Cement composition for additive manufacturing equipment

Abstract

To provide a cement composition for use in an additive manufacturing device, capable of preventing an alkali-silica reaction, hardly allowing a crack to occur, and capable of yielding a molded article with excellent durability.SOLUTION: A cement composition for use in an additive manufacturing device, including cement and diatom earth, is characterized in that an amount of the diatom earth is 3 to 22 pts.mass relative to 100 pts.mass of the cement. The cement included in the cement composition for use in the additive manufacturing device, preferably is Portland cement. The cement composition for use in the additive manufacturing device, preferably includes a water-absorptive resin in an amount of 14 pts.mass or less relative to 100 pts.mass of the cement.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a cement composition for additive manufacturing equipment. [Background technology]

[0002] In recent years, a technique has become widespread in which a photocurable resin is extruded from a nozzle onto the top surface of a 3D printer's stacking bed to form an uncured layered body pre-designed as a two-dimensional shape. This uncured layered body is then cured by light irradiation to obtain a cured layered body. Subsequently, the same operation is repeated on top of this cured layered body to build and cure each layer one by one, ultimately obtaining a laminated object with a pre-designed desired three-dimensional shape (for example, one with an intricate three-dimensional shape). This technique is called additive manufacturing. Additive manufacturing technologies using various materials other than photocurable resins (e.g., cement) have also been developed. Patent Document 1 describes a diatomaceous earth-containing molding material for use with 3D printers and the like, characterized by a mixing ratio in which diatomaceous earth, aggregate, resin adhesive, and fluidity improver are present in that order of increasing proportion, and by adjusting the ratio of aggregate, resin adhesive, and fluidity improver to 31-43 vol% diatomaceous earth. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-175510 [Overview of the project] [Problems that the invention aims to solve]

[0004] When manufacturing molded objects from cement compositions using an extrusion-type additive manufacturing apparatus, the cement composition is typically extruded from a nozzle and built up layer by layer. The stacked molded objects are exposed to the outside air immediately after extrusion, and curing the molded objects is difficult. Therefore, compared to hardened bodies of general cement compositions, densification due to the formation of cement hydrate cannot be expected, and if the molded objects are used for a long period of time, there is a problem that the durability of the molded objects will decrease due to alkali-silica reaction, etc. The object of the present invention is to provide a cement composition for additive manufacturing equipment that suppresses alkali-silica reaction, is less prone to cracking, and can produce molded products with excellent durability. [Means for solving the problem]

[0005] As a result of diligent research to solve the above problems, the inventors of the present invention have found that the above objective can be achieved by a cement composition containing cement and diatomaceous earth, wherein the amount of diatomaceous earth is 3 to 22 parts by mass per 100 parts by mass of cement, and have completed the present invention. In other words, the present invention provides the following [1] to [5]. [1] A cement composition for additive manufacturing equipment comprising cement and diatomaceous earth, characterized in that the amount of diatomaceous earth per 100 parts by mass of cement is 3 to 22 parts by mass. [2] The cement composition for additive manufacturing apparatus according to [1], wherein the cement is Portland cement. [3] The cement composition for additive manufacturing apparatus according to [1] or [2], comprising 14 parts by mass or less of a water-absorbing resin per 100 parts by mass of the cement. [4] A cement composition for additive manufacturing apparatus according to any one of the above [1] to [3], further comprising water. [5] A method for manufacturing a molded object, comprising: a supply step of supplying the cement composition for additive manufacturing equipment described in [4] to an additive manufacturing equipment; and a lamination step of forming a molded object made of the cement composition for additive manufacturing equipment using the cement composition for additive manufacturing equipment in the additive manufacturing equipment.

[0006] According to the cement composition for additive manufacturing equipment of the present invention, alkali-silica reaction is suppressed, making it possible to manufacture molded products that are less prone to cracking and have excellent durability. [Modes for carrying out the invention]

[0007] The cement composition for additive manufacturing equipment of the present invention is a cement composition for additive manufacturing equipment comprising cement and diatomaceous earth, wherein the amount of diatomaceous earth is 3 to 22 parts by mass per 100 parts by mass of cement. In this specification, the term "cement composition for additive manufacturing apparatus" includes water-free compositions (e.g., premixes), water-containing compositions before hardening, and hardened bodies obtained by hardening water-containing compositions. As for the cement, any cement having physical properties suitable for use as a material for molded objects when molding objects using additive manufacturing equipment can be used. Examples of such cements include various Portland cements such as ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, white Portland cement, and ultra-rapid-hardening Portland cement, as well as ultra-fast-setting cement, blast furnace cement, fly ash cement, alumina cement, and eco-cement. These may be used individually or in combination of two or more types. Among these, Portland cement is preferred from the standpoint of ease of availability and other factors.

