What is bitumen?
Bitumen is a dense and highly viscous natural hydrocarbon based on petroleum, which is found in oil sands and lakes of the earth.
There is another type of tar, which is a byproduct of coal. More correctly, it is obtained from the distillation of coal tar. In general, bitumen is identified by the United States Geological Survey as an extra-heavy oil that sinks in water with an API density of less than 10, a bitumen viscosity of more than 10,000 centipoise (centipoise = unit of dynamic and kinematic viscosity). fluid).
Bitumen does not flow at the ambient temperature where natural sediments are usually located. In this way, if there is an intention to transfer bitumen through the pipe, it must be heated first. In some cases, to lubricate the bitumen, it is mixed and diluted with lighter oils. The density and viscosity of bitumen is due to its chemical compounds. These compounds include large hydrocarbon molecules such as asphaltene and resins.
The mentioned molecules are present in bitumen in a concentrated form, and next to them there are metallic elements such as nickel and vanadium and inorganic and non-metallic elements such as: nitrogen, oxygen and sulfur, although these elements and compounds due to their polluting properties according to the application The final bitumen should be removed sometimes.
Types of bitumen and its use
A large amount of natural bitumen is used in asphalt paving in road construction and in building roof insulation. However, in a country like Canada, a large amount of extracted bitumen is sent to refineries to convert into a full range of petroleum products, including gasoline. Bitumen is one of the important components in our world and is used in countless industries.
The function of bitumen is insulation, sealing, and it is used as a strong adhesive in road construction. The use of bitumen in the construction of roads, in addition to reducing current costs, does not require special maintenance. At the same time, it increases the life of the roads. According to the grade, properties and different characteristics of bitumen, its classification is divided into different degrees with different applications.
In order to get better acquainted with bitumen and its structure, there is a need to know how this material is produced.
What is bitumen and how is it produced?
Bitumen is an oil-based material and is used to stabilize the place and stick stones and sand. In addition, bitumen is also used to produce asphalt in road construction. A large amount of bitumen available worldwide is produced through the distillation of crude oil.
In a typical refinery process, crude oil is heated by an atmospheric still. As a result of this heat, different components of crude oil are separated from each other according to the molecular weight.
At the end of the distillation process, the heaviest oily part in the lower part of the distillation tower, which is called the bottom of the vacuum, is the primary and main material in the production of refined bitumen.
To process the vacuum bottom, it is transferred to another refinery. In the new refinery, there are various methods for processing the vacuum bottom, including blowing, mixing, combining the vacuum bottom with water or solvents, and modifying it with polymers.
Sulfur tetrachloride and carbon sulfur are bitumen solvents, and by combining each of these materials in bitumen, its impurities remain. In this way, one of the methods to determine the purity of bitumen is to combine it with tetrachloride and carbon sulfur solvents.
Bitumen production
Before getting acquainted with the types of bitumen, it is necessary to explain the difference between bitumen obtained from oil and coal tar:
The difference between oil tar bitumen and coal tar bitumen
Bitumen is a petroleum element; While tar is distilled from coal (Tar), it is obtained from wood or coal. Each of these materials have different properties and applications based on their primary source, and it is not possible to use bitumen instead of tar.
According to the previously mentioned content, in response to the question, what is bitumen? It should be said that bitumen is an organic substance with a complex chemical composition. This material does not have any special formula and it is classified in different ways.
One of these methods is the classification based on the origin of bitumen, which we have listed below for you based on the types of bitumen
Natural bitumen (Gilsonite): The composition of this material is similar to refinery bitumen and it is extracted as a mass from mines. However, its application method is usually in the form of micronized powder. Natural bitumen contains impurities such as: ash, and for this reason, Gilsonite is classified based on the percentage of ash, dimensions and particle size.
Refinery Bitumen: This type of bitumen, which is called bitumen for short, is extracted from crude oil. To classify bitumen in the past, there was no exact method and engineers used to test the hardness and softness of a bitumen by chewing test. Thus, if the tested bitumen was hard enough, the sample was approved.
If different compounds are added to the pure bitumen produced in the refinery; Modified bitumens are obtained for use in various purposes. To obtain modified bitumen, materials such as solvents, polymers, emulsifiers, or other compounds are added to pure bitumen in the refinery. The properties of the final products derived from pure bitumen are different according to the size of the additive and its type.
