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K. Kappl, R. Blab:
"Enhanced algorithms for the derivation of material parameter from triaxial cyclic compression tests on asphalt specimen";
Talk: 7th International Rilem Symposium ATCBM09 on Acvanced Testind and Characterization of Bituminous Materials, Rhodes, Greece (invited); 2009-05-27 - 2009-05-29; in: "Advanced Testin and Characterization of Bituminous Materials", A. Loizos, M. Partl, T. Scarpas, I. Al-Qadi (ed.); CRC Press; Taylor and Francis Group, vol1+vol2+CD-ROM (2009), ISBN: 978-0-415-55854-9; 357 - 366.

Material parameters, i.e. complex modulus E* and phase lag ϕ as a function of temperature and test frequency of asphalt mixtures, from cyclic material tests on asphalt specimens are fundamental input parameters for material characterization in mix design and numerical calculations of pavement distress. Mostly, these material parameters are calculated by means of a "black box" software supplied by the machine manufacturer on the basis of simple "peak finding" methods. However, it can be proven, that the used post-processing algorithm to interpret measurement data of cyclic tests is crucial on the accuracy of the calculated material parameters. Simple "peak finding methods", where the machine data are used without diligent post processing, are not suitable for the calculation of complex modulus or phase lag, because of potential errors. The paper gives a brief survey of various
mathematical methods for the determination of complex modulus E* and phase lag ϕ calculated from various cyclic tests with sinusoidal loads. Furthermore, an enhanced approach is presented that allows the identification of differences in the evolution of material parameters
during loading and unloading phases of individual load cycles.

Material parameters, i.e. complex modulus E* and phase lag ϕ as a function of temperature and test frequency of asphalt mixtures, from cyclic material tests on asphalt specimens are fundamental input parameters for material characterization in mix design and numerical calculations of pavement distress. Mostly, these material parameters are calculated by means of a "black box" software supplied by the machine manufacturer on the basis of simple "peak finding" methods. However, it can be proven, that the used post-processing algorithm to interpret measurement data of cyclic tests is crucial on the accuracy of the calculated material parameters. Simple "peak finding methods", where the machine data are used without diligent post processing, are not suitable for the calculation of complex modulus or phase lag, because of potential errors. The paper gives a brief survey of various
mathematical methods for the determination of complex modulus E* and phase lag ϕ calculated from various cyclic tests with sinusoidal loads. Furthermore, an enhanced approach is presented that allows the identification of differences in the evolution of material parameters
during loading and unloading phases of individual load cycles.