Author: Emperador

Bitumen, commonly known as asphalt, is a crucial component in the construction and infrastructure industry. It is a versatile and durable material with various grades tailored for specific applications. This article explores the production process of bitumen and delves into the different grades, including penetration grades, viscosity grades, cutback bitumen, oxidized bitumen, emulsion bitumen, AC grades, and performance grades.

Production Process:

Bitumen is derived from crude oil through a process called fractional distillation. This process involves heating crude oil to separate it into different components based on their boiling points. Bitumen is obtained from the heaviest fraction, known as the vacuum residue. This raw bitumen undergoes further processing to achieve desired properties and grades.

Grades of Bitumen:

1. Penetration Grades:

   Penetration grades classify bitumen based on their consistency or hardness. The penetration test measures the depth (in tenths of a millimeter) to which a standard needle penetrates the bitumen sample under specified conditions and load. Higher penetration values indicate softer bitumen suitable for low-temperature applications, while lower values indicate harder bitumen suitable for high-temperature conditions.

2. Viscosity Grades:

   Viscosity grades characterize bitumen based on their flow properties at a specific temperature. The viscosity test measures the kinematic viscosity of bitumen at 60°C. Bitumen with higher viscosity values is more resistant to flow and is often used in high-temperature climates, while lower viscosity grades are suitable for colder regions.

3. Cutback Bitumen:

   Cutback bitumen is produced by blending bitumen with a solvent or cutter oil to reduce its viscosity. This process makes the bitumen more workable and easier to handle. The solvent evaporates after application, leaving behind the bitumen. Cutback bitumen is commonly used in road construction and maintenance.

4. Oxidized Bitumen:

   Oxidized bitumen is produced by blowing air through bitumen at elevated temperatures. This process alters the bitumen’s properties, making it more resistant to temperature variations and aging. Oxidized bitumen is commonly used in roofing applications.

5. Emulsion Bitumen:

   Emulsion bitumen is a mixture of bitumen and water stabilized by an emulsifying agent. This grade is advantageous for its easy handling and storage. Emulsion bitumen finds applications in surface treatments, tack coats, and cold mix asphalt.

6. AC Grades (Asphalt Cement):

   AC grades are unmodified bitumen used as a binder in hot mix asphalt (HMA) for road construction. These grades are designed to provide the necessary adhesive and cohesive properties to bind aggregates together in asphalt pavement.

7. Performance Grades:

   Performance grades classify bitumen based on their high- and low-temperature performance characteristics. The Superpave system, widely used in the United States, assigns specific temperature-related properties to bitumen, ensuring optimal performance in different climates.

Bitumen, a vital component in the construction industry, comes in various grades to suit specific applications. The production process involves refining crude oil through fractional distillation and subsequent processing. Whether it’s penetration grades for consistency, viscosity grades for flow properties, cutback bitumen for workability, or specialized grades like oxidized and emulsion bitumen, each type serves a unique purpose in construction and infrastructure development. Understanding these grades empowers engineers and industry professionals to select the right bitumen for optimal performance in diverse environmental conditions.

Cutback bitumen refers to a group of binders created by blending penetration grade bitumen with a hydrocarbon solvent, such as paraffin or mineral turpentine. The blending process involves mixing these components, and once the solvent evaporates, the binder returns to its original penetration grade, effectively binding particles together. The term “cutback” originates from the solvent’s role in the process, as it “cuts back” or evaporates, leaving the binder to complete its intended function. The solvent, also known as the “cutter” or “flux,” plays a crucial role in this process.

Three types of solvents are commonly used in the blending process: slow-curing, medium-curing, or rapid-curing solvents, with the latter two being more prevalent in South Africa. The choice of solvent determines the bitumen’s curing rate when exposed to air, affecting its setting time. Rapid-curing solvents evaporate more quickly than medium-curing solvents. The viscosity of cutback bitumen is influenced by the proportion of solvent added—the higher the solvent proportion, the lower the viscosity. Industries requiring low viscosity bitumen, or situations where preheating bitumen for asphalt is not feasible, commonly use cutback bitumen.

