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     Investigation of rheological behaviours of dense bituminous mixtures  under repeated creep testing utilising polypropylene fibers as a modifier.pdf


    Investigation of rheological behaviours of dense bituminous mixtures  under

    repeated creep testing utilising polypropylene fibers as a modifier


    Serkan Tapkın, Ün Uşar, Ahmet Tuncan and Mustafa Tuncan
    The heavy vehicles in the composition of traffic, non-foresightable axle loads and tire pressures have motivated the highway engineers to search for new pursuits. Especially in our country, the addition of the overloaded vehicles into traffic stream and the occurrence of rutting, because of the hot climatic conditions, has become one of the most predominant distress parameters. Because of the above mentioned reasons, the modification of physical and chemical properties of the bituminous binders has been assimilated to ensure the desirable performance in the flexible pavements. Starting from the beginning of seventies, because of their engineering importance, much research has been devoted to the permanent deformation phenomenon in flexible pavements. In order to prevent this phenomenon, namely rutting and also fatigue and low-temperature cracking, different types of polymer modifiers have been utilised in different types of projects carried out worldwide. Polypropylene (PP) fibers are one of these modifiers which can be obtained locally. Therefore when compared to other types of modifiers, they provide in real economy for developing countries. These are some of the main reasons why PP fibers are used in all throughout the tests carried out in the study. In the proposed study, first of all, Marshall design is carried out in order to find out the optimum bitumen contents for control and PP fiber modified specimens. These designs were carried out with one type of bitumen and a single gradation. Different types of PP fibers are used in order to determine the optimum bitumen content and the optimum PP amount in the prepared Marshall specimens. Then with these optimum amounts in hand, first of all the bitumen samples have been modified at a standard mixing temperature. With these modified bitumen samples, again, Marshall specimens have been fabricated and tests are carried out with Universal Testing Machine in order to determine the rheological behaviours of dense bituminous mixtures under repeated creep testing. Different load values and loading patterns have been applied to the previously prepared specimens at a predetermined temperature in order to determine the rutting susceptibility of the mixtures. After examining the obtained results, it has been found out that the PP modification of bituminous binders has developed the physical and mechanical properties of the mixture and substantially improved the resistance to permanent deformations. Besides, the polypropylene modification results in 30% economy form bitumen which is very important for the costly asphalt concrete production in recent times. 

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