Recycled Pavements Using Foamed Asphalt in Minnesota

Foamed asphalt was discovered in Iowa by Csanyi in 1956, and has become a useful road rehabilitation tool when used in conjunction with cold in-place recycle (CIR) and full-depth reclamation (FDR) processes. The advance of pavement recycling and foaming technology has made foamed asphalt a common rehabilitation technique in many parts of the world including Europe, Asia, Africa, Canada, and parts of the United States. Iowa has used the technique extensively and has developed specifications for the construction of foamed asphalt FDR and CIR stabilized roadways. The intention of this research project, Investigation 873, is to develop FDR and CIR foamed asphalt specifications and report data and information that will assist engineers in Minnesota with successfully implementing foamed asphalt recycling techniques. There are already several foamed asphalt CIR projects in Minnesota that have been completed on low volume roads. The roadways were rehabilitated in Fillmore and Olmsted Counties from 2004 to 2008, and are performing quite well to date. The Minnesota Department of Transportation (Mn/DOT) has taken Falling Weight Deflectometer (FWD) and core data from these projects in order to examine the in-situ properties of the stabilized pavement layer, as well as the material properties of the foamed asphalt itself. The FWD data analysis reveals that the recycled pavement layer develops a relatively uniform strength despite the high variability inherent in most low-volume roads. Core data indicates that the foamed asphalt forms a cohesive matrix when mixed with the fines from the reclaimed material, which does not disintegrate when cored. Overall PG grade of the recycled layer changed significantly from the original mix in some cases, but not in others. The cause of this is unknown, however, differences in the procedures used and materials present at the different projects may help explain this. It is recommended that FWD, ground penetrating radar (GPR), and core analysis be performed before and after foamed asphalt projects to more accurately define these differences.