WO1992004293A1

WO1992004293A1 - Bonded aggregate compositions and binders for the same

Info

Publication number: WO1992004293A1
Application number: PCT/US1991/006260
Authority: WO
Inventors: Calvin Shubow
Original assignee: Calvin Shubow
Priority date: 1990-08-31
Filing date: 1991-08-30
Publication date: 1992-03-19
Also published as: AU8509091A

Abstract

Bonded aggregate compositions such as concrete, concrete repair products, high temperature refractories, high temperature insulation and fire resistant insulation are made from an aqueous solution of phosphoric acid and a separate, storable dry mixture of a suitable aggregate, monocalcium phosphate, and calcium in the form of calcium aluminate cement or calcium oxide. The proportion of wet to dry constituents is variable so as to select the working time and strength of the aggregate composition, typically upon the order of three to eight minutes. The mixture of the preferred dry constituents, and the binder to be mixed with the aggregate to yield the preferred dry mixture, are also disclosed. The binder system is particularly advantageous in that the same set of binder constituents can readily be employed with a variety of aggregates, reducing the cost of providing a variety of aggregate compositions due to the ready availability of the raw materials and obviating the need to stock different binders for different aggregate compositions.

Description

BONDED AGGREGATE COMPOSITIONS

AND BINDERS FOR THE SAME BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to bonded aggregate structures, compositions for forming such structures, and binders for use in such compositions.

II. Description of the Prior Art

Bonded aggregate compositions are a class of known materials useful for many structural purposes. The class includes such products as concrete, concrete patching, refractory materials, high temperature insulation materials, and fire resistant materials. Bonded aggregate compositions generally comprise a suitable aggregate (a filler which determines the structural characteristics of the composition) bound by a binder, such as a cement.

Conventional cements used for binding aggregates include aluminous cements, hydraulic cements, and Portland cements. Hydraulic cements a re mixtures of fine-ground lime, alumina, and silica which set to a hard product upon admixture with water, the water combining chemically with the cement constituents to form a hydrate. Portland cements are particular hydraulic cements composed of lime, alumina, silica and iron oxide (as tetracalcium aluminoferrate); tricalcium aluminate; tricalcium silicate; and dicalcium silicate. Portland cements typically contain less than five percent alumina. Aluminous cements, in contrast, are hydraulic cements which contain at least thirty to thirty-five percent alumina, which is usually supplied by the inclusion of bauxite.

The cement or binder is selected to match the particular use to which the bonded composition will be put and to match the particular aggregate employed, which is similarly chosen in view of the ultimate use of the bonded composition. For example, if the end use of the composition is as a roadbed or roadway, a concrete formed as a conglomerate of gravel, pebbles, sand, broken stone, glass-furnace slag or cinders (collectively, the aggregate) embedded in a matrix of a suitable cement (typically standard Portland cement) is particularly preferred.

While conventional cements have long served adequately to bind aggregates into formed structures, the use of conventional cements has entailed some drawbacks. Most noteably, bound aggregate compositions formed with cementitious binders require a relatively long time to set. It has been known to modify such cements by the addition of aqueous ammonium phosphate and magnesium oxide to them, in order to decrease their setting time. The use of ammonium phosphate, however, possesses the disadvantage that the °binders cannot be practically used in locations inside closed vessels or places lacking adequate ventilation, since such binders release ammonia gas upon curing.

Moreover, there has traditionally been an increased cost associated with the provision of a variety of aggregate structures, because different binder compositions have generally been required for the different purposes to which the bonded aggregate structures were intended to be put. For example, a binder adequate for one purpose (such as for bonding a concrete aggregate into a concrete) has not been viewed as useful as a binder for forming other aggregate structures (for example, for binding a refractory aggregate into a refractory structure such as a furnace lining). The use of conventional cementitious binders has usually also required that the constituents forming the binders be relatively refined or purified, since the ability of the cement to bind the aggregate has conventionally been found to be ve ry sensitive to contamination in the constituents.

