Method and composition for preventing volume change of rapid curing flowable impermeable cement specific tissue

(42) Date of commencement of the patent: 15.12.1989 (45) Date of issue: 25. 6.1990 (30) Priority:

11th 5.1981 US 262175 claims.

(56) Documents:

DE-0SZ547765 DE-OS3033376 GB-PS2033367 FR-PS2140954 US-PS 3922172 US-PS4108930 US-PS4045237 US-PS4157263 US-PS4216022 (73) Patentee:

INTERNATIONAL CONSTRUCTION PRODUCTS RESEARCH INC. 06430 FAIRFIELD (US).

(54) CEMENT COMPOSITION AND CEMENT MANUFACTURED THEREOF

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AT 390 786

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No. 390,786

The invention relates to a cement composition which after mixing with water is capable of binding to a hard mass, with inhibited wet expansion in the cured state. The composition should allow to control the volume change in the rapid setting of non-flowable material impermeable cementitious systems.

The term cement composition as used herein means compositions which generally have the property of hardening under water, including cementitious waterproofing materials, covering materials and protective coatings, and the like. Like. And of mixtures with aggregates and water, such as concrete, mortar, grout and products made therefrom.

The term wet expansion is intended to mean the expansion of a cement composition in the hardened state, ie after the end-tying, under moisture conditions, as generally determined according to the Standard Test Method ATSM C 157-75 for Length Change of Hardened Cement, Mortar and Concrete.

The terms inhibiting wet expansion and wet expansion action as used herein are virtually interchangeable and mean at least a reduction in the wet expansion of the cementitious system and / or advantageously maintaining a volume equal to or greater than the volume at Application of the system is, and also include similar expressions such. B. switching off the wet expansion.

US Pat. No. 3,861,929 now describes the particular shrinkage properties of concretes made with conventional cements, resulting in breaks in curing and drying. It also describes an expansion cement, which significantly increased its volume during and after setting and hardening. The expansion cement described in the aforementioned US patent comprises a mixture consisting essentially of Portland cement and calcium aluminate cements and an amount of calcium sulfate which may be in the form of gypsum

The term Portland Cement, as used herein and hereinafter, is intended to include cements commonly known to those skilled in the art as Portland Cement, as also described in ASTM C 150, with Types I and C being particularly preferred for the purposes of the invention Other Portland cement types are suitable. The Portland cement has the effect of inhibiting the drying shrinkage and increases the wet expansion of the inventive composition.

Accordingly, other cements which act as drying shrinkage inhibitors, although not specifically referred to as Portland cements, are also suitable for use in the invention, and the term as used herein is intended to encompass such other cements. Such other drying shrinkage inhibitors may include, for example, expansion accelerators, such as expansion cements, which are compatible with the other components of the system.

The term gypsum, as used herein and hereinafter, is intended to include gypsum, as is well known to those skilled in the art, including calcium sulfate (CaSO₄) and its various forms, calcium sulfate anhydrate, calcium sulfate hemihydrate, calcium sulfate dihydrate, as well as calcined gypsum, calcined gypsum and Paris gypsum (model gypsum). Examples of commercial gypsum products suitable for the purposes of the invention are gypsum grade G-5 commercial grade from Georgia Pacific Corporation or Hydrostone of United States Gypsum Company.

US Pat. No. 3,775,143 further describes a so-called stressing cement which contains Portland cement and an expansion component consisting of calcium sulfate, calcium oxide and an aluminate-containing material such as alumina cement or highly alkaline calcium hydroaluminate. This cement should be waterproof as well as petrol-resistant and gas-tight.

U.S. Patent No. 3,147,129 discloses some of the problems with basic processes for making sulfoaluminate cements, including difficulties in controlling the properties of such cements. Further, there is also proposed therein a sulfoaluminate cement composition which is mentioned as having uniform properties and can be used as an expansion cement after inclusion of appropriate additives such as zinc sulfate and sodium bisulfate. It is further noted that certain components can be added as retarders that do not cause appreciable expansion and even tend to neutralize the expansion effect of additives such as zinc sulfate and sodium bisulfate. Such ingredients may include sucrose, hydrated lime and silica mixtures.

