Use of Reclaimed Asphalt Pavement in Superpave Hot-Mix Asphalt Applications

Abstract

Implementation of the Superpave mix design method has encouraged the use of coarser hot-mix asphalt (HMA) mixtures, which require tight control of both the overall gradation and the percent passing the 0.075-mm (No. 200) screen. There is some concern that use of reclaimed asphalt pavement (RAP) in Superpave mixtures may be seriously limited because stockpiles of RAP may have widely variable gradations as well as high percentages of minus 0.075-mm material. The possibility of splitting RAP stockpiles by using the coarser RAP fraction in a typical 12.5 mm below-the-restricted-zone Superpave gradation has been evaluated. The finer RAP fraction was used in an above-the-restricted zone 12.5-mm Superpave gradation. Two sources of RAP (Georgia and Minnesota) were used so that a wide range of asphalt and aggregate properties would be represented. Screening the RAP allowed up to 40 percent of the coarse RAP fraction to be used and still meet below-the-restricted zone Superpave gradation requirements. This was mainly due to the significant reduction in the finer aggregate fractions, especially the minus 0.075-mm material. The use of RAP in these mixtures resulted in a savings of between 18 and 25 percent in the required neat asphalt. A noticeable increase in mixture stiffness with as little as 15 percent RAP was observed. This change in mixture properties suggested that a softer grade of neat binder might be needed. A maximum of 15 percent of the fine RAP fraction was used to produce an acceptable above-the-restricted-zone Superpave gradation. The net savings in neat asphalt content was 25 percent. Little change was observed in tensile strengths because of the addition of this RAP fraction. However, there was a substantial increase in mixture stiffness at intermediate to warm temperatures. This increase was also observed as a 20 percent reduction in the asphalt pavement analyzer rut depth when RAP was used. The indirect tensile creep compliance decreased when RAP was added. Although there was little difference in compliance at -20°C, there were decreases of about 30 and 50 percent at -10°C and 0°C test temperatures, respectively.