Thermal measuring and testing – Thermal testing of a nonthermal quantity – Of cure or hardenability
Patent
1983-05-31
1986-01-28
Frankfort, Charles
Thermal measuring and testing
Thermal testing of a nonthermal quantity
Of cure or hardenability
374 45, G01N 326
Patent
active
045668060
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of controlling the curing rate of concrete comprising the step of influencing the heat supply or dissipation for a given period of time.
In the concrete building industry, for example, it is common practice to set up the casing for part of a building during the day, to pour the concrete and to mount the heating device. During the 16 hours between the end of the workday and the start of the next the fresh concrete is heated so that at the beginning of the next workday it is sufficiently strong to permit of removing the casing. This casing can be set up again the same day for pouring the concrete of a further part of the building. By heating the concrete the curing time of many days in a natural process can be reduced to 16 hours between two workdays. In order to assess whether the concrete is, indeed, sufficiently strong to allow removal of the casing, test cubes are made simultaneously with the building part and also subjected to the thermal treatment. At the beginning of the workday the strength of said test cubes is checked and if it is found sufficient, the casing can be removed. If it is found that the strength of the test cubes is not sufficient, the casing cannot be removed so that it is no longer possible to set up this casing again the same day for a next building part. In this case a whole workday is lost.
It is assumed, of course, that the strength of the test cubes is, with reasonable accuracy, representative, of that of the concrete in the casing. However, it has been found in practice that said accuracy is poor. It may, therefore, occur that the casing is removed whereas this would not be allowed for reasons of strength of the concrete and otherwise that costly workdays get lost by not removing the casing where removal were allowed without hazards.
The object of the invention is to provide a method of the kind set forth in the preamble, which does not exhibit these disadvantages. For this purpose the method embodying the invention comprises the steps of measuring the temperature of the concrete, assessing the momentaneous maturity of the concrete by means of the temperature course and controlling the heat supply or dissipation on the basis of the momentaneous maturity in a manner such that at the end of the period the concrete has the desired maturity. The maturity of concrete is characterized as the integral of an exponential function of the concrete temperature with time. In this function a constant depending on the kind of concrete plays an important part. There has been shown a relationship between the relative strength of the concrete and the maturity, wherein the relative strength is the ratio between the strength at a given instant and the strength attained under standard conditions i.e. after 28 days at 20.degree. C. In a given kind of concrete a given relative strength is associated with a given maturity. By regulating the maturity in accordance with the invention by means of temperature-control, it can be ensured that after a given period the concrete has attained a given maturity and hence a given relative strength.
Although in the foregoing reference is made to acceleration of curing of concrete by raising the temperature, the invention may also be applied for decelerating the curing process by temperature reduction.
In the method according to the invention the concrete temperature is preferably measured at a plurality of areas, whilst the heat supply or dissipation is controlled on the basis of a given, momentaneous extreme maturity at the measured temperature. With accelerated curing this extreme maturity will be the lowest given maturity and with decelerated curing this extreme maturity will be the highest assessed maturity. In this way it is ensured that after a given period each part of the concrete has obtained the desired properties.
A simple, but reliable operation is obtained when in accordance with the invention the control is an on/off control on the basis of the temperature variation of the introduced heat after cutting off the heat sup
REFERENCES:
patent: 3649729 (1972-03-01), Davis et al.
patent: 3718721 (1973-02-01), Gould et al.
patent: 4044600 (1977-08-01), Claxton et al.
Frankfort Charles
Schuster David R.
Snyder John P.
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