hydraulic components

Abstract

We propose a hydraulic composition that ensures the desired design strength and fluidity even when the amount of Portland cement used is reduced by including calcium carbonate. [Solution] A hydraulic composition comprising powder and water. The powder comprises calcium carbonate and at least one of blast furnace slag, expansive agent, slaked lime, quicklime, fly ash, and Portland cement. In addition, at least one of nitrite ions is added separately in an amount ranging from 0.5% to 5.6% by mass per 100% by mass of the powder, and the proportion of calcium carbonate in the powder is 8.5% by mass or more.

Description

[Technical Field]

[0001] This invention relates to a hydraulic composition containing calcium carbonate. [Background technology]

[0002] In the case of hydraulic compositions (e.g., concrete, mortar, cement paste), a portion of the powder may be replaced with calcium carbonate in order to reduce CO2 (carbon dioxide) emissions. For example, Patent Document 1 discloses a cement-based material comprising cement, calcium carbonate, aggregate, additives, and a porous material. In recent years, technologies have been developed to capture CO2 and produce calcium carbonate. Calcium carbonate produced using this technology fixes CO2 from the atmosphere and exhaust gases. By incorporating calcium carbonate into hydraulic compositions, CO2 can be fixed or stored, contributing to a reduction in overall CO2 emissions for society. Furthermore, replacing relatively expensive cement with industrial by-products such as blast furnace slag and fly ash can reduce CO2 emissions related to cement production, promote the effective use of industrial by-products, and lower costs. However, calcium carbonate is an inert substance in reaction with water and does not undergo hydration. Therefore, if hydration-reactive materials such as cement or blast furnace slag in a hydraulic composition are replaced with calcium carbonate, the strength of the hardened body after completion will decrease. On the other hand, if the proportion of water in the water-to-powder ratio is reduced to improve strength, mixing becomes difficult, and fluidity decreases, significantly reducing workability. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-051117 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention aims to propose a hydraulic composition that can ensure the desired design strength and fluidity even when the amount of Portland cement used is reduced by containing calcium carbonate. [Means for solving the problem]

[0005] The inventors of the present invention have discovered that by adding nitrate ions or nitrite ions to a hydraulic composition in which the amount of Portland cement used is reduced (or omitted) by containing calcium carbonate in the powder, the decrease in strength can be suppressed, leading to the creation of the present invention. Specifically, the present invention relates to a hydraulic composition comprising powder and water, wherein the powder contains calcium carbonate and at least one of blast furnace slag, expansive agent, slaked lime, quicklime, fly ash, and Portland cement, and further, nitrite ions are added in an external proportion in the range of 0.5% to 5.6% by mass per 100% by mass of the powder. In addition, the proportion of calcium carbonate in the powder is 8.5% by mass or more. Furthermore, if the powder contains blast furnace slag, it is desirable that the proportion of blast furnace slag in the powder be 35% by mass or more. In addition, at least one of aggregate, fiber, and chemical admixture may be added. Such a hydraulic composition exhibits good fluidity before hardening, develops the necessary strength after hardening, reduces CO2 emissions by decreasing cement usage, and enables stable retention and storage of CO2 through the use of calcium carbonate. Furthermore, because this hydraulic composition contains a large amount of industrial by-products such as blast furnace slag and fly ash, it can contribute to the efficient use of resources. [Effects of the Invention]

[0006] According to the hydraulic composition of the present invention, even when the amount of Portland cement used is reduced by including calcium carbonate, it is possible to ensure the desired design strength and fluidity. [Brief explanation of the drawing]

[0007] [Figure 1] It is a diagram showing the experimental results of Example 1, and it is a graph showing the relationship between the addition rates of nitrate ions and nitrite ions and the compressive strength ratio at 7 days of age of the material. [Figure 2] It is a diagram showing the experimental results of Example 1, and it is a graph showing the relationship between the addition rates of nitrate ions and nitrite ions and the compressive strength ratio at 28 days of age of the material. [Figure 3] It is a diagram showing the experimental results of Example 2, and it is a graph showing the relationship between the addition rate of nitrate ions and the compressive strength ratio at 7 days of age of the material. [Figure 4] It is a diagram showing the experimental results of Example 2, and it is a graph showing the relationship between the addition rate of nitrate ions and the compressive strength ratio at 28 days of age of the material. [Figure 5] It is a diagram showing the experimental results of Examples 1 and 2, and it is a graph showing the relationship between the amount of blast furnace slag and the compressive strength ratio.

