Cement composition and concrete

Abstract

This invention provides a cement composition that, despite containing blast furnace slag fine powder, is resistant to cracking, does not experience a large temperature rise due to the hydration reaction, and exhibits excellent initial strength development. [Solution] A cement composition comprising Portland cement, blast furnace slag fine powder, and fly ash, wherein the blast furnace slag fine powder satisfies all of the following conditions (1) to (3), and in a total of 100% by mass of Portland cement, blast furnace slag fine powder, and fly ash, the proportion of Portland cement is 25 to 45% by mass, the proportion of blast furnace slag fine powder is 35 to 65% by mass, and the proportion of fly ash is 10 to 20% by mass. (1) The Blaine specific surface area of ​​the blast furnace slag fine powder is 4,100 to 4,500 cm² 2 (1) The basicity of the blast furnace slag fine powder is 1.80 to 2.00. (2) The MgO content in the blast furnace slag fine powder is 3.0 to 6.0% by mass, and the SO3 content is 1.5 to 2.5% by mass.

Description

[Technical Field]

[0001] The present invention relates to a cement composition and concrete containing the cement composition. [Background technology]

[0002] In the cement industry, blast furnace slag powder, obtained from blast furnace granulated slag and other by-products generated during the production of pig iron in blast furnaces, has traditionally been used as a cement mixer. Patent Document 1 describes a cement composition containing a large amount of blast furnace slag fine powder, which includes ordinary Portland cement clinker powder with an iron content (IM) of 1.88 to 2.00, gypsum, and a Blaine specific surface area of ​​2,500 cm². 2 The present invention describes a cement composition containing fly ash in an amount of 1 / g or more and blast furnace slag powder, wherein the proportion of gypsum (in SO3 equivalent) in the total amount of ordinary Portland cement clinker powder and the amount of gypsum (in SO3 equivalent) is 1.0 to 3.0% by mass, and the proportion of fly ash is 1.0 to 10.0% by mass and the proportion of blast furnace slag powder is 30 to 75% by mass in the total amount of ordinary Portland cement clinker powder, gypsum (in SO3 equivalent), fly ash, and blast furnace slag powder.

[0003] Furthermore, as a hydraulic composition that reduces the amount of cement and uses fly ash and blast furnace slag fine powder as the main materials, Patent Document 2 describes a hydraulic composition characterized by containing 10 to 40% by weight of either cement or slaked lime, with the content of cement and slaked lime each being 20% ​​by weight or less of the total, and containing a total of 40 to 90% by weight of fly ash and blast furnace slag fine powder, with the content of fly ash being 15% by weight or more of the total. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-137586 [Patent Document 2] Japanese Patent Publication No. 2009-269786 [Overview of the project] [Problems that the invention aims to solve]

[0005] Concrete containing a large amount of blast furnace slag powder has the problem of being prone to cracking due to autologous shrinkage strain. The object of the present invention is to provide a cement composition that, despite containing a high content (e.g., 35-65% by mass) of blast furnace slag fine powder, is less prone to cracking due to autologous shrinkage strain, does not cause an excessively large temperature rise in the cement composition due to the hydration reaction of the cement, and exhibits excellent initial strength development. [Means for solving the problem]