Binder systems based upon phosphate have also been employed, but the use of such systems has encountered other drawbacks. Phosphate-based binder systems normally employ phosphoric acid ( o r a salt thereof in the presence of water) in combination with an inorganic metal oxide such as magnesium oxide or aluminum oxide. Two types of products can be formed from such systems: some experiencing high temperatures during setting while ultimately achieving a high PSI strength, arising from the quick setting of the product at ambient temperatures (15°F to 85°F); and others having a controlled set by the application of significant heat (200°F to 500°F) to bring about final setting. Perhaps the major drawback of such systems is the relatively short working time available for a user to work or apply the aggregate compositions once mixed, typically on the order of one minute. While it is preferred in working with bonded aggregates of any type that the composition set fairly rapidly, it would be preferred that the composition once mixed should be workable for at least three minutes, and preferably workable in the range of seven to ten minutes, or longer.

SUMMARY OF THE INVENTION

Applicant has discovered that the problems of the control of the setting speed of the aggregate composition, the sensitivity of the composition to impurities, and the additional costs associated with providing a variety of binders for different aggregates, can all be overcome by the use of a binder system comprising at least one dry phosphate-providing component, at least one wet or aqueous phosphate-providing component, and at least one calcium-providing component. One of the dry phosphate- providing components and one of the calcium-providing components are preferably contained in a single material, such as a hydrated monocalcium phosphate (Ca(H₂PO₄)₂ H₂O). However, when these two components are contained in a single material, an additional cal ci um-providi ng material (such as a calcium aluminate cement, calcium oxide, or mixtures of them) will normally be required.

The strength and speed of curing can be controlled by selectively varying the concentration and ratio of the wet and dry components. Because the ratio of wet to dry component can be varied, the invention permits the use of commercial or agricultural grade materials at a significantly lower cost than the purified constituents presently required. In general, it is preferred that the optimal proportion of the wet component to the dry components be determined empirically from conventionally-sized test blocks, such as two inch by two inch by two inch cubes, or three inch by six inch circular cylinders.

The invention is also directed to an admixture of only the dry binder components, wherein the binder is mixed with the aggregate and the wet phosphate-providing component only at a remote location at which the bound aggregate structure is to be formed. In addition, the invention is directed to a mixture of an appropriate aggregate and the dry binder components, the dry mixture being mixed with the wet phosphate-providing component at the remote location. The basis for binding in this binder system is believed to be the admixture of a calcium-providing component such as a calcium aluminate with a wet phosphate-providing constituent, such as dilute phosphoric acid. Applicant has found that the addition of a dry phosphate-providing component to this basic binder not only lengthens the setting time by a controllable amount, but by varying the percentage strengths of the aqueous phosphates to the percentage strengths of the dry phosphates also unexpectedly improves the strength and refractory characteristics of aggregate structures including the multiple-component binder.

Applicant has also found that the binder system of the present invention unexpectedly possesses some degree of utility with ammonium phosphate-based materials. The particularly preferred phosphoric acid solution neutralizes the ammonia smell conventionally encountered with such materials. The use of a wet phosphate-providing component in ammonium phosphate-based binders appears, however, to be fairly sensitive to the amount of impurities contained in the aqueous component, so that the commercial utility of such mixtures may be questionable. For example, the impurities conventionally present in a pickling solution containing twenty-three percent phosphoric acid may easily be adequate to interfere with the utility of the present binder in ammonium phosphate-based materials. This does not detract, however, from the broad utility of the present invention.

The binder of the present invention can typically be employed with a variety of aggregate structures, such as concrete structures, refactory structures, high temperature insulation structures, and fire resistant structures, as well as in concrete patching. The dry phosphate and dry calcium-providing components of the present invention are preferably contained in a single material such as monocalcium phosphate, while the wet phosphate-providing component is typically a phosphoric acid solution. Optionally, an additional calcium-providing component can be included in the binder, particularly when the dry phosphate and primary calcium components are contained in a single material. This additional calcium- providing component usually comprises either a calcium aluminate cement or calcium oxide, or a mixture of them.

A dry aggregate composition in accordance with the present invention can typically comprise between seventy and ninety-five percent by weight of the aggregate, five to twenty-five percent by weight of the calcium-providing component, and about one to thirty percent by weight of the dry phosphate-providing component. If the calcium and phosphate are provided in a single material, that material can alternatively make up one to thirty percent by weight of the dry aggregate composition. Such a dry aggregate composition can be admixed with about eight to sixty percent by weight of a wet phosphate-providing component, such as a solution of about twenty to fifty percent by volume in water of a strong, commercially available phosphoric acid solution.

