Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-09-10
2003-12-02
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S600000, C073S602000
Reexamination Certificate
active
06655213
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns the examination of a solidifying and/or hardening material, such as cement, concrete or the like, using ultrasound waves, emitted from an ultrasound transmitter to an ultrasound receiver, which penetrate the material and are continuously measured and analyzed.
PRIOR ART
Such examinations are known e.g. from the publication “Kontinuierliche Ultraschallmessungen während des Erstarrens and Aushärtens von Beton” (continuous ultrasound measurements during solidification and hardening of concrete) by Chr. U. Grosse and H.-W-Reinhardt in Otto-Graf-Journal, Vol. 5, 1994.
Ultrasound waves can penetrate a material without causing damage thereby being influenced by the elastic properties of the material, which produces information about the elastic properties.
With concrete, these are e.g. its current solidification and hardening state, composition (grading curve, water-cement value etc.) and the entrained air content and possibly utilized additional means.
In industrial construction e.g., determination of solidification start and end of cement paste according to DIN EN 196, part 3, is carried out through the Vicat method. A measurement of this type is not possible with concrete due to the aggregate and is therefore not provided in the above-mentioned standard. Examination methods for unset concrete have been, on the one hand, consistency measuring methods such as the propagation test and compacting test according to DIN 1048 part 1, the penetrometer according to ASTM C-403 and the setting test according to DIN ISO 4109. On the other hand, there is the air content measurement according to DIN 1048 part 1 including pressure compensation method and furthermore methods for determining the water content.
The latter methods permit only individual measurements at fixed points in time and give information about a certain property. It is not possible to obtain detailed information about the composition of the material nor about the further hardening of the material after solidification.
OBJECT OF THE INVENTION
It is therefore the underlying purpose of the invention to provide reliable use of an ultrasound test method in industrial practice and permit easy continuous monitoring of the state of a solidifying and/or hardening material.
SUBJECT MATTER AND ADVANTAGES OF THE INVENTION
This object is achieved by a method for examining a solidifying and/or hardening material such as cement, concrete or the like, using ultrasound waves emitted by an ultrasound transmitter, which penetrate the solidifying and/or hardening material, are continuously measured and analyzed, comprising the following method steps:
i) during solidification and/or hardening of the material, the signal shapes of the ultrasound waves penetrating the material are recorded;
ii) The change with time of the compression wave velocity and/or the relative energy of the ultrasound waves and/or the frequency spectra of the ultrasound waves is extracted from the ultrasound wave shapes during the entire course of solidification and/or hardening of the material.
iii) This change with time of the compression wave velocity and/or the relative energy o the ultrasound waves and/or the frequency spectra of the ultrasound waves is approximated through a compensating function, preferably the Boltzmann function.
iv) the free parameters of the compensation function are associated with material properties.
v) the free parameters of the compensation function permit comparison of a current measurement with reference values of these parameters to permit determination of material properties of the examined material.
Automatic measuring and analysis of the data is largely possible and information about the material itself can be obtained already during the solidifying/hardening phase.
For the measurement, the material to be examined is introduced into a receptacle and compacted. The opposing sides of the receptacle are provided with a preferably broad-band (i.e. adequately linear frequency response function over a broad spectral range) ultra sound transmitter and a corresponding receiver. Same transforms the acceleration signal into a voltage signal and transmits it to a computer-controlled analog-digital transformer card which stores the signal in digital form thereby making it accessible for further analysis.
For an analysis, the velocity of the compression wave v
p
(T), the relative energy E(T) of a measured signal, and the frequency spectrum f(T) of the signal can be extracted with corresponding algorithms. The velocity of the compression wave v
p
(T), the relative energy E(T) of a measured signal and the frequency spectrum f(T) of the signal depend on the time T elapsed since production of the material and form together a complete parameter set which contains the entire information about the material which can be obtained from elastic waves.
The wave velocity of the compression waves in the material can be determined from the quotient between running distance s and running time t(T) of the waves according to v
p
(T)=s/(t(T)−t
0
). While the running distance s, determined through the dimensions of the receptacle, is constant, the running time t(T) of the signals is reduced with increasing solidification of the material during the duration T of the test. In this calculation, constant parts for the running time of the waves through the walls of the container and for the time delay, caused by the measuring means, must be subtracted from the determined running time. This dead time t
0
of the system which is not related to the material can be determined through calibration measurement, which can be achieved in the most simple fashion through running time measurement with direct coupling of transmitter and receiver container walls.
The relative energy E(T) is defined as a quotient of the wave energy which can be measured after passage of the wave through the material, and the energy which was introduced into the material by the ultrasound pulse. The individual energies are thereby calculated from the integral of the amplitude squares of the respective signals. If the introduced energy cannot be used as measuring value, it can be assumed to be constant when using a suitable ultrasound transmitter. The relative energy increases with increasing hardening or solidification of the material. The energy can further be represented as its integral overtime.
If the utilized ultrasound transmitter can generate sufficiently short impulses, the transmitted ultrasound wave contains more than one certain frequency. A broad continuous frequency spectrum up to a certain limit frequency is excited which is reciprocal to the impulse duration. Depending on the hardening or solidifying state, the material can transmit different frequency portions in a different manner. After the measurement, the spectrum of the signals can be calculated through Fourier transformation. If these individual spectra are normalized to their maximum, added chronologically and the spectral amplitudes are graphically represented as grey values, one obtains so-called contour plots. This three-dimensional representation permits calculation of frequency time curves or frequency time areas per individual measurement e.g. through calculation of average frequency maxima. These representations permit tracking of the spectral transition properties of the material as a function of time.
Correlation with previous measurements or with existing reference curves for velocity and energy produces e.g. findings concerning the composition of the material.
The measured curve shapes are examined more closely with respect to use of ultrasound technology within quality control with the aim of modelling the variation of the measured values (velocity, energy, frequency) with time in dependence on the material composition and nature. This is thus the solution of an inversion problem with unknown material properties. The inventive method facilitates classification of the material within quality control after adjustment to the respective task.
To achieve this objec
Grosse Christian W.
Herb Alexander
Reinhardt H. W.
Schmidt Günther
Weiler Bernd
Edwards & Angell LLP
Miller Rose M.
Neuner George W.
Universitat Stuttgart
Williams Hezron
LandOfFree
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