Mix design

Mixture design of 100% recycled asphalt

Update: This webpage summarizes my PhD research. Since then I have done a lot of new research. Please visit the publications section to read the newest articles.

For full description of the design principles and proposed mix design methodology see article:

100% Recycled Hot Mix Asphalt: A Reviewand Analysis, Resources, Conservation and Recycling

The traditional mix design methodology, especially with respect to design of optimal binder content, has to be modified for totally recycled hot asphalt mixtures. The mix designer will have to make compromises when choosing how to process the reclaimed asphalt and what size fractions best satisfy the mixture gradation, binder content, mixture volumetric and performance-property requirements while efficiently utilizing the available material. Choice of recycling agent and its dose is another significant aspect.

Full description of the design principle can be found in the article.

Mix design principle

The aggregates are tested for required properties. The chosen RAP fractions are combined in an initial mixture composition. The binder is then extracted from the mixture to determine its properties and choose the necessary rejuvenator type and dose. The asphalt is mixed and compacted in laboratory to determine the required volumetric and performance-related properties. The steps are repeated by taking appropriate modification if correspondence to the specification requirements is not ensured at any stage. If due to properties of milled RAP (especially fines and binder content) the design of mixture with 100% RAP is not possible, virgin binder and aggregates can be added. However, care should be given to ensure sufficient blending of RAP and virgin binder as well as homogeneous coating of virgin and RAP aggregates.

Full description of each of these steps can be found in the article.

Adjusting Binder Content

As an example, method for adjusting binder content are summarized, for other steps see article:

  • Choose source RAP with higher binder content.

    • Increase fines content in the mixture, since they usually contain higher binder content [57, 58].

    • Choose less effective recycling agent. Organic products tend to be much more effective at a select dose compared to petroleum products [59, 46, 45].

  • Increase recycling agent dose. Care should be given to comply with the performance specification requirements, especially rutting.

  • Add virgin binder.