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H. Grothe, F. Handle, S. Neudl:
"Study of the Adhesion between Bitumen and Aggregates in Asphalt Mixes";
2013; 128 S.

The use of asphalt in road construction has been developed in Europe since the beginning of the 20th century. Asphalt is a mixture of mineral aggregates that are embedded in a matrix of bitumen. The quality of the roads depends on the adhesion between bitumen and aggregate. This project was initiated in order to improve the quality of the asphalt mixtures by investigating the adhesion between bitumen and aggregate.
The project "Adhesion between Bitumen and Mineral Aggregates" was conducted on behalf of OMV Marketing & Refining GmbH starting in the year 2008, the last experiments were performed in September and October 2012. The Institute of Materials Chemistry (IMC) of Vienna University of Technology and Braunschweig Pavement Engineering Center (ISBS) of Braunschweig University of Technology worked together to advance the understanding of the complex composite material asphalt.
Different bitumen samples and mineral aggregates were studied separately as well as in different material combinations to assess and study the contributions of various physical and chemical characteristics of the single materials to the composite. The goal of the study was to identify analytical procedures and testing methods, which produce reliable and reproducible parameters that can be used to assess the applicability of a given combination of bitumen and mineral aggregate as high quality pavement. Furthermore, understanding of fundamental principles of a material offers the prospect of cheap, easy, and fast laboratory tests.
While the colleagues at Braunschweig Pavement Engineering Center worked on the enhancement of application focused testing procedures testing mechanical and rheological properties, the IMC tried to obtain and extract the basic properties and fundamental interactions inside bitumen as well as between bitumen and mineral aggregates. To further that goal many different analytical techniques were employed ranging from different spectroscopic and spectrometric techniques to the latest microscopic setups and more direct methods to assess surface phenomena.
The contact angle measurement has been employed for the determination of the surface free energy components of the bitumen in order to predict its adhesion ability to different aggregates. The method was studied in great detail. The various variations and techniques were analyzed in depth employing statistical tests. To ascertain the outlook on this method, an interlaboratory study together with three scientific partners in Germany. The results strongly advise a larger study on the statistical reliability of the measurements before further efforts are made to establish or discard this technique as a standard method.
Among the characterization techniques used in this study, conventional mass spectroscopy has turned out to be inappropriate for the analysis of bitumen, although more sophisticated Fourier transform mass spectrometry yielded intriguing results concerning functionalities in bitumen and has been proven capable of differentiation between very similar bitumen samples. Raman spectroscopy itself also has not delivered interesting information on the bitumen structure because of interfering fluorescence, but it has led to the use of fluorescence microscopy, by which the organisation of the fluorescent micelles in the bitumen has been observed. This technique in turn revealed the necessity of fluorescence spectroscopic analysis of the samples and fragmentation of bitumen by chromatographic techniques. Infrared Spectroscopy suffers from similar problems, as were encountered by conventional mass spectrometry. Cryo X-Ray Diffraction was used to reveal possible crystallization phenomena at low temperatures. Surface morphologies have also been investigated by a scanning electron microscope using a cryostat for sample preparation (cryo-SEM).
As far as the investigated aggregates are concerned, X-Ray Diffraction delivered their phase composition. The surface morphologies have been visualized with SEM and fluorescence microscopy and their specific surfaces have been determined by N2 adsorption applying the BET method. Specific morphological areas of special interest were investigated with EDX, yielding highly localized information on the elemental composition. Thermal programmed desorption was not applicable, due to thermic and chemical degeneration of carbonate phases of the mineral aggregate, gravely affecting the chemical composition of the mineral aggregate. The combined results led to the conclusion, that the adhesion properties of the Loya aggregate are superior to those of the Fröstl aggregate. This result has been confirmed by the immersion water test, which has proven the much better adhesion of the bitumen to the Loya aggregate.
The scientific achievements of this study were presented to the scientific community at two occasions: An oral presentation dealing with the application of CLSM on bitumen was given in Berlin at the Annual German Conference for Physical Chemistry in June 2011. Two posters were presented regarding CLSM observed structural phenomena in polymer modified bitumen and regarding the use of contact angle measurement as a routine laboratory technique at the 5th annual Euroasphalt & Eurobitume Conference 2012: Destination Istanbul. Papers of all three presentations were published in the conference proceedings of the conferences.