Use of Recycled Asphalt

The term Reclaimed Asphalt Pavement (RAP) is used to designate a material obtained from the removal of pavement materials. RAP is used across the US in multiple applications, largely on asphalt pavement layers. RAP can be described as a uniform granular non-plastic material, with a very low percentage of fines. It is formed by aggregate coated with a thin layer of asphalt. It is often used mixed with other granular materials. The addition of RAP to aggregates decreases the maximum dry unit weight of the mixture and decreases the optimum water content. It also increases the Resilient Modulus of the blend, but decreases permeability. RAP can be used safely, as it does not pose any environmental concerns. The most important disadvantage of RAP is that it displays significant creep. It seems that this is caused by the presence of the asphaltic layer coating the aggregate. Creep increases with pressure and with temperature, and decreases with the degree of compaction. Creep can be mitigated by either blending RAP with aggregate or by stabilization with chemical compounds. Fly ash and cement have shown to decrease, albeit not eliminate, the amount of creep. Mechanical stabilizing agents such as geotextiles may also be used.