The present invention is thus not only directed to the bonded aggregate composition or structure, but is also directed to a dry binder comprising a mixture of the dry phosphate component and dry calcium component; to a binder comprising a mixture of the dry phosphate component, the wet phosphate component and the calcium component; and to a dry aggregate composition useful for forming an aggregate structure upon the addition of a wet phosphate component, the dry aggregate composition comprising an aggregate, a dry phosphate component and a dry calcium component. The invention is also directed to a method of forming a bonded aggregate structure comprising the steps of mixing a wet phosphorous-providing component with this dry aggregate composition, forming the admixture into an appropriate shape, and allowing the admixture to set.

Again, the specific proportions of components optimal for a particular purpose can readily be selected on a trial-by-error basis, but in any event are selected so as to be adequate to achieve a bonded aggregate composition of adequate strength and utility after admixture and working. It is believed, however, that the wet-to-dry ratios are governed by the structural requirements of the finished, cured aggregate structure. Generally, a lower wet-to-dry ratio will be expected to result in a bonded aggregate structure of higher strength and stability. Dilution of the aqueous phosphate while increasing the proportion of, for example, dry phosphate and calcium aluminate, is expected to yield materials having high strengths in a lower temperature range (1200°F to 2200°F), but suffering structural failure above that range. Increasing the phosphate content in the aqueous component while simultaneously decreasing the proportions of, for example, dry phosphate and calcium aluminate, is expected to yield materials having high strengths in a higher temperature range (2200°F - 3100°F) and to simultaneously extend the limit of structural failure to a higher temperature. The most important features to consider with respect to the dry phosphate-providing component are its solubility in water and its percentage content of phosphate. The advantage of the dry phosphate-providing component is that it provides adequate working time to the admixture while maintaining the total percentage of phosphate in the admixture, particularly when using cheaper aqueous phosphate solutions. To put it another way, the soluble dry phosphate makes up for the lower concentration of phosphate present in the cheaper (eg. industrial) acid solutions; adequate working time of the admixture and bonding strength in the resultant structures are thereby achieved at a lower cost, because cheaper acid solutions can be successfully used.

Detailed Description of the Preferred Embodiment of the Present Invention

A better understanding of the present invention will now be had upon reference to the following detailed Examples falling within the scope of the appended claims. A bonded aggregate structure according to the present invention is generally formed by the admixture of an aqueous or wet phosphate-providing component with a previously constituted admixture of three dry components: an aggregate; a dry phosphate-providing and calcium-providing material; and an additional calcium-providing component, preferably a calcium aluminate cement. The proportions of these components in various compositions are set forth in the following Examples.

The wet phosphate-providing component is preferably a dilute solution of industrial grade phosphoric acid, although commercial, agricultural and technical grades can also be used. The wet phosphate-providing component is added in an amount adequate to render the admixture workable yet also adequate to provide a sufficient content of dissolved or soluble phosphate to permit rapid setting, on the order of three to ninety minutes. An aggregate structure can then be readily formed from thirty-three kilogram batches of the aggregate and dry component mixture, mixed with an appropriate amount of such a phosphoric acid solution at seventy degrees Fahrenheit.

A wet phosphate-providing component especially useful for refractory and fireproofing aggregates (when magnesium and lime are also included) is shown in the Examples and was prepared as a 1:1 to 4:1 dilution of C-134, an orthophosphoric acid of formula H₃PO₄ previously available from Texasgulf Chemicals Co., Raleigh, N.C. A typical composition for C-134 is:

Phosphoric Acid, as P₂O₅ 52.6%

Sulfuric Acid, as SO₄ 2.9%

Fluoride Compounds, as F 0.5%

C-134 is a green, viscous liquid having an acrid odor. Its boiling point is about 275 F and it has a vapor pressure of 16mm of mercury at 77°F. It possesses a specific gravity of 1.68. At 52% P ₂ O ₅ , it has a melting point of -38°F. A 1% by weight solution in water has a pH of 2.1.

As of the filing of this application, Texasgulf appears to have replaced its C-134 with a substantially similar industrial grade phosphoric acid solution, designated by its code C-434. Because of its availability and its similarity to C-134, C-434 is expected to be a preferred aqueous or wet phosphate-providing component in the present invention. A typical composition for C-434 is: Phosphoric Acid, as P₂O₅ 56.3 %

Solids 0.1 %

Iron, as Fe₂O₃ 1.3 %

Aluminum, as Al₂O₃ 0.6 %

Magnesium, as MgO 1.3 %

Fluoride, as F 0.5 %

Sulphate, as SO₄ 0.8 %

Calcium, as CaO 0.2 %

Arsenic, as As 0.5 ppm

Organic Carbon, as TOC 55 ppm C-434 is a light green liquid having a specific gravity of 1.71 and an Apparent Brookfield Viscosity of 150 centipoise at 75° F. Its freezing point at a concentration of 56.3% P₂O₅ is below -20 ° F. Its slightly higher phosphate content may require a proportional adjustment of the concentrations on amounts of the other constituents in the embodiments of the invention recited in the following Examples.

