Properties of Bitumen – Bitumen is a viscous black mixture of hydrocarbons that can be found in nature or as a byproduct of petroleum distillation or purification. In this post, we will talk about the properties of bitumen.
Bitumen is used to build roads, roofs, dams, and other structures. It has a strong adhesive property and is used to join two or more materials. It is also found in the Damp Proof Course (DPC).
All bituminous substances have general property of resisting the passage of water. Other factors being equal, those products containing the highest percentage of the base material— i.e., pitch or bitumen—will give the greatest protection. Pigmented products, light in colour, are therefore less efficient in this respect than those in which the quantity of pitch or bitumen necessitates a dark colour.
In general the hot applied material and those constituted with solvent—i.e., not an emulsion— are more likely to withstand pressure: on other hand, emulsions are satisfactory when their purpose is to shed water from vertical or near vertical surface.
What Is Bitumen?
Bitumen, also known as asphalt in the United States, is a substance that is produced by distilling crude oil and is used for its waterproofing and adhesive properties. Distillation of bitumen removes lighter crude oil components like gasoline and diesel, leaving behind the “heavier” bitumen. To improve its grade, the producer often refines it several times.
Bitumen can also be found in nature: naturally occurring bitumen deposits can be found at the bottom of ancient lakes, where prehistoric organisms have decayed and been exposed to heat and pressure.
Properties Of Bitumen
The following characteristics should be present in a good bitumen:
- Chemical Resistive
- Loss on heating
- Softening Point
- Viscosity and Flow
- Water Content
- Water Proof
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.
Impurities present in the bitumen are the biggest reason behind the bad adhesion of bitumen in most cases.
Bitumen has to deal with a variety of chemicals, either directly or indirectly (E.g. It has to tackle with acids in the form of acid rain). As a result, it should be chemically resistant.
Bitumen’s ductility refers to its ability to withstand significant deformation or elongation. Depending on the type of bitumen, ductility can range from 0 to over 150.
Temperature, group composition, and structure nature all influence ductility. At low temperatures, viscous bitumens containing solid paraffins are extremely ductile.
Bituminous materials are known to have a long life—some asphalt mastic roofs are 100 years old—but they may be affected by sunlight and by other agencies such as acid, fats, etc. and also by mechanical damage. Defects due to natural weathering may be overcome by periodic maintenance and renewal of the top dressing. Effects of acid, mechanical damage etc. may be overcome by choosing the correct type and grade of material.
The decision as to choice of material is one for which the architect must rely very largely on the manufacturer, but in so far as it is possible to generalize, those product incorporating principally natural bitumens are thought to be superior to those incorporating derivative bitumens.
Bitumen must be accessible at a reasonable price. Bitumen costs vary depending on its grade, but it should be cost-effective to use.
The penetration test is used to determine the bitumen’s hardness. In other words, the hardness of penetrating depth. For various tasks, the best hardness is:
- 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 must be tough enough to withstand the effects of loads and chemicals.
Loss on heating
When bitumen is heated, volatiles are released, resulting in a loss of mass or weight. As a result, bitumen loss during heating should be minimal.
The lower the temperature susceptibility, the higher the softening point value. In hot climates, bitumen with a high softening value is preferred.
Though mineral or filler materials (such as aggregate) are the primary bearing components, binding material must be strong enough to withstand a variety of live and dead loads ( like self-weight and wheel load ).
Bitumen should have a wide range of applications. During the construction phase, it must be workable, and during the operation phase, it must be rigid.
Viscosity and Flow
Because high viscosity makes it difficult to apply bitumen, and low viscosity makes it difficult to bind materials because it flows quickly, viscosity should not be very low or very high.
To prevent the bitumen from foaming when heated above the boiling point of water, it should contain as little water as possible.
Bitumen is primarily used in exposed applications such as road construction, waterproofing, and roofing. It must deal with a variety of weather conditions, including rain. As a result, it should be water insoluble and act as a waterproofing agent.
Bitumen with a lower water-resistive property has a lower durability and strength. It also causes a lack of adhesion. As a result, bitumen should have a high water resistance.
The Shanghai Futures Exchange launched the world’s first Bitumen futures contracts in October 2013, aimed at operators of crude oil refineries, bitumen dealers, and end-users of the product.
The monthly futures contract calls for the physical delivery of 10 tonnes of bitumen per lot when it expires. The Shanghai Futures Exchange must certify the final product for delivery, and it must meet the quality specifications outlined in the Bitumen Futures Delivery Rules.