Tests of HMA Overlays Using Geosynthetics to Reduce Reflection Cracking (0-1777-3)

The primary objective of this field phase of the research project was to evaluate geosynthetic products placed under or within hot mix asphalt overlays to reduce the severity or delay the appearance of reflection cracks and to calibrate and validate FPS-19 Design Check. Multiple end-to-end test pavements incorporating geosynthetic products (fabrics, grids, and composites) and including control sections were constructed in three different regions of Texas (Amarillo, Waco, and Pharr Districts) with widely different climates and geological characteristics. Performance of these test pavements has been monitored for five to six years, depending on the date of construction. The oldest test pavements (Pharr) are exhibiting essentially no cracking. The Amarillo and Waco test pavements are exhibiting a fair amount of low severity and a very small amount of medium-severity reflective cracking. Based on measured cracks in the original pavement before overlaying, the percentage of reflective cracking in each test section was calculated and plotted with time of pavement in service. Calibration of FPS-19 Design Check could not be accomplished due to the absence of sufficient amount of cracks with medium-severity level. Instead, using the field data, relative life ratio of test sections was projected. Field specimens obtained from these test pavements were tested using the large overlay tester. Field monitoring revealed that some geosynthetic products are effective in delaying reflective cracking. They were relatively more effective in the Waco test pavement (concrete in mild climate) than the Amarillo test pavement (flexible in harsh climate).