NETC 04-4 Determining the Effective PG Grade of Binder in RAP Mixes
Funding Source: New England Transportation Consortium (NETC)
ATMC Materials Lab Involvement: Co-Principle Investigator
Partnering Universities: University of New Hampshire
Start Date: October 2004
End Date: March 2007
Summary:
The use of reclaimed asphalt pavement (RAP) material is increasing as local, state and federal transportation agencies make more efficient use of their resources. RAP material is generated when old, damaged pavement materials are milled and crushed for addition as a component to new mixtures placed in the pavement structure. Historically, old pavement material was removed and disposed of in landfills. As landfilling these materials has become less practical and more expensive and the availability of quality virgin materials declines, the addition of RAP to pavement mixtures has become more and more prevalent. Recycling of pavement material can be done as an in-place process or a central plant process. The in-place process combines the reclamation, mixing, laydown, and compaction procedures into a single paving train in the field. In-place recycled materials are typically used for base or binder courses and are typically overlaid with a surface course. The central plant process involves stockpiling RAP at the asphalt plant, which is then mixed with virgin materials at the plant and trucked to the construction site for laydown and compaction
The addition of RAP to an asphalt mixture changes the mechanistic properties (i.e., strength) of the mixture and affects its performance (i.e., resistance to cracking and deformation) in the field. The mechanistic properties change as a result of the aged binder introduced to the mixture as part of the RAP. The binder in the RAP will have a different chemical composition and different properties than the virgin binder added during the mixing process. Various studies have shown that these two binders will mix to some extent, changing the properties of the mixture containing RAP from one that contains only virgin material. The actual extent of the blending is unknown and may be different for various RAP sources and virgin binders. The actual, or effective, properties of the binder in mixtures containing RAP cannot be tested directly, as the process of extracting the binder for testing results in complete blending of the virgin and RAP binder. Therefore, testing must be performed on the mixtures to determine the effective binder properties.
The main objective of this research is to develop a method to determine or estimate the binder grade in mixtures designed with RAP from the properties of the mixture itself.
