Re-use of existing Base for New Pavement Section 2

[Geotech_Pavement]

We have designed a new (re-construction) flexible pavement section (AC over AB) for an existing parking lot and now the project is going for bidding. The existing section is 4" AC over 4" AB.

The bidding contractors want to know if they can re-use the existing AB and place new AC over it.
Is it normal to remove the entire old AC section and place a new AC section on top of the old AB ?

 

[Ron]

You might consider using a mix-in-place recycling of existing surface and base supplemented with emulsified asphalt to create a new base for the new surface. Works well and is cost effective. I've done many miles of this procedure and it works well.

 

[geotechguy1]

We used to do this for projects I was involved in, located in Alberta, Canada. We called it a 'mill and inlay'. Typically the mill would be a minimum of 80-100mm thickness. I believe there are some requirements about tac coats between the old asphalt and new. I this around Edmonton, Red Deer, and Calgary from both government agencies and private consulting firms. Not sure about practice in the rest of the world.

From a pavement design perspective, when using AASHTO 93, I believe we reduced the structural number of the remaining asphalt when making calculations of service life.