The aqueous or wet phosphate-providing component can alternatively be any composition which contains soluble phosphate but which is not saturated with phosphate, and which dissolves some of the phosphate contained in the dry phosphate-providing component. Liquid Activator No. 30 is a dilute acidic monoaluminum phosphate solution found to be useful in the present invention. Also useful are materials such as polyphosphoric acid (SPA) in aqueous solution, orthophosphoric acid (merchant acid or industrial acid) in aqueous solution, monoaluminum phosphate (MALP) in aqueous solution, or magnesium phosphate in aqueous solution.

The dry phosphate-providing component can be any material containing a soluble phosphate in a concentration adequate to react with the calcium-providing component and provide an adequate bond to the aggregate. Suitable dry phosphate components are dibasic ammonium phosphate (DAP), ammonium dihydrogen phosphate (MAP or monoammonium phosphate), monoaluminum phosphate, magnesium phosphate, sodium acid pyrophosphate (disodium pyrophosphate), monosodium phosphate, boron phosphate, trimagnesium phosphate, trisodium phosphate dodecahydrate, sodium aluminum phosphate, phosphorous acid flake or granular triple superphosphate. The use of the ammonium materials may be restricted in view of the possibility of evolving ammonia gas during use, while the use of materials having other safety concerns (for example, phosphorus pentoxide) may first require resolution of those concerns. Sodium hexametaphosphate and tetrapotassi urn pyrophosphate appear unlikely to be useful in the present invention.

Similarly, the dry calcium-providing component can be any material capable of providing an amount of calcium adequate to react with the wet and dry phosphate components in order to yield satisfactory bonding of the selected aggregate. However, it is advantageous to employ a single dry material combining both the dry phosphate-providing component and the calcium-providing component. The material can be dibasic calcium phosphate (dicalcium phosphate), monobasic calcium phosphate (monocalcium phosphate), or tricalcium phosphate (DFP). Preferably, the combined dry phosphate-providing and calcium-providing material is C-38, a monocalcium phosphate of formula Ca(H₂PO₄)₂

H₂O from Texasgulf Chemicals Co., Raleigh, N.C. A typical composition for C-38 is:

Phosphorus, as P₂O₅ 48 %

Calcium, as CaO 21 % Free Acid, as H₃PO₄ 3.9%

Fluoride Compounds, as F 1.9% Sulfate, as SO₄ 3 %

C-38 is an ordorless, gray, granular solid having a specific gravity between 1.1 and 1.2 and possessing a melting point of 230°F. A 1% suspension in water has a pH of about 2.5 to 2.8.

The additional calcium-providing component can be any material capable of providing supplemental calcium to react with the phosphate components in order to provide adequate bonding in the aggregate structure desired. Calcium aluminate cements are preferred materials, as are calcium oxide or lime. More particularly, preferred calcium sources for either the primary dry calcium-providing component or the additional calcium-providing component can be burned or soft burned lime (dolomitic quicklime, CaO MgO), dolomitic limestone (dolomite, PG lime, CaCO MgCO₃), type N hydrated lime (lime hydrate, baked or hydrated lime, Ca(OH)₂ MgO), or industrial or tremolitic talc (hydrous calcium magnesium silicate minerial mixture); or calcium aluminate cements such as Secar, Lumnite, Refcon, CaO Al₂O₃, CaO Al₂O₃ Fe₂O₃, CaO Al₂O₃ SiO₂, or CaO Al₂O₃ SO₃.

A particularly preferred additional calcium- providing material is the calcium aluminate cement sold under the name Refcon by Lehigh Cement Co., Allentown, Pa. Refcon is formed by sintering a pelletized, solid mixture of bauxite and limestone. A typical composition comprises:

Al₂O₃ + TiO₂ 57.4 %

Total Iron, as Fe₂O₃ 1.2 %

CaO 34.2 %

SiO₂ 5.7 % SO₃ 0.36%

MgO no appreciable concentration Refcon typically has a bulk density of about 1500 kg/m³ and a specific gravity of 3.02. It possesses a Blaine specific surface of 3300 cm²/g. It has a one day compressive strength of 6500 PSI when measured by ASTM

C-109.

