Thermomechanical analysis (TMA) techniques were used to characterize 60 original and aged asphalt cements. The objectives were to find better methods to characterize asphalts at low temperatures, to predict low-temperature cracking potentials, and to develop correlations between thermal properties of asphalts and their field performance for specification purposes.
A DuPont 943 Thermomechanical Analyzer was used in conjunction with a DuPont 1090 Thermal Analyzer Programmer. Glass transition temperatures of some asphalts, both original and aged, were also determined by both thermomechanical and differential scanning calorimetry (DSC) techniques. Although a number of test variables were examined, the results presented for TMA were run under expansion mode between -70 and 25°C, and those presented for DSC were obtained by scanning between -80 and 80°C, both at heating rate of 5°C per min. Thermal analysis results were correlated with Theological properties and molecular size distribution of asphalts based on high performance gel permeation chromatography (HP-GPC) profiles.
Glass transition temperatures varied between -22.5 and -35.0°C for original asphalts and between -22.0 and -37.0°C for aged asphalts, depending on viscosity grade, source, and rate of heating. Reasonable correlations were obtained between glass transition temperature determined by DSC and TMA methods. It was also found that TMA parameters correlated with ring-and-ball softening point, predicted cracking temperature, temperature corresponding to critical stiffness of 138 MPa (20 ksi) at long loading time, and molecular size distribution data.