HOW TO PAVE RAP MIXES Produce consistently in the field for successful paving with reclaimed asphalt pavement mixes
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BY BRYCE WUORI
The asphalt industry is seeing more state departments of transportation (DOTs) incorporating higher percentages of reclaimed asphalt pavement (RAP) in mix designs. Whether your project specifies 5% or 50% RAP, there are practices you can perform in the field to produce consistency and complete a successful RAP project. When working with RAP, the key from start to finish is consistency. Plant production, stockpile management, paver speed, roller patterns and even the milling operations from which the RAP is sourced, are just a few of the main variables that will need to be managed with great consideration. There are many more variables that must be managed correctly for success with RAP. The few listed above can be identified as more common and can take the least amount of effort to improve quality and produce consistency on your next RAP project.
CONSISTENCY FROM START TO FINISH
It all begins with the RAP source that will be used in the mix design. The condition of the RAP source can affect the consistency of the mix leaving the plant. RAP mix that leaves the plant with inconsistencies will produce problems in the field for the paving and rolling operations. The foundation to producing consistency while paving with RAP starts with the RAP source itself. Without this foundation in place the potential for all other procedures to be successful can decrease considerably. If the RAP source is not from the existing project, further research and investigation of the material should be made prior to producing and paving. A few of the common variables that should be investigated with the RAP sources include: • depth of the milling to produce the RAP material; • age and condition of the road or RAP source being used; 40 | FEBRUARY 2022
Paving with RAP in Eastern Montana
• existing section of roadway where RAP material was extracted from; and • types of binder used in extracted road pavement. These are just a few questions that can better determine what kind of consistency may be expected from the RAP source provided for the specific project. If the RAP is coming from the existing road on the project, there will be a better chance at managing some of the variables that may cause future issues with the RAP material.
MANAGE MOISTURE
If the RAP source is extracted by milling operations, there are some management techniques that will assist with producing a more consistent RAP mix through the plant. Managing water during milling operations and RAP stockpile management techniques are two ways moisture can be managed when paving with RAP mixes. It is a well-known fact
that moisture in the RAP source will cause issues at the plant with production and developing a consistent asphalt field mix. Increases in RAP moisture being placed through the asphalt plant can cause volumetric issues that may include air void variability, asphalt binder variability (chasing AC) and plant production issues. When moisture is present in the RAP source, it will naturally take more thermal energy to remove this variable which causes strain on an asphalt plant producing the asphalt mix. If the moisture is not fully removed during plant production, we can see issues in the field or develop moisture in the asphalt field mix. When there is a high amount of moisture in the asphalt field mix, often sweat dripping from the mix trucks can be detected. This is moisture leaving the mix through a thermodynamic process and is a very good indication that there is a moisture issue at the plant or with our RAP source.
