Modeling of combined physical-mechanical moisture induced damage in asphaltic mixes

Abstract

Moisture induced damage in asphaltic mixes is recognized as a major issue, resulting to the need for frequent maintenance operations. This does not only imply high maintenance costs, but also temporary closure of traffic and hence increased road congestion. Given the high costs for the road authorities and the inconvenience for the road users, it is greatly desired to shift the solution from a repair philosophy to a prevention one. Moisture induced damage in asphalt can not be solved by mechanical considerations alone. Clearly, our current asphalt wearing surfaces show that moisture has an effect on the material characteristics of the asphalt components and their bond. This implies that moisture makes a physical change to the material, which exhibits itself in the early development of damage patterns which, without the moisture, may have not occurred or may have occurred in a much later stage of its service life. The aim of this dissertation is the development of a computational tool for the fundamental analysis of combined mechanical and moisture induced damage of asphaltic mixes which includes both physical and mechanical moisture damage inducing processes. Such a tool can greatly contribute to an improved material selection procedure and give insight into the various competing damage inducing processes within the asphalt mix. To achieve this aim, the physical and mechanical moisture induced damage processes were identified, procedures to determine the controlling parameters were developed, an international experimental framework to quantify these parameters was set-up and numerical tools were developed and demonstrated in this dissertation. From the numerical simulations it becomes clear that it is very important to know the moisture susceptibility parameters of the components of the mix, and the moisture susceptibility of its bond. It was shown that, for different parameters, completely different damage patterns may occur in the asphalt. Based on the phenomena that were demonstrated in this thesis, it is therefore highly recommended that from purchase time on, the asphalt engineering community starts determining: 1. the moisture diffusion coefficients of the aggregates and the mastic and the moisture capacity the materials can hold; 2. the changing material response, in time, as a function of moisture content; 3. the bond strength of the aggregate-mastic combinations, with and without moisture; 4. the loss of concentration of the mastic, in the presence of high water pressures. A better awareness of the fundamental material properties of the asphalt components will not only contribute to improving the currently produced asphalt mixes, but will assist the development of better, new mixes which come with their own well-defined maintenance schedule. The pavement engineering community, the material suppliers, the road-authorities and the society at large would benefit tremendously from better controllable and longer lasting asphalt pavements. Identifying specific issues, and dedicating focussed research on tackling these, is the only way to come with novel solutions and to progress the industry in a way where all parties involved in developing infrastructural systems can benefit from each others knowledge and put it to practise.