Volume 2, Issue 10 (November 2005)
Laboratory Investigation of HMA Performance Using Hamburg Wheel Tracking and DSR Torsional Creep Tests
Lack of existing fundamental mechanistic tests to evaluate performance potential of HMA mixtures has given rise to a number of empirical and mechanical-empirical test procedures. In an effort to understand how one of these tests, the Hamburg rutting test, was impacted by differences in HMA mixture variables, the following experimental work was conducted. Three aggregate types consisting of a crushed granite, a crushed siliceous gravel, and a crushed limestone were evaluated at four design ESAL levels. These four ESAL levels were 300 000, 1 million, 3 million, and 10 million. For each of these aggregate types and ESAL levels, 5 PG graded binders were investigated. The binders were PG 58-28, PG 64-28C (chemically modified), PG 64-28P, PG 64-34, and PG 70-28; the latter 3 binders were polymer modified. For all mixtures, Hamburg Wheel Tracking tests were performed under water at 50°C. In addition, a DSR Creep Test developed at MTE was performed on each mixture at 58°C and 34 kPa stress to determine the dry strength characteristics. The Hamburg test showed consistently better results as the ESAL level of the mix increased and as the high temperature PG grade of the binder increased for a given base asphalt. In the Hamburg test, mixes produced with PG 64-34 did not perform as well as PG 70-28 or PG 64-28P, while in the DSR Creep Test, mixes produced with PG 64-34 performed significantly better than PG 64-28P. This leads to speculation that the modulus of the base asphalt plays a more significant role in stress applied moisture resistance tests and that dry high temperature permanent deformation tests are influenced by the modified binder properties.