[0006] The inventors have diligently studied to solve the above problems and have found a material comprising Portland cement, blast furnace slag fine powder, and fly ash, wherein, out of a total of 100% by mass of Portland cement, blast furnace slag fine powder, and fly ash, the proportion of Portland cement is 25-45% by mass, the proportion of blast furnace slag fine powder is 35-65% by mass, and the proportion of fly ash is 10-20% by mass, and the Blaine specific surface area of ​​the blast furnace slag fine powder is 4,100-4,500 cm². 2 We have found that the above objective can be achieved by a cement composition in which the basicity of the blast furnace slag fine powder is 1.80 to 2.00 / g, and the MgO content in the blast furnace slag fine powder is 3.0 to 6.0% by mass, and the SO3 content is 1.5 to 2.5% by mass, and thus completed the present invention. In other words, the present invention provides the following [1] to [5]. [1] A cement composition comprising Portland cement, blast furnace slag fine powder, and fly ash, wherein the blast furnace slag fine powder satisfies all of the following conditions (1) to (3), and the proportion of Portland cement is 25 to 45% by mass, the proportion of blast furnace slag fine powder is 35 to 65% by mass, and the proportion of fly ash is 10 to 20% by mass, out of a total of 100% by mass of the Portland cement, blast furnace slag fine powder, and fly ash. (1) The Blaine specific surface area of ​​the above blast furnace slag fine powder is 4,100 to 4,500 cm². 2 / g (2) The basicity of the blast furnace slag fine powder is 1.80 to 2.00. (3) The blast furnace slag fine powder has an MgO content of 3.0 to 6.0% by mass and an SO3 content of 1.5 to 2.5% by mass. [2] The cement composition according to [1], wherein the blast furnace slag fine powder further satisfies the following condition (4). (4) The blast furnace slag fine powder has an SiO2 content of 32.0 to 35.0% by mass and a CaO content of 40.0 to 44.0% by mass.

[0007] [3] Concrete comprising the cement composition, fine aggregate, coarse aggregate, and water described in [1] or [2] above. [4] A method for producing a hardened concrete body using the concrete described in [3] above, comprising: a mixture preparation step of mixing the constituent materials of the concrete to prepare a mixture; a casting step of casting the mixture into a formwork; and a demolding step of removing the hardened mixture from the formwork after the mixture in the formwork has hardened, wherein each step from the mixture preparation step to the demolding step is performed at a temperature of 25°C or higher. [5] The method for manufacturing a concrete hardened body according to [4] above, including a blast furnace slag fine powder selection step of examining whether blast furnace slag fine powder, which should be determined whether to be used as a material of the cement composition before the kneaded mixture preparation step, satisfies all the conditions required as a material of the cement composition, and selecting the blast furnace slag fine powder as a material of the cement composition when the blast furnace slag fine powder satisfies all the conditions, and not selecting the blast furnace slag fine powder as a material of the cement composition when the blast furnace slag fine powder does not satisfy all the conditions.

Effects of the Invention

[0008] The cement composition of the present invention, despite containing blast furnace slag fine powder at a high content rate (for example, 35 to 65% by mass), is less likely to crack due to self - shrinkage strain, the temperature rise amount of the cement composition due to the hydration reaction of cement does not become excessively large, and it has excellent initial strength development property. Also, by reducing the blending amount of cement, the production amount of cement can be reduced, and the total amount of carbon dioxide generated during the production of cement can be decreased.

Brief Description of the Drawings

[0009] [Figure 1] In the examples, it is a side view in the longitudinal direction and a front view in the short - hand direction of a member made of invar steel installed in a formwork. [Figure 2] In the examples, it is a plan view of a heat - insulating curing tank for simulating the temperature history inside mass concrete with the lid of the styrofoam removed. [Figure 3] In the examples, it is a cross - sectional view showing a state where the lid of the styrofoam of a heat - insulating curing tank for simulating the temperature history inside mass concrete is covered, and is cut in a direction perpendicular to the axis of the member made of invar steel at the position of the A - A line in FIG. 2.

Modes for Carrying Out the Invention

[0010] The cement composition of the present invention is a cement composition comprising Portland cement, blast furnace slag fine powder, and fly ash, wherein the blast furnace slag fine powder satisfies all of the following conditions (1) to (3), and of the total 100% by mass of Portland cement, blast furnace slag fine powder, and fly ash, the proportion of Portland cement is 25 to 45% by mass, the proportion of blast furnace slag fine powder is 35 to 65% by mass, and the proportion of fly ash is 10 to 20% by mass. (1) The Blaine specific surface area of ​​the blast furnace slag fine powder is 4,100 to 4,500 cm². 2 / g (2) The basicity of the blast furnace slag fine powder is 1.80 to 2.00. (3) The blast furnace slag fine powder has an MgO content of 3.0 to 6.0% by mass and an SO3 content of 1.5 to 2.5% by mass. The following explains in detail.

