Method for manufacturing cement hardened body

Abstract

To provide a method for manufacturing a cement hardened body, capable of improving strength without increasing heat of hydration of cement.SOLUTION: A method for manufacturing a cement hardened body includes: a preparation step of preparing a cement composition including cement, water, and fine aggregate; a first dispersion step of dispersing graphene oxide in the cement composition; and a hardening step of hardening the cement composition in which the graphene oxide is dispersed. In the first dispersion step, the graphene oxide is dispersed in the cement composition such that a mass of the graphene oxide is 0.02 mass% or more and 0.10 mass% or less relative to a total mass of cement in a hardened body of the cement composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a hardened cement product. [Background technology]

[0002] A high water-cement ratio has the advantage of being easier to mix and pour into formwork, but it also reduces the strength of the concrete (hardened cement paste).The lower the water-cement ratio, the more concentrated the cement paste (cement composition) will be, and the stronger the hardened cement will be.

[0003] Therefore, in order to improve the strength of the hardened cement body without changing the water-cement ratio of the hardened cement body, it is necessary to accelerate the hydration reaction of the cement. When the hydration reaction of the cement is accelerated, the amount of heat generated by hydration increases, which poses a problem of, for example, increasing the rate of temperature rise of the concrete during insulation and the amount of adiabatic temperature rise (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Harutaka Imoto et al.: Early hardening properties and bleeding suppression effect of concrete using CSH-based early strength admixture, Proceedings of the Japan Concrete Institute, Vol. 36, No. 1, 2014 Summary of the Invention [Problem to be solved by the invention]

[0005] Non-patent document 1 reports that by replacing 4% of the cement mass with an additive and mixing it with water, the reaction rate of alite (the main component of cement) increases, which in turn increases the rate of heat generated by hydration, resulting in an increase in strength at 7 days of age of approximately 5% and at 28 days of age of approximately 7%.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a method for producing a hardened cement product that can improve the strength without increasing the heat of the hydration reaction of cement. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A preparation step of preparing a cement composition containing cement, water, and fine aggregate; a first dispersing step of dispersing graphene oxide in the cement composition; and a hardening step of hardening the cement composition in which the graphene oxide is dispersed, a method for producing a hardened cement body, wherein in the first dispersing step, the graphene oxide is dispersed in the cement composition so that a mass of the graphene oxide is 0.02 mass% or more and 0.10 mass% or less relative to a total mass of cement in the hardened cement body of the cement composition. [2] The method for producing a hardened cement product according to [1], wherein in the hardening step, the heat generation history when the cement composition having dispersed therein the graphene oxide is hardened is made to match the heat generation history when a cement composition not containing the graphene oxide is hardened. [3] The method for producing a hardened cement body according to [1] or [2], wherein in the first dispersion step, the graphene oxide is dispersed in the cement composition using a graphene oxide dispersion containing the graphene oxide. [4] The method for producing a hardened cement product according to [1] or [2], wherein in the first dispersion step, the graphene oxide is dispersed in the cement composition using a mixture obtained by drying a slurry containing the graphene oxide and substituting the graphene oxide with water. [5] a second dispersing step of dispersing graphene oxide in water to prepare a graphene oxide dispersion, before the first dispersing step; an ultrasonic treatment step of ultrasonically treating the graphene oxide dispersion and adding a dispersant to the graphene oxide dispersion to prepare a dispersant-containing graphene oxide dispersion; a homogenization step of homogenizing the dispersant-containing graphene oxide dispersion to form a suspension, in the ultrasonic treatment step, adding the dispersant to the graphene oxide dispersion 15 minutes or more after the start of the ultrasonic treatment of the graphene oxide dispersion; The method for producing a hardened cement product according to any one of [1] to [4], wherein in the first dispersion step, the graphene oxide is dispersed in the cement composition using the suspension. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a hardened cement body that can improve the strength without increasing the heat of hydration reaction of cement. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a graph showing the heat generation rate of a hardened cement body in Example 1. [Figure 2] 1 is a diagram showing the integrated calorific value of the hardened cement body in Example 1. FIG. [Figure 3] FIG. 10 is a graph showing the relationship between the time for adding a dispersant to a graphene oxide dispersion and the particle size of graphene oxide particles contained in a GO-PS suspension in Example 4. [Figure 4] FIG. 10 shows the dispersion stability over time when the GO-PS suspension was allowed to stand for up to 24 hours in Example 4. [Figure 5] FIG. 10 is a graph showing the compressive strength of mortar specimens in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Manufacturing method for hardened cement] A method for producing a hardened cement product according to one embodiment of the present invention includes: a preparation step of preparing a cement composition containing cement, water, and fine aggregate; a first dispersion step of dispersing graphene oxide in the cement composition; and a hardening step of hardening the cement composition in which graphene oxide is dispersed.

