Infoscience

Thesis

Évaluation des performances et des impacts des enrobés bitumineux tièdes

By decreasing the mixing and laying temperatures, warm mix asphalts (WMA) allow a reduction of the energy consumption as well as the emissions, thus contributing to the sustainable development. However researches are necessary for these asphalt mixtures to be considered as a credible option to hot mix asphalts (HMA). The experience regarding mixture behavior is limited and some critical or unverified parameters have to be assessed. Besides, a tool assisting in the choice of the most adapted technology is also necessary. The first research phase consists in a detailed analysis of the mechanical performances from a representative selection of warm mix asphalts. The mix viscosity has been first evaluated, in particular by focusing on the bitumen and mastic behavior. Then, the evaluation of the characteristics and performances have been devoted to the potential critical parameters, with a special emphasis on the performance increases process during the first three months after production and on the samples storage conditions. The results highlight the high performances of WMA containing Fischer-Tropsch wax in the rutting susceptibility temperature domain. The low temperature behavior of this WMA is however more brittle than the reference hot mix asphalt (HMA). WMA with chemical additive (surfactants) shows performances comparable to the reference HMA while the mixture with moisture control proves to have lower mechanical performances in particular due to the reduced ageing of its binder. The various tests performed do not highlight any significant performance increases of the tested mixtures. Moreover, confining the samples in plastics bags does not seem to affect the asphalt mixtures mechanical behavior. In a second phase, an indirect tensile test has been setup and assessed. This test offers a relevant and efficient alternative to traditional complex modulus test on trapezoidal samples, allowing determining the secant modulus of an asphalt sample. A detailed analysis as well as the realization of various tests on asphalt mixtures highlighted some research strands in order to improve the reliability and further develop the testing method. A multi-attribute evaluation methodology of asphalt mixtures has been proposed in the third phase of the research. Various greenhouse gas and energy consumption calculators allowing a comparison of different road projects exist. However, despite the important effect of the asphalt mixture type on the energy consumption and emissions, few of these tools are able to perform a comparison at the asphalt mixture scale. The performances and other qualitative aspects are also not considered. The proposed multi-criteria model takes into account emissions, energy consumption and economical aspects over the whole life cycle of the asphalt mixture. The mechanical performances are also taken into account in the decision process; the databases being provided by the first two phases of the present research. The developed and implemented methodology contains four distinct levels. In the first two levels, some graphical analyses allow identifying the dominant processes and the potential alternatives outranking. The preference and some qualitative criterions are introduced from the third analysis level where a partial aggregation method using pseudo-criterions is proposed. In the last analysis level, data uncertainty and unknown data are considered through an innovative method. To achieve this, a complete aggregation method based on an algorithm derived from the Evidential reasoning approach is selected. The final multicriteria evaluation method proposed offers a pertinent, flexible and robust tool that helps in improving the decision process and thus encouraging innovation.

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