Technical information

2-2
vertical compressive stresses on top of the base and subgrade, moisture in the unbound
materials and temperature within the HMA. Additionally, these sections were
investigated by periodic deflection testing and monitored for structural distresses by
employing routine surface condition surveys. Reportedly this was done to allow for
later validation of the MEPDG. The focus herein is on sections N1 and N2, which were
the only sections from the ‘structural study’ replicated in the INDOT APT.
Figure 2.1.1: Schematic layout of the 46 test sections at NCAT (Phase II) experiment.
Traffic loadings at the track are applied using a designated fleet of tractor-trailer
trucks (triple trailer), each traveling at 45 mph or 792 in./s (72.4 km/h or 20.1 m/s).
Drivers are utilized to operate the trucks, and their operation consists of two 7.5 hour
shifts, five days a week. Typically, each truck completes about 26 laps in an hour. A
picture of one NCAT truck is provided in Figure 2.1.2. As can be seen, the truck has
several wheel assemblies: single-axle single-wheels (steer axle); tandem-axle dual-
wheels (drive axle); and single-axle dual-wheels (trailer axle). The ‘average’ weight
carried by the individual axles is shown in table 2.1.1. This is an ‘average’ weight
because each of the five trucks in the fleet has a slightly different load. The coefficient
of variation (COV) of the loads is also shown in the table with values in the range of