Pavement Design for a Road Widening Scheme

[anogramatic]

When designing a road widening scheme, I can design the pavement for the new section (based on Traffic Loadings), but do I need to test the existing pavement to see if it will be suitable under the new loading conditions? I have core samples which show the existing pavement is not as thick as the thickness required for the road widening scheme. I am sure no road operator would want to rip out pavement that is already in the ground, but I am constrained by levels and cannot simply build above existing pavement to make up the difference in thickness..

 

[caenright]

Verifying the existing pavement design is not a bad idea, and if the widened road expects and increase in ESALs you can expect differential pavement wear and potentially an odd transition between the zones of new and old. Placing a new course of asphalt over the existing is probably not a good solution (as you suspected), but milling down for a new course is a good option to have a uniform and single mat as the top layer of asphalt. Just excavate the widened section a bit deeper so there is a deeper asphalt section on the new pavement, and the finished surface is level with the existing (or milled/repaved) surface.

It is entirely feasible to do a full-depth reconstruction of the existing roadway when widening, and it is often done on major highway widening projects. I suggest you work out the required cost for both options (widen and widen+full depth reconstruction) and consider presenting both. The reconstruction may be justified based on pavement condition that exists presently.

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Chris Enright
PE, Colorado
Roads and Trains