[0011] The Portland cement used in this invention is not particularly limited and includes various types of Portland cement such as ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement. These may be used individually or in combination of two or more types. Of the total 100% by mass of Portland cement, blast furnace slag powder, and fly ash, the proportion of Portland cement is 25% by mass or more, preferably 27% by mass or more, more preferably 30% by mass or more, and particularly preferably 38% by mass or more, from the viewpoint of improving the strength development of the cement composition and further suppressing cracking. Furthermore, from the viewpoint of reducing the amount of cement produced by reducing the amount of cement mixed in, thereby reducing the total amount of carbon dioxide generated during cement production, and suppressing the temperature rise of the cement composition due to the hydration reaction of cement (hereinafter also simply referred to as "temperature rise"), the above proportion is 45% by mass or less, preferably 43% by mass or less, more preferably 38% by mass or less, and particularly preferably 30% by mass or less.

[0012] The blast furnace slag fine powder of the present invention satisfies all of the above-described conditions (1) to (3). By using blast furnace slag fine powder that satisfies all of the conditions (1) to (3), cracks in concrete or the like containing a cement composition are less likely to occur, the amount of temperature rise does not become excessively large, and the initial strength development property of the cement composition can be made excellent. [Condition (1)] The Blaine specific surface area of the blast furnace slag fine powder is 4,100 to 4,500 cm 2 / g, preferably 4,200 to 4,450 cm 2 / g, more preferably 4,250 to 4,400 cm 2 / g. When the above Blaine specific surface area is less than 4,100 cm 2 / g, the strength development property of the cement composition deteriorates. When the above Blaine specific surface area exceeds 4,500 cm 2 / g, the amount of temperature rise and autogenous shrinkage increase, so cracks are likely to occur. Also, the fluidity before hardening of concrete or the like containing the cement composition decreases.

[0013] [Condition (2)] The basicity of the blast furnace slag fine powder is 1.80 to 2.00, preferably 1.82 to 1.98, more preferably 1.85 to 1.95. When the above basicity is less than 1.80, the initial strength development property of the cement composition deteriorates. When the above basicity exceeds 2.00, the amount of temperature rise increases. Note that the basicity can be determined by the basicity calculation formula (the following formula (i)) defined in "JIS A 6206:2013 (Ground Granulated Blast-Furnace Slag for Concrete)". Basicity = (CaO + MgO + Al2O3) / SiO2 ··· (i) (In the above formula (i), CaO, MgO, Al2O3, and SiO2 are the content ratios of CaO, MgO, Al2O3, and SiO2 (mass%) in the blast furnace slag fine powder, respectively.)

[0014] [Condition (3)] The MgO content in the blast furnace slag fine powder is 3.0 to 6.0% by mass, preferably 4.0 to 5.8% by mass, and more preferably 4.5 to 5.5% by mass. If the above content is within the above numerical range, cracking of concrete and the like containing the cement composition is less likely to occur, the temperature rise will not be excessively large, and the initial strength development of the cement composition can be improved. The SO3 content in the blast furnace slag fine powder is 1.5 to 2.5% by mass, preferably 1.8 to 2.4% by mass, and more preferably 2.0 to 2.2% by mass. If the above content is within the above numerical range, cracking of concrete and the like containing the cement composition is less likely to occur, the temperature rise will not be excessively large, and the initial strength development of the cement composition can be improved.

[0015] In addition to the conditions (1) to (3) described above, the blast furnace slag fine powder of the present invention preferably also satisfies the following condition (4). [Condition (4)] (4) The blast furnace slag fine powder has an SiO2 content of 32.0 to 35.0% by mass and a CaO content of 40.0 to 44.0% by mass. The SiO2 content in the blast furnace slag fine powder is preferably 32.0 to 35.0% by mass, more preferably 32.2 to 34.0% by mass, and particularly preferably 32.5 to 33.0% by mass. If the above content is 32.0% by mass or higher, the temperature rise can be further suppressed. If the above content is 35.0% by mass or lower, the initial strength development of the cement composition can be further improved. The CaO content in the blast furnace slag fine powder is preferably 40.0 to 44.0% by mass, more preferably 41.0 to 43.9% by mass, and particularly preferably 42.0 to 43.9% by mass. If the above content is 40.0% by mass or higher, the strength development of the cement composition can be further improved. If the above content is 44.0% by mass or lower, the temperature rise can be further suppressed.

