Pavement (material) - AbsoluteAstronomy.com

Road surface or pavement (American English

American English

American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

) is the durable surface material laid down on an area intended to sustain vehicular or foot traffic

Traffic

Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

, such as a road

Road

A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...

or walkway

Walkway

In US English, a walkway is a composite or umbrella term for all engineered surfaces or structures which support the use of trails. These include sidewalks, footbridges, stiles, stairs, ramps, paseos or tunnels...

. In the past cobblestone

Cobblestone

Cobblestones are stones that were frequently used in the pavement of early streets. "Cobblestone" is derived from the very old English word "cob", which had a wide range of meanings, one of which was "rounded lump" with overtones of large size...

s and granite setts

Sett (paving)

A sett, usually the plural setts and in some places called a Belgian block, often incorrectly called "cobblestone", is a broadly rectangular quarried stone used originally for paving roads, today a decorative stone paving used in landscape architecture...

were extensively used, but these surfaces have mostly been replaced by asphalt

Asphalt

Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...

or concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

. Such surfaces are frequently marked to guide traffic

Road surface marking

Road surface marking is any kind of device or material that is used on a road surface in order to convey official information. They can also be applied in other facilities used by vehicles to mark parking spaces or designate areas for other uses....

. Today, permeable paving

Permeable paving

Permeable paving is a range of materials and techniques for paving roads, cycle-paths, parking lots and sidewalks that allow the movement of water and air around the paving material. Although some porous paving materials appear nearly indistinguishable from nonporous materials, their environmental...

methods are beginning to be used for low-impact roadways and walkways.

Metalling

The term road metal refers to the broken stone

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

or cinder

Cinder

A cinder is a pyroclastic material. Cinders are extrusive igneous rocks. Cinders are similar to pumice, which has so many cavities and is such low-density that it can float on water...

s used in the construction or repair of roads or railways, and is derived from the Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

metallum, which means both "mine

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

" and "quarry

Quarry

A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...

". Metalling is known to have been used extensively in the construction of roads by soldiers of the Roman Empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

(see Roman road

Roman road

The Roman roads were a vital part of the development of the Roman state, from about 500 BC through the expansion during the Roman Republic and the Roman Empire. Roman roads enabled the Romans to move armies and trade goods and to communicate. The Roman road system spanned more than 400,000 km...

) but a limestone-surfaced road, thought to date back to the Bronze Age

Bronze Age

The Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...

, has been found in Britain.
Metalling has had two distinct usages in road surfacing. The term originally referred to the process of creating a gravel roadway. The route of the roadway would first be dug down several feet and, depending on local conditions, French drain

French drain

A French drain, blind drain, rubble drain, rock drain, drain tile, perimeter drain, land drain or French ditch is a trench covered with gravel or rock that redirects surface and groundwater away from an area...

s may or may not have been added. Next, large stones were placed and compacted, followed by successive layers of smaller stones, until the road surface was composed of small stones compacted into a hard, durable surface. "Road metal" later became the name of stone

Rock (geology)

chippings mixed with tar

Tar

Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...

to form the road surfacing material tarmac

Tarmac

Tarmac is a type of road surface. Tarmac refers to a material patented by Edgar Purnell Hooley in 1901...

. A road of such material is called a "metalled road" in Britain, a "paved road" in the USA, or a "sealed road" in Australia.

Asphalt

Asphalt (specifically, asphalt concrete

Asphalt concrete

Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, airports and parking lots. It consists of asphalt and mineral aggregate mixed together, then laid down in layers and compacted...

) has been widely used since 1920–1930. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue

Fatigue (material)

'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...

from repeated loading over time is the most common failure mechanism. Most asphalt surfaces are laid on a gravel base, which is generally at least as thick as the asphalt layer, although some 'full depth' asphalt surfaces are laid directly on the native subgrade

Subgrade

In transport engineering, subgrade is the native material underneath a constructed road, pavement or railway track. It is also called formation level.The term can also refer to imported material that has been used to build an embankment....

. In areas with very soft or expansive subgrades such as clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

or peat

Peat

Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...

