Geosynthetics, such as fabrics, grids, and composites, were introduced to asphalt pavements to mitigate reflective cracking or the creation of moisture barriers or both. Reinforcing interlayer systems, such as grids, have been shown to be effective in retarding the reflection of cracks in the underlying pavement into the upper layers. However, the effect of different interlayer systems on the performance of the pavement varies. The aim of this research was to compare the effects of fiberglass grids, paving fabric, and paving mat systems on the fatigue and fracture performance of double-layer beam specimens under four-point notched bending beam fatigue loading. Double-layer asphalt concrete beam specimens were loaded in a displacement control mode until full-depth cracking was observed. Haversine displacements with zero and maximum deflection peaks were applied to the specimens at frequencies of 5 and 10 Hz. The digital image correlation technique was used to determine and compare the damage mechanisms with stiffness curves plotted by using load and displacement data. A comparison of the results from beams with different interlayer systems showed that the type of interlayer system can noticeably affect the damage mechanisms and the performance of the fatigue specimen. In general, grid systems performed better when the interface bond was stronger. In nongrid interlayers, while interfacial damage created a discontinuity that increased the risk of interfacial debonding, a more flexible interlayer dissipated more energy at the interface and delayed the full vertical cracking of the beams under four-point bending beam fatigue loading.