Finally, modified bitumens are classified by different tests on bitumen. Modified bitumens are classified into the following three categories:
Cutback bitumen
Polymer modified bitumen
Emulsion bitumen
In addition to the categories in the above section, there is another category that does not belong to any of the mentioned groups. This group includes the following:
oxidized bitumen
Crystal tar
Getting to know more about the types of modified bitumen and its uses
What is cut-back bitumen?
Cut-back bitumen is a modification of pure refinery bitumen that has a low viscosity. To produce this type of bitumen, refinery bitumen is combined with a certain amount of organic solvents, which include diesel, naphtha, diesel oil, and fuel oil.
The mentioned solvents have a low boiling point and evaporate very quickly. In this way, when Cutback bitumen is placed on the surface, the solvent in it evaporates and bitumen remains. This type of bitumen is obtained in three different cooking models, which include slow, medium and fast cooking.
The uses of this bitumen include the following:
Industries that need bitumen with low viscosity
When making asphalt without heating bitumen
What is emulsion bitumen?
Emulsified bitumen is produced by mixing a certain amount of water in pure bitumen. In order to dissolve bitumen in water, they use a suitable emulsifier. Emulsion bitumen is a type of bitumen with low viscosity and in liquid form, which is used for road maintenance and repair.
If this type of bitumen is consumed using cold techniques, it can be considered environmentally friendly. This material is water and splash resistant and is classified based on the following two important factors:
1- Electrostatic charge of emulsifier particles
Cation
anionic
2- Breaking time, that is, the time required for water to evaporate
Slow setting (Slow Setting type = SS)
Medium setting (Medium Setting type = MS)
Rapid setting (Rapid setting type = RS)
Modified polymer bitumen
To improve bitumen efficiency in asphalt paving operations, polymer modified bitumen (PMB) is used, which has been popular since the 20th century. Polymer materials are added to bitumen with a ratio of 1 to 5% by weight, and the maximum amount of polymer used is 3% by weight. In some special cases, the amount of added polymers reaches 7% by weight.
Types of polymers used in modified bitumen include the following:
Natural polymers
Lignin
Thermoplastics/plastomers
Polypropylene
PE
Ethylene vinyl acetate
Elastomers
Natural rubber
synthetic rubber
Polybutadiene
Butyl rubber
Thermoplastic elastomers
Styrenic block copolymers
Mixed polyolefin
Thermoplastic polyurethane
Ground rubber
Recycled waste tires
Among the mentioned polymers, thermoplastic elastomers are the most used.
Elastic polymer bitumen
The reason for the popularity of this polymer is due to the increase in the elasticity of bitumen, which causes less amount of bitumen to be used when used in the industry.
In addition, it increases bitumen’s resistance to fatigue-induced plasticity and prevents bitumen from softening when exposed to high temperatures and bitumen cracking at low temperatures. The presence of polymer reduces the temperature sensitivity of bitumen and increases its adhesion and plasticity.
In the United States, polymer bitumen is produced using ground rubber. This type of polymer constitutes 5 to 20% of the total weight of the material. Bitumen modified by this method helps to protect the environment and returns unusable tires to the consumption cycle.
Other benefits of using rubber as a polymer in bitumen include slip resistance, improved flexibility, reduced road traffic noise, and cracking resistance.
oxidized bitumen
This bitumen is obtained by blowing hot air into the vacuum floor. By using this method, a hard and brittle bitumen is obtained, which is used as a moisture insulator for building construction.
In the process of oxidation, sometimes pure bitumen is transferred to other towers. Compared to pure bitumen, oxide bitumen has a lower degree of penetration and a higher softening point.
Based on the degree of penetration and softening point, oxidized bitumen is classified as follows:
Low grade oxidized bitumen
R75/30
R85/25
R85/40
R90/40
R95/25
Medium oxidized bitumen
R90/10
R90/15
Oxidized bitumen with hard grade
R105/35
R115/15
Crystal tar
After the various processes in the distillation and refining of crude oil are finished, some hard and brittle organic matter remains in the distillation tower. These remaining materials in the distillation tower are called crystalline bitumen. The size of penetration and plasticity of crystalline bitumen is below 30 and 10 cm, respectively.