Mode for Carrying Out the Invention

[0008] In this embodiment, for the purpose of reducing CO2 emissions, a hydraulic composition that contains calcium carbonate to omit or reduce Portland cement while ensuring the desired design standard strength and fluidity will be described. The hydraulic composition of this embodiment includes powder, water, aggregate, and a high-performance AE water reducer. The powder includes calcium carbonate (CaCO3), blast furnace slag, an expansive agent, and slaked lime. Also, at least one of nitrate ions or nitrite ions is added externally in the range of 0.5% to 5.6% by mass based on 100% by mass of the powder.

[0009] The proportion in the powder of calcium carbonate is 8.5% by mass or more. As calcium carbonate, for example, natural calcium carbonate called heavy calcium carbonate obtained by pulverizing and classifying limestone, and synthetic calcium carbonate called light calcium carbonate in which fine crystals are precipitated by a chemical reaction can be used. Also, calcium carbonate obtained by fixing CO2 in exhaust gas or the atmosphere may be used. The proportion of blast furnace slag in the powder should be 35% by mass or more. It is desirable to use blast furnace slag fine powder that conforms to JIS R5211 "Blast Furnace Cement" or JIS A6206 "Blast Furnace Slag for Concrete". Furthermore, the specific surface area of ​​the blast furnace slag should be 2000 to 10000 cm². 2 / g, preferably 3500-7000cm 2 It is preferable to use the one that is / g.

[0010] The hydraulic composition of this embodiment exhibits good fluidity before hardening, develops the necessary strength after hardening, and reduces CO2 emissions by decreasing the amount of cement used. Furthermore, the inclusion of calcium carbonate enables the stable retention and storage of CO2. When calcium carbonate is included, the amount of powder increases, which necessitates an increase in the amount of water per unit area to ensure fluidity, raising concerns about a decrease in strength. However, the inventors have found that adding nitrite ions or nitrate ions to the hydraulic composition improves the strength by more than 1.2 times. Furthermore, because this hydraulic composition contains a large amount of industrial by-products such as blast furnace slag, it can contribute to the effective utilization of resources.

[0011] The experimental results (Examples 1-3) obtained using the hydraulic composition of this embodiment will be described below. <Example 1> In Example 1, a mortar (hydraulic composition) containing large amounts of calcium carbonate and blast furnace slag was mixed with at least one of nitrate ions or nitrite ions, varying the amount added, and the compressive strength after hardening (strength at 7 days and strength at 28 days) was measured. In Example 1, the amount of calcium carbonate in the powder was 45% by mass, and the amount of blast furnace slag was 46% by mass. Furthermore, as a comparative example, the compressive strength of mortar in which neither nitrate ions nor nitrite ions were added was also measured.

[0012] The following materials were used in both the examples and comparative examples. Water: Tap water Blast furnace slag: Fine powder of blast furnace slag, density 2.89 g / cm 3 , Blaine specific surface area 4410 cm 2 / g, JIS A6206 Expansion material: Lime-based expansion material, density 3.15 g / cm 3 , Blaine specific surface area 4000 cm 2 / g, JIS A6202 Hydrated lime: Special grade hydrated lime, density 2.20 g / cm 3 , Passing through a 600 μm sieve, JIS R9001 CaCO3: Light calcium carbonate, density 2.64 g / cm 3 , Blaine specific surface area 4350 cm 2 / g Calcium nitrite monohydrate: Ca(NO2)2·H2O, special grade reagent, manufactured by Kanto Chemical Co., Inc. Calcium nitrate tetrahydrate: Ca(NO3)2·4H2O, special grade reagent, manufactured by Kanto Chemical Co., Inc. Hardening accelerator: Master Set FZP99, manufactured by Pozolith Solutions, nitric acid ion equivalent content 24 mass%, nitrous acid ion equivalent content 24 mass%, JIS A6204 Fine aggregate: Mixed sand produced in Kimitsu, surface dry density 2.60 g / cm 3 Water absorption rate 2.07% High-performance AE water reducer: Master Glenium SP8HUH, manufactured by Pozolith Solutions, JIS A6204

