Definition, Types, and Applications
Bitumen, a highly versatile material, finds extensive utilization across various industries. With over 85% of global production dedicated to road construction, 10% utilized in other building projects, and the remaining 5% serving diverse sectors like insulation, bitumen holds immense significance.
Delve further into this article to gain comprehensive knowledge about bitumen.
Bitumen can be described as a viscous substance transitioning from a liquid to a semi-solid state, exhibiting a distinctive blackish-brown hue. It primarily consists of asphaltene resin and other petroleum compounds, the specific compositions of which contribute to the varying characteristics of different types of bitumen.
Origin of Bitumen: Natural and Crude Oil Extraction
Bitumen originates from both natural sources and the extraction of crude oil.
1. Natural Bitumen:
Millions of years ago, microscopic algae known as diatoms thrived in swamps, aquatic environments, and sedimentary rock formations. Over time, these organic remnants became buried under layers of sedimentary rocks. With the pressure from the upper layers and temperatures exceeding 50°C, these organic residues underwent a transformation, resulting in the formation of natural bitumen.
Today, natural bitumen can be found in oil lakes and hills, with abundant resources located in countries like Canada, Venezuela, Oman, and western Iran. It possesses varying ash content and often contains impurities such as sulfur and heavy metals. Extraction and utilization of natural bitumen are more expensive compared to bitumen derived from crude oil. It is commonly used as an additive for waterproofing coatings, mud drilling, and road construction.
2. Crude Oil Distillation:
The primary source of bitumen for the industry is crude oil. Crude oil is a mixture of diverse compounds that undergoes separation in a distillation tower. The residual product from the distillation process, known as vacuum bottom, is then further processed to produce bitumen.
Various types of bitumen, such as penetration bitumen and oxidized bitumen, are derived from specific processes involving the treatment of vacuum bottom in refineries. These types of bitumen primarily find application in road construction.
Distinguishing Bitumen, Tar, and Asphalt:
In the United States, the terms bitumen and asphalt are often used interchangeably, specifically referring to the combination of aggregates and bitumen used in road construction.
Bitumen is a hydrocarbon substance that can be found naturally or obtained through refining processes from crude oil. It serves as a binder in the composition of asphalt.
Tar is another dark hydrocarbon material, but its production differs from that of bitumen. Tar is derived from a specific distillation process involving wood or coal. Coal-based tar contains high levels of benzene, a known carcinogen.
Tar is primarily used in road construction. Historically, tar derived from wood has been utilized in Northern Europe for waterproofing boats and various other applications. Additionally, tar derived from coal and wood possesses medicinal properties and is employed in the treatment of psoriasis and as a germicide.
In general, asphalt refers to the combination of aggregates and bitumen used for road construction. In the United States, asphalt and bitumen are considered synonymous.
It’s important to note that the terms and their specific meanings may vary depending on regional usage and context.
Bitumen Types and Their Applications: A Comprehensive Overview
Due to the diverse properties exhibited by different types of bitumen derived from various crude oils, it is crucial to classify and grade bitumen accordingly.
Refineries employ standardized tests to evaluate factors such as viscosity level, penetration value, performance, and consistency in order to grade bitumen based on its properties. This grading process yields bitumen penetration grades and viscosity grades.
In addition to these grades, other types of bitumen are classified based on their specific production processes:
1. Gilsonite (Natural Bitumen):
Gilsonite refers to a type of natural bitumen that possesses a smooth, shiny, and solid appearance. Its classification is based on the ash content and solubility in organic solvents.
Due to its hard and brittle nature, Gilsonite is commonly used in powder form. Its composition closely resembles that of refinery bitumen. In the road construction industry, Gilsonite is sometimes combined with refined bitumen. While it exhibits higher resistance to water penetration, it has lower penetration and deformation properties.
Applications of Gilsonite:
- Printing Industries: Gilsonite finds application in the printing industry.
- Painting Industry: It is utilized in the painting industry for various purposes.
- Drilling Mud and Cement: Gilsonite is employed in drilling mud and cement for its beneficial properties.
- Asphalt and Road Construction: It is utilized in asphalt and road construction projects.
- Casting Sand Additive: Gilsonite serves as an additive in casting sand.
- Chemical Products: It finds usage in the production of various chemical products.
- Improving the Quality of Bitumen: Gilsonite can be utilized to enhance the quality of bitumen in different applications.
2. Penetration Grade Bitumen:
Penetration grade bitumen is extensively used in the construction of roads.
After being produced in refineries, bitumen undergoes classification based on a penetration test using a penetrometer apparatus. The depth to which a needle penetrates the bitumen surface determines its softness and suitability for different weather conditions. The most commonly used penetration grades for road construction are 60/70 and 80/100. The 60/70 grade is also widely utilized as a waterproofing material in buildings.
When using penetration grade bitumen, it is important to consider the average temperature of the area and the volume of traffic.
Refer to the table below to see the different grades of penetration bitumen along with their applications:
Suitable for tropical areas with
Ideal for regions with mild
Designed for use in cold climate
Primarily used for road repairs
By selecting the appropriate penetration grade based on temperature conditions, bitumen can be effectively utilized for road construction and repair, ensuring durability and performance.
3. Viscosity Grade Bitumen:
Viscosity grade bitumen is classified based on its viscosity after production in the refinery. This classification system is relatively newer compared to penetration grading. India is the largest consumer of viscosity grade bitumen.
Viscosity grade bitumen has four different grades: VG 10, VG 20, VG 30, and VG 40, each with its own unique applications.