[0011] A method for producing a hardened cement body according to one embodiment of the present invention preferably includes, before the first dispersion step, a second dispersion step of dispersing graphene oxide in water to prepare a graphene oxide dispersion, an ultrasonic treatment step of ultrasonically treating the graphene oxide dispersion and adding a dispersant to the graphene oxide dispersion to prepare a dispersant-containing graphene oxide dispersion, and a homogenization step of homogenizing the dispersant-containing graphene oxide dispersion to form a suspension. The second dispersion step, ultrasonic treatment step, and homogenization step are performed before the first dispersion step.

[0012] "Preparation process" In the preparation step, a cement composition containing cement, water, and fine aggregate is prepared.

[0013] "Cement composition" The cement composition is a hardenable cement composition containing cement, water, and fine aggregate.

[0014] <Ingredients> (cement) The cement is not particularly limited as long as it is a powder whose main raw material is limestone, clay, silica stone, iron oxide raw material, or the like, and which hardens through a chemical reaction with water. Examples of the cement include portland cement (JIS R 5210:2009), blast furnace cement (JIS R5211:2009), silica cement (JIS R 5212:2009), fly ash cement (JIS R 5213:2009), and ecocement (JIS R 5214:2009). The cement is preferably at least one selected from the group consisting of Portland cement and blast furnace cement, and more preferably at least one selected from the group consisting of ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, blast furnace cement type A, blast furnace cement type B, and blast furnace cement type C.

[0015] There are six types of Portland cement standardized as normal, early strength, extra early strength, medium heat, low heat, and sulfate-resistant, as well as low-alkali types of each, for a total of 12 types (JIS R 5210:2009).

[0016] Blast furnace cement is classified into Type A, Type B, and Type C blast furnace cement depending on the amount of blast furnace slag mixed in (JIS R 5211:2009). Blast-furnace cement type A: Blast-furnace slag content 5-30% by mass Blast-furnace cement type B: Blast-furnace slag content 30-60% by mass Blast furnace cement type C: blast furnace slag content 60-70% by mass

[0017] Portland cement generates carbon dioxide during the calcination process, due to the thermal decomposition of limestone (CaCO3 → CaO + CO2↑) and the fuel required for calcination. On the other hand, ground granulated blast furnace slag, an admixture for blast furnace cement, does not require calcination, so the amount of carbon dioxide generated during cement production can be reduced in proportion to the amount of granulated blast furnace slag added. Therefore, blast furnace cement is preferred as the cement used in hardenable cement compositions. Blast furnace cement type B or C, which contain a large amount of blast furnace slag, is more preferred, with C being even more preferred. Furthermore, ECM (registered trademark) (Energy, CO2, Minimum) cement, which contains the same amount of blast furnace slag as C blast furnace cement, may also be used.

[0018] The content of cement in the hardenable cement composition is not particularly limited, but is preferably 200 kg / m 3 More than 500kg / m 3It is preferable that the saturation is 250 kg / m or less. 3 More than 400kg / m 3 More preferably, it is 300 kg / m or less. 3 More than 350kg / m 3 It is even more preferable that:

[0019] (water) The water is not particularly limited, and water that is normally used when mixing cement, such as tap water, well water, or groundwater, can be used.

