Asphalt Forum

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.

Greg Sholar, Florida DOT
Are any other agencies having difficulties with trackless tack materials?

Jerry Geib, Minnesota DOT
In 2017, as part of the NRRA pooled fund, we will build different overlay combinations on the old PCC of I-94 (MnROAD bypass). These will be the first HMA overlays placed on the old PCC.

Asphalt Forum Responses

The following responses have been received to questions shared in the previous issue.

For states that require fractionated RAP, at what RAP percentage do you start to require fractionation, and how are the sizes handled? Have you noticed if this has helped eliminate segregation due to too much RAP? -Eric Biehl, Ohio DOT

Michael Stanford, Colorado DOT
We do not require fractionated RAP.

Jerry Geib, Minnesota DOT
We do not require fractionated RAP.

Cliff Selkinghaus, South Carolina DOT
We allow up to 10% more aged binder when the contractors choose to fractionate. We require a RAP/RAS QC plan by contractors to show how they are fractionating the recycled materials. We require a high frequency fractionating device and frequency of testing, and our specification is SC-M-407. This has not completely eliminated segregation; it also depends on stockpile management and the time between crushing, screening, and actually feeding the materials into the plant.

I would also like to point out an issue that should be looked at on all milling jobs. Be sure the milling contractor is aware that the material is not a waste product; it is recycled material, and the road should be broomed prior to milling to prevent pick up of unwanted debris and trash.

Matthew Chandler, Tennessee DOT
Binder layers: 30%-35%, maximum 3/4”; Scratch layers: 15%-25%, maximum 5/16”; Unmodified surface layers: 15%-20%, maximum 1/2” (5/16” for thinlifts); Modified surface layers: 10%-15%, maximum 1/2” (5/16” for thinlifts); Shoulders: 30%-35%, maximum 1/2”.

The contractor may use the higher percentage of fractionated RAP specified only if individual fractions of two different maximum particles size are introduced into the plant as separate material sources for increased control.

How many states are using WMA as a tool to assist with placement issues that sometimes occur when paving over pavements that have previously been crack sealed? Do you have a minimum curing time in your specifications for paving over crack sealants? Do you use any other sealants besides ASTM D6690 Type 1 material to seal cracks? -Cliff Selkinghaus, South Carolina DOT

Michael Stanford, Colorado DOT
We have specified WMA on two projects to assist with this issue. We do not have a minimum curing time, and we use ASTM D6690 Type II and Type IV materials. Our approved products list is online at: http://apps.coloradodot.info/apl/SearchRpt.cfm?cid=Sealant+%5BJoint+and+Crack%5D.

Eric Biehl, Ohio DOT
We are not currently using WMA in this type of situation. We are mainly a water-injection foamed WMA state but are looking at using WMA in this application and possibly others including thin, highly modified overlays. We do not have a minimum curing time, but the longer it can cure, the better. We have four types of material under ODOT Construction and Materials Specification 702.17: ODOT Type 1 is the same as ASTM D6690 Type 2. ODOT Type 2 and 3 use PG 64-22 with either polyester or polypropylene fibers. ODOT Type 4 uses a modified binder (similar to D6690 Type 2) with polyester fibers.

Matthew Chandler, Tennessee DOT
We permissively allow the use of WMA but do not call for it in this situation. Generally, we recommend to the districts to crack seal about a year before resurfacing. We use ASTM D6690 type II.

Jerry Geib, Minnesota DOT
We have used WMA for this situation. We have three types of sealants. Type I, II and IV, all of which are modifications of the ASTM D6690 specification. We do not have a minimum curing time.

What experience do other states have with adhesives for longitudinal joints during construction? If successful, was the application pre-applied, post-applied, or both? -Matthew Chandler, Tennessee DOT

Michael Stanford, Colorado DOT
We do not have any experience with this.

Eric Biehl, Ohio DOT
We have a Supplemental Specification 875 for the joint adhesive material and placement. In the past few years, we have required contractors to use a certified PG binder or joint adhesive that’s pre-applied to the cold vertical face prior to the hot mat being placed for our longitudinal joints. We’ve been successful overall, with one of our twelve districts using this method for a decade or more. The only issue we’ve had is over application and pooling in the corner of the existing surface and vertical face.

Jerry Geib, Minnesota DOT
We use Crafco joint adhesive during the construction of the joint.

Have any states successfully implemented a post-milling sweeping/vacuum performance specification? -Matthew Chandler, Tennessee DOT

Michael Stanford, Colorado DOT
Yes, our specification language is: All milled surfaces shall be broomed with a pick-up broom, unless otherwise specified, before being opened to traffic. A sufficient number of brooms shall be used immediately after planing to remove all milled material remaining in the roadway. If the Contractor fails to adequately clean the roadway, work shall cease until the Engineer has approved the Contractor’s revised written proposal to adequately clean the roadway.

Eric Biehl, Ohio DOT
We require the surface to be clean after milling and prior to tacking and placing the new mix. Most use sweepers.

Jerry Geib, Minnesota DOT
We have not implemented any specifications for post-milling sweeping or vacuuming.

Have any states had trouble with their AC suppliers meeting the % recovery curve for a single grade bumped binder (i.e. H grades under MSCR)? -Matthew Chandler, Tennessee DOT

Michael Stanford, Colorado DOT
We do not perform MSCR testing.

Jason Davis, Louisiana DOTD
Louisiana has had trouble with our PG 70-22m (basically an “H” grade) meeting the MSCR curve. Our research group is conducting a study to determine if the materials not meeting the curve are providing adequate mix performance. At least one contractor has reported positive results on mix tests by limiting the lower and upper Jnr values on the base asphalt. Part of the research may be to determine the Jnr limits to place on the base grade, particularly with plant-blended materials (i.e. latex-modified). The crude stock may have significant influence on the potential for modification.

Eric Biehl, Ohio DOT
We do not use MSCR and still follow ODOT’s version of AASHTO T 301. We also still follow AASHTO M320 PG grading. If we were to use MSCR to replace elastic recovery, we would not follow the curve, but would set a minimum value for each PG binder grade. We have concerns with repeatability of the MSCR test.