Bitumen Properties and It's Detail - Why bitumen is used?

Bitumen

Bitumen Carpeting

Bituminous materials or asphalts are much used for roadway construction, at first because of their excellent binding characteristics, water proofing properties and relatively low cost than other binding material. Bituminous materials consists of bitumen which is a black or dark in colour solid or viscous cementations substances consists chiefly high molecular weight hydrocarbons derived from distillation of petroleum or natural asphalt, has adhesive properties, and is soluble in carbon disulphide. Tars are residues from the destructive distillation of organic substances such as coal, wood, or petroleum and are temperature sensitive than bitumen. Bitumen will be dissolved in petroleum oils where unlike tar.

• Bitumen oxidizes slowly,
• Most bitumen are colloidal in nature,
• Bitumen are insoluble in water,
• Bitumen are thermoplastics,
• They have no specific melting, boiling or freezing point,
• They are highly impermeable to the passage of water,
• They are generally hydrophobic,
• They are chemically inert.

Why bitumen is used? 

     Because of these properties bitumen is used for roadways construction as paving material

Properties of Bitumen and Bituminous Materials

Following are the properties of Bitumen

1. Adhesion
2. Resistance to Water
3. Hardness
4. Viscosity and Flow
5. Softening Point
6. Ductility
7. Specific Gravity
8. Durability
9. Versatility 
10. Economical
11. Strength

1. Adhesion:

          This property of bitumen cans bines all the components together without changing any properties of their road material. Bitumen has the ability to adhere to a solid surface in a fluid state depending on the nature of the surface. The water presence on the surface will prevent adhesion.

2. Resistance to Water:

We all know that bitumen is insoluble in water and can serve as effective sealant bitumen is water resistant capacity. Under some conditions water may be absorbed by minute quantities of inorganic salts in the bitumen or filler in it.

3. Hardness:

          The hardness of bitumen can be measure by the penetration test which is measures the depth of penetration in tenths of m, the weighted needle is penetrate in bitumen after a given time, at a known temperature maintained in bitumen.

The bitumen grades measure by penetration, if penetrations greater than 40 than that type of bitumen mostly used in road construction and occasionally in industrial applications. If the penetrations less than 40 than that type of bitumen used exclusively in industrial applications. At hot climate lower grades bitumen is used.

4. Viscosity and Flow:

          Bitumen are thermoplastic, viscoelastic materials, which behavior depends on temperature, speed and size of the load. Viscoelastic character means that by impact of external forces partially elastic deformation occurs (elastic component) and partially plastic strain occurs (viscosity component). At low temperatures, respectively, at high frequencies of load (fast passing cars), the bitumen behave as an elastic and solid material. The elastic unit is deformed under load and after reducing the load, it is returned to the original shape. This behavior, however, lasts continues as long as exceeding the limits of bearing capacity and materials damage, it means the bitumen binders crack. At high temperatures, respectively, during long-term loading (parking vehicles), the bitumen behaves as a viscous material. Resultantly, decrease in adhesive and flow properties and an increase in the softening point temperature and coefficient of thermal expansion.

5. Softening point:

Bitumen with lower softening point tends to melt on the road in summer and start flowing under the impact of temperature and traffic. Therefore it can be concluded that bitumen’s with higher softening point melt at higher temperature and having better rutting resistance. This property make us to know whether given bitumen can be used at the particular place i.e. softening point value should be higher than pavement temperature otherwise bitumen present in the layer get soften and come out. These Properties of material can be tested in lab.

6. Ductility:

          Bitumen is a highly ductile material, we can change the bitumen at solid and liquid state easily, Ductility test is conducted to determine the amount bitumen will stretch at temperature below its softening point. A briquette having a cross sectional area of 1 in² is placed in a tester at 77 °F. Ductility values ranges from 0 to over 150 depending on the type of bitumen. If bitumen is more ductile than it is very easy to form or formation of the film and coating would be proper.

7. Specific Gravity

          Specific gravity of a binder does not influence  its behaviour . But all the same, its value is needed in mix design. The property is determined at 27º C.

8. Durability:

          Bitumen durability refers to the long-term resistance to oxidative hardening of the Material in the field. Although, in-service, all bitumen harden with time through reaction. With oxygen in the air, excessive rates of hardening (poor durability) can lead to premature binder embrittlement and surfacing failure resulting in cracking and chip loss. Bitumen lives upto twenty years if maintained properly throughout the pavement life.

9. Versatility:

         Bitumen have versatile properties due to versatility properties of Bitumen it is relatively easy to use it in many applications because of its thermoplastic property. It can be spread easily along the underlying pavement layers as it liquefies when heated making the job easier and hardens in a solid mass when cooled.

10. Economical:

          At road construction bitumen is used as a main road construction material because it is available in cheaper rates as compare to another binder material almost all over the world which makes it feasible and affordable in many applications.

11. Strength:

          Though the coarse aggregates are the main load bearing component in a pavement, bitumen or asphalt also play a vital role in distributing the traffic loads to the layers beneath.