Determination of Structural Layer Coefficient for Roadway Recycling Using Foamed Asphalt

Project 26 is an extension of earlier work done by Maine DOT and Worcester Polytechnic Institute (WPI) on mix designs for foamed asphalt in full depth reclamation (see Projects 16 and 17). Pavements are made up of several layers (such as subgrade, subbase, base and surface) consisting of bound (such as asphalt) and unbound (such as granular) materials. The thickness of each layer depends on the load-bearing properties of the materials that make up that layer. The weaker the material, the greater the thickness required to provide the same structural support. Generally, the surface mix, consisting of Hot Mix Asphalt (HMA) is the most costly of all the layers. Therefore, every effort is made to provide a strong subsurface pave-ment structure (consisting of subgrade and subbase and/or base) and to minimize the thickness of the surface layer. Foamed asphalt is stabilization technology that uses a mixture of asphalt binder, water and air combined with granular material to form a "foam" that can be compacted into a stabilized pavement layer. Foam-ed asphalt has been used in cold pavement recycling projects where the asphalt layer and part of the base are processed and stabilized to form a new base layer which can support an asphalt concrete surface layer. The potential of foamed asphalt is that it can produce strong, durable pavement sublayers that allow a thinner asphalt surface layer, which results in significant cost savings. While mix designs exist for foamed asphalt, there is very little information on layer coefficients available for designing pavements with foamed asphalt layers. Foamed asphalt projects in New Jersey and Maine will provide foamed asphalt samples for analysis and will allow field testing. The laboratory testing will include characterizing the stress-strain behavior of the foamed asphalt using the new AASHTO compressive dynamic modulus test. Dynamic modulus testing will be performed at critical performance temperatures to verify the temperature dependence of the mix. Additional data will be collected using Falling Weight Deflectometer tests on foamed asphalt projects in Maine. The laboratory results and field test data will be used to develop layer coefficients for the mix designs.