The freeze-thaw deformation and inter-layer interface contact characteristics of toughened cement stabilized macadam: an experimental study based on the high-speed railway subgrade

The research involved replacing fine particles with solid waste rubber powder to prepare the toughened cement stabilized macadam/TCSM. Based on vertical full-scale model tests of frost heave and thaw settlement, vertical stress transmission tests between layers, and inter-layer interface adhesion effect evaluation tests, the freeze-thaw deformation and inter-layer interface contact characteristics of TCSM were discussed. The results indicated: 1) Under test conditions where cement and rubber powder were added simultaneously, the TCSM could effectively eliminate thaw settlement deformation, with frost heave deformation reduced from 2.53 mm to 0.26 mm, a decrease of 90.4%. The hydration and adhesion of cement, combined with the elastic filling of rubber powder, played a positive role in resisting volume deformation caused by ice-water phase transitions. 2) The contact area between the TCSM and the surface of the sub-grade fill material was more extensive than that of cement stabilized macadam under the same conditions, exhibited better stress diffusion behaviour. Under low stress conditions, stress diffusion effects were pronounced, while under high stress conditions, stress concentration continued to increase. 3) Under identical micro-deformation conditions, the fixed interface bending load-bearing capacity was 4 times that of a free interface for the composite inter-layer structure, and a calculation method for the interface adhesion contact coefficient/ IBC was provided. The TCSM shown the better inter-layer adhesion effect when combined with SBS/rubber powder blended modified asphalt mixture, with an index value of 3.9 under small deformation conditions of 0.2 mm, approaching the ideal fixed state. The research could understand the freeze-thaw deformation characteristics and its contact state with the upper and lower layers for TCSM, which was crucial for enhancing the toughness of the subgrade surface layer.