Compositions containing high-toned cement and Portland cement for use as fast-setting mixtures are known

The term alumina cement, as used herein and hereinafter, is meant to include cementitious materials as will be understood by those skilled in the art, thus materials containing as major cementitious constituents monocalcium aluminate (CaCkA) (Oj), such as high alumina cement and calcium aluminate cement. Examples of commercial alumina cements suitable for use in the invention are Lumnite of the Lehigh Portland Cement Company and the high toned deodorants Fondu or Secar of the Lone Star LaFarge Aluminous Cement Company Ltd.

For example, it is noted in US Pat. No. 4,012,264 that very rapidly setting and

-2Nr. 390 786 hardening cement can be prepared by mixing Portland cement and high-grade earth cement and / or by using different accelerators and it is described in said US-PS a composition of calcium aluminate and Portland cement including retarders and / or accelerators. High-grade earth cement has also been added to Paris gypsum or to anhydrite for more resistant molds or casts.

TDRobson, High Alumina Cements and Concretes, John Wiley & Sons, NY, 1962, 1226-7 reports that lithium salts have been proposed as high-titer cement accelerators. However, it was found that compositions containing alumina cement, gypsum and lithium salts as accelerators alone exhibited excessive drying shrinkage upon hardening. Additionally, compositions containing alumina cement and gypsum alone exhibited excessive wet expansion in the cured state.

U.S. Patent 2,339,163 discloses a composition for a protective cement coating, the calcium aluminate cement and an inorganic additive selected from the group of calcium chloride, calcium sulfate, magnesium sulfate, ferric sulfate, aluminum sulfate and carbonates of alkali metals to accelerate setting and casein to limit water evaporation to prevent rapid drying and shrinkage. It is mentioned that the material gives a coating which does not break after setting and hardening, apparently due to the reduced drying shrinkage.

U.S. Patent Nos. 4,045,237 and 4,157,263 disclose cementitious compositions having a high degree of impermeability to liquids and steam and reduced long-term shrinkage, consisting of a particular blend of Portland cement, a calcined gypsum, and high-tonnage cement. Alternatively, the composition may consist of a particular mixture of high-toned cement and calcined gypsum.

Attempts have been made so far to provide cement compositions that meet the requirements of the construction industry, in particular with regard to the protection, waterproofing and repair of concrete structures. For such compositions, non-flammability, nontoxicity and setting within a relatively short period of time to a hard mass or coating of sufficient strength, rub resistance and corrosion resistance is desired. Products made from the composition should also have impermeability to flowable materials, especially liquids. At the same time, products made from the composition should not show excessive changes in the hardened volume even under wet or dry conditions. For use, these types of cement compositions must also have good bonding properties to wet or dry surfaces, early strength as well as long term strength and good processability. They should also be able to withstand frost and thaw, as well as the action of salts, solvents and other corrosive substances.

Although there are cement compositions having one or more of the desired properties listed, previous attempts to combine all of the listed properties in a single composition have met with limited success. Many mixed cement compositions show wet expansion. Other compositions containing accelerators to reduce setting time show excessive drying shrinkage. Thus, prior attempts to provide cementitious compositions of practical value to the construction industry have generally been specific or have exhibited particular properties disregarding or, in some cases, detrimental to other desirable properties.

The invention is based on the object to create a cement composition which is capable of mixing with water, rapidly becoming a hard mass of high compressive strength, without causing significant shrinkage during setting and which can be provided with reduced volume changes in wet and dry conditions in the hardened state, nevertheless, they have a high degree of impermeability to flowable materials and resistance to scrubbing, Has erosion and chemicals, as well as similar properties, as desired for a composition for practical and useful use in the construction industry. This is achieved according to the invention in that the cement composition 60 to 90 parts by weight of alumina cement, 10 to 40 parts by weight of gypsum, 0.1 to 25 parts by weight Portland cement or an expansion cement as inhibitor and 0.01 to 0.5 parts by weight of a lithium salt. In addition to the aforementioned essential ingredients of the cement composition of the present invention, other ingredients such as viscosity control, surfactants, retarders, accelerators, gas generating or gas releasing agents, plasticizers, blowing agents, water retention aids, fillers and additives may be employed. The lithium salt inhibits wet expansion.

The composition of the present invention, in admixture with water, binds to a hard mass within a relatively short period of time without excessive changes in the set volume in wet or dry conditions

The lithium salt which inhibits wet expansion may be contained in an amount effective in the range of 0.01 to 0.5% by weight based on alumina cement and gypsum, preferably 0.1 to 0.3% by weight, be added. The drying shrinkage inhibitor after hardening, the Portland cement, is dissolved in

-3Nr. 390 786 an amount of 0.1 to 25 wt .-%, based on the alumina cement and gypsum, and preferably in an amount of 1 to 20 wt .-% added.

