Cement composition and method for producing same

Abstract

To provide a cement composition that can suppress the heat generation associated with hardening and exhibit excellent initial strength even when the content of granulated blast furnace slag is high.SOLUTION: In one aspect of the present disclosure, a cement composition contains cement, granulated blast furnace slag having an aluminum oxide content of 14 mass% or less and a basicity of 1.55-1.95, and an accelerator. A content of the granulated blast furnace slag is 30.0-90.0 mass%, taking the total amount of the cement and the granulated blast furnace slag as 100 mass%. A content of the accelerator is 0.5-10.0 pts.mass for 100 pts.mass of the granulated blast furnace slag.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a cement composition and a method for producing the same, and more particularly to a cement composition containing granulated blast furnace slag and a method for producing the same. [Background technology]

[0002] In recent years, with the increasing demand for measures to combat global warming, there has been a demand for a reduction in the amount of CO2 emitted in cement production. As a method for reducing CO2 emissions, methods of replacing part of cement with admixtures have been widely studied. Among admixtures, steel slag such as granulated blast furnace slag (BFS) is expected to increase the long-term strength of concrete and improve its salt-shielding effect. Therefore, research is being conducted on cement that uses steel slag as an admixture and increases its mixing ratio.

[0003] On the other hand, increasing the mixing ratio of BFS tends to decrease the early strength of the cement when it hardens compared to ordinary Portland cement (OPC), necessitating a longer curing period in order to achieve a strength similar to that of OPC. In response to this, methods have been reported in which early strength is improved by further adding calcium hydroxide fine powder (e.g., Non-Patent Document 1) or by using blast-furnace cement prepared with high C3S clinker (e.g., Non-Patent Document 2). According to Non-Patent Document 1, the early strength of a cement composition is improved by adding 2 to 8 mass% of calcium hydroxide fine powder. Furthermore, the use of other inorganic or organic accelerators has also been investigated as a method for improving the early strength of cement compositions. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Hiroaki Yoshiga et al., "Effect of Fine Calcium Hydroxide Powder on Cement Containing Blast Furnace Slag," Proceedings of the Cement and Concrete Journal, Vol. 67, No. 1, 2013, pp. 151-156 [Non-patent document 2] Atsushi Yatagai et al., "Effect of Specific Surface Area of ​​Ground Blast Furnace Slag on the Properties of Blast Furnace Cement Using High C3S Clinker," Proceedings of the Cement and Concrete Society, Vol. 67, No. 1, 2013, pp. 296-303 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the strength and other properties of blast furnace cement containing a high proportion of granulated blast furnace slag are strongly affected by the quality (e.g., composition, reactivity, etc.) of the granulated blast furnace slag used, and the addition of an accelerator often fails to achieve the desired effect. The reactivity of granulated blast furnace slag is often evaluated using an index called basicity, which is expressed as the value of (CaO + MgO + Al2O3) / SiO2 (the ratio of the total content of calcium oxide, magnesium oxide, and aluminum oxide to the content of silicon dioxide in the granulated blast furnace slag). However, even when granulated blast furnace slag with the same basicity is used, the strength exhibited when the cement composition hardens may differ.

[0006] Furthermore, when a retarder or the like is added or when the slag mixing rate is high, the effect of differences in the quality of the granulated blast furnace slag on the properties of blast furnace cement tends to become more pronounced. Although studies have been conducted to activate granulated blast furnace slag using accelerators, it cannot be said that the effect of using accelerators on the properties of blast furnace cement prepared using granulated blast furnace slag of different qualities has been fully studied.

[0007] Furthermore, blast-furnace slag cement has significantly lower early strength than ordinary cement. Therefore, the use of accelerators to improve early strength has been investigated. However, the reaction-accelerating effect of these accelerators increases the heat generated as the blast-furnace slag hardens, which may lead to abnormal setting. However, research to date has focused primarily on the activation of granulated blast-furnace slag by accelerators, and no detailed consideration has been given to the impact of the increased heat generated. Therefore, no research has been conducted that attempts to simultaneously suppress the heat generated as the blast-furnace slag cement hardens and improve its early strength.

