Example R02.2: Mill and Overlay

As shown in the previous subsection, removing all of the old HMA and replacing with new RHMA-G/HMA is more than sufficient. It may be feasible to only remove and replace a portion of the old HMA, which will be evaluated in this option.

To evaluate this option, save a copy of the "SBL3_540-495: Remove HMA and Replace" trial under a new name "SBL3_540-495: Partial Removal and Overlay".

Option 1: 0.2' RHMA-G over 0.25' of HMA with PG70-10 binder

It is recommended to keep a minimum of 0.2' of old HMA. The first structure to try for this option is the following:

•0.2 ft RHMA-G with PG64-16 base binder

•0.25 ft of HMA with PG70-10 binder

•0.2 ft of old HMA

The project inputs, simulation parameters, and the simulation results are shown below.

Note:  In this case Layer 3 to Layer 5 are marked as cracked to account for reflection cracking. The old HMA layer needs to be marked as cracked as well, and the type of reflection cracking is still "AC on Cemented Base" since there is cemented layer involved.

The results show that the design is not sufficient and lasts only 7.7 years before it fails in cracking.

Option 2: 0.2' HMA with polymer modified binder over 0.25' of HMA with PG70-10 binder

This option is the save as above except the surface is replaced with an HMA with polymer modified binder. The project inputs, simulation parameters, and the simulation results are shown below.

As one can see, the design is not sufficient and lasts only than 9.8 years before it fails in cracking.