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 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?
Cliff Selkinghaus, South Carolina DOT
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?
Matthew Chandler, Tennessee DOT
What experience do other states have with adhesives for longitudinal joints during construction? If successful, was the application pre-applied, post-applied, or both?
Have any states successfully implemented a post-milling sweeping/vacuum performance specification?
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)?
The following responses have been received to questions shared in the previous issue.
Are the Gsb values used in mix designs in your state determined by the highway department or by the contractor (or mix design lab)? How often are the Gsb values tested? -Randy West, NCAT
Michael Stanford, Colorado DOT
Gsb values used in mix designs are determined by the contractor and verified by the highway department.
Eric Biehl, Ohio DOT
Ohio DOT performs the testing, which is typically done annually for all sources. If something happens and we can't make it to a source, then we use the quarry's results if their lab is AMRL accredited.
Greg Sholar, Florida DOT
Gsb values are determined at the aggregate mines and published on a FDOT website. These values are used by contractors for mix design purposes. The frequency of testing Gsb values at the mine varies depending on the running target and standard deviation values, but a rule of thumb is once every two weeks. The DOT's district offices also randomly obtain samples for verification of Gsb values.
Mark Zitzka, Montana DOT
Gsb is calculated by the contractor's consultant when a mix design is proposed and again by the DOT when the mix design is verified and approved.
Cliff Selkinghaus, South Carolina DOT
SCDOT uses the Gsb from our Qualified Products List No. 1 for coarse aggregates. The values are used for information only to track and estimate the binder film thickness on mix designs. These tests are conducted internally at a minimum of once per year by the SCDOT.
Matthew Chandler, Tennessee DOT
TDOT uses Gse in the the mix design instead of Gsb. Contractors submit this information on their JMF for verification by the TDOT Regional Materials Lab for each design.