Cement composition and concrete

Abstract

Provided is a cement composition which contains a blast-furnace-slag fine powder and, despite this, is less apt to crack, does not have a large increase in temperature due to hydration reaction, and shows an excellent initial strength development.　The cement composition comprises portland cement, a blast-furnace-slag fine powder, and fly ash, wherein the blast-furnace-slag fine powder satisfies all of the following requirements (1) to (3) and the proportions of the portland cement, the blast-furnace-slag fine powder, and the fly ash are 25-45 mass%, 35-65 mass%, and 10-20 mass%, respectively, relative to a total of 100 mass% of the portland cement, blast-furnace-slag fine powder, and fly ash. Requirement (1): The blast-furnace-slag fine powder has a Blaine specific surface area of 4,100-4,500 cm2 / g. Requirement (2): The blast-furnace-slag fine powder has a basicity of 1.80-2.00. Requirement (3): The blast-furnace-slag fine powder has an MgO content of 3.0-6.0 mass% and an SO3 content of 1.5-2.5 mass%.

Description

Cement composition and concrete

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

[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 admixture. Patent Document 1 describes a cement composition containing a large amount of blast furnace slag powder, comprising ordinary Portland cement clinker powder with an iron content (I.M.) of 1.88 to 2.00, gypsum, and a Blaine specific surface area of ​​2,500 cm². ２ A cement composition comprising fly ash in a quantity of 1 / g or more and blast furnace slag powder, wherein the amount of the above ordinary Portland cement clinker powder and the amount of the above gypsum (SO ３ The amount of gypsum (SO) in the total of 100% by mass (converted) ３ The ratio (converted) is 1.0 to 3.0% by mass, and the amount of the above ordinary Portland cement clinker powder and the amount of the above gypsum (SO ３ The following cement composition is described, characterized in that, in a total of 100% by mass of the amount of fly ash and the amount of blast furnace slag powder (converted), 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.

[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.

[0004] Japanese Patent Publication No. 2019-137586 Japanese Patent Publication No. 2009-269786

[0005] Concrete containing a large amount of blast furnace slag fine 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 of blast furnace slag fine powder (for example, 35 to 65% by mass), 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.

[0006] The inventors have diligently studied to solve the above problems and have found a solution comprising Portland cement, blast furnace slag fine powder, and fly ash, wherein, 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, and the Blaine specific surface area of ​​the blast furnace slag fine powder is 4,100 to 4,500 cm². ２ The blast furnace slag fine powder has a basicity of 1.80 to 2.00, and the MgO content in the blast furnace slag fine powder is 3.0 to 6.0% by mass, SO ３ We have found that the above objective can be achieved by a cement composition having a content of 1.5 to 2.5% by mass, and have completed the present invention. That is, 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 blast furnace slag fine powder is 4,100 to 4,500 cm² ２ (2) The basicity of the blast furnace slag fine powder is 1.80 to 2.00. (3) The MgO content in the blast furnace slag fine powder is 3.0 to 6.0% by mass, SO ３The content ratio is 1.5 to 2.5% by mass. [2] The cement composition according to [1] above, wherein the blast furnace slag fine powder further satisfies the following condition (4). (4) In the blast furnace slag fine powder, the content ratio of SiO ２ is 32.0 to 35.0% by mass, and the content ratio of CaO is 40.0 to 44.0% by mass.

[0007] [3] Concrete containing the cement composition according to [1] or [2] above, fine aggregate, coarse aggregate, and water. [4] A method for producing a concrete hardened body made of the above concrete using the above concrete, comprising a kneading step of kneading each material constituting the above concrete to prepare a kneaded material, a placing step of placing the above kneaded material in a mold, and after the kneaded material in the above mold has hardened, demolding the hardened body of the above kneaded material from the above mold to obtain the above concrete hardened body, and each step from the above kneading step to the above demolding step is performed at a temperature of 25°C or higher. A method for producing a concrete hardened body, characterized in that. [5] Before the above kneading step, it is examined whether the blast furnace slag fine powder to be judged whether to be used as a material of the cement composition satisfies all the conditions required as a material of the above cement composition, and when the above blast furnace slag fine powder satisfies all the above conditions, the above blast furnace slag fine powder is selected as a material of the above cement composition, and when the above blast furnace slag fine powder does not satisfy all the above conditions, the method for producing a concrete hardened body according to [4] above, including a blast furnace slag fine powder selection step of not selecting the above blast furnace slag fine powder as a material of the above cement composition.

