Shear behaviour of polyurethane-stabilized recycled ballast

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4. Shear behaviour of polyurethane-stabilized recycled ballast

The ballast layer is discrete in nature, and it undergoes degradation and deformation upon application of repeated train loading. Over a period of time, the track requires frequent maintenance operations such as cleaning and replacement of ballast, subsequently producing a huge amount of discarded ballast. Whereas treating the ballast layer with polyurethane significantly enhanced the shear behaviour and reduced the deformation and degradation of ballast.  Further, replacing natural ballast with recycled ballast (discarded ballast particles) in polyurethane treatment applications without compromising the performance of the track can be a way forward to sustainable railway infrastructure. The current study assessed the shear behaviour of polyurethane-stabilized recycled ballast based on large-scale direct shear tests. The large-scale direct shear tests were performed on 100% natural ballast, 50% natural + 50% recycled ballast, and 100% recycled ballast with and without polyurethane treatment at normal stresses of 80 and 120 kPa at a shearing rate (S_r) of 9 mm/min. The test results indicated that the polyurethane treatment has significantly improved the shear strength of ballast. The peak shear strength of polyurethane-treated 100% natural ballast, 50% natural + 50% recycled ballast, and 100% recycled ballast was increased by 51%, 34%, and 12%, respectively, in comparison to untreated 100% natural ballast at normal stress of of 80 kPa. It was observed that the peak shear strength, friction angle, and dilation angle of untreated ballast samples reduced with the increase in recycled ballast content. Whereas the polyurethane treatment significantly improved the shear behaviour of 50% natural + 50% recycled ballast and 100% recycled ballast until complete breakage of polyurethane bonds (shear strain of about 10%), beyond that the sample started to behave as untreated sample. The current research highlighted that treating recycled ballast with polyurethane can be considered beneficial rather than disposing of it as waste.

4th Asia-Pacific Conference on Physical Modelling in Geotechnics (ACPMG2024)

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