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Etude de la prise de ciment Portland par une technique de champ proche acoustique
Two horn shapes are examined, one with a conical probe, the second one with a stepped cylindrical probe. The horn operating has been modelled, in order to optimize the design sensitivity to the change in the rheological properties of the viscoelastic material. We have seen that the variation of the load impedance, brought about by a change of the rheological properties of the material in contact with the probe. involves an alteration of the electric impedance. The features of the electrical impedance, for instance f and Z, can be established by frequency scan. The experimental variations Deltaf and Delta(1/Z) can be simulated, for a given medium, knowing its load impedance Zload. Therefore, the electrical impedance Zelect. can be calculated for given experimental conditions (kind of material, horn design, immersion depth of the probe). For weak or mean loads (simulating a fluid sample). the resonance curve of the horn with stepped cylindrical probe showed two peaks. When the probe of the stepped cylindrical horn was free or immersed in a liquid medium, the horn operated like two coupled resonators. Neither of the two cylinders vibrated at its proper frequency, the vibration mode of each one being modified by the coupling with the other. If the load applied by the immersion medium was increased, the dissipated energy increased. This lessened the energy stored in the horn and involved a lessening of the resonance peaks of both cylinders. When the immersion medium was stiff, the stepped cylindrical probe was jammed and one resonance peak was detected. Its frequency was that of a resonator equivalent to the whole horn having one end fixed. The energy remained mainly stored. The dissipation was weak and decreased when the stiffness of the medium increased. The value of the resonance frequency became close to the natural frequency of the equivalent resonator. This theoretical study has shown that the evolution of the properties of the immersion medium can be controlled, without discontinuity, until the solid state occurs. The shear threshold corresponds to the change of operating mode of the horn with stepped cylindrical tip. It can be experimentally characterized by this horn by the vanishing of peak 2 and, more accurately, by the minimum of peak 2. The variation Delta (1/Z) of the inverse of the maximum of the real part of the impedance of the electrical resonance has a physical significance. It is mainly related to the energy dissipated in the sample by the horn and is rather representative of the variation the loss modulus G' of the material (the viscous contribution of the complex shear modulus). Delta(1/Z) will be experimentally studied. The shape of the resonance curve and its change, expected according to the modelling, were found again through the experimental study of a water/cement mixture as a function of time.
Etude de la prise de ciment Portland par une technique de champ proche acoustique
Two horn shapes are examined, one with a conical probe, the second one with a stepped cylindrical probe. The horn operating has been modelled, in order to optimize the design sensitivity to the change in the rheological properties of the viscoelastic material. We have seen that the variation of the load impedance, brought about by a change of the rheological properties of the material in contact with the probe. involves an alteration of the electric impedance. The features of the electrical impedance, for instance f and Z, can be established by frequency scan. The experimental variations Deltaf and Delta(1/Z) can be simulated, for a given medium, knowing its load impedance Zload. Therefore, the electrical impedance Zelect. can be calculated for given experimental conditions (kind of material, horn design, immersion depth of the probe). For weak or mean loads (simulating a fluid sample). the resonance curve of the horn with stepped cylindrical probe showed two peaks. When the probe of the stepped cylindrical horn was free or immersed in a liquid medium, the horn operated like two coupled resonators. Neither of the two cylinders vibrated at its proper frequency, the vibration mode of each one being modified by the coupling with the other. If the load applied by the immersion medium was increased, the dissipated energy increased. This lessened the energy stored in the horn and involved a lessening of the resonance peaks of both cylinders. When the immersion medium was stiff, the stepped cylindrical probe was jammed and one resonance peak was detected. Its frequency was that of a resonator equivalent to the whole horn having one end fixed. The energy remained mainly stored. The dissipation was weak and decreased when the stiffness of the medium increased. The value of the resonance frequency became close to the natural frequency of the equivalent resonator. This theoretical study has shown that the evolution of the properties of the immersion medium can be controlled, without discontinuity, until the solid state occurs. The shear threshold corresponds to the change of operating mode of the horn with stepped cylindrical tip. It can be experimentally characterized by this horn by the vanishing of peak 2 and, more accurately, by the minimum of peak 2. The variation Delta (1/Z) of the inverse of the maximum of the real part of the impedance of the electrical resonance has a physical significance. It is mainly related to the energy dissipated in the sample by the horn and is rather representative of the variation the loss modulus G' of the material (the viscous contribution of the complex shear modulus). Delta(1/Z) will be experimentally studied. The shape of the resonance curve and its change, expected according to the modelling, were found again through the experimental study of a water/cement mixture as a function of time.
Etude de la prise de ciment Portland par une technique de champ proche acoustique
Untersuchung des Abbindens von Portland-Zement mit einer akustischen Nahfeldtechnik
Study of the setting of Portland cement by an acoustic near field technique
Cros, B. (author) / Ramdani, A. (author) / Ferrandis, J.Y. (author)
Revue de Metallurgie, Cahiers d'Informations Techniques ; 97 ; 1525-1533
2000
9 Seiten, 12 Bilder, 18 Quellen
Article (Journal)
French
Procedes de suivi rheologique par champ proche acoustique appliques aux bitumes
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Engineering Index Backfile | 1918
Ciment fondu and mixtures of ciment fondu and Portland cement
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