Introduction:
Bitumen is a byproduct of refining petroleum crude through distillation. In its refined form, petroleum can be anything from the simplest hydrocarbon gas—methane—to the hardest bitumen, whose components have molecular weights in the millions. Thermoplastic amorphous aromatic rubber (TAR) is a byproduct of destructive distillation. Paving grades refer to bitumen that is used for waterproofing structures and industrial floors, whereas industrial grades are used for paving roadways and airfields.
Fig1: Bitumen
Courtesy: saharabizz.com
What is Bitumen?
Bitumen, also known as asphalt, is a black, sticky, highly viscous liquid or semi-solid form of petroleum. It is a naturally occurring substance and is one of the primary components of crude oil. Bitumen is a complex mixture of hydrocarbons, mainly aromatic compounds, and polycyclic hydrocarbons. Bitumen is widely used for paving and repairing roads. A binder or adhesive holds together aggregates, such as sand, gravel, and crushed stone, to create asphalt concrete. This mixture is then used to pave roads, highways, airport runways, and other surfaces. Bitumen provides strength, durability, and resistance to weather and traffic loads, making it ideal for road construction.
Apart from its use in road paving, bitumen has various other applications. It is used in waterproofing products, such as roofing felt, membranes, and shingles. Bitumen also manufactures coatings, sealants, adhesives, and insulation materials. In some regions, bitumen is utilized as a fuel source for heating and industrial processes.
How is Bitumen Made?
The procedure for the manufacturing of bitumen can be described as follows:
- Crude oil is extracted from oil wells in oil fields or offshore drilling sites. It is a mixture of various hydrocarbons, including bitumen, gasoline, diesel, and other petroleum products.
- The crude oil is transported to a refinery, undergoing several processes to separate and purify its components. The first step is atmospheric distillation, where the crude oil is heated in a large tower called a distillation column. The different hydrocarbons vaporize at different temperatures, allowing them to be collected and further processed.
- In the distillation column, the crude oil is heated at the bottom, and as the temperature rises, the various components with different boiling points vaporize. The column is equipped with trays or packing materials to maximize the surface area for vaporization and condensation.
- Bitumen has a high boiling point and is one of the heaviest components in crude oil. As the vapor rises in the distillation column, it eventually reaches a section where the temperature and pressure are suitable for bitumen to condense and collect. This section is usually near the bottom of the column.
- The collected bitumen, which may still contain impurities, undergoes additional processing steps to improve its quality. It may include removing solids, water, and other contaminants. The specific refining processes can vary depending on the desired characteristics of the final product.
- Once the bitumen is refined, it is typically stored in tanks or transported via specialized tanker trucks or pipelines to various manufacturing plants or construction sites, where it is used for its intended applications.
Properties Of Bitumen:
(i) Viscosity: Bitumen has a high viscosity, which means it is thick and flows slowly. This property allows it to adhere to aggregates and form a strong bond, making it an excellent binder for road construction.
(ii) Adhesion: Bitumen exhibits strong adhesive properties, allowing it to stick to various surfaces such as aggregates, concrete, and metals. This property is essential for creating durable asphalt pavements and waterproofing structures.
(iii) Waterproofing: Bitumen is highly impervious to water, making it ideal for waterproofing applications. It is a barrier, preventing water penetration and protecting structures from moisture damage.
(iv) Elasticity: Bitumen displays elasticity, meaning it can deform under stress and return to its original shape once removed. This property allows bitumen pavements to withstand traffic loads and temperature changes without significant cracking.
(v) Thermal Properties: Bitumen has good thermal stability and can withstand various temperatures. It remains solid at lower temperatures and does not melt or flow excessively at high temperatures, which is crucial for maintaining the structural integrity of roads in different climates.
(vi) Durability: Bitumen is known for its durability and resistance to aging. It can withstand the effects of weathering, oxidation, and chemical attacks, ensuring the longevity of asphalt pavements.
