Concrete Composition

Abstract

To provide a concrete composition that can be used in 3D printing and can also be cured while retaining a shape formed by 3D printing.SOLUTION: A concrete composition for use in 3D printing is provided, the concrete composition comprising a cement-containing composition and cellulose nanofibers.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to concrete compositions. [Background technology]

[0002] Concrete structures made of concrete, mortar, etc. are strong in compression but weak in tension and bending. Methods for strengthening concrete structures against tension and bending include, for example, placing reinforcing bars in the concrete structure or blending various fibers into the concrete structure.

[0003] A three-dimensional (3D) printer may be used to form a three-dimensional concrete structure. This 3D printer ejects a concrete composition from a nozzle while moving the nozzle to form layers of the concrete composition, and gradually stacks the formed layers to form a three-dimensional shape (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-26099 Summary of the Invention [Problem to be solved by the invention]

[0005] With 3D printers, concrete structures are built up in layers, like soft-serve ice cream. When using conventional concrete compositions, the built-up concrete composition is soft and crumbles over time before hardening. As a result, concrete structures built with 3D printers have been unable to achieve the desired shape.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a concrete composition that can be used for 3D printing and that can harden while maintaining the shape formed by 3D printing. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A concrete composition for use in 3D printing, comprising a cement-containing composition and cellulose nanofibers. [2] The concrete composition according to [1], wherein the content of the cellulose nanofibers is 0.005% by mass or more and 0.2% by mass or less. [3] The concrete composition according to [1] or [2], wherein the cellulose nanofibers have a fiber width of 1000 nm or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a concrete composition that can be used for 3D printing and that can harden while maintaining the shape formed by 3D printing. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the concrete composition of the present invention will be described. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0010] [Concrete composition] The concrete composition of this embodiment is a concrete composition used for 3D printing, and includes a cement-containing composition and cellulose nanofibers. In other words, the concrete composition of this embodiment is composed mainly of a cement-containing composition to which cellulose nanofibers are added.

[0011] "Cement-containing composition" The cement-containing composition contains cement and water. Examples of cement-containing compositions include concrete, mortar, and cement milk. Concrete is a mixture of cement, fine aggregate (sand), and coarse aggregate (gravel (crushed stone)), mixed with water. Mortar is a mixture of cement and fine aggregate (sand) mixed with water. Cement milk is cement mixed with only water.

[0012] Cement is a powder made primarily from limestone, clay, silica, iron oxide, etc., that hardens through a chemical reaction with water. Fine aggregate is sand with a diameter of 5 mm or less. Coarse aggregate is gravel (crushed stone) with a diameter of more than 5 mm. The diameter of coarse aggregate is preferably 25 mm or less.

[0013] The mixing ratio of cement, fine aggregate, and coarse aggregate in concrete can be determined appropriately depending on the strength required of the concrete. The mixing ratio of cement, fine aggregate, and coarse aggregate, in mass ratio, is preferably, for example, 1 part cement, 2 to 3 parts fine aggregate, and 4 to 6 parts coarse aggregate.

[0014] The mixing ratio of cement to fine aggregate in the mortar can be determined appropriately depending on the strength required for the mortar. The mixing ratio of cement to fine aggregate is preferably, for example, 1 part cement to 2 to 4 parts fine aggregate by mass.

[0015] The water content in the concrete is preferably 5% by mass or more and 15% by mass or less based on the total amount of the concrete. The water content in the mortar is preferably 10% by mass or more and 20% by mass or less based on the total amount of the mortar. The content of water in the cement milk is preferably 30% by mass or more and 50% by mass or less with respect to the total amount of the cement milk.

[0016] The content of the cement-containing composition in the concrete composition of the present embodiment is preferably 10% by mass or more and 20% by mass or less with respect to the total amount of the concrete composition.

[0017] "Cellulose nanofiber" The cellulose nanofibers are preferably fine fibrous cellulose having a fiber width of 1000 nm or less.

