Ultrasonic Shear Wave Reflection Research Articles

Ultrasonic Shear Wave Reflection Method for Direct Determination of Porosity and Shear Modulus in Early-Age Cement Paste and Mortar

AbstractAn ultrasonic technique for measuring reflection of horizontally polarized shear (SH) waves at different angles of incidence from early-age hydrating mortar and cement paste is described. Measurements from mortar with varying sand content are presented. A poroelastic formulation for predicting wave reflection from hydrating mortar, which considers mortar as a two-phase, water-filled solid skeleton, is developed. In this representation, the solid phase in early-age hydrating mortar consists of sand, products of hydration and unhydrated cement. Reflection at the mortar interface is predicted using the poroelastic theory. Changes in the reflected amplitude of SH waves are used to obtain changes in the water-filled pore space and the shear modulus of the porous skeleton within the two-phase poroelastic idealization. The water-filled pore space in mortar is identified with the porosity in the two-phase poroelastic material. The porosity of mortar obtained from the poroelastic idealization when referrin...

Monitoring of bitumen hardening with a non-destructive ultrasonic shear wave reflection technique

The article presents a possibility of using a non-destructive ultrasonic shear wave reflection technique for monitoring hardening process of bitumen. The technique relies on the use of a new measuring instrument called USWR-4 Hardening meter, which was developed to be applicable directly in situ and has been effectively used for cement-based materials so far. It works on the principle of continuous measurement of change of a shear wave reflection coefficient. Three different types of paving grade and two polymer-modified bitumens were used. Results show that the presented ultrasound technique can effectively track a temperature-dependent hardening process of bitumen.

Monitoring setting and hardening process of mortar and concrete using ultrasonic shear waves

Ultrasonic wave methods have been extensively investigated for monitoring the setting and hardening process of cementitious materials. However, the commonly used P wave velocity parameter is affected by air voids in the material in the fresh state. In addition, the conventional ultrasonic wave velocity test setup typically needs access to both sides of a structural member, which is not always possible for in-situ field testing. The ultrasonic shear wave reflection method measures the acoustic property of the near surface material only. In this paper, ultrasonic shear waves, measured by embedded piezoceramic bender elements, are used to monitor the setting and hardening process of mortar and concrete. Experimental results from mortar and concrete mixtures with different water to cement ratios show a clear relationship between the shear wave velocity and the penetration resistance (ASTM C403), which indicates that the shear wave velocity is a more reliable indicator than the P wave velocity for in-situ monitoring of the setting and hardening process of cementitious materials.

Monitoring Setting of Geopolymers

AbstractThe setting behavior of geopolymer pastes as a function of time was studied using two methods: penetration resistance and ultrasonic shear wave reflection. Several starting materials were included—metakaolin, Class C and Class F fly ashes, and slag—and chemical parameters known to affect set were varied. The geopolymers showed a wide range of set times compared to a reference Portland cement paste: some were much more rapid, some were similar, and some were much slower. Although most geopolymers formed gels that were both solid and had measurable strength, some, initially, formed a soft gel that had no measurable strength. Therefore, to fully characterize setting behavior, it is necessary to use both types of tests. It was seen that setting behavior was sensitive to chemical parameters, with setting delayed somewhat with increasing silica/alumina and increasing water/alkali, and accelerated substantially with calcium hydroxide substitution.

Measurement of setting process of cement pastes using non-destructive ultrasonic shear wave reflection technique

In this paper a new setup for measuring, setting and hardening process of cementitious materials, using a non-destructive ultrasonic shear wave reflection technique and design with the objective to be easily used in-situ, is described. Using the developed setup, the measurements can be performed by slight deepening of a measuring head into a paste in a mold or by placing the paste into a mold fixed on a measuring head. To test the proposed methodology, cement pastes with different compositions were prepared and exposed to different curing temperatures. Significant differences in the evolution of a change of a shear wave reflection coefficient Δr in time were observed, indicating the ability of the method to monitor setting process of cement pastes. Moreover, some interesting phenomena in the solidification process of the materials can be identified. A linear relationship between development of Δr and penetration resistance dP values in time was found, allowing development of a simplified procedure to determine both initial and final setting times of the material.

