A comparison of fracture properties of selected geosynthetic products using pseudo strain damage theory

Abstract

Reflective cracking is one of the more serious distresses associated with existing hot mix asphalt (HMA) or portland concrete cement (PCC) pavements overlaid with a thin bituminous layer. This phenomenon is commonly defined as the propagation of cracks from the movement of the underlying pavement or base course into and through the newly placed bituminous layer as a result of load-induced and/or temperature-induced stresses. Preventive maintenance techniques have included incorporating geosynthetic materials, defined herein as grids, fabrics, or composites, into the pavement structure. These materials have had varying success and their use within agencies have been based primarily on local experience or a willingness to try a product that appears to have merit. The objective of this research was to develop information that would aid in the evaluation of the relative effectiveness of commercially available geosynthetic materials in reducing the severity or delaying the appearance of reflective cracking in HMA overlays. To accomplish this objective, laboratory specimens were fabricated and tested to failure using a fatigue-testing machine called the TTI Overlay Tester. This investigation used elementary engineering fracture mechanics concepts as well as the elastic-viscoelastic correspondence principle and the theory of nonlinear viscoelasticity as analytical methods of characterizing the nonlinear viscoelastic response of HMA materials to time-dependent loads. Pseudo displacement equations were developed that, when plotted against measured loads from the TTI Overlay Tester, were used to calculate the pseudo J-Integral. A modified version of Paris' Law was then used to back-calculate the crack propagation properties of the HMA material. By considering the effects of the geosynthetic products on the loading and unloading paths of the HMA specimens, the reinforcing factor, R, was developed. The crack speed index was developed to summarize the complex interactions of the material properties and used to compare the relative effectiveness of each geosynthetic material. Design equations were developed between the fracture properties of the geosynthetic-mixture system and the relaxation modulus properties of the HMA. These equations 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.