Cement composition for three-dimensional modeling

Abstract

The purpose is to provide a cement composition for three-dimensional modeling that can reduce shrinkage when cured. A cement composition for three-dimensional modeling contains cement, aggregate, a thickener, and a shrinkage reducing agent. The shrinkage reducing agent is preferably a polyether-based or alkylene oxide-based shrinkage reducing agent. The shrinkage reducing agent is preferably contained in an amount of 0.5-7 mass parts per 100 mass parts of cement.

Description

Cement composition for three-dimensional modeling

[0001] The present invention relates to a cement composition for three-dimensional modeling, which is mainly used in the fields of civil engineering, construction and factory products.

[0002] In recent years, a new three-dimensional modeling technology has been proposed for producing large-scale objects such as construction components using cement materials such as mortar and concrete. Using this technology, automated construction machines are already being used in Europe, the United States, and China to manufacture large-scale objects on the scale of detached houses.

[0003] For example, Patent Document 1 discloses a three-dimensional modeling technique using cement materials, in which three-dimensional data created by a computer is cut at a predetermined thickness to create two-dimensional slice data, mortar mixed with an accelerator is sprayed onto a bed (table) while controlling the movement of a spray nozzle in the vertical and horizontal directions based on the two-dimensional slice data, and the sprayed mortar is allowed to self-harden to form a solidified layer in the shape based on the two-dimensional slice data, and this solidified layer formation process is repeated to sequentially stack the layers vertically to form a model. Patent Document 2 describes a material for creating molds for producing castings using a 3D printer, and discloses a material consisting of cement, sand, and a water-soluble silicate as an accelerator.

[0004] Japanese Patent Application Laid-Open No. 10-235623 U.S. Patent No. 8,211,226

[0005] Hardened cement products made from cement materials are at risk of cracking due to a decrease in volume as the cement dries. The occurrence of cracks not only impairs the aesthetic appearance but also has the risk of adversely affecting the stability, waterproofing, and watertightness of the structure. Cement compositions for three-dimensional modeling are also required to reduce the occurrence of cracks.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cement composition for three-dimensional modeling that can reduce shrinkage when hardened.

[0007] After extensive research to solve the above problems, the present inventors have conceived the following invention and found that it can solve the above problems. Specifically, the present invention is as follows: [1] A cement composition for 3D printing containing cement, aggregate, a thickener, and a shrinkage-reducing agent. [2] The cement composition for 3D printing according to [1], wherein the shrinkage-reducing agent is a polyether-based or alkylene oxide-based shrinkage-reducing agent. [3] The cement composition for 3D printing according to [1] or [2], wherein the thickener includes at least one of an organic thickener and an inorganic thickener. [4] The cement composition for 3D printing according to any one of [1] to [3], wherein the shrinkage-reducing agent is contained in an amount of 0.5 to 7 parts by mass per 100 parts by mass of the cement. [5] The cement composition for 3D printing according to any one of [1] to [4], wherein the thickener is contained in an amount of 0.03 to 1.0 part by mass per 100 parts by mass of the cement. [6] The cement composition for 3D printing according to any one of [1] to [5], wherein the thickener is a natural polysaccharide-based thickener. [7] The cement composition for 3D printing according to any one of [1] to [6], further containing a hardening agent. [8] The cement composition for 3D printing according to any one of [1] to [7], further containing aluminum sulfate.

[0008] According to the present invention, it is possible to provide a cement composition for three-dimensional modeling that can reduce shrinkage when hardened.

[0009] The cement composition for 3D modeling of the present invention will be described in detail below, but the present invention is not limited to this embodiment. In this specification, "%" and "parts" are based on mass unless otherwise specified. Furthermore, a numerical range defined using the symbol "to" includes the numerical values ​​at both ends (upper and lower limits) of "to". Furthermore, in this invention, "3D modeling" refers to a technology for producing a molded body of any shape by directly additively manufacturing a cross-sectional shape based on three-dimensional data without using dedicated tools such as formwork. This is sometimes called "additive manufacturing" or "rapid prototyping". Furthermore, in this invention, the cement composition is a general term for cement paste, mortar, and concrete.