[0016] The proportion of blast furnace slag fine powder in the total 100% by mass of Portland cement, blast furnace slag fine powder, and fly ash is 35 to 65% by mass, preferably 38 to 63% by mass, and particularly preferably 45 to 55% by mass. If the above proportion is less than 35% by mass, the temperature rise will be greater. If the above proportion exceeds 65% by mass, the amount of cement will be relatively small, and the strength development of the cement composition will decrease.

[0017] The specific surface area of ​​the fly ash used in this invention is preferably 1,500 to 8,000 cm². 2 / g, more preferably 2,500~6,000cm 2 / g, particularly preferably 3,500~4,500cm 2 The value is / g. The above Brain specific surface area is 1,500 cm². 2 If the value is 1 / g or higher, the strength development of the cement composition will be further improved. The above Blaine specific surface area is 8,000 cm². 2 If the value is less than / g, the fluidity of concrete and other materials containing cement composition before hardening will be further improved. The proportion of fly ash in the total 100% by mass of Portland cement, blast furnace slag powder, and fly ash is 10 to 20% by mass, preferably 11 to 19% by mass, and more preferably 13 to 17% by mass. If the above proportion is less than 10% by mass, the temperature rise of the cement composition can be further suppressed, and self-shrinkage is reduced, making it less prone to cracking. If the above proportion exceeds 20% by mass, the initial strength development of the cement composition decreases.

[0018] Furthermore, other powdered materials may be added to the cement composition as needed. Examples of other powdered materials that may be added as needed include silica fume, limestone, and various cement admixtures (admixtures) such as natural pozzolanes. These may be used individually or in combination of two or more. The content of other powdered materials in the cement composition is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

[0019] The concrete of the present invention contains, in addition to the cement composition described above, fine aggregate, coarse aggregate, and water. In this specification, the term "concrete" includes not only fully hardened concrete but also its fluid form before hardening. The fine aggregate is not particularly limited and includes, for example, river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, and lightweight fine aggregate. These may be used individually or in combination of two or more types. The unit quantity of fine aggregate is not particularly limited and can be any unit quantity common in concrete. For example, the above unit quantity is preferably 500 to 1,200 kg / m³. 3 Comfortable 600-1,100 kg / m 3 Particularly preferred is 650 to 1,000 kg / m 3 That is the case.

[0020] The coarse aggregate is not particularly limited and includes, for example, river gravel, mountain gravel, land gravel, sea gravel, crushed stone, slag coarse aggregate, and lightweight coarse aggregate. These may be used individually or in combination of two or more types. Furthermore, the fine aggregate ratio of the concrete is preferably 20-60%, more preferably 25-55%, and particularly preferably 30-50%. If the fine aggregate ratio is within the above numerical range, the workability and ease of molding of the concrete will be improved. The fine aggregate ratio refers to the volume percentage of fine aggregate in the total amount of fine aggregate and coarse aggregate. Furthermore, the concrete of the present invention may optionally contain various admixtures such as cement dispersants (water-reducing agents, AE water-reducing agents, high-performance water-reducing agents, or high-performance AE water-reducing agents), AE agents, defoaming agents, and shrinkage-reducing agents. When manufacturing concrete in a high-temperature environment (for example, in an environment where the ambient temperature is 25°C or higher, or in the central part of mass concrete), or when using a hardened concrete body in a high-temperature environment, there is less need to improve the freeze-thaw resistance of the concrete, and from the viewpoint of reducing material costs, it is preferable not to include air-entraining agents, air-entraining water-reducing agents, or high-performance air-entraining water-reducing agents.

[0021] Furthermore, the mass ratio of water to cement composition (water / cement composition) is preferably 0.25 to 0.65, more preferably 0.3 to 0.6, and particularly preferably 0.3 to 0.4. If the above mass ratio is 0.25 or higher, the workability (fluidity) of mixing and other processes during the manufacture of concrete is further improved. If the above mass ratio is 0.65 or lower, the strength of the concrete after hardening is further improved.

