Experimental evaluation on the cyclic behavior of reclaimed asphalt pavement (RAP) as railway tracks subballast

The repetitive loading in railway tracks and the passage of high-speed trains lead to amplifying structural and vibrational effects at different levels of the railway structure. The damaging compound effects on the ballast and subgrade have motivated the use of suitable and beneficial materials in the railway structure. Reclaimed asphalt pavement (RAP) mixtures are sustainable materials that could address the mentioned issues when used in railway tracks. This study investigated the reclaimed asphalt pavement (RAP) mixtures cyclic behavioral as railway tracks subballast. For this purpose, RAP100 % materials (one layer consisting of 100 % recycled asphalt materials`) were utilized. To determine the optimum subballast layer thickness, 5, 10, 15, and 20 cm thicknesses were examined using the ballast box test (BBT) under 100 thousands cycles of vertical loading. To account for the effects of ballast feature on the subballast, two ballast gradations (fine and coarse) were used in sample preparation. Comparison of settlement, stiffness, and damping of the arrangements showed that the best performance was related to the structure with fine ballast and 20 cm thick RAP100 % subballast, which decreased the track settlement by about 70 % and increased the ballast layer stiffness and damping by 138 % and 233 %, respectively. Although extensive non-structural aspects could be investigated in this issue, it seems that this layer with the mentioned thicknesses could be used as a straightforward constant strategy to enhance track stiffness and vibrational performance of railway tracks, especially high-speed tracks in comparison to common subballast granular layer.