Materials which are being used for bond between different constituents of pavement, and that bond remains strong under different conditions. Binding materials actually increase the resistance between individual elements of mixture and increase its strength against impact loading on pavement. Sub grade material contains larger quantity of binding materials. Sub base course also requires the binding materials to bind the stone particles in the specified ratio. The base course also requires the binding materials in the certain ratio to bind the crushed materials each other. The base course consists of crushed stones, without sufficient binding materials, the base course layer will not function well.
The construction materials that are bound together with bitumen are called bituminous materials. The use of bituminous materials was only upto the road construction. Now the bitumen can be used for roof construction, industrial purposes, carpet tiles, paints and as a special coating for waterproofing. There are different types of bitumen available in the market with different properties, specifications and based on requirements of consuming industry. The various types of bitumen used in Road construction as follow:
Types of bitumen
A. Penetration Grade Bitumen:
The penetration grade bitumen is refinery bitumen. Based on the hardness, the penetration test is carried out to characterize the bitumen. The penetration bitumen grades of range from 15 to 450 for road bitumen. But 25-200 is the commonly used range. This is obtained 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 gaining the required hardness.
B. Cutback Bitumen
Cutback bitumen is the bitumen that comes under penetration grade bitumen. Cutback bitumen is a mixture of bitumen and a volatile oil. The volatile material is evaporated, and bitumen gain its original viscosity. In areas of road construction, cut back bitumen is necessary at the time of laying i.e. during surface dressing. Cutback bitumen is commonly used in cold weather and for the spraying purposes.
C. Emulsion Bitumen
Emulsion bitumen have wide range of application in road construction and maintenance work. The common examples in the construction of bituminous pavement layers are the interface treatment as prime coat and tack coat and in various other works such as seal coat, surface dressing, bituminous carpet, etc. The emulsion bitumen is usually used in maintenance work.
D. Polymer-Modified Bitumen (PMB)
It is the type of bitumen obtained by the modification of strength and the deformation of the penetration graded bitumen. Here for this 2 to 8% of polymer is added. The polymer can be used is either plastic or rubber. This is achieved by Elastic response increase, Improvement in cohesive property, Improvement in, Fracture strength, providing ductility Some of the examples of rubber polymers used are styrene block copolymers, synthetic rubbers, natural and recycled rubbers. Plastics that are thermoplastic polymers are also used.
E. Oxidized Bitumen
The oxidized bitumen is produced by blowing the air in penetration grade bitumen. By maintaining a well-controlled temperature, the air is blown under pressure into soft bitumen. Compounds of higher molecular weight are formed by Approved by the reaction of this introduced oxygen and bitumen components. Oxidized bitumen is used in industrial applications such as roofing and coating for pipes, sealing cuts, joints. By this method of processing, the bitumen that has a lower penetration can be manufactured, which can be employed for paving roads.
Requirements for Bitumen
1. Viscosity: Bitumen are thermoplastic, which behavior depends on speed, temperature, and size of the load. It is achieved by raising the temperature of bitumen and aggregate by adding cutbacks or emulsion of suitable grade.
2. Adhesion: Bitumen can bind all the components together without changing any physical properties of their road material. Bitumen has ability to change to a solid in a liquid state depending on the nature of the surface.
3. Hardness: The hardness of bitumen can be checked by the penetration test, it measures the depth of the penetration. If the penetration is greater than 40 than the bitumen is used in road construction. During hot climate, lower grade bitumen is suitable to use.
4. Softening point: Bitumen with lower softening point melt on the road during hot climate in contact with traffic.
5. Economical: As compared to other materials, bitumen is cheaper to use in road construction. It is feasible and affordable.
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