(vii) Flexibility: Bitumen pavements have inherent flexibility, enabling them to accommodate slight movements in the underlying soil or traffic loads without cracking. This flexibility contributes to the overall strength and durability of asphalt roads.
(viii) UV Resistance: Bitumen resists sun ultraviolet (UV) radiation. It can withstand prolonged exposure to sunlight without significant degradation or color fading, making it suitable for outdoor applications.
(ix) Insulating Properties: Bitumen has relatively good thermally and electrically insulating properties. It can act as a thermal barrier, reduce heat transfer, and provide electrical insulation in certain applications.
(x) Recycling: Bitumen is a recyclable material that can be reclaimed and reused in various ways. Reclaimed bitumen can be incorporated into new asphalt mixtures, reducing the demand for new bitumen and promoting sustainability in road construction.
Uses of Bitumen:
(i) Road Construction: Bitumen is primarily used in road construction and paving. It is a binder in asphalt concrete, creating durable and flexible road surfaces. Bitumen binds the aggregates, providing strength and resistance to heavy traffic loads.
(ii) Roofing and Waterproofing: Bitumen is widely used in the construction industry for roofing and waterproofing purposes. It is a waterproofing material in flat roofs, forming a protective layer against water penetration and providing excellent weather resistance.
(iii) Pavement Preservation: Bitumen-based products are used for pavement preservation to extend the life of existing asphalt roads. Techniques like chip sealing and slurry sealing involve applying bitumen emulsions or thin layers of bitumen on the road surface to seal cracks, prevent moisture intrusion, and improve skid resistance.
(iv) Airport Runways: Bitumen is used in constructing airports and taxiways due to its ability to withstand heavy aircraft loads. Asphalt concrete with bitumen provides a smooth, durable surface for safe landing and takeoff.
(v) Bridge Deck Waterproofing: Bitumen membranes are employed to waterproof bridge decks, protecting the underlying structure from water damage and corrosion. These membranes provide a flexible barrier that prevents moisture ingress, extending bridges’ lifespan.
(vi) Pipe Coating: Bitumen coatings protect pipes against corrosion and abrasion. The coatings provide a protective layer that ensures the longevity and integrity of the pipes, particularly in oil and gas transportation.
(vii)Paints and Coatings: Bitumen is used to manufacture paints and coatings. Bituminous paints provide excellent corrosion resistance and are applied to metal surfaces, such as pipes, tanks, and structural elements, to protect them from the elements.
Fig2: Tar
Courtesy: hpdconsult.com
What is Tar?
Tar is a black, sticky liquid with a high carbon concentration. Tar is a highly viscous liquid. Similar to bitumen, tar is a mixture of several chemical compounds. Tar is a pitch-black substance. Temperature extremes have a profound effect on tar. Tar is hard and brittle at low temperatures and malleable and liquefied at high ones. Because of this, tar is not a good choice for places with extreme temperature swings. Tar has a low viscosity compared to bitumen. Tar’s low cost and abundance make it a versatile substance with many applications.
How is Tar Made?
Here are the primary steps involved in making tar:
- Commonly used organic materials for tar production include wood, coal, peat, or petroleum. The choice of material depends on the desired properties of the tar.
- The organic material is loaded into a closed container to withstand high temperatures. The retort is sealed to prevent air from entering.
- The retort is heated to high temperatures, typically between 400 to 700 degrees Celsius (750 to 1300 degrees Fahrenheit), using an external heat source such as fire or an electric furnace. The absence of air prevents the combustion of the organic material.
- The organic material undergoes decomposition and vaporization as the retort heats up. Complex organic compounds break down into simpler molecules, releasing volatile gases and leaving behind a residue known as tar.
- The vapors produced during the process are captured and condensed to separate the tar from other byproducts. The condensed vapors are collected in a cooling system, condensing into a liquid form.
- The collected liquid, which contains tar and other substances, undergoes further purification to separate impurities and unwanted components. Various methods, such as filtration or distillation, can refine the tar.
