Interlayer failure characteristics of semi-flexible composite pavement structures (SFCPS) at high temperatures

Interlayer failure characteristics of two semi-flexible composite pavement structures (SFCPS) were investigated: one with a semi-flexible pavement (SFP) top layer and an asphalt concrete (AC) bottom layer (denoted by SFP-T), and the other with the reverse configuration (denoted by SFP-B). Two factors related to interlayer contact were considered: gradation types (SFP13, SFP16, SFP20, AC13, AC16, AC20) and interlayer bondings (without tack coat, with SBS modified asphalt, with emulsified asphalt, with epoxy emulsified asphalt). The failure characteristics of these structures were assessed using three testing methods: uniaxial penetration, pull-off, and oblique shear tests. The temperature for these tests were set at 60 °C to simulate a harsh environmental condition. The results indicate that the penetration strength of composite structures is insensitive to the interlayer contact, whereas the interlayer contact plays a significant role in the interlayer adhesion of SFCPS. The experimental results suggest against the application of tack coats in SFP-T, recommending an AC mixture with Dmax (maximum nominal size) of 20 mm. Since the grouts can penetrate through the voids and create a rigid joint between the top and bottom layers of the SFCPS with no tack coat. For the SFP-B structure, emulsified asphalt with minimal resistance weakening under high temperature is suggested to be taken as the tack coat. Furthermore, Dmax for SFP bottom layer is proposed to be 16 mm, which exhibits the smallest fractal dimension. The research findings can guide the structural design and application of semi-flexible pavements. •Interlayer failure characteristics of semi-flexible pavement are investigated.•Two factors, namely gradation and tack coat, related to interlayer contact are considered.•Cross-layer infiltration of slurry can significantly enhance interlayer strength.•Weakening of interlayer friction resistance originated from gradation and tack coat is found.•Optimum combinations of gradations and tack coats are suggested separately.