Application of fracture mechanics to assess reflective cracking potential in airfield pavements

A two-dimensional (2-D) fracture finite element model of rehabilitated pavements subjected to mixed-mode loadings was developed in this study to obtain accurate and reliable critical overlay responses (J-value and stress intensity factors) in asphalt overlays placed over rigid airfield pavements.; The phenomenon and causes of reflective cracking, the current FAA flexible overlay design procedures, and the principles of Linear Elastic Fracture Mechanics were reviewed. ABAQUS, a general-purpose finite element software was utilized to develop an efficient and versatile 2-D model to evaluate assumptions used in the current flexible overlay design and to overcome many inherent limitations that cannot be addressed using the layered elastic program. A critical gear position of the Boeing 777 aircraft was selected among eleven analyzed positions. For rehabilitated airfield pavements with an internal joint reflective crack at the bottom of the overlay, it was determined that gear wheels positioned around the middle of the slab would be most critical, considering both the model extent and the responses at the crack-tip.; The predicted stress intensity factors (SIFs) of 2-D rehabilitated pavement models were validated by comparison with reference solutions using displacement correlation technique (DCT). When modeling a flat plate with an angled crack, the reference SIFs via DCT correlated favorably with the analytical solutions with errors of 2.8 percent or less. The predicted SIFs through the interaction integral by ABAQUS matched excellently with the SIFs supplied via DCT under the critical loading position.; The 2-D model was applied to investigate a number of complicated effects and interactions in rehabilitated airfield pavements. When temperature gradients were present in overlay systems, the critical overlay responses were raised dramatically. As the friction coefficients between slabs and CTB increased, the calculated J-value and mode I SIFs were reduced gradually. Since the center of Boeing 777 gear loads was away from the joint and the temperature loading was mainly mode I loading associated, higher degree of aggregate interlock across PCC joints did not directly contribute to the reduction of critical overlay responses. Due to the stiff underlying rigid pavement, the critical overlay responses were relatively unaffected by quality of subgrade support.