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S. Nahar, J. Qiu, A. Schmets, E. Schlangen, M. Shirazi, M. F. C. Van de Ven, G. Schitter, A. Scarpas:
"Turning Back Time: Rheological and Microstructural Assessment of Rejuvenated Bitumen";
Poster: Transportation Research Board (TRB) 93rd Annual Meeting, Washington DC, USA; 12.01.2014 - 16.01.2014; in: "Proceedings of the Transportation Research Board 93rd annual meeting 2014", (2014), 16 S.

Countermeasures to the ageing of bituminous asphalt binders is a highly important topic, both for service-life extension of asphalt `in the field´ and for recycling old pavements (RAP) into new structures with similar functional requirements as the original structure. Usually this is achieved by applying additives that restore the adhesive and mechanical properties of the original bituminous binder. These additives are commonly termed (asphalt) rejuvenators. In this paper we examine the performance of two very distinct rejuvenating agents. Usually the effectiveness of rejuvenators is measured by comparing the penetration and softening point of the rejuvenator-aged bitumen blend to reference values of the virgin binder. We firstly evaluate the rejuvenating capabilities of the two additives in terms of rheology using a dynamic shear rheometer. Then the microstructures of the virgin binder and the rejuvenated blends are obtained by means of atomic force microscopy. Subsequently the rheological results are related to the microstructure morphologies.
One finds from the rheological experiments that both rejuvenators exhibit the desired softening and property restoring performance. Though, there is a strong difference in the amount of rejuvenator needed for achieving complete rejuvenation. By correlating rheology to the microstructural observations one finds that the effect of both rejuvenators is very distinct at microscopic length scales: rejuvenation is achieved by distinct chemo-physical mechanisms. One of the rejuvenators restores the virgin microstructure, whereas the other rejuvenator generates a new morphology.
Thus, it is demonstrated that by combining rheological and microstructural techniques, the mechanism and performance of rejuvenation can be understood. This may guide future designs and optimization of asphalt rejuvenating agents.