HMA is one of the most recycled products in the U.S. It is estimated that as much as 91 million tonnes (100 million tons) of HMA are milled off roads during resurfacing and widening projects each year (APA, 2001a). Of this amount, 73 million tonnes (80 million tons) are recycled as “reclaimed asphalt pavement” (RAP – see Figure 1) (APA, 2001a). RAP is typically generated by rehabilitation or reconstruction projects and can be used in a variety of ways such as:
- As an addition to regular HMA.
- As an aggregate in cold-mix asphalt.
- As a granular base course when pulverized.
- As a fill or embankment material.
HMA recycling can be divided into two basic categories based on the recycling methods used: hot recycling and cold recycling. This section presents the basic recycling process as well as typical uses and considerations for each of these recycling methods.
Hot recycling is so named because RAP is used as an aggregate in HMA (hot mix asphalt). In hot recycling, old HMA pavement is removed, broken down into aggregate-sized chunks and then incorporated into new HMA as an aggregate. There are two basic methods for accomplishing this:
Cold recycling is so named because RAP is used as an aggregate in cold mix asphalt. In cold recycling, old HMA pavement is removed, broken down into aggregate-sized chunks and then combined with an emulsified or foamed asphalt. This mix is then typically used as a stabilized base course for reconstructed pavements. There are two basic cold recycling methods:
CIR can also be extended to the full pavement as Full Depth Reclamation (FDR):