NCAT invites comments and questions submitted to Kyle Lubinsky at kal0105@auburn.edu.
Which state DOTs pay for binder as a separate binder vs. which consider it incidental to the pant mix payment? Wyoming pays for it separately but I've heard that the majority of states don't.
-Greg Milburn, Wyoming DOT
Has anyone experience significant issues achieving compaction in the field with some of the "extreme" MSCR grades, i.e., 58V-34? or 58E-34? Any other issues when moving to MSCR from the field? Our switch from -28 to -34 has everyone nervous.
-Oak Metcalfe, Montana DOT
What type of mix design program do you use or allow? (Web based, spreadsheet, or other, and why)?
-Tony Collins, North Carolina DOT
I would like to share a positive experience on improving density. Indiana DOT has fully implemented Superpave5, which is a tweak to the Superpave method that targets 5% air voids in mix design and 5% in-place air voids (95% density) in the field. INDOT implemented Superpave5 as a contractor option in 2019, with full implementation in 2020. We have seen approximately 1.3% increase in in-place density, with no increase in cost of the mixture. We have implemented on all categories and traffic levels, and have not experienced rutting or other adverse issues. The statewide average density results per year are shown below. 2017 S4 = 93.19% 2018 S4 = 93.05% 2019 S4 = 93.16% 2019 S5 = 94.41% 2020 S5 = 94.46% 2021 S5 = 94.41% 2022 S5 = 94.47%
-Matt Beeson, Indiana DOT
Are there any states who are using bag house fines as "mineral filler" in SMA mixes? Are you experiencing any issues with using them?
-Susan Dukes, South Carolina DOT
The following responses were received to questions shared in the previous issue.
We continue to adapt to dwindling gravel sources, as permitting and volume are causing us to explore new options. As such, we’re seeking guidance on quarry/ledge rock and how to specify/accept it. In one situation, a contractor with a quality (anecdotally) limestone source did not bid a job because they claimed to meet all specifications except a 75 gyration mix design. In another situation, we had a contractor use a limestone source that met all durability requirements, as well as a 75 gyration design, but it performed poorly in the field. What we found was the aggregate didn't completely degrade, but "resized" in the plant so the 3/4" NMAS design ended up being a 1/2" NMAS (more or less). Any information or insight on how to guard against that phenomenon would be helpful.
-Oak Metcalfe, Montana DOT
Zane Hertzog, Alabama DOT
Alabama DOT uses L.A. Abrasion AASHTO T96 as a measure of an aggregates resistance to breaking down during mixing processes. For bituminous work the general requirement is less than 48% loss. More details can be found in our standard specifications section 801.03(b) on PDF page 713, linked here : https://www.dot.state.al.us/publications/Construction/pdf/Specifications/2022/SpecBookComplete.pdf
Greg Sholar, Florida DOT
We use limestone in Florida, with some of it being softer than others. If during production, the gradation of a sample after burning in the ignition oven changes NMAS (say from 12.5 to 9.5) we ignore this. We still expect the mixtures to meet all the pay properties (Roadway density, Air voids, AC content, % passing #8, % passing -200).
John Garrity, Minnesota DOT
LAR requirements for the aggregate from the quarry might help. Also, the use of a Vertical Shaft Impact crusher will remove the unsound portion of the aggregate during crushing operations.
Charlie Pan, Nevada DOT
I assume the "degradation" happened during the heating and mixing process in the barrel. Before paving. A "hot drop" can be produced at the plant to verify the aggregate gradation after mixing. a gradation sample can also be obtained at cold feed belt to evaluate the gradation before heating and mixing.