, thick gravel bases or stabilization of the subgrade with Portland cement

Portland cement

Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

or lime

Lime (mineral)

Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...

may be required. Polypropylene and polyester geosynthetics have also been used for this purpose and in some northern countries, a layer of polystyrene

Polystyrene

Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...

boards have been used to delay and minimize frost penetration into the subgrade.

Depending on the temperature at which it is applied, asphalt is categorized as hot mix asphalt (HMA), warm mix asphalt, or cold mix asphalt. Hot mix asphalt is applied at temperatures over 300 F with a free floating screed

Free floating screed

The free floating screed is a device pioneered by Barber Greene Company in the 1930s that revolutionized the asphalt paving process.The device is designed to flatten the material The free floating screed is a device pioneered by Barber Greene Company in the 1930s that revolutionized the asphalt...

. Warm mix asphalt is applied at temperatures of 200 to 250 degrees F, resulting in reduced energy usage and emissions of volatile organic compounds. Cold mix asphalt is often used on lower volume rural roads, where hot mix asphalt would cool too much on the long trip from the asphalt plant to the construction site.

An asphalt concrete surface will generally be constructed for high volume primary highways having an Average Annual Daily Traffic load higher than 1200 vehicles per day. Advantages of asphalt roadways include relatively low noise, relatively low cost compared with other paving methods, and perceived ease of repair. Disadvantages include less durability than other paving methods, less tensile strength than concrete, the tendency to become slick and soft in hot weather and a certain amount of hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

pollution to soil and groundwater

Groundwater

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

or waterway

Waterway

A waterway is any navigable body of water. Waterways can include rivers, lakes, seas, oceans, and canals. In order for a waterway to be navigable, it must meet several criteria:...

s.

In the 1960s, rubberized asphalt

Rubberized asphalt

Rubberized asphalt concrete , also known as asphalt rubber or just rubberized asphalt, is pavement material that consists of regular asphalt concrete mixed with crumb rubber–ground, used tires that might otherwise be discarded, taking up space in landfills, if they were not re-directed for use as...

was used for the first time, mixing crumb rubber from used tires with asphalt. In addition to using tires that would otherwise fill landfills and present a fire hazard, rubberized asphalt is more durable and provides a 7–12 decibel noise reduction over conventional asphalt. However, application of rubberized asphalt is more temperature-sensitive, and in many locations can only be applied at certain times of the year.

Concrete

Concrete surfaces (specifically, Portland cement concrete) are created using a concrete mix of Portland cement

Portland cement

Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

, gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

, sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

and water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. 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 water allows the mix to combine molecularly in a chemical reaction called hydration

Mineral hydration

Mineral hydration is an inorganic chemical reaction where water is added to the crystal structure of a mineral, usually creating a new mineral, usually called a hydrate....

.

Concrete surfaces have been refined into three common types: jointed plain (JPCP), jointed reinforced (JRCP) and continuously reinforced (CRCP). The one item that distinguishes each type is the jointing system used to control crack development.

Jointed Plain Concrete Pavements (JPCP) contain enough joints to control the location of all the expected natural cracks. The concrete cracks at the joints and not elsewhere in the slabs. Jointed plain pavements do not contain any steel reinforcement. However, there may be smooth steel bars at transverse joints and deformed steel bars at longitudinal joints. The spacing between transverse joints is typically about 15 feet (4.6 m) for slabs 7–12 inches thick. Today, a majority of the U.S. state agencies build jointed plain pavements.

Jointed Reinforced Concrete Pavements (JRCP) contain steel mesh reinforcement (sometimes called distributed steel). In jointed reinforced concrete pavements, designers increase the joint spacing purposely, and include reinforcing steel to hold together intermediate cracks in each slab. The spacing between transverse joints is typically 30 feet (9.1 m) or more. In the past, some agencies used a spacing as great as 100 feet (30.5 m). During construction of the interstate system, most agencies in the Eastern and Midwestern U.S. laid jointed-reinforced pavement. Today only a handful of agencies employ this design, and its use is generally not recommended as JPCP and CRCP offer better performance and are easier to repair.