[0008] The present disclosure aims to provide a cement composition that suppresses the amount of heat generated during hardening and exhibits excellent early strength even when it contains a large amount of granulated blast furnace slag, and a method for producing the same. [Means for solving the problem]

[0009] One aspect of the present disclosure provides a cement composition comprising cement, granulated blast furnace slag having an aluminum oxide content of 14 mass% or less and a basicity of 1.55 to 1.95, and an accelerator, wherein the content of the granulated blast furnace slag is 30.0 to 90.0 mass%, where the total amount of the cement and the granulated blast furnace slag is 100 mass%, and the content of the accelerator is 0.5 to 10.0 parts by mass per 100 parts by mass of the granulated blast furnace slag.

[0010] The cement composition contains specific granulated blast furnace slag whose aluminum oxide content is equal to or less than a predetermined value and whose basicity (the ratio of the total content of calcium oxide, magnesium oxide, and aluminum oxide to the content of silicon dioxide) is within a predetermined range, and contains a predetermined content of an accelerator, so that the amount of heat generated by hydration during hardening is suppressed and the early strength development can be excellent.

[0011] The accelerator may contain at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts. By including an alkali metal salt or an alkaline earth metal salt in the accelerator, the reactivity of the granulated blast furnace slag can be further improved.

[0012] The accelerator may contain a salt having a monovalent anion, which adjusts the formation of hydrates on the surface of the granulated blast furnace slag and further improves the reactivity of the granulated blast furnace slag.

[0013] The accelerator may contain a calcium salt. When the accelerator contains a calcium salt, calcium ions (Ca 2+ ) concentration increases, which can promote the production of calcium silicate hydrate (CSH), the main component of the hardened body, resulting in better early strength development.

[0014] The accelerator may contain at least one selected from the group consisting of nitrites, nitrates, and chlorides. By containing at least one selected from the group consisting of nitrites, nitrates, and chlorides, the accelerator can achieve better early strength development.

[0015] The content of the accelerator may be 0.5 to 5.0 parts by mass relative to 100 parts by mass of the granulated blast furnace slag. By setting the content of the accelerator within the above range, it is possible to achieve a higher level of both a reduction in the heat of hydration during hardening of the cement composition and an improvement in early strength.

[0016] One aspect of the present disclosure provides a method for producing a cement composition, comprising the step of mixing granulated blast furnace slag having an aluminum oxide content of 14 mass% or less and a basicity of 1.55 to 1.95 with an accelerator to prepare a cement composition, wherein the mixing step is performed so that the content of the granulated blast furnace slag is 30 to 90 mass%, where the total amount of the cement and the granulated blast furnace slag is 100 mass%, and the content of the accelerator is 0.5 to 10.0 parts by mass per 100 parts by mass of the granulated blast furnace slag.

[0017] The method for producing the cement composition includes a step of blending an accelerator with specific granulated blast furnace slag having an aluminum oxide content of not more than a predetermined value and a basicity within a predetermined range, and adjusting the contents of the granulated blast furnace slag and accelerator to fall within the predetermined ranges. This makes it possible to produce a cement composition that suppresses the heat of hydration during hardening and also exhibits excellent early strength development, as described above.

[0018] The method may further include a step of sorting the granulated blast furnace slag. [Effects of the Invention]

[0019] According to the present disclosure, it is possible to provide a cement composition that suppresses the amount of heat generated during hardening and that can exhibit excellent early strength even when the content of granulated blast furnace slag is high, and a method for producing the same. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content. In the following description, when it is written "X to Y" (X and Y are arbitrary numbers), it means "X or more and Y or less" unless otherwise specified.

[0021] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0022] One embodiment of the cement composition includes cement, granulated blast furnace slag having an aluminum oxide content of 14 mass% or less and a basicity of 1.55 to 1.95, and an accelerator, wherein the content of the granulated blast furnace slag is 30.0 to 90.0 mass%, where the total amount of the cement and the granulated blast furnace slag is 100 mass%, and the content of the accelerator is 0.5 to 10.0 mass%, relative to 100 parts by mass of the total amount of the granulated blast furnace slag.

