Concrete composition and method of producing the same

Abstract

To provide a concrete composition mixed with blast furnace slag fine powder and light calcium carbonate, capable of yielding necessary compression strength and solving the problems of a slump loss and increase of a time required for kneading, while emitting a small amount of CO2 and imposing a low environmental load, and a method of producing the same.SOLUTION: The concrete composition contains Portland cement, blast furnace slag fine powder and light calcium carbonate, as powder, with the ratio of the blast furnace slag fine powder relative to the Portland cement and the blast furnace slag fine powder being in the range of 20-95 mass%, the ratio of the light calcium carbonate relative to the whole powder being in the range of 25-75 mass%, the amount of CO2 emission being 200 kg-CO2 / m3 or less, and the compression strength thereof being 10 N / mm2 or higher.SELECTED DRAWING: Figure 3-4

Description

Technical Field

[0001] The present invention relates to a concrete composition obtained by mixing blast furnace slag fine powder and light calcium carbonate, which has a low CO2 (carbon dioxide) emission and a small environmental load, and a method for producing the same.

Background Art

[0002] Portland cement used in concrete compositions emits a large amount of CO2 from the decarbonation of raw materials during production and fuel during firing. Therefore, in response to the increasing interest in climate change mitigation in recent years, it is required to reduce the CO2 emission of the concrete composition itself.

[0003] As one method for reducing the CO2 emission of concrete compositions, a blended cement in which a part of the Portland cement in the concrete composition is replaced with blast furnace slag fine powder with a low CO2 emission has been proposed and widely used (for example, see Patent Document 1).

[0004] In recent years, in order to further reduce the CO2 emission of concrete compositions, it has been proposed to mix calcium carbonate (light calcium carbonate) produced by fixing CO2 in the atmosphere or exhaust gas into the concrete compositions (for example, see Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, a concrete composition obtained by mixing blast furnace slag fine powder and lightweight calcium carbonate can reduce the CO2 emissions of the concrete composition. However, compared with a general concrete composition using Portland cement, in particular, as the addition rate of lightweight calcium carbonate increases, the compressive strength decreases, slump loss is likely to occur, the time required for mixing increases, and there is a problem that it is difficult to handle.

[0007] An object of the present invention is to provide a concrete composition obtained by mixing blast furnace slag fine powder and lightweight calcium carbonate, which can obtain a required compressive strength, solve the problems of slump loss and an increase in the time required for mixing, has a small CO2 emission amount, and has a small environmental load, and a method for producing the same.

Means for Solving the Problems

[0008] In order to achieve the above object, the concrete composition of the present invention is a concrete composition containing Portland cement, blast furnace slag fine powder, and lightweight calcium carbonate as powders, wherein the ratio of blast furnace slag fine powder to the Portland cement and blast furnace slag fine powder is within the range of 20 to 95% by mass, and the ratio of lightweight calcium carbonate to the total powder is within the range of 25 to 75% by mass, and the CO2 emission amount is 200 kg-CO2 / m 3 Hereinafter, preferably, 0 kg-CO2 / m 3 Hereinafter, and the compressive strength is 10 N / mm 2 The above is characterized. In this specification (including demonstration experiments), the compressive strength refers to the compressive strength at an age of 14 days.

[0009] In this case, lightweight calcium carbonate having a water content of 10% by mass or less can be used for the lightweight calcium carbonate.

[0010] Furthermore, the concrete composition can contain gypsum.

[0011] The gypsum can be one that has been previously added to fine blast furnace slag powder.

[0012] Also, to achieve the same object, a method for producing a concrete composition of the present invention is characterized in that a slurry obtained by stirring and mixing light calcium carbonate, a high-performance water reducing agent, a retarder and water is added to a mixture obtained by stirring and mixing Portland cement, fine blast furnace slag powder and aggregates, and then stirring and mixing is performed.

[0013] In this case, the fine blast furnace slag powder can be composed of one to which gypsum has been previously added.