It should be noted that, when monocalcium phosphate is used as a single source for both of the dry phosphate- and dry calcium-providing components, it appears that it is necessary to include the additional calcium-providing material mentioned above, in order to achieve adequate bonding.

As can be seen from the compositions of these materials, the present invention is advantageous in that it permits satisfactory bound aggregate structures to be formed from commercial-grade materials, particularly from a concentrated phosphoric acid such as C-134 or C-434. The invention is also advantageous in that the binder incorporating the preferred materials described above can be used with a variety of aggregates for different structural purposes. The binder of the present invention can be employed with concrete aggregates, concrete patching aggregates, refractory aggregates, high temperature insulation aggregates, and fire insulation aggregates.

For example, typical aggregates useful for forming a bonded concrete structure in accordance with the present invention include sand, stone, pea gravel, silica aggregate, ash, flint clay (in combination with other aggregates only), pumice, volcanic glass, ground glass or glass beads, or mixtures thereof. Sand is the preferred aggregate for a concrete composition under the present invention, and it is particularly preferred that the sand be a mixture of mesh sizes, for example, No. 140, No. 430 and No. 530.

The typical aggregate can also be a refactory aggregate comprising at least one of Flint clay, Mulcoa, Kyanite, mullite, chromite, tabular alumina, aluminum oxide, alumina, silicon oxide, silica, calcined bauxite, chrome oxide, magnesium oxide and iron oxide, and mixtures thereof. It is believed that some appreciable amount of an aluminum-containing material must be included in any refractory aggregate, in order to achieve adequate binding in the product ultimately formed. The preferred refractory aggregates include Flint clay 47-8, Mulcoa 47-8, Mulcoa 47-4, Mulcoa 50-4, Mulcoa 60-4, Mulcoa 70-4, Kyanite No. 325, chromite coarse, Mullite No. 200, chromite flour, bauxite, tabular alumina 48-325, and tabular alumina 8-0, and mixtures thereof. As the intended temperature of use of the refractory increases, the aluminum content of the aggregate must increase as well.

An aggregate useful in the present invention can also be an expandable insulation aggregate selected from at least one of expanded pearlite, expanded vermiculite, dolomite, dolomitic lime, talc, lime, calcium magnesium carbonate, calcium carbonate, tabular alumina, Mullite, Kyanite, sand and magnesium silicate, and mixtures thereof. A preferred aggregate for expandable insulation comprises a mixture of sand No. 140, dolomitic lime and talc; the talc controls the size of the bubbles of carbon dioxide released during expansion, and thereby makes the grain size in the expanded insulation more uniform.

An aggregate useful in the present invention can also comprise a high temperature or fire insulation aggregate comprising at least one of expanded pearlite, expanded vermiculite, dolomite, dolomitic lime, talc, lime, calcium magnesium carbonate, No. 140 sand, mullite and magnesium silicate, and mixtures thereof. A preferred aggregate for high temperature or fire insulation purposes comprises a mixture of No. 140 sand or Mullite 200, dolomitic lime and talc.

The chemical composition of these aggregates is well known to those skilled in this art. Mulcoa, Mullite, Flint clay and Kyanite comprise, in major part, aluminum (III) oxide and silica dioxide (that is, silicon tetroxide). Chrome sand (chromite coarse) and chromite flour (chrome flour) comprise, in major part, chromium (III) oxide, aluminum oxide and magnesium oxide. Chrome sand also includes iron (II) oxide, while chrome flour includes ferrosoferric oxide. Tabular alumina, of course, comprises substantially pure aluminum (III) oxide, while sand comprises in major part silica (silicon dioxide). Lime consists in major part of calcium oxide, while dolomitic lime is a mixture of lime and dolomite (calcium magnesium bicarbonate). Talc is a natural foliated hydrous magnesium silicate.

This list of aggregates which can be bound by the binder of the present invention is not intended to be an exhaustive list of aggregates useful in the present invention. To the contrary, it is expected that many other conventional aggregates can be bound by the binder system of the present invention and can be used to form bound aggregate structures. Which aggregate to use is chosen in accordance with the end use requirements of the bound structure and the purity of product needed.