[0023] The cement may be any of the various Portland cements specified in JIS R 5210:2003 "Portland cement." From the viewpoints of availability and further improving early-age strength, the cement preferably includes at least one of ordinary Portland cement and high-early-strength Portland cement, more preferably ordinary Portland cement, or may be ordinary Portland cement.

[0024] The Blaine specific surface area of ​​cement is, for example, 3000 to 8000 cm 2 / g, 3000-7000cm 2 / g, 3000-6000cm 2 / g, 3000-5000cm 2 / g, or 3000-4000cm 2 / g.

[0025] In this specification, the term "Blaine specific surface area" refers to a value measured in accordance with the method described in JIS R 5201:2015 "Physical testing methods for cement."

[0026] The granulated blast furnace slag may be, for example, commercially available, or may be prepared by hand to produce a slag equivalent to granulated blast furnace slag. The cement composition of the present disclosure uses granulated blast furnace slag that has a low aluminum oxide content (Al2O3 content) and a basicity within a predetermined range.

[0027] The aluminum oxide content in the granulated blast furnace slag is 14% by mass or less, and may be, for example, 13.8% by mass or less, 13.7% by mass or less, 13.5% by mass or less, or 13.0% by mass or less. When the upper limit of the aluminum oxide content is within the above range, the amount of aluminate hydrates produced during hardening of the cement composition can be reduced, thereby further suppressing the heat generated during hardening. The lower limit of the aluminum oxide content in the granulated blast furnace slag may be, for example, 8.0% by mass or more, 10.0% by mass or more, or 11.0% by mass or more. When the lower limit of the aluminum oxide content is within the above range, the reactivity of the hardening reaction of the cement composition can be improved, and the early strength can be further improved. The aluminum oxide content in the granulated blast furnace slag may be adjusted within the above range, and may be, for example, 8.0 to 13.8% by mass or 11.0 to 13.0% by mass.

[0028] The ratio of the calcium oxide content (mass%) to the silicon dioxide content (mass%) in the chemical composition of granulated blast furnace slag (CaO / SiO2 value, also referred to as the C / S ratio) may be, for example, 1.00 to 1.35, preferably 1.05 to 1.28, more preferably 1.10 to 1.28, and even more preferably 1.14 to 1.19.

[0029] The basicity of the granulated blast furnace slag is 1.55 to 1.95. The upper limit of the basicity of the granulated blast furnace slag may be, for example, 1.90 or less, 1.85 or less, or 1.80 or less. The lower limit of the basicity of the granulated blast furnace slag may be, for example, 1.60 or more, 1.65 or more, or 1.70 or more. When the lower limit of the basicity is within the above range, the early strength of the cement composition can be further improved. The basicity of the granulated blast furnace slag can be adjusted within the above range.

[0030] The basicity in this specification is a value measured in accordance with the description in JIS A 6206:2013 "Ground granulated blast furnace slag for concrete," and specifically means the value of (CaO + MgO + Al2O3) / SiO2 (the ratio of the total content of calcium oxide, magnesium oxide, and aluminum oxide to the content of silicon dioxide).

[0031] The specific surface area of ​​granulated blast furnace slag is, for example, 3000 to 5000 cm 2 / g, 4000-5000cm 2 / g, or 4000 to 4500 cm 2 / g.

[0032] The content of granulated blast furnace slag is 30.0 to 90.0 mass%, assuming the total amount of the cement and the granulated blast furnace slag to be 100 mass%, which can contribute to suppressing the amount of carbon dioxide generated in the production of the cement composition. Because the cement composition of the present disclosure uses the above-mentioned granulated blast furnace slag, the proportion of cement replaced by granulated blast furnace slag can be increased.