To produce cutback bitumen, viscosity bitumen is mixed with organic solvents, including diesel, naphtha, diesel oil, and fuel oil, all of which have low boiling points and readily evaporate. The curing time depends on the speed of solvent evaporation, with cutback bitumen having different curing types: Slow Curing (SC), Medium Curing (MC), and Rapid Curing (RC).

Cutback bitumens, such as MC 30 and RC 250, are known for being more workable than penetration grade bitumen, requiring less heat for liquefaction and easier reshaping at lower temperatures. Notably, cutbacks offer a higher residual bitumen percentage compared to emulsions, providing more bitumen on the roadway after curing.

However, cutback asphalts pose environmental challenges due to the volatile chemicals evaporating into the atmosphere. They also require more energy-intensive solvents compared to the water and emulsifying agents used in emulsified asphalts.

The manufacturing process involves blending penetration grade bitumen with kerosene to meet viscosity specifications, with cutback bitumens categorized by flow time through a standard tar viscometer. Different grades are available, such as 50 sec, 100 sec, and 200 sec. Additional testing includes distillation and penetration requirements on the residual bitumen.

AASHTO specifies three groups of cutback bitumen: RC, MC, and SC, with viscosity measured at 60°C. British Standards define viscosity grades using a discharge viscometer at 40°C.

The SHELPHALT range may include a suffix “X,” indicating the addition of a heat-stable passive adhesion agent for improved wetting of aggregate and resistance to stripping in the presence of water.

Cutback bitumen, despite its advantages in lower application temperatures, has the drawback of consuming non-renewable energy resources lost through evaporation.

Applications of Cutback Bitumen in Bituminous Pavement Construction and Maintenance:

1. Prime and Tack Coating: Involves applying low viscosity binder for better absorption by unbound aggregate base, aiding subsequent bituminous covering adhesion. Primers are applied at rates between 0.5 and 1.4 L/m2. Tack coats assist in the adhesion of subsequent asphalt layers, with typical application rates between 0.2 and 0.4 L/m2.
2. Prime Sealing: Used where temperatures or traffic conditions may disrupt priming, offering pavement protection for 6 to 12 months.
3. Spray Sealing: Widely used in sprayed sealing applications, particularly in cooler weather, providing improved stone retention due to lower viscosity. The appropriate cutback bitumen is sprayed onto the primed pavement, followed by aggregate.

Standards for Cutback Bitumen:

• ASTM D 2026, D 2027, and D 2028 for Slow, Medium, and Rapid Curing Cutback.
• AASHTO M 81, M 82 for Rapid and Medium Curing Cutback.
• EN 15522 for Cutback and Fluxed Bituminous Binder.

Understanding Bitumen Composition:

Bitumen’s specific gravity, ranging between 0.97 and 1.02, underscores its status as a mixture of heavy organic molecules. Exhibiting a semi-solid, viscous consistency in shades of brown to black, bitumen lacks a singular composition formula. Its classification hinges on physical attributes like hardness and viscosity.

Molecular Components:

Bitumen comprises two primary molecular groups: asphaltene and maltene. Maltene influences bitumen’s adherence properties, while asphaltene molecules impact its hardness and viscosity. Classified as a thermoplastic material, bitumen reacts to temperature changes without defined melting, boiling, or freezing points, highlighting its unique organic composition.

Chemical Inertness and Waterproofing:

Bitumen’s chemical inertness and insolubility in water, typical of hydrocarbon materials, contribute to its suitability as a waterproof and anti-rust material. The chemical reaction of bitumen with oxygen, known as oxidation, occurs gradually, ensuring its long-lasting durability.