[0020] The water content in the hardenable cement composition is not particularly limited, but is preferably 50 kg / m 3 More than 250kg / m 3 It is preferable that the saturation is 100 kg / m or less. 3 More than 200kg / m 3 More preferably, it is:

[0021] The ratio (mass %) of water to cement in the hardenable cement composition is not particularly limited, but is preferably 20% to 65%, more preferably 30% to 60%.

[0022] (fine aggregate) There are no particular restrictions on the fine aggregate, and any fine aggregate that is normally mixed with cement can be used, but sand with a particle size of 5 mm or less is preferred. The particle size of the fine aggregate is the particle size measured in accordance with the sieving test method for aggregates (JIS A 1102:2014).

[0023] The content of the fine aggregate in the hardenable cement composition is not particularly limited, but is preferably 600 kg / m 3 More than 1000kg / m 3 Preferably, it is 700 kg / m or less. 3 More than 900kg / m 3 More preferably, it is:

[0024] (coarse aggregate) The cement composition may contain coarse aggregate. The coarse aggregate is not particularly limited, and a coarse aggregate that is usually mixed with cement can be used, but gravel (crushed stone) with a particle size of more than 5 mm is preferred. There is no particular upper limit to the particle size of the gravel (crushed stone), but it is preferably 25 mm or less. The particle size of the coarse aggregate is the particle size obtained by measurement in accordance with the sieving test method for aggregates (JIS A 1102:2014).

[0025] The content of the coarse aggregate in the hardenable cement composition is not particularly limited, but is preferably 800 kg / m 3 More than 1200kg / m 3 It is preferable that the saturation is 900 kg / m or less. 3 More than 1100kg / m 3 More preferably, it is:

[0026] (Other ingredients) The cement composition may be a mixture of conventionally used components, provided that the effects of the present invention are not impaired.

[0027] The cement-water mass ratio (W / C) is preferably 0.2 or more and 0.7 or less, more preferably 0.25 or more and 0.65 or less, and even more preferably 0.3 or more and 0.6 or less. When the cement-water mass ratio (W / C) is equal to or more than the lower limit, fluidity can be ensured. When the cement-water mass ratio (W / C) is equal to or less than the upper limit, strength can be ensured.

[0028] The cement composition can be prepared by kneading cement, water, and fine aggregate. The kneading method is not particularly limited, and can be carried out by a conventionally known method for kneading cement compositions using a gravity mixer (such as a tilting drum mixer) or a forced mixing mixer (such as a horizontal single-shaft mixer, a horizontal double-shaft mixer, or a pan mixer).

[0029] "Second dispersion process" In the second dispersion step, graphene oxide is dispersed in water to prepare a graphene oxide dispersion. The method for dispersing graphene oxide in water is not particularly limited, but it is preferable to use a homogenizer, for example.

[0030] "Ultrasonic treatment process" In the ultrasonic treatment step, the graphene oxide dispersion is ultrasonically treated, and a dispersant is added to the graphene oxide dispersion to prepare a dispersant-containing graphene oxide dispersion. In the ultrasonic treatment step, for example, ultrasonic treatment is performed 5 to 60 cycles, with one cycle consisting of one minute of continuous ultrasonic irradiation of the graphene oxide dispersion and one minute of pause from ultrasonic irradiation.

[0031] In the ultrasonic treatment step, the dispersant is preferably added to the graphene oxide dispersion 15 minutes or more after the start of ultrasonic treatment of the graphene oxide dispersion, and more preferably added within a range of 15 minutes to 30 minutes after the start of ultrasonic treatment of the graphene oxide dispersion. Adding the dispersant to the graphene oxide dispersion 15 minutes or more after the start of ultrasonic treatment of the graphene oxide dispersion reduces the particle size of the graphene oxide particles contained in the dispersant-containing graphene oxide dispersion. As a result, the dispersion stability of the suspension, which will be described later, is improved.

[0032] The dispersant is not particularly limited, but for example, polycarboxylic acid ether compounds, modified polycarboxylic acid salts, etc. can be used.

