BACKGROUND OF THE INVENTION
This application claims priority from the following Australian provisional patent applications, the full contents of which are hereby incorporated by cross-reference.
|Application No ||Title ||Date Filed |
|PR3474 ||A Composite Product ||2 Mar. 2001 |
|PR3475 ||Spattering Apparatus ||2 Mar. 2001 |
|PR3476 ||Additive for a Dewaterable Slurry ||2 Mar. 2001 |
|PR3477 ||A Method and Apparatus for Forming a ||2 Mar. 2001 |
| ||Laminated Sheet Material by Spattering |
|PR3478 ||Coatings for Building Products ||2 Mar. 2001 |
1. Field of the Invention
The present invention relates to admixtures for slurries and in particular cementitious slurry compositions.
2. Description of the Related Art
As is well known in the art, most cementitious compositions are laid down or used in a slurry form. Increasing difficulty and expense in obtaining high quality aggregate for use in such cementitious material such as concrete has forced manufacturers to resort to low grade materials such as crushed stone, marine sand and even recycled crushed concrete obtained from demolitions or old structures. This leads to problems with the concrete such as a higher water demand, bleeding (where, as the slurry settles, water migrates to the surface), lower workability and pumpability.
In the past, these problems have been overcome by the addition of certain additives to the cementitious composition. These plasticisers, sometimes known as water reducers, dispersion agents or super plasticisers, act to increase the workability and validity of the slurry for a given quantity of water. Examples include lignosulphonates, naphthalene sulphonate-formaldehyde condensates.
Typically, these water reducers are added at around 0.3% by weight of cement and provide between 8 and 12% reduction in the water cement ratio, depending upon the addition procedure. Additions of up to 1% by cement provide up to 35% reduction in the water to cement ratio. In high performance concrete application, eg ultra high strength concrete, it is common to overdose in plasticiser/water reducer, (or combinations thereof) to obtain further water reduction of up to 50%. However, at such dosage levels detrimental effects are produced, eg setting times increased and compressive strength of a cementitious mixture reduced.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
SUMMARY OF THE INVENTION
In a broad aspect, the present invention provides an additive for a cementitious slurry comprising of one or both of the following mineral components:
i) fly ash having a predominant particle size of up to about 10 microns, and
ii) aluminous material having a predominant particle size of up to about 150 microns.
The applicants have found that use of the small particle size fraction fly ash or large particle size fraction aluminous material acts as an efficient water reducer for cementitious slurries. The applicants have found that addition of a suitable quantity of such a mineral additive indeed provides a substantial reduction in water required to maintain a predetermined viscosity without any of the aforementioned detrimental effects arising from conventional techniques. The aforementioned additive does not significantly increase set times or cause excessive aeration, which can be a major problem with some known admixtures. Further, it inhibits bleeding and improves workability.
In a preferred embodiment, the aforementioned mineral additive can be used in combination with a conventional water reducer/plasticiser to enhance the water reduction capabilities of such a conventional additive.
In a second aspect, the present invention provides a cementitious slurry comprising an hydraulic binder, water, a plasticiser and a mineral additive including one or both of the following components:
i) fly ash having a predominant particle size of up to about 10 microns,
ii) aluminous material having a predominant particle size of up to about 150 microns, and the mineral additive being added in a quantity sufficient to provide a water reduction effect.
In a third aspect, the present invention provides a method of reducing the water requirements of a cementitious slurry comprising adding an effective amount of one or both of the following mineral components: i) fly ash having a predominant particle size of up to about 10 microns, and ii) aluminous material having a predominant particle size of up to about 150 microns.
In a fourth aspect, the present invention provides a method of improving the properties of a cementitious slurry comprising adding an effective amount of one or both of the following mineral components: i) fly ash having a predominant particle size of up to about 10 microns, and ii) aluminous material having a predominant particle size of up to about 150 microns.