Continuously Reinforced Concrete Pavements (CRCP) do not require any transverse contraction joints. Transverse cracks are expected in the slab, usually at intervals of 3–5 ft. CRCP pavements are designed with enough steel, 0.6–0.7% by cross-sectional area, so that cracks are held together tightly. Determining an appropriate spacing between the cracks is part of the design process for this type of pavement.

Continuously reinforced designs generally cost more than jointed reinforced or jointed plain designs initially due to increased quantities of steel. However, they can demonstrate superior long-term performance and cost-effectiveness. A number of agencies choose to use CRCP designs in their heavy urban traffic corridors.

One advantage of cement concrete roadways is that they are typically stronger and more durable than asphalt roadways. They also can easily be grooved to provide a durable skid-resistant surface. Disadvantages are that they typically have a higher initial cost, are far rougher to drive on, crack continuously, and are more difficult to repair in a satisfactory manner. A sampling of interstate highways recently found that those concrete roads are in poor condition and cause damage to freight carried by truck. Repairs are expensive and time consuming, thus are often delayed until the road becomes quite unsatisfactory for travel.

The first street in the United States to be paved with concrete was Court Avenue in Bellefontaine, Ohio

Bellefontaine, Ohio

Bellefontaine is a city in and the county seat of Logan County, Ohio, United States. The population was 13,069 at the 2000 census. It is the center of the Bellefontaine Micropolitan Statistical Area, as defined by the United States Census Bureau in 2003...

in 1891. The first mile of concrete pavement in the United States was on Woodward Avenue in Detroit, Michigan

Detroit, Michigan

Detroit is the major city among the primary cultural, financial, and transportation centers in the Metro Detroit area, a region of 5.2 million people. As the seat of Wayne County, the city of Detroit is the largest city in the U.S. state of Michigan and serves as a major port on the Detroit River...

in 1909.

Composite surfaces

Composite surfaces combine Portland cement concrete and asphalt. They are usually used to rehabilitate existing roadways rather than in new construction.

Asphalt overlays are sometimes laid over distressed concrete to restore a smooth wearing surface. A disadvantage of this method is that movement in the joints between the underlying concrete slabs, whether from thermal expansion and contraction, or from deflection of the concrete slabs from truck axle loads, usually cause cracks, called reflective cracks in the asphalt.

Whitetopping

Whitetopping

Whitetopping is the covering of an existing asphalt pavement with a layer of Portland cement concrete. Whitetopping is divided into types depending on the thickness of the concrete layer and whether the layer is bonded to the asphalt substrate. Unbonded whitetopping, also called conventional...

uses Portland cement concrete to resurface a distressed asphalt road.

Recycling

Distressed road materials can be reused when rehabilitating a roadway. The existing pavement is ground or broken up into small pieces. It can then be transported to an asphalt or concrete plant and incorporated into new pavement, or recycled in place to form the base or subbase for new pavement. Some methods used include:

In-place recycling

Rubblizing of concrete pavement. Existing concrete pavement is broken into gravel-sized particles. Any steel reinforcing is removed, then the remaining gravel-sized particles are compacted and overlaid with asphalt pavement.
Cold in-place recycling. Bituminous pavement is ground or milled into small particles. The asphalt millings are blended with a small amount of asphalt emulsion, paved and compacted, allowed to cure for seven to ten days, then overlaid with asphalt.
Hot in-place recycling. Bituminous pavement is heated to 250 to 300°F (120 to 150°C), milled, combined with a rejuvenating agent or virgin asphalt binder, and compacted. It may then be overlaid with a new asphalt overlay. This process only recycles the top two inches (50 mm) or less, so it can be used to correct rutting, polishing or other surface defects. It is not a good procedure for roads with structural failures. It also generates high heat and vapor emissions, and may not be a good candidate for built-up areas.
Full depth reclamation
Full depth recycling
Full depth recycling or full depth reclamation , is a process that rebuilds worn out asphalt pavements by recycling the existing roadway.Old asphalt and base materials are pulverized using a specialized machine called a reclaimer...

