bitumen or ashpalt
what is bitumen or asphalt?
Bitumen, also referred to as asphalt in some regions, is a sticky, black, and highly viscous liquid or semi-solid petroleum by-product. It can be naturally occurring or refined, and it is classed as a type of pitch. Historically, the term “asphaltum” was also used. In road construction, which accounts for about 70% of its usage, bitumen serves as a binder mixed with aggregate to produce asphalt concrete. Other significant applications include waterproofing products, such as roofing felt and materials for sealing flat roofs.
Terminology and Global Usage
Bitumen is composed of four primary classes of compounds: Naphthene Aromatics: Partially hydrogenated polycyclic aromatic compounds. Polar Aromatics: High molecular weight phenols and carboxylic acids, formed through partial oxidation. Saturated Hydrocarbons: The proportion of saturated compounds correlates with the softening point of the material. Asphaltenes: High molecular weight phenols and heterocyclic compounds, often dispersed within the material. The majority of bitumen comprises naphthene and polar aromatics. Natural bitumen contains organosulfur compounds, with sulfur content reaching up to 4%, as well as trace amounts of nickel and vanadium. It is modeled as a colloid, with asphaltenes as the dispersed phase within a continuous phase of maltenes.
Distinction from Coal Tar
Bitumen is often mistaken for coal tar due to its similar appearance. However, coal tar is derived from the destructive distillation of coal, while bitumen is a petroleum-based product. Historically, coal tar was widely used in road construction when town gas production provided it as a by-product. Over time, asphalt replaced coal tar, especially after the rise of natural gas in the 1970s. The term "tarmac" originated from coal tar-based roads but is now used broadly for road materials, including those made with asphalt.
Modern Applications and Significance
Bitumen remains a critical component in infrastructure, particularly in road construction and waterproofing. Its versatility and availability as a by-product of crude oil refining ensure its continued use in various industrial and construction applications. Although often confused with other substances like coal tar or pitch, bitumen's unique properties and chemical composition distinguish it as an essential material in modern engineering.