How to Recycle Asphalt?
Recycling asphalt helps to conserve natural resources and reduce debris while also providing cost savings for pavement construction and maintenance. In this process, the old asphalt material is collected, crushed, and mixed with new materials to create a recycled asphalt mixture.
Asphalt milling is the process of removing a layer of asphalt from a paved surface, such as a road or parking lot, by grinding or cutting it away. The removed material, called “millings,” can be recycled and used in other paving projects or processed further to create new asphalt. Milling is typically done with specialized equipment that grinds the surface to a specific depth and collects the debris for disposal or recycling. This process can help restore a surface’s smoothness, levelness, and skid resistance, as well as extend the pavement’s lifespan.
The specialized equipment used in asphalt milling for recycling purposes typically includes a milling machine, which is a self-propelled unit equipped with a large rotating drum that grinds and removes the existing asphalt surface. These machines can vary in size and complexity, depending on the project’s scope and the type of milling required.
2. Stockpiling Asphalt Materials
When asphalt material is removed from the road and not used immediately, stockpiling of recycled asphalt becomes an essential part of the recycling process. It’s crucial to take great care when stockpiling recycled asphalt material to ensure the full benefits of comprehensive material testing are not lost. Depending on the variability found during testing, it might be necessary to build separate stockpiles of materials taken from different sections of a road. When each load arrives at storage, it’s important to record the details, including the type and amount of material, place of origin, and any undesirable contaminants.
To prevent caking under the influence of generated heat, the stockpiled recycled asphalt pavement should not be piled higher than 3m. Additionally, asphalt scheduled for regeneration should either be covered with a layer of sand or kept under a roof to prevent water penetration. It’s also recommended to remove any 250 to 300mm crust that may form at the surface of the stockpile prior to recycling. Finally, to prevent any unauthorized dumping of other types of debris, it’s essential to ensure that storage areas or collection points are not accessible to the public.
3. Mixing Asphalt Millings in an Asphalt Recycler
The milled asphalt material is then mixed with new asphalt binder and aggregate in an asphalt recycler. The recycler heats the old asphalt material to soften it and then mixes it with the new materials to create a recycled asphalt mixture. The recycled asphalt mixture is then transported to the construction site for use in pavement construction. There are 2 main methods of asphalt recycling: hot recycling and cold recycling.
Hot recycling, also known as hot in-place recycling (HIR), is a process that involves heating the existing pavement to a high temperature (up to 350°F) to soften the asphalt. Once the pavement is heated, it is scarified and mixed with new asphalt and/or aggregate, then compacted to create a new, durable surface. This method is typically used for pavements with deeper structural damage and can be done with either a train or single-unit method.
Cold recycling, on the other hand, is a process that involves milling off the top layer of the existing pavement and mixing it with new asphalt and/or aggregate at ambient temperatures. The new mixture is then laid back down and compacted to create a new surface. Cold recycling is typically used for pavements with less structural damage and is often used as a preventative maintenance measure. This method can be done on-site or off-site and can be further categorized as either in-place cold recycling or central plant cold recycling.
4. Screening and Sizing
After the recycled asphalt mixture is produced, it is screened and sized to ensure that it meets the required specifications for the pavement construction project. The recycled asphalt mixture is tested for various properties, such as strength, durability, and workability, to ensure that it will perform well in the final pavement structure.