Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-11-30
2001-04-24
Marcheschi, Michael (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S486000, C106S416000, C106S718000, C106S694000, C241S016000, C241S022000, C241S021000
Reexamination Certificate
active
06221148
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to novel methods of making a metakaolin material well suited for cement-based composites and alkali-activated systems.
BACKGROUND OF THE INVENTION
The use of metakaolin in cement is known. For example, U.S. Pat. No. 4,793,861 describes a cement-based product which is reinforced with glass fibers having good resistance to alkaline environments. The product contains, for each 100 parts by weight of cement, about 10 to 40 parts by weight of metakaolin, the latter exhibiting a reactivity to the modified Chapelle test greater than 500 mg of CaO per gram of metakaolin.
U.S. Pat. No. 4,842,649 describes a blended hydraulic cement composition composed of portland cement, slag, pozzolans including metakaolin, and admixtures including potassium carbonate and water reducing compositions.
U.S. Pat. No. 4,975,396 describes a process for producing reinforced cementitious compositions in which the following constituents are mixed in the aqueous phase in the following order: about 35-55 parts by weight of water mixed with about 3-12 parts of a polymer, by weight of dry polymer; up to about 5 parts of a water-reducing auxiliary agent and/or a liquefying agent; from about 15-30 parts of metakaolin; from about 50-120 parts of silica sand; and about 100 parts of cement. Continuous mixing is maintained until a homogeneous, thixotropic paste is obtained. Then between 2 and 15% by weight of alkaline-resistant glass fibers, relative to the weight of the paste, is introduced into the paste.
U.S. Pat. No. 4,994,114 describes method for selecting a pozzolan (for example metakaolin) for incorporation into a composite material comprising cement and glass.
U.S. Pat. No. 5,167,710 describes a process for making a cement mixture containing fibers wherein a paste is formed by mixing cement and, per 100 parts by weight of cement, approximately 5 to 20 parts by weight of a first pulverized material of which the grains have an average diameter of between ⅕ and {fraction (1/10)} of the average diameter of the grains of the cement and approximately 20 to 35 parts by weight of water. The paste is then mixed with reinforcing fibers. The paste may also include a second pulverized material the average grain diameter of which is between ⅕ and {fraction (1/10)} of the average diameter of the first pulverized material.
U.S. Pat. No. 5,372,640 describes cement-based products reinforced with alkali-resistant glass fibers that become almost insensitive to aging when 30 to 40 parts by weight of a metakaolin composition are added for each 100 parts of cement.
U.S. Pat. NO. 5,624,489 describes a conversion-preventing additive for high-alumina cement-based compositions, the additive comprising: siliceous pozzolanic powder, e.g. zeolite, granulated blast-furnace slag, fly ash, silica fume, rice hulls, metakaolin; inorganic salts containing sodium or potassium cations and sulphate, carbonate, nitrate, silicate, phosphate, chloride or bromide anions, and optionally other chemical admixtures, e.g. superplasticizers.
U.S. Pat. No. 5,626,665 describes cementitious systems comprised of gypsum, calcined clay, and clinker.
Pozzolans are finely divided materials which can react with alkali to form cementitious products. The fine particle size and large pore volume of pozzolans, however, can lead to an increase in water demand. In cement-based systems, the addition of extra water can reduce the performance of the system by reducing the strength and increasing the permeability of the resultant cement-based structures. The diminished strength is undesirable for several reasons. Initially, delay in early strength development results in surface cracking due to evaporation. Secondly, jobs take longer because the concrete form must remain in place substantially longer, and finishing is delayed.
Reactive pozzolans can be made by dry grinding metakaolin using ball milling. However, ball milling is an expensive and time consuming process. In this connection, ball milling often requires 6 hours of milling time. Such long processing times restricts the commercial manufacturability of dry milled pozzolans. Dry milling is not therefore frequently employed on the raw metakaolin. However, the addition of metakaolin to finishing mills or mills for clinker or slag grinding (dry milling) is employed for incorporating pozzolans into cement-based systems.
Nevertheless, there is still a need for pozzolans having improved activity to provide cement-based systems and alkali activated systems having lower water demand and higher compressive strength, as well as improved flowability as a dry powder and a higher bulk density to reduce shipping and storage costs.
SUMMARY OF THE INVENTION
This invention relates to cement-based compositions containing a highly reactive pozzolan based upon a wet milled metakaolin. The cement-based compositions have lower water demand and equivalent or improved flowability in dry form compared to conventional cement-based compositions. Resultant structures or composites made from the cement-based compositions according to the present invention have high compressive strength compared to structures made from cement-based compositions made with conventional pozzolans (dry milled metakaolin and unprocessed metakaolin).
In one embodiment, the present invention relates to a method of making a highly reactive pozzolan, involving the steps of forming a slurry comprising metakaolin and a liquid; wet milling the slurry; and separating the metakaolin from the liquid to provide the highly reactive pozzolan.
In another embodiment, the present invention relates to a method of making a cement-based composition involving the steps of providing a highly reactive pozzolan by forming a slurry comprising metakaolin and a liquid, wet milling the slurry, and separating the metakaolin from the liquid; and combining the highly reactive pozzolan with at least one cementitious material.
In yet another embodiment, the present invention relates to a method of making an alkali-activated composition involving the steps of providing a highly reactive pozzolan by forming a slurry comprising metakaolin and a liquid, wet milling the slurry for a period of time from about 2 minutes to about 30 minutes, and separating the metakaolin from the liquid; and combining the highly reactive pozzolan with at least one geopolymeric material.
In still yet another embodiment, the present invention relates to a method of making a highly reactive pozzolan composition involving the steps of forming a slurry comprising from about 20% to about 80% by weight of metakaolin and from about 20% to about 80% by weight of a liquid and wet milling the slurry for a period of time from about 1 minute to about 60 minutes to provide the highly reactive pozzolan composition.
DETAILED DESCRIPTION OF THE INVENTION
The cement-based compositions of this invention are intended for use in cement-based applications such as swimming pool plasters, grouts, mortars and concrete. The alkali-activated compositions of this invention are intended for use in geopolymer and zeolitic applications such as the formation of cast and molded bodies, the storage of toxic chemicals and radioactive waste, and in specialty concretes. The cement-based composites or compositions of the present invention contain at least one cementitious material, at least one highly reactive pozzolan, and optionally at least one dispersant. The cement-based composition is the total combined dry mixture of the cementitious composition and highly reactive pozzolan materials which react with water to form the binder in concrete or other material. Concrete is a construction material comprised of the cement-based composition, water, optional admixtures, and aggregates.
Cementitious materials include those materials typically required to make cement; that is, those materials that can react with lime or other alkali and exhibit cementing properties. Generally speaking, cementitious materials are binder materials that harden to form a connecting medium between solids. Cementitious materials i
Gruber Karen Ann
Mathur Sharad
Reid Harry J.
Engelhard Corporation
Keller Raymond F.
Marcheschi Michael
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