[0033] "Homogenization process" In the homogenization step, the dispersant-containing graphene oxide dispersion is homogenized to form a suspension. The method for homogenizing the dispersant-containing graphene oxide dispersion is not particularly limited, but it is preferable to use a homogenizer, for example.

[0034] "First dispersion process" In the first dispersion step, graphene oxide is dispersed in the cement composition obtained in the preparation step.

[0035] In the first dispersing step, graphene oxide is dispersed in the cement composition so that the mass of graphene oxide is 0.02 mass % or more and 0.10 mass % or less relative to the total mass of cement in the hardened cement composition.

[0036] The mass of graphene oxide relative to the total mass of the hardened cement body is 0.02 mass% or more and 0.10 mass% or less, preferably 0.01 mass% or more and 0.8 mass% or less, and more preferably 0.02 mass% or more and 0.6 mass% or less. When the mass of graphene oxide is within this range, an increase in the heat generation rate when hardening a cement composition having graphene oxide dispersed therein can be suppressed relative to the heat generation rate when hardening a cement composition not containing graphene oxide. Furthermore, when the mass of graphene oxide is within this range, an increase in the integrated heat generation rate when hardening a cement composition having graphene oxide dispersed therein can be suppressed relative to the integrated heat generation rate when hardening a cement composition not containing graphene oxide. When the mass of graphene oxide is equal to or greater than the lower limit, the strength of the hardened cement body can be increased. When the mass of graphene oxide is equal to or less than the upper limit, the fluidity of the hardened cement body can be ensured.

[0037] In the first dispersion step, graphene oxide may be dispersed in the cement composition as it is, or a graphene oxide dispersion containing graphene oxide may be used to disperse graphene oxide in the cement composition, or a slurry containing graphene oxide may be dried to obtain graphene oxide, and the graphene oxide may be replaced with water, and the graphene oxide may be dispersed in the cement composition using the suspension obtained in the homogenization step.

[0038] Graphene oxide can be made of various materials containing carbon, oxygen, and hydrogen in various ratios. Hereinafter, graphene oxide alone will be referred to as "GO."

[0039] The average particle size of graphene oxide measured by dynamic light scattering is preferably 0.5 μm to 10 μm, more preferably 1 μm to 8 μm, and even more preferably 1.5 μm to 6 μm. When the average particle size of graphene oxide is equal to or greater than the lower limit, the strength of the hardened cement body can be increased. When the average particle size of graphene oxide is equal to or less than the upper limit, the fluidity of the hardened cement body can be ensured.

[0040] The graphene oxide dispersion contains graphene oxide and water. Hereinafter, the graphene oxide dispersion may be referred to as "GOE."

[0041] The graphene oxide content relative to the total mass of the graphene oxide dispersion is preferably 0.1 mass% to 5 mass%, more preferably 0.3 mass% to 3 mass%, and even more preferably 0.5 mass% to 1 mass%. When the graphene oxide content is within the above range, an increase in the heat generation rate during hardening of a cement composition containing dispersed graphene oxide can be suppressed relative to the heat generation rate during hardening of a cement composition not containing graphene oxide. Furthermore, when the graphene oxide content is within the above range, an increase in the cumulative heat generation rate during hardening of a cement composition containing dispersed graphene oxide can be suppressed relative to the cumulative heat generation rate during hardening of a cement composition not containing graphene oxide. When the graphene oxide content is equal to or greater than the lower limit, the strength of the hardened cement body can be increased. When the graphene oxide content is equal to or less than the upper limit, graphene oxide can be efficiently dispersed in the dispersion.

[0042] The graphene oxide-containing slurry contains graphene oxide and water.

[0043] The graphene oxide obtained by drying the slurry containing graphene oxide has a structure in which graphene oxide aggregates.

[0044] The graphene oxide obtained by drying a slurry containing graphene oxide and substituting water for the graphene oxide is a graphene oxide dispersion containing graphene oxide, water, and a dispersant. Hereinafter, the graphene oxide obtained by drying a slurry containing graphene oxide may be referred to as "GOP."