[0013] Table 1 shows the formulations of the examples and comparative examples. In Table 1, the total volume of each formulation is about 1.5 L, and the unit is "g (gram)". Table 2 shows the strength test results of the examples and comparative examples. The mixing composition ratio was water: powder: sand = 1:2:4.5 (mass ratio). Furthermore, Fig. 1 shows the relationship between the addition rates of nitrate ions and nitrite ions in the examples and the compressive strength ratio at 7 days of age, and Fig. 2 shows the relationship between the addition rates of nitrate ions and nitrite ions in the examples and the compressive strength ratio at 28 days of age. Calcium nitrite monohydrate and calcium nitrate tetrahydrate were added externally to the powder. Also, the amount of water corresponding to the crystal water (H2O) contained in calcium nitrite monohydrate and calcium nitrate tetrahydrate was subtracted from the mixing water. The amount of high-performance AE water-reducing agent added was 1.2% to 1.7% by mass relative to 100% by mass of the powder. The amount of water equivalent to the amount of high-performance AE water-reducing agent and hardening accelerator added was reduced from the mixing water. In Comparative Example 1-2, the amount of slaked lime was increased so that the calcium content was equivalent to that of calcium nitrate tetrahydrate added in Example 1-3.

[0014] [Table 1]

[0015] [Table 2]

[0016] As shown in Table 2 and Figures 1 and 2, calcium nitrate tetrahydrate is added to 100% by mass of the powder, along with nitrate ions NO3. - Examples 1-1 to 1-3, in which 0.5 to 2.8% by mass was added, showed a compressive strength ratio at 7 days and 28 days of age of 1.2 times or more compared to Comparative Example 1-1. In addition, calcium nitrite monohydrate was added to 100% by mass of the powder, along with nitrite ions NO2 - Examples 1-6 to 1-8, in which 1.4 to 5.6% by mass of the additive was used, also showed a compressive strength ratio of 1.2 times or more compared to Comparative Example 1-1. Furthermore, in Example 1-9, in which calcium nitrite monohydrate and calcium nitrate tetrahydrate were added to 100% by mass of the powder, the compressive strength ratio also showed a compressive strength ratio of 1.2 times or more compared to Comparative Example 1-1. Similarly, in Example 1-10, in which a hardening accelerator containing nitrite ions and nitrate ions was added, an increase in strength was also confirmed. Furthermore, calcium nitrate tetrahydrate is added to 100% by mass of the powder, along with nitrate ions NO3. - In Example 1-4, where 4.2% by mass was added, the compressive strength ratio at 28 days was 1.18 times higher than that of Comparative Example 1-1. Furthermore, calcium nitrate tetrahydrate was added to 100% by mass of the powder, along with nitrate ions (NO3). -In Examples 1-5, where 5.6% by mass was added, the compressive strength ratio at 28 days was 1.16 times higher than that of Comparative Example 1-1. On the other hand, in Comparative Example 1-2, where the amount of slaked lime was increased compared to Comparative Example 1-1 and the amount of calcium was increased to the same amount as in Example 1-3, the increase in compressive strength ratio was only 5% or less. This confirmed that adding calcium alone does not increase strength. Therefore, for mortar containing a large amount of calcium carbonate (45% by mass of powder), nitrite ions (NO2 - ) or nitrate ion (NO3 - It was confirmed that adding 0.5 to 5.6% by mass, preferably 0.5 to 2.8% by mass, of the powder improved its strength.

[0017] <Example 2> In Example 2, nitrate ions were added externally to a mortar (hydraulic composition) containing a large amount of powder with calcium carbonate and blast furnace slag, and water, and the compressive strength after hardening (strength at 7 days and strength at 28 days) was measured (Examples 2-1, 2-2, and 2-3). In each example, calcium nitrate tetrahydrate was added to 100% by mass of the powder, and nitrate ions NO3 were added. - An amount equivalent to 1.4% by mass was added. Furthermore, as Comparative Examples 2-1, 2-2, and 2-3, the compressive strength was measured for mortar with the same formulation as the example, but without the addition of nitrate ions. Furthermore, as Comparative Example 2-4, a mortar made of Portland cement powder with no added nitrate ions was also measured for compressive strength, and as Comparative Example 2-5, a mortar made of Portland cement powder with added nitrate ions was also measured for compressive strength. In Example 2-1 and Comparative Example 2-1, the ratio of Portland cement:blast furnace slag:calcium carbonate was 16.5:38.5:45. In Example 2-2 and Comparative Example 2-2, the ratio of Portland cement:fly ash:blast furnace slag:calcium carbonate was 8.25:11:35.75:45. Furthermore, in Examples 2-3 and Comparative Examples 2-3, the ratio of blast furnace slag:expanding agent:slaked lime:calcium carbonate was set to 22.6:5.4:2:70.

