Analysis of the Effect of Interlayer Bond Strength on the Suppression of Reflective Cracks in Asphalt Overlays on Cement Concrete Pavements

Asphalt overlays are the most commonly used method for the secondary utilization of cement concrete pavements. However, the widespread presence of pre-existing cracks in cement concrete pavements often leads to the formation of reflection cracks in the overlay. This study investigates the mechanism by which interlayer bond strength affects the propagation of reflection cracks in asphalt overlays through laboratory experiments. Flexural, shear failure, and fatigue tests were conducted to evaluate the influence of different interlayer bonding materials (SBS-modified asphalt, 90# basis asphalt, rubber-modified asphalt) and overlay thicknesses (70–100 mm) on crack propagation parameters. The results show that rubber-modified asphalt exhibits the best overall performance, with the lowest crack tip opening displacement (CTOD) of 0.492 mm at a thickness of 80 mm, which is 25.6% and 61.5% lower than 90# basis asphalt and SBS-modified asphalt, respectively. Fatigue tests further confirm that rubber-modified asphalt significantly improves the fatigue life of the overlay, with fatigue failure cycles reducing by 59.9% and 73.1% under flexural and shear conditions, respectively, compared to other materials, resulting in an improvement of 22.8% to 28.3%. The study also finds a significant positive correlation between interlayer bond strength and crack resistance (R²= 0.86–0.91), and that flexural load has a significantly greater destructive effect on the overlay compared to shear load. These findings provide important theoretical guidance for optimizing overlay design.