Pavement or road surface is the durable surface material laid down on an area intended to sustain traffic (vehicular or foot traffic). The most common modern paving methods are asphalt and concrete. In the past, bricks were extensively used, as was metalling. There are mainly 4 types of pavements and a couple of other less frequently construction methods, namely Metalling, Asphalt paving, Concrete paving, Bituminous Surface Treatment (BST) and other paving methods.
Metalling originally referred to the process of creating a carefully engineered gravel roadway. The route of the roadway would first be dug down several feet. Depending on local conditions, French drains may have been added. Next, large stones will be placed and compacted, followed by successive layers of smaller stones. The process of laying and compacting of small stones is repeated until the small stones are compacted into a hard, durable surface. Road metal later became the name of stone chippings mixed with tar to form the road surfacing material tarmac. A road of such material was called a “metalled road” in British usage, although this would be very rare in modern usage. It would be more common to refer to a macadam road. The word metal is derived from the Latin word “metallum”, which means both “mine” and “quarry”, hence the roadbuilding terminology.
The next method of constructing pavements is Asphalt paving. Most asphalt pavements are built on a gravel base which is generally at least as thick as the asphalt layer, although some ‘full depth’ pavements are built directly on the native subgrade. In areas with very soft or expansive subgrades such as clay or peat, thick gravel bases or stabilization of the subgrade with Portland cement or lime is required. In some countries with soft soils, a foundation of polystyrene blocks is used instead.
The third method of pavement construction is concrete paving. Concrete pavements (specifically, Portland cement concrete) are created using a concrete mix of Portland cement, gravel, and sand. The material is applied in a freshly-mixed slurry, and worked mechanically to compact the interior and force some of the thinner cement slurry to the surface to produce a smoother, denser surface free from honeycombing. The mix or slurry is then laid, spread and smoothed before leaving it to dry.
The fourth common pavement construction method is known as Bituminous Surface Treatment (BST). Bituminous Surface Treatment (BST) is used mainly on low-traffic roads, but also as a sealing coat to rejuvenate an asphalt concrete pavement. It generally consists of aggregate spread over a sprayed-on asphalt emulsion or cut-back asphalt cement. The aggregate is then embedded into the asphalt by rolling it, typically with a rubber-tired roller. Other types of Bituminous Surface Treatments (BSTs) include micropaving, slurry seals and Novachip. These are laid down using specialized and proprietary equipment. They are most often used in urban areas where the roughness and loose stone associated with chip seals is considered undesirable.
Other pavements are constructed using less frequently used methods. Pavers, generally in the form of pre-cast concrete blocks, are often used for aesthetic purposes. In some areas, pavements are made from bricks, cobblestones and wood planks. These pavements are mainly constructed and maintained historical reasons.