This bitumen has no elasticity and is completely brittle and crystal-like. This bitumen has special uses and is economical.
Application of bitumen in road construction
Bitumen is used in a large amount, about 85%, in the road construction industry. Another use of bitumen can be mentioned as a waterproofing. In general, it is possible to use bitumen in more than 7 different fields, and in these 7 fields, there are more than 130 types of applications.
In the following section, we have mentioned some important cases of bitumen application in construction operations:
Construction of roads, runways and platforms
As insulation and waterproof to prevent moisture leakage
Flooring of factories
Covering water channels to prevent erosion
What is the reason for using bitumen in the construction of buildings? Due to its adhesion and sealing properties, bitumen is widely used in all aspects of civil engineering and construction. Penetration bitumen and emulsion are used to build railway lines, and modified polymer bitumen is also used in the railway industry to reduce noise and vibration.
Due to the resistant structure of PMB, the coating of airport runways is modified from polymer. Bitumen is used in wide and important dimensions for the marine construction industry, such as: covering of canals, underground tunnels, protection of river banks, construction of dams and piers in the sea.
You may be interested to know that bitumen is also used in roofing felt, printing ink, packaging paper, electrical cable insulation, junction box, etc.
What are the characteristics and technical specifications of bitumen?
In order to recognize the quality type of bitumen, you must be aware of its technical characteristics and specifications in order to choose a bitumen with a long service life according to your needs.
The technical specifications of bitumen types are as follows, by using them, you will choose a higher quality bitumen:
Degree of penetration
As much as the amount of bitumen penetration in terms of tenths of millimeters is lower; The resistance of bitumen is higher and it benefits from better quality and application. To measure the degree of penetration, they use a standard needle under a load of 100 grams for 5 seconds at a temperature of 25 degrees Celsius. The amount of penetration is specified in tenths of millimeters.
viscosity
The amount of viscosity is measured by the Saybolt Furol device or by the kinematic method, and the higher the viscosity, the higher the solid property of bitumen.
flash point
The temperature at which if the bitumen reaches that point, the gases inside it will ignite with the proximity of the flame. The maximum heating temperature of bitumen in the workshop is limited to the ignition point of bitumen.
Weight loss during heating
What is the reason for the weight loss of bitumen? During heating, due to the evaporation of part of the oil and petroleum compounds in the bitumen, its weight decreases. Weight loss of bitumen is one of its significant and important features, which is measured at 163 degrees Celsius in a period of 5 hours. This temperature and time are approximate conditions for bitumen curing during asphalting.
Plasticity
If we put a sample of bitumen in a cross-sectional area of 1 cm2 at a speed of 5 cm/min, the plasticity of bitumen before tearing is determined by increasing the length of the sample.
softening point
The temperature at which the bitumen becomes fluid is called the softening point. The higher the bitumen softening point, the less sensitive it is to temperature changes. The softening point of ordinary bitumen is around 60 to 70.
Solubility in CS2
Considering that tetrachloride and sulfur carbon are bitumen solvents; As bitumen dissolves in each of them, bitumen impurities remain. In this way, you can find the percentage of bitumen purity. The degree of purity of bitumen can be found from the following formula:
(weight of sample bitumen) ÷ (weight of impurity – weight of bitumen)
Conclusion
Buying all kinds of bitumen
What is bitumen? Bitumen is one of the most important petroleum products on earth, which is used in many industries due to its adhesive and anti-moisture properties. Bitumen has a high viscosity percentage and unique properties that cover more than 130 sectors in the industry due to its existence in different types. Some bitumens are naturally liquid and usable in the ground, and others are obtained through oil or coal tar in a refinery.
In this article, we tried to familiarize you with the types of bitumen, the application of bitumen and the technical specifications of all types of bitumen. To achieve the technical characteristics of a bitumen, it must be tested and checked in different situations to reach the desired index. The important technical indicators and specifications of bitumen include weight loss, viscosity, softness, temperature, purity and penetration degree of bitumen.
When buying bitumen or producing it, they definitely check the mentioned indicators.