- Once the tar is purified, it is cooled to room temperature, causing it to solidify into a thick, viscous substance. The exact consistency of the tar depends on the type of organic material used and the specific manufacturing process.
Uses of Tar:
(i) Roofing: Tar is widely used in roofing materials, particularly in built-up systems. It is combined with roofing felt or fiberglass layers to create a durable and waterproof barrier.
(ii) Waterproofing: Tar is an effective waterproofing agent to seal and protect various construction elements. It can be applied to foundations, basements, tunnels, and underground structures to prevent water infiltration and damage.
(iii) Road construction: Tar forms asphalt when mixed with aggregate materials. Asphalt is extensively used in road construction for surfacing roads and highways. It provides a smooth, durable, weather-resistant surface that can withstand heavy traffic loads.
(iv) Paving and surfacing: Tar-based materials like asphalt are used for parking lots, driveways, walkways, and other surfaces. These materials offer excellent strength, flexibility, and resistance to weathering, making them suitable for a wide range of applications.
(v) Preservation of wood: Tar, specifically creosote derived from coal tar, is utilized for preserving wood in construction. It is commonly applied to utility poles, railway ties, and other wooden structures to enhance their resistance to decay, insects, and fungi.
Difference between Bitumen and Tar:
- Bitumen is a semi-solid form of petroleum. It is a sticky, black substance primarily composed of hydrocarbon molecules. It occurs naturally or can be obtained from crude oil through a refining process. Tar is a dense, black material derived from various organic materials, such as coal, wood, peat, or petroleum. It is a byproduct of destructive distillation or carbonization processes.
- Bitumen is primarily manufactured during the crude oil refining process. It involves the separation of bitumen from other components of crude oil, such as lighter hydrocarbons. Tar is produced through destructive distillation or carbonization processes. Physical Properties and Applications:
- Bitumen is known for its excellent waterproofing properties and resistance to weathering and oxidation. Tar is highly adhesive and has excellent water resistance properties.
- Bitumen is considered to have a lower environmental impact compared to tar. However, its extraction and refining processes still have associated environmental concerns, such as greenhouse gas emissions and habitat disruption. Tar, particularly coal tar, has environmental concerns due to toxic substances like PAHs, which are known to harm human health and the environment.
Conclusion:
In summary, bitumen and tar is black, sticky substances used in construction applications, but they differ in composition, manufacturing processes, physical properties, and environmental considerations. Bitumen is derived from petroleum, while tar can be obtained from various organic materials. Bitumen is widely used in road construction and has lower environmental concerns, whereas tar’s usage has decreased due to its toxicity and environmental impact.
References:
1. Yadav, P. (2020, October 12). Bitumen vs Tar: Difference and Comparison. Ask Any Difference. https://askanydifference.com/difference-between-bitumen-and-tar/
2. Applications & Uses of Bitumen in Construction. (2020, February 12). Applications & Uses of Bitumen in Construction -BuildersMART. https://www.buildersmart.in/blogs/bitumen/
3. What is Tar | Uses of Tar | Difference Between Asphalt and Bitumen & Tar | What is Road Tar (2023). (2020, December 3). HPD TEAM. https://www.hpdconsult.com/what-is-tar/
4. Darbandizadeh, M. (2020, September 14). What are the Differences between Bitumen, Tar and Asphalt? Infinity Galaxy. https://infinitygalaxy.org/difference-bitumen-asphalt-tar/
5. Definition and difference between bitumen and Tar – Advantages and disadvantages of Bitumen. (2020, May 16). Definition and Difference Between Bitumen and Tar – Advantages and Disadvantages of Bitumen. https://www.civilworkstudy.com/2020/05/definition-and-difference-bitumen-and.html
6. M. (2022, November 5). Difference between Bitumen And Tar – MDM Tool Supply. MDM Tool Supply. https://mdmtool.com/difference-between-bitumen-and-tar/
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