[0022] An example of a method for producing a hardened body made of the concrete of the present invention is a method that includes a mixture preparation step of mixing the constituent materials of the concrete to prepare a mixture, a casting step of pouring the mixture into a formwork, and a demolding step of removing the hardened mixture from the formwork after the mixture in the formwork has hardened to obtain a hardened concrete body, wherein each step from the mixture preparation step to the demolding step is carried out at a temperature of 25°C or higher. In the compound preparation process, there are no particular limitations on the method of mixing each material. For example, each material may be put into a mixer all at once and mixed, or each material constituting the cement composition may be put into a mixer and mixed (combined), and then other materials (materials other than those constituting the cement composition) may be put into the mixer and mixed. In the above manufacturing method, each step from the mixing preparation step to the demolding step is carried out at a temperature of 25°C or higher, preferably 26°C or higher, and particularly preferably 27°C or higher. According to the manufacturing method of the present invention, even when manufactured at a temperature (environment) of 25°C or higher, the resulting concrete is less prone to cracking and the temperature rise is not excessively large. The upper limit of the above temperature is not particularly limited, but is usually 70°C, preferably 50°C.

[0023] Before the compounding process, a blast furnace slag fine powder selection step may be provided in which it is checked whether the blast furnace slag fine powder, which should be judged as to be used as a material for the cement composition, satisfies all the conditions required for a material for a cement composition (conditions (1) to (3) or conditions (1) to (4) described above). If the blast furnace slag fine powder satisfies all of the above conditions, it is selected as a material for the cement composition, and if the blast furnace slag fine powder does not satisfy all of the above conditions, it is not selected as a material for the cement composition. In this step, the Blaine specific surface area and chemical composition are measured for each of at least one type of blast furnace slag fine powder from different sources, etc., and the basicity is calculated. By selecting and using the blast furnace slag fine powder that satisfies the above conditions as a material for the cement composition, a concrete hardened body made of the concrete of the present invention can be obtained. [Examples]

[0024] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Portland cement; manufactured by Taiheiyo Cement Corporation, ordinary Portland cement, density: 3.15 g / cm³ 3 (2) Fly ash; Blaine specific surface area: 3,310 cm² 2 / g (3) Blast furnace slag fine powder 1-9 (referred to as "BS1-BS9" in Tables 1-2); details are shown in Table 1. (4) Fine aggregate A; crushed stone powder, density: 2.57 g / cm³ 3 (5) Fine aggregate B; natural sand, density: 2.56g / cm 3 (6) Coarse aggregate; crushed stone, density: 2.55 g / cm³ 3 (7) Water-reducing agent (indicated as "AD" in Table 2); manufactured by Pozzolith Solutions, product name "Master Pozzolith R168" (8) High-performance water-reducing agent A; Polycarboxylic acid-based high-performance water-reducing agent, manufactured by Pozzolith Solutions, product name "Master Glenium SKY8703" (9) High-performance water-reducing agent B; Polycarboxylic acid-based high-performance water-reducing agent, manufactured by Pozzolith Solutions, product name "Master Leobilt R1000" (10) High-performance water-reducing agent C (indicated as "SP2" in Table 2); Polycarboxylic acid-based high-performance water-reducing agent, manufactured by Pozzolith Solutions, trade name "Master Glenium ACE8538" (11) Water; tap water

[0025] The chemical composition of the blast furnace slag fine powder was measured in accordance with "JIS R 5204:2019 (X-ray fluorescence analysis method for cement)". Furthermore, the density, Blaine specific surface area, and basicity of the blast furnace slag fine powder were measured in accordance with "JIS A 6206:2013 (Blast Furnace Slag Fine Powder for Concrete)".