As shown in the following Examples, a dry aggregate composition in accordance with the present invention can be formed from a mixture of about 70 to 95 percent by weight of a suitable aggregate, 5 to 20 percent by weight of a dry calcium-providing component, and 1 to 30 percent by weight of a dry phosphate-providing component; and preferably from a mixture including 1 to 30 percent by weight of a single material providing both of the phosphate and calcium provi ding-components, as well as an additional calcium component. Thereafter, depending upon the type of bound aggregate structure that is desired, from about 8 to 60 percent by weight of a wet phosphate-providing component is admixed with the dry aggregate composition. For a refractory or concrete structure, between 10 and 30 percent by weight of the wet component will typically be employed. However, if it is desired that the admixed materials be expanded or pumped into the location of use (for example, if they are used as an expandable insulation or a pumpable high temperature insulation or refractory) more of the wet component will be employed, for example, preferably between 30 and 60 percent by weight.

A dry burned (calcined) magnesium oxide such as Mag Chem 10-40 can optionally be added to the aggregate compositions and binders of the present invention.

Table 1 recites Examples R1 through R12 which define refactory compositions falling within the scope of the present invention:

Table 2 recites the numerical PSI strength and the letter grade of abrasion resistance achieved (P: poor, F: fair, G: good, VG: very good, E: excellent) at various temperatures by the compositions of Examples R1 through R12:

The PSI strength and abrasion resistance of the Examples R1 through R12 were measured in accordance with prevailing ASTM standards, for example, by ASTM C-133-84 (Cold Crushing Strength and Modulus of Rupture of Refractory Bricks and Shapes) and ASTM 704-88 (Abrasion Resistance of Refractory Materials at Room Temperature), respectively. Samples were prepared for such testing by slowly pouring 2.5 kg increments of the blended aggregate and binder mixture into an appropriate volume of aqueous phosphate solution, and hand mixing the materials with a two-inch trowel until the mixture was completely wetted-out (typically for thirty to forty-five seconds), then depositing the mixture into appropriately dimensioned molds.

Table 3 shows the percentage of shrinkage typically encountered by some of the refractory composition Examples:

It can be seen from Examples R1 through R12 that the binder system of the present invention is useful for forming a variety of different refractory materials of different utilities from a single binder system. The proportions in Examples R1 through R12 are adjustable to optimize the resulting aggregate structure, depending upon its intended use, or depending upon the costs of materials. For example, the cost of Examples R2 and R8 is reduced by employing a dilute solution of monoaluminum phosphate as the wet component. The total phosphate concentration is made up in the dry component, so that costs are saved in two ways: dilution of the expensive monoaluminum phosphate, so that less of it is used; and replacement of it with a less expensive dry phosphate.

However, this same binder system is also useful for forming a variety of concrete compositions, as shown by examples C1 through C12 set out in Table 4:

Table 5 below recites the typical PSI strength of some of the Examples of concrete compositions falling under the present invention, as measured under prevailing ASTM standards for two inch by two inch cube breakage:

1 11

Table 6 recites the typical PSI strength of some of the Examples of concrete compositions falling under the present invention, as measured by prevailing ASTM standards for three inch by six inch cylinder breakage:

1

It is clear from Examples C1 through C12 that the binder system of the present invention is useful for forming a variety of concrete compositions which possess more than adequate structural strength yet which also possess a setting time which can be varied as desired.

Table 7 recites an Example of an expandable concrete insulation which can applied by bucket mixing, mortar mixing, or pumping the admixed materials through a nozzle:

Preferably, the ratio of water to C-134 (or C-434) is varied (that is, the phosphoric acid solution can be diluted or rendered more concentrated) in order to select the density and strength of the bonded aggregate structure ultimately formed and to select the pressure needed to pump the mixed materials. For ease of handling, it may be preferred under some circumstances to admix the dry aggregate composition (that is, the mixture of the aggregate, the calcium component and the dry phosphate component) with a quantity of water adequate to render the mixture pumpable, and then inject an appropriate quantity of concentrated phosphoric acid into the mixture when it reaches the application nozzle.

In accordance with the present invention, a pumpable high temperature fire insulation or refractory composition can be formed from the same constituents and in the same fashion as in Example E, with the exception that the sand #140 of the expandable concrete insulation is replaced with an equal weight of Mullite 200.