The reference to water reduction effect relates to the ability of the mineral additive to effectively reduce the quantity of water required to obtain a particular viscosity. As will be clear to persons skilled in the art, for certain applications, a slurry is designed to have a particular predetermined viscosity for flowability, pumpability or application reasons. The mineral additive described above provides excellent water reduction properties for a slurry. As discussed, it can be used on its own to provide water reduction to the slurry or in combination with a conventional plasticiser/water reducer.
When used in combination with an amount of conventional plasticiser/water reducer, it has been found that the aforementioned mineral additive enhances the water reduction properties of the slurry as will be discussed below.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention relate to the use of a mineral additive to manufacture and improve the properties of a cementitious slurry. More preferably, one or both of the following mineral additives may be used: i) fly ash having a predominant particle size of up to about 10 microns, and ii) aluminous material having a predominant particle size of up to about 150 microns.
The fly ash in the mineral additive refers to fly ash with a predominant particle size of up to about 10 microns. As will be clear to persons skilled in the art, fly ash is a solid powder having a chemical composition similar to or the same as the composition of material that is produced during the combustion of powdered coal. The composition typically comprises about 25 to 60% silica, about 10 to 30% Al2 O3, about 5 to 25% Fe2O3, up to about 20% CaO and up to about 5% MgO.
Fly ash particles are typically spherical and range in diameter from about 1 to 100 microns. It is the smaller size fraction of fly ash particles with a predominant size below about 10 microns that has surprising water reduction properties.
The fly ash preferably makes up about 30-100% based on weight of cement. Preferably, the fly ash is between about 40 and 90% and most preferably about 50 to 70% based on weight of cement.
Larger size fly ash particles have been known in the past to provide a water reduction effect. Smaller size particles, however, have always been considered unsuitable for water reduction for a few reasons. Firstly, it is expected in the art that the smaller the particle size, the more reactive the particle. Fly ash is a reactive pozzalan and accordingly, smaller size fraction fly ash was considered inappropriately reactive to act as a water reducer.
In addition, due to the high specific surface area of the smaller size fraction fly ash, it was expected that this material would in fact increase water demand. The applicants have surprisingly found that the opposite is in fact the case. The smaller size fraction fly ash boosts the water reducing properties of conventional water reduction agents by a substantial extent.
The aluminous material in the mineral additive preferably has a predominant particle size less than about 150 microns. The reference to “aluminous material” should not be taken literally but refers to alumina type materials including hydrated, partially hydrated and unhydrated alumina. Preferably, the alumina content of aluminous material based on the weight of cement is between about 5 and 30%, preferably about 10 to 25% and most preferably about 15 to 20%.
If a blend of hydrated alumina and fly ash is used in the mineral additive, the ratio of hydrated alumina:fly ash is preferably between about 1:1 to 1:10.
The term “hydraulic or cementitious binder” as used herein, means all inorganic materials which comprise compounds of calcium, aluminum, silicon, oxygen, and/or sulfur which exhibit “hydraulic activity” that is, which set solid and harden in the presence of water. Cements of this type include common Portland cements, fast setting or extra fast setting, sulphate resisting cements, modified cements, alumina cements, high alumina cements, calcium aluminate cements and cements which contain secondary components such as fly ash, slag and the like. The amount of cement present in the composition of the preferred embodiments of the present invention has a lower limit of about 10 weight percent based on the total dry ingredients, preferably about 15 weight percent, more preferably about 20 weight percent, the upper limit of the amount of the cement is about 50 weight percent, preferably about 40 weight percent, more preferably about 30 weight percent.
The cementitious composition may optionally but preferably include at least one filler material, e.g. graded and ungraded aggregate such as washed river gravel, crushed igneous rock or limestone, lightweight aggregate, crushed hard-burnt clay bricks or air-cooled blast furnace slag, sand, calcium carbonate, silica flour, vermiculite, perlite, gypsum, etc.
The amount of filler present in the cementitious composition preferably has a lower limit of about 5 weight percent based on the total dry ingredients, preferably about 10 weight percent, more preferably about 15 weight percent; the upper limit being about 30 weight percent, preferably about 25 weight percent, more preferably about 20 weight percent.
