How to Properly Lay Crushed Asphalt: A Comprehensive Guide

Crushed asphalt, also known as asphalt milling, pavement milling, and recycled asphalt pavement, is widely used in driveway and parking lot construction. This cost-effective and durable material not only reduces waste but also ensures a seamless and long-lasting surface. This guide provides a detailed, step-by-step process on how to properly lay crushed asphalt, ensuring a successful project.

Preparation and Subgrade Evaluation

Before laying crushed asphalt, it's crucial to evaluate the existing subgrade. This involves assessing the quality of the soil and determining its strength. If the subgrade is weak, it's advisable to remove and replace it with a more robust material, such as stone. This preparatory step ensures that the base supports the new layer of crushed asphalt effectively, preventing future issues and ensuring the longevity of the surface.

Adding the Emulsion

Once the subgrade is in good condition, the next step is to add an emulsion to the crushed asphalt millings. Emulsion is an essential additive that contains suspended droplets of asphalt in water. This additive helps to bind the mix, making it more cohesive and durable. The ideal ratio for this emulsion is between 2.5 to 3.5 percent, depending on the specifics of the project.

Screening and Mixing

To ensure the quality of the crushed asphalt, it's crucial to screen the millings to remove any oversized particles. If the millings are larger than 2 inches, they should be crushed down to the required size to maintain a uniform mix. Once the material is properly screened, it can be loaded into a pug mill for mixing. The pug mill combines the emulsion and screened millings to create a homogeneous material, which is essential for a smooth and durable finish.

Spread and Spread Evenly

The next step is to spread the mixed material using a spreader or an asphalt paver. A minimum thickness of 3.5 inches is recommended over a soil subgrade to ensure proper coverage. This step is critical, as the thickness of the asphalt directly impacts its durability and appearance. Even spreading is key to achieving a smooth finish and ensuring that the material is properly distributed across the surface.

Compaction

After spreading the material, it's time to compact it. The first compaction should be done using a 25-ton pneumatic-tired roller to ensure initial flattening. Once the initial compaction is complete, switch to a 12-ton or larger double drum vibratory steel-wheeled roller for final compaction. Proper compaction is essential to prevent settling and ensure that the asphalt layer is secure and level.

Sealing the Surface

Finally, for a long-lasting and protected surface, a chip seal mix or a 1.25-inch layer of new asphalt surface course should be placed over the recycled milled pavement mat. This seal helps to further protect the surface from environmental factors and extends the life of the construction. Both options effectively sealing the surface, ensuring that the crushed asphalt remains durable and aesthetically pleasing for years to come.

Following these steps carefully will ensure the success of any crushed asphalt project. Proper preparation, mixing, spreading, and sealing each play a crucial role in creating a long-lasting and cost-effective solution for driveways and parking lots.