[0010] [Cement Composition for Three-Dimensional Forming] The cement composition for three-dimensional form forming of the present embodiment contains cement, aggregate, a thickener, and a shrinkage-reducing agent.

[0011] (Cement) The cement used in the present invention includes various Portland cements such as normal, early strength, ultra-early strength, low heat, and medium heat, various mixed cements obtained by mixing these Portland cements with blast furnace slag, fly ash, or silica, and cements having a Blaine specific surface area of ​​2000 cm ２ Examples include filler cements containing limestone powder or slowly cooled blast furnace slag powder with a specific surface area of ​​3000 cm or more, environmentally friendly cements (ecocement) made from municipal waste incineration ash or sewage sludge incineration ash, and alumina cements used for refractories. One or more of these can be used. The Blaine specific surface area of ​​the cement is 3000 cm. ２ / g or more is preferred.

[0012] (Aggregate) The aggregate used in the present invention is not particularly limited, and commercially available aggregates derived from natural limestone, aggregates derived from siliceous materials, and heavy aggregates with a specific gravity of more than 3.0 can be used. Furthermore, for the purpose of improving self-supporting properties, a portion of the aggregate used can be replaced with balloon-type aggregate. Balloon-type aggregates are generally called lightweight aggregates, and examples include fly ash balloons, shirasu balloons, and balloons obtained by firing and foaming obsidian in a kiln. The specific gravity of the lightweight aggregate is preferably 2.0 or less, more preferably 1.8 or less, and most preferably 0.3 to 1.0.

[0013] The maximum particle size of the aggregate (including balloon-type aggregate) is preferably 10 mm or less, more preferably 5 mm or less, taking pumpability into consideration. The amount of aggregate used is preferably 50 to 300 parts by mass, more preferably 100 to 200 parts by mass, per 100 parts by mass of cement. By setting the amount used within the above range, self-supporting properties can be ensured and pumping can be performed smoothly. When balloon-type aggregate is used, the amount used is preferably 25 parts by mass or less, more preferably 1 to 25 parts by mass, and even more preferably 3 to 15 parts by mass, per 100 parts by mass of aggregate. By setting the amount used within the above range, self-supporting properties can be ensured, strength development can be improved, and pumping can be performed smoothly.

[0014] (Thickener) The thickener used in the present invention can be a commercially available thickener commonly used in cement compositions. Both organic and inorganic thickeners can be used, and it is preferable to use at least one of them. Examples of organic thickeners include acrylic thickeners, starch thickeners, vinyl thickeners, cellulose thickeners, glycol thickeners, amino acid thickeners, and natural polysaccharide thickeners produced by microorganisms. In particular, natural polysaccharide thickeners and / or cellulose thickeners with a viscosity of 30,000 mPa·s or more in a 2% by weight aqueous solution are preferred because of their high thixotropic properties. Here, the viscosity of the 2% by weight aqueous solution is measured at 20°C using a B-type viscometer at 10 rpm. Among the natural polysaccharide thickeners, diutan gum is more preferred. Diutan gum is a natural polymeric polysaccharide whose constituent units are, for example, two glucose units, one glucuronic acid unit, and three rhamnose units. Examples of cellulose-based thickeners include carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and cellulose nanofiber. Examples of inorganic thickeners include gypsum, bentonite, kaolinite, sepiolite, talc, and silica fume. Gypsum is preferred, and gypsum hemihydrate is particularly preferred.

[0015] The amount of thickener used is preferably 0.03 to 1.0 part by mass, more preferably 0.05 to 0.5 part by mass, per 100 parts by mass of cement. By using an amount within this range, sufficient thixotropy can be imparted, and good pumpability and strength development can be achieved.

