pavement, the wearing surface of a road, street, or sidewalk. Parts of Babylon and Troy are believed to have been paved; Roman roads were noted for their durable stone paving. Cobblestones were common from late medieval times into the 19th cent. A pavement known as macadam road, introduced in England in the 19th cent., is still used today; it consists basically of compacted layers of small stones cemented into a hard surface by means of stone dust and water (water-bound macadam). However, the main pavement surfaces in use today are bituminous/asphalt coverings and concrete. Desirable qualities in pavements include durability, smoothness, quietness, ease of cleaning, and a nonslippery surface. The requirements conflict to a degree, so no one material is ideal in all respects. The foundation of a pavement must be crowned, or slightly arched, for rapid shedding of water; it must be strong enough to withstand heavy dynamic loads, but capable of responding to temperature changes. In the bituminous macadam pavement, the foundation is macadam, upon which a bituminous material that penetrates at least 2 in (5 cm) into the foundation is poured, forming an impervious binder. In the bituminous-mixed macadam pavement, a mixture of crushed rock, ground glass and other additives, and bituminous binder is spread over a macadam foundation and rolled into a compact mass. The two other pavement types use a concrete road slab as a foundation. In the sheet asphalt pavement, a binder course and a wearing course are laid over a concrete foundation. The binder course, whose function is to prevent creepage of the upper course, is composed of broken stone and asphalt cement. The wearing surface is a mixture of fine sand, filler, and asphalt. By far the most common type of pavement for heavy use is rigid concrete. The first concrete pavement was laid in Bellefontaine, Ohio, in 1894. A modern highway will have a 6 in (15 cm) base of concrete, on top of which 3 in (7.5 cm) of steel-reinforced concrete will be laid. Pavements that must withstand only pedestrian traffic may use brick or wood-blocks, set in a 1 in. (2.5 cm) bedding of sand, cement mortar, or mastic. For ornamental pavements, see mosaic ; tile.

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