Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
2002-01-30
2003-11-04
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S724000, C106S727000, C106S729000, C106S823000, C524S005000
Reexamination Certificate
active
06641661
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to additives for cements, and more particularly to additives for increasing early strength of cements, methods for improving the early strength of cements, and high early strength cements.
BACKGROUND OF THE INVENTION
The term “cement” has used herein means and refers to hydratable cementitious binder that is used for making materials such as mortar and concrete. Cements may comprise, for example, Ordinary Portland Cement (OPC), or “blended cements,” the latter of which can refer to OPC blended with ground limestone or OPC blended with pozzolanic materials to form “pozzolanic” cements. Pozzolanic cements therefore typically incorporate one or more of the following pozzolanic materials—such as slag, metakaolin, fly ash, natural pozzolans—to allow manufacturers to substitute for portions of Portland cement clinker, thereby providing an economic benefit.
There is economic competition between manufacturers of pozzolanic cements and manufacturers of the more expensive ordinary Portland cements (OPC). Customers thus frequently need to choose between OPC and the less expensive pozzolanic cements, which can have comparatively less early strength and a higher water demand. Accordingly, the present inventors believe that novel additives for improving early strength in cements, and in particular pozzolanic cements, while decreasing water demand, are needed.
SUMMARY OF THE INVENTION
The present invention provides high early strength cement additives, cement compositions, and methods for increasing early strength in cements and cementitious compositions. The additives of the invention are believed to be useful for pozzolanic cements, blended cements, e.g., Ordinary Portland Cement and ground limestone, as well as OPC by itself, although it is believed that the benefits with pozzolanic cements would be most valued by customers due to reduction of costs.
An exemplary method of the present invention for increasing early strength in cement (e.g., preferably blended cement, and most preferably pozzolanic cement), comprises introducing into the cement, preferably during the grinding thereof, (a) at least one water reducer comprising polyoxyalkylene groups; (b) a sugar; and (c) an alkali or alkaline earth metal chloride. An amine is optionally added into the grinding process in further exemplary methods.
Exemplary additives of the present invention for improving early strength of cement (preferably blended cement, and most preferably pozzolanic cement), comprises (a) at least one water reducer comprising polyoxyalkylene groups; (b) a sugar; (c) an alkali or alkaline earth metal chloride; and (d) optionally an amine. Preferably, the additives are introduced as an aqueous solution during the grinding of the cement. Exemplary cement compositions of the invention comprise a mixture of cement (preferably blended cement, and most preferably pozzolanic cement), in combination with the above-described polyoxyalkylene water reducer, sugar, and alkali or alkaline earth metal chloride.
Further features and advantages of the invention may be described in detail hereinafter.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The present invention can be achieved in the form of an additive (comprising a polyoxyalkylene water reducer, a sugar, and an alkali or alkaline earth metal chloride) which can be added into a cement (preferably blended cement, and most preferably pozzolanic cement) during the grinding stage, or into a cementitious composition (including one that contains blended or pozzolanic cement with fine aggregate (sand) and/or course aggregate (gravel, stones); a cement (or cementitious composition such as masonry cement, mortar, or concrete) containing the aforementioned components (either as an admixture or, more preferably, incorporated during the manufacture of cement as interground additives); and also as a method for improving the early strength of cement by incorporating the additive components during grinding of cement.
Polyoxyalkylene polymers have been used as water reducers for Portland cement. Preferably, the polymers are comb polymers having a backbone and pendant groups, with the polyoxyalkylene groups contained in the backbone, in the pendant groups, or in both. Comb polymer-type water reducers are known and believed to be suitable for use in the present invention. For example, U.S. Pat. 5,393,343 of Darwin et al., which is incorporated fully herein by reference, taught an EO/PO type comb polymer useful as a superplasticizer or water-reducer for retaining in concrete a high degree of slump (e.g., high flowability) over a sustained period of time. The term “EO/PO” is sometimes synonymous with the term “oxyalkylene group” and serves as a convenient short-hand to designate polyoxyalkylene groups which are combinations of ethylene oxide (EO)/propylene oxide (PO) repeating units.
Preferably, an EO/PO type comb polymer is employed having a polymer backbone, e.g., carbon backbone, to which are attached both carboxylate groups (which function as cement anchoring groups in the cementitious mixture) and pendant groups such as ethylene oxide (EO) groups, propylene oxide (PO) groups, and/or a combination of EO/PO groups. The pendant groups may be ionic or non-ionic. Further examples of EO/PO type comb polymer water-reducers are shown in U.S. Pat. Nos. 4,946,904, 4,471,100, 5,100,984 and 5,369,198. These patents describe comb polymers which are, for example, copolymers of, polycarboxylic monomers such as maleic acid or anhydride and polymerizable EO/PO—containing monomers such as polyalkylene glycol monoallyl ethers, etc.
In U.S. Pat. No. 5,840,114, there is disclosed an exemplary polyoxyalkylene polymer which may be suitable for the invention. The polymer comprises a carbon containing backbone to which is attached to groups shown by the structures (I) and (II), and optionally groups shown by structures (II) and (IV) as shown below:
wherein each R independently represents a hydrogen atom or a methyl group (—CH
3
) group; A represents hydrogen atom, a C
1
-C
10
alkyl group, R′ or an alkali metal cation or a mixture thereof; R′ represents a hydrogen atom or a C
2
-C
10
oxyalkylene group represented by (BO)
n
R″ in which O represents an oxygen atom, B represents a C
2
-C
10
alkylene group, R″ represents a C
1
-C
10
alkyl and n represents an integer of from 1-200, or mixtures thereof; and a, b, c, and d are numerical values representing molar percentage of the polymer's structure such that a is a value of about 50-70; the sum of c plus d is at least 2 to a value of (100−a) and is preferably from 3 to 10; and b is not more than [100−(a+c+d)].
(The letter “B” is being used for lexographical convenience herein to denote an alkylene group. Those of ordinary skill in the art will realise that “B” herein does not represent boron).
A commercially available polyoxyalkylene polymer which is suitable for the purposes of the present invention is available from Grace Construciton Products under the brandname ADVA®. This product is specifically a polyacrylic acid comb polymer made by grafting a polyoxyalkylene amine onto a polycarboxylic acid backbone (amidization/imidization reaction).
Another polyoxyalkylene polymer which is believed to be suitable can be obtained by polymerization of maleic anhydride and an ethylenically-polymerizable polyalkylene, as prepared in U.S. Pat. No. 4,471,100, the entire disclosure of which is incorporated herein by reference. This is believed to be sold in the form of metallic salts formed by final reaction of the polymers with a base such sodium or calcium hydroxide.
It is also contemplated that polyoxyalkylene polymers may not necessarily require comb structures (i.e., backbone with pendant groups), but may have a linear or branched structure, or other structures.
Exemplary polyoxyalkylene polymers will preferably have a molecular weight of between 3,000-100,000 and more preferably 15,000-50,000.
The preferred amount of polyoxyalkylene water reducer used in the invent
Cheung Josephine H.
Freitas Walter M.
Jardine Leslie A.
Baker William L.
Leon Craig K.
Marcantoni Paul
W. R. Grace & Co.,-Conn.
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