Experimental Survey on Dry Asphalt Rubber Concrete for Sub-ballast Layers

The railway traffic through a town or near built-up areas causes heavy effects such as noise and vibration on surroundings. In order to minimize the level of these impacts the railway companies with researchers and practitioners seek suitable solutions especially in the field of the rail-track because the main source of the ground borne vibrations and noise is the bad wheel-track contact. In particular, a big effort is addressed to new materials with high mechanical and environmental performance that can be utilized within the sub-ballast layer. This paper presents the results of an experimental survey on the potential application of Dry Asphalt Rubber Concrete (DARC) in sub-ballast layers by measuring its damping and mechanical properties. In relation to the environmental issues the DARC can be doubly significant because the rubber comes from the waste tires of truck and so its production at maximum speed could start up a big recycling process. After a preliminary mix-design of several DARCs, with different rubber content using the Marshall test, the stiffness modulus and damping ratio both of a standard bituminous mixture and of dry asphalt rubber concrete with a rubber content equal to 1,5% were determined using the four point bending device. The experimental results were compared and a numerical analysis by means of a 2D lumped mass model was developed in order to evaluate the different performance within the rail superstructure in terms both of the deflection and of the pressure on sub-grade. Both the results on the mechanical and dissipative properties of the DARC and the mechanical behavior of the correlate rail superstructure encourage the authors to continue the research on the application of such material for sub-ballast layers.