Specimen Instrumentation Techniques for Permanent Deformation Testing of Asphalt Mixtures

This paper presents research efforts undertaken to develop, evaluate, and recommend proper laboratory specimen instrumentation and preparation techniques. The instrumentation was intended specifically to capture test parameters in permanent deformation tests for asphalt mixtures. The study evaluated axial deformation measurements and test parameters using the traditional clamps compared to on-specimen glued studs, both being holding devices for linear variable differential transformers (LVDTs). Sawed, "as compacted," and capped specimen end conditions were also compared. The test results for specimens using clamps and/or capped ends indicated that the specimens were being restrained from deforming freely during the test. In addition, the permanent deformation parameters from both instrumentation types (clamps versus glued studs) were substantially different. The recommendation for permanent deformation testing of asphalt mixtures is to use the instrumentation setup with glued studs and sawed specimen ends with thin lubricated membranes at the ends to insure frictionless surface conditions.