Modelling of combined physical-mechanical moisture-induced damage in asphaltic mixes, Part 1: Governing processes and formulations

Moisture has for a long time been recognised as a serious contributor to premature degradation of asphaltic pavements. Many studies have been performed to collect, describe and measure the moisture susceptibility of asphaltic mixes. Most of these are aimed at a comparative measure of moisture damage, either via visual observations from field data or laboratory tests or via mechanical tests, which give a so called moisture damage index parameter. The research presented in this paper is part of an ongoing effort at Delft University of Technology, to move away from such comparative or empirical measures of moisture-induced damage and start treating moisture-induced damage in a comprehensive energy based framework. Such a framework would enable realistic predictions and time-assessment of the failure pattern occurring in an asphaltic pavement under the given environmental and traffic loading which could be rutting, cracking, ravelling or any combination or manifestation thereof. The modelling of moisture-induced damage is a complex problem, which involves a coupling between physical and mechanical damage processes. This paper discusses several modes of moisture infiltration into asphaltic mixes and derives the governing equations for their simulations. Moisture diffusion into the mastic film, towards the aggregate-mastic interface and mastic erosion, due to high water pressures caused by the pumping action of traffic loading, are identified as the main moisture-induced damage processes and are implemented in a new finite element program, named RoAM. The paper discusses the necessary model parameters and gives detailed verification of the moisture diffusion and advective transport simulations. In the accompanying paper the developed finite element model is demonstrated via an elaborate parametric study and the fundamental moisture-induced damage parameters are discussed.