IMPROVEMENTS IN THE MIX-DESIGN, PERFORMANCE FEATURES AND RATIONAL METHODOLOGY OF RUBBER MODIFIED BINDERS FOR THE THERMAL EVALUATION OF THE RAILWAY SUB-BALLAST

Abstract

The objectives of this study are focused on the ideal methodology and the dimensioning of the railway superstructure, involving the use of a bituminous sub-ballast layer modified with recycled natural rubber tire out-ofuse. The previous study of the thermal transmission in each Railtrack layer, the analysis of the traffic in highspeed lines and the revision of the thermal-mechanical models have motivated this research. An experimental methodology has been optimized for the application of the volumetric mix-design with the gyratory compactor (SGC). According to the meteorological situation and applying experimental models based on thermal conductivity interpolated by sinusoidal functions, a laboratory study of conventional bituminous mixtures and improved mixtures of asphalt modified with coarse rubber waste tires is illustrated. The enhanced methodology entails a case study where compacted mixes are used by SGC, replacing rubber between 1.5 and 3 percent of rubber (particle size 0.2-4 mm) in the total weight of the blend. After the evaluation of the average seasonal temperatures, the mixtures were designed considering the dry process, as an advanced measure of sustainability and for their demonstrated improvements in thermal behavior and resistance to fatigue. A step-by-step manufacturing process is provided to avoid swelling problems in the post-compaction phase characteristic of dry mixes. The purpose of using rubber modifiers in the hot mix asphalt has been achieved to obtain an elastic sustainable material for the evaluation of its behavior in sub-ballast layers.