Road surface
A road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, macadam, hoggin, cobblestone and granite setts were extensively used, but these have mostly been replaced by asphalt or concrete laid on a compacted base course. Asphalt mixtures have been used in pavement construction since the beginning of the 20th century and are of two types: metalled and unmetalled roads. Metalled roadways are made to sustain vehicular load and so are usually made on frequently used roads. Unmetalled roads, also known as gravel roads or dirt roads, are rough and can sustain less weight. Road surfaces are frequently marked to guide traffic.
Today, permeable paving methods are beginning to be used for low-impact roadways and walkways to prevent flooding. Pavements are crucial to countries such as United States and Canada, which heavily depend on road transportation. Therefore, research projects such as Long-Term Pavement Performance have been launched to optimize the life cycle of different road surfaces.
Pavement, in construction, is an outdoor floor or superficial surface covering. Paving materials include asphalt, concrete, stones such as flagstone, cobblestone, and setts, artificial stone, bricks, tiles, and sometimes wood. In landscape architecture, pavements are part of the hardscape and are used on sidewalks, road surfaces, patios, and courtyards, among others.
The term pavement comes from Latin , meaning a floor beaten or rammed down, through Old French pavement. The meaning of a beaten-down floor was obsolete before the word entered English.
Pavement, in the form of beaten gravel, dates back before the emergence of anatomically modern humans. Pavement laid in patterns like mosaics were commonly used by the Romans.
The bearing capacity and service life of a pavement can be raised significantly by arranging good drainage by an open ditch or covered drains to reduce moisture content in the pavements subbase and subgrade.
Development
Wheeled transport created the need for better roads. Generally, natural materials cannot be both soft enough to form well-graded surfaces and strong enough to bear wheeled vehicles, especially when wet, and stay intact. In urban areas it was worthwhile to build stone-paved streets and, in fact, the first paved streets appear to have been built in Ur in 4000 BC. Corduroy roads were built in Glastonbury, England, in 3300 BC, and brick-paved roads were built in the Indus Valley Civilisation on the Indian subcontinent from around the same time. Improvements in metallurgy meant that by 2000 BC stone-cutting tools were generally available in the Middle East and Greece allowing local streets to be paved. Notably, in about 2000 BC, the Minoans built a 50 km paved road from Knossos in northern Crete through the mountains to Gortyn and Lebena, a port on the south coast of the island, which had side drains, a 200 mm thick pavement of sandstone blocks bound with clay-gypsum mortar, covered by a layer of basaltic flagstones and had separate shoulders. This road could be considered superior to any Roman road. Roman roads varied from simple corduroy roads to paved roads using deep roadbeds of tamped rubble as an underlying layer to ensure that they kept dry, as the water would flow out from between the stones and fragments of rubble, instead of becoming mud in clay soils.Although there were attempts to rediscover Roman methods, there was little useful innovation in road building before the 18th century. The first professional road builder to emerge during the Industrial Revolution was John Metcalf, who constructed about of turnpike road, mainly in the north of England, from 1765, when Parliament passed an act authorising the creation of turnpike trusts to build toll funded roads in the Knaresborough area.
Pierre-Marie-Jérôme Trésaguet is widely credited with establishing the first scientific approach to road building in France at the same time as Metcalf. He wrote a memorandum on his method in 1775, which became general practice in France. It involved a layer of large rocks, covered by a layer of smaller gravel.
By the late 18th and early 19th centuries, new methods of highway construction had been pioneered by the work of two British engineers: Thomas Telford and John Loudon McAdam. Telford's method of road building involved the digging of a large trench in which a foundation of heavy rock was set. He designed his roads so that they sloped downwards from the centre, allowing drainage to take place, a major improvement on the work of Trésaguet. The surface of his roads consisted of broken stone. McAdam developed an inexpensive paving material of soil and stone aggregate. His road building method was simpler than Telford's, yet more effective at protecting roadways: he discovered that massive foundations of rock upon rock were unnecessary, and asserted that native soil alone would support the road and traffic upon it, as long as it was covered by a road crust that would protect the soil underneath from water and wear. Size of stones was central to McAdam's road building theory. The lower road thickness was restricted to stones no larger than.
Modern tarmac was patented by British civil engineer Edgar Purnell Hooley, who noticed that spilled tar on the roadway kept the dust down and created a smooth surface. He took out a patent in 1901 for tarmac. Hooley's 1901 patent for tarmac involved mechanically mixing tar and aggregate prior to lay-down, and then compacting the mixture with a steamroller. The tar was modified by adding small amounts of Portland cement, resin, and pitch.
