Effects of Warm-Mix Asphalt Additives on Workability and Mechanical Properties of Reclaimed Asphalt Pavement Material

Abstract

The soaring cost of liquid asphalt binder and anticipated stricter environmental regulations have driven highway agencies to maximize the amount of reclaimed asphalt pavement (RAP) used for pavement construction. However, because of already aged and stiffened asphalt binder in RAP, the use of high percentages of RAP in hot-mix asphalt (HMA) presents many challenges. Problems with workability and compactability during construction need to be resolved first. This study investigated the feasibility of using 100% RAP HMA as a base course with warm-mix asphalt (WMA) additives (Sasobit H8 or Advera zeolite) at a lower temperature (125°C). Mix samples (control set with 100% RAP; a set with 100% RAP plus Sasobit H8 at 1.5%, 2.0%, and 5.0%; and a set with 100% RAP plus Advera zeolite at 0.3%, 0.5%, and 0.7%) were compacted with 50 gyrations. Their workability, bulk specific gravity, indirect tensile strength at 0°C, and moduli at 0°C, 26.7°C, and 50°C were determined. The effects of different amounts of WMA additives were compared. The results showed that workability of the 100% RAP HMA improved with the addition of Sasobit H8 or Advera zeolite at temperatures as low as 110°C. At temperatures less than 80°C, the addition of Sasobit H8 or Advera zeolite tended to stiffen the mix, as also reflected in increased seismic moduli and indirect tensile strength. Seismic modulus of the mixes was also found to be dependent on bulk specific gravity. The addition of Sasobit H8 proportionally increased bulk specific gravity of the mixes. The effect of amounts of Advera zeolite on bulk specific gravity was less well defined. It seemed that stiff asphalt binder in the RAP also affected compaction by preventing asphalt foam from fully forming, as it would when Advera zeolite was mixed with a virgin asphalt binder.