This example is taken from Example 3 of the NAPA HMA Pavement Mix Type Selection Guide. It shows how two different representative States would select mixes for a specific situation. The idea is to show the basic rationale for mix type selection and to show that there are most likely several alternatives that will work well.
A 200 mm (8 inch) structural overlay is required for rehabilitation of what is becoming a high volume urban highway. Current surface distresses are:
- Low to medium severity alligator cracking covering 10 percent of the surface area
- Wheelpath rutting approximately 12.5 mm (0.5- inch) deep.
The pavement was constructed 10 years ago and there has been no rehabilitation since. The existing structure is 100 mm (4 inches) of HMA over 300 mm (12 inches) of unstabilized aggregate base.
- Get rid of the distressed surface in the existing pavement. This is typically done by milling.
- Increase the pavement structure to accommodate the high volume of traffic. The previous pavement section appears to have been designed for a much lower traffic volume and loading.
- Use some type of wearing course that can resist rutting.