(FDR) is a process which pulverizes the full thickness of the asphalt pavement and some of the underlying material to provide a uniform blend of material. A binding agent may be mixed in to form a base course for the new pavement, or it may be left unbound to form a subbase course. Common binding agents include asphalt emulsion, fly ash, Portland cement or calcium chloride. It can also be mixed with aggregate
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...

, recycled asphalt millings, or crushed Portland cement to improve the gradation
Soil gradation
Soil gradation is a classification of a coarse-grained soil that ranks the soil based on the different particle sizes contained in the soil. Soil gradation is an important aspect of soil mechanics and geotechnical engineering because it is an indicator of other engineering properties such as...

of the material. FDR can provide a design life cycle of 30 years with proper lab testing and field verification.

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

Emulsion

An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...

or cut-back asphalt cement. The aggregate is then embedded into the asphalt by rolling it, typically with a rubber-tired roller

Road roller

A road roller is a compactor type engineering vehicle used to compact soil, gravel, concrete, or asphalt in the construction of roads and foundations, similar rollers are used also at landfills or in agriculture.In some parts of the world, road rollers are still known colloquially as steam...

. BSTs of this type are described by a wide variety of regional terms including "chip seal"

Chipseal

Chip seal is a pavement surface treatment that combines a layer of asphalt with a layer of fine aggregate. In the United States, chip seals are typically used on rural roads carrying lower traffic volumes, and the process is often referred to as "asphaltic surface treatment"...

, "tar and chip", "oil and stone", "seal coat", "sprayed seal" or "surface dressing".

BST is used on hundreds of miles of the Alaska Highway

Alaska Highway

The Alaska Highway was constructed during World War II for the purpose of connecting the contiguous U.S. to Alaska through Canada. It begins at the junction with several Canadian highways in Dawson Creek, British Columbia and runs to Delta Junction, Alaska, via Whitehorse, Yukon...

and other similar roadways in Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

, the Yukon Territory, and northern British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

. The ease of application of BST is one reason for its popularity, but another is its flexibility, which is important when roadways are laid down over unstable terrain that thaws and softens in the spring.

Other types of 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.

Thin membrane surface

A thin membrane surface (TMS) is an oil

Oil

An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

treated aggregate

Construction Aggregate

Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...

which is laid down upon a gravel road

Gravel road

A gravel road is a type of unpaved road surfaced with gravel that has been brought to the site from a quarry or stream bed. They are common in less-developed nations, and also in the rural areas of developed nations such as Canada and the United States. In New Zealand, they are known as 'metal roads'...

bed producing a dust free road. A TMS road reduces mud problems and provides stone free roads for local residents where loaded truck traffic is negligible. The TMS layer adds no significant structural strength, and so is used on secondary highways with low traffic volume and minimal weight loading. Construction involves minimal subgrade preparation, following by covering with a 50 to 100 mm (2 to 3.9 in) cold mix asphalt

Asphalt

aggregate. The Operation Division of the Ministry of Highways and Infrastructure

Ministry of Highways and Infrastructure (Saskatchewan)

The Ministry of Highways and Infrastructure or Highways and Infrastructure — Government of Saskatchewan Ministry of Highways is divided into the Operations, Policy and Programs, and Corporate Services Divisions and the Communications Branch. The ministry is the employer of over 1,476...

in Saskatchewan

Saskatchewan

Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

has the responsibility of maintaining 6102 kilometres (3,791.6 mi) of thin membrane surface (TMS) highways.

Otta seal

- History : Otta seal is a type of bituminous surface treatment that was developed by the Norwegian Road Research Laboratory . Its name is based off of the location in which it was created in, The Otta Valley...

is a low-cost road surface using a 16 – thick mixture of bitumen and crushed rock.

Granular Surface

A granular surface can be used with a traffic volume where the average annual daily traffic is 1,200 vehicles per day or less. There is some structural strength as the road surface combines a sub base and base and is topped with a double graded seal aggregate with emulsion. Besides the 4929 kilometres (3,062.7 mi) of granular pavements maintained in Saskatchewan, over 90% of New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

roads are unbound granular pavement structures.

