JPH0776121B2 - Volume stable hardening hydraulic cement - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to improving the composition of hydraulic cements. More particularly, the invention relates to improvements in cements consisting of a mixture of Portland cement, lime aluminate cement and sulphate, preferably calcium or aluminum sulphate or gypsum.

By definition, the term "hydraulic cement" refers to Portland cement, expansive cement, air-entren Portland cement, volcanic ash mixed cement, slag cement, masonry cement, white Portland cement, colored cement, antibacterial cement, waterproof cement, fire resistant cement. It means cement, self-stressed cement, alumina cement and similar substances.

The term "gypsum" as used is intended to include gypsum as is commonly understood in the art. This includes calcium sulphate (CaSo ₄ ) and its various forms such as calcium sulphate dehydrate, calcium sulphate hemihydrate and calcium sulphate dihydrate, as well as baked gypsum, pressure baked gypsum and plaster of Paris. ) Etc. are included.

The term "alumina cement" used was aluminate as a main cement component - shall usually include technical cement material to be understood to include calcium _{(CaC × Al 2 O 3)} . This includes high alumina cement (HAC), lime aluminate cement and many other commercially available alumina cements.

The term "Portland cement" as used is intended to include cements commonly understood to be "Portland cements", such as those described in ASTM Standard C-150. The Portland cement component of these cement mixtures acts to reduce dry shrinkage and increase wet expansion. The term "Portland cement" should be understood to encompass these other cements, as other cements that act as dry shrinkage inhibitors but are not specifically designated as Portland cements are also suitable for this application. Examples of dry shrinkage inhibitors include expansion promoters such as expansion cements that are compatible with the other components of the system.

BACKGROUND OF THE INVENTION Many prior attempts have been made to provide cement systems that meet the requirements of the construction industry, especially in the protection, waterproofing and restoration of concrete structures. The optimum system should set in a relatively short time into a hard mass or coating with sufficient strength, wear resistance and corrosion resistance. It is also highly desirable for these systems to be impermeable to fluids, especially aqueous solutions. Also, such systems should not undergo excessive cure volume changes under wet or dry conditions.

For commercial use, these types of cement systems must also have good bonding properties to wet and dry surfaces, initial and long-term strength and practical field workability. They must be able to withstand freezing and thawing and the action of salts, solvents and other corrosive substances. Although there are many cement mixtures with one or more of the desirable properties listed above, none of the prior art to date
Not all of the above can be achieved in the composition and previous attempts have had only limited success. U.S. Pat.No. 4,357,
No. 166 discusses some of the limitations of these prior art compositions in columns 2 and 3.

Although a mixture of Portland cement, lime aluminate cement and gypsum has been used for many years, various problems associated with their use have been encountered.

Previous compositions containing other hydraulic cements such as alumina cement and gypsum have been shown to exhibit long term wet expansion. For example, U.S. Pat.No. 4,357,166 discloses a cement composition which, when mixed with water, is capable of rapidly setting into a high compressive strength hard mass without substantial shrinkage during setting and which exhibits low wet and dry volume changes in the hardened state. There is. The invention also has some impermeability to fluids and abrasion, erosion and chemical resistance, as well as other properties desired in compositions having commercial utility in the construction industry. The advantages of the invention are achieved by a cement composition comprising a mixture of alumina cement, gypsum, a dry shrinkage inhibitor and a wet expansion inhibitor. The composition of the invention preferably uses Portland cement as a dry shrinkage inhibitor and a lithium salt as a wet expansion inhibitor. However, the addition of various accelerators, retarders and other mixtures to alumina cement and gypsum compositions can significantly affect the cure volume change (wet and dry), thus limiting their usefulness. It

In addition, previous attempts to mix gypsum with other hydraulic cements produced the desired effects, such as fast setting or low shrinkage, but also the stability, durability, and durability of hydraulic cements.
It affected workability, water resistance or wet / dry cycling stability or durability of the resulting cement.

U.S. Pat.No. 4,045,237 discloses a cement composition that, when mixed with water, can set into a hard mass in a short time without substantial shrinkage during setting and initial setting, and can have a high degree of impermeability to fluids. There is. The composition comprises a powder mixture of calcined gypsum, high alumina cement and Portland cement, or it comprises a mixture of high alumina cement without the use of Portland cement and particles of pressure calcined gypsum.

Portland cement consists mainly of tricalcium silicate and dicalcium silicate. Two types of raw materials are usually required to make this formulation-high in calcium content, such as limestone or chalk, and rich in silica, such as clay or sheer. These raw materials usually contain significant concentrations of iron-bearing compounds. The presence of these compounds during the heating process results in the formation of clinker containing a few% of iron oxide.

The structure of this Portland cement clinker therefore changes significantly due to variations in the composition and particle size of the raw materials and inconsistencies in the firing conditions, which vary in clinker porosity and the size and size of the crystals found in the crystallite aggregates. Differences in morphology occur.

