Determination of moisture susceptibility of mastic-stone bond strength and comparison to thermodynamical properties

The fundamental characterization and quantification of the moisture susceptibility of asphaltic mixes is a very important and timely topic for the asphaltic pavements industry, and has thus far posed a serious challenge for asphalt mix designers. In this research a fundamental computational-experimental test procedure is demonstrated to measure the moisture susceptibility of the mastic-aggregate bond strength and bond energy. The methodology combines displacement controlled direct tension tests with numerical moisture diffusion analyses and is demonstrated for six different mastic-stone combinations which are frequently used in the Dutch open friction courses. From the results it can be seen that the computed adhesive moisture susceptibilities are consistent with the expected field performance. The measured bond moisture susceptibilities are furthermore compared with the thermodynamical work of adhesion. It is shown that, qualitatively, the moisture resistance performance ranking is similar, but that the actual bond energies show three to four orders of magnitude difference. From this it can be concluded that, even though the surface energy approach can be very useful in enhancing material selection procedures, it is still important to actually measure the mechanical strength of the selected aggregate-mastic bond with a mechanical test.