Forensic Evaluation of the LTPP Specific Pavement Study Projects in Arizona

This paper presents a forensic investigation of selected Arizona specific pavement study (SPS) SPS-5 test sections. The investigation focused on identifying the causes of pavement failures, examining the pavement structural and functional performances, and measuring within-section layer thicknesses and material properties. In addition, the investigation addressed the potential effects of overlay thickness and overlay materials used (recycled and virgin asphalt) and the extent of surface preparation (minimum and intensive) on pavement performance. Destructive and nondestructive tests were conducted following the long-term pavement performance (LTPP) program test protocols. The main pavement distresses identified in the test sections included fatigue cracking, longitudinal cracking, transverse cracking, rutting, block cracking, and pumping. Based on the observations of the coring and trenching operations, most of the cracks were top-down cracks exhibiting high severity at the top and low severity at the bottom of the layer. Wheelpath rutting was observed in the overlay layer only, and virtually no rutting was detected in the lower layers. The maintenance activities (fog seals and crack sealing) applied over the years appeared to have reduced the propagation of fatigue and transverse cracks temporarily and did not significantly improve the postrehabilitation structural performance. While all sections performed well compared with the virgin asphalt overlay, the recycled overlay test sections exhibited the largest postrehabilitation rate of increase in roughness and rutting (with thinner overlays) over their monitoring period. Pavement deterioration was not associated with the base and subgrade layers. The extent of distress was also found to be associated with high binder content and air voids.