[0033] The lower limit of the granulated blast furnace slag content may be, for example, 40% by mass or more, 46% by mass or more, or 50% by mass or more, based on 100% by mass of the total amount of the cement and the granulated blast furnace slag. By ensuring that the lower limit of the granulated blast furnace slag content is within the above range, the amount of cement used can be further reduced. The upper limit of the granulated blast furnace slag content may be, for example, 85% by mass or less, 80% by mass or less, 75% by mass or less, or 70% by mass or less, based on 100% by mass of the total amount of the cement and the granulated blast furnace slag. By ensuring that the upper limit of the granulated blast furnace slag content is within the above range, the decrease in early strength can be further suppressed, and the effect of using an accelerator in combination can be further improved. The granulated blast furnace slag content may be adjusted within the above range, and may be 46 to 70% by mass or 50 to 70% by mass, based on 100% by mass of the total amount of the cement and the granulated blast furnace slag.

[0034] The accelerator is a compound that accelerates the reaction of granulated blast furnace slag and improves its early strength.

[0035] The accelerator may contain at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts. The accelerator containing an alkali metal salt or an alkaline earth metal salt can further improve the reactivity of the granulated blast furnace slag. Examples of the alkali metal include sodium and potassium, and examples of the alkaline earth metal include magnesium and calcium. From the viewpoints of the hydrates produced and the compressive strength, calcium is preferred.

[0036] The accelerator may contain a salt having a monovalent anion, or may contain a calcium salt. The accelerator may contain at least one selected from the group consisting of nitrites, nitrates, and chlorides. By including a nitrite in the accelerator, it is possible to achieve a higher level of both a reduction in the heat of hydration during hardening of the cement composition and an improvement in early strength.

[0037] More specific examples of the accelerator include calcium nitrite, calcium nitrate, calcium chloride, calcium hydroxide, sodium nitrite, potassium nitrite, sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, etc. Among the above compounds, the accelerator preferably contains an alkali metal nitrite, more preferably contains calcium nitrite, and even more preferably is calcium nitrite.

[0038] The content of the accelerator is 0.5 to 10.0 parts by mass relative to 100 parts by mass of the granulated blast furnace slag. The upper limit of the accelerator content may be, for example, 9.0 parts by mass or less, 8.0 parts by mass or less, 7.0 parts by mass or less, 6.0 parts by mass or less, or 5.0 parts by mass or less relative to 100 parts by mass of the granulated blast furnace slag. When the upper limit of the accelerator content is within the above range, the occurrence of abnormal coagulation when the reaction of the granulated blast furnace slag or the like is excessively promoted can be more reliably suppressed. The lower limit of the accelerator content may be, for example, 1.0 parts by mass or more, 2.0 parts by mass or more, or 3.0 parts by mass or more relative to 100 parts by mass of the granulated blast furnace slag. When the lower limit of the accelerator content is within the above range, the reaction of the granulated blast furnace slag can be further promoted. The content of the accelerator may be adjusted within the above range, and may be, for example, 0.5 to 5.0 parts by mass per 100 parts by mass of the granulated blast furnace slag.

[0039] In addition to cement, granulated blast furnace slag, and an accelerator, the cement composition may contain other components, such as limestone, gypsum, calcium hydroxide, silica powder, other calcium-containing inorganic powders, concrete water reducers, and retarders.

[0040] The above-mentioned cement composition can be produced, for example, by the following method. One embodiment of the method for producing a cement composition includes a step of selecting granulated blast furnace slag having an aluminum oxide content of 14 mass% or less and a basicity of 1.55 to 1.95 (hereinafter also referred to as the selection step), and a step of mixing cement, the granulated blast furnace slag, and an accelerator to prepare a cement composition (hereinafter referred to as the mixing step).

[0041] In the sorting step, granulated blast furnace slag having an aluminum oxide content of 14 mass% or less and a basicity of 1.55 to 1.95 is selected. If granulated blast furnace slag that satisfies the requirements for the aluminum oxide content and basicity is available, the sorting step is not necessary. In other words, the sorting step may be an optional step.

