Stone Matrix Asphalt: The Wisconsin Experience

In 1991, the Wisconsin Department of Transportation and the asphalt paving industry in the state decided to construct a trial installation of an asphalt paving technology that had piqued the interest of a group of professionals who had recently toured Europe. The success of that initial trial was the basis of the decision to conduct a thorough evaluation of stone matrix asphalt (SMA). Subsequently, six projects were constructed at various locations around the state. Each project contained six test sections utilizing various fiber and polymer-modified SMA mixes. Besides evaluating the various types of SMAs, this research effort also contained elements for evaluating the impact of aggregate size and aggregate hardness on the effectiveness of the SMA mixes. These projects were constructed over a period of 3 years; the last one was constructed in 1994. All the projects were evaluated from the standpoint of ease of construction and performance. Although the ease of construction was to be evaluated mostly on a subjective basis, the performance measures were established to be objective and measurable. The performance measures were amount of cracking, friction characteristics, overall pavement distress, amount of rutting, noise impacts, and ride. Although the data collected so far are limited because of the short time the pavements have been in place, they point to an asphalt pavement that resists cracking and rutting, while providing a good ride and excellent frictional qualities. The SMAs demonstrate promise of being a durable and long-lasting asphalt pavement.