Gravel and unsurfaced roads

See also gravel road
Gravel road
A gravel road is a type of unpaved road surfaced with gravel that has been brought to the site from a quarry or stream bed. They are common in less-developed nations, and also in the rural areas of developed nations such as Canada and the United States. In New Zealand, they are known as 'metal roads'...

and dirt road
Dirt road
Dirt road is a common term for an unpaved road made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Dirt roads are suitable for vehicles; a narrower path for pedestrians, animals, and possibly small vehicles would be called a...

Many low-volume roads are not paved or treated, and instead are surfaced with gravel. Dirt road

Dirt road

Dirt road is a common term for an unpaved road made from the native material of the land surface through which it passes, known to highway engineers as subgrade material. Dirt roads are suitable for vehicles; a narrower path for pedestrians, animals, and possibly small vehicles would be called a...

s are roads where traffic runs on the soil native to the location. The traffic volume that unsurfaced roads can carry varies on traffic, soil and weather conditions.

The decision whether to pave a road or not often hinges on traffic volume. It has been found that maintenance costs for gravel roads often exceed the maintenance costs for paved or surface treated roads when traffic volumes exceed 200 vehicles per day.

Some communities are finding it makes sense to convert their low volume paved roads to aggregate surfaces.

Other surfaces

Pavers (or paviours), generally in the form of pre-cast concrete blocks, are often used for aesthetic purposes, or sometimes at port

Harbor

A harbor or harbour , or haven, is a place where ships, boats, and barges can seek shelter from stormy weather, or else are stored for future use. Harbors can be natural or artificial...

facilities that see long-duration pavement loading. Pavers are rarely used in areas that see high-speed vehicle traffic.

Brick

Brick

A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

, cobblestone

Cobblestone

, sett

Sett (paving)

, and wood

Wood

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

plank pavements were once common in urban area

Urban area

An urban area is characterized by higher population density and vast human features in comparison to areas surrounding it. Urban areas may be cities, towns or conurbations, but the term is not commonly extended to rural settlements such as villages and hamlets.Urban areas are created and further...

s throughout the world, but fell out of fashion in most countries, due to the high cost of labor required to lay and maintain them, and are typically only kept for historical or aesthetic reasons. In some countries, however, they are still common in local streets. Likewise, macadam

Macadam

Macadam is a type of road construction pioneered by the Scotsman John Loudon McAdam in around 1820. The method simplified what had been considered state-of-the-art at that point...

and tarmac

Tarmac

Tarmac is a type of road surface. Tarmac refers to a material patented by Edgar Purnell Hooley in 1901...

pavements can still sometimes be found buried underneath asphalt concrete or Portland cement concrete pavements, but are rarely constructed today.

Acoustical implications

Roadway surfacing choices are known to affect the intensity and spectrum of sound emanating from the tire/surface interaction. Initial applications of this knowledge occurred in the early 1970s. Roadway surface types contribute differential noise effects of up to four dB

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

, with chip seal type and grooved roads being the loudest and concrete surfaces without spacers being the quietest. Asphalt

Asphalt

ic surfaces perform intermediately relative to concrete and chip seal. These phenomena are, of course, highly influenced by vehicle speed. Rubberized asphalt

Rubberized asphalt

has been shown to give a very significant 7–12 decibel reduction in road noise when compared to conventional asphalt applications.

Surface deterioration

As pavement systems primarily fail due to fatigue

Fatigue (material)

(in a manner similar to metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s), the damage done to pavement increases with the fourth power of the axle load of the vehicles traveling on it. According to the AASHO Road Test

AASHO Road Test

The AASHO Road Test was a series of experiments carried out by the American Association of State Highway and Transportation Officials to determine how traffic contributed to the deterioration of highway pavements...

, heavily loaded truck

Truck

A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

s can do more than 10,000 times the damage done by a normal passenger car. Tax

Tax

To tax is to impose a financial charge or other levy upon a taxpayer by a state or the functional equivalent of a state such that failure to pay is punishable by law. Taxes are also imposed by many subnational entities...

rates for trucks are higher than those for cars in most countries for this reason, though they are not levied in proportion to the damage done. Passenger cars are considered to have no practical effect on a pavement's service life, from a fatigue perspective.

