OAK METCALFE, MONTANA DOT
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.
Where do you take the longitudinal joint (density) cores? Our current specification requires them to be taken from the center of the visible joint— the local contractors continually fight us on this stating that it should be taken over the top of the "wedge" created by the safety edge. Has there been any recent research on this topic? -Michael Stanford, Colorado DOT
BRIAN HILL, ILLINOIS DOT
Longitudinal joint density testing is completed in Illinois at 4 inches from the longitudinal joint to the near edge of the core barrel (assuming density testing is completed using cores). If longitudinal joint sealant (a.k.a. Void Reducing Asphalt Membrane – VRAM) is present at the longitudinal joint, IDOT does not complete longitudinal joint density testing.
RICK BRADBURY, MAINE DOT
From MaineDOT's specification: "For vertical longitudinal joints, cores shall be taken directly centered over the construction joint. For notch-wedge longitudinal joints, the cores shall be cut directly over the center of the tapered portion of the wedge."
OAK METCALFE, MONTANA DOT
I don't know of any research, but here is an excerpt from our specifications dealing with this issue: "The joint area is defined as the tapered area at the overlap of the hot and cold lanes. Furnish the Department with a 4-inch or 6-inch core of the compacted joint for every 4000 feet (1219 m) of joint constructed, and at least 3 per project, at locations directed by the Project Manager. Center the core within the tapered area to include both the hot lane and cold lane. Mark the core as directed." So, it appears we agree with your contractors. If you center the core on the visible joint, you get significantly more volume of "cold" mix than "hot" mix and a thinner wedge of "hot" mix, lending to potential edge conditions, for lack of a better term.
CHARLIE PAN, NEVADA DOT
NDOT's joint density tests are not required on unconfined edges (like safety edge). Joint density tests are completed on the hot side of the mat (within 6 inches).
STEVE HEFEL, WISCONSIN DOT
WisDOT uses correlated gauges centered 6 inches off the centerline joint. Both sides of the joint are tested.