Transportation through roads is the basic mode of connection to any place, and we all know that it is made of asphalt, but has it ever crossed your mind: What is Asphalt? How is it made?
When crude oil is processed in oil refineries, we usually get pure complex mixtures known as petroleum products. Heavier fractions of the crude oil are used to produce asphalt, tar, paraffin wax, and other heavy oils.
Asphalt, also known as bitumen, is a refined semi-solid product of petroleum. It may also be found in natural deposits. It occurs as a black viscous liquid and is classed as a pitch.
Pitch is a name for a number of viscoelastic polymers. It can be natural or manufactured, basically derived from petroleum, tar. Its primary use is in the construction where it is used as the glue or binder and mixed with other aggregate particles to create asphalt concrete. It is a composite material used in surfacing roads, airports, the core of embankment dams. It is made by mixing mineral aggregate with asphalt and then laying it in layers and compaction. It can be natural as well as refined.
The asphalt that naturally occurs is commonly called as “crude bitumen,” whereas when it is obtained by fractional distillation of crude oil at 525 degrees Celcius is referred to as “refined bitumen.”
Contents
Properties Of Asphalt
The main properties are as follows:
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Viscosity
The viscosity of a material is defined as its ability to resist deformation under external forces. The viscosity of different asphalts varies according to the composition and the environmental temperature. With more asphaltene, certain content of resin but less oil, then it has a high viscosity.
- Plasticity
Plasticity of petroleum asphalt is defined as its ability to deform but without destruction under external force. The more is the resin with suitable content of other constituents; the greater is the plasticity.
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Temperature Stability
The temperature stability is related to plasticity and viscosity. Within the same temperature range, different asphalts with varying composition change differently in viscosity and plasticity. It should have a small temperature sensibility, i.e., the better temperature stability of it should be used in construction projects.
Composition of Asphalt
The composition of petroleum asphalt is quite complex. It includes various kinds of macromolecular compounds and derivatives. The main components are as follows:
- Oil– It is a viscous yellow colored liquid that provides certain fluidity and decreases its consistency so as to be easily applied.
- Resin– It is a thick viscous brown colored fluid that gives it good plasticity and bonding power. Higher the content of resin, better is the quality.
- Asphaltene– It is a dark brown to the black amorphous solid material which is a key constituent, as it determines the viscosity and the temperature sensitivity. The higher viscosity makes it harder and more brittle.
Wax present in petroleum asphalt decreases the viscosity and plasticity. Since wax is temperature sensitive, it weakens the temperature stability.
Production Of Asphalt
- It is obtained as the heavier fraction when crude oil is distilled. It has a boiling point higher than 500 degrees Celsius.
- When crude oil is vacuum distilled, it is separated from other components in crude oil such as gasoline, naphtha, etc.
- After the distillation is carried out, the resulting mixture is treated to extract small amounts of lubricants.
- In a de-asphalting unit, the crude asphalt is either treated with propane or butane to extract the lighter molecules.7
- By blowing the remaining product with oxygen, it makes it harder and more viscous.
It is stored and transported at temperatures around 150 degrees Celsius. In order to retain liquidity, it is mixed with kerosene or diesel oil upon transportation.
Uses Of Asphalt
They are used in combination with other materials in many engineering fields.
- Construction
Asphaltic bitumen has a good binding capacity; they are waterproof and have the ability to provide a flexible surface. So, because of these qualities, it is used extensively in road foundations and as surface materials. The three types of asphaltic mixtures that are used in roadway construction are: rolled, mastic, and compressed rock asphalt.
- Electrical Uses
High-grade asphalts are mixed with resin, tar, and used in the electrical industry. A good example is a battery container.
- Asphaltic Paints
Bituminous asphalts are used as essential ingredients in certain paints which are useful for damp walls and over concrete structures.
- Asphalt Concrete
It is made by mixing asphalt cement with fine and coarse aggregates. This is used in airport and highway paving since it gives the desired flexibility and strength.
- Asphalt Emulsion
It contains 70% asphalt and less than 1.5% of chemical additives. They are sprayed on the road surface followed by a layer of crushed rocks.
- Asphalt Plant
It is a plant used for the manufacture of asphalt and other forms of road stone, collectively known as asphalt concrete. The plant is used for mixing the dry, warm aggregate, padding, and asphalt for homogeneous mixture at the required temperature. The plant is composed of the cold aggregate supply system, drum dryer, coal burner, coal feeder, dust collector, etc.
Plant Health And Safety Concerns
Health, safety, and environmental control are a critical part of asphalt storage and handling. Control of fumes such as hydrogen sulfide fumes is a safety consideration. H2S fumes from its storage tanks can cause disorientation and injury to workers.