This work presents a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixture. The fracture resistance of six asphalt mixtures, which represent a combination of factors such as binder type, binder modifier, aggregate type, and air voids, and two testing conditions of loading rate and initial notch length, was evaluated by performing SCB fracture tests at three low temperatures. Fracture energy was calculated from the experimental data. Experimental results indicated strong dependence of the low temperature fracture resistance on the test temperature. Experimental plots and low coefficient of variation (COV) values from three replicates show a satisfactory repeatability from the test. The results of the analysis showed that fracture resistance of asphalt mixtures is significantly affected by type of aggregate and air void content. Experimental results also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Analysis of result also indicated that both the loading rate and initial notch length had significant effect on the fracture energy at the highest test temperature, whereas the effect was strongly diluted at the two lower temperatures. No clear trend was found with the fracture peak load from either the effect of loading rate or notch length.

The original SuperPave asphalt binder specification criterion for fatigue, G* sin δ, has received considerable criticism. Recently, a time sweep using the dynamic shear rheometer (DSR) has been proposed as an alternative test method for developing load-associated fatigue information for asphalt binders. This proposed test method is examined with respect to a phenomenon called edge fracture. Edge fracture is reported in the literature for steady state and oscillatory flow in DSR, but it has not been reported for asphalt binders. The modulus, when plotted versus number of cycles generated in a time sweep test, has the appearance typical of fatigue behavior; however, the actual response of the material depends markedly on the initial modulus of the material. The development of the modulus with repeated shearing is described with respect to flow of the asphalt binder at its circumference. The data are examined with respect to their validity as a measure of fatigue, and recommendations with respect to the use of time sweep data in a binder specification are presented.

Reclaimed asphalt pavement (RAP) has been used in the United States for more than 25 years because of the benefits in costs and environmental stewardship. The recent substantial increases in asphalt prices have led asphalt technologists to examine the increase in RAP use. The evaluation of the performance of the asphalt mixture containing RAP is therefore a priority for the asphalt materials community. This paper investigates the effect of RAP percentage and sources on the properties of asphalt mixtures. Ten asphalt mixtures, including two different RAP sources, three RAP content percentages (0%, 20%, 40%), and two different asphalt binders (PG 58-28 and PG 58-34) were investigated in this study. The complex dynamic modulus was performed on all mixtures at different temperatures and frequencies, and semicircular bend (SCB) fracture testing was performed for all mixtures at three low temperatures. Experimental results indicate that asphalt mixtures containing RAP have higher dynamic modulus values than the control mixtures containing no RAP. The stiffer asphalt binder was found to result in higher dynamic modulus values for both the control and the RAP-modified mixtures. Experimental data also show that the RAP source is not a significant factor for the dynamic modulus at low temperatures, although it significantly affects dynamic modulus values at high temperatures. In addition to test temperature, the RAP percentage was found to significantly affect the SCB fracture resistance of mixtures. However, for the dynamic modulus, values for the softer binder were higher than for the stiffer one at low temperatures. No significant statistical relationship between dynamic modulus and fracture energy was found.

Physical hardening (physical aging) is a process that occurs below room temperature in asphalt binders. Physical hardening causes time-dependent isothermal changes in the rheological behavior and specific volume of asphalt binders. The process is reversible: when the asphalt binder is heated to room temperature or above, the effect of physical hardening is completely removed. Physical hardening for amorphous materials is generally reported as occurring below the glass transition temperature ( Tg), but this is not the case for asphalt binders, in which physical hardening is observed both above and below Tg. The glass transition temperature of asphalt binders is measured by using three different techniques: dilatometry, differential scanning calorimetry, and rheological considerations (peak in the loss modulus versus temperature). These three techniques give roughly equivalent estimates of the glass transition temperature. The behavior of physical hardening in asphalt binders is somewhat different than that reported for polymers and other organic materials. This difference is explained in terms of the presence of crystalline fractions in the asphalt binder. Techniques for modeling physical hardening are described, and possible explanations for the anomalous behavior of asphalt binders are given.

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