[0016] (Shrinkage Reducing Agent) The shrinkage reducing agent used in the present invention may be a polyether-based shrinkage reducing agent or an alkylene oxide-based shrinkage reducing agent. Examples of polyether-based shrinkage reducing agents include polyoxyalkylene-based shrinkage reducing agents. Examples of alkylene oxide-based shrinkage reducing agents include lower alcohol alkylene oxide adduct-based shrinkage reducing agents and low-molecular-weight alkylene oxide copolymer-based shrinkage reducing agents. Other examples of shrinkage reducing agents include alcohol-based shrinkage reducing agents, glycol ether / aminoalcohol derivative-based shrinkage reducing agents, and shrinkage reducing agents consisting of a mixture of polyoxyalkylene alcohol ether and inorganic filler. Among these, polyoxyalkylene-based shrinkage reducing agents are preferred from the viewpoint of initial and long-term shrinkage reduction. The addition of a shrinkage reducing agent can improve fluidity. By improving fluidity, the pumpability during pumping through a pumping pipe can be improved. The content of the shrinkage-reducing agent is preferably 0.5 to 7 parts by mass, more preferably 0.7 to 5 parts by mass, and even more preferably 0.9 to 3 parts by mass, per 100 parts by mass of cement. By setting the content of the shrinkage-reducing agent within the above range, it is possible to obtain the effect of suppressing shrinkage cracking. In addition, it is possible to improve the fluidity of the cement composition for three-dimensional modeling, thereby improving the pumpability. Furthermore, by setting the content of the shrinkage-reducing agent to the above upper limit or less, it is possible to prevent a decrease in the fluidity of the cement composition and also to prevent a decrease in the strength of the hardened body produced.

[0017] (Hardening agent) The cement composition for three-dimensional modeling of the present invention preferably contains a hardening agent. As the hardening agent, amorphous calcium aluminosilicate (hereinafter referred to as "calcium aluminosilicate") is preferably used. Calcium aluminosilicate is a raw material containing CaO, Al ２ O ３ Raw material, SiO ２ It can be obtained by subjecting a mixture of raw materials to heat treatment such as firing in a kiln or melting in an electric furnace. Si in calcium aluminosilicate is converted into silicon dioxide (SiO ２The Si content is preferably 10 to 25 mass % in terms of Si content, and the composition is preferably amorphous. By making the composition amorphous, the reactivity can be increased. Furthermore, by setting the Si content within the above range, an appropriate curing speed can be obtained and the self-supporting property can be improved.

[0018] Calcium aluminosilicate is CaO and Al converted into oxides. ２ O ３ Molar ratio of CaO / Al ２ O ３ is preferably 1.5 to 3.5, and more preferably 1.7 to 2.0. As other components, alkali metals such as sodium, potassium, and lithium may be partially dissolved. The particle size of calcium aluminosilicate is 3000 cm in Blaine value. ２ If the Blaine value is too small, the strength development may decrease.

[0019] It is preferable to use gypsum in combination with calcium aluminosilicate as the rapid hardening material. By using gypsum and calcium aluminosilicate in combination, strength can be improved. Types of gypsum include anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum, and gypsum produced as a by-product in factories or naturally occurring gypsum can be used. Of these, the use of anhydrous gypsum is preferred in terms of strength development.

[0020] The particle size of the gypsum is 3000 cm in Blaine value. ２ / g or more is preferred. If the Blaine value is too small, the effect of improving strength development may not be obtained. The ratio of gypsum to the calcium aluminosilicate is preferably 50 to 250 parts by mass, more preferably 100 to 200 parts by mass, per 100 parts by mass of the calcium aluminosilicate. By setting the ratio of gypsum within the above range, the strength of the hardened body (laminate) produced can be improved.

[0021] The amount of the hardening agent used is preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, per 100 parts by mass of cement. By setting the amount of the hardening agent used within the above range, it is possible to ensure a sufficient working life and improve strength development.

[0022] (Aluminum Sulfate) The cement composition for three-dimensional modeling of the present invention preferably contains aluminum sulfate. Aluminum sulfate mainly imparts the effect of accelerating the setting rate to the cement composition. Aluminum sulfate is preferably added as an aqueous aluminum sulfate solution, and the concentration of aluminum sulfate in the aqueous aluminum sulfate solution is preferably 20 to 35%, more preferably 23 to 30%, and even more preferably 25 to 28%. When the concentration of aluminum sulfate is within the above range, the viscosity of the cement composition can be prevented from increasing, thereby improving pumpability.

