Mechanical characterization of bituminous mixtures in the linear viscoelastic (LVE) domain is commonly limited to the measurement of a single (mono--dimensional) material function, either the Young's modulus or the shear modulus. Even under the additional hypothesis of isotropy, a complete (three-dimensional) description of the LVE response requires two material functions to be determined simultaneously and in the same experimental conditions. The measurement of viscoelastic Poisson's ratio, though generally overlooked because of the high accuracy and precision required, offers the opportunity to put aside this limitation because it can be achieved in experimental conditions that are very similar to those employed to obtain the Young's modulus. In the present experimental research the concurrent determination of the complex Poisson's ratio and the complex Young's modulus of a bituminous mixture is presented. A rheological model is employed to fit the measured complex-valued material functions and the validity of the time-temperature superposition principle is investigated. The experimental program consists of cyclic compression tests performed on cylindrical samples, with the measurement of axial and transverse strains. A conventional frequency sweep procedure is followed in a range of intermediate service temperatures. Two strain levels are chosen focusing the attention on the linear domain. In addition, samples with different air voids content are tested to observe the effect of the aggregate skeleton. Results allowed to characterize frequency and temperature dependance of the complex Poisson's ratio and make a comparison to that of the complex Young's modulus on the basis of the selected rheological model. Experimental data confirm the validity of the time--temperature superposition principle but suggest that different shift factors may be required to correctly translate the time--temperature dependance of different material functions.

Complex Poisson’s ratio of bituminous mixtures: measurement and modeling

GRAZIANI, Andrea;BOCCI, MAURIZIO;CANESTRARI, FRANCESCO
2014

Abstract

Mechanical characterization of bituminous mixtures in the linear viscoelastic (LVE) domain is commonly limited to the measurement of a single (mono--dimensional) material function, either the Young's modulus or the shear modulus. Even under the additional hypothesis of isotropy, a complete (three-dimensional) description of the LVE response requires two material functions to be determined simultaneously and in the same experimental conditions. The measurement of viscoelastic Poisson's ratio, though generally overlooked because of the high accuracy and precision required, offers the opportunity to put aside this limitation because it can be achieved in experimental conditions that are very similar to those employed to obtain the Young's modulus. In the present experimental research the concurrent determination of the complex Poisson's ratio and the complex Young's modulus of a bituminous mixture is presented. A rheological model is employed to fit the measured complex-valued material functions and the validity of the time-temperature superposition principle is investigated. The experimental program consists of cyclic compression tests performed on cylindrical samples, with the measurement of axial and transverse strains. A conventional frequency sweep procedure is followed in a range of intermediate service temperatures. Two strain levels are chosen focusing the attention on the linear domain. In addition, samples with different air voids content are tested to observe the effect of the aggregate skeleton. Results allowed to characterize frequency and temperature dependance of the complex Poisson's ratio and make a comparison to that of the complex Young's modulus on the basis of the selected rheological model. Experimental data confirm the validity of the time--temperature superposition principle but suggest that different shift factors may be required to correctly translate the time--temperature dependance of different material functions.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11566/112464
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