Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1998-12-28
2001-07-03
Noori, Max (Department: 2855)
Measuring and testing
Vibration
By mechanical waves
C073S766000
Reexamination Certificate
active
06253617
ABSTRACT:
The invention concerns a method for testing the freeze-thaw resistance and/or the freeze-thaw and deicing agent resistance of solid bodies. In particular, the invention deals with an enlargement of and supplementation of a known test method for the freeze-thaw resistance or of the freeze thaw and de-icing agent resistance, respectively.
In civil engineering, materials, solid bodies or construction components are frequently subjected to attack by special environmental conditions. Typical forms of attack by the environment are freeze-thaw cycles with and without the effect of de-icing agents. In the former case, the solid bodies exposed to environmental attack require an enhanced freeze-thaw resistance; in the latter case an enhanced freeze-thaw and de-icing agent resistance. As already mentioned in the starting publication the term “enhanced freeze-thaw and de-icing agent resistance” can be applied without restriction to aqueous solutions, as far as the test method described here is concerned.
The resistance test for porous solid bodies comprises two test method stages:
1. The simulation of the external attack corresponding to the environmental attack; and
2. the measurement or the determination of the damage to the solid body resulting from this external attack.
When determining the damage, two types of damage can be distinguished:
a) The external damage, in particular the scaling; and
b) the internal damage which is rarely outwardly visible and which considerably reduces several materials properties, for example strength and elasticity.
Both types of damage occur at or near the exposed surfaces. The internal damage is also usually limited to a zone in the region of the surface under attack or starts from the surface of exposure. However in the case of internal damage, the transition from the damaged to the undamaged region is continuous. Thus it is extremely difficult to specify reproducible precise criteria, which should be universally applicable to a whole group of materials, for the internal damage.
The test method described in the starting publication is concerned in particular with the external damage or the degree of scaling. The accuracy and reproducibility of this test method were improved by guaranteeing that the specimens under investigation are a defined content of water, with or without dissolved substances, i.e. de-icing agent. For this purpose, the solid body is conditioned, in particular pre-dried, before commencement of the actual test method. Afterwards, the specimens with the exposure surfaces are immersed in the solution or water. The solution or water is then allowed to penetrate into the specimens by capillary suction. This is followed by freeze-thaw cycles to simulate the attack by freeze-thaw or freeze-thaw and de-icing agent.
So far, the known method and the improved test method, as given by the present invention, correspond to a large degree.
It is the object of the present invention to provide a test method of the kind specified in the beginning, with which the internal damage of the solid body or the specimen can also be determined with high accuracy and reproducible results.
In accordance with the invention this object is accomplished by a method for testing at least one resistance of the group consisting of the freeze-thaw resistance and the de-icing agent resistance of solid bodies, forming test specimens, the method comprising several steps. The first step includes conditioning at least one test specimen by adjusting a defined moisture condition to the ensuing conditions of use. Next, the conditioned solid body having a surface of exposure is placed into a specimen container for at test medium in such a manner that the surface of exposure is downwardly faced and is in close contact with the test medium. The specimen is immersed in a coolant bath deeply enough to provide a good and uniform thermal contact between the coolant bath and test medium. Contact is maintained between the solid body and the test medium long enough to reach a defined degree of saturation of the solid body. The test medium above the coolant bath is subjected to a predetermined temperature-time profile to simulate a continuous freeze-thaw cycle in the solid body. The test specimen is held throughout the preceding steps in the specimen container in such a manner that moisture as well as heat are transported uniaxially and substantially perpendicular to the surface of exposure into the body. At least one reference measurement is carried out to determine the change of a physical quantity of a solid body before and after the preceding steps, whereby the internal damage of said body owing to the preceding attacks by freeze-thaw cycles and said test medium is determined.
The simulation of the conditions of attack is particularly good because heat or coldness is supplied uniaxially across the surface of exposure.
The internal damage of a solid body, subjected to freeze-thaw cycles as in the described methods, is expressed, as has been established in investigations, particularly by the following physical quantities:
Decrease in strength, irreversible changes in length, decrease in the static modulus of elasticity, decrease in the dynamic modulus of elasticity, change in the damping of the dynamic modulus of elasticity and change in propagation of an ultrasonic signal.
Thus at least one of these physical quantities is measured according to the invention. The results of the measurement of the complete test method are reproducible and repeatable according to the criteria of ISO 5725 and enable a reliable quantification of the internal damage.
The invention is, however, not limited to a particular measuring method. The choice of the measuring method used depends on the particular conditions of use and accuracy requirements. It is possible to use known or newly developed measuring methods which enable the measurement of the physical quantity at least in the region of the location of use, or in the environment of the testing equipment.
The following measuring methods can be used, without claiming completeness, to determine the internal damage:
A. Measurement of Strength Reduction
The compressive strength, flexural tensile strength, the splitting strength or a similar strength quantity is measured destructively on non-exposed reference specimens and the treated specimens. This method is expensive and complicated and has the disadvantage that a specimen can only be compared once with the reference specimen and is finally destroyed afterwards. A control of the change of the damage in the different phases of the freeze thaw test is not possible.
B. Measuring of the Static Modulus of Elasticity
The static modulus of elasticity can be investigated by a suitable test loading machine. However, porous solids, especially concrete, do not deform only elastically but also plastically. Therefore, any loading leads to a irreversible deformation. Additionally, the modulus of elasticity of concrete is not linear and, thus a minimum load is necessary. The decrease of the static modulus of elasticity caused by frost action is directly coupled with a transgression of the critical degree of water saturation. If the critical degree of saturation is reached the modulus of elasticity decreases significantly after a few freeze thaw cycles.
C. Measuring of the Dynamic Modulus of Elasticity
The dynamic modulus of elasticity, and here the real and imaginary part, can be measured in different ways.
C.1 Measuring of the Self-Oscillations (Eigen-Vibrations)
A proved method is the measuring of the self-oscillations of a given test beam. In a suitable way, for instance with an hammer, the self-oscillation is generated. Preferably, the first ground vibration is excited. It is meaningful if the hammer is equipped with an accelerometer, by which the loading can be applied reproducibly. Out of the self-oscillation the modulus of elasticity can be calculated.
If the test beam is excited to an self-oscillation and if it is at the same time supported in such a way that it is swinging without damping, then besides the natural
Fay Sharpe Fagan Minnich & McKee LLP
Noori Max
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