[0008] Although the cement composition of the present invention contains a high content ratio (for example, 35 to 65% by mass) of blast furnace slag fine powder, cracks caused by autogenous shrinkage strain are unlikely to occur, and the temperature increase amount of the cement composition due to the hydration reaction of the cement does not become excessively large, and it has excellent initial strength development properties. In addition, by reducing the 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 reduced.

[0009] Figure 2 shows a cross-sectional view of the member made of Invar steel, which is installed in the formwork in the embodiment, showing a longitudinal side view and a transverse front view. Figure 3 shows a cross-sectional view of the member made of Invar steel, taken at the position of line A-A in Figure 2, with the polystyrene foam lid removed, in the state with the polystyrene foam lid in place.

[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 (2) The basicity of the blast furnace slag fine powder is 1.80 to 2.00. (3) The MgO content in the blast furnace slag fine powder is 3.0 to 6.0% by mass, SO ３ The content of this substance is 1.5 to 2.5% by mass, which will be explained in detail below.

[0011] The Portland cement used in the present 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 added, 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 conditions (1) to (3). By using blast furnace slag fine powder that satisfies all of the above conditions (1) to (3), cracking of concrete and the like containing cement compositions is less likely to occur, the temperature rise is not excessively large, and the initial strength development of the cement composition can be improved. [Condition (1)] The Blaine specific surface area of ​​the blast furnace slag fine powder is 4,100 to 4,500 cm². ２ / g, preferably 4,200 to 4,450 cm ２ / g, more preferably 4,250 to 4,400 cm ２ The value is / g. The Braine specific surface area is 4,100 cm². ２ If the amount is less than / g, the strength development of the cement composition will decrease. ２ When the concentration exceeds [amount] / g, the temperature rise and auto-shrinkage increase significantly, making cracking more likely. In addition, the fluidity of concrete and other materials containing cement composition before hardening 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, and more preferably 1.85 to 1.95. If the basicity is less than 1.80, the initial strength development of the cement composition will decrease. If the basicity exceeds 2.00, the temperature rise will be large. The basicity can be determined by the basicity calculation formula (formula (i) below) specified in "JIS A 6206:2013 (Blast Furnace Slag Fine Powder for Concrete)". Basicity = (CaO + MgO + Al ２ O ３ ) / SiO ２ ... (i) (In formula (i) above, CaO, MgO, Al ２ O ３ , and SiO ２ These are the respective percentages of CaO, MgO, and Al in the blast furnace slag fine powder. ２ O ３ The content of, and SiO ２ This is the content (mass %).

[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 made excellent. SO in blast furnace slag fine powder ３ The content 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 contains SiO ２The content of SiO in blast furnace slag fine powder is 32.0 to 35.0% by mass, and the content of CaO is 40.0 to 44.0% by mass. ２ The content of 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 more, the temperature rise can be further suppressed. If the above content is 35.0% by mass or less, 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 more, the strength development of the cement composition can be further improved. If the above content is 44.0% by mass or less, 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 Blaine 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 to 6,000 cm ２ / g, particularly preferably 3,500 to 4,500 cm ２ The value is / g. The above Braine specific surface area is 1,500 cm². ２ If the amount is greater than or equal to / g, the strength development of the cement composition will be further improved. The above Blaine specific surface area is 8,000 cm². ２If the amount is less than / g, the fluidity of concrete and other materials containing the cement composition before hardening is further improved. The proportion of fly ash in the total 100% by mass of Portland cement, blast furnace slag fine 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 likely for cracks to occur. 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 various cement admixtures (compounds) such as silica fume, limestone, and 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 comprises, in addition to the cement composition described above, fine aggregate, coarse aggregate, and water. In this specification, the term "concrete" includes not only a fully hardened body but also a 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. The unit amount of fine aggregate is not particularly limited and can be any unit amount common in concrete. For example, the above unit amount is preferably 500 to 1,200 kg / m³. ３ , more preferably 600 to 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 examples thereof include river gravel, mountain gravel, land gravel, sea gravel, crushed stone, slag coarse aggregate, and lightweight coarse aggregate. These may be used alone or in combination of two or more. The fine aggregate ratio of the concrete is preferably 20 to 60%, more preferably 25 to 55%, and particularly preferably 30 to 50%. If the fine aggregate ratio is within the above numerical range, the workability and ease of molding of the concrete are improved. The fine aggregate ratio refers to the volume ratio of the fine aggregate in the total amount of the fine aggregate and the coarse aggregate. Further, the concrete of the present invention may contain various admixtures such as a cement dispersant (water reducing agent, AE water reducing agent, high performance water reducing agent or high performance AE water reducing agent), AE agent, antifoaming agent, and shrinkage reducing agent, as necessary. When producing concrete in a high temperature environment (for example, an environment where the ambient temperature is 25°C or higher or the central part of mass concrete) or when using a hardened body made of concrete in a high temperature environment, there is little need to improve the freeze-thaw resistance of the concrete, and from the viewpoint of reducing the cost of materials, it is preferable not to contain an AE agent, AE water reducing agent, or high performance AE water reducing agent.

