Shear Modulus and Damping Ratio of Rubber-modified Asphalt Mixes and Unsaturated Subgrade Soils

This paper presents the results of an investigation into the potential application of rubber-modified asphalt in railroad trackbeds by measuring its shear modulus and damping ratio. The measurements of the shear modulus and damping ratio were also conducted on typical subgrade soils. A number of resonant column tests were conducted on subgrade soil samples and the crumb rubber-modified asphalt (CRMA) mix samples with different rubber contents and rubber types. The fine crumb rubber is dissolved in the hot asphalt binder (for a period of time) as an additive to modify the properties of the binder. The measurements were conducted under a wide range of confining pressures and strain levels to simulate stress and strain conditions expected in the typical railway foundation. Cyclic triaxial tests were conducted on subgrade soil samples to study soil characteristics under dynamic loads. It was found that CRMA is a material with high shear stiffness and damping ratio, making it a very attractive material for vibration attenuation of railroad trackbeds.