[0023] The amount of aluminum sulfate used is preferably 0.5 to 4.0 parts by mass, more preferably 0.7 to 3.5 parts by mass, and even more preferably 1 to 3 parts by mass, per 100 parts by mass of cement. When the amount of aluminum sulfate used is equal to or greater than the above lower limit, excellent quick-setting properties are obtained, and when the amount of aluminum sulfate used is equal to or less than the above upper limit, good long-term strength development is obtained.

[0024] (Dispersant) The cement composition for three-dimensional modeling of the present invention preferably contains a dispersant. The dispersant preferably comprises a lignin sulfonic acid-based dispersant (R) and a melamine sulfonic acid-based dispersant (M) in a mass ratio of R:M = 100:30-400. The use of such a dispersant ensures the fluidity of the cement composition after mixing with water and improves its thixotropy. The ratio R:M is more preferably 100:50-300. By setting the mass ratio of the lignin sulfonic acid-based dispersant (R) to the melamine sulfonic acid-based dispersant (M) at or above the lower limit, initial fluidity can be achieved and changes in fluidity over time can be suppressed, thereby enabling stable pumping of the cement composition. Furthermore, by setting the mass ratio of the lignin sulfonic acid-based dispersant (R) to the melamine sulfonic acid-based dispersant (M) at or below the upper limit, setting delay can be prevented, preventing excessive changes in fluidity over time and ensuring self-sustaining properties after pumping. The amount of dispersant used is preferably 0.2 to 3 parts by mass, more preferably 0.5 to 2 parts by mass, per 100 parts by mass of cement. By using an amount of dispersant within the above range, sufficient fluidity can be obtained and delay in setting can be prevented, so that the change in fluidity over time does not become too small and self-sustaining properties can be ensured.

[0025] (Short Fibers) The cement composition for three-dimensional modeling of the present invention preferably contains short fibers. Short fibers generally available commercially for cement admixture can be used. Examples include vinylon fibers, acrylic fibers, nylon fibers, steel fibers, glass fibers, polypropylene fibers, polyethylene fibers, polyester fibers, and basalt fibers. One or more of these fibers can be used in combination. Among these, vinylon fibers, which have a wide variety of fiber diameters and lengths, and nylon fibers, which have excellent dispersibility, are preferred.

[0026] Considering that the short fibers are premixed in advance, the average fiber length is preferably in the range of 5 to 15 mm. The average fiber diameter of the short fibers is preferably 20 to 250 μm, more preferably 100 to 250 μm. Because fibers with too small an average diameter may be difficult to obtain, the average fiber diameter is preferably equal to or greater than the above-mentioned lower limit. Furthermore, by setting the average fiber diameter equal to or less than the above-mentioned upper limit, the pumpability of the cement composition can be improved and an increase in the temperature of the cement composition can be prevented, thereby preventing a shortened setting time and improving moldability. By setting the average fiber diameter of the short fibers to 20 μm or more, particularly 100 μm or more, the frictional heat generated when pumping the cement composition increases, which increases the temperature of the cement composition discharged from the nozzle tip and appropriately shortens the setting time, thereby achieving continuous, higher lamination.

[0027] Short fibers in the form of bundled fibers, in which monofilaments are bundled together with a binder, are preferred over monofilament fibers, as this allows for a larger number of fibers to be incorporated. The number of short fibers per gram is preferably 5,000 or more. If the number per gram is too low, the reinforcing and initial crack suppression effects of the short fibers may not be fully realized. The number of fibers per gram of short fibers is calculated using the following formula, where fineness (dtex) is the weight (g) per 10,000 m of monofilament: Number of fibers (fibers / g) = [1 / (fineness / 10,000 (m))] / average fiber length (m / fiber). The amount of short fibers used is preferably 0.1 to 1.0 parts by mass, more preferably 0.2 to 0.8 parts by mass, per 100 parts by mass of cement and aggregate combined. By using an amount within the above range, the hardened body (laminate) produced can be reinforced and pumping can be performed smoothly.

