Effects of air voids on ultrasonic wave propagation in early age cement pastes (original) (raw)
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Cement and Concrete Research, 2008
In this paper, the applicability of the ultrasonic wave transmission method to estimate the initial setting time of an arbitrary cement paste is discussed. Ultrasonic pulse velocity measurements were fully automated and measured continuously. The Vicat Needle Test was used in order to determine the initial setting time of cement pastes. Different cement pastes were prepared in order to check the influence of the water/cement ratio, type of cement, curing temperature, cement fineness, and some clinker compositions, on the relationship between the initial setting time and ultrasonic pulse velocity. It was found that the initial setting time of an arbitrary cement paste can be estimated very accurately by the time the first inflection point appears on the ultrasonic pulse velocity curve. Moreover, it can be estimated quite accurately by the time the ultrasonic pulse velocity reaches a fixed value, close to the value of the ultrasonic pulse velocity in water.
Cement and Concrete Research, 2009
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.
Characterization of entrained air voids in cement paste with scattered ultrasound
Ndt & E International, 2006
This research develops a technique that uses the attenuation of ultrasonic waves to characterize the average size and volume fraction of entrained air voids in hardened cement paste. Quantitative knowledge of entrained air void size and distribution helps ensure that an adequate design strength is developed, while maintaining resistance to freeze-thaw damage in cement-based materials. Ultrasonic attenuation coefficients obtained from pulse-burst signals are measured in the frequency range of 500 kHz-5 MHz. From these parameters, the average size and the volume fraction of the entrained air voids are determined using a combination of an ultrasonic scattering model and an inversion algorithm. Experiments are performed on specimens produced with and without entrained air voids. There is a good agreement between the model prediction and the experiments in these systems that contained o10% by volume of entrained air voids. r
Application of Ultrasonic Measurements for Determination of Setting and Hardening in Cement Paste
Journal of Civil Engineering and Architecture, 2011
Concrete setting and hardening processes are the most critical phases during construction works, influencing properties of a concrete structure. The initial set is important as it provides an estimate when concrete has reached a point that it can no longer be vibrated without damaging concrete. The point at which final set occurs is important since it provides an estimate when the development of concrete strength and stiffness starts. In this study, experimental work is performed under laboratory conditions to indentify the setting time of cement paste using ultrasonic waves. Correlation between the ultrasonic wave parameters (speed, amplitude and energy) passing through the fresh cement paste and setting time determined using the Vicat test method is analyzed. A method of acoustic emission is also used and acoustic signals recorded in cement paste during hydration are presented.
The use of frequency spectrum of ultrasonic P-waves to monitor the setting process of cement pastes
Cement and Concrete Research, 2013
In this paper, a possibility of using a frequency spectrum of ultrasonic P-waves to monitor the formation of structure of cement pastes at early ages is studied. A new parameter, labeled as a TG parameter, is defined as a dimensionless ratio between maximum amplitudes of two dominant frequency ranges that appear in a frequency spectrum of received ultrasound signals. Four stages and three characteristic points can be identified on the TG-vs.-time graphs, indicating that the development of the frequency spectrum is closely related to the setting phenomena. By comparing the TG parameter with the P-wave velocity and temperature evolutions in time, important milestones in the process of formation of microstructure were identified, such as the time of reduced workability and a period of intensive setting. The combined use of P-wave velocity and TG parameter results in a comprehensive ultrasonic method that gives a more complete picture of setting.
Characterization of multi-scale porosity in cement paste by advanced ultrasonic techniques
Cement and Concrete Research, 2007
The effectiveness of advanced ultrasonic techniques to quantitatively characterize the capillary porosity and entrained air content in hardened cement paste is examined. Direct measurements of ultrasonic attenuation are used to measure the volume fraction and average size of entrained air voids and to assess variations in intrinsic porosityas influenced by water-to-cement ratio (w/c)in hardened cement paste samples. For the air entrained specimens, an inversion procedure based on a theoretical attenuation model is used to predict the average size and volume fraction of entrained air voids in each specimen, producing results in very good agreement with results obtained by standard petrographic methods and by gravimetric analysis. In addition, ultrasonic attenuation measurements are related to w/c to quantify the relationship between increasing porosity (with increasing w/c) and ultrasonic wave characteristics.
NDT & E International, 2018
The heterogeneity of cement-based materials and the severe wave-microstructure interactions at the fresh state render the thorough investigation of ultrasonic wave propagation imperative, especially when the latter is used for material characterization and quality control. In this study, parallel to the advanced ultrasonic wave dispersion and attenuation experiments, numerical simulations are also performed offering faster, reliable and accurate solutions at low cost, as well as flexibility on the design and measured properties. Cement pastes and mortars are investigated and the observed dispersive and attenuative trends are further explained with scattering theories reinforcing the characterization potential. The results pinpoint air bubbles and sand grains as causes of the dispersion and attenuation frequency dependent trends. The distinct frequency regimes where these phenomena are observed allow for the more accurate characterization of the microstructure. For the first time, the strong qualitative and quantitative agreement between experiments, scattering theories, and numerical simulations provides holistic insights into wave propagation in fresh cementitious materials and firmly connects the dispersion and attenuation of waves to their origin.
NDT & E International, 2013
In the paper a new setup for measuring setting and hardening process of cementitious materials, using a non-destructive ultrasonic shear wave reflection technique and designed 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 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 the Δr and penetration resistance d P values in time was found, allowing development of a simplified procedure to determine both initial and final setting times of the material.
Investigation of the ultrasonic sound signals during the cementing materials induration
MATEC Web of Conferences, 2017
The paper is devoted to investigation mechanism of cement mixture setting and stiffening. Method for registration of the acoustic oscillations induced during the heterophase transitions executing in liquid medium was proposed (method of acoustic emission (AE)). Using of conical vessel serving as a resonator allows the amplification of registered acoustic signal and provides high sensitivity of the registration. The experimental results show that the using of AE-method allows remote monitoring of the dynamics of concrete mixtures condition during setting. Therefore, this method can be successfully applied in building as a nondestructive method for determining the start and end of the solidification of the cement solution.