Florida DOT
Based on research conducted by NCAT, Florida DOT developed an Open-Graded Friction Course (OGFC) with a Nominal Maximum Aggregate Size (NMAS) of 9.5 mm. The OGFC mixture with smaller NMAS will be applied on arterials to enhance durability.
Georgia DOT
GDOT issued a bituminous bulletin in September 2022 allowing the use of liquid anti-strip additives in Superpave and 4.75mm mixes designed using 20% or greater RAP for non-interstate projects with ADT's less than 25,000.
Utah DOT
HiMod or highly modified high-density asphalt has gradually replaced our SMA pavements and become a major go to mix for us on interstates and state routes.
Maryland State
Highway Administration
BMD spec is being implemented in a pilot stage for selected projects. It is currently being considered only for surface course mixes. We are also considering implementing the Delta Tc spec for all high RAP mixes to address the relaxation behavior of the binder in addition to the blending charts, which are used currently for all high RAP mixes.
Vermont Agency of Transportation
Fully implementing our 2024 specifications. MSCR to binder grading, requiring PG 58E-28 for mainline paving, expanding QA to cover all mix quantities, implementing QA for bonded wearing courses, increasing allowable RAP in 19mm NMAS mixes to 25%, and introducing HWT requirements for mix design approval. IDEAL-CT is also under development.
Asphalt Forum
Florida DOT
FDOT experience with the Ideal CT cracking performance test indicates that it does not reflect the in-situ benefits of using polymer-modified binders, specifically PG 76-22 PMA binders. Field observations indicate better crack resistance of PG 76-22 PMA mixtures compared to neat mixtures. Results of CT-index concluded insignificant difference between crack resistance of polymer modified (PG 76-22) and neat (unmodified) mixtures.
Georgia DOT
How many states have implemented BMD specifications for asphalt mixtures? For those states who have BMD specifications, please kindly provide specification links.
Maryland State Highway Administration
We recently placed a CRM dry process mix, and within two weeks shoving developed at high-traffic intersections. The mix contained an average of 15% rubber by weight of binder, which should provide two performance grade bumps. Despite that, the mixture still showed instability under stopping and slow-moving traffic at intersections, although the rest of the paving areas are performing well.
We had optimized the mix and designed it for BMD, so it’s unclear what might have gone wrong. Has anyone else encountered similar issues? In your experience, does SBS-modified binder perform better than CRM mixes in certain situations?
NCAT invites comments, questions, and answers to be submitted
to Allison Killingsworth at allisonk@auburn.edu.