[0028] (Set Regulator) The cement composition for three-dimensional modeling of the present invention preferably contains a set regulator. The set regulator may be any agent that delays the setting of the cement composition. Examples of set regulators that can be used include one or more selected from the group consisting of organic acids such as citric acid, gluconic acid, tartaric acid, malic acid, etc., or their salts; boric acid, borates such as sodium borate, phosphates, inorganic salts such as alkali metal carbonates and alkali metal bicarbonates; and sugars. From the viewpoint of adjusting the setting time and developing early strength, it is more preferable that the set regulator contains one or more selected from the group consisting of citric acid, citrates, tartaric acid, tartrates, and alkali metal carbonates. It is particularly preferable to use an organic acid in combination with an alkali metal carbonate, and when used in combination, it is preferable to use potassium carbonate as the alkali metal carbonate.

[0029] The amount of set regulator used is preferably 0.05 to 1.2 parts by mass, more preferably 0.07 to 1.0 parts by mass, per 100 parts by mass of cement. By using an amount equal to or greater than the lower limit, a usable time can be ensured, taking into account the mixing time and pumping time. Furthermore, by using an amount equal to or less than the upper limit, the hardening time can be prevented from becoming too long, thereby ensuring self-supporting properties.

[0030] (Other Components) In the present invention, various additives such as antifoaming agents, anticorrosive agents, antifreeze agents, inorganic minerals such as bentonite and sepiolite, anion exchangers such as hydrotalcite, polymer emulsions, etc. can be added within the range that does not impair application or the performance of the hardened body. Furthermore, it is also possible to use inorganic powders with hydration activity such as blast furnace slag, silica fume, and fly ash, apart from those pre-mixed with the cement.

[0031] (Water) The cement composition of the present invention contains water, and is mixed with water to prepare a wet material, which is then used for three-dimensional modeling. The amount of water used is preferably 30 to 45 parts by mass, more preferably 34 to 41 parts by mass, per 100 parts by mass of cement. By using water in the above range, mixing can be easily performed and a decrease in self-supporting ability can be prevented.

[0032] (3D Modeling Method) Next, a 3D modeling method using the cement composition of the present invention will be described. The 3D modeling method can be classified into a mixing step of the cement composition, a pumping step of the mixed cement composition, and a 3D modeling step using controlled nozzle movement.

[0033] The mixing method used in the mixing step of the cement composition is not particularly limited, and the mixing can be performed using a commercially available mixer, such as a pan mixer, a forced twin-screw mixer, or a continuous mixing mixer pump that combines a mixer and a pressure pump (a rotary positive displacement single-shaft eccentric screw pump).

[0034] The pump used in the pumping process of the cement composition is not particularly limited as long as it can pump the cement composition without degrading its quality. However, a rotary positive displacement uniaxial eccentric screw pump is preferred. Rotary positive displacement uniaxial eccentric screw pumps, also known as mono pumps or snake pumps, are capable of constant pumping without pulsation compared to squeeze pumps, and the discharge rate can be adjusted by controlling the motor rotation speed. Furthermore, due to their structure, rotary positive displacement uniaxial eccentric screw pumps are considered to be more likely to increase the temperature of the pumped cement composition, which allows the cement composition's hardening reaction to proceed in a short time, improving self-supporting stability and enabling a large continuous stack height. Specifically, rotary positive displacement uniaxial eccentric screw pumps have a rotor corresponding to the male thread and a stator corresponding to the female thread. When the rotor is inserted into the stator, a sealed space called a cavity (e.g., the space between the rotor and the stator) is formed in the gap. As the rotor rotates within the stator, a strong suction force is generated, and the cavity moves toward the discharge side, thereby continuously transporting materials. During transfer, for example, the rotor rotates eccentrically around the central axis of the stator while revolving around it. It is believed that as the material in the first cavity moves to the previous (discharge) cavity due to suction, it is heated by frictional resistance with the stator surface. By utilizing this heating phenomenon, it is possible to achieve a three-dimensional object with superior self-sustaining stability while ensuring usable life. For example, a rotary positive displacement uniaxial eccentric screw pump is exemplified in paragraphs 0063-0064 of International Publication No. 2014 / 142239. The pressure-feeding piping can be a flexible hose with a pressure resistance of 2-4 MPa or a partial combination of metal piping. Depending on the desired discharge rate, the inner diameter of the piping is preferably 20-50 mm. The length of the pressure-feeding piping is not particularly limited, but a length of 20 m or less is preferable considering pumpability.

