When lightweight geomaterials are used in the pavement subbase in cold regions, it is necessary to consider their resistance to freeze–thaw and frost heaving. However, little conventional research has addressed this. A lightweight geomaterial recycled from expansive shale and sewage sludge was subjected to a frost heave test to address its suitability for use in the subbase in a cold region. A frost heave test and a soil particle density test conducted under different conditions showed this lightweight geomaterial to afford high quality when used in the subbase course. The material was found to restrain frost heaving, and the California bearing ratio value was not lower after freeze–thaw, despite this lightweight geomaterial having a high water content, with many pores distributed in each particle. The deformation characteristics were also investigated with reference to the geomaterial’s suitability for the subbase course. Three materials whose particle size distributions were adjusted by the addition of silica sand were used. In a series of cyclic tests, specimens at the optimum moisture content were subjected to 10,000 cycles at two confining pressures. It was found that the deformation modulus tended to be constant under stress with a constant amplitude and that the deformation properties were stable.