Properties of Roadbeds

The ability of a roadbed to resist forces that tend to destroy it can be adequately measured only by the weight of the load that it is expected to support and by its resistance to the loss and gain of. saturation. Inasmuch as no specified strength is required by the AASHO and modified AASHO tests, materials of inferior gradation are apt to offer inadequate resistance to loads or to the penetration of excessive volumes of water. Instead of measuring the quality of a roadbed by the prescribed amount of effort applied in its compaction, quality should be measured by the ability of the roadbed to resist prescribed forces tending to destroy it. Constant pore space and saturation must be maintained. Because water in fine grain materials can only be removed by evaporation, water content in these tests are controlled by a reduction of pore space or a covering of the surface with an air-tight crust of asphalt and sand.