A GROWING NEED

The use of the Superpave design process for hot-mix asphalt (HMA) mixtures is growing across the United States. In some areas of the country contractors have experienced problems, but there have been many projects that have been constructed successfully. In many cases, modifications to the original Superpave specifications and guidelines have been necessary in order to accomplish the goal of building a high-quality long-lasting HMA pavement. A major gap in the Superpave mixture design technology is the lack of a practical, rapid performance-related mixture test to evaluate the mechanical properties of HMA. Experience has shown that HMA can be successfully produced using reclaimed asphalt pavement and that the resulting pavement can be expected to perform as well as, or better than, mixes made with all-virgin materials. Over 4 million tons of stone matrix asphalt has been placed across the United States. It has proven to be a very successful mix type for heavy traffic pavements. Aggregate particle size can have a significant effect on the density achieved if the maximum particle size is too large for the lift thickness of mix being placed. One of the biggest changes affecting the HMA producer in the last few years has been the implementation of quality control systems to control the production process.