[0035] The discharge section (the tip of the pressure pipe) from which the cement composition is discharged is equipped with a nozzle. The diameter of the discharge port is not particularly limited, but may be set appropriately depending on the diameter of the aggregate used and the stacking width. For example, if the aggregate diameter is 5 mm or less and the stacking width is 50 mm or less, the diameter of the discharge port is preferably 8 to 15 mm. The shape of the discharge port is not particularly limited, but examples include circular, elliptical, rectangular, cross, and star shapes, and a brim may be provided around the discharge port to impart smoothness to the surface of the discharged cement composition. In these devices, the discharge port is provided perpendicular to the bed, but in some cases, the discharge port may be provided horizontally.

[0036] Control of the horizontal and vertical nozzle movement in the three-dimensional modeling process is preferably performed by, for example, fixing the nozzle to a robot arm or a portal plotter and controlling it by computer. For example, a method is possible in which three-dimensional data created by a computer is cut at a predetermined thickness to create two-dimensional slice data, and the horizontal movement of the spray nozzle is controlled based on the two-dimensional slice data while the cement composition is ejected from the nozzle onto the bed and the nozzle is moved vertically, repeatedly layering the layers sequentially to form the model. The nozzle movement speed is not particularly limited and can be changed depending on the layer width. When the amount of cement composition ejected is constant, slowing the speed increases the layer width, while increasing the speed decreases the layer width.

[0037] The cement composition used in three-dimensional modeling is required to have good fluidity because it is pumped through a pumping pipe and layered while being discharged from a nozzle. In the cement composition of this embodiment, the inclusion of a shrinkage-reducing agent improves the fluidity, thereby improving the pumpability of the pumping pipe. Furthermore, if the improved fluidity reduces the layerability when discharged from a nozzle, a two-component system can be used in which the rapid-hardening material and the other cement compositions are pumped through different pipes and mixed before being discharged from the nozzle. The two-component system can improve the pumpability of the cement composition, and by mixing the rapid-hardening material with the cement composition before being discharged from the nozzle, sagging of the cement composition discharged from the nozzle can be reduced, thereby improving layerability. The above-mentioned aluminum sulfate aqueous solution can be used as the rapid-hardening material.

[0038] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0039] (Materials used) Cement: Ordinary Portland cement (manufactured by Denka Co., Ltd., Blaine specific surface area 3400 cm ２ / g) Aggregate: lime sand (manufactured by Denka Co., Ltd., maximum particle size 1.2 mm, specific gravity 2.71) Calcium aluminosilicate: commercially available special grade reagent SiO ２ , CaCO ３ , Al ２ O ３ The above were mixed in a predetermined ratio, heated and melted at about 2000°C using a high-frequency furnace, quenched in water, and pulverized to prepare a powder (amorphous, SiO ２ Content 15.2%, CaO / Al ２ O ３ Molar ratio 1.85, Blaine specific surface area 5800 cm ２ / g) Thickener: Diutan gum (manufactured by Sansho Co., Ltd., trade name "Kercovis DG") Dispersant: Melamine sulfonic acid-based dispersant (M) (manufactured by Sika Japan Co., Ltd., trade name "Sikament") Dispersant: Lignin sulfonic acid-based dispersant (R) (manufactured by Nippon Paper Industries Co., Ltd., trade name "Vanilex N") Short fiber: Vinylon fiber (average fiber length 12 mm, average fiber diameter 50 μm, number of fibers per 1 g 55,500) Setting modifier: Reagent, citric acid (anhydrous) 25%; potassium carbonate 75% Aluminum sulfate: Reagent, aluminum sulfate was diluted with water to make a 27% aqueous aluminum sulfate solution. Gypsum: Natural anhydrous gypsum pulverized product (Blaine specific surface area 5000 cm ２ / g) Shrinkage reducing agent: Polyoxyalkylene powder shrinkage reducing agent (manufactured by NOF Corporation, product name "Sydox") Shrinkage reducing agent: Polyoxyalkylene powder shrinkage reducing agent (manufactured by ADEKA Corporation, product name "Semsurf")

