Modelling of combined physical-mechanical moisture-induced damage in asphaltic mixes Part 2: Moisture susceptibility parameters

Moisture-induced damage in asphaltic mixes is a complex problem which needs to be approached 'from the inside out'. It is of essence to determine the fundamental physical and mechanical processes which contribute to moisture-induced damage. Once these processes are determined, the controlling parameters need to be defined and measured. The research described in this and the previous paper is focusing on the development of an energy-based computational framework which incorporates moisture-induced damage by integrating the physical and mechanical moisture-induced damage processes within the (dry) elasto-visco-plastic constitutive model. In the previous paper, the moisture infiltration processes and their formulations were derived and verified. In this paper, focus is placed on the determination of the moisture susceptibility parameters of the computational model. Determination of moisture diffusion coefficients of the mastic is discussed and a computational study is performed to show the effect of filler concentration in the mastic. A computational-experimental procedure to determine the moisture susceptibility of the aggregate-mastic bond is shown and demonstrated. Finally, an extensive parametric analyses is performed which shows the impact of moisture damage on the asphalt mix response by varying the moisture susceptibility parameters. It is concluded, among others, that to avoid moisture-induced damage, bitumen should have as low as possible moisture diffusion properties; the amount of filler in the mastic should be decided upon, on the basis of a combination of the mechanical properties of the mastic, the diffusion coefficients of the filler and the bitumen and the mastic moisture damage parameters. Furthermore, the aggregate-mastic bond strength should be maximised by keeping the moisture susceptibility parameters as low as possible; combinations of mastics with low moisture diffusion coefficients and low moisture susceptible aggregate-mastic bonds should be preferred, and it should be avoided at all times to introduce moisture into the mix before and during the time of mixing. Above all, the research in this paper shows the importance of determining the fundamental moisture susceptibility parameters and the effect they may have on the lifetime performance of asphaltic pavements.