Asphalt course

The asphalter, in the list of professions in Italy, is that worker assigned to asphalting a road or waterproofing work with the aid of the vibratory finishing machine or laying bitumen conglomerates for waterproofing operations. Asphalt is a natural mixture of solid and semi-fluid hydrocarbons, mostly made up of bitumen; solid and dark in color it is found as an impregnator of limestone rocks, the whole is called asphaltic rock; bitumen proper is extracted from the asphalt. Bitumen is the residue left by the evaporation of oil which, rising from the underground reservoir in which it had accumulated, is subject to chemical and bacteriological degradation on the surface. Together with the tar, the bitumen and the tar pitch, it belongs to the category of bituminous materials. Currently, for the construction of the surface layers of the road pavement, the term "asphalt" refers to the artificial bituminous conglomerate. In an asphalt the content of calcium carbonate generally varies between 50% and 90%, while that of natural bitumen is between 7% and 15%; the remainder is made up of other mineral materials and volatile substances. Since ancient times, an oil has been extracted by distillation used mainly to waterproof and protect the wood from parasites, as a lubricant and even as a human and animal medicine. In order to use the asphalt, the asphalt blocks (a combination of purified bitumen and asphalt flour) had to be melted in boilers with the addition of other bitumen; then sand and gravel of variable thicknesses and quantities were added according to the work to be carried out. When the mass was boiling and semi-fluid, it was poured onto the area to be covered, stretched and then compressed. Sometimes it is said that the sidewalk or the road are tarred but this is not correct: tar is a thick liquid that is obtained from the distillation of wood, lignite, bones, hard coal, etc., and is sometimes used in place of asphalt but does not meet the requirements.