Field of the Invention

This invention relates to improvements in the composition of hydraulic cement. More particularly, it relates to improvements in cement which consists of blends o Portland cement, calcium aluminate cement and a sulfate compound, preferably of a calcium or aluminum sulfate or gypsum.

Definitions

The term "hydraulic cement" as used herein is intended to mean portland cements, expansive cements, air entraining portland cements, pozzolanic cements, slag cement masonry cement, white portland cement, colored cement, antibacterial cement, waterproof cement, refractory cement, self-stressing cement, aluminous cement, and similar materials.

The term "gypsum" as used herein is intended to include gypsum such as is normally understood in the art. This would include calcium sulfate (CaSO ) and its various forms such .as calcium sulfate anhydrate, calcium sulfate hemihydrate, and calcium sulfate dihydrate, as well as calcined gypsum, pressure calcined gypsum, and plaster of Paris.

The term "aluminous cement" as used herein is intended to include those cementitious materials normally understood in the art to contain as the main cementitious constituent, mono calcium aluminate (CaO x Al 0 ) . This

would include high alumina cement (HAC) , calcium aluminate cement, and many other commercially available alumina cements.

The term "Portland cement" as used herein is intended to include those cements normally understood in th art to be "Portland cement," such as those described in AST Standard C-150. The Portland cement component of these cementitious mixtures acts to reduce drying shrinkage and increase wet expansion. Other cements which act as drying shrinkage inhibitors, although not specifically referred to as Portland cement, are also suitable for use herein so tha the term "Portland Cement" should be understood as encompassing those other cements. Examples of drying shrinkage inhibitors include expansion promoters such as expansive cements which are compatible with the other constituents of the system.

BACKGROUND OF THE INVENTION

There have been numerous prior attempts at providing cementitious systems to meet the needs of the construction industry, particularly in the protection, waterproofing, and repair of concrete structures. The optimum system should set within a relatively short period time into a hard mass or coating that has sufficient strength, abrasion resistance, and corrosion resistance. I is also highly desirable that these systems possess impermeability to fluids, particularly aqueous solutions. Also, such systems should not undergo excessive hardened volume changes under either wet or dry conditions.

For commercial use, these types of cementitious systems must also possess good bonding characteristics to damp or dry surfaces, early as well as long term strength,

and practical field workability. They should be capable of withstanding freezing and thawing, as well as the action of salts, solvents and other corrosive substances. Although there have been a number of cementitious mixtures that possess one or more of the above-described desirable properties, none of the prior art to date has been able to achieve all of the foregoing in one composition and previous attempts have had only limited success. U.S. Patent No. 4,357,166 discusses some of the limitations of these prior art compositions in columns 2 and 3.

While mixtures of Portland cement, calcium aluminate cement and gypsum have been in use for years, various problems concerning their use have been encountered.

Previous compositions containing other hydraulic cements such as aluminous cement and gypsum have been shown to exhibit long term wet expansion. For example, U.S. Paten No. 4,357,166 discloses a cementitious composition which, when mixed with water, is capable of setting rapidly to a hard mass of high compressive strength without substantial shrinkage during setting and which exhibits reduced wet and dry volume changes in the hardened state. That invention also possesses a degree of impermeability to fluids along with abrasion, erosion, and chemical resistance, as well as other characteristics which are desirable in a composition having commercial usefulness in the construction industry. The advantages of that invention are achieved by a cementitious composition comprising a mixture of an aluminou cement, a gypsum, a drying shrinkage inhibitor, and a wet expansion inhibitor. The compositions of that invention preferably use Portland cement as a drying shrinkage inhibitor and a lithium salt as the wet expansion inhibitor. However, various accelerators, retarders and other

admixtures, when added to aluminous cement and gypsum compositions, can significantly affect the hardened volume change (wet or dry) , thus limiting their usefulness.

Additionally, previous attempts to blend gypsum with other hydraulic cements, while producing the desired effect such as fast-setting or reduced shrinkage, have also affected the hydraulic cement's soundness, durability, workability, resistance to water or wet/dry cycling stabilit or permanence of the resulting cement.

U.S. Patent No. 4,045,237 discloses a cementitious composition which, when mixed with water, is capable of setting into a hard mass in a short period of time without substantial shrinkage during setting and early hardening an possessing a high degree of impermeability to fluids. The composition comprises a particulate admixture of calcined gypsum, high alumina cement and portland cement, or it may comprise a mixture of particles of high alumina cement and pressure calcined gypsum, without the use of Portland cemen

Portland cement consists mainly of tri-calcium silicate and dicalcium silicate. To prepare this compound, two types of raw materials are usually required - one high calcium content, such as limestone or chalk, and the other rich in silica, such as clay or shale. These raw materials ordinarially contain an appreciable concentration of iron- bearing compounds. The presence of these compounds during the heating process leads to the formation of a clinker containing several percent of iron oxide.