The present invention thus provides a method for forming a bonded aggregate structure, as well as providing a binder system for such aggregate structures; a dry aggregate composition incorporating the dry constituents of the binder system; and a mixture of dry constituents useful in making the binder system. The present invention is advantageous over prior binder systems in that the constiuents of the binder system can be commercial grade materials, rather than materials which have been refined or purified. The calcium-providing component is normally significantly less expensive than the monoaluminum phosphate and magnesium phosphates employed in prior binders and aggregate structures. These other materials have refractory properties which fall significantly short of those generally enjoyed by the aggregate structures of the present invention.

Moreover, the present invention advantageously reduces the expense of providing a variety of aggregate structures, because a single binder system can be employed to bind a wide variety of aggregates. The invention reduces the cost of supplying, manufacturing or keeping in inventory different binder constituents.

With at least the refractory aggregate compositions of the present invention using silica or Mullite, the resulting aggregate structures possess unexpectedly improved refractory characteristics over comparable prior art structures. The resulting structures are less susceptible to thermal shock; in many cases, the aggregate does not need to be pre-dried or pre-fired after its initial setting, before it can be used at high temperatures. Even more surprising, the use of calcium as the divalent binder cation permits the refractory characteristics to depend upon the proportion and concentration of the wet and dry phosphate providing components, specifically, a selection of the temperature range in which optional refractory characteristics are obtained. Such selectivity is absent in monoaluminum phosphate and magnesium phosphate-based systems. These other phosphates may, of course, be included in the binders of the present invention as sources of wet or dry phosphate.

Having described my invention, however, many modifications thereto will become apparent to those skilled in the art to which it pertains, without deviation from the sprit of the present invention, as defined by the scope of the appended claims.

I claim:

Claims

1. A binder useful for bonding an aggregate into a rigid structure upon mixing and setting of said binder and said aggregate, said binder comprising: at least one dry phosphate-providing component; at least one aqueous or wet phosphate-providing component; and at least one calcium- providing component; in proportions adequate to allow working upon mixing of said binder and said aggregate and adequate to yield a rigid structure upon setting of said mixed binder and aggregate.

2. The binder according to claim 1, wherein one of said dry phosphate-providing components and one of said calcium-providing components are constituted in a si ngl e material.

3. The binder according to claim 2, wherein said single material comprises monocalcium phosphate.

4. The binder according to claim 1, wherein said wet phosphate-providing component is a phosphoric acid solution.

5. The binder according to claim 1, wherein said binder comprises an additional calcium-providing component comprising at least one of a calcium aluminate cement and calcium oxide, and mixtures thereof.

6. The binder according to claim 2, wherein said single material comprises monocalcium phosphate, said wet phosphate-providing component is a phosphoric acid solution, and said binder comprises an additional calcium-providing component comprising at least one of a calcium aluminate cement and calcium oxide.

7. A bondable aggregate composition containing a mixture of an aggregate and the binder of claim 1, in proportions adequate to allow working upon mixing of said aggregate and binder and adequate to yield a rigid structure upon setting of said mixed aggregate and binder.

8. The composition according to claim 7, wherein said aggregate is a concrete aggregate comprising at least one of sand, stone, Flint clay, pea gravel, silica aggregate, ash, pumice, volcanic glass and glass beads, and mixtures thereof.

9. The composition according to claim 7, wherein said aggregate is refractory aggregate comprising at least one of Flint clay, Mulcoa, Kyanite, Mullite, chromite, bauxite, tabular alumina, aluminum oxide, alumina, silicon oxide, silica, chrome oxide, magnesium oxide and iron oxide, and mixtures thereof.

10. The composition according to claim 7, wherein said aggregate is an expandable insulation aggregate comprising at least one of expanded perlite, expanded vermiculite, dolomite, dolomitic lime, talc, lime, calcium magnesium carbonate, calcium carbonate, tabular alumina, Mullite, Kyanite, sand and magnes i um silicate, and mixtures thereof.

11. The composition according to claim 7, wherein said aggregate is a high temperature fire insulation aggregate comprising at least one of expanded perlite, expanded vermiculite, dolomite, dolomitic lime, talc, lime, calcium magnesium carbonate, sand, Mullite and magnesium silicate, and mixtures thereof.

12. A dry, storable binder component useful for binding an aggregate and a wet or aqueous phosphate- providing component into a rigid structure upon mixing and setting thereof, said binder comprising an admixture of at least one dry phosphate-providing component and at least one calcium-providing component, in proportions adequate to allow working upon mixing of said binder component, said aggregate and said wet component, and adequate to yield a rigid structure upon setting of said mixed binder component, aggregate and wet component.

