Bitumen is a black or dark-colored solid, semi-solid or highly viscous liquid that can be found in different forms such us: rock asphalt, natural bitumen, tar and bitumen derived from oil, which is referred to as petroleum bitumen.
Often coal tar that is drive from oil-shale, wood or other organic materials confused with bitumen. However they are two entirely chemically different products and should not be mistaken.
Bitumen is a low grade of crude oil which is composed of complex heavy hydrocarbons and residue distillation tower refinery that is called Vacuum Bottom.
Most refined bitumen is used in the construction industry. Mainly, it serves its use in paving and roofing applications, most of all bitumen is used as a binder in asphalt for roads, runways, Airport, Dams, Pipe coating, Paints, pools water proofing, cable coatings and many other applications.
Gravel and crushed rock are mixed with thick bitumen, holding it together and it is then applied to roadways.
Bitumen packed normally as below:
Air Blowing Bitumen
The Air Blowing Bitumen is produced by process of vacuum Bottom (VB) and air in the reactor or batch. And due to the control of the process conditions, different grades are produced.
The regular distillation process is discontinued at some point while the topped crude is still liquid. The heavy fraction is into a converter and air is blown through it while it is maintained at a high temperature. This process is continued until the asphalt has attained desired properties. Often, such asphalts are called Blown asphalt. However, this is not strictly a true term because not only oxidation but also vaporization, Dehydrogenation, condensation, polymerization and other reactions occur during the air blowing process.
Types of Air Blowing Bitumen
Penetration Grades Bitumen
Penetration Grades Bitumen is refinery bitumen that is manufactured at different viscosities. It produced by manufactured from fractional/vacuum distillation of crude oil (feed stock).
The penetration test is carried out to characterize the bitumen, based on the hardness. Thus, it has the name penetration bitumen. It is usually used as a Paving Grade Bitumen essential for road construction and for the production of asphalt pavements with superior properties, and it’s very important once it bounds the aggregates and creates a unique cohesion and stability to the bituminous mix.
Penetration Grade Bitumen is specified by the penetration and softening point test. The designation is by penetration range only.
Oxidized bitumen is categorized based on softening points and penetration rate. For example, oxidized bitumen 85/40 is a type of bitumen which softening point is 85±5 degree centigrade and its penetration are is 40±5 dmm. These types of bitumen is also expected to make up for weight loss under heat. And the softening point is much higher than in regular bitumen. Oxidized Bitumen is mainly used for industrial purposes such as roof insulation, pipe coating, paints, industrial mastics, etc.
Performance Grades Bitumen (PG)
Performance grades based on binder specification with a new set of tests (SHRP). And its performance at different temperatures, in Super pave grading system, binders are classified according to their performance in extreme hot and cold temperatures and called as performance grade (PG) bitumen. The PG system uses a common set of tests to measure physical properties of the binder that can be directly related to field performance of the pavement at its service temperatures by engineering principles. PG grades nomenclature with two factors: traffic and pavement temperature.
Application of grades PG Bitumen are used in paving for both new construction and pavement rehabilitation and in both dense-graded and open graded Hot Mix Asphalt. And could also be used for sealing of edges of new to told paving and crack sealing. Other uses include spray applications for bridge deck and pavement protective membrane with fabrics.
Viscosity Grades Bitumen (VG)
The viscosity grade bitumen has been specified in terms of their penetration grade and behavior changes according to its temperature. The viscosity Grade bitumen is specified by ASTM Standard and based on absolute Viscosity at 60 ̊C(140°F) or Kinematic Viscosity at 135 ̊C.
Viscosity thus defines the fluid property of the bituminous material. Viscosity is the general term for consistency, and it is a measure of resistance to flow. Many researchers believe that grading of bitumen should be by an absolute viscosity in instead of the conventional penetration units.
Application of Viscosity grade bitumen:
Viscosity Grade Bitumen is a standard grade Bitumen usually used as a Paving Grade Bitumen suitable for road construction and for the production of asphalt pavements with superior properties. This grade of Bitumen is mainly used in the manufacture of hot mix asphalt for bases and wearing courses and possesses characteristics and qualities unique sand quite different from other agents. Cutback Bitumen: Bitumen is ‘cutback’ by adding controlled amounts of petroleum distillates such as kerosene. This is done to reduce the viscosity of the bitumen temporarily so it can penetrate pavements more effectively or to allow spraying at temperatures that are too cold for successful sprayed sealing with neat bitumen. The materials used to cutback bitumen will evaporate after application to leave the remaining material similar in hardness to the original bitumen.
Cutback Bitumen is categorized in 3 groups according to their curing time:
Bitumen Emulsion: Description Bitumen emulsion consists of three basic ingredients: bitumen, water, and an emulsifying agent. Based on specifications it may contain other additives, such as stabilizers, coating improvers, anti-strips, or break control agents, it is well known that water and asphalt. But as the bitumen is a petroleum product it doesn’t mix with water and as it is sticky in nature, it doesn’t easily gets disintegrated into fine droplets. To overcome this problem an emulsifier is used.
Application of Bitumen Emulsions
Bitumen emulsions are applied on aggregates, water starts to evaporate causing separation of bitumen from water. And then bitumen spreads on the surface of the aggregate and acts as a binding material and slowly attains its strength. Also they are especially helpful for maintenance and patch repair works. And can be used in wet weather even when it is raining, have been used in soil stabilization, particularly for stabilization of sands in desert areas, for surface dressing and penetration macadam type of construction and overall allows better coating of the bitumen on the surface of aggregate.
Types of Bitumen Emulsion
The term anionic is derived from the migration of particles of bitumen under an electric field. The droplets migrate toward the anode (positive electrode), and hence the emulsion is called anionic. In an anionic emulsion, there are “billions and billions” of bitumen droplets with emulsifying agent at the water bitumen interface.
The term cationic is derived from the migration of particles of bitumen under an electric field also. The droplets migrate toward the cathode (negative electrode), and hence the emulsion is called cationic. The cationic emulsifying agent functions similarly to the anionic; the negative portion of the head floats around in the water leaving a positively charged head.
The main grades for bitumen emulsions are classified as follows:
The most Iranian apply of bitumen emulsion is Cationic grades.
Polymer Modified Bitumen
Polymers represent the most important family of bitumen modifiers. The specifications of bitumen under different temperatures change, for example, polymers make bitumen resistant to heating cracks. Modifying the bitumen specifications boosts the quality of the product and increases its longevity. Under these special circumstances, structural destructions happen more quickly than in natural state in asphalt pavement and that would significantly increase road maintenance costs.
Variety of Polymers: The most polymers that used for modifying bitumen are SBS, EVA, APP, LDPE, LLDE. HDPE, SBR, SEBS and SIS.
SBS is one of the best modifying polymers with both thermoplastic and rubber specifications.
Application of Polymer Modified Bitumen
Polymer Modified Bitumen are used in making pavement, roads for heavy duty traffic and home roofing solutions to withstand extreme weather conditions. PMB is a normal bitumen with the added polymer, which gives it extra strength, high cohesiveness and resistance to fatigue, stripping and deformations, making it a favorable material for infrastructure.