Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1991-03-25
1995-12-19
Yoon, Tae H.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524 5, 524 8, 524558, 5253301, 5253303, 526318, 526325, 526932, 5263184, C08F 300, C08F 814
Patent
active
054768853
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a cement additive having an ability to prevent slump loss. More particularly, the invention relates to a chemical which is combined with a cement composition such as cement mortar and concrete etc. and elevates efficiency in the workability by increasing the flowability of the cement composition and its decrease with time passage (hereinafter, referred to as the "slump loss") is prevented. The present invention also relates to a method for producing such a cement additive. Furthermore, the present invention relates to a cement composition which is combined with a cement additive of the above kind.
BACKGROUND ART
A cement composition such as mortar and concrete etc. shows a decrease in consistency with passage of time after combination by the hydration of cement with water or others and thereby, the efficiency in the execution of works lowers. This phenomenon is generally called slump loss.
The slump loss in the cement composition causes, on ready mixed concrete, trouble such as limitation of time allowed for transportation, degeneration of quality and impairment of workability owing to a waiting time in a concrete-placing field, and a decrease in durability due to a cold joint and so on. Also, in a factory for producing concrete secondary products, when transportation of a cement composition by a pump pressure is temporarily stopped by taking a lunch time or due to any trouble and, some times later, the transportation by pressure is reopened, the slump loss may cause such an accident as a sudden increase in the transportation pressure or full closure of a pump and may cause such a problem as incomplete filling in a delaying case of moulding such as compaction for some reason. Therefore, in the factories for producing ready-mixed concrete and for producing concrete secondary products and in the other places, the slump loss in a cement composition is an important problem to be solved in order to control the quality of cement compositions and to improve the efficiency in the execution of work.
The following methods to prevent the slump loss have been proposed.
(1) A method in which an unit amount of water in concrete is increased.
(2) A method which comprises a post-addition of a cement additive.
(3) A method which comprises a repetitive addition of a cement additive.
(4) A method which comprises an addition of a retarder or a combined use with a cement additive.
(5) A method in which a cement additive of a granular type is used.
(6) A method in which a cement additive is contained in an organic hydrogel.
(7) A method which comprises an addition of a cement additive that undergoes slow-release of a dispersing effect for cement resulting from slow hydrolysis by an alkali.
Said method (1) comprises an increase of an unit amount of water which is estimated with the slump loss up to placing of a cement composition. Even if an improvement in the workability is attempted by this method, the method may be accompanied by such a disadvantage in quality as a loss of strength of a hardened product and crack occurrence resulting from shrinkage during drying, which causes a decrease in durability or such an economic disadvantage as an increase in an unit amount of cement which is required to obtain a defined strength.
Said method (2) is a temporary improvement for a flowability. However, the cement additive remains locally in the cement composition after an attempt to maintain the slump has been completed and, as a result, there will be brought a bad effect such as occurrence of local bleeding and thereby, a loss of strength.
Said method (3) comprises a readdition of an additive when the slump loss occurs. However and it is not a complete prevention for the slump loss. Also, there is a disadvantage in the workability and economy due to the repetitive addition.
Said method (4) seeks to maintain flowability by lengthening the time necessary for coagulation of a cement composition by using only a delaying agent such as a hydroxycarboxylate, a ligninsulfonate, a dextrin, an
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Ito Hiroshi
Mizushima Makoto
Mori Yasuhiro
Tahara Hideyuki
Nippon Shokubai Co. , Ltd.
Yoon Tae H.
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