Construction of Stone Matrix Asphalt Section at Edwards Air Force Base

In February 1993, the U.S. Air Force Civil Engineering Support Agency asked the U.S. Army Engineer Waterways Experiment Station to provide technical assistance for construction of a stone matrix asphalt (SMA) pavement demonstration project at Edwards Air Force Base (AFB). In August 1993, approximately 0.8 km (0.5 mi) of SMA pavement was placed on a road at Edwards AFB. The SMA mixture contained crushed stone, natural sand, fly ash, cellulose fiber, and an AR-4000 asphalt cement. The following summer, it was reported that excessive amounts of bleeding had occurred in all wheelpaths. An inspection in August 1994 confirmed this finding, and it was noted that the bleeding was worse near the intersections. The SMA mixture apparently contained too much asphalt cement. Several factors contributed to the bleeding: (a) the SMA mixture as designed contained too many fines, especially in passing the No. 4 sieve, compared with current guidance from the National Asphalt Paving Association and others; (b) the void content of the mixture may have been inadequate; and (c) samples obtained from the in-place pavement had a finer grading and higher asphalt content than specified. The bleeding has caused concern; however, no maintenance has been performed on the SMA pavement and no measurable rutting has occurred in the wheelpaths.