Bitumen is a black viscous mixture of hydrocarbons obtained naturally or as a residue from petroleum distillation or purification. We will discuss the properties of bitumen in this post.
Bitumen is used in the construction of roads, roofs, Dams, etc. It is highly adhesive in nature and used to bind two or 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 several 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 the 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. It should bind materials together properly without affecting the properties of other materials.
Low adhesion leads to short life and stripping of materials ( like striping of aggregates in the flexible pavement) whereas high adhesion leads to the long life of roads, roofs, etc where bitumen is used.
Moisture is the biggest reason behind the bad adhesion of bitumen in most cases.
Mainly, bitumen is used in exposed works like road construction, waterproofing, roofing, etc. It has to tackle different climatic conditions including rain. So, it should be insoluble in water and should serve as a waterproofing agent.
Lower water-resistive property leads to lower durability and lower strength of bitumen. It also leads to low adhesion. Hence, bitumen should be highly resistive towards the water.
Though mineral or filler materials ( like aggregate in the road construction) are the main bearing component; binding material should also have sufficient strength to resist different live & dead loads ( like self-weight and wheel load in road construction).
Bitumen should bind all construction materials 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.
Bitumen should show a versatile nature. It must be workable during the construction phase and must be 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 penetrating depth
Roofing Asphalt – 15 to 40 mm penetrating depth
Waterproofing bitumen – up to 100 or more penetrating depth
Bitumen should be hard enough to resist the action of loads and chemicals but it should not be brittle in nature.
Higher the softening point value, lower will be the temperature susceptibility. So, bitumen with high softening value is preferred for hot climates.
Ductility is the property of bitumen that permits it to undergo great deformation or elongation. The value of ductility ranges from 0 to over 150 depending on the types of bitumen. Its value also depends upon the temperature, briquette dimension, pulling rate, etc.
Viscosity and Flow:
Viscosity should not be very low as well as very high because high viscosity leads to difficulties 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 bitumen on heating should be minimum.
Bitumen has to tackle with different chemicals directly or indirectly (For e.g. It has to tackle with acids in the form of acid rain). So, it should be highly resistive against chemicals.
Some of the General 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.
Read More: 18 Differences between Bitumen and Tar
Read More: Flexible Pavement
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