Road surface

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past, gravel road surfaces, macadam, hoggin, cobblestone and granite setts were extensively used, but these have mostly been replaced by asphalt or concrete laid on a compacted base course.Therefore, research projects such as Long-Term Pavement Performance have been launched to optimize the life cycle of different road surfaces.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.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.[9] 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.Pierre-Marie-Jérôme Trésaguet is widely credited with establishing the first scientific approach to road building in France at the same time as Metcalf.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.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.[13] 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 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.Polypropylene and polyester geosynthetics are also used for this purpose,[15] and in some northern countries a layer of polystyrene boards are used to delay and minimize frost penetration into the subgrade.Warm mix asphalt is applied at temperatures of 95–120 °C (200–250 °F), resulting in reduced energy usage and emissions of volatile organic compounds.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.[20] 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.Compared to traditional passive attenuating measures (e.g., noise walls and earth berms), rubberized asphalt provides shorter-lasting and lesser acoustic benefits at typically much greater expense.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.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.Bituminous surface treatment (BST) or chipseal is used mainly on low-traffic roads, but also as a sealing coat to rejuvenate an asphalt concrete pavement.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.The TMS layer adds no significant structural strength, and so is used on secondary highways with low traffic volume and minimal weight loading.[52] Pavers (or paviours), 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, cobblestone, sett, wood plank, and wood block pavements such as Nicolson pavement, were once common in urban areas 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.From 1998 through 2007, more than 41,000 km of city streets were converted to local access roads with a speed limit of 30 km/h, for the purpose of traffic calming.A similar method is to use rubber imprinting tools to press over a thin layer of cement to create decorative concrete.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.