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Rheological investigation of asphalt and bitumen

difference between bitumen and asphalt

Oil is the refined residue obtained through the distillation of crude oil. It is a complex mixture comprising various petrochemical components. Asphalt, on the other hand, is a combination of bitumen and mineral components, serving as an adhesive. In certain countries, such as the United States of America, the terms asphalt and bitumen are used interchangeably.

Road pavement or asphalt concrete is composed of a blend of mineral materials like stone, gravel, crushed stone, sand, etc., with bitumen serving as the binder (or asphalt, respectively). Pavements are subjected to diverse weather conditions and heavy traffic loads, resulting in significant maintenance costs for road construction authorities. Common types of damage include the formation of rutting or cracks due to material fatigue or thermal stress.

Rutting occurs due to constant traffic loads, which weaken the structural integrity of the mixture, potentially leading to progressive and permanent deformation of the pavement. This can result in issues like water pooling.

Fatigue and thermal cracking often arise from temperature fluctuations throughout the seasons. Small cracks may develop that are unable to self-repair. Consequently, these cracks can expand, and pieces of rock or asphalt can be dislodged from the pavement surface due to the frictional forces exerted by tires. In a chain reaction, the infiltration of water and ice during winter further accelerates this damage process, particularly in colder climates.

The objective of government management, road builders, construction material manufacturers, and research institutes is to enhance the performance and lifespan of asphalt concrete. This can be achieved by utilizing high-quality raw materials and finding the appropriate texture and mixture of bitumen and minerals. Such improvements result in enhanced workability, dimensional stability, resistance to seasonal weather changes, reduced liquid and dust retention, and improved traction characteristics.

Rheological Characteristics of Asphalt and Bitumen

When it comes to high-quality export bitumen, significant attention is placed on the adhesive properties of the bitumen, which can be assessed through rheometry. Different stages of processing and application require varying consistencies. In the field of road engineering, hot asphalt-concrete mixtures are manufactured and homogenized at different temperatures. Asphalt plants, used for the continuous processing of these mixtures, can be either stationary or mobile, necessitating the mixtures to be pumpable and pourable.

During the subsequent cooling phase after application, the mixture is continuously compacted into the road. The properties of bitumen can be optimized by evaluating its viscosity and other rheological parameters that characterize its stiffness and consistency. To ensure highly accurate results, a range of measuring geometries and accessories are employed, such as heating devices specifically designed for testing bitumen (or asphalt).

Typically, the materials subjected to measurement include:

- Bitumen

- Polymer modified bitumen (PMB)

- Rubber-modified asphalt

Additionally, various other materials and applications may be considered.

Bitumen

The term "bitumen" has Celtic origins and refers to mineral earth or "soil resin." This flammable liquid ranges in color from brown-yellow to black and demonstrates hard and viscoelastic properties at room temperature. It is composed of a multitude of high and low molecular weight compounds, including hydrocarbons, resins, paraffins, waxes, fats, heavy oils, lignins, proteins, and asphaltenes. Unlike asphalt, bitumen does not contain solids such as minerals. Natural bitumen is derived from organic materials.

Bitumen primarily acts as an asphalt binder in road pavement mixtures, where it binds solid mineral additives like sand or small stones. It is essential for bitumen to exhibit stability at high temperatures while avoiding brittle fracture at low temperatures.

Polymer Modified Bitumen (PMB)

Rheology of Polymer Modified Bitumen

To meet specific requirements, such as road paving, bitumen or asphalt binders are often blended with polymers to create polymer-modified bitumen (PMB). Compared to conventional bitumen, PMB demonstrates enhanced cohesiveness with mineral particles and a wider temperature range between its softening point and breaking point. It exhibits improved recovery and resistance to material fatigue after the removal of load. PMB also offers superior water resistance, increased stiffness, and enhanced durability. It is commonly utilized in areas subjected to extremely heavy traffic loads, such as bridges, as well as in open-cell asphalt concrete, which helps reduce road noise.

Rheological Testing of Polymer Modified Bitumen

Measurement of PMB Rheology

The primary objective of incorporating polymers into bitumen is to expand its range of plasticity, making it stiffer at high temperatures and more flexible at low temperatures. Additives, which can account for up to seven percent of the total mixture, often include combinations of thermoplastic polymers such as styrene-butadiene-styrene (SBS), ethylene-vinyl acetate (EVA), or ground tire rubber (GTR). Rheological tests, such as temperature tests using an oscilloscope, can be employed to assess the temperature-dependent behavior of PMB during heating or melting. Although the added polymer percentage is relatively small compared to bitumen, the temperature curve clearly indicates the significant influence of polymer molecules on the viscoelastic properties of the mixture.

Asphalt Modified with Rubber Powder

Rheology of Modified Rubber Asphalt and Asphalt Constituents

The growing number of vehicles on the roads in both industrialized and developing countries results in millions of worn-out tires annually. Utilizing rubber powder derived from recycled tires in asphalt production for road construction not only helps mitigate the environmental impact of discarded tires but also positively alters the properties of asphalt for highway construction. The advantages include longer-lasting road surfaces, reduced maintenance requirements, decreased road noise, and shorter braking distances. It is not surprising that pulverized asphalt rubber has become the largest market segment for recycled tires, consuming approximately 12 million tires per year. California and Arizona are the leading consumers of pulverized asphalt rubber in highway construction, with over 80 percent of the asphalt used in these regions being asphalt rubber. However, asphalt rubber can be engineered to perform well in various weather conditions.

In addition to SBS (styrene-butadiene-styrene), EVA (ethylene-vinyl acetate), and GTR (ground tire rubber), there are several other common additives used in polymer modified bitumen. Some of these additives include:

  1. Styrene-Butadiene Rubber (SBR): SBR is another type of synthetic rubber commonly used as an additive in polymer modified bitumen. It can improve the elasticity and durability of the bitumen, especially at lower temperatures.
  2. Polyethylene (PE): Polyethylene, a thermoplastic polymer, can be added to enhance the stiffness and resistance to deformation of the bitumen. It helps improve the rutting resistance of the pavement.
  3. Polypropylene (PP): Polypropylene is another thermoplastic polymer that can be utilized in polymer modified bitumen. It improves the stiffness and temperature susceptibility of the bitumen, contributing to better performance under varying weather conditions.
  4. Natural Rubber (NR): Natural rubber, derived from the latex of rubber trees, can be used as an additive in polymer modified bitumen. It can enhance the elasticity and resilience of the bitumen, improving its resistance to cracking and deformation.
  5. Styrene-Butadiene-Styrene Block Copolymer (SEBS): SEBS is a block copolymer similar to SBS but with a higher proportion of styrene. It offers improved elasticity, adhesion, and resistance to aging, making it suitable for various applications requiring polymer modification of bitumen.

These are just a few examples of common additives used in polymer modified bitumen. The selection of additives depends on the specific performance requirements and desired characteristics of the modified bitumen for different applications and climate conditions.

ATDM CO is a reputable manufacturer and exporter specializing in Bitumen 60/70 and Bitumen 80/100 and more. We offer a diverse range of quality grades available in drums, bags, and bulk quantities. Our product portfolio consists of three distinct types: premium, second, and third, each tailored to meet specific customer preferences and volume requirements. We take pride in providing a comprehensive selection of options to cater to a wide range of customer needs. Our products are manufactured with utmost care and adhere to stringent quality standards, ensuring reliable performance and customer satisfaction.

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