Asphalt

Asphalt is also referred to as bitumen whose main source is petroleum from where it is derived as the semi-solid compound and it is a thick, sticky, black, highly viscous liquid. It is classed as pitch and it is found in both natural deposits as well as in refined products. Asphaltum was the term that was used for asphalt before the 20th century. The Pitch Lake located in La Brea in southwest Trinidad which is Antilles island located on the northeastern coast of Venezuela within the Siparia Regional Corporation consist of the largest natural asphalt deposits in the world that are accounted for almost 10 million tons.

The primary use of the asphalt goes into the construction of the road which accounts for 70% of the asphalt that is explored.  Here the asphalt is used as glue and the binder is mixed with the construction aggregate materials in order to develop the asphalt concrete. Sealing flat roofs, production of roofing felts and bituminous waterproofing products are the main products that are developed from asphalt other than concrete. Naturally occurring asphalt whose viscosity is very similar to that of cold molasses is referred to as “crude bitumen”. But when the crude oil undergoes fractional distillation where it is heated at a temperature of  525 °C (977 °F), the asphalt that is generated in the process is referred to as “refined bitumen”. The widest reserve of natural asphalt is in the Canadian province of Alberta where asphalt is mostly found in Athabasca oil sand that covers about 142000 square kilometres which is an area larger than the geography of England. 

With the change in the temperature, the properties of the asphalt also changes. It is because the specific range when attained by the asphalt, its viscosity results in the compaction by providing enough lubrication to the particles during the process of compaction. When the temperature is low, the particles of aggregate cannot move swiftly, thus the required density is not reached. Asphalt plant is responsible for producing asphalt where the plant could be fixed or it could be a mobile mixture in a plant. It is possible to produce asphalt in a plant that accounts for almost 800 tonnes per hour. The average temperature that is required to produce a hot mix of asphalt is between 150 and 180°C. But the new techniques are developed these days to produce a mix of asphalt at low temperatures. 

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.

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.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.

Types of Asphalt

Asphalt mainly is obtained from petroleum. Crushed rock, sand, gravel or slags are used as aggregates for the mixture of asphalt. Today certain types of wastes such as by-products and products of constructions such as demolition debris are used as an alternative aggregate for asphalt mixture which increases the sustainability of asphalt. A binder is commonly used to bind the aggregates into a cohesive mixture and the most commonly used binder used to date is a bitumen. But these days many of the bio-binders came into the market that is actively used for binding the aggregates into the mixture so as to minimize the impact on the environment of the roads. The average pavement that is structured with the help of asphalt is always a level up above the formation of the road. It includes bounded and unbounded bituminous materials. This gives the pavements the ability to distribute the load of the traffic that arrives before it is being formed. 

To be able to provide the best performance, many varieties of asphalts are used for various requirements. For various requirements of the roads such as heavy traffic, noise control, weather conditions, heavy vehicles running on the road, various pressure and temperature fluctuation etc. different grades of asphalts are required that could be sufficiently stiff and hard enough to withstand the pressure the weels of various weighed vehicles and heavy traffic creat on it. On the other hand, it has to be flexible enough to avoid any cracking due to temperature and pressure variations.  In order to achieve complete durability, a fully compacted good workable mixture of asphalt is required during application. Thus the various kind of asphalt mixture at various temperature is as follows:-

1. Hot Mix Asphalt (HMA): Generally hot asphalt mixes are produced at a temperature between 150 to 180 0C. Different asphalt mixtures can be used on the basis of the usage and their application area. It is mostly used for paving and patching. It is easier to work with asphalts when their temperature is high. It needs to be used immediately after the purchase and it is a permanent solution to all the paving and patching problems.

2. MC cold mix: It is temporary used asphalt and is used for a temporary fix. As it is used in a cold form thus its temperature is also cold and therefore it has a slow cure. Thus it is best fit in the areas that have very minimal or no traffic at all. 

3. UPM: It is also a cold asphalt, but unlike the MC cold mix it is used for the permanent solution to any of the asphalt mix or concrete problems. It is made durable for any weather conditions and can witness any traffic load. Thus it is used to fix both the dry and the wet holes. This makes the repair in any condition really easy. It is immediately ready to be tread upon once the asphalt is compacted. 

4. Warm Mix: As it is mixed and shipped when it is at a lower temperature thus it is not cooled off as faster as the hot mix.  It is easier to pour and spread due to the emulsion used in it. 

5. Cut back asphalt: Cut back asphalt materials are asphalt cement as well as petroleum solvent. It has a decreased viscosity and thickness and because of this property, it is being preferred over other asphalts. It is restricted in many areas as it contains some volatile materials.

6. Mastic asphalt: It is a dense and durable formulation of asphalt and is also a waterproofing medium in itself. The mastic asphalt materials consist of stone fillers, a mixture of asphalt and mineral powder that is heated and mixed at high temperatures. 

Uses of Asphalt

Though asphalt is mainly used for taking rows its versatility has made it such a widely used material. Therefore it is also used for various other purposes like transportation recreation agriculture industrial and building construction. Therefore some of the  applications and uses of Asphalt is mentioned below:

1. Asphalt pavement in tunnels: most of the roads that are paved around the world are made of Asphalt as it is highly durable and gives good performance mostly for heavy traffic conditions. It gives long-lasting performance and durability under a wide range of temperature and climatic conditions. Asphalt sir is also used mostly in the industrial areas for some specific applications such as building airports and the base course of railway tracks, buildings and is also widely used for making tunnels.

2. Asphalt on bridge decks: most of the bridges that are made up of concrete have Asphalt surfaces on top in most of the European countries. Using Asphalt to protect the steel and concrete structure from de-icing salts and water is one of the main reasons that it is used as a surfacing material. Nice fault bridge payment system is split into four different layers namely a ceiling or bonding layer which is known as a primer, waterproofing layer, a protective layer and a surface layer of Asphalt.

3. Asphalt railway tracks: The Asphalt mixture has proved to be the best alternative for several elements of traditional railway constructions. In particular, the use of the Asphalt in construction of the tracks superstructure that consists of rails the sleepers fastings and the ballast and the sub-ballast layer has proven that these kinds of constructions have fully met the requirements that were needed to construct the modern railway system. Because of the properties of bitumen and Asphalt, they offer good opportunities as a construction material for modern railway tracks. For both the heavily loaded tracks and for high-speed tracks this has been proven as one of the best alternatives to traditional railway construction. They provide a positive contribution to the bearing capacity of the structure along with improving the stability and durability of the structure. This results in the reduction of the need for maintenance. It is also used for reducing vibration and noise.

4. Airfield uses of Asphalt: most of the roads in the world are paved with asphalts because it has high durability and good performance under most heavy traffic conditions. Asphalt is also used for the construction of high-standing and parking roads that are meant for both light and heavy vehicles. For the construction and surfacing of access roads, perimeter roads and vehicle parking areas on airfields, they are eminently suitable. Most of the airport pavements are constructed with asphalt. Airports are comprised of runways, taxiways, aprons and parking areas. Different types of surface courses are required for different types of specifications. Good resistance is needed to puncturing, to fuel and to chemical agents for parking and apron areas. For the runway, an anti-skid property needs to be ensured. Asphalt comes to the rescue for all the specifications.

Disadvantages

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.

Conclusion

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.