Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
1999-11-23
2002-07-16
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S705000, C106S709000, C106S713000, C106S714000, C106S772000, C106S789000
Reexamination Certificate
active
06419741
ABSTRACT:
TECHNICAL FIELD
The present invention relates to cement clinker and cement containing the cement clinker, and more particularly to an improvement in cement for use in concrete of high strength and high flowability, mass concrete, shrinkage compensating concrete or concrete of high resistibility which are employed in the field of engineering and architecture or as building material through incremental launching method or wet formation of cement slurry.
BACKGROUND ART
Accompanying promotion of rationalization and energy saving in the field of construction and working techniques in these years, needs for cement of large variety and complexity are increasing, and such cement is being applied to concrete of high strength and high flowability for use in high-rise reinforced concrete buildings or buildings of concrete filled steel tubular column (CFT). Such cement is also applied to so-called mass concrete for use in concrete dams or concrete buildings of large sized members.
In order to obtain concrete of high strength, the water cement ratio is required to be decreased which results in an increase in viscosity of the concrete and a loss in flowability which in turn leads to a drawback in that the workability may be degraded, for instance, the pumpability may be degraded.
Further, a decrease in water cement ratio results in an increase in the amount of cement and thus causes an increase in calorific value at the time of hydration reaction, whereby a drawback is presented in that the strength development of the structure decreases by the effect of thermal hysteresis of high temperature.
Due to these drawbacks, it is generally the case that normal portland cement can only be used at a specified concrete strength of not more than 45 N/mm
2
when employed for constructing high-rise reinforced concrete buildings or CFT buildings. In other words, in order to achieve a specified concrete strength of approximately 60 N/mm
2
, the water cement ratio needs to be decreased to approximately 30%, which, however, results in a remarkably high viscosity of concrete and a loss in flowability so that the pumpability may be degraded.
Further, when using blended cement, the viscosity of concrete becomes lower than that of normal portland cement when both are prepared employing the same water cement ratio. However, since the strength development of the blended cement is inferior to that of normal portland cement, to obtain equivalent strength, it is required to set a lower water cement ratio for the blended cement than that of normal portland cement. This, in turn, results in an increase in viscosity of concrete with no sufficient flowability being maintained. Consequently, such blended cement can be used to obtain only a level of strength equivalent to that of normal portland cement.
In contrast to that, when using low-heat portland cement, the viscosity of concrete becomes lower than that of normal portland cement when both are prepared employing the same water cement ratio, and their strength developments are equal to each other. Thus, it is capable to pump the low-heat portland cement by a pump in a strength region being higher than that of normal portland cement, and more particularly, at a specified concrete strength of up to approximately 60 N/mm
2
.
The use of low-heat portland cement is desirable also in view of the decrease in the calorific value of hydration.
However, even by employing low-heat portland cement, the viscosity can still not be sufficiently decreased, and when the specified concrete strength is set to be as high as approximately 80 N/mm
2
(approximately 25% in a water cement ratio), its viscosity is remarkably increased. Therefore, it can not be pumped by using a general pump and types of pumps and conditions for the pumping are limited.
Low-heat portland cement presents an additional drawback in that its initial strength is lower than those of normal portland cement or blast-furnace slag cement. In order to solve this drawback, measures are taken in that the fineness as well as the amount of contained SO
3
are increased for the purpose of improving the initial strength.
However, while an increase in the fineness and the amount of SO
3
contributes to improvements in strength, it simultaneously results in a drawback of increasing the calorific value of hydration and of decreasing the flowability of cement.
In any case, in order to further improve cement of high strength and high flowability in strength, it is required to improve the flowability of the whole binder including cement, to further decrease the unit water content while maintaining the flowability of concrete, or to restrict the calorific value of hydration of the whole binder including cement to improve the strength development of the binder.
However, flowability and strength are essentially conflicting with each other, and there exists a relationship between these that if one is improved, the other is degraded. Therefore, it is not easy to solve these two subjects simultaneously. In addition, it is difficult to achieve an additional subject of decreasing the calorific value of hydration, and it had not been possible by the prior art to solve all of these subjects.
It should be noted that various types of concrete of high flowability and high strength are being used in these years, and while these kinds of concrete exhibit superior characteristics, they also present a drawback in that they increase the autogenious shrinkage (phenomenon in which a volumetric decrease occurs after initial setting of cement by the hydration reaction) thereof.
On the other hand, in case of a concrete member having a large sectional area, the heat of hydration of the cement member is accumulated in the proximity of its center to result in a rise of internal temperature. During its temperature rising process or cooling process, a considerable temperature difference occurs between the exterior (portions coming into contact with open air) and interior of the placed concrete and causes partial strains, whereby so-called thermal cracks are apt to occur.
In case such thermal cracks are likely to occur, it needs to be treated as mass concrete in terms of design and working.
While there are various methods of preventing thermal cracks in mass concrete, the use of cement of low calorific value is considered to be most effective and economical.
An example of such cement of low calorific value is blended cement in which ground granulated of blast-furnace slag and/or fly ash are admixed to portland cement by huge amounts. However, this blended cement presents a drawback in that the appearance of initial strength is small and thus results in delays in removal of forms or in inferiority in view of resistibility.
Low-heat portland cement is employed in order to solve these problems, but since such low-heat portland cement is still not capable of sufficiently decreasing the calorific value, it can not exhibit satisfactory effects in preventing thermal cracks.
The problem of autogenious shrinkage does also apply to mass concrete. That is, instances are reported in which cracks occurred which can not be simply explained by the reason accompanying the above described temperature differences, and it is pointed out that it is possible that autogenious shrinkage largely influences the occurrence of such cracks.
DISCLOSURE OF INVENTION
It is an object of the present invention to solve the problem of preventing heat of hydration simultaneously with improving the flowability of cement and maintaining a long-term strength thereof in order to further improve concrete of high strength and high flowability in strength.
It is another object of the present invention to provide cement for concrete of high strength and high flowability that exhibits high flowability and low viscosity at low water cement ratio, high strength development even after receiving thermal hysteresis, and a low amount of autogenious shrinkage.
It is still another object of the present invention to provide cement for mass concrete that exhibits superior effects of preventing cracks owing to ther
Akiyama Tatsushi
Ikabata Tatsuo
Nagaoka Seiichi
Yamamoto Takanori
Yasumoto Ayaji
Arent Fox Kintner Plotkin & Kahn
Green Anthony
Sumitomo Osaka Cement Co. Ltd.
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