Binder selection
Asphalt is a complex material made from the combination of aggregate, liquid binder and, sometimes, additives and modifiers. The proper selection binder is greatly influenced by the conditions of service, environmental factors, and desired performance characteristics.
Binder selection begins with characterization of the existing material and includes a comparison of binder properties in order to develop desired performance expectations as well as assessment of a paving site. Asphalt binders can be classified according to their susceptibility to temperature degradation, aging, polarity, and the presence of certain additives. Generally, asphalt binders are divided into three categories: asphalt cements, cutbacks, and emulsions.
Asphalt cements are the most common type of binder used in the asphalt industry. Asphalt cements are made up of a combination of asphalt with other materials such as sand, gravel, and rubber. Asphalt cements are usually heated to temperatures between 250°F-350°F in order to be used in paving operations. Because they are heated at such high temperatures, they tend to become more brittle over time and can become susceptible to cracking.
Cutbacks are asphalt binders mixed with kerosene or diesel fuel in order to decrease their stiffness or viscosity at ambient temperatures. This makes them easier to work with in the field during paving operations. However, cutbacks can be volatile, depending on the type and amount of fuel used. Additionally, the fuel will evaporate over time, resulting in a loss of binder material.
Emulsions are asphalt binders that have been mixed with water and an emulsifying agent. The suspended particles of asphalt are stabilized by the emulsifying agent in order to prevent them from separating and settling out. Emulsions are much more temperature-sensitive than asphalt cements. Generally, they are created with a more flexible grade of asphalt, making them less susceptible to cracking due to low-temperature zone vulnerability.
Each type of binder has different characteristics which must be considered when selecting the appropriate asphalt for a given application. Additionally, factors such as local climatic conditions, expected traffic volume and load, and pavement type can play a role in determining the type and grade of binder best suited to a job. In order to properly select the most suitable binder for a job, it is important to understand the strengths and weaknesses of each type of binder as well as assess the specific requirements of the paving project.
It is also important to remember that asphalt binders tend to degrade over time due to exposure to the elements. As such, it is usually necessary to use an asphalt binder with additives or modifiers in order to prolong its service life. Polymers, rubber, and other modifiers are commonly added to asphalt binders in order to alter their performance characteristics and make them more resistant to the effects of temperature changes, oxidation, and UV radiation.
Regardless of the type of binder chosen, it is important to remember that the quality of the asphalt paving will depend largely on the quality of the binder material. As such, selecting the appropriate binder for a given application is essential for producing a successful paving project.