[0026] [Table 1]

[0027] [Explanation of the insulated curing tank] The formwork, which is equipped with members made of Invar steel for producing the uniaxially restrained specimens used in the examples and comparative examples, and the insulated curing tank for curing the concrete poured into the formwork while simulating the temperature history inside the mass concrete, will be described with reference to Figures 1 to 3. The specimen formwork 3a, 3b, and 3c for fabricating uniaxially restrained specimens are formwork with internal dimensions of 100 × 100 × 850 mm, with members made of Invar steel installed inside. Member 1 (corresponding to members 4a, 4b, and 4c described later) consists of a rod-shaped body 1a made of Invar steel and a restraining end plate 1b made of Invar steel. The members 4a, 4b, and 4c installed in the specimen formwork 3a, 3b, and 3c have rod-shaped diameters of 26 mm, 15 mm, and 9.2 mm, respectively. The restraining steel ratios (the ratio of the cross-sectional area of ​​the rod-shaped material to the cross-sectional area of ​​the concrete, expressed as a percentage) of the specimen formwork 3a, 3b, and 3c are 0.7%, 1.7%, and 5.7%, respectively. Embedded strain gauges 5a, 5b, and 5c are installed approximately in the center of the rod-shaped parts of members 4a, 4b, and 4c. Wiring 9 for transmitting data obtained from the strain gauges is connected to strain gauges 5a, 5b, and 5c (not shown in Figure 2). Furthermore, the strength test formwork 3d is a cylindrical formwork with an inner diameter of 100 mm and a height of 200 mm. A total of six such formworks were prepared. In the measurement of compressive strength in this example and comparative example, the concrete poured into the strength test formwork 3d was not used. The coefficient of linear expansion of the above Invar steel is 0.5 × 10⁻⁶ -6 The temperature is / ℃ and is negligibly small. Furthermore, the Young's modulus of the above Invar steel is 140,000 N / mm². 2 That is the case.

[0028] The insulated curing tank 10 includes polystyrene foam containers 2 and 2b made of expanded polystyrene, a polystyrene foam lid 2a made of expanded polystyrene, a formwork 6 for increasing heat generation, formwork 3a, 3b, and 3c for test specimens, and a formwork 3d for strength testing. The insulated curing tank 10 uses formwork 3a, 3b, and 3c for test specimens and formwork 3d for strength testing, each with different conditions, in order to obtain various test specimens. The formwork 6 for increasing heat generation is designed to simulate the temperature history inside mass concrete by increasing the amount of concrete in the insulated curing tank 10 and thus increasing its heat generation through the placement of concrete 7 within the formwork. Furthermore, the formwork 6 for increasing heat generation is the same as the formwork 3a, 3b, and 3c for test specimens, except for the absence of a member made of Invar steel and its length. Four heat-generating molds 6 are arranged inside the polystyrene container 2b. The specimen molds 3a, 3b, and 3c are placed on top of the heat-generating mold 6 such that the direction perpendicular to the longitudinal direction of the heat-generating mold 6 is the longitudinal direction of the specimen molds 3a, 3b, and 3c. After concrete 8 is poured into the specimen formwork 3a, 3b, 3c and the strength test formwork 3d, the gap between the polystyrene container 2b and the formwork is filled with polystyrene beads, and then the polystyrene lid 2a is placed on top of the specimen formwork 3a, 3b, 3c and the strength test formwork 3d.

[0029] [Example 1] The types and unit quantities of cement compositions shown in Table 2 (consisting of cement, blast furnace slag powder, and fly ash in the mixing ratios shown in Table 2), fine aggregates A to B, and coarse aggregate were put into a twin-screw forced mixer and dry-mixed for 30 seconds. Next, a liquid mixture of water, water-reducing agent, high-performance water-reducing agent A, and high-performance water-reducing agent C was added to the twin-screw forced mixer and mixed for 90 seconds. After scraping off the mixture adhering to the inner wall of the twin-screw forced mixer, the mixture was mixed for another 90 seconds to prepare the concrete. The amounts of water-reducing agent and high-performance water-reducing agent C per 100 parts by mass of cement composition were set at 0.4 parts by mass and 0.5 parts by mass, respectively. Furthermore, the amount of high-performance water-reducing agent A was appropriately adjusted to achieve a concrete slump of 21 cm ± 2.5 cm and an air content of 2.0% or less. After pouring concrete into the aforementioned specimen formwork 3a, 3b, 3c, strength test formwork 3d, and heat generation increase formwork 6 (4 pieces), the specimen formwork and other components were placed in the aforementioned insulated curing tank 10. After placement, the concrete was left to stand for 20 days until its temperature equaled the ambient temperature (27°C). The temperature was measured using a thermocouple (not shown in Figure 2) placed directly below strain gauge 5b. For the specimens in the specimen formwork 3a (with a rod-shaped body diameter of 26 mm), the tensile stress was calculated using the following method. Furthermore, the concrete preparation and other related processes were carried out in an environment of 27°C.