Advantages of the Invention

[0014] According to the concrete composition and its production method of the present invention, it is possible to obtain the required compressive strength, solve the problems of slump loss and increase in the time required for mixing, and obtain a concrete composition mixed with fine blast furnace slag powder and light calcium carbonate with low CO2 emissions and low environmental load.

[0015] Also, by using light calcium carbonate with a water content of 10% by mass or less for light calcium carbonate, it can be transported in a state where the water content of light calcium carbonate is 10% by mass or less. For example, it is prepared so that the water content of the slurry becomes 38% by mass or more, and by making it in a state where it can be pressure-fed by a slurry pump, the energy consumption during transportation can be reduced.

[0016] Also, by using a composition containing gypsum for the concrete composition, a large initial compressive strength can be obtained, the time until demolding during the production of concrete products such as concrete blocks can be shortened, and the production process of concrete products can be made more efficient.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3-1

Figure 3-2

Figure 3-3

Figure 3-4

Figure 3-5

Figure 4

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the concrete composition of the present invention and its manufacturing method will be described.

[0019] The concrete composition of the present invention relates to a concrete composition containing Portland cement, blast furnace slag fine powder, and light calcium carbonate as powders, and by reducing the amount of Portland cement used, a concrete composition with low CO2 emissions and a small environmental load is obtained.

[0020] Hereinafter, the concrete composition of the present invention and its manufacturing method will be described based on verification experiments.

[0021] [Verification Experiment 1] With the blending ratios (mass ratios) of the materials described in Table 1, the replacement rate of fine blast furnace slag (slag) (the ratio of fine blast furnace slag to Portland cement and fine blast furnace slag: fine blast furnace slag / (Portland cement + fine blast furnace slag) (mass ratio)) was changed from 0 to 95%, and the replacement rate of light calcium carbonate (light Ca) (the ratio of light calcium carbonate to the whole powder: light calcium carbonate / (Portland cement + fine blast furnace slag + light calcium carbonate) (mass ratio)) was changed from 0 to 95%, and kneading was carried out by Manufacturing Method 1 (only adding liquid materials later and stirring) shown in Figure 1. Here, the addition rate of the high-performance water reducer was set to an amount that could obtain fluidity, and no retarder was added. The kneading time until fluidity was obtained was measured. The CO₂ emissions of each formulation were determined. Here, for the calculation of the CO₂ emissions of each formulation, the CO₂ emission per unit of each material was as follows: water: 0.235 kg-CO₂ / t, cement: 766.6 kg-CO₂ / t, slag: 26.5 kg-CO₂ / t, light calcium carbonate: -390 kg-CO₂ / t, fine aggregate: 3.7 kg-CO₂ / t, coarse aggregate: 2.9 kg-CO₂ / t, high-performance water reducer: 350 kg-CO₂ / t. After curing, a uniaxial compressive strength test was carried out in accordance with the concrete compressive strength test method (JIS A 1108).

[0022]

Table 1

[0023] As the materials described in Table 1, the following can be used.

[0024] [Aggregate] As the aggregate that becomes the base material of the concrete composition, general-purpose coarse aggregate and fine aggregate can be used.

[0025] [Fine blast furnace slag] In addition to the blast furnace slag fine powder alone, gypsum additives (a premix of one or more of anhydrite and gypsum in an amount of 4% or less by mass of SO3 in advance with the blast furnace slag fine powder) can be used for the blast furnace slag fine powder. The blast furnace slag fine powder has an excellent economy and is easy to procure when it has a specific surface area of 3500 - 5000 cm 2 / g, but it is not limited to this. Even when using those with a specific surface area of 5000 - 12000 cm 2 / g, performance equivalent to or better than that can be obtained.

