Cold Mill & Overlay Adjacent to Full Depth Road Widening

[raydefan]

I have been the roadway designer on multiple roadway widening project for various cities. I have had a few cities request that we provide a 2 foot wide and 2" thick cold mill and overlay adjacent to the saw cut line which is typically 1' from the edge of gutter. I have also seen this on utility trench details as well.

What is the purpose of this? I always thought that it was to allow for the top 2" wearing course to be laid together and it would somehow create a better join condition. This logic made sense to me, so I typically provide the cold milling.

I am now working for another city which is absolutely against this idea and thinks that the cold milling won't produce as clean and straight of an edge. I have never heard of this being an issue and think that maybe the contractor was not using the correct cold milling equipment or techniques to produce a clean and straight edge.

Anyone have any thoughts?

 

[hmcrae]

Offsetting the top course joint 2-feet will strengthen the pavement by spacing the vertical joints apart, rather than stacking. If the milling did not provide a good clean joint, I would think operator error or poor machine maintenance (missing teeth or sockets, incorrect teeth) would be the cause.

 

[Debaser]

Stepping the reinstatement of the bituminous courses is standard practice in the UK as well;

http://www.peterborough.gov.uk/PDF/env-pl-dev-estate-appx-I.pdf

As stated by hmcrae, offsetting the joints in the various layers to provide strength/lessen the effects of water ingress is usually the given reason.

 

[Debaser]

This is a materials engineers (brief) comments on the merits of stepping back in pavement reinstatement;

http://www.highwaysmaintenance.com/JPEGunch.htm#CRACKING

OF FINISHED WIDENING AFTER TWO YEARS TRAFFICKING

 

[eea]

The article Debaser quotes discusses full depth widening; I think Raydefan is asking about a 2" overlay. My experience is that staggered joints this thin just promotes two surface cracks (and delamination) rather than one. What is the shear strength of bituminous, effectively little to none against pavement heave.

Cold milling does not produce as clean of an edge as saw cutting. Compare the "teeth" of the two pieces of equipment. The mill grinds and tears the pavement away. Rub your hands along the mill's remaining cut face, it is full of voids. Now do you really need a saw cut line next to a mill removal line, probably not but the two are not equal.

Curious as to why the locals like this detail. Are they trying to keep the mill away from gnawing up the curb? I've only had to use this where the State owned the mainline and the local city didn't want to pay to overlay the parking lanes. We milled a line between the two and just overlayed the mainline.