[0030] [Calculation of tensile stress] Tensile stress was calculated using a common calculation method. Specifically, after measuring the strain (εs) of the steel material (Invar steel), the following equation (2) is used: The tensile stress (σc) of the concrete was calculated. σc = -As / Ac × Es × εs ···(2) (In equation (2), σc represents the tensile stress of the concrete (stress occurring in the concrete), As represents the cross-sectional area of ​​the steel (Invar steel), Ac represents the cross-sectional area of ​​the concrete, Es represents the elastic modulus of the steel (Invar steel), and εs represents the strain of the steel (Invar steel).)

[0031] [Calculation of splitting tensile strength] The splitting tensile strength was measured using specimens obtained from the strength test formwork, in accordance with "JIA A 1113:2018 (Test Method for Splitting Tensile Strength of Concrete)". Next, the stress-to-strength ratio (tensile stress / splitting tensile strength) was calculated using the tensile stress of the specimen in the specimen formwork 3b and the splitting tensile strength described above. Furthermore, a smaller stress-to-strength ratio indicates a lower likelihood of cracking.

[0032] In accordance with "JIS A 1108:2018 (Test Method for Compressive Strength of Concrete)," the concrete was demolded 24 hours after placement. The demolded specimens were then cured in water at 27°C until they reached the ages shown in Table 2, and the compressive strength at each age was measured. The adiabatic temperature rise of concrete (indicated as "temperature rise" in Table 3) was measured in accordance with "JCI-SQA3 (Draft Test Method for Adiabatic Temperature Rise of Concrete)".

[0033] [Examples 2-4, Comparative Examples 3-11] Concrete was prepared in the same manner as in Example 1. The compressive strength and other properties were measured using the obtained concrete in the same manner as in Example 1. Tensile stress and stress-to-strength ratio were calculated only in Examples 2-4 and Comparative Examples 4 and 9. [Comparative Examples 1-2] Concrete was prepared in the same manner as in Example 1, except that fly ash was not used. The compressive strength and other properties of the obtained concrete were measured in the same manner as in Example 1.

[0034] [Example 5] Concrete was prepared in the same manner as in Example 1, except that high-performance water-reducing agent B was used instead of high-performance water-reducing agent A, and the amount of high-performance water-reducing agent B was appropriately adjusted to an amount that resulted in a concrete slump of 12 cm ± 2.5 cm and an air content of 2.0% or less. The obtained concrete was used to measure the compressive strength and other properties in the same manner as in Example 1. [Comparative Example 12] Concrete was prepared in the same manner as in Example 5, except that fly ash was not used. The compressive strength and other properties of the obtained concrete were measured in the same manner as in Example 1.

[0035] [Table 2]

[0036] [Table 3]

