Field Tests Using Geosynthetics in Flexible and Rigid Pavements to Reduce Reflection Cracking

The primary objective of this field phase of the research project was to evaluate geosynthetic products placed under or within hot mix asphalt (HMA) overlays to reduce the severity or delay the appearance of reflection cracks. In the laboratory phase of this study, researchers evaluated six geosynthetic products, representing fabrics, grids, and composites, using the large TTI Overlay Tester. Phase I produced comprehensive guidelines for using geosynthetics with HMA overlays to reduce reflection cracking; a design check for considering a geosynthetic product during pavement design using FPS-19; recommended new specifications for fabrics, grids, and composites; summarized results of a statewide questionnaire; and a review of pertinent literature. Comparative field test pavements were established in three different regions of Texas (Amarillo, Waco, and Pharr Districts) with widely different climates and geological characteristics. Tests in the Amarillo and Pharr Districts utilized flexible pavements; whereas, the test in the Waco District utilized an old, jointed rigid pavement. Performance of these test pavements has been monitored for three to four years, depending on the date of construction. The oldest test pavements (Pharr District) are exhibiting essentially no cracking. The Amarillo District test pavements are exhibiting only a small percentage of reflective cracking. The Waco District test pavements are exhibiting significant reflection of underlying joints and cracks. Construction and preliminary performance of the test pavements are described. Cost of selected geosynthetic materials for reducing reflection cracking and their installation are discussed. Based on first cost alone, installation of an inexpensive fabric must increase the service life of an overlay by more than 15 percent to be cost effective. On a similar basis and, of course, depending on the actual geosynthetic product and installation cost, a more expensive grid or composite material may need to double the service life of an overlay to be cost effective.