When it comes to basic ingredients, paving asphalt couldn’t be much simpler. Two main substances make up the vast bulk of asphalt: crushed gravel aggregate and asphalt cement. Yet while asphalt pavement can be successfully created using these basic ingredients, contractors often choose to augment the mix with certain additives.
These additives – usually incorporated into the asphalt binder – improve the pavement in a variety of ways, from ease of installation to long-term durability. If you would like to improve your knowledge about the different additives used to improve asphalt mixes, keep reading. This article will introduce you to three key varieties of asphalt modifiers.
1. Activated Mineral Stabilizer
In recent years, more contractors have come to appreciate the benefits of a type of asphalt known as stone matrix asphalt. Stone matrix asphalt omits medium-sized aggregate. This omission increases the amount of contact between large aggregate particles, thus leading to a stiffer and more rut-resistant form of asphalt.
Yet the larger gaps inside of stone matrix asphalt can lead to an excessive amount of binder drainage. In other words, the asphalt binder meant to hold the asphalt together ends up migrating downward, leaving the upper layers with insufficient bonding. Many contractors choose to add mineral stabilizers to help counteract this tendency.
Mineral stabilizers consist largely of finely ground silica. Manufacturers activate this silica through a physicochemical reaction. This activation process makes the mineral particles capable of swelling in volume when they come in contact with organic compounds like asphalt binder. This swelling, in turn, makes the asphalt less susceptible to slipping through the cracks between aggregate particles.
Rubber has come to be one of the most widely incorporated asphalt modifiers in recent years. Much of this rubber comes from recycled car tires. Once non-rubber parts of a tire have been stripped out, workers grind the tread down into what is known as crumb rubber. Manufacturers then incorporate this crumb rubber into the hot asphalt mix.
Rubber-modified asphalt possesses a number of key advantages. Most importantly, the rubber acts to improve the asphalt’s elasticity. As a result, the asphalt can better withstand the unwanted phenomenon known as rutting. As its name implies, rutting involves portions of the asphalt that deform over time under the weight of passing vehicles.
Rubber-modified asphalt also markedly improves the traction of the roadway. Exposed rubber particles at the surface of the asphalt provide a friction boost, allowing car tires to better grip the roadway. This friction proves especially useful when it comes to icy wintertime weather, where rubber-modified asphalt can promote a 25 percent improvement in the average stopping distance of a vehicle.
Manufacturers have long used fiber as a way to improve the overall performance of hot mix asphalt. A variety of different fiber types may achieve this goal. These include both natural fibers such as rock wool and asbestos, as well as synthetic fibers such as cellulose, polypropylene, and fiberglass.
All fiber types display similar benefits, with the most important being an improvement in the tensile strength of the pavement. In other words, the fibers help the asphalt to hold together more firmly. Thus, cracks and other forms of surface damage related to normal stresses occur less often.
Not only that, but when cracks do occur, fiber reinforcements help to prevent the crack from growing. In addition, much like mineral stabilizers, fiber has been found to reduce the downward migration of asphalt binder. As a result, strength and stability improve at all depths of the asphalt.
Virtually all asphalt mixes contain some form of modifier meant to improve its performance as time goes on. For more information about the best modifiers for your next asphalt project, please contact the paving pros at Harding Group.