[0018] The fiber width of the fine fibrous cellulose in this embodiment is preferably 1 nm to 1000 nm, more preferably 2 nm to 500 nm, and even more preferably 4 nm to 100 nm, as observed with an electron microscope. If the fiber width of the fine fibrous cellulose is less than 1 nm, the cellulose molecules will dissolve in water, and the physical properties of fine fibrous cellulose (good thickening properties) will not be exhibited. On the other hand, if the fiber width of the fine fibrous cellulose exceeds 1000 nm, it cannot be called fine fibrous cellulose, and is merely the fiber contained in ordinary pulp, so it does not form a gel and does not exhibit a sufficient thickening effect.

[0019] The content of cellulose nanofibers in the concrete composition of this embodiment is preferably 0.005% by mass or more and 0.2% by mass or less, and more preferably 0.01% by mass or more and 0.1% by mass or less, based on the total amount of the concrete composition. When the content of cellulose nanofibers is above the lower limit, the cellulose nanofibers spread in a matrix-like manner in the cement-containing composition, which is the main component, and can impart thixotropy to the concrete composition (the property of reducing the viscosity of a fluid when a certain pressure is applied and returning to its original state after a certain period of time). When the content of cellulose nanofibers is below the upper limit, a concrete composition can be provided that hardens while maintaining the shape formed by 3D printing.

[0020] <Production of fine fibrous cellulose> The above-mentioned fine fibrous cellulose can be produced by a defibration treatment step in which a fibrous raw material containing cellulose is defibrated.

[0021] Before the defibration treatment, ionic groups may be introduced into the cellulose-containing fiber raw material by a known method to form fine fibrous modified cellulose.

[0022] The concrete composition of this embodiment contains a cement-containing composition and cellulose nanofibers, and therefore has excellent thixotropy due to the cellulose nanofibers spreading in a matrix-like manner in the cement-containing composition, which is the main component. In other words, the concrete composition of this embodiment is imparted with thixotropy to suppress fluidity at rest, and therefore can be used in 3D printing and can harden while maintaining the shape formed by 3D printing.

[0023] [Method of using concrete composition] The concrete composition of this embodiment is used for 3D printing. A 3D printer used for 3D printing includes, for example, a nozzle that discharges the concrete composition, a robot arm that supports the nozzle and enables the nozzle to be moved to any position, and a control device that controls the operation of the nozzle, the robot arm, etc.

[0024] To form a concrete structure using the concrete composition of this embodiment, the concrete composition is discharged from the nozzle of a 3D printer while the nozzle is moved to form layers of the concrete composition, and the formed layers are gradually stacked to form a three-dimensional shape. The concrete composition of this embodiment has excellent thixotropy, and therefore has fluidity when it is pressurized through the 3D printer by gas such as compressed air and discharged from the nozzle. Therefore, the concrete composition of this embodiment can easily form the desired three-dimensional shape. Furthermore, the concrete composition discharged from the nozzle is no longer pressurized by gas or the like. As a result, the concrete composition loses its fluidity and maintains the shape formed by the 3D printer without crumbling over time. Therefore, the shape formed by the 3D printer is maintained until the concrete composition hardens to form a concrete structure. [Example]

[0025] The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to the following experimental examples.

[0026] [Experimental Example] An experiment was carried out to confirm the thixotropy of the concrete composition of the present invention. A flexible resin pipe was connected to the tip of the nozzle of the 3D printer described above. The concrete composition of the present invention was injected (pressurized) into a resin pipe from the tip of a nozzle. It was confirmed that the concrete composition moved smoothly through the resin pipe while pressure was being applied to the concrete composition using a gas such as compressed air. Furthermore, when pressure was stopped from being applied to the concrete composition, the concrete composition stopped moving through the resin pipe. It was also confirmed that the concrete composition did not move (drip) through the resin pipe even when the resin pipe was pointed downward in this state. From these results, it was found that the concrete composition of the present invention has thixotropy.

Claims

1. 1. A concrete composition for use in 3D printing, comprising: A cement-containing composition and cellulose nanofibers, A concrete composition, wherein the content of the cellulose nanofibers is 0.01 mass% or more and 0.1 mass% or less relative to the total amount of the concrete composition.

2. The concrete composition of claim 1 , wherein the cellulose nanofibers have a fiber width of 1000 nm or less.