[0042] The mixing step is a step of mixing cement, the granulated blast furnace slag, and an accelerator so that the content of the granulated blast furnace slag is 30 to 90 mass%, with the total amount of the cement and the granulated blast furnace slag being 100 mass%, and the content of the accelerator is 0.5 to 10.0 mass parts per 100 mass parts of the granulated blast furnace slag.

[0043] In the mixing step, in addition to mixing the main components, each main component may be crushed, and the order of mixing and crushing is not particularly limited. That is, the main components may be mixed and then crushed, or the main components may be crushed and then mixed, or mixing and crushing of the main components may be performed simultaneously. The mixing of the various components in the mixing step may be performed using a mixer such as a pan mixer, a tilting mixer, or a ribbon mixer, or may be mixed and crushed using a crusher such as a ball mill, a vertical roller mill, or a roller press, or each main component may be crushed separately and then mixed using a mixer such as a mechanical mixer.

[0044] When using granulated blast furnace slag with an aluminum oxide content of 14% by mass or less and a basicity of 1.55 to 1.95 selected in the selection step, the amount of accelerator added in the subsequent mixing step is 0.5 to 10.0 parts by mass per 100 parts by mass of the granulated blast furnace slag, but may be, for example, 2.0 to 8.0 parts by mass. In the case of granulated blast furnace slag with an aluminum oxide content of more than 14% by mass, the amount of accelerator added is adjusted to less than 2 parts by mass per 100 parts by mass of the target granulated blast furnace slag.

[0045] The cement composition produced by the above-mentioned production method may be mixed with fine aggregate, coarse aggregate, water, admixtures, etc. and used as mortar.

[0046] The fine aggregate may be one specified in JIS A 5005:2020 "Crushed Stone and Crushed Sand for Concrete." Examples of fine aggregate include river sand, land sand, sea sand, crushed sand, silica sand, copper slag fine aggregate, and electric furnace oxidizing slag fine aggregate. When using fine aggregate, the amount of fine aggregate used may be, for example, 50 to 500 parts by mass, 100 to 300 parts by mass, or 200 to 250 parts by mass per 100 parts by mass of the cement composition.

[0047] The coarse aggregate may be one specified in JIS A 5005:2020 "Crushed stone and crushed sand for concrete." Examples of coarse aggregate include gravel and crushed stone. When using coarse aggregate, the amount of coarse aggregate used may be, for example, 50 to 500 parts by mass, 100 to 300 parts by mass, or 200 to 250 parts by mass per 100 parts by mass of the cement composition.

[0048] Fine aggregate and coarse aggregate can also be used in combination. In this case, the total amount of the fine aggregate and coarse aggregate used may be 100 to 300 parts by mass, or 200 to 250 parts by mass, per 100 parts by mass of the cement composition.

[0049] Examples of water include tap water, distilled water, deionized water, etc. The amount of water used may be 20 to 100 parts by mass, or 40 to 70 parts by mass, relative to 100 parts by mass of the cement composition.

[0050] Examples of the admixture include air-entraining agents, water-reducing agents, air-entraining water-reducing agents, high-performance water-reducing agents, superplasticizers, antifoaming agents, shrinkage-reducing agents, set accelerators, set retarders, and thickeners. The amount of the admixture used may be, for example, 0.01 to 2 parts by mass per 100 parts by mass of the above-mentioned cement composition.

[0051] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Furthermore, the descriptions of the above embodiments can be applied to each other. [Example]

[0052] The present disclosure will be described in more detail below with reference to experimental examples, but the present disclosure is not limited to the disclosed contents of the following experimental examples.

[0053] [Raw materials for cement compositions] The following materials were used as raw materials for the cement composition.

[0054] (cement) Ordinary Portland cement was used as the cement. The chemical composition of the ordinary Portland cement, measured in accordance with JIS R 5202:2015 "Methods for chemical analysis of cement," is shown in Table 1. In Table 1, ordinary Portland cement is abbreviated as OPC.

