Laboratory and numerical investigation on the behavior of reclaimed asphalt pavement (RAP) as railway track subballast layer

Abstract

The use of asphalt mixtures in different places of the structure of railway tracks has been increased, given their acceptable performance and properties. Using bituminous materials in subballast layers is of great importance due to the structurally, vibrationally, and geometrically improving properties of these infrastructures. In order to enhance the mechanical behavior of railway tracks under heavy loads and high-speed trains, the tendency to use sustainable development approaches such as reuse of discarded and recycled materials has increased. The asphalt is recycled in the maintenance activities of road pavements and, in some cases, reused in the road construction and pavement industry, raising the question of whether reclaimed asphalt pavement (RAP) mixtures can be utilized in railway tracks? Has not been so extensively studied on RAP materials to be used as an interlayer in the structure of railway tracks. Accordingly, the present study seeks to investigate the behavior of these materials as the railway tracks subballast by experimental and numerical through structural approach. Given the complex behavior of these materials due to their bitumen aging, researchers are concerned about the quantity of them that can be reused. In this study, subballast layers containing RAP with percentages varying from 25 % to 100 % without any additive material and thicknesses from 5 cm to 20 cm were numerically modeled. At first, the behavioral models of the RAP materials without any additive material in a laboratory were determined for the model inputs. Using the dynamic modulus and relaxation behavior remarkably helped to identify the behavior of these materials. Numerical models were developed for RAP materials by assuming the linear elastic (LE) behavior for granular materials and linear viscoelastic (LVE) behavior for RAP materials. A conventional ballast track model with granular subballast was also simulated for validation and comparison. Eventually, by evaluating the effect of using RAP on the track settlement, the tensile strain of the bottom of the subballast layer, and compressive stress imposed on the subgrade, the subballast layer with 100 % RAP and a thickness of 20 cm was found to have the best performance, reducing the mentioned Strain and Stress parameters by 40 %. Accordingly, such a layer can be utilized as a simple permanent solution to improve the stiffness and performance of tracks.