[0040] [Experimental Example 1] (Production Method) A cement material was prepared according to the blending ratio shown in Table 1. The dispersant used was a mixture of a lignin sulfonic acid-based dispersant (R) and a melamine sulfonic acid-based dispersant (M) in a mass ratio of R / M = 100 / 70. The hardening accelerator used was a mixture of 100 parts by mass of calcium aluminosilicate and 100 parts by mass of gypsum. Furthermore, a shrinkage-reducing agent was added to the prepared cement material in the blending ratio shown in Table 2 per 100 parts by mass of cement in the cement material, and the mixture was mixed in a pan mixer to prepare a cement composition for three-dimensional modeling.

[0041]

[0042] The length change rate of the prepared cement compositions for 3D modeling was measured using the following method. Free shrinkage strain was measured as the length change rate based on "JIS A 1129-3: Methods for Measuring Length Change in Mortar and Concrete - Part 3: Dial Gauge Method, Appendix A (Reference) Test Method for Free Shrinkage Strain Due to Drying of Mortar and Concrete." First, a 4 x 4 x 16 cm test specimen was molded, demolded 24 hours later, and the base length was measured. The time when the base length was measured was defined as day 0 of age. Next, after curing at 20°C and 60% RH to each age, the length was measured again and the length change rate was calculated. The results are shown in Table 2. Furthermore, the mini-slump of the prepared cement compositions for 3D modeling was measured. Mini-slump (MS) was measured in accordance with JIS A 1171. The measurement was performed immediately after mixing. The results are shown in Table 2. From the viewpoint of achieving both pumpability and lamination properties of the cement composition for three-dimensional modeling, the mini-slump is preferably 35 mm to 90 mm, and more preferably 50 mm to 85 mm.

[0043] As shown in Table 2, Tests Nos. 1-2 to 1-8 (Examples), which contained a shrinkage-reducing agent, were able to reduce the shrinkage of the cured body produced compared to Test No. 1-1 (Comparative Example), which did not contain a shrinkage-reducing agent.

[0044] The cement composition for three-dimensional modeling of the present invention can suppress the rate of change in length of the hardened body produced, thereby preventing the occurrence of cracks, and is therefore suitable for use in the fields of construction and factory products.

Claims

1. A cement composition for three-dimensional modeling, comprising cement, aggregate, a thickener, and a shrinkage-reducing agent.

2. The cement composition for three-dimensional modeling according to claim 1, wherein the shrinkage reducing agent is a polyether-based or alkylene oxide-based shrinkage reducing agent.

3. The cement composition for three-dimensional modeling according to claim 1 or 2, wherein the thickener comprises at least one of an organic thickener and an inorganic thickener.

4. The cement composition for three-dimensional modeling according to claim 1 or 2, which contains 0.5 to 7 parts by mass of the shrinkage reducing agent per 100 parts by mass of the cement.

5. The cement composition for three-dimensional modeling according to claim 1 or 2, which contains 0.03 to 1.0 parts by mass of the thickener per 100 parts by mass of the cement.

6. The cement composition for three-dimensional modeling according to claim 3, wherein the thickener is a natural polysaccharide-based thickener.

7. The cement composition for three-dimensional modeling according to claim 1 or 2, further comprising a rapid hardening agent.

8. The cement composition for three-dimensional modeling according to claim 1 or 2, further comprising aluminum sulfate.

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