The above and other objects, features and advantages of the invention will become more apparent from the following description of the details thereof and from the claims.

Description of preferred embodiments

The invention is illustrated by the following examples which demonstrate that, surprisingly, the addition of lithium salts to cement compositions containing alumina cement, gypsum and Portland cement as an inhibitor of drying shrinkage after cure inhibits the wet expansion of the compositions in the cured state.

In the examples, the ingredients were mixed as dry powders and then mixed with tap water to give a mass of fluffy ready to use condition. In general, the ratio of ingredients to sand or aggregates was 1: 1 or 1: 2. The homogenous mixture was then placed in 10 (25.4 mm) rod steel molds according to the standard description for Apparatus for Use in Measurement of Length Change of Hardened Cement Paste, Mortar and Concrete ASTM C 490. The molds were coated with a resin-based release agent and a thin polyethylene film well lined to facilitate the removal of the delicate hardened specimens. The specimens were demoulded as soon as possible after being cured without causing damage to them, usually 1/2 to 2 hours after the final bonding.

First, immediately after demolding, measurements of changes in length of the specimens were made to best determine the actual change in length in the set state. Two coupons of each mixture were tested; One specimen was used to determine the change in length in the wet and the second specimen was used to determine the change in length in the dry The wet test specimens were completely submerged in water for the duration of the test, whereas the dry test specimens allowed to cure in air for the duration of the test. The 10 test pieces were measured down to ten-thousandths of an inch using a length-change comparator according to the requirements of the aforementioned ASTM C 490 specification. The measurement of length changes was made essentially in accordance with the Standard Test Method for Length Change of Hardened Cement Mortar and Concrete ASTM C-157. All length change results were obtained from or based on a mixture of 1 part cement and 1 part sand , The rub resistance was determined on a coating of the mixture which had been applied to a cement block.

The following examples illustrate the results achievable in carrying out the invention:

Example 1:

A comparative coupon was prepared as previously described using 80% by weight of alumina cement (Lumnite) and 20% by weight of gypsum (Densite K-5). After aging for 4 days, the percent elongation change in the cured state was measured a wet expansion of 0.321% and a drying shrinkage of 0.012% could be found. The abrasion resistance was 4, measured on a scale of 1 to 10, with 10 being the highest hardness.

Example 2:

The composition of Example 1 and the method of Example 1 were used except that the composition was 0.2% by weight, based on alumina cement and gypsum (which will hereinafter be the base, unless otherwise specified) of an inhibitor for wet expansion, including lithium carbonate. The percentage change in length in the cured state after 4 days was 0.065% wet expansion and 0.179% drying shrinkage, with a scuff resistance of 6.

Example 3:

The composition of and the procedure of Example 1 were used except that Portland Type III cement was added as an inhibitor of the drying shrinkage in an amount of 19% by weight based on the combined amount of alumina cement and gypsum. The percent change in length was measured after 2 hours because the wet expansion was such that the specimen broke. After the period of 2 hours, the wet expansion was 1.33%. There was no drying shrinkage but a drying expansion of 0.84%. The abrasion resistance was 7.

Example 4:

The composition of and the method of Example 2 were used with addition of Portland cement, type ΙΠ, as an inhibitor of drying shrinkage, and the like. in an amount of 10% by weight. After 4 days, the percent change in length was measured with 0.188% wet expansion and 0.100% drying shrinkage. The abrasion resistance was 10.

From the foregoing Examples 1 to 4, it is found that lithium salts are effective inhibitors of the

-4Nr. 390 786

Wet expansion in formulations of alumina cement and gypsum, while compositions containing alumina cement, gypsum and lithium salts and, as further additive, portland cement as an inhibitor of drying shrinkage, give compositions which have favorable elongational properties. Besides the lithium carbonate, other lithium salts are advantageous as inhibitors of wet expansion. Examples of such lithium salts which have been found to be satisfactory are lithium citrate, lithium hydroxide and lithium acetate.

Example 5:

The composition and procedure of Example 4 were used, but with the change that Portland cement was now used in an amount of 11% and a post curing hardener. After 30 days, the percentage change in length in the dry state was measured and was zero. The abrasion resistance was 10.

