Every six seconds, a full-size truck axle rolls silently over the pavements constructed at the Civil Infrastructure Systems Laboratory, Kansas State University, Manhattan, Kan. The laboratory houses the first full-scale accelerated pavement test program in Kansas. In 1995, the program was initiated by a group of engineers from the Kansas Department of Transportation and faculty from the Civil Engineering department at KSU. In the seven years of activity, 11 experiments have been conducted. The research is now supported through a pool funded by four Midwestern states: Iowa, Kansas, Missouri and Nebraska. Cooperation with the pavement construction industry and other state highway agencies also is possible in the future.
Wanting to fail
The research program is well established. State highway representatives from the four Midwestern states, together with KSU professors, select the topic of a new project every year. For each experiment, four full-scale pavements are constructed in two 10-ft-deep pits using conventional construction methods. After construction is finished, the pavements are loaded until they fail. During trafficking, longitudinal and transverse profiles, cracking, stresses and strains in the test roads are recorded. After the pavements have failed, a post-mortem investigation is conducted. Cores and trenches are cut into the pavements to measure the material properties and to extract samples for additional laboratory tests. The distress data and the results of the post-mortem tests are used to determine the causes for failure and to evaluate the performance of individual layers.
Full-scale accelerated pavement tests (APT) have been used successfully in the past to verify and calibrate existing pavement structural design methods, and to determine the performance of innovative construction methods and materials. The advantage of the APT experiments is that 20 years of cumulative truck traffic can be applied to the tested pavements only in a couple of months. This way, new materials and construction methods can be fast evaluated. The facility at KSU is the only one in the country entirely owned and operated by a university.
For more on the story, read the October issue of ROADS & BRIDGES.
