Milled Asphalt as Road Surfacing Material: Advantages and Considerations

[MikePhua]

Milled asphalt, also known as reclaimed asphalt pavement (RAP), is becoming an increasingly popular material for road surfacing. It is derived from milling the top layer of existing asphalt roads during resurfacing projects. This process grinds up the old material, making it suitable for reuse, thus providing an environmentally friendly and cost-effective alternative to new asphalt. However, like any material, milled asphalt has its pros and cons. This article explores the benefits, challenges, and best practices for using milled asphalt in road construction and resurfacing projects.
What is Milled Asphalt?
Milled asphalt is created through a process known as cold milling. When a road needs resurfacing, the top layer of asphalt is removed using a milling machine. The machine cuts through the asphalt and collects the milled material, which can then be processed and reused for new road construction or repairs.
The material is typically composed of bitumen (asphalt binder) and aggregates, which are mixed together to form a durable surface. Once milled, the material can be cleaned and sized for various uses, including road base construction, resurfacing of existing roads, or even in the creation of new asphalt mixtures.
Advantages of Using Milled Asphalt

1. Cost-Effectiveness
   One of the primary advantages of using milled asphalt is its cost-effectiveness. Since the material is recycled, it is significantly less expensive than using virgin asphalt. The savings come from both the reduced cost of raw materials and the decreased need for new raw materials. For municipal governments and contractors, this can mean significant savings on large-scale projects, as well as a reduction in disposal fees for old asphalt.
   
2. Environmental Benefits
   The recycling of asphalt significantly reduces the environmental impact of road construction. Asphalt is one of the most recycled materials in the world, with millions of tons reused annually. By using milled asphalt, construction companies are reducing the demand for virgin materials and minimizing waste, which is a critical step toward more sustainable infrastructure practices.
   
3. Durability
   Milled asphalt, when processed and used properly, provides a highly durable and stable surface. It has the same structural integrity as new asphalt and can withstand the same stresses and environmental conditions, making it suitable for use in both base and surface layers of roads. When mixed with fresh asphalt, RAP can enhance the overall durability of the road.
   
4. Versatility
   Milled asphalt can be used in various applications, from resurfacing roads to making pothole repairs. It can also be used in lower traffic areas or as a base layer, which reduces the overall cost of road construction projects. Additionally, milled asphalt can be combined with other materials, such as recycled concrete or slag, to improve its performance for specific uses.
   
5. Quick and Efficient Installation
   Since milled asphalt is already processed, it can be quickly transported and applied, leading to faster construction timelines. This is especially important in areas where road closures or delays can be a significant inconvenience. The ability to reuse existing materials also means there is no need to wait for the production of new materials, allowing for quicker project turnarounds.
   

Challenges and Considerations
Despite the many advantages of milled asphalt, there are some challenges and considerations that need to be taken into account before deciding to use it as a road surfacing material.

1. Quality Control
   The quality of milled asphalt can vary, especially if it is sourced from older or heavily deteriorated roads. It is important to ensure that the RAP is properly processed and cleaned before use. Contaminants such as soil, debris, and water can affect the performance of the final product. High-quality milling equipment and thorough screening processes are necessary to ensure the asphalt meets the required standards.
   
2. Performance Variability
   Milled asphalt can sometimes exhibit variable performance when compared to freshly mixed asphalt. This is particularly true when it is used in surface applications. While it provides adequate durability and performance, it may not perform as consistently as new asphalt in high-stress areas or under heavy traffic conditions. Proper mix design and testing are crucial to ensure optimal performance.
   
3. Limited Use in Certain Environments
   In some cases, milled asphalt is better suited for base layers or low-traffic roads. Its use as a surface material may not always provide the same smoothness or longevity as fresh asphalt. In regions with extreme weather conditions or heavy traffic loads, the longevity of RAP may be compromised, requiring more frequent maintenance or resurfacing.
   
4. Regulatory and Specification Challenges
   There may be restrictions or specific guidelines regarding the use of recycled materials like RAP in certain regions. Municipalities and regulatory bodies may have standards on the percentage of RAP that can be included in a mix. As the use of RAP increases, it is important to stay informed about the latest specifications and ensure compliance with local regulations.
   

Best Practices for Using Milled Asphalt

1. Proper Processing and Screening
   To ensure the highest quality of milled asphalt, it is essential to thoroughly process and screen the material. This involves removing contaminants and ensuring that the size and quality of the aggregates meet the project’s requirements. Using modern milling equipment with advanced screening technology can improve the overall quality of the RAP.
   
2. Mix Design and Testing
   When using RAP as a surface layer, the mix design is critical to ensure durability and performance. Combining milled asphalt with virgin materials in the right proportions can result in a high-quality product that performs well under traffic loads. Comprehensive testing should be done to confirm the mix’s structural integrity and long-term performance.
   
3. Proper Storage and Handling
   Milled asphalt should be stored in a clean, dry environment to prevent contamination from moisture or debris. When stored improperly, RAP can degrade and lose its beneficial properties. Ensuring proper handling and storage can extend the lifespan of the material and help maintain its quality.
   
4. Monitoring Long-Term Performance
   After installation, it is important to monitor the long-term performance of roads built with milled asphalt. Regular inspections can help identify any issues such as cracking or rutting that may indicate a problem with the mix design or the application of the material. Addressing issues early can prevent costly repairs down the line.
   

Conclusion
Milled asphalt offers a sustainable, cost-effective, and durable solution for road surfacing. As the demand for environmentally friendly and efficient construction materials grows, milled asphalt is proving to be an increasingly viable option. However, its success depends on proper processing, mix design, and application. With careful planning and attention to quality, milled asphalt can be a valuable material for both resurfacing and new road construction, contributing to more sustainable infrastructure development worldwide.