Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1997-12-08
2000-02-08
Ballato, Josie
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324650, 324687, G01N 2722
Patent
active
06023170&
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and apparatus for determining the degree of hardening of hardenable materials, in particular materials which harden as a result of water binding, such as concrete, plaster or cement, in which method the complex electrical permittivity of the material is determined at various instants in time.
Such a method is known from the JOURNAL OF PHYSICS D APPLIED PHYSICS., vol. 23, no. 2, Feb. 14, 1990, pages 234-236, XP000099844 M. A. BARI: "COMMENT ON `DYNAMIC DIELECTRIC ANALYSIS DURING EARLY-STAGE HYDRATION OF ORDINARY PORTLAND CEMENT`". In this document the frequency dependence of the imaginary part and the real part of the capacitance of a sample block of hardening cement is given after 24 hours, 10 days and 50 days of dehydration. No indication is given how the degree of hardening of the concrete can be determined from the observed change in these parameters.
Various other methods have been proposed for determining the degree of hardening. The development of the compressive strength, the ageing or the degree of hydration of hardening, setting or curing materials, in particular materials which become hard as a result of water binding, such as hardening stone-like materials such as concrete, cement and plaster. The development of compressive strength, the ageing or the degree of hydration is a measure of the hardening. The most widely known method is to monitor the development of heat during hardening. The development of heat appears to be linked to the extent of water binding, or hydration. However, said method suffers from some disadvantages. One of the most important disadvantages is that the development of heat has to be followed in a conditioned space so that the necessary measurements have to be carried out on one or more test samples in order to predict the degree of hardening of the actual structure on the basis of said measurements. The temperature of the actual structure may, however, differ appreciably from that in the laboratory. In addition, the measurement of the development of heat is inaccurate and susceptible to errors because of the dependence on various parameters.
IEEE PROCEEDINGS--A PHYSICAL SCIENCE, MEASUREMENT & INSTRUMENTATION, MANAGEMENT & EDUCATION, part 137, No. Sep. 5, 1990, STEVENAGE GB, pages 246-254, XP000150889, J. G. WILSON ET AL.: "VARIATIONS IN THE ELECTRICAL PROPERTIES OF CONCRETE WITH CHANGE IN FREQUENCY" describes how the dielectric constant (or the electrical permittivity) and the conductivity alters for concrete during hardening over a period of not more than 1 day. Again no indication is given of how the degree of hardening of the concrete can be determined reliably and accurately from the observed change in said parameters.
The object of the present invention is to provide a more accurate method for determining the degree of hardening of a material. Moreover, the subject of the invention is a more reliable method of this type. The object of the invention is also to provide a method with which the degree of hardening of the material can be measured accurately and reliably, without the need for separate test samples, directly on the structure itself, preferably in a particularly simple and not very time-consuming manner.
For this purpose, the method according to the present invention is characterized in that the ratio .di-elect cons."(t=0)/.di-elect cons."(t) of the imaginary part, .di-elect cons."(t), of the complex electrical permittivity, .di-elect cons.'(t)-j.di-elect cons."(t), at a reference instant in time t=0 and at an instant in time t and/or the ratio .di-elect cons.'max/.di-elect cons.'(t) of the maximum value of the real part of the complex electrical permittivity, .di-elect cons.'max, over the time interval t=0 to t and the real part of the complex electrical permittivity, .di-elect cons.'(t), at the instant in time t, the time t occuring after the time at which .di-elect cons.'max has occurred, are determined as a measure of the strength of the material at an instant in time t.
The dielectric behaviour of a material such as co
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J. G. Wilson, et al., "Variations in the Electrical Properties of Concrete with Change in Frequency", IEE Proceedings, vol. 137, Pt. A, No. 5, Sep. 1990, pp. 246-254.
M.A. Bari, "Comment on Dynamic dielectric analysis during early-stage hydration of ordinary Portland cement", Journal of Physics D; Applied Physics, vol. 23, No. 2, Feb. 1990, pp. 234-236.
Hilhorst Maximus Andreas
Stenfert Kroese Willem Herman
Ballato Josie
Instituut voor Milieu- en Agritechniek
Solis Jose M.
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