Example 5 shows that by selecting the formulation of the composition, it is useful to control the exact length to achieve exactly zero shrinkage or expansion. In addition, it has been found that the cement composition of the present invention can be varied by selecting the inhibitors or the cement combinations so that the precise change in length can be controlled in a particular environment such as wet, dry or alternating wet and dry.

Example 6:

To the composition of Example 5 was added 1% by weight of surfactant (Lomar D) and 0.1% by weight of anhydrous (citric acid in powder form and the ingredients were mixed to a first dry mixture. This cement mixture was treated with an abrasive scuff additive Ratio of 3: 7 mixed. The resulting mixture was then mixed with water to give a self-regulating consistency and then applied to a concrete block. The composition broke within 20 minutes and developed a compressive strength of about 422 bar (6,000 psi) after 24 hours, tested according to ASTM C 109. The composition showed very high binding properties after 24 h and was very hard and abrasion resistant. In addition, the composition showed high resistance to frost and thawing, as well as resistance to corrosive substances. The composition coagulated without any appreciable shrinkage, surface fractures or dusting, and no need for a post-treatment moisture or aftertreatment agent. In addition, the surface of the coated block was exposed to a fine jet of water at a pressure of about 1.75 bar for one week, without appreciable erosion.

Example 7:

Using the procedure previously described for Examples 1-4, another comparative coupon was prepared from a composition containing 80% by weight, based on alumina cement and gypsum, of Portland Cement, Type ΠΙ, as an inhibitor of drying shrinkage. The percent change in length was measured after 2 days and 0.383% wet expansion was found without any drying shrinkage or drying expansion.

Example 8:

To the composition described in Example 7 was added 0.2% by weight of sodium carbonate, a known accelerator, to determine its effectiveness as a wet expansion inhibitor. After 2 days, the percent change in length was 0.366% wet expansion and 0.026% dry expansion. Thus, the dry expansion was higher than that found in the Comparative Sample of Example 7, whereas the wet expansion was approximately as large as that of the Comparative Sample and unacceptable.

Example 9:

To the composition of Example 7, 0.2% by weight of aluminum sulfate, a known accelerator, was added to determine its effectiveness as a wet expansion inhibitor. After 2 days, the percent change in length was 0.415% wet expansion and 0.017% dry expansion, indicating that, like sodium carbonate, aluminum sulfate was not effective in satisfactorily inhibiting wet expansion in alumina cement, gypsum and Portland cement compositions.

Example 10:

To the composition of Example 7, 0.2% by weight of lithium citrate was added to determine its effectiveness as a wet expansion inhibitor. After 2 days, the percent change in length was only 0.186% wet expansion, less than half that of the control coupon, and 0.006% drying shrinkage.

This indicates that lithium salts in such cementitious compositions are clearly effective as wet-expansion inhibitors. The lithium salts exert no appreciable adverse effect on the

-5Nr. 390 786

Impermeability to flowable materials of the cementitious compositions, so that this system is one having excellent waterproofing properties.

For the inventive cementitious compositions containing alumina cement, gypsum and inhibitors for wet and dry volume change, it is preferred to use 60 to 90% alumina cement and 10 to 40% gypsum. In general, the drying shrinkage inhibitor upon hardening, the Portland cement, the total weight of alumina cement and gypsum may be added in an amount of from 0.1 to 25%, most preferably, and preferably from 1 to 20%. In general, the lithium salts should be added in an amount of 0.01 to 0.5 wt .-%, based on alumina cement and gypsum, advantageously, and preferably from 0.1 to 0.3%.

In addition to the aforementioned essential ingredients of the cementitious compositions of the present invention, other additives for modifying the properties may generally be added without loss of the benefits of inhibiting wet expansion obtained, on the other hand being compatible with the essential ingredients. Such other additives include viscosity control agents, expansion agents, surfactants, retarders, accelerators, gas generating or gas releasing agents, fly ash, fillers, blowing agents, water retention aids, and aggregates to achieve targeted improvements of particular properties. Other additives normally used in the industry for cement systems may also be used, provided that they are not incompatible with the desired results described herein.

The lithium salts can be mixed with the other ingredients in the dry state or added at the time of addition of water or added to the water or added after the addition of water. It does not matter when the materials concerned are added to the mixture, as long as only all are incorporated to achieve a homogeneous mixture in the slurry. It will be understood by those skilled in the art that known methods of making cement compositions can also be used to prepare the compositions of the present invention, including mixing methods prior to carrying out the actual process steps, such as firing, grinding or mixing the final ingredients, provided that the stages are not detrimental to any of the components.