Types, resources and usages of bitumen
Oil bitumen is obtained from distillation of petroleum in refinery. In the distillation column, superheat steam flow is passed bottom-up. As a result, steam flow causes division of volatiles and they leave the top of the tower and devise in other columns. Non-volatile substances which much of them are bitumen exit from the end of the column. The remaining or residual of vacuum tower is used as source to make 20 types of different grades of bitumen. Slit tower’s viscosity depends on type of petroleum, temperature and pressure of vacuum tower in the process. Also depends on obtained bitumen, can design the column in a way to obtain bitumen in variety of grades. Although the bitumen can be used directly from the vacuum tower, but in some cases, the physical properties of the bitumen is not appropriate and reforms should be carried out on which its main reform is blowing air on bitumen which will be described below.
For the first time, blown bitumen obtained from the reaction of hot bitumen to oxygen in 1890 and many researches about the process variables, design and control of chemical reactions being followed. Aeration of bitumen is a process which hot liquid bitumen is connected to air. Because of the contact, bitumen being hardened and its heat sensitivity decreases. Blown bitumen is used in construction of insulation layers, asphalt molds, sealing of roofs, roads asphalt, etc. that each one has ASTM special standards. Bitumen aeration is the result of dehydrogenation, polymerization and oxidation processes. Naming blown bitumen, from left to right, after R word first softening point then penetration comes.
In some road operations, because of technical and economic problems, there is no possibility to use pure bitumen which is completely solid. As a result, cutback bitumen is used. Cutback bitumen obtained from mixture of pure bitumen and petroleum oils. Type and quality of cutback bitumen depends on pure bitumen, type and quantity of petroleum oils. There is a direct relationship between the quantity of oil solvents and viscosity. Usually, the using percentage of solvents in Iran’s cutback bitumen is between 10 to 50 percent. Lack of heating instrument of bitumen, disintegration of bitumen in high temperatures, cooling of bitumen while working, inability of bitumen to penetrate to porous minerals, need for worker safety, danger of fire and wasting time causes to use cutback bitumen instead of other types, in some cases. To stick bitumen to wet materials, consumable cutback bitumen should have appropriate acidity. Cutback bitumen used for making roads in surface or columnar coating, asphalt surface, industrial cold asphalt or mixed, in place of operation.
Emulsion is a mixture of two immiscible liquid phases which the internal phase is dispersed as droplets within the outer phase. The emulsion particle diameter is between 1/0 to 5 micron but particle diameter is larger than real cutback and colloidal states. Without using substances called emulsifier, the suspension would not be stable and the two immiscible liquids (e.g. oil and water) will quickly separated into two distinct phases. This is due to the increased contact area between two phases, resulting in increased interfacial energy level, the system has an unstable mode and by separation of the two phases, the system reaches a stable state. Bitumen emulsions used in making roads for preparation of cold asphalt, surface asphalt, one coat, etc. in addition, usages such as mulch in sand dune stabilization, protective coatings, and roof insulation are widespread too.