the spray paver with larger NMAS mixes? -Jerry Geib, John Garrity; Minnesota DOT
Zane Hartzog, Alabama DOT
No, we don't use mixes that small. We use a spray paver to apply some tack coats, such as UltraFuse.
Michael Stanford, Colorado DOT
Spray pavers are not used on Colorado DOT projects.
Shane Biddle, Delaware DOT
No.
Greg Sholar, Florida DOT
Florida DOT does not use spray pavers.
Kevin Kennedy, Michigan DOT
We do not use a spray paver with dense graded mixtures, but we are discussing pilot projects. We do have nova-chip projects.
Dan Oesch, Missouri DOT
We have had occasional issues with blistering when utilizing a spray paver with 4.75 mm dense graded mixtures.
Eric Biehl, Ohio DOT
We don't see spray pavers used in Ohio.
Kevin Suitor, Oklahoma DOT
Oklahoma DOT uses a spray paver almost exclusively in several divisions. Divisions have limited use of 4.75mm mixes. However, we do see use of larger NMAS mixes. There has been no mention of issues of water between the lifts.
Matthew Chandler, Tennessee DOT
We do not use spray pavers.
Howard Anderson, Utah DOT
We are starting to use and see spray pavers more. We have no concerns with the emulsion being between the two lifts as we mostly use spray payers for bonded wearing courses (BWC), which have a thin top lift. We are looking at using spray pavers for larger NMAS mixes, but have no experience to help you yet.
Aaron Schwartz, Vermont AOT
Vermont doesn't currently allow spray pavers other than for our ultra-thin bonded wearing course (UTBWC) mixtures.
Shawn Jack, West Virginia DOT
West Virginia has not used spray pavers.
I am curious to know how other states have been affected by the changes to AASHTO T 324 Standard Method of Test for Hamburg Wheel-Track Testing of Compacted Asphalt Mixtures. Research conducted for the purpose of better standardizing equipment requirements resulted in changes to the method that caused one widely used manufacturer's legacy equipment to be out of compliance. However, there is a long history of performance using that particular device. The changes to T 324 allow an agency to deviate from certain requirements and I'm curious if any have done so. We are trying to develop a comparative database to show that the legacy machine is still accurate, but are currently using another manufacturer for contract quality assurance (QA) and payment. -Oak Metcalfe, Montana DOT
Michael Stanford, Colorado DOT
Colorado DOT uses a newer Hamburg that meets the T 324. We have not seen a significant difference in test data from the original Hamburg Wheel Tracker versus the newer equipment.
Shane Biddle, Delaware DOT
At this time, Delaware DOT does not run T 324.
Greg Sholar, Florida DOT
Florida DOT retrofitted our Hamburg, which is used only for research purposes. We have not developed a comparison database between old and new, as we just had the machine retrofitted.
Kevin Kennedy, Michigan DOT
Michigan does not use the Hamburg as part of our mix design process.
Dan Oesch, Missouri DOT
Luckily our equipment was new enough that it meets the new requirement.
Eric Biehl, Ohio DOT
Ohio currently uses the asphalt pavement analyzer (APA).
Kevin Suitor, Oklahoma DOT
Oklahoma DOT has a long history of using the legacy equipment. We are reluctant to automatically update our machines and hold the contractors to new performance measures. We are developing a small database comparing the old equipment with the new and are seeing a small difference. We will be addressing these issues with the industry over the next few months.
Cliff Selkinghaus, South Carolina DOT
We have one of those machines and the manufacturer does not support/offer a package to upgrade the unit for this change in test compliance. We had a research project that utilized this machine and we in turn received it once completed, and later found it to not be compliant to the most recent T 324.
Howard Anderson, Utah DOT
Utah has continued to use our own Hamburg procedure along with AASHTO T 324. We continue to use the PMW equipment and have a new Cox machine. We get similar results with it and the PMW or Troxler machine.
Aaron Schwartz, Vermont AOT
Vermont doesn't deviate from the equipment requirements in AASHTO T 324 overall, but we do have other deviations (test temperature, definition of average rut depth, etc.) from the procedure that are covered in Section 406 of our Standard Specifications for Construction and our Bituminous Concrete Mix Design Submittal Policy.
Shawn Jack, West Virginia DOT
West Virginia has not yet implemented use of AASHTO 324, though we plan to implement it as is.
How many revisions do you allow on a job mix formula (JMF) before the mix needs to be redesigned? -Tony Collins, North Carolina DOT
Zane Hartzog, Alabama DOT
We allow three revisions.
Michael Stanford, Colorado DOT
It varies depending on what is being revised.
Shane Biddle, Delaware DOT
We have no set limit.
Greg Sholar, Florida DOT
Florida DOT does not have a limit on the number of revisions. However, each revision must meet strict specification revision requirements and must then be proven with field test results.
