This study evaluated the impact of geosynthetic interlayers on crack retardation and delamination within hot-mix asphalt mixtures. Five different geosynthetic interlayers (three geogrids, one geotextile, and one geocomposite) were considered in this study and varied in opening size, tensile strength, and bonding additive. Two asphalt binder tack coats—PG 64-22 and PG 76-22—were selected and applied at a rate of 0.95 L/m2 (0.21 gal/yd2) based on literature and manufacturer recommendations. Three-point bending (3PB) tests were conducted to assess the cracking and delamination resistance of geosynthetic interlayers. Digital images were recorded during 3PB testing and analyzed using digital image correlation to track specimen movements at the interface under flexural loading. The results showed that specimens with geosynthetic interlayers had higher fracture energy and slower crack propagation rates compared with control specimens. More specifically, fiberglass geogrid interlayers showed the greatest ability to retard crack propagation, with crack propagation rates of 0.07 mm per second (mm/s) compared with control (0.14 mm/s) and other geosynthetics (between 0.08 mm/s and 0.10 mm/s). With respect to delamination, control two-lift and geotextile interlayer (GTX-P) specimens showed the least amount of horizontal delamination. When evaluating the rate at which delamination spread, geotextile specimens (GTX-P) and geocomposite specimens showed slower spread of delamination compared with geogrid interlayers. Overall, the results from this study showed the use of geosynthetic interlayers improved cracking resistance and caused little to no delamination along the asphalt interface.
