Curiosity Question..."Micro" Milling Before Overlay?

[Birken Vogt]

This is the second or third time I have seen this...the contractor is milling between the lines but leaving the lines as-is. Taking so little you don't even feel a bump or shoulder when driving on or off it. In sunken areas and ruts sometimes the mill doesn't even touch the surface. Maybe 3/4" at the most.

What is the purpose? Improve bonding of the overlay to the base? Uniform thickness? Do they leave the lines so they don't have to worry about traffic safety?

 

[CM1995]

It's pretty common here except they mill the center lines as well and temp. paint them back.

I'm no paving contractor but it seems to work well on the newly surfaced roads. The potholes and alligatored sections they mill deeper and fill back with binder, then wear surface.

What I've seen more often lately is after milling the county chip seals the surface and then puts the wear course down.

 

[Birken Vogt]

What happened a few months ago on this section was the DOT sealed all the cracks with oil by hand.

Now that was all milled off but maybe they wanted to fill the cracks that way first? Or maybe it was just wasted effort.

Before the final fine milling the contractor deeply milled out the really bad spots and laid base course in them and then that nice smooth surface was milled along with everything else. But those were relatively small patches.

 

[Milling Boy]

Micro milling is usually done when the state wants to mill now to get a smoother driving surface but is going to pave it later. The surface left behind from micro milling is safe to drive on for quite a while. Standard milled asphalt leaves a surface that is not safe to drive on (especially if on a motor cycle) and removes the wear course and causes a bunch of cracked windshields when left to be driven on. A micro milled leaves most of the wear course in place and leaves a nice smooth ride that will stay that way for months.
I'm seeing this done in more areas as a way to increase the life of the roadway until major rehab is needed.

 

[Bls repair]

Sealed cracks can bleed through new asphalt ,causing bad spots and bumps. Milling over the patches gets everything to the same grade

 

[Birken Vogt]

Well this is OK to drive on but not great. Definitely done in preparation for paving but the milling machines are long gone and no sign of any activity for paving. Which is probably why they left the lines.

They milled through some alligatored sections which are breaking up/potholing a little as the crack sealing was all that was holding them together.

The best part is the milling machines left quite a bounce in some sections that made me think I had a bad tire until I realized it was the same bounce in the same place every time.

 

[Birken Vogt]

Well the mystery is partially solved. This was done in preparation for a recycled-in-place first course.

They have a huge train of mill, water tanks, asphalt oil tanks, mixing machine of some type, etc., etc., etc.

They are milling several inches deep, going through all this machinery and placing it as a base course for a final overlay.

I presume the initial micro milling was done to get rid of the chip seal and whatever garbage was in the traffic lane?

Now it is definitely for sure that the DOT was wasting time and money doing crack sealing before this since the cracks are getting ground to powder along with everything else. Oh well.