Thus, the Portland cement component of the cement compositions disclosed in US Pat. Nos. 4,357,166 and 4,045,237 contain significant amounts of iron oxide as described above. For example, in U.S. Pat.
It is critical to use% Portland cement. Addition of more than 10% Portland cement causes difficulties in the cement hydration reaction due to the proportion of ferric oxide formed in the Portland cement-calculated gypsum-high alumina cement mixture.

U.S. Pat.No. 4,157,263 is a division of that application leading to the issuance of the 4,045,237 patent, which uses the composition claimed in the 4,045,237 patent in the repair and waterproofing of concrete structures and a stable foundation for machinery or heavy equipment. Alternatively, a method used to fill voids or holes to form a foundation is disclosed. The Portland cement used in the practice of this method contains significant amounts of ferric oxide, as described above, which limits the amount of Portland cement that can be added to the mixture and thus reduce the strength of the composition.

Applicants have taken into account the change in setting volume of concrete, grouts, patching substances and waterproofing substances made from a mixture of calcium sulphate hemihydrate, lime aluminate cement and Portland cement, of Portland cement containing low levels of iron oxide. It was found that it can be reduced by use. Applicants have further determined that such a reduction in the iron oxide used in the Portland cement component results in a surprising increase in the compressive strength of this composition and an improvement in its binding capacity to previously set concrete.

The maximum iron oxide content can vary, but as a general rule it will be up to about 2% by weight. Preferably the iron oxide content should be as low as possible, but as a practical matter amounts below 0.1% by weight are difficult to achieve.

SUMMARY OF THE INVENTION The present invention relates to improvements in hydraulic cement compositions.
More particularly, the present invention relates to improvements in cement consisting of blends of Portland cement, lime aluminate cement and calcium or aluminum sulphate compounds.

The composition disclosed by the applicant is about 0.1 to about 80 parts by weight of Portland cement made from a raw material containing low levels of iron compounds to have a low iron oxide content, a sulfate compound, preferably about 0.1 to about 40 gypsum. Parts by weight and about 2 to about 95 parts by weight of alumina cement. The most preferred composition comprises about 2 to 20 parts by weight low iron Portland cement, 55 to 95 parts by weight alumina cement and 2 to 10 parts by weight gypsum.

Although any sulfate compound can be used in the present invention, organic or inorganic sulfate salts are preferred. Calcium sulphate gives the best results, and its use as a pure chemical, in situ formed, or its common form, addition in gypsum is most advantageous. Ammonium sulfate aluminum [AlNH ₄ (S
O _{4) 2]} and potassium aluminum sulfate [AlK (SO _4)
2 ] also gives good results. No other alkali metal sulphate is found to be useful and satisfactory performance is observed only with calcium and / or aluminum sulphate. Based on availability, gypsum is the most advantageous sulfate compound in its various forms.

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

In one embodiment of the cement composition, the maximum iron oxide content of Portland cement is 2 wt% as measured by ferric oxide according to ASTM test method C-114. In another embodiment, the gypsum selected for use in Applicant's composition is calcium sulfate hemihydrate.

Applicant's composition may include many other ingredients and additives, including Portland cement in the composition,
Up to about 90% by weight aggregate can be included, based on the total weight of the sulfate compound and alumina cement. Additional components can include compounds that can evolve gas on contact with water, surfactants, water reducing agents, and set time control agents.

Applicant's volume stable cement composition therefore has a Portland cement content of about 0.1 to about 2% by weight maximum iron oxide content.
About 80 parts by weight, preferably 2 to 20 parts by weight; about sulfate compound
0.1 to about 40 parts by weight, preferably 2 to 10 parts by weight; and about 2 to about 95 parts by weight of alumina cement, preferably 55 to 95 parts by weight.

Applicant has also found that about 0.1 to about 80 parts by weight of Portland cement made from raw materials containing low levels of iron compounds to contain up to about 2% iron oxide; about 0.1 to about 40 parts by weight calcium or aluminum sulfate compounds. Parts; and about 2 to about 95 parts by weight of alumina cement are mixed for a predetermined duration of time, followed by hydration of the mixture with water to find a novel process for making a volume stable cement composition.

The method developed by Applicant adds aggregate to the mixture prior to hydrating the mixture with water in an amount of about 1 to about 90 parts by weight based on the total weight of Portland cement, sulfate compound and alumina cement. Some additional steps can be included, including Furthermore, the mixture may also contain accelerators, retarders,
At least one of pigments, water reducing agents or gas generating agents can be added.

The products resulting from the practice of the methods disclosed herein by the Applicant are also novel and should be considered part of this invention.

The improvement in the cement composition disclosed by the Applicant is to increase the maximum iron content of Portland cement to about 2% by weight in order to obtain improved volume stability, high strength and good bond strength to other cement compositions. Including control. The improvement further comprises reducing the setting time of the composition by reducing the iron oxide content of the cement to the lowest possible value. The iron oxide content should be in the range of 0.1 to 2% by weight in Applicants' composition.

Detailed Description of the Preferred Embodiments The following examples are given to illustrate, without limitation, the novel cement compositions of the present invention and their advantages. In the examples, parts and percentages are by weight unless otherwise indicated.