Setting Time Measurement Using Ultrasonic Wave Reflection

Ultrasonic shear wave reflection was used to investigate setting times of cement pastes by measuring the reflection coefficient at the interface between hydrating cement pastes of varying water-to-cement ratio and an ultrasonic buffer material. Several different buffer materials were employed, and the choice of buffer was seen to strongly affect measurement sensitivity; high impact polystyrene showed the highest sensitivity to setting processes because it had the lowest acoustic impedance value. The results show that ultrasonic shear-wave reflection can be used successfully to monitor early setting processes of cement paste with good sensitivity when such a very low impedance buffer is employed. Criteria are proposed to define set times, and the resulting initial and final set times agreed broadly with those determined using the standard penetration resistance test.

Comparison between two ultrasonic methods in their ability to monitor the setting process of cement pastes

This paper presents the comparison between ultrasonic wave transmission (USWT) method and ultrasonic wave reflection (USWR) method in their ability to monitor the setting process of cement pastes. The velocity of ultrasonic longitudinal waves and shear wave reflection coefficient were measured simultaneously on cement pastes with different hydration kinetics. Even though both methods are able to reliably monitor the hydration process and formation of structure of an arbitrary cement paste, they monitor the setting process in different ways. The relationship between the velocity of longitudinal waves and shear wave reflection coefficient can be simplified into three characteristic phases and the end of the first phase can be used to define the beginning of the setting process of cement paste.

Temperature Effects on Strength Evaluation of Cement-Based Materials with Ultrasonic Wave Reflection Technique

Among the various factors that influence the strength gain of cementitious materials at early age, curing temperature can be regarded as an important parameter due to its great effect on the hydration kinetics of portlandcement. The temperature effects on the relationship between the compressive strength of paste, mortar, or concrete and the reflection loss obtained with ultrasonic shear-wave reflection measurements were observed. In the study, three different constant curing temperatures (15, 25, and 35 °C) were used for a given paste or mortar. The temperature effects were observed by comparing the established relationship between reflection loss and compressive strength for portland cement mortar under different isothermal curing conditions. Additionally, the established correlations between the two studied parameters were verified by applying alternating curing temperatures to the mortar. As a third step, the temperature dependence of the relationship between the two studied parameters was further verified by observing concrete cured under various conditions. The study shows that for a given material, the relationship between the reflection loss and the compressive strength is independent of curing temperature.

Measuring Newtonian viscosity from the phase of reflected ultrasonic shear wave

In this paper, an acoustic shear impedance model is employed to obtain a relation between the viscosity of a Newtonian fluid and phase characteristics of ultrasonic shear wave reflection from a solid–fluid interface. The phase and magnitude of the reflection coefficient can be decoupled in this model. The decoupling allows an independent relation between the acoustic shear impedance (viscosity–density product) and phase of the reflection coefficient. The model was experimentally verified for different fluid–solid combinations. Comparison of the results with the commonly used absolute reflection coefficient method demonstrates that phase measurement provides improved measurements.

Film foration and crystallization kinetics of polychloroprene studied by an ultrasonic shear wave reflection method

We report the application of an ultrasonic shear wave reflection technique for the investigation of film formation and crystallization kinetics of one amorphous and two semicrystalline polychloroprene samples with different gel content. Both isothermal and temperature-dependent measurements of the complex dynamic shear modulus (G* = G′ + iG″) have been performed at a frequency of 5.32 MHz. The process of film formation during the evaporation of water is expressed by a stepwise increase of the shear modulus. For the semicrystalline samples a further increase, which is due to crystallization, can be observed. Film formation and crystallization are delayed for the sample with high gel content and its minor final modulus is explained by a lower degree of crystallinity. The time-dependent increase of the shear modulus due to the growth of spherulites has been analyzed by the Avrami equation combined with the Kerner model for the modulus of a two-phase composite (spherulites in an amorphous matrix). The dynamic shear modulus for the spherulites has been estimated by a model introduced by Halpin and Kardos. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2949–2959, 1998