[0026] [Light calcium carbonate] Light calcium carbonate is replaced as a part of the powder and mixed. Light calcium carbonate is produced by immobilizing CO2 on a calcium source such as slaked lime. Among them, light calcium carbonate as a material for carbon dioxide capture and effective utilization (CCU: Carbon dioxide Capture and Utilization) aimed at reducing CO2 emissions is produced by immobilizing CO2 from exhaust gas on a by-product-derived calcium source (350 - 440 kg-CO2 / t of CO2 is immobilized). For example, when a concrete composition is used as a ground improvement material, since CO2 is mineralized in the form of calcium carbonate and then stored underground as part of ground improvement, it is expected to be stored more easily and inexpensively compared to the carbon dioxide capture and storage technology (CCS: Carbon dioxide Capture and Storage) that injects it into a deep underground storage layer. In addition, there is an advantage that there is no concern such as leakage of the injected CO2 outside the storage layer due to external forces such as earthquakes. In addition, for the production of light calcium carbonate as a CCU material, light calcium carbonate other than that derived from concrete sludge as a by-product can be used as a calcium source, for example, by-products during acetylene gas production, by-products during ironmaking, waste concrete, etc. The purity of the lightweight calcium carbonate used in the demonstration experiment (lightweight calcium carbonate "Eco Tan Cal" (registered trademark) manufactured by Nippon Concrete Industry Co., Ltd.) was 90 to 99%, and 350 to 440 kg-CO2 / t of CO2 was fixed. In addition, the moisture content of this lightweight calcium carbonate was 10% by mass or less.

[0027] [Admixture] As a result of conducting preliminary tests using several types of admixtures, it was found that a high-performance water-reducing agent mainly composed of a carboxyl group-containing polyether compound (for example, the high-performance water-reducing agent "Mighty 21HF" (trade name) manufactured by Kao Corporation.) was highly effective in ensuring the workability of concrete, so it was used in this test.

[0028] The results of Demonstration Experiment 1 are shown in Tables 2-1 to 2-5 and Figures 3-1 to 3-5.

[0029]

Table 2-1

[0030]

Table 2-2

[0031]

Table 2-3

[0032]

Table 2-4

[0033]

Table 2-5

[0034] From Demonstration Experiment 1, it can be said that the concrete composition of the present invention has the following effects. · When the substitution rate of light calcium carbonate (light cal) increases, the compressive strength decreases, but the compressive strength ratio is higher compared to the results of Patent Document 2 and heavy calcium carbonate (heavy cal). · At a substitution rate of 50% of light calcium carbonate (light cal), with a compressive strength ratio of 0.58 or more, a concrete composition obtained by mixing Portland cement, blast furnace slag fine powder, light calcium carbonate (purity 90% or more), fine aggregate, coarse aggregate, high-performance water reducing agent, (retarder), and water has a large strength development per unit amount of binder (B) in the coexistence of the above materials. In particular, when the substitution rate of blast furnace slag fine powder (slag) is 80 - 95%, at a substitution rate of 50% of light calcium carbonate (light cal), with a compressive strength ratio of 0.73 - 0.85, a concrete composition obtained by mixing Portland cement, blast furnace slag fine powder, light calcium carbonate (purity 90% or more), fine aggregate, coarse aggregate, high-performance water reducing agent, (retarder), and water has a large strength development per unit amount of binder (B) in the coexistence of the above materials. · At a substitution rate of 50% or more of light calcium carbonate (light cal), a concrete composition obtained by substituting 50% or more of the powder (P) with light calcium carbonate (purity 90% or more) of the present invention in Portland cement, blast furnace slag fine powder, fine aggregate, coarse aggregate, high-performance water reducing agent, (retarder), water, and mixing them has a substitution rate of blast furnace slag fine powder (slag) of 20 - 80% when compared to a substitution rate of 0%, the compressive strength ratio becomes 1.13 times larger. In particular, when the substitution rate of blast furnace slag fine powder (slag) is 40 - 80%, the compressive strength ratio becomes 1.15 times larger compared to a substitution rate of 0%.

[0035] [Verification Experiment 2] In order to suppress slump loss, in addition to a high-performance water reducing agent (carboxyl group-containing polyether compound), a retarder (oxycarboxylate) (for example, the retarder "Floric T" (trade name) manufactured by Floric Co., Ltd.) was added and the concrete was kneaded. The addition amount of the retarder was changed to 6 levels of 0, 0.05, 0.1, 0.2, 0.5, and 1%.