Kevin Kennedy, Michigan DOT
We have no defined limit.
Dan Oesch, Missouri DOT
We have no set number.
Oak Metcalfe, Montana DOT
We don't control JMF other than the control sieves after mix verification. Our specification is based on the contractor choosing volumetric "targets" within the acceptable ranges for VMA, VFA, Voids, and D/A. We follow that up with a Hamburg test at least once per project with a maximum of 13mm of rut after 10,000 passes, tested at 14oC below the high PG temp. Density is 93% minimum. As long as those parameters are met, they can alter their JMF as they choose.
Eric Biehl, Ohio DOT
Ohio DOT doesn't allow a mix design to be revised. However, during production, there can be one adjustment to the gradation and/or a reduction of RAP within the first three days of production for a project. We allow binder additions of the same PG grade and modifier with a one AC point design to confirm the volumetrics and any performance tests are met (PG 64-22 and PG 58-28 don't require a one point design).
Kevin Suitor, Oklahoma DOT
Oklahoma DOT allows three changes to the JMF before the mix is terminated and the contractor has to redesign.
Cliff Selkinghaus, South Carolina DOT
Three revisions are allowed in South Carolina; however, we require a redesign if the request is too far away from the original design.
Matthew Chandler, Tennessee DOT
In Tennessee, the gradation of one screen size is generally allowed after the JMF is approved, though it is somewhat unofficial. We also accept binder grade change, switching between terminals/suppliers or change of the anti-strip agents on the basis of TSRs only. As we move to a more balanced mix design approach, I see the same options becoming less or going away.
Aaron Schwartz, Vermont AOT
Vermont doesn't specify a maximum cap on the number of allowed revisions so long as test results substantiating the revisions are provided with each request made by the producer. A new mix design will be required if the aim on four or more sieves is changed, if the aim on one sieve changes by more than 5% (0.5% on the #200 sieve) and/or if the binder content deviates by more than 0.2% from the original design binder content. All of this is described in our bituminous concrete mix design submittal policy.
Shawn Jack, West Virginia DOT
West Virginia has a mix verification process that allows yearly changes to maintain volumetric requirements. Specific testing (e.g. sand equivalency and fine aggregate angularity) related to aggregate blend changes must occur, but the mix does not need to be redesigned. Any revisions to binder grade require a new design.
What states require the use of liquid antistrip agents in all mixes and what are the required dosage rates? -Kevin Suitor, Oklahoma DOT
Zane Hartzog, Alabama DOT
The TSR dictates the amount of antistrip to be added (minimum of 0.25%). Antistrip is required for OGFC.
Michael Stanford, Colorado DOT
Colorado DOT still requires lime (1%) in all HMA.
Shane Biddle, Delaware DOT
Delaware DOT does not require antistrip.
Greg Sholar, Florida DOT
Florida DOT's OGFC mix type containing granite aggregate requires hydrated lime. However, all other mix types require liquid antistrip (LAS) or lime, but no contractor uses lime where not mandated. Therefore, in the majority of our mixtures, LAS is required. Most are approved at a 0.5% dosage rate, but a few have been approved at a lower dosage rate. For LAS approval, FDOT tests eight mixture types, comprising two NMAS (9.5 and 12.5) and four aggregate types commonly used in Florida (two granites and two limestones). A minimum TSR of 0.8 and a minimum dry tensile strength of 100 psi for all eight mixtures must be obtained for a LAS to be included on our approved products list.
Kevin Kennedy, Michigan DOT
If a mix design passes the TSR test, no antistrip is required. If it fails, it is up to the designer to determine the amount needed to pass the test.
Dan Oesch, Missouri DOT
We have a TSR requirement but no requirement to use liquid antistrip.
Eric Biehl, Ohio DOT
Ohio DOT doesn't require all mixes to have antistrips. We have stipulations on what mixes may need them and only require it if the TSR fails.
Cliff Selkinghaus, South Carolina DOT
We permit antistrips in any mixes that require PG 64-22 in South Carolina. The dosage rate is 0.7%, terminally blended only.
Matthew Chandler, Tennessee DOT
Tennessee requires antistrip agents in all mixes. The minimum rate is 0.3% and the maximum is 0.5% by weight of binder.
Howard Anderson, Utah DOT
The state of Utah requires 1.0% hydrated lime by dry weight of the virgin aggregate in all of our HMA type materials using a pugmill/slurry method. We have done this for about 25-plus years and have eliminated our stripping problems.
Aaron Schwartz, Vermont AOT
We are in the process of eliminating our 0.5% minimum dosage requirement for liquid antistrip agents.
Shawn Jack, West Virginia DOT
West Virginia does not require the use of antistrip agents.