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.
Eric Biehl, Ohio DOT
For those that use liquid antistrip agents, what method(s) do you allow to introduce them for asphalt mix during production (i.e. in-line at the mix plant, terminal blended, etc.)? What is the preferred method by contractors that use them and why?
With the increased useof RAP and the growing RAP piles, consistency of these piles is important in good quality control and pavement uniformity. What are other DOTs requiring for quality control measures by contractors for testing the RAP piles? What tests are required and at what frequency?
How are other DOTs handling approval for mix designs for using a specific RAP pile and then switching to another RAP pile? Is a new mix design submittal required? Is verification required to ensure that the RAP used is similar to the original pile?
The following responses have been received to questions shared in the previous issue.
Has anyone been successful in using alternate crack sealing materials? We typically require ASTM 6690 Type I, and most northern states use Type II. The materials do perform fairly well, but my concern is with these materials being milled up along with the old pavements. These crack filling materials usually contain large amounts of rubber compounds and are typically crushed and processed in RAP piles. These rubber materials cause lay down crews to dig out and remove them, or else pop outs show up on the new asphalt surface, which are esthetically unpleasing and may cause for concern for pavement failure. The unknown of these materials below the exposed surface may also pose a potential for issues later in the pavement life, perhaps even the start of mid-level cracking. This is a growing concern with the amount of RAP now being permitted in most asphalt mixtures.
-Cliff Selkinghaus, South Carolina DOT
Michael Stanford, Colorado DOT
No, CDOT still uses ASTM D6690 Type II.
Eric Biehl, Ohio DOT
Ohio has three crack sealant types: ASTM D6690 Type II (a modified binder similar to Type II with 2.0% polyester fiber), and a PG 64-22 neat binder with 5.0% polyester fiber. We are also looking at a mastic sealant for wider cracks. The determination on which would be used would depend on the application and when the next planned resurfacing/pavement preservation activity would occur.
We've seen crack sealant in RAP piles and in new pavements. We don't typically see it that often in mixes on the road because most mix plants process their RAP over a 9/16-inch screen for surface and intermediate layers and a 1.5-inch screen for base layers.