Do you see a plume of blue smoke when introducing large percentages of reclaimed asphalt pavement (RAP) to your continuous mixing process?
If you still see blue smoke when introducing high percentages of RAP to your production process, you may be allowing the binder in the RAP to encounter the flame.
Solution: Introduce RAP/FRAP differently.When the recycle material is allowed to heat away from the flame, the existing AC binder is less likely to be negatively affected. Malcolm Swanson of Astec Industries shared that finding a solution is not easy, and is more of an equipment solution. Consultant Clarence Richard of Clarence Richard Companies and President Lennie Loesch of Stansteel both weighed in on some equipment modifications that can help.
“Look at plant modifications to help superheat the aggregate material and thereby conductively heat more RAP,” Loesch suggested. “A number of contractors have kept their existing dryers and parallel flow dryers/drum mixers and converted them to a counterflow design. By the counterflow design, they are better able to superheat the virgin aggregate and process more RAP without any environmental concerns such as blue smoke or high temperatures to the baghouse.”
Richard explained, “Counterflow allows the RAP to be raised in temperature by conductive means only. The superheated aggregate is the only method used to heat and dry the RAP.” Richard suggested that the minimal amount of blue smoke developed from this method is then incinerated by the flame before it can be expelled to the atmosphere.
Look at your RAP collar placement, as well.
Another solution Richard offered involves an additive. “Bringing the temperature of the mix down helps,” he said. “Warm-mix is a big plus, either by continuously emulsifying the asphalt cement with water or adding chemicals.”