Example N01.1: Thicker AB

In this subsection, the alternative of increasing AB thickness is examined. Specifically, the AB thickness is increased from 0.50 ft to 1.0 ft.

To evaluate this option, create a new trial using the "Save Trial As" button to make a copy of the current trial and save it under "Example N01.1 Thicker AB" (see below):

A 20-simulation Monte Carlo analysis indicates that the HMA thickness can be reduced from 1.00 ft to 0.95 ft. The new structure is shown below:

The simulation results are shown below:

This confirms that a 0.50 ft increase in AB thickness can reduce the HMA thickness by 0.10 ft (from 1.05 ft to 0.95 ft). It also shows that the failure probability is very close to the 5% threshold. To find out exactly how long would it last, increase the simulation duration from 20 to 25 years and re-run the analysis. The results are shown below:

As shown in the screen shot, the time to failure is 20.3 years, which is very close to the design life. As pointed out in the last section, the 20-simulation run may provide different design conclusion. In fact, the 20-simulation Monte Carlo analysis indicates that the design will fail in 17.0 years (see below).

Given that the pavement is expected to barely last 20 years, it is probably better to use 1.0 ft HMA, which is 0.05 ft thicker than the minimum required value.