History of hot mix asphalt mixture design in the United States

Asphalt has been used as a construction material from the earliest days of civilization, but though it has long been used as a waterproofing material in shipbuilding and hydraulics, its use in roadway construction is much more recent. A recent survey revealed a total of over 2.3 million miles of hard-surfaced (asphalt or concrete) roads in the United States, of which approximately 96% have asphalt surfaces. Asphalt mixture consists of asphalt, coarse and fine aggregate, and a number of additives occasionally used to improve its engineering properties. The purpose of mixture design is to select an optimum asphalt content for a desired aggregate structure to meet prescribed criteria. The demands and reliance upon America's roadways for mobility and commerce have increased substantially over the past three decades. The highway network is not only the economic backbone of the country, but it also provides the only transportation access to a growing number of communities. This paper presents a review of the past, present, and future trends in asphalt mixture design as the methods have evolved in an attempt to meet the ever-increasing demands of traffic.