Asphalt Pavement Analyzer (APA)
The APA is a second-generation loaded wheel tester. It has the capability of testing compacted brick or pill samples under various environmental conditions in both rutting (high temperature permanent deformation) and fatigue (low temperature cracking). The device can also be linked to a computer and data acquisition system so the user can measure the rutting of the HMA for each load cycle.
Basically, a moving wheel load is applied at a rate of about one cycle per second to a ¾ inch pressurized hose that rests atop the HMA samples. This simulates (on a small scale) the traffic loading that occurs in the field. The major benefit of using the device is as a comparative tool for mixture selection (i.e. one would select the mix that ruts the least from the APA testing).
The APA is typically run at a test temperature of 64oC. The samples are conditioned under this temperature for minimum of 4 hours prior to testing. The loading configurations typically used within the APA are a wheel load of 100 lbs and a hose pressure of 100 psi, although some other researchers have had success with increased loads and pressures. Once conditioned, the samples under-go a 25 cycle seating load. Once the 25 cycles have completed, the initial rut depths are measured. Testing then usually continues until a minimum of 8,000 cycles are completed. The difference between the initial and final rut depth measurements is calculated as the APA rut depth.
 Figure 2 - Asphalt Pavement Analyzer |