[0021] Further, the mass ratio of water to the 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 more, the workability (fluidity) such as kneading during the production of concrete is further improved. If the above mass ratio is 0.65 or less, the strength of the concrete after hardening is further improved.

[0022] An example of a method for producing a hardened body made of concrete using the concrete of the present invention is a method that includes a mixture preparation step of mixing the materials constituting the concrete to prepare a mixture, a casting step of placing 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 mixture preparation step, the method of mixing each material is not particularly limited; for example, each material may be put into a mixer or the like all at once and mixed, or each material constituting the cement composition may be put into a mixer or the like and mixed (mixed), and then other materials (materials other than each material constituting the cement composition) may be put into the mixer or the like and mixed. In the above production method, each step from the mixture 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 temperatures (environments) of 25°C or higher, the resulting concrete is less prone to cracking and the temperature rise does not become 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.

[0024] Hereinafter, the present invention will be specifically described by way of 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 / cm ３ (2) Fly ash; Blaine specific surface area: 3,310 cm ２ / g (3) Ground granulated blast-furnace slag 1 - 9 (indicated as "BS1 - BS9" in Tables 1 - 2); details are shown in Table 1. (4) Fine aggregate A; crushed stone powder, density: 2.57 g / cm ３ (5) Fine aggregate B; natural sand, density: 2.56 g / cm ３ (6) Coarse aggregate; crushed stone, density: 2.55 g / cm ３ (7) Water reducing agent (indicated as "AD" in Table 2); manufactured by Pozolith Solutions Co., Ltd., trade name "Master Pozolith R168" (8) High-performance water reducing agent A; polycarboxylic acid-based high-performance water reducing agent, manufactured by Pozolith Solutions Co., Ltd., trade name "Master Glenium SKY8703" (9) High-performance water reducing agent B; polycarboxylic acid-based high-performance water reducing agent, manufactured by Pozolith Solutions Co., Ltd., trade name "Master Rebuilt R1000" (10) High-performance water reducing agent C (indicated as "SP2" in Table 2); polycarboxylic acid-based high-performance water reducing agent, manufactured by Pozolith Solutions Co., Ltd., trade name "Master Glenium ACE8538" (11) Water; tap water

[0025] The chemical composition of the ground granulated blast-furnace slag was measured in accordance with "JIS R 5204:2019 (Fluorescent X-ray analysis method for cement)". Also, the density, Blaine specific surface area (indicated as "Blaine" in Table 1), and basicity of the ground granulated blast-furnace slag were measured in accordance with "JIS A 6206:2013 (Ground granulated blast-furnace slag for concrete)".

[0026]