[0055] (Granulated blast furnace slag: Slag(A)~Slag(F)) Granulated blast furnace slag (Slag (A) to Slag (F)) was prepared as follows. First, commercially available reagents, calcium carbonate (CaCO), silicon dioxide (SiO), aluminum oxide (AlO), iron oxide (FeO), magnesium oxide (MgO), sodium carbonate (NaCO), and potassium carbonate (KCO), were mixed to prepare mixtures (A) to (F) with the compositions shown in Table 1. Mixtures (A) to (F) were placed in carbon crucibles and melted in an electric furnace at 1500°C for 30 minutes. Next, the melt was removed from the electric furnace along with the carbon crucible and immediately poured into water to vitrify the melt, yielding a solid. The solid recovered from the water was dried at 105°C to obtain Slag (A) to Slag (F). The chemical composition of the obtained Slag (A) to Slag (F) was measured in accordance with JIS R 5202:2015 "Methods for Chemical Analysis of Cement," and the crystalline phase was evaluated by X-ray diffraction. Aluminum oxide was used as the standard material for the evaluation of the crystalline phase by X-ray diffraction. Since no crystalline phase was detected in the obtained Slag (A) to Slag (F) and the vitrification rate was nearly 100%, it was confirmed that all of the slags were equivalent to commonly available granulated blast furnace slag. The measured chemical composition of each of Slag (A) to Slag (F) is shown in Table 1.

[0056] (Granulated blast furnace slag: Slag(G), Slag(H)) The commercially available granulated blast furnace slag was designated Slag (G) and Slag (H). The chemical compositions of each granulated blast furnace slag were measured in accordance with JIS R 5202:2015 "Methods for Chemical Analysis of Cement," and are shown in Table 1.

[0057] [Table 1]

[0058] The ignition loss (also abbreviated as ig.loss) in Table 1 is a value measured at a heating temperature of 700°C in accordance with the method described in "5.2 For materials other than blast furnace cement and blast furnace slag" in "5. Method for determining ignition loss" of JIS R 5202:2010.

[0059] (accelerator) An inorganic accelerator, calcium nitrite monohydrate (hereinafter sometimes referred to as CN) manufactured by Kishida Chemical Co., Ltd., was used.

[0060] (Experimental Example I-1) Equal amounts of ordinary Portland cement and granulated blast furnace slag (Slag (A)) were weighed and mixed to obtain a mixture. 8 parts by mass of calcium nitrite monohydrate was added as an inorganic accelerator to 100 parts by mass of the granulated blast furnace slag to prepare the cement composition of Experimental Example I-1.

[0061] (Experimental Examples I-2, I-3, Experimental Examples II-1, II-2) Cement compositions of Experimental Examples I-2, I-3, II-1, and II-2 were prepared in the same manner as Experimental Example I-1, except that the components and blending amounts were changed to those shown in Table 2.

[0062] <Evaluation of heat release during hardening: Measurement of heat of hydration> Using the cement compositions prepared in Experimental Examples I-1, I-2, I-3, II-1, and II-2 (cement compositions containing 8 parts by mass of accelerator), the effect of granulated blast furnace slag on the heat generation associated with hardening in a system in which cement, granulated blast furnace slag, and accelerator coexist was evaluated.

[0063] Specifically, for each of the cement compositions prepared in Experimental Examples I-1, I-2, I-3, II-1, and II-2 (cement compositions containing 8 parts by mass of accelerator), 40 parts by mass of water was added to 100 parts by mass of the cement composition to prepare an evaluation sample.Then, using a cement hydration heat generation rate measuring device (Tokyo Riko Co., Ltd., conduction calorimeter), the integrated heat generation over 7 days from the start of measurement was measured, and this was used to evaluate the heat of hydration.The results are shown in Table 2.

[0064] [Table 2]

[0065] The results shown in Table 2 confirm that even when granulated blast furnace slag has the same level of basicity, the heat of hydration that occurs when combined with an accelerator tends to be suppressed when the Al2O3 content is below a certain value.

