ABSTRACT
Top-Down Cracking (TDC) is a pavement distress that has been recognized in many projects around the world. It is caused by horizontal tensile strains generated at the edge of the tire. Factors affecting the magnitude of the horizontal tensile strains is a combination of applied load, tire configuration and structure, stiffness and thickness variation of the asphalt layers, and strength of underlying layers to the asphalt layers. This paper, adopting the principal of Foundation Surface Modulus (FSM), determines the total thickness of the asphalt layers, with the same or different stiffness modulus, above which top-down cracking is the predominant pavement deterioration mechanism in comparison to the bottom up cracking in a conventional flexible pavement. This study considered one uniform asphalt layer of variable thickness and two distinct asphalt layers (surface layer and binder/asphalt base) of variable thickness, in both cases 100 mm. The type of axle load and tire structure was assumed to be single axle-dual tire load of 80 kN with smooth tire surface. The findings concluded that for an asphalt layer stiffness ratio (S1/S2) equal to 1,0 when the thickness of the asphalt layers is greater than a value within the range of 160 mm to 210 m, approximately, depending on FSM and asphalt stiffness value, the flexible pavement will fail only due to top-down cracking and not due to bottom-up cracking. Different behaviour with TDC exists when the asphalt layer stiffness ratio is less than or greater to 1.0.
