Roads are made up of four layers. These include: Layers of road construction Sub-grade: Native soil underneath a road. Sub-base: Layer of aggregate materials on top of the sub-grade Base (also base course) : Layer of material under the surface course. Surface (also surface course): The upper layer of the road. The surface can consist of asphalt, concrete, cobblestones, tiles or earth materials. Asphalt and concrete are the most common surface materials. Asphalt: Black or brown sticky substance, mixed with crushed stone, sand or gravel, which is used for construction of road surfaces. Concrete: Building material created by mixing together cement, sand, gravel and water. Cobblestone: Rounded stone used to make the surfaces of roads.