Temperature Measurements with Depth and Physical Evidence for the Effect of High Temperature Gradients on Top-Down Fatigue Cracking

Abstract

This paper presents the results of pavement temperature measurements with depth over a year obtained with a setup emulating the heat flow on a pavement with 305 mm (12 in.) of hot mix asphalt (HMA) and 152 mm (6 in.) of aggregate base. Several findings related to top-down fatigue cracking (TDFC) in Hawaii were obtained from these measurements. It was observed that pavement temperatures near the surface, which were both the lowest and the highest in the HMA depending on the time of day, were rarely below 20°C, and thus, that most cracking in Hawaii occurs at higher temperatures. It was also observed that passing rains can cause sudden temperature drops of the order of 15°C within short periods (15 min). HMA moduli estimated using measured temperature profiles indicate that high temperature gradients may lead to inverted moduli profiles that when loaded cause the highest tensile and shear strains to occur near the surface, and that these may be a main reason for TDFC in the state. The simulated stresses and strains under high temperature gradients also indicate they may be conducive to delamination problems related to large horizontal shear strains generated near the surface and combined with nearly vertical but small tensile strains at the layer interface. The observation that cracking suddenly and consistently stops under overpass bridges and immediately resumes after them provides strong evidence consistent with the findings of the stress/strain distributions generated from profiles with high surface temperature and high temperature gradients potentially causing TDFC. The paper provides recommendations for further study.