The cementitious composition may optionally contain other additives including: cement plasticising agents such as melamine sulphonate-formaldehyde condensates, naphthalene sulphonate-formaldehyde condensates, naphthalene sulphonates, calcium lignosulphonates, sodium lignosulphonates, saccharose, sodium gluconate, sulphonic acids, carbohydrates, amino carboxylic acids, polyhydroxy carboxylic acids, sulphonated melamine, and the like.
The amount of conventional plasticiser used in the dry cement composition will vary, depending on the fluidising ability of the particular cement plasticiser selected. Generally, the amount of cement plasticiser is preferably in the range of about 0.3 to about 3 wt %, and more preferably about 0.5 to about 2 wt %, based on the weight of the dry cement composition.
Preferred plasticisers include Melment. F-10, a melamine-formaldehyde-sodium bisulphite polymer dispersant, marketed by SKW-Trostberg in the form of a fine white powder. Another suitable plasticiser is Neosyn, a condensed sodium salt of sulphonated naphthalene formaldehyde, available from Hodgson Chemicals.
Thickener may also be used in the cementitious composition including one or more of the polysaccharide rheology modifiers which can be further subdivided into cellulose based materials and derivatives thereof, starch based materials and derivatives thereof, and other polysaccharides.
Suitable cellulose based rheology-modifying agents include, for example, methylhydroxyethylcellulose, hydroxymethylethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxyethylpropylcellulose, etc. The entire range of suitable rheology modifiers will not be listed here, nevertheless, many other cellulose materials have the same or similar properties as these and are equivalent.
Suitable starch based materials include, for example, amylopectin, amylose, sea-gel, starch acetates, starch hydroxyethyl ethers, ionic starches, long-chain alkylstarches, dextrins, amine starches, phosphate starches, and dialdehyde starches.
Other natural polysaccharide based rheology-modifying agents include, for example, alginic acid, phycocolloids, agar, gum arabic, guar gum, welan gum, locust bean gum, gum karaya, and gum tragacanth.
The thickener addition rate in the cementitious composition may range between 0.0001 and 0.5% based on the weight of the dry cement composition.
Latex addition of at least one latex selected from the group consisting of: an acrylic latex, a styrene latex , and a butadiene latex is also preferred. This component improves adherence, elasticity, stability and impermeability of the cementitious compositions containing it, and also favours formation of flexible films.
The latex may be used in solid amounts of about 0.5 to about 20 wt %, based on the weight of the dry cement composition. Preferably, it is present in an amount of about 1 to about 15 wt %, and more preferably about 10 wt %, based on the weight of the dry cement composition.
The cementitious composition may optionally incorporate as a substitute to the latex emulsion a proportion of a powdered vinyl polymer or other equivalent polymeric material, to enhance the adhesion; resilience and flexural strength; and abrasion resistance of the composition.
The powdered vinyl polymer is preferably polyvinyl acetate or a copolymer of vinyl acetate with another monomer, such as ethylene. A preferred vinyl acetate resin is VINNAPAS LL5044 thermoplastic resin powder, containing a vinyl acetate-ethylene copolymer, available from WACKER.
The powdered vinyl polymer may be used in amounts of about 0.5 to about 20 wt %, based on the weight of the dry cement composition. Preferably, it is present in an amount of about 1 to about 15 wt %, and more preferably about 10 wt %, based on the weight of the dry cement composition.
The cementitious composition may optionally contain about 0-40 wt % of other fillers/additives such as mineral oxides, hydroxides and clays, metal oxides and hydroxides, fire retardants such as magnesite, thickeners, silica fume or amorphous silica, colorants, pigments, water sealing agents, water reducing agents, setting rate modifiers, hardeners, filtering aids, plasticisers, dispersants, foaming agents or flocculating agents, water-proofing agents, density modifiers or other processing aids