Hydraulic conductivity of fresh railway ballast mixed with crumb rubber considering size and percentage of crumb rubber as well as aggregate gradation

Degradation of ballast aggregate leads to the drainage problem along with less stability of the ballasted railway track. Using crumb rubber (CR) as waste material incorporated in ballast aggregate results in attenuation of aggregate degradation as well as reduction of the noise level generated from passing trains. The size and quantity of rubber material mixed with ballast aggregate are important factors which affect the stability and hydraulic conductivity of ballast course. Therefore, the present study investigates the influence of size and percentage of CR on hydraulic conductivity of fresh ballast aggregate mixed with rubber particles. For this purpose, large-scale constant head permeability test is conducted on rubber modified ballast aggregate by taking into account the initial gradation of aggregate along with the size and amount of CR. Generally, using smaller-sized rubber particles and increasing the percentage of CR leads to further decrement of hydraulic conductivity of ballast, especially for more broadly-graded aggregate. However, the permeability level characterized by laminar and non-laminar flow regime is still acceptable. In addition, the hydraulic conductivity of ballast comprised of more uniform range of aggregate is further reduced by adding larger-sized CR particles. Furthermore, water movement through prepared specimens of rubber modified ballast obeys nonlinear relationship characterized as flow regime between laminar and turbulent. (C) 2020 Elsevier Ltd. All rights reserved.