Effects of laboratory asphalt concrete specimen preparation variables on fatigue and permanent deformation test results using strategic highway research program A-003A proposed testing equipment

A study was carried out to determine the effects of laboratory specimen preparation variables on permanent deformation, fatigue, and flexural stiffness performance, as measured with test equipment and methods by a Strategic Highway Research Program contractor. The specimen preparation variables included in the project were binder type, aggregate type, fines content, air-void content, compaction method, mixing viscosity, and compaction viscosity. Asphalt rubber was included as one of the binders in the experiment. The test methods used were the constant-height repetitive shear test for permanent deformation and the controlled-stress beam apparatus for flexural fatigue and stiffness. The investigation indicates that the variables included in the study affect the test results. Of particular interest were the results showing that (a) compaction method (gyratory, rolling wheel, and kneading compaction were included in the study) is a significant factor in permanent deformation performance; (b) a reduction in fines content of 3% significantly affects both permanent deformation and fatigue performance; and (c) the temperatures at which a mix is mixed and compacted also significantly affect fatigue performance. In addition, the constant-height repetitive shear test results showed asphalt-rubber mixes to be superior to the conventional asphalt mixes at 60 deg C (140 deg F).