Performance Analysis of Asphalt Railway Sub-Ballast Through Punching Test

The use of asphalt mixtures in railway sub-ballast layers is increasingly recognized as an effective strategy to enhance track performance and durability, particularly under high-speed and heavy-load conditions. Conventional pavement tests, however, often fail to capture the localized loading mechanisms that occur at the ballast/sub-ballast interface, limiting their applicability to railway-specific design. This study presents an experimental investigation of three asphalt mixtures specifically formulated for sub-ballast applications, using an innovative mechanical characterization method known as the punching test. This laboratory test was developed to assess the mechanical response of cylindrical asphalt specimens under localized vertical loading, closely simulating the stresses imposed by the discrete contact of crushed-stone ballast particles. To this end, a dedicated device, named Adaptive Indentation Plate (AIP), was conceived to reproduce realistic contact conditions between ballast and asphalt sub-ballast. Cylindrical specimens were tested under displacement control, at multiple temperatures and deformation rates, to evaluate their resistance to plastic deformation and their indentation behavior. The initial results demonstrate the effectiveness of the punching test in capturing key mechanical characteristics that are not fully reflected by traditional testing methods. Overall, the findings provide complementary insights that support an upgrade of selection and acceptance requirements for asphalt mixtures intended for railway applications.