Bitumen is a black viscous mixture of hydrocarbons obtained naturally or as a residue from petroleum distillation or purification. It is used in the construction of roads, roofs, Dams, etc. It is highly adhesive in nature and uses to bind two more materials together. It is also used in Damp Proof Course (DPC). The quality of bitumen is separated in terms of grade. Because of its use in many sectors, it should have quality characteristics. Some of the desirable properties of bitumen are given below.
Desirable Properties Of Bitumen
A Good Bitumen Should Have Following Properties:
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 the long life of roads, roofs, etc where bitumen is used.
It Should be insoluble in water and should serve as a waterproofing agent. Lower 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 another 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 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 a loss in mass or weight. So, loss of 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.
5) It oxidizes slowly.
6) It is chemically inert and hydrophobic in nature.
7) It is insoluble and highly resistive towards the water.
8) It is colloidal in nature.
Quality of bitumen depends upon the grade of bitumen. High-grade bitumen is durable, hard, waterproof and ductile. So, the use of high-grade bitumen should be done on quality works. Low-grade bitumens are generally used for temporary structures.
Quality bitumen is always resistive towards the alternate weather, chemical attacks and many more. They also have a life period of about 15 to 20 years.
In the construction of roofs, damp proof course and roads; quality bitumens are prefered.