Construction quality, temperature and rutting effect on top-down cracking initiation

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