[0008] Diatomaceous earth is a material containing one or more (usually two or more) amorphous silica minerals selected from opal A, opal CT (a silica mineral with a more advanced crystallization than opal A, consisting of cristobalite and tridymite structures), and opal C (a silica mineral with a more advanced crystallization than opal A, consisting of cristobalite structures). Among these, diatomaceous earth containing opal CT is preferred. The proportion of opal CT in the diatomaceous earth is preferably 5% by mass or more, more preferably 10-50% by mass, even more preferably 15-40% by mass, and particularly preferably 20-30% by mass. If the above proportion is 5% by mass or more, it is possible to produce molded products in which the alkali-silica reaction is further suppressed. Furthermore, if the above proportion is 50% by mass or less, diatomaceous earth becomes easier to obtain. The amount of diatomaceous earth per 100 parts by mass of cement is 3 to 22 parts by mass, preferably 4 to 21 parts by mass, and more preferably 8 to 15 parts by mass. If the amount is less than 3 parts by mass, it is not possible to produce a molded object in which the alkali-silica reaction is suppressed. If the amount exceeds 22 parts by mass, the shrinkage of the molded object will increase, and the shape stability of the molded object will decrease.

[0009] The cement composition for additive manufacturing equipment may contain a water-absorbing resin from the viewpoint of further suppressing the shrinkage of the molded object and improving the freeze-thaw resistance (frost damage resistance) of the molded object. In the present invention, a superabsorbent resin is preferably used that has a maximum water absorption capacity of 50 g / g or more and a water absorption rate of 10 g / g·min or more (hereinafter, such a resin is also referred to as a "superabsorbent resin"). In this specification, "maximum water absorption" means the maximum amount of pure water (in grams) that a unit mass (1 g) of superabsorbent resin can absorb. "Water absorption rate" refers to the amount of pure water absorbed per minute (average value over 3 minutes; unit: g) when a unit mass (1 g) of water-absorbing resin is allowed to absorb pure water from the start of water absorption until 3 minutes have elapsed. The above maximum water absorption capacity is more preferably 100 g / g or more, even more preferably 200 g / g or more, and particularly preferably 300 g / g or more. The upper limit of the maximum water absorption mentioned above is not particularly limited, but is usually 600 g / g. The above water absorption rate is more preferably 20 g / g·min or more, even more preferably 25 g / g·min or more, and particularly preferably 30 g / g·min or more. The upper limit of the above water absorption rate is not particularly limited, but is usually 50 g / g·min.

[0010] An example of a superabsorbent polymer is a crosslinked polymer of an alkali metal salt of (meth)acrylic acid. Here, "(meth)acrylic acid" refers to acrylic acid, methacrylic acid, or a combination of acrylic acid and methacrylic acid. Examples of alkali metals include sodium and potassium. An example of a crosslinked polymer of an alkali metal salt of (meth)acrylic acid is obtained by polymerizing sodium acrylate, which is a monomer, to obtain sodium polyacrylate, and then crosslinking the sodium polyacrylates together (a crosslinked polyacrylate). Cross-linked sodium polyacrylate is known as a superabsorbent polymer (superabsorbent resin) found in disposable diapers. Cross-linked sodium polyacrylate is commercially available in powder form and can absorb up to approximately 400 times its own weight in pure water (approximately 200-300 times its own weight in tap water), and can absorb about 100 times its own weight in water within 3 minutes of the start of water absorption.

[0011] The amount of water-absorbing resin per 100 parts by mass of cement is preferably 14 parts by mass or less, more preferably 0.01 to 13 parts by mass, even more preferably 0.50 to 12 parts by mass, even more preferably 3 to 12 parts by mass, and particularly preferably 5 to 12 parts by mass. If the above amount is 14 parts by mass or less, the cost of materials can be reduced. In addition, the mixing of the cement composition for additive manufacturing equipment can be made easier. If the above amount is 0.01 parts by mass or more, the shrinkage of the molded object can be further suppressed, and the shape stability of the molded object can be improved. In addition, the freeze-thaw resistance (frost damage resistance) of the molded object can be improved, and the strength of the molded object can be increased.

[0012] When supplying the cement composition for additive manufacturing equipment of the present invention to additive manufacturing equipment, the cement composition for additive manufacturing equipment contains water, and the materials constituting the composition are supplied in the form of a mixed, unhardened paste. The water is not particularly limited, and examples thereof include tap water, recycled water defined in "JIS A 5308:2019 (Ready Mixed Concrete)", etc. The amount of water is determined such that the water-to-binder ratio is preferably 25 to 60%, more preferably 30 to 55%, and particularly preferably 40 to 50%. If the above ratio is 25% or more, the strength of the shaped object can be made larger. If the above ratio is 60% or less, the shaped object can be made less likely to deform during the process of laminating the cement composition for the additive manufacturing apparatus. The water-to-binder ratio is the mass ratio of water to binder (water / binder) expressed as a percentage (%). The binder means cement and inorganic powder other than cement.