[0045] The graphene oxide content relative to the total mass of the graphene oxide-water mixture obtained by drying a graphene oxide-containing slurry is preferably 0.1% by mass to 5% by mass, more preferably 0.3% by mass to 3% by mass, and even more preferably 0.5% by mass to 1% by mass. When the graphene oxide content is within the above range, an increase in the heat generation rate during hardening of a cement composition containing dispersed graphene oxide can be suppressed relative to the heat generation rate during hardening of a cement composition not containing graphene oxide. Furthermore, when the graphene oxide content is within the above range, an increase in the cumulative heat generation rate during hardening of a cement composition containing dispersed graphene oxide can be suppressed relative to the cumulative heat generation rate during hardening of a cement composition not containing graphene oxide. When the graphene oxide content is equal to or greater than the lower limit, the strength of the hardened cement body can be increased. When the graphene oxide content is equal to or less than the upper limit, graphene oxide can be efficiently dispersed in the dispersion.

[0046] To disperse graphene oxide in a cement composition, the cement composition is kneaded with GO, GOP, or GOE. The kneading method is not particularly limited, and can be carried out by a conventionally known method for kneading cement compositions using a gravity mixer (such as a tilting drum mixer) or a forced mixing mixer (such as a horizontal single-shaft mixer, horizontal double-shaft mixer, or pan mixer).

[0047] "Curing process" In the hardening step, the cement composition in which graphene oxide has been dispersed in the dispersing step is hardened.

[0048] In the hardening step, it is preferable to make the heat generation history of the cement composition having dispersed graphene oxide during hardening similar to the heat generation history of the cement composition not containing graphene oxide during hardening. That is, the cement composition having dispersed graphene oxide is hardened so that the heat generation history of the cement composition having dispersed graphene oxide during hardening is similar to the heat generation history of the cement composition not containing graphene oxide during hardening. Specifically, by setting the mass of graphene oxide to 0.02 mass% or more and 0.10 mass% or less relative to the total mass of cement in the hardened cement composition, the heat generation history of the cement composition having dispersed graphene oxide during hardening is made similar to the heat generation history of the cement composition not containing graphene oxide during hardening.

[0049] In the hardening step, the cement composition having the graphene oxide dispersed therein is hardened to obtain a hardened cement body.

[0050] The cement composition containing graphene oxide is usually hardened by leaving it to stand at a temperature of 0°C or higher and 50°C or lower.

[0051] According to the method for producing a hardened cement body of the present embodiment, in the dispersing step of dispersing graphene oxide in a cement composition, graphene oxide is dispersed in the cement composition so that the mass of graphene oxide is 0.02 mass % or more and 0.10 mass % or less relative to the total mass of cement in the hardened cement body of the cement composition. This makes it possible to improve the strength of the hardened cement body without increasing the heat of hydration reaction of the cement.

[0052] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims. [Example]

[0053] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0054] [Manufacturing example] "Cement composition" <Material> (W)Water tap water (C) Cement Portland cement Blast furnace cement type B (containing 30-60% by mass of blast furnace slag) ECM cement (blast furnace slag 60-70% by mass, equivalent to blast furnace cement type C) (S) Fine aggregate Standard sand for cement testing

[0055] <Manufacturing method> A cement composition was produced by kneading water (W), cement (C), and fine aggregate (S) using a Hobart mixer in the proportions shown in Table 1. The cement-water mass ratio was 0.42.

[0056] [Table 1]

[0057] "Preparation of graphene oxide" To obtain a 10 g / L GO dispersion, a GO slurry with 80% water content was mixed with purified water (50 g GO slurry and 960 g water) at 3000 rpm for 15 minutes under shear. The mixture was then sonicated for 10 cycles (1 minute at 30 kHz, followed by a 1 minute rest period) to prepare a GO dispersion (GOE). We also prepared a GO powder (GOP) by replacing the water with dried GO slurry.