[0037] Table 4 shows the compressive strength of Examples 1-4 at 3 or 7 days of age (3 days of age: 34.3-37.8 N / mm²). 2 , material age 7 days: 54.7~58.2N / mm 2 ) represents the compressive strength of Comparative Examples 1 to 11 at 3 or 7 days of age (3 days of age: 24.2 to 31.6 N / mm²). 2 , material age 7 days: 40.5~53.2N / mm 2 This is larger than the values ​​shown, indicating that the cement compositions of Examples 1-4 exhibit superior initial strength development. Furthermore, the compressive strength at each age in Example 5 was greater than that at each age in Comparative Example 12, indicating that the cement composition of Example 5 exhibits superior strength development. The adiabatic temperature rise in Example 1 (51.6°C) was smaller than that of Comparative Example 3 (same as Example 1 except for the type of blast furnace slag fine powder) (62.2°C), indicating that the cement composition of Example 1 exhibits a smaller temperature rise due to the hydration reaction. This trend was also observed in the comparison between Example 3 and Comparative Example 5. Furthermore, the adiabatic temperature rise in Example 2 (47.5°C) was comparable to or smaller than that of Comparative Examples 4, 6-11 (same as Example 2 except for the type of blast furnace slag fine powder) (47.4-61.2°C). The stress-to-strength ratios of Examples 1-4 (0.54-0.65) are smaller than those of Comparative Examples 1-2 (0.67-0.73), indicating that the concrete of Examples 1-4 is less prone to cracking than the concrete of Comparative Examples 1-2. Furthermore, the stress-to-strength ratio of Example 2 (0.55) is lower than the stress-to-strength ratios of Comparative Examples 4 and 9 (which were the same as Example 2 except for the type of blast furnace slag fine powder used) (0.58-0.60), indicating that the concrete of Example 2 is less prone to cracking than the concrete of Comparative Examples 4 and 9. [Explanation of symbols]

[0038] 1 component 1a Rod-shaped body 1b Restraint end plate 2, 2b Styrofoam container 2a Styrofoam lid 3a, 3b, 3c Formwork for specimen 3D strength testing formwork 4a. Component (using a rod-shaped body with a diameter of 26 mm) 4b. Component (using a rod-shaped body with a diameter of 15 mm) 4c component (using a rod-shaped body with a diameter of 9.2 mm) 5a, 5b, 5c strain gauges 6. Formwork for increasing heat generation 7, 8 Concrete 9 Wiring 10 Insulated curing tank

Claims

1. A cement composition comprising Portland cement, blast furnace slag powder, and fly ash, The above blast furnace slag fine powder satisfies all of the following conditions (1) to (3): A cement composition characterized in that, of the total mass of the above-mentioned Portland cement, blast furnace slag fine powder, and fly ash, the proportion of the above-mentioned Portland cement is 25 to 45% by mass, the proportion of the above-mentioned blast furnace slag fine powder is 35 to 65% by mass, and the proportion of the above-mentioned fly ash is 10 to 20% by mass. (1) The Blaine specific surface area of ​​the above blast furnace slag fine powder is 4,100 to 4,500 cm². ２ / g (2) The basicity of the blast furnace slag fine powder is 1.80 to 2.

00. (3) In the above blast furnace slag fine powder, the content of MgO is 3.0 to 6.0% by mass, SO ３ The content of is 1.5 to 2.5% by mass.

2. The cement composition according to claim 1, wherein the blast furnace slag fine powder further satisfies the following condition (4). (4) In the blast furnace slag fine powder mentioned above, SiO ２ The content of [substance] is 32.0 to 35.0% by mass, and the content of CaO is 40.0 to 44.0% by mass.

3. Concrete comprising the cement composition, fine aggregate, coarse aggregate, and water according to claim 1 or 2.

4. A method for producing a hardened concrete body made of the concrete described in claim 3, The process of preparing a mixture involves mixing the various materials that make up the concrete mentioned above, The above-mentioned mixture is poured into the formwork in a pouring process, The process includes a demolding step in which, after the mixture in the formwork has hardened, the hardened mixture is removed from the formwork to obtain the hardened concrete body. A method for producing a hardened concrete body, characterized in that each step from the above-mentioned mixing preparation step to the above-mentioned demolding step is carried out at a temperature of 25°C or higher.

5. A method for producing a hardened concrete body according to claim 4, comprising a blast furnace slag powder selection step, in which, prior to the above-mentioned mixing preparation step, the blast furnace slag powder to be determined as to be used as a material for the cement composition is checked to see if it satisfies all the conditions required for being a material for the cement composition, and if the blast furnace slag powder satisfies all the conditions, the blast furnace slag powder is selected as a material for the cement composition, and if the blast furnace slag powder does not satisfy all the conditions, the blast furnace slag powder is not selected as a material for the cement composition.

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