Bitumen | Asphalt
Bitumen | Asphalt
28/2/23, 10:00 pm
Bitumen, also known as asphalt, is a dense, sticky substance derived from petroleum. Predominantly utilized (70%) in road construction, it serves as the binding agent when mixed with aggregate to form asphalt concrete. Additionally, it finds application in bituminous waterproofing products like roofing felt and flat roof sealants. Historically, "asphaltum" was a term used interchangeably with "bitumen" before the 20th century. In American English, "asphalt" or "asphalt cement" denotes the refined residue from specific crude oil distillation processes, while internationally, it's often referred to as "bitumen." Geologists globally prefer "bitumen" for the naturally occurring variety. Informally, various asphalt forms are colloquially termed "tar," as seen in the La Brea Tar Pits.
ASPHALT comprises four main classes of compounds:
NAPHTHENE AROMATICS
Partially hydrogenated polycyclic aromatic compounds, such as naphthalene.
POLAR AROMATICS
High molecular weight phenols and carboxylic acids resulting from partial oxidation.
SATURATED HYDROCARBONS
The softening point of asphalt correlates with the percentage of saturated compounds it contains.
ASPHALTENES
High molecular weight phenols and heterocyclic compounds.
Naphthene aromatics and polar aromatics typically constitute the majority of asphalt's composition.
ADDITIONAL PROPERITIES
Asphalt often contains organosulfur compounds, leading to a sulfur content of up to 4%.
Nickel and vanadium are present at <10 parts per million, typical of petroleum.
PHYSICAL CHARACTERISTICS
- Soluble in carbon disulfide
Asphalt is commonly modeled as a colloid, with Asphaltenes as the dispersed phase and Maltenes as the continuous phase. It is almost impossible to separate and identify all the different molecules of asphalt, because the number of molecules with different chemical structures is extremely large.
- Distinction from Coal Tar
Coal tar, visually similar to asphalt, is a thermoplastic material produced by the destructive distillation of coal.
Historically, coal tar was extensively used as a road binder, leading to the term "Tarmac."
Since the 1970s, asphalt has largely replaced coal tar in road applications due to changes in gas production.
Examples of confusion include the La Brea Tar Pits and Canadian oil sands, which contain natural bitumen, not tar.
INFORMAL TERMINOLOGY
"Pitch" is sometimes informally used to refer to asphalt.