Can I Run More RAP

In this article, the author suggests that the use of reclaimed asphalt pavement (RAP) in hot mix asphalt (HMA) has a long history, but that poor mixing of the new and recycled products can result in pavements that fail in a short period of time. The result is that many agencies have been cautious about using more than ten to 20 percent RAP in their mixes. The author suggests that improvements in RAP processing equipment and HMA plants make it possible to produce mixtures with up to 50 percent RAP. This article reviews new testing equipment to evaluate a producer’s processes without limiting RAP content. The article also provides examples of good mixing and poor mixing, and describes the dynamic modulus test to measure the stiffness of an HMA mixture.