[0013] The cement composition for the additive manufacturing apparatus preferably contains fine aggregate from the viewpoint of reducing the heat generation during the preparation of the cement composition for the additive manufacturing apparatus. The fine aggregate is not particularly limited, and examples thereof include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, and slag fine aggregate. These may be used alone or in combination of two or more. The amount of the fine aggregate relative to 100 parts by mass of the cement is preferably from 5 to l,000 parts by mass, more preferably from 20 to 800 parts by mass, still more preferably from 50 to 500 parts by mass, and particularly preferably from 100 to 300 parts by mass. If the above amount is 5 parts by mass or more, the effect of reducing the amount of heat generation during the preparation of the cement composition for the additive manufacturing apparatus becomes greater. If the amount is 1,000 parts by mass or less, the strength of the shaped object can be made larger.

[0014] The cement composition for the additive manufacturing apparatus can optionally contain other materials that can be blended. Examples of other materials include (i) inorganic powders such as silica fume, blast furnace slag fine powder, fly ash, limestone fine powder, and silica fine powder, (ii) coarse aggregate, and (iii)) admixtures such as cement dispersants, setting retarders, and setting accelerators. The amount of inorganic powder (or the total amount if there are two or more types of inorganic powder) is preferably 2 to 150 parts by mass, more preferably 3 to 120 parts by mass, per 100 parts by mass of cement, from the viewpoint of preventing blockage in the additive manufacturing apparatus. Examples of coarse aggregates include river gravel, land gravel, sea gravel, and crushed stone (for example, crushed stone made of limestone). When the composition of the present invention contains coarse aggregate, it is mainly used for forming relatively large construction structures with a simple structure. Examples of cement dispersants include water-reducing agents, AE water-reducing agents, high-performance water-reducing agents, and high-performance AE water-reducing agents.

[0015] The cement composition for additive manufacturing equipment, in accordance with "JIS A 1129-3:2010" (Method for measuring length change of mortar and concrete - Part 3: Dial gauge method), has a length change rate of preferably 700 × 10 when cured in air for up to 28 days at a temperature of 20°C and a relative humidity of 60%. -6 The following is more convenient: 690 x 10 -6 More preferably, 600 × 10 -6 More preferably, 500 × 10 -6 The following is particularly preferred: 400 × 10 -6 The following applies. Note that a smaller rate of change in length means that the resulting molded object will have less shrinkage.

[0016] Furthermore, the cement composition for additive manufacturing equipment is preferably one that satisfies the following conditions (i) to (ii) from the viewpoint of facilitating the manufacture of molded objects using additive manufacturing equipment. (i) The flow value (zero pour flow value) measured without 15 drop tests in accordance with "12 Flow Test" of "JIS R 5201:2015 (Physical Testing Methods for Cement)" shall be 120 mm or less. (ii) The settling time, when measured in accordance with "JIS A 1147:2019 (Test method for concrete setting time)", is less than 4 hours.

[0017] An example of a method for manufacturing a molded object using the cement composition for additive manufacturing equipment of the present invention is a method that includes a supply step of supplying the cement composition for additive manufacturing equipment to an additive manufacturing equipment, and a lamination step of forming a molded object made of the cement composition for additive manufacturing equipment in the additive manufacturing equipment. A cement composition for additive manufacturing equipment can be prepared by mixing the constituent materials (including at least cement, diatomaceous earth, and water). The mixing means for mixing the materials is not particularly limited, and a mixer commonly used in mixing mortar and concrete can be used. Specifically, examples include vertical mixers, horizontal mixers, Nauter mixers, tilting cylinder mixers, forced mixers, and twin-screw mixers. Examples of vertical mixers include the "Hobart Mixer" manufactured by Hobart and the "Henschel Mixer" manufactured by Henschel. Examples of horizontal mixers include the "Redige Mixer" manufactured by Redige. The prepared cement composition for additive manufacturing is fed into the additive manufacturing apparatus during the supply process. A commercially available general additive manufacturing apparatus (3D printer) can be used as the additive manufacturing apparatus. In the lamination process, a cement composition for additive manufacturing is extruded from a nozzle or the like of an additive manufacturing apparatus to form a two-dimensional layered body. Subsequently, a second layered body is formed on top of this layered body, and the same operation is repeated thereafter to finally form a molded object consisting of a laminate with the desired shape. [Examples]

