Papers by Keyword: Ultrasonic Velocity

Abstract: Concrete is a complex porous material. This porosity comes from the air trapped during mixing and also from the free water that did not react with the cement. In this work, we varied the porosity rate in concrete specimens, in order to evaluate its effect on the acoustic and mechanical properties of the material during its maturation age. These test pieces were made according to EN 196-1: 2016 of different dimensions and with three mass ratios Water/Cement (W/C=0.45, W/C=0.50 and W/C=0.65). The ultrasonic measurements were done in the direct transmission mode, using 54 kHz nominal frequency transducers, transmitting in the longitudinal mode. The results showed an increase in the propagation velocity with the age of maturation for all W/C ratios and an overall decrease in its value with this ratio. On the other hand, the attenuation coefficient increased slightly with the frequency in a quasi-linear manner, while its overall value decreased with the age of maturity of the concrete. For comparison, a destructive method was used. This consisted of crushing tests to determine the compressive strength. This latter increased with the age of maturation of the concrete for all W/C ratios, but decreased when these ratios increased. These results showed the same trend as those obtained for the ultrasonic group velocity. This allowed us to deduce a correlation law between the acoustical and mechanical parameters for all ratios with a high determination coefficient. These investigations confirm the effectiveness of ultrasonic methods in evaluating the quality of concrete.

Abstract: PbBa₂Y_1-xCa_xCu₃O_7+δ (x = 0.00, 0.15, 0.20, 0.25 and 0.50) samples were prepared via solid state reaction. All samples except x = 0.50 exhibited various critical temperatures T_c. The X-ray diffraction patterns show all samples were in mixed phase. Longitudinal and shear ultrasonic velocities in these samples were measured using the pulsed-echo-overlap method with frequency 5-10 MHz in the temperature range 80-300 K. There are no obvious elastic anomalies which are usually observed in most high temperature superconductors were observed in any of the samples in both longitudinal and shear modes. Furthermore, there is no significant variation in the percentage of velocity change in both longitudinal and shear modes with the different content of x doped for all samples.

Abstract: Ultrasonic velocity and density of salicilaldehyde with iodine in hexane has been measured at 293.15K, 298.15K, 303.15K and 308.15K in different concentration. Ultrasonic velocity has been measured using single frequency interferometer at 2MHz (Model F-81). By using the Ultrasonic velocity (u), density (ρ) and coefficient of viscosity (η) and the other acoustical parameters adiabatic compressibility (κ), free length (L_f), interaction parameter (α), Free volume (V_f) were calculated. The addition of hexane with a mixture leads to a compact structure due to presence of dipolar type interaction. This contributes to the decrease in free volume values and the internal pressure shows an increasing trend. The results have been discussed in terms of solute-solute and solute-solvent interactions between the component and the compatibility of these methods in predicting the interactions in these mixtures has also been discussed.Key Words salicilaldehyde, iodine, hexane, Ultrasonic velocity, molecular interactions.

Abstract: Ultrasonic parameters of CuO: Diethylamine-Isopropaonol binary nanofluids at six different concentrations have been reported at three different temperatures like 298K, 308K and 318K. The acoustical parameters such as Ultrasonic sound velocity (v), Compressibility (β), Inter molecular free length (Lf), Acoustic impedance (Z) are calculated from experimental data. The variation of these parameters with composition of the mixture helps us in understanding the nature and extent of interaction between particles and the binary liquid mixtures. Keywords Ultrasonic velocity, Compressibility, Acoustic impedance, Inter molecular free length, Nanofluids

Abstract: The interface between the surface hardened layer and the base layer would produce while the 20CrMo axis is treated with high frequency induction quenching method; therefore, the hardened case depth can be measured by high frequency ultrasonic wave based on the echo technique. The test results compared with those from the metallographic method show good qualitative agreements.

Abstract: The objective of this work was to examine the influence of accelerated carbonation on the microstructural and macroscopic properties of thermally damage cement mortar. A normalised CEM II mortar was treated at 500°C then submitted to carbonation at 20°C, 65% relative humidity and 20% of CO₂ concentration. The pores size distributions were determined from nitrogen adsorption. We also followed changes in electrical resistivity and ultrasonic velocity. The results showed that losses of macroscopic properties caused by cracks appeared at high temperature were restored due to carbonation. This highlighted the self-healing effect by accelerated carbonation which allowed the thermally damaged mortar to recover its initial properties.

Abstract: Rheology and ultrasonic velocity (at 2 MHz frequency) properties of Ethylene glycol (EG)-water mixed nano-coolants are studied at different temperatures. Variation in density and viscosity is found to be non-linear with increasing EG concentration. The viscosity of the mix system varies from 3.5 to 16.9 mPa.s. The results show that with increasing EG concentration in the system the ultrasonic velocity increases, reaches maximum and then decreases. The similar trend is observed for all the temperature under investigation. From these data, the adiabatic compressibility, mean free path and attenuation co-efficient have been calculated. The observed variation is explained considering the relative strength of hydrogen bond between EG and water.

Abstract: Cube concrete (150×150×150mm) of five ages (7, 14, 21, 28 and 35 days) under different stress conducted the ultrasound examination by non-metallic detector and universal testing machine. The results show that the relationship curve of the stress and the ultrasonic velocity can be divided into three stages, the smooth straight stage, the linear deceleration stage and the attenuation destruction stage from the load beginning to the ultimate strength for the same age. There is a growing trend about the ultrasonic velocity with the increase of the age to concrete samples of C10 and C20 in the same loading; however, the overall growth trend of the velocity is not obvious to concrete samples of C30, C35, C40 and C45. It also shows that the relationship curve of strength level and the velocity can be divided into two distinct stages, the sharply increasing stage (C10-C30) and the fluctuating stage (C30-C45). Simultaneously, the paper further illustrates and explains the reasons to appear these stages and the phenomena.

Abstract: An experimental study of the damage behavior of two kinds of concrete with different strength grades has been performed using 100mm cubes subjected to increasing hydrostatic loading history, namely, the isotropic compression at high pressure. The compressive strength and ultrasonic velocity are measured before and after loading history, respectively. The damage degree of these cubes is defined as the reduction of compressive strength based on the continuum damage mechanics theory. Linear and exponential curve fit of experimental data is performed respectively to describe the evolution of damage as well as the descent of ultrasonic velocity with respect to the loading history. It can be seen that, the influence of hydrostatic loading history upon strength and ultrasonic velocity could really reflect that upon the degree of damage development. In general, ultrasonic inspection is convenient and applicable to estimation of damage of concrete due to loading history in engineering practice.