Asphalt
Asphalt, sometimes called flexible pavement since its viscosity causes minute deformations as it distributes loads, has been widely used since the 1920s. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue 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. 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 may be required. Polypropylene and polyester geosynthetics are also used for this purpose, and in some northern countries a layer of polystyrene boards are 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, warm mix, half warm mix, or cold mix. Hot mix asphalt is applied at temperatures over with a free floating screed. Warm mix asphalt is applied at temperatures of, 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 greater than 1,200 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 pollution to soil and groundwater or waterways.In the mid-1960s, rubberized asphalt was used for the first time, mixing crumb rubber from used tires with asphalt. While a potential use for tires that would otherwise fill landfills and present a fire hazard, rubberized asphalt has shown greater incidence of wear in freeze-thaw cycles in temperate zones because of the non-homogeneous expansion and contraction with non-rubber components. The application of rubberized asphalt is more temperature-sensitive and in many locations can only be applied at certain times of the year. Study results of the long-term acoustic benefits of rubberized asphalt are inconclusive. Initial application of rubberized asphalt may provide a reduction of 3–5 decibels in tire-pavement-source noise emissions; however, this translates to only 1–3 dB in total traffic-noise reduction when combined with the other components of traffic noise. Compared to traditional passive attenuating measures, rubberized asphalt provides shorter-lasting and lesser acoustic benefits at typically much greater expense.
Concrete
Concrete surfaces are created using a concrete mix of Portland cement, coarse aggregate, sand, and water. In virtually all modern mixes there will also be various admixtures added to increase workability, reduce the required amount of water, mitigate harmful chemical reactions, and for other beneficial purposes. In many cases there will also be Portland cement substitutes added, such as fly ash. This can reduce the cost of the concrete and improve its physical properties. The material is applied in a freshly mixed slurry and worked mechanically to compact the interior and force some of the 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.Concrete surfaces have been classified into three common types: jointed plain, jointed reinforced and continuously reinforced. The one item that distinguishes each type is the jointing system used to control crack development.
One of the major advantages of concrete pavements is they are typically stronger and more durable than asphalt roadways. The surface can be grooved to provide a durable skid-resistant surface. Concrete roads are more economical to drive in terms of fuel consumption, they reflect light better, and they last significantly longer than other paving surfaces; but they have a much smaller market share than other paving solutions. Modern paving methods and design methods have changed the economics of concrete paving so that a well-designed and placed concrete pavement will be cheaper in initial cost and significantly cheaper over the life cycle. Another important advantage is that waterproof concrete can be used, which eliminates the need to place storm drains next to the road and reduces the need for a slightly sloped driveway to drain rainwater. Avoiding rainwater discharge by using runoff also means less electricity is needed and rainwater is not polluted because it no longer mixes with polluted water. Rather, it is immediately absorbed by the earth. A previous disadvantage was that they had a higher initial cost and could be more time-consuming to construct. This cost can typically be offset through the long life cycle of the pavement and the higher cost of bitumen. Concrete pavement can be maintained over time utilizing a series of methods known as concrete pavement restoration which include diamond grinding, dowel bar retrofits, joint and crack sealing, and cross-stitching. Diamond grinding is also useful in reducing noise and restoring skid resistance in older concrete pavement.
The first street in the United States to be paved with concrete was Court Avenue in Bellefontaine, Ohio, in 1893. The first mile of concrete pavement in the United States was on Woodward Avenue in Detroit, Michigan, in 1909. Following these pioneering uses, the Lincoln Highway Association, established in October 1913 to oversee the creation of one of the United States' earliest east-west transcontinental highways for the automobile, began to establish "seedling miles" of specifically concrete-paved roadbed in various places in the American Midwest, starting in 1914 west of Malta, Illinois, while using concrete with the specified concrete "ideal section" for the Lincoln Highway in Lake County, Indiana, during 1922 and 1923.
Concrete roadways may produce more noise than asphalt from tire noise on cracks and expansion joints. A concrete pavement composed of multiple slabs of uniform size will produce a periodic sound and vibration in each vehicle as its tires pass over each expansion joint. These monotonous repeated sounds and vibrations can cause a fatiguing or hypnotic effect upon the driver over the course of a long journey.