BITUMEN SPECIFICATIONS AND CHARACTERISTICS In order to specify the components of Bitumen different methods are used and in most of these methods Bitumen solved in sulfur carbon is divided in three major parts:
• Carbon: the part which is insoluble in tetra chloride carbon
• Asphaltine: insoluble part in solvents such as light aliphatic hydrocarbons such as ether
• Malton: solved part in light aliphatic hydrocarbons such as heptane. Maltons are divided into two minor groups, resins and oils, and while resin materials are brown and semi hard, they provide Bitumen flexibility and adhesiveness. Heavy oils make Bitumen soft, the more its amount the softer Bitumen will be.
The kind and the percentage of the mentioned materials depend completely on the oil or mineral basis of the Bitumen and the percentage of these materials can be changed with the help of their oxidation process.
GENERAL CLASSIFICATION OF BITUMEN IS PRESENTED IN THE FOLLOWING TABLE:
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Natural Asphalt Petroleum Coal tar Wood tar
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Gilsonite Lake Asphalt Rock Bitumen Road Tar Asphalt
Petroleum bitumen is known by different names throughout the world. For example, the term “BITUMEN” is used as synonymous with the term “ASPHALT”, or “ASPHALT BINDER” used in North America. In lots of countries, the term “ASPHALT” is used to describe mixtures of bitumen with mineral materials. Coal derived products such as coal tar or coal-tar pitches are very different from bitumen. These are manufactured by the high-temperature pyrolysis (>800°C) of bituminous coals and differ from bitumen substantially in composition, physical characteristics, and potential health risks. Petroleum pitches, which are often highly aromatic residuums, produced by thermal cracking, coking or oxidation from selected petroleum fractions are also significantly different from bitumen.
Bitumen also should not be confused with natural or lake asphalt such as Trinidad Lake Asphalt, Gilsonite, rock asphalt and Selenice that are sometimes used as additives in end use applications. These products are unrefined and not produced by refining of crude oils. They often contain a high proportion of mineral matter (up to 37% by weight) and light components, leading to a higher loss of mass when heated.
In the world more than seven kinds of BITUMEN are produced which depends on climate and region conditions, but in Iran BITUMEN production is limited to two kinds due to high expenses. At present BITUMEN 85/ 100 with high penetration and BITUMEN 60 /70 with less penetration is produced. According to this classification in cold places BITUMEN 85/100 and in warm places BITUMEN 60/70 BITUMEN are used.
The BITUMEN flexibility makes asphalts lose their resistance in cold and hot climates. In desert regions, cold nights make asphalt contract and the warmth of its days separates its components and the asphalt breaks.
In many countries in order to increase the BITUMEN flexibility, polymer is added to it. In this way they increase the flexibility of the BITUMEN. The production of multi grit BITUMEN in developed countries isn’t an extraordinary or hard affair. They know that for five year BITUMEN shouldn’t be repaired or dug, and they increase the life of asphalt to 20 years in this way, and never ignore its repair and maintenance.
Besides BITUMEN type, roadbed and preparation of asphalt bed is also important. In making asphalt, 4 to 5 percent BITUMEN and 96 percent other materials are used; many of the faults lie on drainage, improper roadbed, neglecting region traffic volume and uncoordinated fulfillment of the project. The method of fulfillment in asphalt section is not according to established principles, and in order to gain more benefit most of the norms are disregarded.