RAP Stockpile Management and Processing in Texas: State of the Practice and Proposed Guidelines

In addition to conserving energy and protecting the environment, the use of reclaimed asphalt pavement (RAP) can significantly reduce the increasing cost of asphalt mixes. However, one of the key problems with RAP mixes is its variability, which is the main reason why many states including Texas Department of Transportation (TxDOT) limit the use of RAP. In most circumstances, RAP variability is closely related to RAP stockpiles management and RAP processing. This report first documents the state of the practice of RAP stockpile management and RAP processing in Texas. In contrast to the RAP stockpiles owned by TxDOT, most contractors currently combine materials from different RAP sources and sometimes waste into a single pile and then process it into a usable material by crushing and/or fractionation. During the first year of this study it was found that the contractors visited are doing a good job of managing the processed RAP stockpiles. To quantify the RAP variability, samples were collected from several stockpiles and evaluated using asphalt ignition oven test. The results showed that both TxDOT's and contractors' RAP materials, in terms of aggregate gradation and asphalt content, are consistent and slightly better than those reported at the national level. However, one concern raised during the visits is with mixing multiple source RAP stockpiles before crushing or fractionation. RAP stockpiles are often processed or dug from a single angle or sequentially and then directly fed into a crushing or fractionating machine. If there is no further blending after crushing or fractionation, the processed RAP may still be multiple-source. In this report guidelines are proposed to address this and other issues related to stockpiles management and RAP processing. The key points are to 1) eliminate contamination of RAP stockpiles, 2) keep RAP stockpiles separate as possible, 3) blend thoroughly before processing or fractionating the multiple-source RAP stockpiles, 4) avoid over-processing (avoid generating too much fines passing # 200 sieve size), 5) use good practices when storing the processed RAP (such as using paved, sloped storage area), and 6) characterize and number the processed RAP stockpiles. To better control the RAP variability, both good stockpile management practices and RAP processing techniques described in this report should be followed.