Using Pseudostrain Damage Theory to Characterize Reinforcing Benefits of Geosynthetic Materials in Asphalt Concrete Overlays

Reflective cracking is one of the more serious distresses associated with existing hot-mix asphalt (HMA) or portland concrete cement pavements overlaid with a thin bituminous layer. Preventive maintenance techniques have included incorporating geosynthetic materials (defined here as grids, fabrics, or composites) into the pavement structure. These materials have exhibited varying degrees of success, and their use within a particular agency has been based primarily on local experience or a willingness to try a product that appears to have merit. A methodology is described that was used to compare the relative effectiveness of six commercially available geosynthetic materials in reducing the severity or delaying the appearance of reflective cracking in HMA overlay. Each geosynthetic material was incorporated into compacted HMA specimens and tested to failure. Engineering fracture mechanics and pseudostrain energy concepts based on the elastic-viscoelastic correspondence principle were used and demonstrated to be appropriate and efficient in characterizing the fatigue damage process. By considering the effects of the geosynthetic products on the loading and unloading paths of the HMA specimens, a new concept was developed and termed the reinforcing factor, R. The use of this value allows the industry to characterize the relative reinforcing benefits of geosynthetic materials in reducing reflective cracking in HMA overlays. A crack speed index was then derived to summarize the complex interactions of the material properties. In general, grids and composites performed better than fabrics, which in turn performed better than a thin tacked surface as compared with unreinforced specimens. Design equations were developed between the fracture properties of the geosyntheticmixture system and the relaxation modulus properties of the HMA, which can be used in forward-calculating design methods to predict the rate of crack growth and support the design of an HMA overlay to resist reflective cracking. To calibrate the design equations, comparative field test pavements were constructed in three regions of Texas (Amarillo, Waco, and McAllen) using each geosynthetic material. These pavements will be monitored over the next 4 years.