There are different types of bitumen available with different properties, specifications and uses based on requirements of consuming industry.
The specification of bitumen also shows variation with the safety, solubility, physical properties, and the durability.
To understand the performance of the bitumen when it is on service, the design of physical properties of the material is highly essential. The standard testing methods are carried out to grade bitumen.
Types of Bitumen and their Properties and UsesThe bitumen can be classified into the following grade types:
- Penetration Grade Bitumen
- Oxidized Bitumen Grades
- Cut Back Bitumen
- Bitumen Emulsion
- Polymer Modified Bitumen
Penetration Grade BitumenThe penetration grade bitumen is refinery bitumen that is manufactured at different viscosities. The penetration test is carried out to characterize the bitumen, based on the hardness. Thus, it has the name penetration bitumen. The penetration bitumen grades range from 15 to 450 for road bitumen. But the most commonly used range is 25 to 200. This is acquired by controlling the test carried out i.e. the distillation process. The partial control of fluxing the residual bitumen with the oils can help in bringing the required hardness.
Table.1. Paving Grade Bitumen Specification As per BS EN 12591
Oxidized BitumenThe refinery bitumen is further treated by the introduction of processed air. This will give us oxidized bitumen. By maintaining a controlled temperature, the air is introduced under pressure into soft bitumen. Compounds of higher molecular weight are formed by the reaction of this introduced oxygen and bitumen components. Thus, the Asphaltenes and the Maltenes content increases resulting in a harder mix. This harder mix has a lower ductility and temperature susceptibility.
Cutback BitumenThese are a grade of bitumen that comes under penetration grade bitumen. This type of bitumen has a temporarily reduced viscosity by the introduction of a volatile oil. Once after the application, the volatile material is evaporated and bitumen gain its original viscosity. The penetration grade bitumen is a thermoplastic material. It shows the different value of viscosity for different temperature. In areas of road construction, it is necessary for the material to be fluid in nature at the time of laying i.e. during surface dressing. It is also essential for the material to regain back to its original hardness and property after setting. This is ensured by cutback bitumen. The fluidity is obtained for any bitumen by raising the temperature. But when it is necessary to have fluidity at lower temperatures during surface dressing, cutback bitumen is employed. The time for curing and the viscosity of cutback bitumen can be varied and controlled by the
- dilution of volatile oil, and
- the volatility of the oil added.
Table-2: The Cutback Bitumen Specification As per BS 3690: Part 1 & BS EN 12591
Bitumen EmulsionThe this type of bitumen forms a two-phase system with two immiscible liquids. One of them is dispersed as fine globules within the other liquid. When discrete globules of bitumen are dispersed in a continuous form of water, bitumen emulsion is formed. This is a form of penetration grade bitumen that is mixed and used for laying purposes. An emulsifier having a long hydrocarbon chain with either a cationic or anionic ending is used for dispersing the bitumen globules. This emulsifier provides an electrochemical environment. The ionic part of the chain has an affinity towards water and the bitumen is attracted by hydrocarbon part.
Bitumen during Dispersion in an emulsifier
The stability of emulsions is dependent on the following factors:
- Types of bitumen emulsifier and its quantity
- Water evaporation rate
- Bitumen quantity
- Bitumen globules size
- Mechanical forces
Polymer - Modified BitumenPolymer modified bitumen is the type of bitumen obtained by the modification of strength and the rheological properties of the penetration graded bitumen. Here for this 2 to 8% of polymer is added.
- Elastic response increase
- Improvement in cohesive property
- Improvement in Fracture strength
- Providing ductility