[0036] The results of Verification Experiment 2 are shown in Figure 4.

[0037] From Demonstration Experiment 2, it can be said that the concrete composition of the present invention has the following effects. · When the retarder (oxycarboxylate) was in the range of 0 to 0.05%, the slump loss was large after 30 minutes. · When the retarder (oxycarboxylate) was in the range of 0.1 to 0.5%, there was no slump loss after 30 minutes. · When the retarder (oxycarboxylate) was 1%, there was no slump loss after 30 minutes, but there was after - elongation. · When the optimum addition amount of the retarder (oxycarboxylate) was used, the result of no slump loss was obtained even after 30 minutes.

[0038] [Demonstration Experiment 3] When the replacement ratio of light calcium carbonate (light cal) exceeded 50%, the mixing time became too long. Therefore, for the formulations with a light calcium carbonate (light cal) replacement ratio of 0 to 95%, concrete was mixed using Manufacturing Method 2. In Manufacturing Method 2, a light calcium carbonate slurry (light calcium carbonate + water + high - performance water - reducing agent + retarder + defoaming agent (if necessary)) was prepared in advance, and then the concrete was mixed. The mixing time was measured as the time from dry - mixing Portland cement + blast - furnace slag fine powder + fine aggregate, then adding the light calcium carbonate slurry until it became fluidized. After mixing the concrete by Manufacturing Method 2, for comparison, a formulation with a 50% replacement ratio of light calcium carbonate (light cal) was mixed by Manufacturing Method 3.

[0039] The results of Demonstration Experiment 3 are shown in Table 3.

[0040]

Table 3

[0041] From Demonstration Experiment 3, it can be said that the concrete composition of the present invention and its manufacturing method have the following effects. · When the water content of the light calcium carbonate - containing slurry was 38% or more, the slurry was slurried to a state where it could be pumped by a slurry pump. · When the water content of the slurry containing light calcium carbonate was in the range of 30 - 36%, it could not be slurried to a state that could be pumped by a slurry pump. · When the substitution rate of light calcium carbonate (light cal) was 50 - 65%, the kneading time was shortened to 90 seconds. · When the substitution rate of light calcium carbonate (light cal) was 70 - 95%, light calcium carbonate + water + high - performance water - reducing agent did not show a slurry state, but the kneading time could be shortened to less than half. · As a result of kneading the mixture with a 50% substitution rate of light calcium carbonate (light cal) by production method 3, the kneading time was 90 seconds, and the same effect as production method 2 was obtained.

[0042] [Demonstration Experiment 4] By the way, for blast furnace slag fine powder, in addition to blast furnace slag fine powder alone, gypsum - added products (premixed with blast furnace slag fine powder in advance in a range of 4% (mass ratio) or less of SO3 content with one or more of anhydrite and gypsum) can be used. A demonstration experiment was conducted on the influence of the presence or absence of gypsum addition on concrete products. Table 4 shows the blast furnace slag fine powder used in the demonstration experiment, and Tables 5 - 1 to 5 - 2 show the mixing ratios (mass ratio) of the materials and the results of their compressive strength tests (average value of 3 samples). Note that the fine aggregate ratio (S / a) was 41.0% (mass ratio).

[0043] [Table 4]

[0044] [Table 5 - 1]

[0045] [Table 5 - 2]

[0046] From Demonstration Experiment 4, it was confirmed that as the blending ratio of fine blast furnace slag increases, the compressive strength tends to decrease, and by using fine blast furnace slag with gypsum added in advance, a large initial compressive strength (at 1-day age) can be obtained. Note that Demonstration Experiment 4 was conducted on mortar without adding lightweight calcium carbonate, but it is considered that the same tendency will be shown in the concrete composition of the present invention containing lightweight calcium carbonate.

