Description
Top-down cracking (TDC) is a flexible pavement distress caused by a number of factors, including high contact
stresses from truck tires, mix design characteristics, (e.g., binder type and aggregate gradation) and poor
construction quality, (e.g., segregation and compaction methods). This paper presents the findings of a study
seeking to quantify the effect of these factors on TDC. It consists of a laboratory component involving an
accelerated Wheel Tracking device and a modeling component involving a 3-D non-linear viscoelastic finite
element model. The laboratory component of the study involved 17 asphalt bituminous slabs, constructed to
simulate the variation in material properties observed in the field as part of an earlier forensic TDC study. The
effect of air voids, bitumen content and type, aggregate gradation and segregation on TDC were studied under 3
temperature conditions. Air voids, segregation and binder content were found to have a significant effect on
TDC for all the temperatures tested. Modeling the TDC involved laboratory testing to establish the viscoelastic
and tensile strength properties of the asphalt mixtures tested. It was found that the rutted surface contributes
significantly to TDC initiation.