Important Terms from A to Z
Bitumen & Asphalt
According to DIN EN 12597, bitumen is an almost non-volatile, sticky, and sealing oil-based product that is extremely viscous or nearly solid at ambient temperatures. It has excellent sealing properties.
Chemically, bitumen is a mixture of various hydrocarbons. More specifically, it is a system consisting of an oily base material (maltene), in which the dark asphaltenes, which have a higher molecular mass, are finely distributed. Bitumen should not be confused with tar, which is made from coal and has not been permitted for use as a building material in Germany for a long time.
Bitumen also occurs naturally as natural bitumen, for example at the La Brea Pitch Lake on the island of Trinidad. However, it is usually industrially produced from crude oil as a residue during the vacuum distillation of crude. Bitumen is usually further treated by blowing in air (“air blowing”) to modify its properties. A short amount of air blowing produces bitumen suitable for road construction. A long reaction time produces oxidized bitumen, which is used exclusively for industrial purposes.
Bitumen is not a health hazard or water-polluting. However, bitumen vapors contain carcinogenic polycyclic aromatic hydrocarbons (PAH) that are released at hot finishing. Bitumen is chemically stable against non-oxidizing acids and bases, but reacts violently with oxygen in a fire drill. At high temperatures, it begins to decompose slowly. In water, it is practically insoluble, so it is used to protect sensitive materials and building components against water.
Bitumen’s properties can be systematically adjusted with additives. Mixing it with polymers produces polymer-modified bitumen (PMB), which has better stability at higher temperatures and better fatigue behavior, for example, and is used on surfaces subject to a high degree of wear and tear such as highways and airports.
Bitumen cannot be transported at ambient temperatures and must be heated to over 100°C. For easier processing, fluxing agents (flux oils) are often added to reduce its viscosity.
The main application area of bitumen is asphalt, a mixture of aggregates with bitumen as a binding agent. Industrial bitumen is processed into roofing and sealing membranes, asphalt coatings, and sealants.
Bitumen for road construction is classified by the needle penetration test according to DIN EN 1426. For example, “bitumen 50/70” means that the test needle penetrates to a depth of 5-7 mm. Common varieties are 70/100, 50/70, 30/45 and 20/30. The smaller the numbers, the “harder” the bitumen type.
In 2014, 3.7 million tons of bitumen was produced in Germany. Global consumption is around 100 million tons. Asphalt for roads, airfield runways and paths accounts for approximately 85% of the production, roofs for 10%, and other building materials for 5%. Bitumen consumption is highly cyclical and depends especially on the economic situation in road and building construction.