Paving – Mix Design Basics
High-quality asphalt pavement starts with a good asphalt mix. The types and proportions of the ingredients selected can have a major impact on the quality of the installed pavement. Furthermore, adjusting the formula can enhance certain properties that may be desirable for specific uses. An experienced, reliable asphalt contractor will know how to match the mix to your specific needs. Whether the project is driveway paving or commercial paving, a quality mix design is essential.
Paving – Mix Design Basics – Ingredients Commonly Found in Asphalt Mix
Most hot mix asphalt is approximately 5 percent asphalt cement. The rest of the mix is composed of sand, stone and gravel; these are called aggregates. The asphalt cement binds the aggregates together.
Aggregates can vary in size, and the size differential can affect the properties that the finished pavement will possess. In addition, the proportion of fine and coarse aggregates as well as the proportion of sand to stone and gravel can alter the pavement’s characteristics. The amount of asphalt cement can be adjusted if such an adjustment is necessary to provide the properties desired. An experienced, reliable asphalt contractor will know how to match the mix to your specific needs.
Paving – Mix Design Basics – Typical Desirable Properties for Asphalt Pavement
There are many factors that can influence the quality of asphalt pavement. These include the overall design, the soil preparation, the mix and the installation. When all factors are satisfactorily addressed, asphalt pavement can have the following properties.
• Stability: Stability refers to the ability of an asphalt pavement to resist rutting, shoving, rippling or other deformations. Stability is related to the roughness and angularity of the aggregates in the mix, the roughness of the stones exposed at the surface and the amount of internal cohesion achieved by the asphalt binder that coats the aggregates.
• Skid Resistance: Minimizing the chances that the tires on vehicles will skid or slip is extremely important for most pavements. Incorporating aggregates with rough surface textures can help reduce skidding, especially on wet pavements.
• Flexibility: Flexibility refers to the pavement’s ability to adjust to movements in the subgrade and to gradual settlements without cracking. This is a highly desirable property; virtually all subgrades will experience settling once subjected to loads, and the subgrade may also rise and fall due to ground heave or moisture fluctuations. Typically, flexibility is enhanced by using a mix with open-graded aggregates and a high asphalt cement content.
• Durability: The durability of asphalt pavement includes its resistance to numerous factors, including oxidation, the loss of asphalt from the aggregate’s surface and aggregate disintegration. A mix designed for durability will typically use quality, well-graded aggregates and the optimum amount of asphalt cement.
• Fatigue Resistance: Fatigue resistance refers to the pavement’s ability to resist cracking when subjected to repeated bending by wheel loads. The amount of asphalt binder and air voids in the mix can affect the pavement’s fatigue resistance. However, other factors, including the load magnitude, pavement thickness, underlying layers, asphalt aging and pavement strength, can also affect the pavement’s fatigue resistance.
If your pavement will be subjected to heavy trucks repeatedly, the mix should be optimized to provide the maximum stability. However, if your pavement will be subjected to few or no heavy loads, durability will likely be more important.
Dirtworks, Inc. is an asphalt paving company delivering exceptional work and extraordinary customer service at competitive rates. We offer a full range of asphalt paving and excavation services, including asphalt resurfacing, pavement replacements, new construction, asphalt repairs, sealcoating, asphalt milling, asphalt reclamation, site work, parking lot striping and dirt road repair. If you have more questions about Paving – Mix Design Basics or would like a free estimate, fill out the quote request online or call our office at 508-240-5541.
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