The structure of this Portland cement clinker will therefore, vary considerably due to variations in the composition and particle size of the raw materials as well a inconsistencies in the burning conditions, which leads to

variations in clinker porosity as well as differences in crystalline sizes and forms found in the aggregates of crystallites.

Thus, the Portland cement component of the cementitious compositions disclosed in U.S. Patent Nos. 4,357,166 and 4,045,237 contains an appreciable quantity of iron oxide as described above. In U.S. Patent No. 4,045,237 for example, it is critical to employ between 0.1-10% of Portland cement in the mixture. The addition of greater tha 10% of Portland cement leads to difficulties with the cement hydration reactions due to the resulting proportion of ferri oxide in the Portland cement-calcined gypsum-high alumina cement mixture.

U.S. Patent No. 4,157,263, which is a division of the application leading to the issuance of the '237 patent discloses a method for using the compositions claimed in the ' 221 patent for use in repairing and waterproofing concrete structures and for filling voids and holes to form stable underpinnings or foundations for machinery or heavy equipment. The Portland cement utilized in the performance of this method contains, as noted above, appreciable quantities of ferric oxide, which restricts the amount of Portland cement which may be added to the mixture, thus reducing the strength of the composition.

Applicants have discovered that the hardened volum changes which occur in concrete, grout, patching material an water-proofing material made from blends of calcium sulfate hemihydrate, calcium aluminate cement and Portland cement ca be reduced by using Portland cement containing reduced level of iron oxide. Applicants have further determined that such a reduction of the iron oxide used in the Portland cement

component dramatically increases the compressive strength of this composition and improves its bonding capacity to previously set concrete.

The maximum iron oxide content may vary, but as a general principle it should be a maximum of about 2 weight percent. Preferably, the iron oxide content should be as lo as possible, but as a practical matter, amounts lower than 0.1 weight percent are difficult to achieve.

SUMMARY OF THE INVENTION

This invention relates to improvements in the composition of hydraulic cement. More particularly it relates to improvements in cement which consists of blends o Portland cement, calcium aluminate cement and a calcium or aluminum sulfate compound.

The composition disclosed by the applicants comprises from about 0.1 to about 80 parts by weight of a Portland cement manufactured from raw materials containing' low levels of iron compounds so as to have a low iron oxide content; from about 0.1 to about 40 parts by weight of a sulfate compound, preferably gypsum, and from about 2 to about 90 parts by weight of an aluminous cement. The most advantageous composition includes about 2 to 20 parts by weight of the low iron Portland cement, 55 to 95 parts by weight of the aluminous cement and 2 to 10 parts by weight o gypsum.

While any sulfate compound can be used in this invention, organic or inorganic sulfate salts are preferred. Calcium sulfate provides the best results and is the most advantageous whether used as a pure chemical, formed in situ or added in its common form, gypsum. Aluminum ammonium

sulfate (A1NH.(S0.) ) and aluminum potassium sulfate (A1K (SO.),,) also provide good results. Other alkali metal sulfates have not been found to be useful, and satisfactory performance is found only with the calcium and/or aluminum 5 sulfates. Due to its availability, gypsum in any of its various forms, is most advantageous sulfate compound.

It is also possible to form the most preferred compound, calcium sulfate, in situ, by reacting a mixture of ₁₀ sodium sulfate with calcium nitrate, for example. Other calcium compounds which react with various sulfate salts can be used.

In one embodiment of the cementitious composition,

,15_ the maximum iron oxide content of the Portland cement is 2 weight percent, measured as ferric oxide according to ASTM test method C-114. In a further embodiment the gypsum selected for use in applicants' ^* composition is calcium sulfate hemihydrate.

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Applicants' composition may further comprise a number of additional ingredients and additives, which may include up to about 90% by weight of an aggregate based upon a total weight of Portland cement, sulfate compound and aluminous cement in the composition. Additional ingredients may include a compound capable of generating a volume of gas upon contact with water, a surface active agent, a water reducing agent and a set time controlling agent.

Applicants' volume-stable cementitious composition

30 therefore comprises from about 0.1 to about 80, and preferably 2 to 20, parts by weight of a Portland cement having a maximum iron oxide content of 2 weight percent; from

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about 0.1 to about 40, preferably 2 to 10, parts by weight o a sulfate compound and from about 2 to about 95, preferably 55-95, parts by weight of an aluminous cement.

Applicants have also discovered a novel method for producing their volume-stable cementitious composition which comprises blending, for a predetermined duration, a mixture comprising from about 0.1 to about 80 parts by weight of a Portland cement manufactured from raw materials containing low levels of iron compounds so as to contain less than abou 2% of iron oxide; from about 0.1 to about 40 parts by weight of a calcium or aluminum sulfate compound and from about 2 t about 90 parts of weight of aluminous cement, and thereafter hydrating this mixture with water.