[0018] The following materials were used in both the examples and comparative examples. Water: Tap water OPC: Ordinary Portland cement, density 3.16 g / cm³ 3 Brain specific surface area 3270 cm² 2 / g, JIS R5210 FA: Fly ash type II, density 2.30 g / cm³ 3 Brain specific surface area 4640 cm² 2 / g, JIS A6201 Blast furnace slag: Fine blast furnace slag powder, density 2.89 g / cm³ 3 Brain specific surface area 4410 cm² 2 / g, JIS A6206 Expansion agent: Lime-based expansion agent, density 3.15 g / cm³ 3 Brain specific surface area 4000 cm² 2 / g, JIS A6202 Slaked lime:Special slaked lime density 2.20g / cm 3 600μm sieve, full passage, JIS R9001 CaCO3: Light calcium carbonate, density 2.64 g / cm³ 3 Brain specific surface area 4350 cm² 2 / g Calcium nitrate tetrahydrate: Ca(NO3)2·4H2O, special grade reagent, manufactured by Kanto Chemical Co., Ltd. Fine aggregate: Mixed sand from Kimitsu, surface dry density 2.60 g / cm³ 3 Water absorption rate 2.07% High-performance AE water-reducing agent: Master Glenium SP8HUH, manufactured by Pozzolith Solutions, JIS A6204

[0019] Table 3 shows the formulations of the examples and comparative examples. In Table 3, the total volume of each formulation is approximately 1.5 L, and the unit is "g (grams)". Table 4 shows the strength test results of the examples and comparative examples, and Figures 3 and 4 show the relationship between the nitrate ion addition rate and the compressive strength ratio. The formulation ratio was water:powder:sand = 1:2:4.5 (mass ratio). Furthermore, calcium nitrate tetrahydrate was added to the powder by external means, such that the nitrate ion addition rate was 1.4% by mass per 100% by mass of powder. In addition, the amount of water equivalent to the amount of crystal water contained in the calcium nitrate tetrahydrate and the amount of high-performance AE water-reducing agent added was reduced from the mixing water.

[0020] [Table 3]

[0021] [Table 4]

[0022] As shown in Table 4 and Figures 3 and 4, the proportions of blast furnace slag and calcium carbonate in the powder were set to 38.5% by mass and 45% by mass, respectively, and calcium nitrate was added as nitrate ions NO3. - Example 2-1, in which 1.4% by mass was added, and the proportions of blast furnace slag and calcium carbonate in the powder were 35.75% by mass and 45% by mass, respectively, and calcium nitrate was added as nitrate ion NO3 - In Example 2-2, where 1.4% by mass was added, calcium nitrate acted effectively. Compared to Comparative Examples 2-1 and 2-2, the compressive strength ratios at 7 days and 28 days of age in Examples 2-1 and 2-2 were 1.2 times or more. On the other hand, the proportions of blast furnace slag and calcium carbonate in the powder were set to 22.6% by mass and 70% by mass, respectively, and calcium nitrate was added as nitrate ions NO3. - In Example 2-3, where 1.4% by mass was added, the compressive strength ratio at 7 days of age was 1.05 times higher and at 28 days of age was 1.08 times higher compared to Comparative Example 2-3, showing only a slight increase. Furthermore, the powder consists of Portland cement and calcium nitrate, and nitrate ions NO3- Comparative Example 2-5, which had 1.4% by mass added, showed a compressive strength ratio of 0.86 times at 7 days and 0.82 times at 28 days compared to Comparative Example 2-4, which was a mortar made of Portland cement powder with no added nitrate ions. This result indicates that adding calcium nitrate reduces strength. Therefore, it was confirmed that adding calcium nitrate to mortar containing calcium carbonate or blast furnace slag in the powder improves its compressive strength. Figure 5 shows the relationship between the amount of blast furnace slag in the powder and the compressive strength ratio for Examples 1-2, 2-1, 2-2, 2-3, and Comparative Example 2-5. As shown in Figure 5, it was confirmed that adding calcium nitrate to mortar with a blast furnace slag content of approximately 35% by mass or more relative to the powder improved the compressive strength.

