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What is Asphalt?

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To define asphalt, it is a black or brown petroleum-like substance with a viscous liquid to glassy solid consistency. It can be used as a byproduct of petroleum distillation or as a natural deposit. Asphalt materials are made up mostly of hydrogen and carbon compounds, with small amounts of nitrogen, sulphur, and oxygen. Natural asphalt, which is thought to have evolved during the early stages of the breakdown of organic marine deposits into petroleum, is mineral-rich, whereas residual petroleum asphalt is mineral-free. Since it includes bitumen, a hydrocarbon substance, asphalt is also known as bituminous material. Bitumen is also present in the tar produced from the destructive distillation of soft coal. 

Bituminous materials include both petroleum asphalt and coal tar. Petroleum asphalt should not be confused with coal tar because their properties are so dissimilar. Unlike petroleum asphalt, which is almost entirely made up of bitumen, coal tar has a low bitumen content. Both materials must be considered as distinct entities. Asphalt's great flexibility is one of its attributes and advantages as an engineering construction and maintenance material. Asphalt can be liquified by applying heat, dissolving it in solvents, or emulsifying it, despite the fact that it is semi-solid at normal temperatures. Asphalt is a solid cement that is easily adherent, waterproof, and long-lasting, making it ideal for road construction. Most acids, alkalis, and salts have a high resistance to their action.

Asphalt materials have been used for a long time, dating back to their use as a water stop between the brick walls of a reservoir at Mohenjo-Daro (about the 3rd millennium BC). It was widely used in the Middle East for paving roads and sealing waterworks, which are still significant applications today.

Types of Asphalt

When heated, asphalt materials soften and become elastic under some conditions. Except when used as a binder or adhesive, asphalt's mechanical properties are of little importance. The grades of asphalt are as follows:

  • Natural Asphalt

  • Residual Asphalt

  • Mastic Asphalt

  • Asphalt Cement

  • Cutback Asphalt

  • Asphalt Emulsion

Natural Asphalt: 

Lake asphalt and Rock asphalt are two types of natural asphalt. At depths of 3 to 60 metres, lake asphalt can be found as fossil deposits in areas like Trinidad's lakes. It is made up of 40 to 70 percent pure bitumen with around 30 percent water content.

Residual Asphalt: 

It's made by combining crude petroleum oil with an aspheric base and distilling it.

Mastic Asphalt: 

This is also known as artificial asphalt, is made by combining the required minerals, such as limestone, dust, fine and coarse aggregates, with black bitumen that has been heated to a liquid state. It hardens into a hard elastic block as it cools. It is reheated on the job site and used for waterproofing and pavement construction. Mastic asphalt is long-lasting, rugged, water-resistant, non-absorbent, non-flammable, and quiet.

Asphalt Cement: 

It is a mixture of bitumen and asphalt with flux oils that have adhesive properties and can be used to make mastic asphalt. In the production of bituminous pavements, it is favoured.

Cutback Asphalt: 

It is a liquid asphalt that is made up of asphalt cement and a petroleum solvent. Since they minimise asphalt viscosity for lower temperatures, they are used in bituminous paints, roof repairs, and other applications.

Asphalt Emulsion: 

This is a suspension of small asphalt cement globules in 50 - 60% water with a 1% emulsifying agent. Tack coats, fog seals, slurry seals, bituminous surface treatments, and material stabilisation are all examples of low-temperature applications.

Asphalt Properties and Uses

Asphalt is classified as a mixture of bitumen (as binding material) and inert minerals such as sand, gravel, and crushed stone in a substantial proportion. It has a blackish-brown colour and is available as a solid at low temperatures and as a liquid at temperatures above 50°C. Asphalt can be found in nature as natural deposits in many parts of the world, as well as being produced artificially. Let's take a look at its properties and applications.

Technical Properties of Asphalt

1. Waterproof Property

Asphalt is a water-repellent material with a lightweight structure that does not dissolve in water. It also has strong plasticity, adhesion strength, and bond force with mineral materials, making it waterproof.

2. Viscosity

Viscosity is a property that indicates how the materials in asphalt impede its fluidity. The hardness and density of asphalt are also reflected in its viscosity. At room temperature, different states of asphalt have different viscosity indexes. At room temperature, penetration is used to express the viscosity of semisolid or solid asphalt; at room temperature, viscosity degree is used to express the viscosity of liquid asphalt.

3. Plasticity

When an external force is applied to the asphalt, it deforms without being broken, and when the external force is removed, the asphalt retains its deformed shape, which is represented by ductility.

4. Temperature Sensitivity

The property that the viscosity and plasticity of asphalt change with temperature change are known as temperature sensitivity. Asphalt is a non-crystal polymer material. Asphalt, on the other hand, has no set melting point and changes shape as the temperature changes. The temperature sensitivity of asphalt is low when the temperature changes at the same rate but the viscosity and plasticity change little, and it is high when the temperature changes at the same rate but the viscosity and plasticity change a lot.