[0058] [Example 1] Graphene oxide was dispersed in the cement composition using water-substituted GOP or GOE so that the amount of GO powder added was 0.04 mass% or 0.06 mass% relative to the total mass of cement in the hardened cement composition. The cement-water mass ratio was 0.42. The cement composition with dispersed graphene oxide was then left to stand at 20°C to harden, yielding a hardened cement paste. Using the above GOE or GOP, the heat of hydration was measured from 1 hour to 672 hours after dispersing graphene oxide in the cement composition. For all tests, 0.22% of the polycarboxylic acid dispersant (cement mass) was replaced with water, and ultrasonic waves were applied at 30 kHz for 10 minutes before mixing with the cement to disperse the GO powder in the water. Figure 1 shows the heat generation rate of the hardened cement paste. Figure 2 shows the cumulative heat generation rate of the hardened cement paste. 1 and 2, GOE0.04 indicates a GOE where the mass of GO powder relative to the total mass of cement in the hardened cement composition was 0.04 mass%, GOE0.06 indicates a GOE where the mass of GO powder relative to the total mass of cement in the hardened cement composition was 0.06 mass%, GOP0.04 indicates a GOP where the mass of GO powder relative to the total mass of cement in the hardened cement composition was 0.04 mass%, and GOP0.06 indicates a GOP where the mass of GO powder relative to the total mass of cement in the hardened cement composition was 0.06 mass%. The base shows only cement paste. Table 2 also shows the cumulative heat value of the hardened cement composition.

[0059] [Table 2]

[0060] As shown in Figures 1 and 2 and Table 2, it was confirmed that the use of either GOP or GOE did not increase the heat release rate or the cumulative heat release compared to the base.

[0061] [Example 2] Mortar specimens were prepared in the same manner as in Example 1, and a compressive strength test was carried out. The mortar specimens were sealed and cured at 20°C. The compressive strength test of the mortar specimens was carried out in accordance with JIS R 5201. The compressive strength test results are shown in Table 3.

[0062] [Table 3]

[0063] As shown in Table 3, it was confirmed that GOP and GOE improved strength compared to the base. It was also confirmed that GOE had a greater effect than GOP.

[0064] [Example 3] The effect of the amount of GOE added on strength was confirmed. Mortar specimens were prepared in the same manner as in Example 1, except that standard sand for cement testing was used as the fine aggregate and the amount of GO powder added was 0.02 mass%, 0.04 mass%, 0.06 mass%, 0.08 mass%, or 0.10 mass% relative to the total mass of cement in the hardened cement composition. The mortar specimens were sealed and cured at 20°C. In the same manner as in Example 2, a compressive strength test was carried out on the mortar specimens. The compressive strength test results are shown in Table 4.

[0065] [Table 4]

[0066] As shown in Table 4, a strength-increasing effect was obtained at all levels of GOE addition from 0.02% by mass to 0.10% by mass, with the strength being greatest at 7 days of age at 0.10% by mass GOE and at 28 days of age at 0.02% by mass GOE.

