Compositions: ceramic – Ceramic compositions – Clay containing
Reexamination Certificate
1999-12-21
2002-03-05
Marcantoni, Paul (Department: 1755)
Compositions: ceramic
Ceramic compositions
Clay containing
C501S148000, C106S416000, C106S724000, C106S727000, C106S728000, C106S803000, C106S808000, C106S810000, C106S823000
Reexamination Certificate
active
06352952
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the improvement of the dosage efficiency of admixtures used in hydraulic cement compositions such as Portland cement concrete, and more particularly to the improvement of the effectiveness of polymer additives having oxyalkylene, or so-called “EO/PO” groups, including comb polymers having a backbone such as a carbon-containing backbone to which are attached oxyalkylene groups.
BACKGROUND OF THE INVENTION
It is known to use so called “EO/PO,” or oxyalkylene, polymers in hydraulic cement compositions such as Portland cement concrete. For example, in U.S. Pat. No. 5,393,343, incorporated fully herein by reference, Darwin et al. disclosed 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. As used herein, the term “EO/PO” is synonymous with the term “oxyalkylene group” and serves as a convenient short-hand to designate polyoxyalkylene groups (e.g., ethylene oxide/propylene oxide copolymers). Thus, for present purposes, the term “EO/PO type comb polymer” means and refers to a polymer having a backbone such as a 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 superplasticizers and 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.
While the aforementioned EO/PO comb polymer superplasticizers have been found effective, the dosage efficiency (the amount of the polymer needed to obtain the desired fluidizing or plasticizing effect) tends to vary among different cement or concrete mixes.
SUMMARY OF THE INVENTION
After substantial research, it has been found that the problem varying EO/PO plasticizer dosage efficiencies can be attributed to the presence of certain swellable clays, namely smectites such as sodium montmorillonite, in the aggregate (e.g. sand) used to make concrete or mortar. It has been found that negative interactions occur between EO/PO superplasticizers and mortar or concrete containing smectite clays. It is theorized that such clays expand when initially wetted by the mix water and in the expanded state absorb or entrap the superplasticizer. These negative interactions result in poor workability of fresh mortar or concrete and lead to poor dosage response. Further, several approaches have been found to be effective in restoring the dosage response of these superplasticizers. The effective approaches in general involve reducing or preventing the expansion of the clay prior to the contact of the clay and superplasticizer and include modifications of mixing procedure, the addition of soluble calcium salts (e.g., calcium nitrite, calcium nitrate), and the addition of EO or EO/PO glycols to fresh mortar or concrete. Combinations of these approaches yield the best performance, especially for very harsh, poor quality (clay-bearing) sands.
In a broader sense, then, the invention involves the preparation of aqueous cement compositions containing a plasticizer and further containing clay which expands when in contact with water, and concerns providing an agent operative to modify clay activity. For example, the EO/PO plasticizer absorbing capability of the clay is reduced. Preferably, the clay activity-modifying agent is added to the clay before water is introduced to the clay, although in certain cases the agent may be added in any sequence if it has an affinity for clay which exceeds that of the EO/PO plasticizer.
In further exemplary methods, the clay is a smectite clay and the plasticizer comprises an EO/PO polymer (including comb polymers having EO/PO moieties in the backbone and/or in pendant groups). In further exemplary methods, the clay-activity-modifying agent comprises an inorganic cation, an organic cation, a polar organic molecule capable of being absorbed by clay, a clay dispersant (e.g., a polyphosphate), or a mixture thereof. Preferably, where a cation or polar organic molecule is used, the clay-activity-modifying agent is added to the clay before water is added to wet the clay in the preparation of the aqueous cementitious composition. Where the clay-activity-modifying agent is a clay dispersant, such as a polyphosphate, or where the cation has a stronger affinity for cationic exchange than the plasticizer (such as the organic cations of quaternary amines), then the agent may be introduced before, during, or after water is added to the clay.
The inventors believe that there are at least three possible mechanisms for modifying the clay. One is by reducing the surface activity (or reactivity) of the clay, such as by reducing the ability of the clay particle to absorb the EO/PO plasticizer. A second mechanism or mode of action is to reduce the viscosity of the clay which contributes to the overall slump of the concrete. This can be achieved either by dispersing the clay (whereby the individual clay platelets are pulled apart) or by flocculating the clay (whereby the clay is collapsed or aggregated into a denser unit which produces less viscosity in the concrete mix). A third mode of action is by pre-absorbing the clay by using a sacrificial agent.
The invention also pertains to admixtures comprising an EO/PO plasticizer and a clay-activity-modifying agent, as described above. Preferred admixture compositions of the invention comprise an EO/PO plasticizer, preferably an EO/PO comb polymer (with EO/PO groups in the backbone and/or in pendant groups) and a clay dispersant, such as a polyphosphate, or an organic cation having a strong affinity for clay such as a quaternary amine, an EO/PO containing polymer (which is different than the EO/PO plasticizer being dosed into the cement mix), or a mixture thereof.
Further advantages and features of the invention may be further apparent from the following detailed description.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The term “cement composition” as may be used herein refers to pastes, mortars, grouts such as oil well cementing grouts, and concrete compositions comprising a hydraulic cement binder. The terms “paste”, “mortar” and “concrete” are terms of art: pastes are mixtures composed of a hydraulic cement binder (usually, but not exclusively, Portland cement, Masonry cement, or Mortar cement and may also include limestone, hydrated lime, fly ash, blast furnace slag, and silica fume or other materials commonly included in such cements) and water; mortars are pastes additionally including fine aggregate, and concretes are mortars additionally including coarse aggregate. The cement compositions tested in this invention are formed by mixing required amounts of certain materials, e.g., a hydraulic cement, water, and fine or coarse aggregate, as may be applicable to make the particular cement composition being formed.
The term “clay” as used in the present invention specifically concerns 2:1 clays which are typically swelling, absorbing clays often labelled as smectites, montmorillonite, illite, hectorite, or the commercially available BENTONITE. It is also contemplated that volcanic ash and amorphous clays are also included in the absorbtive type materials to be considered within the definition of “clay.” The inventors are concerned with the foregoing 2:1 clays (and not 1:1 clays such as kaolin clay which are not typically considered as expanding clays). The problematic 2:1 clays (e.g., smectite) are present in certain sands, and this is what the inventors have surprisingly found as the cause of the EO/PO plasticizer absorption problem which they have solved by the invention described herei
Chun Byong-Wa
Folliard Kevin J.
Hill Christon L.
Jachimowicz Felek
Jardine Leslie A.
Baker William L.
Leon Craig K.
Marcantoni Paul
W. R. Grace & Co. - Conn.
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