A Novel Test Specimen Geometry for Uniaxial Fatigue Testing of Asphalt Concrete

Abstract Two challenges in uniaxial fatigue testing of hot mix asphalt remain: end failures of cylindrical specimens and applicability to in-situ samples. End failures occur frequently, significantly reducing the value of the test. Cored field samples often include several construction lifts, rendering them unsuitable for creating standard test cylinders. This study proposes a specimen geometry for uniaxial fatigue testing addressing these challenges. The proposed geometry is obtained by cutting horizontal slices of laboratory compacted or field-cored cylinders with a 150-mm diameter. The circular slices are reduced to rectangles 110 mm long by 100 mm wide. The thickness can be varied based on lift thickness and nominal maximum aggregate size (19–38 mm have been used successfully). The resulting prism is then tapered along its length over the middle 90 mm to a minimum width of 88 mm at mid-height. The specimen is loaded along its longitudinal axis (normal to the reduced cross section). This article discusses the rationale for the geometry, fabrication, and gluing procedures as well as procedures to reduce loading platen-induced moments before testing and load eccentricity while testing. As a proof of concept, it also presents the results of constant crosshead tests performed at 40°C that to date have resulted in middle failures at a frequency greater than 95 %.