[0066] <Evaluation of early strength: Measurement of compressive strength of mortar> The compressive strength was evaluated using mortar compositions obtained by blending a cement composition, fine aggregate, and water. Specifically, as shown in Table 3, 200 parts by mass of sand as fine aggregate was blended with 100 parts by mass of the cement composition, and 65 parts by mass of water was further blended with 100 parts by mass of the cement composition to prepare mortar compositions for evaluation. These are Experimental Examples I-4 to I-6, and Experimental Examples II-3 to II-5, respectively. The above blends were adjusted so that the ratio of cement composition:sand:water was 100:200:65 (mass ratio).

[0067] Each of the obtained mortar compositions was used to prepare a hardened mortar. First, the mortar composition was mixed as a mortar in a thermostatic chamber at 20°C and packed into a 1 cm x 1 cm x 6 cm form. The form was stored in a humidity chamber and cured for 24 hours. After 24 hours of curing, the form was demolded to obtain a hardened mortar. The obtained hardened mortar was cured underwater in a thermostatic chamber at 20°C until it reached a material age of 7 days. The hardened mortar after underwater curing was used as a test specimen to measure the compressive strength of the hardened mortar. The compressive strength measurement was performed in accordance with JIS R 5201:1992 "Physical Testing Methods for Cement." The results are shown in Table 3.

[0068] To confirm the effect of adding an accelerator, cement compositions were prepared in the same manner as Experimental Examples I-4 to I-6 and Experimental Examples II-3 to II-5, except that no accelerator was added. These compositions were designated Reference Examples 2 to 7. The percentage increase in compressive strength for Experimental Examples I-4 to I-6 and Experimental Examples II-3 to II-5 was determined based on the results of Reference Examples 2 to 7. The percentage increase in compressive strength here refers to the ratio of the increase in compressive strength between an Experimental Example and a Reference Example, which are common except for the presence or absence of an accelerator. Specifically, the percentage increase is, for example, 100 × [(compressive strength of Experimental Example I-4) - (compressive strength of Reference Example 2)] / (compressive strength of Reference Example 2). The results are shown in Table 3.

[0069] For reference, Table 3 also shows the results of using a mortar composition prepared by mixing 200 parts by mass of sand as fine aggregate with 100 parts by mass of ordinary Portland cement (Reference Example 1) and 65 parts by mass of water per 100 parts by mass of ordinary Portland cement.

[0070] [Table 3]

[0071] As shown in Table 3, it was confirmed that the hardened mortars prepared using the mortar compositions of Experimental Examples I-4 to I-6, which were blended with granulated blast furnace slag so that the aluminum hydroxide content and basicity were within the specified range, had a greater improvement in early strength due to the accelerator, as shown by the increase in compressive strength, compared to the hardened mortars prepared using the mortar compositions of Experimental Examples II-3 to II-5.

[0072] <Evaluation of early strength: Evaluation of the effect of the amount of accelerator used> The compressive strength was evaluated using mortar compositions obtained by blending a cement composition, fine aggregate, and water. Specifically, as shown in Table 4, 300 parts by mass of sand as fine aggregate was blended with 100 parts by mass of the cement composition, and 50 parts by mass of water was further blended with 100 parts by mass of the cement composition to prepare mortar compositions for evaluation. These are Experimental Examples I-7 to I-9 and Experimental Examples II-6 to II-8, respectively. The above blends were adjusted so that the cement composition:sand:water ratio was 100:300:50 (mass ratio).

[0073] Each of the obtained mortar compositions was used to prepare a hardened mortar. First, the mortar composition was mixed as a mortar in a thermostatic chamber at 20°C and packed into a 4 cm x 4 cm x 16 cm formwork. The formwork was stored in a humidity chamber and cured for 24 hours. After 24 hours of curing, the formwork was demolded to obtain a hardened mortar. The obtained hardened mortar was cured underwater in a thermostatic chamber at 20°C until it reached a material age of 7 days. The hardened mortar after underwater curing was used as a test specimen to measure the compressive strength of the hardened mortar. The compressive strength measurement was performed in accordance with JIS R 5201:2015 "Physical Testing Methods for Cement." The results are shown in Table 4.

