Road Building

a complex of construction activities that includes both roadbed and pavement construction and the construction of service structures and maintenance buildings. In its narrow aspect, road building is limited to the construction of the automobile highway itself, namely, to the construction of the roadbed and of the road pavement, and in inhabited areas to the construction of high-speed roads away from pedestrians, interchanges at various levels, sidewalks and squares, underground tunnels, and overpasses.

The materials used in building roads include soils, such as clays, loams, sandy loams, and sands for roadbeds; crushed stone, gravel, sand, bitumens, portland cement, asphalt cement, and concrete cement for pavements; various surface-active additives, which improve the properties of paving materials; and prefabricated products, such as blocks, pipes, and curbstones. Road construction starts with the preparatory work: clearing the land by removing trees, shrubs, stones, and the like. The earthwork operations of building embankments up to 1 m in height involve the use of such road-building machinery as power graders and bulldozers, which move and level the soil, and road rollers, which compact the roadbed. The construction of embankments exceeding 2 m in height involves the use of more basic machines, such as scrapers, power graders, and rollers. Earthmoving involves the use of excavators, trucks, and transport carts.

In the construction of the pavement, the number of successive layers and of the required road-building machinery depends on the nature of the roadbed and the type of surfacing. For example, the construction sequence in building an asphalt-cement surface may include laying a lower base layer of sand, an upper base of crushed stone treated with cement, two layers of bitumen-mineral mixtures, and a top coat of asphalt cement. The sequence follows: the sand is transported, leveled, and compacted; the crushed stone, cement, and water are brought and mixed; and the premixed bitumen-mineral and asphalt-cement mixtures are brought, spread, and compacted. The process may be changed depending on the various types of pavement, but the basic operations, such as the transport of materials, deposit, spreading, and compaction remain the same.

The most advanced method of road building is the cascade method, which involves the performance of all steps on separate sections of equal length by specialized crews moving along the road one after the other in a predetermined sequence. The length of the section is, as a rule, between 200 and 600 m.