[0018] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Cement; manufactured by Taiheiyo Cement Corporation, ordinary Portland cement (2) Diatomaceous earth; from Hokkaido, density: 2.43 g / cm³ 3 , BET specific surface area 128m 2 / g, Water absorption rate: 22.7%, Opal CT ratio: 20-30% by mass (3) Fine aggregate; crushed pyroxene andesite sand from Hokkaido, surface dry density: 2.63 g / cm³ 3 , Water absorption rate: 3.09%, FM: 2.47 (4) Superabsorbent polymer; Crosslinked sodium polyacrylate powder, manufactured by Kenis, trade name "Super Absorbent Polymer", with a maximum water absorption capacity of 400 g / g and a water absorption rate of 30-40 g / g·min. (5) Water; tap water

[0019] [Examples 1-7, Comparative Examples 1-4] A cement composition was prepared by adding cement, diatomaceous earth, fine aggregate, water, and a water-absorbing resin in the amounts shown in Table 1 or 2 to a Hobart mixer and mixing for 2 minutes. The resulting cement composition satisfied the above-described conditions (i) to (ii). As an additive manufacturing apparatus, a gantry frame measuring 130 mm in height, 100 mm in width, and 1,200 mm in depth, an extrusion nozzle with an inner diameter of 14 mm, a control computer, and a control panel were used. The prepared cement composition was fed into the cartridge of the additive manufacturing apparatus, and the cement composition was extruded from the extrusion nozzle. Additive manufacturing was performed under the conditions of an injection width of 16 mm, a layer thickness of 8 mm, and a layering speed of 30 mm / second to obtain a fabricated object.

[0020] The expansion rate of the obtained molded material was calculated in accordance with "JIS A 1146:2017 (Test method for alkali-silica reactivity of aggregates (mortar bar method))" when cured in air for 26 weeks at a temperature of 40°C and a relative humidity of 95%. An expansion rate of 0.1% or higher indicates a high likelihood of alkali-silica reaction and cracking. Furthermore, the rate of change in length of the resulting molded material was measured in accordance with "JIS A 1129-3:2010" (Method for measuring length change of mortar and concrete - Part 3: Dial gauge method) when the material was cured in air for up to 28 days at a temperature of 20°C and a relative humidity of 60%. Also, using the shaped object whose length change rate was measured, the compressive strength at 28 days of age was measured in accordance with "JIS R 5201:2015 (Methods of physical tests for cement)". Furthermore, for the obtained shaped object, the durability index (300 cycles) of "ASTM C666 75" was calculated using the value in accordance with "JIS A 1148:2010 (Method of freeze-thaw test for concrete)". Note that the durability index has a maximum value of 100, and the closer it is to the maximum value, the better the resistance to freeze-thaw. The respective results are shown in Tables 3 to 4. Note that in Comparative Example 4, the cement composition could not be kneaded.

[0021]

Table 1

[0022]

Table 2

[0023]

Table 3

[0024]

Table 4

[0025] From Tables 3 to 4, it can be seen that the expansion rates (0.01 to 0.05%) of Examples 1 to 7 are smaller than the expansion rate (0.3%) of Comparative Example 1, and the shaped objects of Examples 1 to 7 have suppressed alkali-silica reaction. Also, although the expansion rates (0.01%) of Comparative Examples 2 to 3 (those with a diatomaceous earth content of 25 to 30 parts by mass) are small, the length change rates (782 to 815×10 -6 ) are large, indicating that shrinkage of the shaped object has occurred. Furthermore, a comparison of Examples 3 to 7 shows that the molded objects containing the water-absorbent resin (Examples 4 to 7) have a smaller rate of change in length than the molded object without the water-absorbent resin (Example 3), indicating that shrinkage of the molded object is more suppressed and the shape stability of the molded object is improved. Furthermore, it can be seen that the durability indices of Examples 1 to 7 are equal to or greater than those of Comparative Examples 1 to 3. In particular, it can be seen that the durability indices of Examples 4 to 7, which contain a water-absorbing resin, are greater than those of Comparative Examples 1 to 3.

Claims

1. A cement composition for additive manufacturing equipment comprising Portland cement, diatomaceous earth, and a water-absorbent resin, The amount of diatomaceous earth per 100 parts by mass of the above-mentioned Portland cement is 8 to 22 parts by mass, and the amount of the above-mentioned water-absorbing resin is 5 to 14 parts by mass. A cement composition for additive manufacturing equipment, characterized in that the above-mentioned water-absorbing resin is a crosslinked product of sodium polyacrylate.

2. The cement composition for additive manufacturing apparatus according to claim 1, further comprising water.

3. A supply step of supplying the cement composition for additive manufacturing apparatus described in claim 2 to an additive manufacturing apparatus, In the additive manufacturing apparatus described above, a lamination step is performed in which a molded object made of the cement composition for the additive manufacturing apparatus is formed using the cement composition for the additive manufacturing apparatus. A method for manufacturing a molded object, characterized by including the following.

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