[0047] From the above, it can be said that the concrete composition of the present invention and its manufacturing method have the following effects. · By mixing Portland cement, fine blast furnace slag, lightweight calcium carbonate (calcium carbonate obtained by immobilizing CO2 derived from exhaust gas to a calcium source derived from by-products; the same shall apply hereinafter), fine aggregate, coarse aggregate, high-performance water reducer, retarder, and water, a carbon-neutral blend can be provided. · By replacing 60 to 80% of Portland cement with fine blast furnace slag, a carbon-neutral blend can be provided while suppressing the amount of lightweight calcium carbonate used. · Even when the addition amount of lightweight calcium carbonate is relatively large, a carbon-neutral concrete composition containing lightweight calcium carbonate and a manufacturing method can be provided, which do not cause slump loss and can shorten the kneading time. · The carbon-neutral concrete composition using the lightweight calcium carbonate of the present invention has a greater strength development per unit amount of binder. · By adding a high-performance water reducer (carboxyl group-containing polyether compound) and a retarder (oxycarboxylate) to the carbon-neutral concrete composition containing the lightweight calcium carbonate of the present invention, a carbon-neutral concrete that does not cause slump loss can be obtained. · According to Manufacturing Method 1, a carbon-neutral concrete that does not cause slump loss can be obtained, but the kneading time becomes long. ·According to Manufacturing Method 2, it is possible to obtain carbon-neutral concrete that does not cause slump loss and can shorten the kneading time. ·According to Manufacturing Method 3, the same effects as those of Manufacturing Method 2 can be obtained. ·By using light calcium carbonate with a purity of 90 to 99%, when transporting light calcium carbonate with a water content of less than 10% and manufacturing it at a plant near the place of use, since the amount of water contained in light calcium carbonate is small, the transportation efficiency can be improved and the CO2 emissions during transportation can be suppressed. ·By using a concrete composition containing gypsum, specifically, a composition in which gypsum is previously added to blast furnace slag fine powder, which is a raw material of the concrete composition, a large initial compressive strength can be obtained, and the time until demolding during the manufacture of concrete products such as concrete blocks can be shortened, thereby improving the manufacturing process of concrete products.

[0048] As described above, the concrete composition and its manufacturing method of the present invention have been described based on their embodiments. However, the present invention is not limited to the configurations described in the above embodiments, and the configuration can be appropriately changed without departing from the gist thereof.

Industrial Applicability

[0049] The concrete composition and its manufacturing method of the present invention can provide a concrete composition obtained by mixing blast furnace slag fine powder and light calcium carbonate, which can obtain the required compressive strength, solve the problems of slump loss and increased kneading time, have low CO2 emissions and a small environmental load, and can be widely used for various purposes.

Claims

1. A concrete composition comprising Portland cement, ground granulated blast furnace slag, and light calcium carbonate as powders, the ratio of the ground granulated blast furnace slag to the Portland cement and ground granulated blast furnace slag being within a range of 20 to 95 mass%, the ratio of the light calcium carbonate to the total powder being within a range of 25 to 75 mass%, and ２ Emissions are 200kg-CO ２ / m ３ and the compressive strength is 10 N / mm ２ A concrete composition characterized by the above.

2. The CO ２ Emissions are 0kg-CO ２ / m ３ 2. The concrete composition according to claim 1, wherein:

3. 3. The concrete composition according to claim 1, wherein the water content of the precipitated calcium carbonate is 10 mass % or less.

4. 3. The concrete composition according to claim 1, further comprising gypsum.

5. 5. The concrete composition according to claim 4, wherein the gypsum is added in advance to ground granulated blast furnace slag.

6. A method for producing a concrete composition, comprising stirring and mixing a mixture of Portland cement, ground granulated blast furnace slag and aggregate, adding a slurry prepared by stirring and mixing light calcium carbonate, a high-performance water reducing agent, a retarder and water, and stirring and mixing the mixture.

7. 7. The method for producing a concrete composition according to claim 6, wherein the ground granulated blast furnace slag contains gypsum added thereto in advance.

Images