Effect of lateral confining stresses on permanent deformation behavior in the conventional wheel tracker test
This research introduces a modified method for the wheel tracker test. Conventionally, the test is conducted by placing asphalt slabs in a fully confined steel mold. The research work undertaken by the author has shown that having the specimen fully confined in all directions by the steel mold would limit or prevent it from lateral (shear) deformation. It is also well-known that shear related permanent deformation is identified as the primary cause for high severity rutting. As a result, a new modified wheel tracker test setup was designed and manufactured to capture the true material response under the applied load. In the conventional wheel tracker, the large majority of samples will only show the primary stage and very small part of the secondary stage of the permanent deformation curve and most of the time the curve will plateau regardless of the number of cycles applied. Therefore, in the conventional wheel tracker test, the tertiary stage is never reached in the vast majority of the tested specimens. In the modified wheel tracker, the three stages of permanent deformation are always captured; therefore, the flow number can be determined. In addition, the effect of the major mix parameters and test conditions such as air voids content, aggregate gradation, binder type and test temperature can be captured and analyzed.