Pavement (roads)

In American English pavement is the hard material on the surface of roads and paths. In British English pavement is usually taken to mean a footpath next to a road, the same as sidewalk in American English. Hard-surfaced roads are often referred to as paved roads, although metalled road is still used to some degree in England. Common modern paving materials are asphalt concrete and Portland cement concrete (generally referred to as just concrete).

Asphalt concrete has been widely used since 1920-1930, though in ancient times asphalt was already used for road-building. The viscous nature of the asphalt binder allows asphalt concrete to sustain significant plastic deformation, although fatigue from repeated loading over time is the most common failure mechanism. Most asphalt pavements are built on an imported 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 can be required.

Portland cement concrete pavements are typically stronger and longer lasting than asphalt concrete pavements, however they have a higher initial cost and are more difficult to repair. They are also generally noisier and less smooth. Concrete pavements can be either reinforced or non reinforced. Non reinforced pavements will typically have joints at a 5 meter interval. Reinforced concrete pavements can have a much longer joint spacing, or no built-in joints at all. Vertical misalignment of the joints, known as joint faulting, can be caused by differential settlement of the slabs and is a major source of driver annoyance. A common failure mode of concrete pavements is loss of support of the slab edges or corners due to erosion of the foundation material. If this condition is caught before it leads to breakup of the slab, support can be restored by filling the void with grout or foam in a process known as 'mud jacking' or 'slab jacking'.

Pavers, generally in the form of pre-cast concrete blocks are often used for aesthetic purposes, or sometimes at port facilities that see long-duration pavement loading. Pavers are rarely used in areas that see high-speed vehicle traffic.

Brick, cobble and wood plank pavements were once common in urban areas throughout the world, but due to their high manual labor requirements they are typically only maintained for historical reasons. Likewise, macadam and tarmac pavements can still sometimes be found buried underneath asphalt concrete or Portland cement concrete pavements, but are rarely constructed anymore.

As pavements primarily fail due to fatigue (in a manner similar to metal fatigue), the damage done to a pavement increases exponentially with the axle load of the vehicles traveling on it. Heavily loaded trucks can do more than 10,000 times the damage done by a normal passenger car. Although tax rates for trucks are higher than those for cars in most countries, they are generally not high enough to make up for this discrepancy.

Several pavement design methods have been developed to determine the thickness and composition of pavement required to carry predicted traffic loads for a given period of time. Among these is the Shell Pavement design method.