Environmental Susceptibility of Base–Prime–Seal–Surface Interlayers in Asphalt Pavements

Reliable bonding between a cement-stabilized base and an asphalt surface course is essential to the integrity of semi-rigid base asphalt pavements. Accordingly, this study evaluated the environmental susceptibility of complete base–prime–seal–surface interlayer systems by introducing adverse conditions at selected construction contact planes and then measuring the peak shear response of the completed system. Four representative seal systems were investigated: a non-tracking emulsified asphalt seal, a fine-chip seal, a hot asphalt chip seal, and a slurry seal. Five specimens were initially prepared for each condition. Field-constructed 150 mm cement-stabilized base cores were combined with a 40 mm AC-13 layer and tested in direct shear at 25 °C. The investigated variables included clean, moist, and soil-contaminated interface conditions, grade 0 automotive diesel contamination, prime-coat omission, pre-placement substrate temperatures from −5 to 35 °C, and 0–10 freeze–thaw cycles. The results showed that diesel contamination at the seal–surface contact reduced strength retention to 73.6–83.6%. Meanwhile, prime-coat omission produced pronounced losses in the fine-chip and slurry systems, whereas the hot asphalt chip seal remained comparatively stable. The temperature response was material-specific: the fine-chip seal showed no significant overall temperature effect (p = 0.1019), while the hot asphalt chip seal reached the higher statistical category only at 25–35 °C. In contrast, the effects of short-term freeze–thaw cycling were relatively limited; after 10 freeze–thaw cycles, strength retention remained at 93.8–98.2%. Overall, the results support material-specific control of surface cleanliness, prime-coat application, and construction temperature.