Asphalt Concrete Thickness tied to Crack Resistance 2

[Riversidean]

Hello All,

The Caltrans highway design manual recommends a minimum thickness on road overlays to help resist cracking. Indeed the idea behind "superpave products" is to make a long lasting road by increasing the Asphalt Concrete section. What I am looking for are reference standards to support the idea that having a thicker asphalt concrete section and not necessarily a stronger structural section would better resist cracking. Any pointers?

-Riversidean

 

[SlideRuleEra]

Maybe the U.S. Army Corps of Engineers, Geotechnical & Structural Laboratory, Final Report, "Minimum Thickness Requirements for Asphalt Surface Course and Base Layer in Airfield Pavements"

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[oldestguy]

Overlays on top of an older pavement of asphaltic concrete over base course seems like wishful thinking to accomplish the goal of no cracks. That old pavement with its cracks will tend to move back and forth with temperature changes due to loss of ductility. The new layer on top will tend to follow that for a year or two, and not crack right away even if thick, depending on its ability to stretch over the cracks below. Seems like a given thickness of new and expect no cracks is unrealistic.

 

[Ron]

Cracking in the asphalt (not weather related) is controlled by the lateral strain at the bottom of the asphalt layer. As you increase the thickness of the asphalt you mitigate the strain levels at the bottom of the layer. Since asphalt overlays are considered bonded overlays, the stresses and strains transfer through this interface unless there are existing cracks in the pavement prior to overlaying. To keep that transfer working we usually span the cracks with a supplemental grid of some type of fabric that is set in asphalt cement or we meticulously fill the cracks.

Rutting is controlled by vertical strain in the subgrade, which is why we need a competent subgrade and base for the pavement section.