The method developed by the applicants may include several additional steps, which include adding to the mixtur an amount of from about 1 to about 90 parts by weight of an aggregate based upon the total weight of Portland cement, sulfate compound and aluminous cement before hydrating the mixture with water. In addition, one may also add to the mixture at least one of an accelerator, a retarder, a pigment, a water reducer or a gas generating agent.

The product produced by practicing the method disclosed herein by the applicants is also novel and should be considered part of their invention.

The improvement in the cementitious composition disclosed by applicant comprises controlling the maximum iro content of the Portland cement to about 2 weight percent in order to obtain improved volume stability, higher strength and better bonding strength to other cementitious co postions. The improvement further comprises decreasing the setting time for the composition by reducing the iron

oxide content of the cement to as low a value as possible. The iron oxide content should range between 0.1 and 2 weight percent in applicants' composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples are presented for the purpose of illustrating, without limitation, the novel cementitious composition of the invention and the advantages thereof. In the examples, parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1

A composition comprising calcium aluminate cement, calcium sulfate hemihydrate and portland cement wherein the ortland cement was manufactured from compounds containing a "normal" amount of ferric oxide, about 23 weight percent, is utilized.

The following ingredients were dry blended for one minute:

Substance Weight Percent

Portland cement 8

Calcium aluminate cement 25

Calcium sulfate hemihydrate 5

Dried Fluid Coke 3

Melment F-10 0.5

Lithium Carbonate 0.09

Citric Acid 0.12

Sand 58.29

100

After dry mixing, 12.5 parts of water were added t hydrate the mix, and the following characteristics were determined:

Time Compressive Strength

1 hour 900 psi

3 hours 3,000 psi

24 hours 6,300 psi

Shrinkage and expansion tests were performed on a hardened 11 inch bar cast from the composition:

Dry shrinkage = 0.0196% after 14 days storage at 50% humidity

Wet expansion = 0.0130% after immersion in water

EXAMPLE 2 t The same components as found in Example 1 were utilized in the same proportions. In this example, however, the Portland cement was manufactured from raw materials containing low levels of iron compounds, ^' id contained 0.4 weight percent of ferric oxide. f

The following improvements over the values from Example 1 were noted after hydration of the composition:

Time Compressive Strength

1 hour 4,500 psi

3 hours 9,000 psi

24 hours 11,000 psi

Dry shrinkage = 0.0003% after 14 days storage at 50% humidity Wet expansion = 0.0004% after immersion in water

A 50% increase in bonding strength over the composition as described in Example 1 was also noted as well as a drastic decrease in the water absorption and permeability of the hydrated product.

Examples 3 and 4 further show the improvement that low iron oxide Portland cements provide.

In Example 3, the following ingredients were dry blended for one minute:

EXAMPLE 3

Substance Weight Percent

Portland cement 8

Calcium aluminate cement 25

Calcium sulfate hemihydrate 5

Dried fluid coke 3

Melment F-10 0.5

Sand 58.5

As in Example 1, the Portland cement contained about 23 weight percent ferric oxide. After dry mixing, 12.5% water was added to hydrate the mix and the following characteristics were determined:

Time Compressive Strength

3 hours 975 psi 24 hours 8,525 psi 7 days 9,500 psi

Dry shrinkage = 0.0736% after 28 days storage at 50% relativ humidity Wet expansion = Could not be determined because the bars would destruct when immersed in water.

EXAMPLE 4

The components used in Example 3 were once again utilized i the same proportions. In this example, however, the Portla cement was manufactured from raw materials containing low levels of iron compounds as in Examples 2 (i.e., a ferric oxide content of 0.4 weight percent).

The following improvements over the values from Example 3 were noted after hydration of the composition:

Time Compressive Strength

3 hours 5,750 psi

24 hours 8,925 psi

7 days 11,075 psi

Dry shrinkage = 0.04% after 28 days at 50% relative humidit Wet expansion = 0.0073% after 28 days immersion in water.

While any gypsum can be utilized in these formulations, calcium sulfate hemihydrate has been found to provide the most effective results. The Melment F-10 compound used in the examples, is a well-known water reduci agent which is available from American Admixtures, Chicago, Illinois. Other water reducing agents can also be used in this invention.

In addition to the three essential components of the cementitious composition of this invention, the normal additives that are added to concrete can, of course, be use These include, but are not limited to, accelerators, retarders, pigments, air entraining agents, water reducers, pumping aids, fly ash, gas generating and releasing agents and, of course, the full range of aggregates.

1?

While it is apparent that the invention disclosed herein is calculated to provide an improved cementitious system over those described in the prior art, it will be appreciated that alternate embodiments may be devised by those skilled in the art. It is therefore intended that the appended claims cover all modifications or embodiments as fall within the true spirit and scope of the present invention.