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The addition of reclaimed asphalt pavement (RAP) in hot mix asphalt is now common practice in Switzerland. With the increases of RAP content in asphalt mixture, the problematic of the mix design optimization becomes an important issue to be considered. The described project deals with the mix design optimization of hot mix asphalt containing 40 % RAP. In a first phase, an analytical mix design has been conducted. The use of such a numerical method presents in particular the advantages of optimizing laboratory testing and allowing the realization of sensitivity analysis. An extensive laboratory study has been conducted in a second phase. This study permitted to clearly identify and quantify the impacts of the aggregates quality and binder content on the final mixture performances. The various tests achieved highlighted that rutting susceptibility is one of the suitable indicators for the assessment of a mix design performances. The research carried out finally permitted to highlight the benefits of an analytical mix design in a mixture optimization process. The major factors influencing the mix design have been identified and quantified through laboratory testing and some recommendations concerning the tests to carry out are also provided.

7th International RILEM Symposium on Advanced Testing and Characterisation of Bituminous Materials -- MAY 27-29, 2009 -- Rhodes, GREECE, WOS: 000280392100047, In this study, first of all, the physical and chemical effects of polypropylene fiber modification on bitumen samples were investigated. Then, the amount of "optimum" polypropylene fibers was determined. In order to determine this value, first, static creep tests and Marshall tests were carried out and then, digital images of the modified binders under fluorescence microscopy were examined. The addition of the polypropylene fibers into the asphalt mixture enhances the mixture properties in a very favorable manner. The decrease of the accumulated strains at the end of the static creep tests correspond to approximately 60%. The initial and final creep stiffness values have increased by 129% and 149% correspondingly. Besides, the polypropylene modification ends up with a 30% economy from bitumen which deserves attention. Finally the optimal polypropylene addition amount was determined as 5.5% by weight of aggregate based on the static creep, Marshall tests and stereo microscopy analyses., RILEM