[0067] [Example 4] The effect of ultrasonic irradiation time on the dispersion of GO in water was investigated. GO manufactured by Ceylon Graphen Technology Co., Ltd. was used. Table 5 shows the amount of dispersant (hereinafter sometimes referred to as "PS") added, the amount of GO added, the amount of ion-exchanged water used in the experiment, and the time required to add PS to the dispersion of GO in ion-exchanged water (hereinafter referred to as "GO dispersion"). Table 6 shows the three types of PS used in the experiment. GO was added to ion-exchanged water, and the GO was dispersed in the ion-exchanged water using a homogenizer (product name: AHG-160D, manufactured by AS ONE Corporation) at 3000 rpm for 15 minutes to prepare a GO dispersion in which GO was uniformly dispersed in the ion-exchanged water. Next, the GO dispersion was ultrasonicated. After the ultrasonic treatment began, PS was added to the GO dispersion. The time from the start of ultrasonic treatment to the addition of PS was set to 0, 15, or 30 minutes. The ultrasonic frequency and power used to irradiate the GO dispersion were 40 kHz and 400 W, respectively. Thirty cycles of ultrasonic treatment were performed, each consisting of 1 minute of continuous ultrasonic irradiation followed by 1 minute of rest. The GO dispersion with added PS was then homogenized using a homogenizer at 3000 rpm for 5 minutes to prepare a GO-PS suspension. Next, the particle size of GO particles in the GO-PS suspension was analyzed to evaluate the stability and dispersibility of GO in the GO-PS suspension and the interaction between the GO-PS suspension and the cement pore solution. To analyze the particle size of GO particles in the GO-PS suspension, a GO-PS suspension with a GO concentration of 0.5 g / L was prepared. The particle size of the GO particles in the resulting GO-PS suspension was measured by dynamic light scattering using a particle size measurement system (product name: ELSZ-1000S, manufactured by Otsuka Electronics Co., Ltd.). The particle size of the GO particles was calculated as the average value of three repeated measurements. Next, a mortar specimen was prepared in the same manner as in Example 1 using a GO-PS suspension with a GO concentration of 0.5 g / L, and a compressive strength test was carried out in the same manner as in Example 2.

[0068] [Table 5]

[0069] [Table 6]

[0070] "Verifying the timing of adding dispersants" Figure 3 shows the relationship between the time PS was added to the GO dispersion and the particle size of GO particles contained in the GO-PS suspension. In Figure 3, GO-PS-A represents a GO-PS suspension using PS-A as a dispersant, GO-PS-B represents a GO-PS suspension using PS-B as a dispersant, and GO-PS-C represents a GO-PS suspension using PS-C as a dispersant. The results shown in Figure 3 confirm that the particle size of GO particles decreases when PS is added 15 minutes or more after the start of ultrasonic treatment of the GO dispersion. This suggests that it is preferable to add PS 15 minutes or more after the start of ultrasonic treatment of the GO dispersion.

[0071] "Verification of dispersion stability of suspension" Figure 4 shows the dispersion stability over time when GO-PS suspensions were left standing for up to 24 hours. In Figure 4, GO-PS-A represents a GO-PS suspension using PS-A as a dispersant, GO-PS-B represents a PS-GO suspension using PS-B as a dispersant, and GO-PS-C represents a GO-PS suspension using PS-C as a dispersant. In this study, PS was added 30 minutes after the start of ultrasonic treatment of the GO dispersion. For comparison, a GO dispersion was prepared by dispersing GO alone in ion-exchanged water without adding PS. The results shown in Figure 4 indicate that the GO dispersion and GO-PS-A showed large variations in particle size over time and had poor dispersion stability. In contrast, the rate of change in particle size over time for GO-PS-B and GO-PS-C was less than 15% compared to immediately after preparation of the GO-PS suspension, demonstrating excellent dispersion stability.