[0023] <Example 3> In Example 3, the compressive strength (7-day and 28-day strength) after hardening was measured when a hardening accelerator containing nitrate ions was added externally to concrete (hydraulic composition) containing a powder consisting of calcium carbonate, blast furnace slag, expansive agent, and slaked lime, along with water (Example 3). In Example 3, the ratio of blast furnace slag:expansive agent:slaked lime:calcium carbonate was 77.1:6.9:7.4:8.5. In addition, as Comparative Example 3, the compressive strength (7-day and 28-day strength) after hardening was also measured when no hardening accelerator was added. Table 5 shows the formulations of the examples and comparative examples. Table 6 shows the strength test results of the examples and comparative examples. Furthermore, the amount of water added was reduced from the mixing water by the amount of high-performance AE water-reducing agent and hardening accelerator added.

[0024] The following materials were used in both the examples and comparative examples. Water: Tap water Blast furnace slag: Fine blast furnace slag powder, density 2.89 g / cm³ 3 Brain specific surface area 4410 cm² 2 / g, JIS A6206 Expansion agent: Lime-based expansion agent, density 3.15 g / cm³ 3 Brain specific surface area 4040 cm²2 / g, JIS A6202 Slaked lime:Special slaked lime density 2.20g / cm 3 600μm sieve, full passage, JIS R9001 CaCO3: Heavy calcium carbonate, density 2.72 g / cm³ 3 Brain specific surface area 4850 cm² 2 / g Fine aggregate: A mixture of mountain sand from Ichihara and crushed limestone sand from Torigatayama. Surface dry density: 2.64 g / cm³ 3 Water absorption rate 1.27% Coarse aggregate 1: Hard sandstone from Ome, with a maximum particle size of 20 mm and a surface-dry density of 2.65 g / cm³. 3 Water absorption rate 0.54% Coarse aggregate 2: Garang limestone crushed stone, maximum particle size 20 mm, surface dry density 2.70 g / cm³ 3 Water absorption rate 0.53% Curing accelerator: Masterset FZP99, manufactured by Pozzolith Solutions, nitrate ion equivalent content 24% by mass, nitrite ion equivalent content 24% by mass, JIS A6204 High-performance AE water-reducing agent: Master Glenium SP8HUH, manufactured by Pozzolith Solutions, JIS A6204

[0025] [Table 5]

[0026] [Table 6]

[0027] As shown in Table 6, Example 3 showed a strength 1.2 times greater than that of Comparative Example 3. Therefore, it was confirmed that adding nitrate ions (hardening accelerator) to concrete containing 8.5% by mass or more of calcium carbonate in the powder and a large amount of blast furnace slag (77.1% by mass in the powder) improves its strength.

[0028] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and each of the above-mentioned components can be modified as appropriate without departing from the spirit of the present invention. For example, in the above embodiment, the powder includes calcium carbonate (CaCO3), blast furnace slag, an expansive agent, and slaked lime. However, the powder is not limited as long as it includes calcium carbonate and at least one of the following: blast furnace slag, an expansive agent, slaked lime, quicklime, fly ash, and Portland cement. For example, fly ash conforming to JIS A6201 "Fly Ash for Concrete" may be used. For example, quicklime specified in JIS R9001 "Industrial Lime" may be used. Furthermore, for Portland cement, for example, ordinary Portland cement, moderate-heat Portland cement, low-heat Portland cement, rapid-hardening Portland cement, ultra-rapid-hardening Portland cement, sulfate-resistant Portland cement, etc., as specified in JIS R5210 "Portland Cement", and JIS R5214 "Eco-Cement" can be used. Furthermore, although the above embodiment includes fine aggregate, at least one of the following may be added: fine aggregate, coarse aggregate, fibers, and chemical admixtures.

Claims

1. A hydraulic composition comprising powder and water, The aforementioned powder is Calcium carbonate and It includes at least one of the following: blast furnace slag, expansive material, slaked lime, quicklime, fly ash, and Portland cement. Nitrite ions are added externally in an amount ranging from 0.5% to 5.6% by mass relative to 100% by mass of the aforementioned powder. A hydraulic composition characterized in that the proportion of calcium carbonate in the powder is 8.5% by mass or more.

2. The hydraulic composition according to claim 1, characterized in that at least one of aggregates, fibers, and chemical admixtures is added.

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