Admixture of cement composition

Details Admixture of cement composition Admixture of cement composition

1999-08-05

2001-02-20

Green, Anthony (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

C106S727000, C106S823000, C562S553000, C562S571000

Reexamination Certificate

active

06190451

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an additive for an admixture of a cement composition, especially, a retarder which exerts set retardation effect when it is added to a cement paste, mortar, concrete or cement hydraulic product analogous thereto (hereinafter collectively called a cement composition). The retarder shows excellent capability of controlling retardation time by the adjustment of the addition amount and does not exhibit water reduction effect.
BACKGROUND OF THE INVENTION
In recent years, with improvement of architectural techniques and diversification of cement application methods, various additives for admixtures of a cement composition are being used according to the purpose of execution including the scale of the structure and the site of placement.
Of these, a retarder for retarding the setting time of the cement composition is widely used. The retarder is previously added to the cement composition or coated on the surface or formwork of concrete still in the unhardened state for various purposes, for example, for preventing a reduction in fluidity of the concrete between hydration and transportation/placement to thereby ensure the working time or for junction integrating adjacent joint parts in the placement process for constructing a large concrete structure by sequentially placing a plurality of concrete layers and/or concrete sections.
The retarder acts such that the active component thereof couples with calcium ion liberated by the initial hydration of cement, into a certain form (for example, formation of a complex compound) and this moiety covers the surface of a cement particle to thereby bring out the effect of retarding the setting of cement. Known examples of active components include hydroxycarboxylic acids or salts thereof such as gluconic acid, glucoheptonic acid, arabonic acid, malic acid, citric acid, tartaric acid, pyruvic acid and glycolic acid, saccharides (e.g., monosaccharides, disaccharides, trisaccharides, oligosaccharides, sugar-alcohols) such as saccharose, glucose, fluctose, galactose, mannose, lactose, raffinose, dextrin and sorbitol, and (hydrogen) carbonates of alkali metals, such as potassium carbonate and sodium carbonate. A retarder (composition) comprising these components individually or in combination of two or more thereof is being used or studied (see, for example, JP-A-54-60372 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-59-156950, JP-B-4-20866 (the term “JP-B” as used herein means an “examined Japanese patent publication”)). In particular, a retarder having blended therein sodium gluconate as a hydroxycarboxylate is one of the most widely used retarders.
The amount of retarder added to the cement composition is usually from 0.1 to 0.7 wt % based on the weight of cement in practical use and thereby, a retardation time of from 1 to 24 hours can be achieved, though it may vary depending on the ambient conditions. The retarder is usually used by adjusting the addition amount according to the desired retardation time.
However, these conventional retarders have the following problems. For example, in the case of saccharose as a saccharide, great retardation may be obtained but the distribution thereof is large and the capability of controlling the retardation time is poor. In the case of sodium gluconate which is a hydroxycarboxylate and which is widely used, the retardation effect is accompanied with water reduction effect, accordingly, the water-cement ratio must be adjusted whenever it is used by taking account of the incidental water reduction effect as well as the adjustment of the addition amount depending on the desired retardation effect, thus, cumbersome operations are necessary. As described above, the amount of the conventional retarder added is in practice from 0.1 to 0.7 wt % based on the weight of cement. However, in view of strength of the cement composition after setting and profitability, it is preferred to achieve higher retardation effect with a smaller addition amount. Existing retarders, even a retarder composition having blended therein two or more active components, have not yet succeeded in solving the problems with respect to the capability of controlling the retardation time and the cumbersomeness the incidental occurrence of undesired water reduction effect which accompanies their use.
The retarder of a concrete composition must show excellent retardation effect with a smaller addition amount, exhibit superior capability of controlling the retardation time as a result of the adjustment of the addition amount, and be free of incidental occurrence of water reduction effect.
SUMMARY OF THE INVENTION
As a result of extensive investigations to solve the above-described problems, the present inventors have found that an additive for an admixture of a cement composition, mainly comprising a specific iminodiacetic acid (salt) shows a retardation effect equal to or higher than that of conventional retarders with a smaller addition amount because of its excellent retardation effect. This can successfully control the retardation time and at the same time, does not exhibit water reduction effect. The present invention has been accomplished based on this finding.
The iminodiacetic acids (salts) for use in the present invention are at least one or more of the compounds represented by the following formula (I) and are synthesized as a corresponding amino acid or amino alcohol derivative using known methods:
wherein the M groups each independently represents a hydrogen atom, an alkali metal atom, an ammonium group or a substituted ammonium group; Y represents a divalent alkyl group having from 1 to 5 carbon atoms and the divalent alkyl group may be substituted by a hydroxyl group or a COOM group wherein M represents a hydrogen atom, an alkali metal atom, an ammonium group or a substituted ammonium group; and W represents a hydrogen atom, a hydroxyl group or a COOM group wherein M represents a hydrogen atom, an alkali metal atom, an ammonium group or a substituted ammonium group.
DETAILED DESCRIPTION OF THE INVENTION
In the iminodiacetic acids (salts) represented by formula I of the present invention, the —COOM group is preferably a carboxyl group or an alkali metal salt or ammonium salt thereof. The alkali metal atom is sodium or potassium and preferably is sodium.
Examples of groups represented by Y in formula I are set forth below.
Examples of iminodiacetic acids (salts) include &agr;-alanine-N,N-diacetic acid (salt), &bgr;-alanine-N,N-diacetic acid (salt), aspartic acid-N,N-diacetic acid (salt), glutamic acid-N,N-diacetic acid (salt), serine-N,N-diacetic acid (salt), ethanolamine-N,N-diacetic acid (salt), iminodiacetic acid (salt) and nitrilotriacetic acid (salt), among which glutamic acid-N,N-diacetic acid (salt) is preferably used in this invention. These iminodiacetic acids (salts) are compounds having a chelating ability and are considered to exert a hardening retardation effect as a result of coupling with the above-described free calcium due to a chelating action. The retarder of the present invention contains one or more of these iminodiacetic acids (salts).
The iminodiacetic acid (salt) is added to cement in an amount of from 0.005 to 3 wt % based on the weight of cement, preferably from 0.01 to 0.3 wt %, whereby a retardation time of from 1 to 24 hours can be achieved, though this may vary depending on the ambient conditions. The retardation time is controlled by increasing or decreasing the addition amount and a desired retardation time depending on the execution time or purpose can be easily obtained. The retarder of the present invention does not show a water reduction effect and therefore, the cumbersome process of adjusting the amount of water added each time the amount of the retarder added increases or decreases is eliminated. The retarder of the present invention may be added at the mixing of concrete or after the concrete is loaded on an agitator-body truck, either in the form of powder or an aqueous solution. Usually,

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