An improved asphalt binder specification development for low-temperature pavement cracking

This thesis focuses towards the problem of low temperature cracking of asphalt pavements, tries to have a better understanding of the various failure mechanisms in the pavement and works towards developing an improved asphalt binder specification for low temperature pavement cracking. A Thermal Stress Restrained Specimen Test (TSRST) for asphalt binders was developed as a part of this research work. The results from the TSRST test on binders provided some important insights. It was observed that the failure properties of the binders depended strongly whether or not there was a notch in the sample; the presence of notch resulting in a significant variation in the failure temperature for some binders. Also, there was not much correlation between the binder and the mix failure properties. The yield stresses of different binders were also measured in this project and combining it with the fracture data from the 3 point bend test, the Crack Tip Opening Displacement (CTOD) of the different binders were calculated. The yield stress varied significantly for the different binders. Also, there was a tremendous difference in the CTOD values for the different binders; the modified binders, for example, sometimes having a value of CTOD which was almost 100 times to that of an unmodified system. A binder with a higher value of CTOD was more likely to provide a much extended stable crack growth as compared to a binder with a lower CTOD, thus resulting in a reduced transverse cracking. The Crack Mouth Opening Displacement (CMOD) for the mix samples was also calculated and again the difference in the results was significant; a mix sample with a higher value of CMOD having a gradual mode of failure as opposed to catastrophic for a mix sample with lower value of CMOD. Thus, a parameter, such as critical CTOD showed a lot of promise to be used as a specification parameter in preventing low-temperature pavement cracking. Field correlation studies were also performed in this project and there appeared to be a good correlation between the fracture properties of the binder and the actual performance of test sections. And, in pursuit of a better binder system, a new system, based on a bismalemide crosslinking agent was developed, which improved the low temperature properties of the asphalt binder to a significant extent and thus showed a very good potential to be used for low temperature applications.