Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Patent
1987-08-03
1989-01-03
Myracle, Jerry W.
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
73823, 73843, G01N 332
Patent
active
047947993
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of measuring the properties, in particular the compactibility of a stiff mass to be cast, such as fresh concrete mass, wherein
a sample having a pre-determined weight is taken from the mass,
the sample is exposed to a compaction effect, and
the magnitude of a compression of the sample and the work used therefore is determined.
In the concrete industry, technical developments have led to the use of concrete masses which contain water to an ever decreasing degree. This is due to the fact that the lower the water content of the mass, the better the strength values obtained thereby, provided that the other mix proportions of the mass are maintained unchanged. The theoretic optimum amount of water required for hydratation is 22 to 40 per cent based on the amount of cement, i.e. the water/cement ratio w/c is within the range 0.22 to 0.40. These so called soil-moist masses are difficult to be shaped and cast also because the present tendency is to grind the cement extremely fine so as to enable a more efficient and rapid utilization of the resulting strength properties of concrete. Such masses are called stiff and semi-stiff.
Soil-moist concrete masses are used mainly in modern slide-mould casting processes. For plastic masses, there exists satisfactory methods and apparatuses for the measurement of the mass properties, compactibility in particular, whereas there are no suitable methods and apparatuses for an accurate measurement of the compactibility of stiff and semi-stiff masses, which is a major disadvantage in the use of concrete masses. The compacter the concrete in the finished cast product is, the higher the strength of the product obtained, and, accordingly, information on the compactibility of a concrete mass to be cast is of great importance for the achievement of an acceptable end result.
The compactibility of a concrete mass is essentially dependent on the stiffness of the mass. If the mass is too stiff, the casting obtained is poorly compacted, containing plenty of air bubbles, whereas too plastic a mass results in low strength values, and further, the shape and tolerances of a product cast without a fixed mould are difficult to control. The compactibility of a mass is not only affected by the amounts and ratios of the different ingredients but also by the quality and size thereof and other such varying factors. Therefore it is important to obtain reliable information on the compactibility of the mass already before the casting thereof.
The plasticity and the compacting properties of plastic concrete masses are nowadays studied by various different methods, among which the following could be mentioned as the most important ones:
Compacting factor test or a measurement of the Mo-value, wherein the concrete mass is caused to pass through a measuring apparatus by means of drop shocks.
Slump test or a depression measurement wherein the mould of a concrete cone compacted in a determined way is removed and the slump formed in the cone is measured.
Remoulding time test or a Vebe-test wherein a slump formed in a conical concrete body is similarly measured but here the slumping is intensified by vibration.
These methods as well as various other ways of examining a mass are suitable for plastic masses and some of them also for so called semi-stiff masses. The stiffer the mass, the worse the possibilities now available for an accurate determination-of the mass properties.
With stiff concrete masses it has previously been necessary, for lack of suitable measuring methods and apparatuses, to try to determine the compactibility of the concrete mass to be cast in any particular case even by feeling with hands on the basis of ones professional skill and experience. Such determination of a fresh stiff mass by hands, however, is unreliable and subjective, thus frequently leading in rejected cast products.
The object of this invention is to provide a method which avoids the above disadvantages and enables a more accurate measurement of the compactibility of a stiff mass to be cast. T
REFERENCES:
patent: 3494172 (1970-02-01), Juve et al.
Meller Michael N.
Myracle Jerry W.
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