On the Road to Sustainability

Abstract

Most state departments of transportation (DOTs) adopted the Superpave® mix design method in the late 1990s. The Superpave mix design method replaced the Marshall method and became mainstream. Superpave came with aggregate, binder, and mix requirements to control rutting and cracking. With a life expectancy of about 15 years, many Superpave roads are now becoming candidates for resurfacing or recycling. Can Superpave mixes undergo hot in-place recycling with success? In fact, Superpave mixes contain expensive and high-quality aggregates, which meet the consensus properties, and high-quality binder, which meets the performance grade (PG) requirements. If these mixes can be recycled in place and meet the original Superpave properties, then substantial savings can be realized. The potential savings are in the 30% to 50% range of the cost to mill and resurface. In addition, emissions could be reduced by 70%, while 100% of the existing material could be reused. This paper reports on an experiment conducted in Gainesville, Florida, in 2010 at the Florida DOT State Materials Office, in which a Superpave mix underwent the hot in-place recycling process. The properties of the aggregate, binder, and mix were compared to answer certain questions about aggregate degradation, binder rejuvenation, and mix properties. The answers to these questions shed light on the possibility of the 100% recycle of Superpave mixes. The results showed that minimal aggregate degradation took place. The recycled mixes met Superpave gradation requirements for the most part. The rejuvenated binder met or exceeded the PG requirement. The mix could be engineered to meet the air voids requirement of Superpave.