Effects of bitumen on shear strength parameters of soil-rubber mixtures

Bitumen has been used in different forms and with various properties in pavement as a binder material. Meanwhile, the properties of soil-rubber mixtures (SRM) have been extensively examined for applications in geotechnical and highway engineering. These applications range from serving as a lightweight fill material, subgrade layers in pavement, and foundation materials for geotechnical seismic isolation (GSI). However, a research gap exists in understanding the effect of the interaction between bitumen and rubber granules on their mechanical properties under a range of confining pressures. In this paper, a series of unconfined compressive strength (UCS) and monotonic triaxial tests were conducted. The results show that a bitumen content as low as 3% of the total mass can significantly increase the shear strength and cohesion of SRM and reduce the deformability. Moreover, the increase in the elastic modulus due to a 3-5% bitumen content is notably less than the reduction obtained from 25-45% rubber replacement, which is favourable for GSI applications. The shear strength and elastic modulus in gravel-based mixtures were found to be more sensitive to changes in rubber and bitumen content compared to sand-based mixtures. Conversely, the effect of confining pressure was more pronounced in sandy soil than in gravely soil.