Physical Characteristics:

1. Hardness or Penetration:

Measured by penetration values, bitumen hardness indicates its suitability for various applications. Higher penetration values signify softer bitumen, ideal for road construction, while lower values indicate harder bitumen, suitable for waterproofing projects. The hardness of bitumen is also influenced by environmental factors like UV exposure and temperature fluctuations.

2. Adhesion:

Bitumen’s adhesive properties, crucial in road construction, make it an effective binder for aggregating materials. Ensuring a dry surface is paramount before applying bitumen to maximize adhesion. The type of bitumen selected depends on the weather conditions of the construction region, with softer grades favored in colder climates and harder grades in hotter environments.

3. Softening Point:

Bitumen’s softening point, determined by the ring and ball test method, is crucial for road construction. Bitumen with a higher softening point is preferable in hot weather, ensuring it maintains its efficiency by melting more slowly.

4. Viscosity and Fluidity:

Viscosity, a key property in achieving uniform asphalt, is influenced by temperature. Lower viscosity makes bitumen suitable for hot weather, maintaining adherence properties, while higher viscosity is preferred in colder conditions to prevent premature hardening and cracking.

5. Ductility:

Bitumen’s ductility and viscoelastic properties contribute to the flexibility of asphalt. The ductility test assesses the bitumen’s ability to return to its original shape after deformation, ensuring a durable and flexible binder for coating aggregates.

The penetration test assesses the consistency and stability of pure bitumen, oxidized bitumen (blown bitumen), and the residue of emulsion bitumen. However, this test is not suitable for very soft materials with low viscosity, such as tars.

This procedure categorizes bitumen based on its hardness, employing a needle with a 100-gram load that vertically penetrates the bitumen for 5 seconds at 25 degrees Celsius. The penetration value, measured in tenths of a millimeter, indicates the hardness of the bitumen. A higher penetration value corresponds to a higher bitumen grade.

For oxidized bitumen, a softening point test is used in conjunction with the penetration test for classification. The softening point test involves preparing bitumen discs and determining the temperature at which these discs can no longer support a standard metal ball.

The penetration test is conducted under specified conditions of time, temperature, and load. Typically performed at 25°C with a 100g load for 5 seconds, the test may also be conducted at different temperatures for low-temperature bitumen. A 200 pen bitumen, for example, has a needle penetration of 200 dmm at 25°C under a 100g load for 5 seconds.

The advantages of penetration grade bitumen include its relevance to typical pavement temperatures, potential correlation with low-temperature asphalt binder properties, and its quick and cost-effective nature, making it suitable for field use.

However, the test has its limitations. It is empirical and does not measure fundamental engineering parameters like viscosity. The variable and high shear rate during the test may impact results, and the test does not provide information for establishing mixing and compaction temperatures.

Bitumen penetration tests are conducted using standard methods, such as ASTM D5, ASTM D946 & AASHTO M 20, EN 12591, EN 1426, DIN 52210, SABS 307, IP 49 50 & 167, and IS Code 1203.

The penetration test apparatus includes components such as a water bath, sample container, transfer dish, penetration needle, stopwatch, thermometer, and penetrometer. The test procedure involves heating the bitumen specimen to 90°C, stirring it to achieve consistency, and then cooling it to atmospheric temperature. The penetration test is conducted by releasing a 100g load needle onto the bitumen surface for 5 seconds, with at least three determinations for each sample.

Accuracy is crucial in the penetration test method to avoid errors. Common pitfalls include poor sampling, inadequate sample preparation, equipment maintenance issues, and inaccuracies in temperature and time control.

German bitumen production fell by almost a quarter in the first half of this year, as refiners have been forced to run lighter crude slates through the country’s refining system.
Consumption fell sharply too.
Early in the year, the 226,000 b/d PCK Schwedt refinery in northeast Germany was producing no bitumen, after an embargo on Russian crude supplies was implemented.
But since the refinery’s restart with a supply of alternative crudes, including from Kazakhstan through the Druzhba pipeline, the refinery has been producing bitumen again although at below 50pc of levels seen pre-sanctions.

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