13. The binder component according to claim

12, wherein one of said dry phosphate-providing components and one of said calcium-providing components are constituted in a single material.

14. The binder component according to claim

13, wherein said single material comprises monocalcium phosphate.

15. The binder component according to claim 12, wherein said binder comprises an additional calcium-providing component comprising at least one of a calcium aluminate cement and calcium oxide, and mixtures thereof.

16. The binder component according to claim 13, wherein said single material comprises monocalcium phosphate, and said binder component comprises an additional calcium-providing component comprising at least one of a calcium aluminate cement and calcium oxide, and mixtures thereof.

17. A dry, storable aggregate composition bondable upon the addition thereto of a wet or aqueous phosphate- providing component, said aggregate composition containing a mixture of an aggregate and the binder component of claim 12, in proportions adequate to allow working upon mixing of said aggregate composition with said wet phosphate-providing component and adequate to yield a rigid structure upon setting of said mixed aggregate composition and said wet phosphate-providing component.

18. The dry aggregate composition of claim 17, comprising about 70 to 95 percent by weight of said aggregate, about 5 to 20 percent by weight of said calcium-providing component, and about 1 to 25 percent by weight of said dry phosphate-providing component.

19. The dry aggregate composition of claim 17, wherein said dry phosphate-providing and calcium- providing components are constituted in a single material.

20. The dry aggregate composition of claim 19, wherein said single material is monocalcium phosphate.

21. A method for forming a bonded aggregate structure, comprising: admixing a wet or aqueous phosphate- providing component with the aggregate composition of Claim 17, in proportions adequate to yield a workable but readily setting mixture; shaping said workable mixture; and allowing said workable mixture to set.

22. The bonded aggregate structure resulting from the method of claim 21.

23. The method according to claim 21, comprising mixing about 10 to 60 percent by weight of said wet phosphate-providing component with said dry aggregate composition.

24. The method according to claim 21, wherein said wet component comprises: about 20 to 50 percent by volume of a phosphoric acid solution having a concentration of about 50 to 60% measured as P₂O₅; ^ancl about 80 to 50 percent by volume water.

25. The method according to claim 21, wherein said aggregate comprises about 70 to 95 percent by weight of said dry aggregate composition.

26. The method according to claim 21, wherein said dry phosphate-providing component about comprises about 1 to 25 percent by weight of said dry aggregate composition.

27. The method according to claim 21, wherein said calcium-providing component comprises about 5 to 20 percent by weight of said dry aggregate composition.

28. The method according to claim 21, wherein said aggregate composition comprises about 70 to 95 percent by weight of said aggregate, about 5 to 20 percent by weight of said calcium-providing component, and about 1 to 25 percent by weight of said dry phosphate-providing component; wherein said wet phosphate-providing component comprises about 20 to 50 percent by volume of a phosphoric acid solution having a concentration of about 50 to 60% measured as P₂O₅, and about 80 to 50 percent by volume water; and wherein said method comprises mixing about 10 to 60 percent by weight of said wet phosphate-providing component with said dry aggregate composition.

29. The method according to claim 28, wherein said at least one calcium-providing component comprises at least one of calcium aluminate cement and calcium oxide, and mixtures thereof; wherein said at least one dry phosphate-providing component comprises monocalcium phosphate; and wherein said aggregate comprises at least one of a concrete aggregate, a refractory aggregate, an expandable insulation aggregate, and a high temperature fire insulation aggregate, or mixtures thereof.

30. The method according to claim 29, wherein said aggregate comprises at least one of sand, stone, pea gravel, silica aggregate, ash, pumice, volcanic glass, glass beads, Flint clay, Mulcoa, Kyanite, Mullite, chromite, bauxite, tabular alumina, aluminum oxide, alumina, silicon oxide, silica, chrome oxide, magnesium oxide, iron oxide, expanded perlite, expanded vermiculite, dolomite, dolomitic lime, talc, lime, calcium magnesium carbonate, calcium carbonate, and magnesium silicate, and mixtures thereof.

31. The method according to claim 21, wherein one of said dry phosphate-providing components and one of said calcium-providing components are constituted in a single material.

32. The method according to claim 31, wherein said single material comprises monocalcium phosphate.