[0027] [Explanation of Insulated Curing Tank] The formwork, which is equipped with a member made of Invar steel for producing 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 explained with reference to Figures 1 to 3. The specimen formwork 3a, 3b, and 3c for producing uniaxially restrained specimens are formwork with internal dimensions of 100 × 100 × 850 mm, with a member 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. Members 4a, 4b, and 4c installed in the specimen formwork 3a, 3b, and 3c have rod-shaped body diameters of 26 mm, 15 mm, and 9.2 mm, respectively. Furthermore, the constraining steel ratios (the ratio of the cross-sectional area of ​​the rod-shaped body 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 bodies of members 4a, 4b, and 4c. Wiring 9 for transmitting data obtained from the strain gauges is connected to the strain gauges 5a, 5b, and 5c (not shown in Figure 2). 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. Note that 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 negligibly small at / °C. Furthermore, the Young's modulus of the 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, formworks 3a, 3b, and 3c for test specimens, and a formwork 3d for strength testing. The insulated curing tank 10 uses formworks 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 used to simulate the temperature history inside mass concrete by increasing the amount of concrete inside the insulated curing tank 10 and increasing its heat generation by pouring concrete 7 into the formwork. Furthermore, the formwork 6 for increasing heat generation is the same as the formworks 3a, 3b, and 3c for test specimens, except that it does not have a member made of Invar steel and has a different length. Four of the formworks 6 for increasing heat generation are lined up inside the expanded polystyrene container 2b. The specimen formwork 3a, 3b, and 3c are placed on top of the heat-generating formwork 6 such that the direction perpendicular to the longitudinal direction of the heat-generating formwork 6 is the longitudinal direction of the specimen formwork 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 amounts 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 mixed material 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 to 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 ensure that the concrete slump was 21 cm ± 2.5 cm and the air content was 2.0% or less. After pouring concrete into the aforementioned specimen formwork 3a, 3b, 3c, strength test formwork 3d, and heat generation increasing formwork 6 (4 pieces), the specimen formwork and other components were left to stand in the aforementioned insulated curing tank 10. After pouring, 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 the strain gauge 5b. The tensile stress of the specimen in specimen formwork 3a (with a rod-shaped body diameter of 26 mm) was calculated using the following method. The concrete preparation was carried out in an environment of 27°C.

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

[0031] [Calculation of Splitting Tensile Strength] 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 above splitting tensile strength. A smaller stress-to-strength ratio indicates that cracking is less likely to occur.

[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 the 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. 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. Compressive strength and other properties were measured using the obtained concrete 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 compressive strength and other properties were measured using the obtained concrete 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 were measured using the obtained concrete in the same manner as in Example 1.

[0035]

[0036]

[0037] Table 4 shows the compressive strength of Examples 1 to 4 at 3 or 7 days of age (3 days of age: 34.3 to 37.8 N / mm²). ２ , material age 7 days: 54.7-58.2N / mm ２ ) is 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 The compressive strength of Examples 1 to 4 is greater than that of Comparative Example 12, indicating that the cement compositions of Examples 1 to 4 exhibit excellent initial strength development. Furthermore, the compressive strength at each age of Example 5 is greater than that of Comparative Example 12, indicating that the cement composition of Example 5 exhibits excellent strength development. The adiabatic temperature rise of Example 1 (51.6°C) is smaller than the adiabatic temperature rise 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 has a smaller temperature rise due to the hydration reaction. This trend was also observed when comparing Example 3 and Comparative Example 5. Furthermore, the adiabatic temperature rise of Example 2 (47.5°C) is equivalent to or smaller than the adiabatic temperature rise of Comparative Examples 4, 6 to 11 (same as Example 2 except for the type of blast furnace slag fine powder) (47.4 to 61.2°C). The stress-to-strength ratios of Examples 1 to 4 (0.54 to 0.65) are smaller than those of Comparative Examples 1 to 2 (0.67 to 0.73), indicating that the concrete of Examples 1 to 4 is less prone to cracking than the concrete of Comparative Examples 1 to 2. Furthermore, the stress-to-strength ratio of Example 2 (0.55) is smaller than that 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 to 0.60), indicating that the concrete of Example 2 is less prone to cracking than the concrete of Comparative Examples 4 and 9.

[0038] 1. Components 1a. Rod-shaped body 1b. Restraining end plate 2, 2b. Styrofoam container 2a. Styrofoam lid 3a, 3b, 3c. Formwork for test specimens 3d. Formwork for strength testing 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 gauge 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 fine powder, and fly ash, wherein the blast furnace slag fine powder satisfies all of the following conditions (1) to (3): 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 blast furnace slag fine powder is 4,100 to 4,500 cm² ２ (2) The basicity of the blast furnace slag fine powder is 1.80 to 2.

00. (3) The MgO content in the blast furnace slag fine powder 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) The blast furnace slag fine powder contains 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 using the concrete described in claim 3, comprising: 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, wherein each step from the mixture preparation step to the demolding step is performed 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 mixture 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 whether 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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