How can you incorporate reclaimed asphalt pavement into your asphalt mix?

1 What is RAP?

RAP is the term used for the aggregate and asphalt binder that are recovered from old pavement layers during milling or removal operations. RAP can vary in size, shape, and composition, depending on the source, age, and condition of the original pavement. RAP can be classified into three types: black RAP, which has a high asphalt content and is usually obtained from surface layers; grey RAP, which has a lower asphalt content and is usually obtained from base or intermediate layers; and white RAP, which has no asphalt content and is usually obtained from subbase or granular layers.

2 Why use RAP?

Using RAP in your asphalt mix can offer several advantages, such as lowering material and transportation costs, as well as reducing the environmental impact of your project. It can also improve the performance of your pavement, with enhanced stiffness, strength, durability, and resistance to rutting and cracking. Moreover, RAP can preserve the existing pavement structure by maintaining or improving its drainage, stability, and load-bearing capacity. Finally, RAP can reduce the need for landfill disposal or stockpiling of waste materials by utilizing existing pavement resources.

3 How to use RAP?

When considering the use of RAP in asphalt mix, it is important to take into account the quality and quantity of the RAP available. Sampling and testing should be done to determine its physical and chemical properties, such as gradation, asphalt content, viscosity, and moisture content. Additionally, the design and production of the asphalt mix should be taken into consideration, as it can affect the compatibility and performance of the mix. A mix design method that accounts for the properties and proportions of RAP in the mix should be used, such as the Superpave method or Marshall method. The plant used should also be able to handle and process RAP efficiently, such as a drum mix plant or a batch mix plant with a RAP collar or bin. Furthermore, best practices for paving and compaction should be followed during construction to ensure adequate temperature control, uniformity, and density of the mix. Lastly, any distresses or defects that may occur in the pavement over time should be monitored and repaired.

4 What are the challenges of using RAP?

Using RAP in your asphalt mix can present some challenges, such as the variability and uncertainty of RAP properties that could affect the consistency and reliability of your mix. To ensure that it meets the specifications and requirements of your project, frequent and accurate testing and quality control should be performed. Additionally, aging and hardening of RAP can affect the workability and flexibility of your mix, so appropriate methods such as adding recycling agents, warm mix additives, or new asphalt binder should be used to rejuvenate or soften it. Moreover, there may be compatibility issues between RAP and new materials that could affect the bonding and cohesion of your mix. To enhance adhesion and compatibility, compatible materials and additives should be used, like using the same or similar asphalt binder grade, modifying the asphalt binder with polymers or elastomers, or adding anti-stripping agents or hydrated lime to your mix.

5 What are some tips for using RAP?

Using RAP in your asphalt mix can be a rewarding and sustainable practice, if you start with a low percentage of RAP and gradually increase it as you gain experience. The optimal percentage of RAP in your mix depends on various factors, such as the type and quality of RAP, the type and grade of asphalt binder, the type and level of traffic, and the climate and location of your project. Generally, the higher the percentage of RAP in your mix, the higher the potential for cost savings and performance improvement, but also the higher the risk. It is important to use a balanced mix design approach that considers both performance and cost criteria. Additionally, keep track of your RAP inventory and usage and document your projects and results. This will help you record, monitor, update databases, report data, share lessons learned, and best practices with other stakeholders.