5. The Stability of Asphalt in the Atmosphere

The property of asphalt to resist ageing in a comprehensive climate of heat, sunlight, and atmosphere for a long time is referred to as its stability in the atmosphere. Low molecular groups will be converted into polymeric groups in the atmosphere's comprehensive setting, and the resin will turn into ground asphaltene at a much faster rate than the oil composition into the resin. The oil composition and resin content decrease, while ground asphaltene content rises, reducing asphalt fluidity, plasticity, and cohesion while increasing hardness and brittleness. Asphalt ageing is the name given to this phenomenon. From the preceding assumptions, it is clear that the property of asphalt to resist ageing, also known as its longevity, is responsible for its stability in the atmosphere.

Uses of Asphalt

Asphalt is most often used for road surfacing, which can be achieved in a number of ways. Repetitive light oil "dust layer" treatments may be used to create a hard surface, or granular aggregate can be applied to an asphalt coat, or earth materials from the road surface can be combined with the asphalt. Other critical applications include canal and reservoir linings, dam facings, and other harbour and sea works; asphalt used in these applications may be a thin, sprayed membrane covered with earth for weathering and mechanical protection or thicker surfaces with riprap (crushed rock). Roofs, coatings, floor tilings, soundproofing, waterproofing, and other building-construction components, as well as a variety of industrial items such as batteries, all, use asphalt. For some applications, an asphaltic emulsion is made by suspending fine globules of asphalt in water.


Because of its many benefits, such as rapid construction, ease of maintenance, driving comfort and protection, low noise levels, and so on, asphalt pavement is widely used in expressways around the world. However, there are several disadvantages of using asphalt pavement. Owing to the effect of thermal, oxygen, light, water, and other environmental influences, asphalt is susceptible to ageing, which can result in problems such as potholes, cracks, loosening, and shortened service life. As a result, improving the road performance of asphalt materials is critical.

Asphalt Pavements

On hot summer days, asphalt pavements become too smooth, but on cold winter nights, they become very brittle. The permanent deformation of the pavement caused by heavy traffic on the soft asphalt paving is known as "rutting." Pavement cracking occurs during the winter months when the asphalt binder becomes too brittle. This means that the asphalt binder only functions well within its application window, where it is visco-elastic enough to dissipate traffic-induced tension. This application window is extended by polymer alteration, which primarily increases viscoelasticity at high temperatures. The modified asphalt also has greater fatigue resistance and increases pavement lifespan, for example, 10 years vs. 15 years with and without modification.

Alternatives and Bio-asphalt

Asphalt can be produced from non-petroleum-based renewable resources such as sugar, molasses, rice, corn, and potato starches, though it is economically uncompetitive. Asphalt may also be made from waste by fractional distillation used motor oil, which is mostly burned or dumped into landfills. In colder climates, the use of motor oil can cause premature cracking, necessitating more frequent repaving. Asphalt binders that aren't dependent on petroleum may be light-coloured. Roads that are lighter in colour absorb less heat from the sun, minimising their contribution to the urban heat island effect. Green parking lots are parking lots that use asphalt alternatives.


Asphalts are different types of bitumen that occur naturally. Asphalts are also produced as a byproduct of the petroleum industry. Both compounds are black and soluble in carbon disulphide to a significant extent. They can range in consistency from a highly viscous fluid to a solid. Asphalts may have a mineral matter or not. Many forms of asphalts can be found in sandstones, siltstones, and limestones as viscous impregnations. The asphalts are fused at 54–60 °C after being treated to eliminate water and volatile constituents and contain approximately 83 percent carbon. The majority of asphalts are of marine origin and are made up of high-molecular-weight compounds found in petroleum residue.

FAQ (Frequently Asked Questions)

1. What is Asphalt?

Ans: Asphalt is known as a mixture of bitumen (as binding material) and a significant amount of inert minerals such as sand, gravel, and crushed stone. It has a blackish-brown colour and is available as a solid at low temperatures and as a liquid at temperatures above 50°C. Asphalt materials can be found in nature as natural deposits in many areas, but they can also be produced artificially.

2. Is Asphalt and Bitumen the Same?

Ans: The liquid binder that binds asphalt together is known as bitumen. A bitumen-sealed surface is one that has been sprayed with bitumen and then coated with aggregate. This is then done again to create a two-coat seal. Asphalt is made in a plant that heats, dries, and combines concrete, bitumen, and sand to form a composite.

3. What is Asphalt Made of?

Ans: Asphalt is a black or brown petroleum-like substance with varying degrees of viscosity ranging from viscous liquid to glassy solid. It is obtained as a byproduct of petroleum distillation or from natural deposits. Asphalt is made up of hydrogen and carbon compounds with trace amounts of nitrogen, sulphur, and oxygen.