Effects of layer interface conditions on top-down fatigue cracking of asphalt pavements

Different types of responses have been considered in the past as the driving forces of the top-down cracking (TDC). The horizontal tensile strain at the surface is the most appropriate response of pavement structures for analysing TDC. In computing the horizontal strains, most of the mechanistic design methods of asphalt pavement consider that pavement layers are fully bonded and bottom-up cracking is the critical type of fatigue distress. The bonding condition between pavement layers is one of the significant factors influencing pavement performance. In this research, the effects of interface bonding conditions on top-down fatigue cracking are investigated based on the horizontal tensile strain at the surface. Analysis procedures are conducted using of Lucas algorithm and integration, summation and extrapolation (ISE) methods to determine the horizontal strain responses of asphalt concrete (AC) layer at the surface accurately. The results reveal that the AC layer thickness, type of base layer material and temperature affect the horizontal strains at the surface and debonded locations significantly. When the layers of thick pavement with cement-treated base (CTB) are fully bonded, the TDC is a dominant type of distress at different temperatures analysed, while for the thick pavement with granular base (GB) the surface-initiated cracking occurs only at high temperature. Due to the interface debonding in the thick pavement, the maximum horizontal strains vary at different locations and failure may appear simultaneously at the top and bottom of AC layers or only at one of those regions. For the thin pavement structure, the layer interface bonding conditions hardly influence the mechanistic response at the surface and the pavement with GB is more vulnerable to bottom-up cracking, whereas the likelihood of TDC increases at high temperature for the thin pavement with CTB.