Bitumen is a black coloured sticky high viscous liquid or semi-solidified petroleum byproduct(e.g crude oil). It is also known as Asphalt. The asphalt is a mixture of aggregates(sand, stone or gravel) and bitumen for surfacing the road park with bituminous materials. The purpose of using asphalt for road construction is to bind the mixture of aggregate particles with each other such that it forms various layers. Some of the desirable properties of bitumen are given below.
Desirable Properties Of Bitumen
A Good Bitumen Should Have Following Properties:
- Softening point
- Water content
- Loss on heating
-A good binder must bring all construction material together and make it a single unit. So, bitumen should be highly adhesive in nature.
– Bad adhesive leads to short life and stripping of materials.
– High adhesion of bitumen leads to long life of roads, roofs, etc where bitumen is used.
– It Should be insoluble in water and should serve as a waterproofing agent.
– Lower the water-resistive property leads to lower durability and strength.
-Though aggregate is the main bearing component, binding material must have sufficient strength to resist wheel load.
-Binding material should bind all construction material together for a long time (about 20 years) in adverse weather condition.
– For exposed work, it should have a minimum of 10 years life and for non exposed work, it should be 20 years.
-Binding material must be workable during construction and rigid in the operation phase.
-Bitumen must be available at low cost.
– The cost of bitumen depends upon its grade but should be economical and cheaper to use.
The hardness of the bitumen is determined using the penetration test. In other word, Penetrating depth is the hardness. The best hardness for different works are:
Hard Coating asphalt – 10 mm
Roofing Asphalt – 15 to 40 mm
Waterproofing bitumen – up to 100 or more
Higher the softening point value, lower will be the temperature susceptibility. So, bitumen with high softening value is preferred in hot climates.
-Ductility is the property of bitumen that permits it to undergo great deformation or elongation. The minimum value for ductility is 75 cm.
Viscosity and Flow
– Viscosity should not be very low as well as very high also because high viscosity leads to very difficult in the application of bitumen and low viscosity leads to improper binding of materials as it flows fast.
The bitumen should contain minimum water to prevent foaming of the bitumen when it is heated above the boiling point of water.
Loss on heating
When bitumen is heated, it leaves out volatiles and causes loss in mass or weight. So, loss on heating bitumen should be minimum.
Some of the other Properties of bitumen
Here are some of the other properties of bitumen. They are:
1) It is in solid or semi-solid or liquid states, black and sticky in nature.
2) It melts and gets soften on the application of heat.
3) It is a binder in all types of asphalt(between with inert mineral material).
4) It has low permittivity and high insulation.
Types of Bitumen:
1) Based on sources:
c) Liquid state
2)Based on Nature
3) Based on use:
a) Road construction
b) Building construction
c) Roofing system
Some Uses of bitumen:
1) It is used as a DPC (Damp proof course) in walls, floors, and lining of tanks, swimming pools.
2) It is used for filling expansion joints in leakage.
3) It is used as road-making materials.
4) It is used for making heat-insulating material for fittings.
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