[0072] "Compression strength test of mortar specimen" GO was added to ion-exchanged water, and the GO was dispersed in the ion-exchanged water using a homogenizer (product name: AHG-160D, manufactured by AS ONE Corporation) at 3000 rpm for 15 minutes to prepare a GO dispersion in which GO was uniformly dispersed in the ion-exchanged water. Next, the GO dispersion was sonicated. After the sonication started, PS was added to the GO dispersion. 30 minutes after the start of sonication, PS was added. The GO dispersion was irradiated with ultrasound at a frequency of 40 kHz and an output of 400 W. Thirty cycles of ultrasonication, consisting of one minute of continuous ultrasonic irradiation followed by one minute of rest, were performed. The GO dispersion with added PS was then homogenized at 3000 rpm for 5 minutes using a homogenizer to prepare GO-PS suspensions (GO-PS-A, GO-PS-B, and GO-PS-C). PS-A, PS-B, and PS-C were used as the PS, respectively. Next, each GO-PS suspension was added to the cement composition so that the water-to-cement ratio (w / c) was 0.4 and the mass of GO relative to the total mass of cement in the hardened cement composition was 0.02 mass%. For comparison, a GO dispersion was prepared by dispersing GO alone in ion-exchanged water without adding PS. The GO dispersion was added to the cement composition in the same manner as in the GO-PS suspension. For comparison, a cement composition without GO was also used. The test specimens were prepared as follows. The cement composition and GO-PS suspension were mixed at low speed for 30 seconds using a planetary mixer (product name: Hobart Type Mixer 5L, manufactured by Kansai Machinery Manufacturing Co., Ltd.). Sand was then added to the resulting mixture, and the mixture was mixed at low speed for 30 seconds and at high speed for 30 seconds. The mixture was then mixed at high speed for another 1 minute to obtain mortar. The resulting mortar was poured into a cylindrical mold with a diameter of 50 mm and a height of 100 mm in two layers, and each layer was vibrated for 20 seconds to remove air bubbles and ensure uniformity. Next, to prevent water loss due to evaporation, the surface of the mold containing the poured mortar was covered with a thin plastic film and placed in a hardening environment controlled at a temperature of 20 ± 2 °C. The mold was stored at a temperature of 20 ± 2 °C for 7 days until the compressive strength test. Next, the hardened mortar specimens were removed from the molds and subjected to a compressive strength test in accordance with JIS A 1108:2018 "Testing Method for Compressive Strength of Concrete." The results are shown in Figure 5. In Figure 5, the control represents a cement composition that does not contain GO and has the same water-binder ratio. Figure 5 shows the compressive strength of mortar specimens. Compared to mortar specimens without GO, the 7-day compressive strengths of the mortar specimens containing GO dispersion (GO shown in Figure 5), cement mortar containing GO-PS-A (GO-PS-A shown in Figure 5), mortar specimens containing GO-PS-B (GO-PS-B shown in Figure 5), and mortar specimens containing GO-PS-C (GO-PS-C shown in Figure 5) increased by 1.9%, 1.7%, 7.5%, and 8.2%, respectively. The results in Figure 5 demonstrate that the use of GO-PS suspensions, such as GO-PS-B and GO-PS-C, which demonstrated dispersion stability in Figure 4, can effectively improve the mechanical strength of cement mortar.

Claims

1. A preparation step of preparing a cement composition including cement, water, and fine aggregate; a first dispersing step of dispersing graphene oxide in the cement composition; and a hardening step of hardening the cement composition in which the graphene oxide is dispersed, the method for producing a hardened cement body, wherein in the first dispersing step, the graphene oxide is dispersed in the cement composition such that a mass of the graphene oxide is 0.02 mass% or more and 0.10 mass% or less with respect to a total mass of cement in the hardened cement body of the cement composition.

2. 2. The method for producing a hardened cement product according to claim 1, wherein in the hardening step, a heat generation history when the cement composition having the graphene oxide dispersed therein is hardened is set to match a heat generation history when a cement composition not containing the graphene oxide is hardened.

3. 2. The method for producing a hardened cement body according to claim 1, wherein in the first dispersing step, the graphene oxide is dispersed in the cement composition by using a graphene oxide dispersion containing the graphene oxide.

4. 2. The method for producing a hardened cement body according to claim 1, wherein in the first dispersing step, the graphene oxide is dispersed in the cement composition using a slurry obtained by drying the graphene oxide-containing slurry and substituting the graphene oxide with water.

5. a second dispersing step of dispersing graphene oxide in water to prepare a graphene oxide dispersion, which is performed before the first dispersing step; an ultrasonic treatment step of ultrasonically treating the graphene oxide dispersion and adding a dispersant to the graphene oxide dispersion to prepare a dispersant-containing graphene oxide dispersion; a homogenization step of homogenizing the dispersant-containing graphene oxide dispersion to form a suspension, in the ultrasonic treatment step, adding the dispersant to the graphene oxide dispersion 15 minutes or more after the start of the ultrasonic treatment of the graphene oxide dispersion; 2. The method for producing a hardened cement product according to claim 1, wherein in the first dispersing step, the graphene oxide is dispersed in the cement composition by using the suspension.

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