Overlay vs. Mill and Resurface

[jgailla]

We have a project on which we are adding turn lanes to an existing two lane, 25-mph, residential roadway. The existing roadway is less than 5 years old and in good shape. We called out for the entire section of roadway to be milled and resurfaced so that the interface between the new lane and the old lanes wouldn't ravel and crack. The contractor, who is reputable, suggests instead to place limerock (it's in Florida) to the level of the existing roadway where the new turn lanes are, lay down a tack coat on existing asphalt, and place 1 1/2" asphalt overlay. This would save the client some money, but I haven't seen overlays like this before.
Any comments?

 

[civilperson]

I doubt the new lanes, 1 1/2" asphalt over 4-6" of rock would equal the strength of the existing lanes with the added overlay. Why not use the 6 " rock with the top elevation 3" below existing finish grade? That would give 4 1/2" of asphalt over rock as the new lane section.

 

[LHA]

Agree with civilperson, 1.5" of BC on top of rock will not hold up. If the SN's are not at least comparable, the new lanes will fail, and may tear at the edges of the new wear course on the ex. paving. You will be worse of than when you started.

Engineering is the practice of the art of science - Steve

 

[jgailla]

The existing roadway is 1 1/2" asphalt. Civilperson, thanks for bringing up the problem with the different SN numbers.

Steve, the tearing at the interface of the new lane and existing roadway was the reason we specified mill and resurface the entire roadway.

We could bring up the limerock on the lane addition only to the level of the limerock on the existing road, then lay 2 1/2" on the new lane along with the 1" overlay so that both lanes have the same thickness of limerock and asphalt. Does this seem reasonable?

 

[civilperson]

Equal SN for both new and existing lanes is the preferred course. A finished section of 3" asphalt on 6" rock is borderline for the normal road with moderate traffic. If only 50 vehicles/day then that would suffice. Call it staged construction with an additional 1 1/2" or 2" to be placed in 24 months,(as well as repair of any failing areas), to sell government budget constraints.

 

[Ron]

jgailla...you will get exactly what you tried to prevent in your design if you do as the contractor suggests...at the interface between the old and the new, you'll have a separation.

You can still do something similar to his suggestion, but I would suggest the following:

1. Mill a 2-foot wide strip at the edge of the existing pavement, adjacent to the new turn lane. Bevel the existing pavement at 45 to 60 degree angle along the milled edge
2. Put the base material in for the turn lane and hold it to the level of the existing base.
3. Put a geotextile over the joint created along the interface of the two base materials.
4. Tack the base and the beveled edge
5. Pave to thickness of existing pavement.

Traffic across the bevel will compress the asphalt, not separate it.

They'll whine about doing the bevel, but you don't have a long run so it shouldn't be an issue.

lha and civilperson....As for the 1-1/2 inches over limerock for light duty pavement...it will work OK, but because it is a turn lane, you get more potential for shoving. If you suggest that much asphalt in this area, they will go nuts! We do not have freeze-thaw issues here, but thicker asphalt tends to rut because of the heat.

 

[jgailla]

Ron,
Thanks for the comments. I think I will suggest what you propose.
Haven't heard from you in a while. Hope you're staying busy.

 

[Ron]

jgailla...yep...busy. Things are good. Hope you're enjoying your "temporary" stint with the Civil side. Call me when you get some time.