Other failure modes include aging and surface abrasion. As years go by, the binder in a bituminous wearing course gets stiffer and less flexible. When it gets "old" enough, the surface will start losing aggregates, and macrotexture

Macrotexture

Macrotexture is a family of wave-shaped road surface characteristics. While vehicle suspension deflection and dynamic tyre loads are affected by longer waves , road texture affects the interaction between the road surface and the tyre footprint. Macrotexture has wavelengths from 0.5 mm up to...

depth increases dramatically. If no maintenance action is done quickly on the wearing course potholing will take place. If the road is still structurally sound, a bituminous surface treatment, such as a chipseal

Chipseal

or surface dressing can prolong the life of the road at low cost. In areas with cold climate, studded tires may be allowed on passenger cars. In Sweden and Finland, studded passenger car tires account for a very large share of pavement rutting.

Several design methods have been developed to determine the thickness and composition of road surfaces required to carry predicted traffic loads for a given period of time. Pavement design methods are continuously evolving. Among these are the Shell Pavement design

Shell Pavement design

The Shell pavement design method is used in many countries for the design of new asphalt roads.In structural road design, the main considerations consist of soil parameters, parameters for the other road foundation materials, and the expected number of times a standard load will pass over. The...

method, and the American Association of State Highway and Transportation Officials

American Association of State Highway and Transportation Officials

AASHTO, the American Association of State Highway and Transportation Officials, is a standards setting body which publishes specifications, test protocols and guidelines which are used in highway design and construction throughout the United States...

(AASHTO) 1993 "Guide for Design of Pavement Structures". A new mechanistic-empirical design guide has been under development by NCHRP (Called Superpave Technology) since 1998. A new design guide called Mechanistic Empirical Pavement Design Guide (MEPDG) was developed and is about to be adopted by AASHTO.

The physical properties of a stretch of pavement can be tested using a falling weight deflectometer

Falling weight deflectometer

A falling weight deflectometer, FWD, is a testing device used by civil engineers to evaluate the physical properties of pavement. FWD data is primary used to estimate pavement structural capacity for 1) overlay design and 2) to determine if a pavement is being overloaded. Use includes highways,...

.

Further research by University College London

University College London

University College London is a public research university located in London, United Kingdom and the oldest and largest constituent college of the federal University of London...

into pavements has led to the development of an indoor, 80-sq-metre artificial pavement at a research centre called Pedestrian Accessibility and Movement Environment Laboratory

Pedestrian Accessibility and Movement Environment Laboratory

The Pedestrian Accessibility and Movement Environment Laboratory is an indoor 80 sq metre artificial pavement at a research center at University College London. It is used to simulate everyday scenarios, from different pavement users to varying pavement conditions...

(PAMELA). It is used to simulate everyday scenarios, from different pavement users to varying pavement conditions. There also exists a research facility near Auburn University

Auburn University

Auburn University is a public university located in Auburn, Alabama, United States. With more than 25,000 students and 1,200 faculty members, it is one of the largest universities in the state. Auburn was chartered on February 7, 1856, as the East Alabama Male College, a private liberal arts...

, the NCAT Pavement Test Track

NCAT Pavement Test Track

The NCAT Pavement Test Track is an oval-shaped track in Lee County, Alabama, long, used for testing experimental asphalt pavements. It is managed by the National Center for Asphalt Technology , the largest asphalt research center in the western hemisphere and a cooperative venture between the...

, that is used to test experimental asphalt pavements for durability.

In addition to repair costs, the condition of a road surface has economic effects for road users. Rolling resistance

Rolling resistance

Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface, in steady velocity straight line motion. It is caused mainly by the deformation of the object, the deformation of the surface, or...

increases on rough pavement, as does wear and tear of vehicle components. It has been estimated that poor road surfaces cost the average US driver $324 per year in vehicle repairs, or a total of $67 billion. Also, it has been estimated that small improvements in road surface conditions can decrease fuel consumption between 1.8 and 4.7%.

External links

"Pavements" website of the US Department of Transportation's Federal Highway Administration

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