Film foration and crystallization kinetics of polychloroprene studied by an ultrasonic shear wave reflection method

Film foration and crystallization kinetics of polychloroprene studied by an ultrasonic shear wave reflection method

Viscoelastic Contrast and Kinetic Frustration during Poly(ethylene oxide) Crystallization in a Homopolymer and a Triblock Copolymer. Comparison of Ultrasonic and Low-Frequency Rheology

We report a combined study using an ultrasonic shear wave reflection technique and conventional low-frequency rheology for the investigation of the crystallization kinetics and melting of a poly(ethylene oxide) (PEO) homopolymer and a poly(ethylene oxide)−polystyrene−poly(ethylene oxide) (PEO−PS−PEO) triblock copolymer. Both isochronal heating and isothermal/isochronal kinetic measurements of the complex dynamic shear modulus G* have been performed with high-frequency (ultrasonic) and conventional low-frequency rheology at frequencies of 3.5 MHz and 0.16 Hz, respectively. The different frequencies create a different viscoelastic contrast between the two phases in the two experiments. In both experiments the system can be regarded as a composite material made of spherulites within the amorphous matrix, and the increase of the shear modulus with time is attributed to the growing of spherulites at the expense of the amorphous matrix. The kinetics of crystallization are analyzed in the framework of the Avrami...

Comparison of ultrasonic shear wave and dynamic-mechanical measurements in acrylic-type copolymers

An ultrasonic shear wave reflection method was applied to study film formation and temperature dependence of the complex shear modulus (G*G′ + iG″) in different amorphous films made of aqueous dispersions of acrylic-type copolymers. The data are compared with dynamic-mechanical measurements in the low frequency range. It is shown that the temperature dependence of the storage (G′) and the loss modulus (G″) for both methods can be fitted by the same set of parameters using the Havriliak–Negami function incorporating the Vogel–Fulcher–Tamman–Hesse equation for the temperature dependence of relaxation times. The temperature dependence of the relaxation times obtained from the fits to the ultrasonic shear modulus is compared to the shift factors of the dynamic-mechanical measurements. The agreement between both methods is good. This suggests an almost thermorheological simplicity of the samples for the main glass–rubber relaxation and demonstrates the capacity of the ultrasonic rheometer. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1703–1711, 1998

Ultrasonic shear wave reflection method for measurements of the viscoelastic properties of polymer films

We report a shear wave reflection technique which allows time- and temperature-dependent measurements of the complex dynamic shear modulus (G*=G′+iG′′) or the dynamic shear viscosity (ηs′) in the ultrasonic frequency range (3–40 MHz). The shear wave reflection method developed by Mason et al. [Phys. Rev. 75, 936 (1949)] was adapted to the possibilities of the high-frequency digital technique. A conventional single-frequency pulse-burst system and a broadband pulsed ultrasonic spectroscopic system using Fourier analysis for detection of phase and amplitude changes of the reflected signals are described alternatively. Due to digital analysis of the received signal it was possible to achieve a simplification of the experimental setup and to extend the limits of the shear wave reflection technique to about one Gigapascal (100 μm film thickness) or to minimum film thickness of about 10 μm (G′<10 MPa). Furthermore, it is possible to monitor time-dependent isothermal processes or reactions with the setup. The basic features of the two different techniques are presented together with brief experimental results on film formation from aqueous polychloroprene dispersions and of the crystallization kinetics in the films. Furthermore, temperature-dependent studies of melting and crystallization on semicrystalline polychloroprene and of the glass transition behavior of amorphous butyl acrylate/styrene copolymer films are reported. The importance of the method is discussed for both investigations of fundamental questions (e.g., film formation, reaction kinetics, or phase transitions) and technological assessment (glues, paints, etc.).