Usuario:NACLE/Taller3

Historia de los firmes de carreteras

Old Roman road, leading from Jerusalem to Beit Gubrin, adjacent to regional hwy 375 in Israel

Different layers of road including asphalt layer. The total thickness of a pavement can be measured using granular base equivalency

El transporte sobre ruedas creó la necesidad de mejores vías. Generalmente los materiales naturales no podían ser a la vez lo suficientemente finos para formar superficies niveladas y fuertes para soportar los vehículos sobre ruedas, especialmente cuando se humedecían, y permanecer intactos. El primer lugar donde mereció la pena pavimentar los caminos fue dentro de las áreas urbanas donde empezaron a crearse calles pavimentadas. Se tiene constancia que las primeras calles pavimentadas fueron construidas en Ur 4000 años antes de Cristo. Las calles de Corduroy construidas en Glastonbury, Inglaterra datan del 3300 a.C.​. También hay constancia de calles pavimentadas por las civilizaciones del valle del Indo y en el subcontinente indio por la misma fecha. Las innovaciones en la metalurgía permitieron por el 2000 a.C. crear herramientas para cortar la piedra, lo que supuso una mejora en la pavimentación de calles en Oriente Medio y Grecia.​ Es destacable la vía realizada por los minoicos de 50 kilómetros desde Knossos en el norte de Creta, cruza las montañas y llegaba hasta Gortyn y Lebena, un puerto en la costa sur de la isla. El camino tenía cunetas de drenaje laterales, un pavimento de 200 mm de espesor de bloques de arenisca, rematado en las juntas con un mortero combinado de arcilla-yeso, cubierto además con una capa de laja basáltica y con arcenes reforzados. La via podía ser considerada superior a cualquier calzada romana posterior.​ Las calzadas romanas variaban desde simples caminos de tierra suelta hasta caminos pavimentados que utilizaban profundas calzadas de escombros apisonados como capa subyacente para asegurar que se mantuvieran secas, ya que el agua fluía de entre las piedras y los fragmentos de escombros, en lugar de convertirse en barro en los suelos de arcilla.

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 began to be 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 Civilization 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 North 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.

In the medieval Islamic world, many roads were built throughout the Arab Empire. The most sophisticated roads were those of Baghdad, Iraq, which were paved with tar in the 8th century. Tar was derived from petroleum accessed from oil fields in the region, through the chemical process of destructive distillation.​

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 180 millas (289,7 km) of turnpike road, mainly in the north of England, from 1765, when Parliament passed an act authorising the creation of turnpike trusts to build new 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 also 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 (known as macadam). 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 200 milímetros (7,9 plg) road thickness was restricted to stones no larger than 75 milímetros (3 plg).

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.​