It is anticipated that asphalt road surfaces can serve road users for many years before requiring maintenance. In fact, there are numerous examples of asphalt roads in various countries that are 40 or 50 years old and still offer a functional pavement, particularly on low-traffic routes.
The term "durability" is commonly used to describe the ability of asphalt to maintain desirable engineering properties and performance throughout its lifespan. In engineering terminology, durability is considered one of the functional characteristics of asphalt.
A definition of asphalt durability can be formulated as follows:
Durability refers to the capacity of constituent materials to withstand the detrimental effects of water, aging, temperature changes, and a certain amount of traffic loading without experiencing deterioration over an extended period.
While the integrity of aggregates plays a significant role in the long-term performance of asphalt, it is primarily the aging characteristics of bitumen that have the most substantial influence on asphalt durability, including surface coatings, chip seals, and fog seals.
Quantifying the durability of bitumen has proven to be challenging, and methods for evaluating this property are approximate. The hardening of bitumen throughout storage, production, and service stages is of utmost importance throughout the lifespan of asphalt.
Long-term studies have demonstrated that bitumen is susceptible to the same effects of oxygen, ultraviolet rays, and temperature changes as many organic materials. These external influences cause the bitumen to harden, resulting in reduced penetration, increased softening point, and typically increased penetration index (PI). In recent years, the phenomenon of bitumen hardening and subsequent asphalt hardening in pavement layers has gained significance as it enhances material hardness and, consequently, load-spreading capability. This hardening process, known as "age hardening," is believed to extend the lifespan of pavements.
In asphalt surfaces, when the bitumen is exposed to environmental conditions, bitumen hardening can have detrimental effects on its performance, leading to the formation of cracks or fissures. This effect is referred to as "age hardening," a term that signifies that changes in bitumen properties negatively impact the useful life of the asphalt surface.
Bitumen hardening
The hardening tendency of bitumen under the influence of atmospheric conditions has been a subject of study and understanding for many years. Researchers have identified fifteen different factors that contribute to bitumen aging, which are outlined below.
Among these fifteen mechanisms, the following are considered the most significant:
- Oxidation
- Evaporation
- Steric or physical factors
- Oil secretion
Oxidation
Oxidation is widely recognized as the primary factor in bitumen hardening. Similar to many organic materials, bitumen undergoes a slow oxidation process upon exposure to oxygen. This oxidation leads to the formation of polar groups containing oxygen, which tend to aggregate into micelles, increasing the overall viscosity of the bitumen. Additionally, the reaction between oxygen and bitumen molecules results in the formation of carbonyl species. This leads to the creation of larger and more complex molecules, making the bitumen hard and less flexible.
The extent of oxidation is highly dependent on factors such as temperature, exposure duration, and the thinness of the bitumen film. The rate of oxidation doubles for every 10 degrees Celsius increase in temperature, up to temperatures exceeding 100 degrees Celsius. The hardening caused by oxidation has long been recognized as the primary cause of bitumen aging, with other factors receiving comparatively less attention. However, while other factors generally have less significance than oxidation, they are still measurable and contribute to the overall aging process.
Loss of volatile substances due to evaporation
The evaporation of volatile components in bitumen is primarily influenced by temperature and exposure conditions. The rate of evaporation is determined by the rate of diffusion and the length or thickness of the diffusion path. Compacted asphalt tends to have a slower diffusion process, whereas open-grained asphalts and surface coatings experience faster evaporation conditions.
However, it is important to note that bitumens used in pavement surfaces are typically non-evaporable, meaning that the degree of hardening resulting from the evaporation of volatiles is generally minimal. The composition of pavement surface bitumens is such that the volatile components have already been largely removed during the manufacturing process, reducing the potential for significant evaporation-induced hardening.
Physical or steric hardening
The occurrence of steric hardening was initially documented by Traxler in 1944, who observed an increase in viscosity in bitumen samples stored at 25°C. This phenomenon is attributed to the presence of slow waxes. The molecular reorientation responsible for the hardening is reversible when heat is applied. Traxler suggested that by raising the storage temperature to 70 degrees Celsius, the altered structure can be reversed, allowing the sample to return to its original viscosity.
Loss of volatile substances by secretion
The hardening of bitumen is the result of the movement of its oily components that seep from the bitumen into the mineral substance, this is a function of the bitumen seepage tendency and the porosity of the aggregate.
Hardening of bitumen during storage, mixing and in use
The conditions that contribute to bitumen hardening can vary significantly. During storage, bitumen is typically stored in large quantities at elevated temperatures for several days or weeks. During processes such as hot storage, mixing, transportation, and delivery, as well as during the application on roads, bitumen exists as a thin film at lower or moderate temperatures for extended periods.
The extent of air exposure experienced by the asphalt during its application is crucial and depends on the void spaces within the mixture. In dense and relatively compacted mixtures, the rate of hardening tends to be relatively low. However, asphalts with a more open structure, such as porous asphalt, are more susceptible to significant hardening due to increased air exposure. Additionally, surface coatings or spray applications have the potential for much greater air exposure compared to compacted asphalt layers.
The durability of bitumen and asphalt is influenced by several factors, including the specific grade of bitumen used. Bitumen 60/70 and bitumen 80/100 are two common grades of bitumen used in asphalt applications.
In general, both grades of bitumen exhibit good durability characteristics. They have been widely used in various asphalt pavement projects and have demonstrated satisfactory performance over time. However, it's important to note that the durability of bitumen and asphalt is not solely determined by the grade of bitumen, but also by other factors such as the quality of the aggregate, construction practices, climate conditions, and maintenance.
Bitumen durability refers to its ability to resist the damaging effects of water, aging, and temperature changes over an extended period. Factors such as oxidation, evaporation, steric hardening, and exposure to air can affect the durability of bitumen and ultimately impact the performance of asphalt.
To ensure the long-term durability of asphalt with bitumen 60/70 or bitumen 80/100, proper construction techniques, regular maintenance, and periodic inspections are essential. This includes measures such as appropriate compaction during installation, adequate drainage to prevent water damage, and timely repairs to address any surface cracks or distress.
Additionally, the use of additives or modifiers in the asphalt mix can enhance the durability of the pavement. These additives can improve the resistance to aging, cracking, and rutting, thereby extending the service life of the asphalt.
Overall, while bitumen 60/70 and bitumen 80/100 are commonly used and offer good durability, it is important to consider all the factors mentioned above to ensure the long-term performance and durability of the asphalt pavement.
ATDM CO is a reputable manufacturer and exporter of Bitumen 60/70. We specialize in offering high-quality bitumen products in various packaging options, including drums, bags, and bulk quantities. Our product line consists of three distinct quality grades: premium, second, and third types. Each grade is produced with meticulous attention to detail, utilizing advanced facilities and processes.
Our diverse range of options is designed to cater to the specific needs and volume requirements of our customers. Whether you require a smaller quantity for a specific project or a larger bulk order, we have the flexibility to accommodate your demands.
At ATDM CO, we prioritize product quality, reliability, and customer satisfaction. Our bitumen 60/70 is manufactured to meet international standards, ensuring optimal performance and durability in various applications. Currently, we have supplies in three countries of the United Arab Emirates (Dubai), Panama and Singapore are available. We take pride in delivering exceptional products that meet the diverse needs of our valued customers, both domestically and internationally.