Compositions: coating or plastic – Materials or ingredients – Additive materials for inorganic cements which contain a...
Reexamination Certificate
2000-01-28
2002-06-04
Lovering, Richard D. (Department: 1712)
Compositions: coating or plastic
Materials or ingredients
Additive materials for inorganic cements which contain a...
C106S727000, C252S001000, C252S194000, C516S067000
Reexamination Certificate
active
06398866
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority of Swiss Patent application 0165/99, filed Jan. 29, 1999, the disclosure of which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
The invention relates to an alkanolamine comprising agent for the reduction of the degree of shrinkage in hydraulic binders (shrinkage reducing agent), whereby said agent contains or consists of specific alkanolamines of formula R—NH—(AOH) alone or in combination with hydroxy compounds and/or ethers. Furthermore, a method for the reduction of the degree of dry shrinkage of binders such as cement, mixed cement, puzzolanes and thereof produced mortars and concretes by means of such a shrinkage reducing agent is described.
During the entire curing process, hydraulic binder systems pass through several steps. The first change in dimension prior to setting, comprising plastic shrinkage, can be compensated by the hardening composition and the therefrom resulting forces can be corrected. However, volume changes due to loss of water in the cured state can no longer be compensated by the system. Thus, such changes, in spite of their low magnitude, lead to the formation of cracks and deformations in said composition. Due to said cracks, the attack of the cement and/or—if present—steel reinforcements by damaging substances are facilitated and penetrating water can lead to the destruction of the structure due to freezing. All these problems lead to a significant reduction of the long time durability of a building due to said dry shrinkage.
Hitherto, already several substances are known that reduce the dry shrinkage of concrete. The most common of them are glycols and polyglycols as well as glycol ethers and polyglycol ethers. All of them are substances that can reduce the degree of shrinkage. Furthermore, types of substances exist that compensate the resulting volume reduction by expansion.
Substances falling under the second class are substances forming gases in an alkaline medium such as hydrazine compounds (nitrogen) or aluminum powder (hydrogen) as well as iron powder, the activity of which is based on a volume enhancement due to formation of iron oxide (rust). Furthermore, also calcium sulfoaluminates that are precursors of the voluminous ettringite and burned calcium oxide are used. All said substances are powders and thus suffer disadvantages in connection with their dosing. Furthermore high percentage of said substances must be added. Gas forming agents per se have the disadvantage that said gas can already be formed prior to the addition of concrete, and the generation of hydrogen in general is considered as very critical on a production site.
The cementituous precursors are very much dependent from the actual conditions, such as cement composition, temperature, environmental humidity and degree of hydration of the cement, and can lead to a spontaneous expansion in the cured state. The also promoted formation of ettringite can affect the durability of such a building.
In general it can be said that by said expansion effecting agents only a correction of the starting point of the thereon following dry shrinkage can be achieved. The magnitude of the degree of shrinkage as such remains the same and therewith deformations as mentioned above nevertheless can lead to damages.
Several substances comprising hydroxyl groups are already known as possible shrinkage reducing agents. For example lower alcohols are proposed (JP 1-129578/89) that, however, raise problems due to their low point of ignition.
Higher molecular systems, such as adducts of alcohol and alkylene oxide or adducts of alkylphenol and alkylene oxide (e.g. JP 37259/81 or 10947/87) have to be added in large amounts in order to achieve the desired result.
Also several small polyols have already been proposed. In 1987 Schulze mentioned terminal hydroxyl groups comprising compounds of the type C
n
H
2n
(OH)
2
as efficient (EP 0 308 950) and several Japanese published applications (e.g. 55-027819 or 06-072748) refer to similar types or special cases. Recently, in particular secondary and tertiary alkanediols were further investigated and found to be efficient.
Ether comprising diols have already generally been mentioned as shrinkage reducing agents by Goto in 1985 (U.S. Pat. No. 4,547,223). More specifically defined types have reached greater interest and are described as effective (WO 95/30630 and WO 96/27563 to Shawl as well as WO 96/27564, WO 96/27565 and U.S. Pat. No. 5,618,344 to Berke).
As further classes of substances water-soluble amino resins in combination with metal salts of fatty acids are mentioned by Okuno in 1989 (EP 0 359 068). In 1994 good results with amides, or generally formyl compounds, respectively, are reported by Abdelrazig in U.S. Pat. Nos. 5,326,396 and 5,326,397.
With regard to alkanolamines U.S. Pat. No. 3,583,880 teaches that the shrinkage of porous products can be reduced by the application of i.a. alkanolamines to already produced inorganic bodies. In 1995 Abdelrazig described (in U.S. Pat. No. 5,389,143) &agr;,&bgr;-alkanolamines that on the one hand can effectively reduce the shrinkage that, however, on the other hand, are very expensive. The alkanolamines described by Abdelrazig show the following general formula
wherein R
1
and R
2
independently of each other represent hydrogen or a linear or a branched alkyl group. R
3
and R
4
can also independently from each other be hydrogen or a linear or a branched alkyl group with the proviso that R
3
and R
4
together have at least two carbon-atoms so that in particular R
3
=H and R
4
=H are excluded.
All the mentioned shrinkage reducing agents have one or more disadvantages. In view of their high dosage and/or their expensive production, they are uneconomical, due to their high surface activity, they destroy the effect of air entraining agents, due to their inflammability/point of ignition they cannot suitably be used at production sites, or they drasticly retard the development of strengths of cementituous systems.
BRIEF SUMMARY OF THE INVENTION
Hence it is a general object of the present invention to provide a shrinkage reducing agent as well as a method for the reduction of the degree of shrinkage of hydraulic binders, that avoids the above-mentioned disadvantages at least in part. It is in particular an object of the present invention to provide a shrinkage reducing agent that on the one hand is cheap, easily producible, allows unproblematic handling and furthermore develops a good shrinkage reducing effect. Furthermore, the shrinkage reducing agent should not affect the frost resistance of the resulting concrete in that, because of the addition of the shrinkage reducing agent, the amount of air present in the concrete is markedly reduced. A further object of the invention is to provide a method for the reduction of the degree of shrinkage of concrete that in particular is cheap and expedient. Said goals are achieved according to the independent claims. Preferred embodiments are mentioned in the dependent claims.
Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceedings, the agent for the reduction of the degree of shrinkage of hydraulic binders contains or consists of
a) at least one alkanolamine of formula I
R—NH—(AOH) I,
wherein R is hydrogen or a linear or a branched aliphatic or cyclic C
1
-C
6
-alkyl group, and A is a C
2
H
4
- or C
3
H
6
-group, alone or in combination with
b) at least one hydroxy compound and/or
c) at least one ether compound.
Another aspect of the present invention is a method for the reduction of the degree of shrinkage of hydraulic binders such as cements according to Euronorm EN 197 in pure form or as admixture with latent hydraulic binders such as fly ash, blast furnace slag, burned oil shale, natural pozzolanas or silicafume or inert fillers such as stone powder, as well as thereof produced mortar or concrete, characterized in that a binder comprising mixture is
Bürge Theodor A.
Mäder Urs
Wombacher Franz
Lovering Richard D.
Sika AG vorm. Kaspar Winkler & Co.
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