As part of RILEM TC 237-SIB, TG3 performed a Round Robin Test to evaluate the capacity to measure Poisson's ratio of an asphalt mixture in the laboratory and to check whether it could be considered as an isotropic property. Five laboratories located in five different countries took part in the testing program. This paper presents the different techniques used by the laboratories, reports the measured Poisson's ratios and comments upon the differences found between the results. Sinusoidal or haversine loading either in tension-compression or pure compression was applied to the specimens over a range of frequencies and temperatures. During the loading both the axial and radial strains were monitored to allow the complex Young's modulus and the complex Poisson's ratios to be calculated. It was found that the complex Young's modulus and the complex Poisson's ratios were very close in the Black Diagrams, but diverge sharply in the Cole-Cole plots. It was observed that the maximum difference between the complex Poisson's ratio in direction 2 and direction 3 is less than 0.05. It would appear that this difference is more related to measurement deviation than anisotropy of the material. Some differences were observed in the master curves of complex Young's modulus and complex Poisson's ratio obtained from the five laboratories; however these differences could in most cases be explained by temperature differences. It was concluded that within the linear viscoelastic range (small strains) the results from the different laboratories show similar rheological behavior and the material response follows the same trend.
Complex modulus characterization of cold-recycled mixtures with foamed bitumen and different content of reclaimed asphalt (RA)Cold-in place recycling with foamed bitumen is currently employed for the rehabilitation of road pavements, from local roads to heavy-duty motorways. The mechanical properties of foamed bitumen mixtures may vary from that of an improved granular material to that of an asphalt concrete, depending on their composition. The objective of the present study was to characterize the linear viscoelastic response of foamed bitumen mixtures with different content of reclaimed asphalt (50, 70 and 0 %). This objective was tackled by measuring the complex Young's modulus by means of uniaxial cyclic compression tests, in a range of temperatures (from -20 to 55 °C) and frequencies (from 0.03 to 10 Hz).The thermo-rheological behaviour was modelled using the Huet-Sayegh model, commonly used for bituminous mixtures. In order to focus on the influence of reclaimed asphalt content, the same grading and foamed bitumen content were used for all the mixtures. In addition, an effort was made to produce mixtures with similar volumetric properties. Considering all the tested mixtures, the stiffness modulus ranged between 171 to 4075 MPa, whereas the phase angle ranged between 4° to 18°. Though these values are well below those normally measured on asphalt mixtures, the frequency and temperature variations clearly highlight a typical asphalt-like behaviour. In addition, the time-temperature superposition principle can be considered valid, regardless of the reclaimed asphalt content. Overall the experimental results showed that it is possible to characterize the linear viscoelastic response of cold recycled foamed bitumen mixtures using the same experimental and analytical approach adopted for asphalt mixtures.
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