Asphalt paving is known for its unique performance profile compared to other paving materials. For example, it provides the durability and strength generally associated with hard materials like concrete. In addition, it offers a natural element of flexibility that allows it to withstand stress and damage. However, there are times when asphalt's flexibility works against it and leads to the development of ruts. These ruts often develop along wheel paths, as they are the areas of the pavement that bear the most incredible level of pressure from above. Our experts on asphalt paving in Vacaville, CA, offer this essential information on the causes of asphalt rutting and how to prevent it.
Asphalt paving is only as stable and robust as the subgrade it is placed upon, the ground below. If the soil and dirt compact or shift over time, your asphalt may not provide the necessary support for rutting prevention. Unfortunately, the soil in particular areas may suffer from natural instability compared to other locations. Fortunately, an experienced asphalt contractor knows that you can improve subgrade stability through soil compaction before asphalt installation proceeds. In addition, compactors and vibrators press the soil together tightly, providing an increased level of strength and stiffness for the pavement.
Unfortunately, asphalt cannot be installed directly onto the subgrade, no matter how well it is compacted. Soil is just too inherently unstable, especially if it becomes saturated with water. To guarantee that your pavement stays in place for years in the future, it needs to be installed over a layer of crushed gravel called an aggregate base or subbase. For an effective sub-base, the aggregate base must be adequately compacted and thick enough to support the asphalt. Sub-base thickness will vary according to individual project needs depending on the application. Pavement that will bear the weight of heavy traffic needs a thicker sub-base. For example, most residential driveways have 4-to-six-inch-thick sub-bases, while roadway aggregate bases are between 6 to 9 inches thick.
Even asphalt surfaces with adequate subgrades and aggregate bases might suffer from ruts. In cases like this, the issue usually involves problems with the asphalt composition. Asphalt requires enough structural integrity to stand up to the force of exertion to which it is exposed. In simpler terms, asphalt needs ample internal strength not to crack beneath the weight of vehicle traffic. The composition of the asphalt mixture should be specifically tailored to the type of traffic to which it will be exposed. For example, pavement that will be exposed to heavy vehicle traffic regularly needs to have a stiff performance profile compared to a residential driveway.
There are a couple of factors that affect asphalt's overall stiffness. The first is the proportions and sizes of the gravel aggregate used to support the structure. An evenly grade mixture with roughly equal proportions of the large, medium, and small-sized aggregate usually performs best under stress because of the minimal void space between aggregate pieces.
The other factor involves the asphalt binder used to hold the pavement together. Manufacturers identify binders based on their stiffness. Binder composition requires a compromise between stiffness and flexibility. Binders with more flexibility resist cracks, while stiffer binders resist ruts.