[0074] To confirm the effect of adding an accelerator, cement compositions were prepared in the same manner as Experimental Examples I-7 to I-9 and Experimental Examples II-6 to II-8, except that no accelerator was added. These compositions were designated Reference Examples 8 and 9. The percentage increase in compressive strength for Experimental Examples I-7 to I-9 and Experimental Examples II-6 to II-8 was determined based on the results of Reference Examples 8 and 9. The percentage increase in compressive strength here refers to the increase in compressive strength between the Experimental Example and the Reference Example, which are common except for the presence or absence of the accelerator. Specifically, the percentage increase in compressive strength is, for example, 100 × [(compressive strength of Experimental Example I-7) - (compressive strength of Reference Example 8)] / (compressive strength of Reference Example 8). The results are shown in Table 4.

[0075] For reference, Table 4 also lists the results of a mortar composition prepared by blending 300 parts by weight of sand as fine aggregate with 100 parts by weight of ordinary Portland cement (Reference Example 1) and blending 50 parts by weight of water per 100 parts by weight of ordinary Portland cement. Also listed are the results of mortar compositions prepared in the same manner as Reference Example 1, except that 8 parts by weight, 4 parts by weight, or 2 parts by weight of calcium nitrite monohydrate was added as an accelerator per 100 parts by weight of ordinary Portland cement.

[0076] [Table 4]

[0077] As shown in Table 4, the hardened mortars prepared using the cement compositions of Experimental Examples I-7 to I-9 also showed an increase in compressive strength, similar to Experimental Examples I-4 to I-6. Furthermore, compared to the hardened mortars prepared using the mortar compositions of Experimental Examples II-6 to II-8, which used blast furnace slag with a high aluminum oxide content, the mortar compositions of Experimental Examples I-7 to I-9 showed a superior increase in compressive strength, confirming that the accelerator contributes to a greater improvement in early strength. It was also confirmed that the addition of an accelerator sometimes reduced compressive strength in the Reference Example, which uses ordinary Portland cement without blast furnace slag. [Industrial Applicability]

[0078] According to the present disclosure, it is possible to provide a cement composition that suppresses the amount of heat generated during hardening and that can exhibit excellent early strength even when the content of granulated blast furnace slag is high, and a method for producing the same.

Claims

1. Cement and Granulated blast furnace slag having an aluminum oxide content of 12.58% by mass or more and 13.7% by mass or less and a basicity of 1.55 to 1.82; a promoter; The content of the granulated blast furnace slag is 30.0 to 90.0% by mass, with the total amount of the cement and the granulated blast furnace slag being 100% by mass, The cement composition, wherein the content of the accelerator is 0.5 to 10.0 parts by mass per 100 parts by mass of the granulated blast furnace slag.

2. 2. The cement composition according to claim 1, wherein the accelerator comprises at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts.

3. 10. The cement composition of claim 1, wherein the accelerator comprises a salt having a monovalent anion.

4. The cement composition according to any one of claims 1 to 3, wherein the accelerator comprises a calcium salt.

5. The cement composition according to any one of claims 1 to 4, wherein the accelerator contains at least one selected from the group consisting of nitrites, nitrates, and chlorides.

6. The cement composition according to any one of claims 1 to 4, wherein the content of the accelerator is 0.5 to 5.0 parts by mass per 100 parts by mass of the granulated blast furnace slag.

7. The method includes a step of preparing a cement composition by mixing cement, granulated blast furnace slag having an aluminum oxide content of 12.58 mass% or more and 13.7 mass% or less and a basicity of 1.55 to 1.82, and an accelerator; The method for producing a cement composition includes mixing the granulated blast furnace slag so that the content of the granulated blast furnace slag in the cement composition is 30 to 90 mass%, with the total amount of the cement and the granulated blast furnace slag being 100 mass%, and the content of the accelerator is 0.5 to 10.0 parts by mass per 100 parts by mass of the total amount of the granulated blast furnace slag.

8. The method according to claim 7, further comprising the step of screening the granulated blast furnace slag.

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