Example 1 A composition prepared from a formulation comprising lime aluminate cement, calcium sulfate hemihydrate and Portland cement, with Portland cement containing a "normal" amount of ferric oxide, about 23% by weight, is used. To be done.

The following ingredients were dry blended for 1 minute: Material wt% Portland Cement 8 Lime Aluminate Cement 25 Calcium Sulfate Hemihydrate 5 Dry Flude 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 was added to hydrate the mixture and the following properties were measured: Time compressive strength 1 hour 900 psi 3 hours 3,000 psi 24 hours 6,300 psi Shrinkage and expansion tests cured from composition 11 Performed on inch specimen castings: Dry shrinkage = 0.0196% (after 14 days storage at 50% humidity) Wet expansion = 0.0130% (after immersion in water) Example 2 The same ingredients as found in Example 1 were used in the same proportions. . However, in this example the Portland cement was made from raw materials containing low levels of iron compounds and contained 0.4% by weight ferric oxide.

After hydration of the composition, the following improvements were shown compared to the values of Example 1: Time compressive strength 1 hour 4,500 psi 3 hours 9,000 psi 24 hours 11,000 psi Dry shrinkage = 0.0003% (14 days at 50% humidity) After storage) Wet swell = 0.0004% (after immersion in water) A 50% increase in bond strength compared to the composition described in Example 1 and a surprising reduction in water absorption and permeability of the hydration product were also shown. .

Examples 3 and 4 further demonstrate the improvement provided by the low iron oxide Portland cement.

The following ingredients were dry blended in Example 3 for 1 minute: Example 3 Material wt% Portland Cement 8 Lime Aluminate Cement 25 Calcium Sulfate Hemihydrate 5 Dry Fluid Coke 3 Melment F-10 0.5 Sand 58.5 As in Example 1. , Portland cement contained about 23% by weight ferric oxide. After dry mixing, the mixture was hydrated by adding 12.5% water and the following properties were measured: Time compressive strength 3 hours 975psi 24 hours 8,525psi 7 days 9,500psi Dry shrinkage = 0.0736% (at 50% relative humidity) After storage for 28 days) Wet expansion = It was not possible to measure because the test piece broke when immersed in water.

Example 4 The components used in Example 3 were again used in the same proportions. However, in this example, Portland cement was produced from a feedstock containing low levels of iron compounds as in Example 2 (ie,
Ferric oxide content 0.4% by weight).

After hydration of the composition, the following improvements were shown compared to the values of Example 3: Time compressive strength 3 hours 5,750 psi 24 hours 8,925 psi 7 days 11,075 psi Dry shrinkage = 0.04% (28% at 50% relative humidity). Day) Wet swell = 0.0073% (28 days immersion in water) Although any gypsum can be used in these formulations, calcium sulfate hemihydrate was found to give the most effective results. Melment F-1 used in the examples
Compound 0 is well known as a water reducing agent, and is known as American Admixtures, Chicago, Illino
is)). Other water reducing agents can also be used in the present invention.

In addition to the three essential components of the cement composition of the present invention, it is of course possible to use the usual additives added to concrete. This includes, but is not limited to, accelerators, retarders, pigments, azeotropic agents, water reducing agents, pumping aids, fly ash, gas generating and releasing agents, and of course the full range of aggregates.

While it is apparent that the invention disclosed herein is considered to provide improved cement systems over those described in the prior art, other embodiments can be devised by those skilled in the art. Will be recognized. Accordingly, the appended claims are intended to cover all modifications or aspects that fall within the true spirit and scope of this invention.

Claims (9)

[Claims] 1. A volume-stable cement composition comprising Portland cement having a maximum iron oxide content of 2% by weight, an alumina cement, and a calcium or aluminum sulphate compound. 2. Portland cement is present in an amount of 0.1 to 80 parts by weight, alumina cement is present in an amount of 2 to 95 parts by weight, and a sulfate compound is present in an amount of 0.1 to 40 parts by weight.
A composition according to claim 1. 3. Portland cement is present in an amount of 2 to 20 parts by weight, alumina cement is present in an amount of 55 to 95 parts by weight, and the sulfate compound is present in an amount of 2 to 10 parts by weight. A composition according to claim 1. 4. The composition according to claim 1, 2, or 3, wherein the sulfate compound is gypsum. 5. A composition according to claim 1, 2 or 3 wherein the sulphate compound is aluminum sulphate, eg ammonium aluminum sulphate or potassium aluminum sulphate. 6. The composition according to claim 1, 2 or 3, wherein the sulfate compound is calcium sulfate. 7. The composition of claim 6 wherein the calcium sulfate compound is formed in situ in the composition by the reaction of an alkali metal sulfate and calcium nitrate. 8. A composition according to any one of claims 1 to 7, further comprising 1 to 90 parts by weight of an aggregate or filler component. 9. The composition according to any one of claims 1 to 8, which further comprises one or more of a gas generating agent, a surfactant, a water reducing agent and a setting time controlling agent. .