Pavement Related Questions
Pavement Related Questions
(OP)
I have two quick pavement related questions.
1. When using a leveling course on an overlay project in order to increase the crown slope, can you place this leveling course directly on the existing surface (on top of tack coat) or should you coldmill an inch or so?
2. Do you still place a tack coat under full depth AC pavement?
Thanks,
Raydefan
1. When using a leveling course on an overlay project in order to increase the crown slope, can you place this leveling course directly on the existing surface (on top of tack coat) or should you coldmill an inch or so?
2. Do you still place a tack coat under full depth AC pavement?
Thanks,
Raydefan





RE: Pavement Related Questions
RE: Pavement Related Questions
Milling takes away bond problems between excessively oxidized asphalt and the tack coat, reduces the need to "clean" the existing surface (not easy to do properly), an mitigates the bond issue due to the high lateral stress at the interface.
After milling, apply tack coat and then install leveling course if you need to raise the crown.
RE: Pavement Related Questions
I would not plane (mill) unless the existing pavement is in distress, and certainly not just because someone does not take the time to apply a tack coat properly.
When planing: you either have to mill at a % slope or a certain depth, you cannot do both. Naturally this causes problems for some. Also there is the pavt. marking (daily) to deal with.
We place a tack coat (usually emulsion) under all Dense Graded ACP layers unless a relatively new under seal (chip seal) is present.
If you are placing ACP with-in air, surface, and mix temperature requirements, and the surface is power broomed, tack placed (and rolled in to distribute satisfactorily) you should be fine.
RE: Pavement Related Questions
While we don't know any traffic information or category of the road, we have to assume that there is some reason to remediate the pavement other than changing the crown elevation.
We don't know the thickness of the existing pavement. Could the slope be obtained by milling, then overlaying with a structural course to the new slope, negating the need for a leveling course?
In high traffic areas with a reasonable percentage of trucks, non-milled overlays often fail early...just a fact. They don't usually fail in their entirety, they fail by delamination in spots, which increases maintenance, lowers ride quality, and creates complaints from the riding public. If the money's there, mill it and do it right.
RE: Pavement Related Questions
"non-milled overlays often fail early...just a fact"
This may be a routine occurrence in some areas; we apparently have not experienced this yet.
The cost of planing is very reasonable, and often provides (after fractionating) a reusable product that is recycled into the ACP for the same milled project and therefore reducing unit cost and being green simultaneously.
Milling is cheap and popular with local industry.
Milling "can" cause a multitude of problems, and we stay away from it until it is absolutely necessary. Our cores usually indicate whether milling is needed.
The level-up layer addition into the new pavement structure adds another opportunity for improved ride quality. A better IRI.
I have witnessed milled sections fall apart far more often than non-milled. As stated, this has a lot to do with the roadway and traffic mix/count.
Either way...milled section or level-up, a one coarse seal (chip seal) is always applied before the new ACP layers are added, in which case we do not use a tack coat over a fresh seal coat.
RE: Pavement Related Questions
RE: Pavement Related Questions
For full-depth pavement, a "Prime Coat" rather than a "Tack Coat" should suffice. Typically, prime coats are a 50/50 asphalt emulsion (50 percent water/50 asphalt) with an emulsifier added (often clay or detergent).