The fatigue mechanism of asphalt mixture with an interlayer under the combined effect of multiple factors

•Immersion leads to a significant increase in the number of voids.•Freeze-thaw leads to a significant increase in void size.•Fatigue life at high frequency is more sensitive to the change of stress ratio.•The interlayer shear fatigue life prediction model considering multiple factors. As a common method of asphalt pavement maintenance, thin overlays performance is easily affected by interlayer bonding performance because of their thinness. To study the effects of immersion, freeze–thaw, stress ratio and loading frequency on the interlayer bonding performance and reveal the interlayer failure mechanism, an asphalt mixture with interlay (AMI) was prepared for direct shear strength test, direct shear fatigue test (DSFT) and CT scanning test. The results verify that the interlay shear fatigue performance of AMI was sensitive to immersion, freeze–thaw, stress ratio and loading frequency. With the increased of immersion days and freeze–thaw cycles the interlay shear fatigue life (ISFL) was decreased. The interlayer shear strength was affected by the tack coat oil and the aggregate inlay and extrusion, and the shear strength provided by the two was basically the same. The interlayer bonding performance was affected significantly more by water than freeze–thaw action, and the main reason for increased void numbers was immersion days, and the main reason for void size expansion was freeze–thaw action. ISFL decreased with the increase of stress ratio, but increased with enhancing of loading frequency; and the fatigue life at high frequency was more susceptible to the alter of stress ratio. Based on Grey Relational Analysis, the influence of the four factors on ISFL was loading frequency > stress ratio > freeze–thaw cycles > immersion days; based on the prediction model of stress ratio obtained by the phenomenological method, the ISFL prediction model under the influence of the four factors was obtained by coefficient correction of loading frequency, freeze–thaw cycles and immersion days.