10 Years of Experience Using Warm Mix Asphalt for Airside Pavements

10 Years of Experience Using Warm Mix Asphalt for Airside Pavements—Boston Logan Airport

Aho, Brian / Hein, David / Dennechuk, Sarah / Bessom, Richard

Boston Logan International Airport (BOS) was the first major airport in the United States to incorporate warm mix asphalt (WMA) into asphalt concrete specifications for both runway and non-runway locations. With the increase in wide-body aircraft in the 1990s, rutting of the airside pavements at BOS became a problem. From 1995 to 2003, attempts were made to address the rutting problem by “stiffening” the asphalt mixes. This led to moisture-sensitive mixes, and in the early 2000s, stripping of the asphalt became an issue. Several WMA projects were completed at BOS between 2006 and 2015. Initially, non-WMA control sections were used in critical locations to provide a baseline for evaluating the rutting performance of WMA sections. The first WMA project, in 2006, was the placement of a WMA binder course on the Terminal C alleyway. In 2007, a 150-mm-thick (6-inch-thick (alternating 2-75 mm (2-3 inch) and 1-150 mm (1-6 inch lift)) WMA test strip was included as part of a mill and overlay research project on Taxiway A. In 2008, 24,000 tonnes (26,000 tons) of WMA was used as a part of the rehabilitation of Runway 22L. This project consisted of a 200-mm (8-inch) inlay on the outboard sections of the runway. In 2009, a larger project—50,000 tonnes (55,000 tons)—was constructed for rehabilitation of Runway 9-27, which consisted of a WMA overlay 75 to 175 mm (3 to 7 inches) thick. The ease of WMA compaction was demonstrated along with reduced emissions and energy savings. Also in 2009, WMA was used in the extension of Taxiway Delta at Logan, 36,000 tonnes (40,000 tons). Additionally, new Taxiway G had 250 mm (10 inches) of WMA placed on newly constructed portions of the taxiways, and existing Taxiway C received a 75-mm (3-inch) inlay of WMA. All of the projects at BOS used Sasobit technology and also incorporated from 15 to 20 percent reclaimed asphalt pavement (RAP). The WMA was placed and compacted in maximum 100-mm (4-inch) lifts, whereas 75-mm (3-inch) lifts are typical. A PG 64-28 virgin binder with 4 percent latex modifier and 1.5 percent Sasobit by weight of binder was used for all projects. An anti-stripping additive consisting of 1 percent lime was added to the mixture to alleviate prior issues with moisture sensitivity. This paper describes the process used to evaluate the potential of WMA for airside pavements, along with the lessons learned from asphalt production and placement. The results of condition monitoring from a variety of production sections are presented along with recommendations for the successful use of WMA.