Different Grades of Viscosity Grade Bitumen:
Used in cold regions for road construction
Maximizes asphalt performance in hot regions, a more reliable choice than bitumen penetration grade 60/70
Works well in areas with high traffic loads, suitable for road construction in hot weather
The reason for using viscosity grading instead of penetration grading is the consideration of the change in bitumen viscosity at high temperatures. Viscosity grade bitumen provides more accurate performance in hot weather conditions. Unlike penetration grading, where a specific grade of bitumen may yield varying results at a specific temperature, viscosity grade bitumen consistently behaves the same.
Advantages of Viscosity Grade (VG) Bitumen over Penetration Grades:
- Consistency in Hot Temperatures: Viscosity grade bitumen ensures consistent performance in hot temperatures. The behavior of specific grades remains stable regardless of temperature fluctuations.
- Predictability: Viscosity grade bitumen is a better choice when predicting bitumen behavior in the hottest time of the year, as well as its properties in normal weather conditions.
- Easier Application: Viscosity grading is based on testing bitumen properties at three different temperatures (25°C, 60°C, and 135°C), making it more practical and easier to apply compared to penetration grading.
By considering viscosity, viscosity grade bitumen offers improved accuracy and reliability, particularly in hot weather conditions, enhancing the overall performance of road construction projects.
4. Emulsion Bitumen
Bitumen emulsion, as its name suggests, is produced by combining bitumen with water. This type of bitumen emerged in the industry as an environmentally friendly alternative to cutback bitumen, as water serves as a reliable substitute for organic solvents in diluting bitumen for specific applications.
Bitumen emulsion finds utility in various applications such as waterproofing, spraying, and acting as tack coats between layers of asphalt pavement. Furthermore, it offers advantages in terms of transportation, handling, and storage, being easy, economical, and safe.
The classification of bitumen emulsions is primarily based on two factors: the electrostatic charge of the particles and the breaking or setting time.
In terms of electrostatic charge, bitumen emulsions can be categorized as anionic (with a negative charge) or cationic (with a positive charge).
The second classification system revolves around the time required for a bitumen emulsion to release water and reach a sticky state, suitable for binding aggregates.
Different grades of bitumen emulsions possess distinct properties, making each type suitable for specific applications. The viscosity level, setting time, and electronic charge of bitumen particles all influence the choice of grade and type of bitumen emulsion for a particular application.
Bitumen emulsions have lower viscosity compared to other bitumen grades due to their mixture with water and emulsifiers. This characteristic makes them particularly suitable for spraying applications.
Additionally, bitumen emulsions are ideal for pavement maintenance and the renovation of old roads.
Major applications of bitumen emulsions in today’s industry include tack coats, chip seals, slurry seals, and micro surfacing. These versatile emulsions play a crucial role in enhancing the durability and performance of road surfaces.
5. Cutback Bitumen
Cutback bitumen is a type of bitumen used in industries that require low viscosity. It is particularly employed in situations where conventional bitumen cannot be preheated for asphalt production.
The preparation of cutback bitumen involves blending penetration bitumen with specific organic solvents. These solvents can include gasoline, naphtha, diesel oil, and furnace oil.
This type of bitumen is well-suited for use in cold climates. When cutback bitumen is applied, the solvents gradually evaporate, leaving behind the bitumen.
Cutback bitumen finds its application primarily in primer sealing and sprayed sealing processes.
One significant concern associated with cutback bitumen is its environmental impact. The volatile solvents present in the mixture pose hazards to nature, human health, and the environment at large. Efforts have been made to mitigate these concerns and promote more environmentally friendly alternatives.
6. Oxidized Bitumen
Oxidized bitumen is produced in refineries through a process known as blowing, which involves introducing hot air into penetration bitumen. This oxidation process results in chemically stable bitumen with enhanced durability. Oxidized bitumen exhibits impermeability to water and is well-suited for insulation purposes.
Compared to pure bitumen, oxidized bitumen has a lower degree of penetration and a higher softening point. It is classified based on these two properties to differentiate its grades.
The applications of oxidized bitumen are diverse. It is commonly used for waterproofing in construction projects such as dams and buildings. Additionally, it finds utility in road construction when combined with other types of bitumen. In industries like oil and gas, oxidized bitumen is utilized to coat pipelines and prevent corrosion.
Overall, oxidized bitumen serves as a reliable and durable material in various industries where waterproofing and protection are essential.
7. Performance Grade Bitumen (PG Bitumen)
Performance Grade (PG) bitumen is a type of bitumen grading system based on its performance characteristics at different temperatures. It takes into account the ability of the bitumen to withstand a wide range of temperatures, addressing issues such as rutting at high temperatures and cracking at low temperatures.
The classification of PG bitumen is determined by evaluating its performance at high and low temperatures. The average maximum and minimum temperatures of the environment where the asphalt will be used are selected. The bitumen is then exposed to these temperatures for a week, and the average high and low temperatures are increased by 6 °C.
PG bitumen grades are represented by a combination of positive and negative numbers, indicating the maximum and minimum temperatures, respectively. For example, PG 64-10 indicates that the bitumen meets the performance requirements at an average maximum pavement temperature of 64 °C and a minimum pavement temperature of -10 °C.
The sum of the high and low temperature numbers determines whether the bitumen is polymer-modified or unmodified. If the sum is more than 90, it is a polymer-modified bitumen, while a sum less than 90 indicates an unmodified bitumen.
Different PG grades have specific performance characteristics. Some grades are more resistant to thermal cracking (e.g., PG 58-34, 64-22, 64-28, 76-22), while others are more resistant to rutting (e.g., PG 70-22, 70-28, 76-28, 82-22).
Performance grade bitumen is commonly used in various construction applications, including pavement construction and reconstruction, edge sealing, and crack sealing in both dense and open-grade Hot Mix Asphalt (HMA). Its performance characteristics make it a suitable choice for withstanding the demanding conditions and temperature fluctuations in asphalt applications.