Freeze-thaw characteristics of subgrade macadam fillings influenced by cement content and grain-size composition

Motivated by the practical application of cement-stabilized macadam to high-speed railway subgrade in cold regions, a series of tests are conducted using an integrated method learnt from an evaluation system used for semi-rigid highway foundations considering the characteristics of high-speed railway subgrade in cold regions. The compaction results, frost-heave property, permeability, freeze-thaw durability and shrinkage property of subgrade macadam fillings influenced by cement content and grain size composition are deeply studied and analyzed. The following results are obtained. The compaction indexes of cement-stabilized macadam subgrade are satisfied or exceed the compaction standard under the tested compositions. The lack of large-sized soil particles weakens the frost-heave sensibility, improves the permeability, and reduces the compressive strength and moisture stability of cement-stabilized macadam samples. In addition, a mixture of cement effectively compensates for the reduction in compressive strength and increases the shrinkage deformation of cement-stabilized macadam samples. The compressive strength decreases with every increment of freeze-thaw cycles, and then levels off after 10 freeze-thaw cycles. For the engineering practice of high-speed railway subgrade in cold regions, the cement-stabilized macadam with 3% of fines and 3% of cement addition is suitable for the subgrade without any demand for permeability, and the cement-stabilized macadam with grains greater than 0.5 mm in size and 3% of cement addition is suitable for the required permeability of subgrade.