ABSTRACT
Top-down cracking (TDC) is a deterioration mechanism where cracks initiate at the pavement surface and propagate downwards with time. It is caused by horizontal tensile strains generated at the tire-pavement contact area. This paper, adopting the principal of Foundation Surface Modulus (FSM), determines the thickness of the asphalt layer having a uniform stiffness modulus or two different stiffness moduli (surface course and rest of asphalt layers), above which TDC will be the predominant deterioration mechanism in comparison to the bottom up cracking. The findings concluded that, in the case of uniform asphalt stiffness, when the thickness of the asphalt layers is greater, or less than, depending on the magnitude of FSM and asphalt stiffness, approximately 210 mm, 250 mm, 220 mm and 330 mm, for the above-mentioned axle loads respectively, the flexible or semi-flexible pavement will fail due to top-down cracking and not due to bottom up cracking. Different behavior exists when the stiffness of the wearing course (S1) varies in comparison to the stiffness of the rest of asphalt layers (S2). In this case when the ratio S1/S2 is less than 1.0 the TDC is the most likely type of failure in almost all cases.
