Cement composition and method for producing the cement composition

Abstract

To provide a cement composition capable of being produced with more reduction of the amount of CO2 emission during cement production than before even when there is a large amount of C3A, suppressing DEF expansion, and excellent in form removal strength after high temperature curing.SOLUTION: Provided is a cement composition containing cement clinker in which the amount of C3S calculated by Bogue's formula is 20.0-80.0 mass% and the amount of C3A is 6.0-15.0 mass%, gypsum, and an admixture. In the cement composition, the content of the admixture, assuming that the total amount of the cement clinker, the gypsum and the admixture is 100 mass%, is 2.0-30.0 mass%. The amount of C3S, the amount of C3A, and the content of coal ash based on 100 mass% of the total content of the cement clinker, the gypsum and the admixture, satisfy the relation of [amount of C3S (mass%)]≤-3.3×[amount of C3A (mass%)]+2.0×[content of coal ash (mass%)]+β...formula (1).[In the formula (1), β denotes a real number of 91.0 or less.]SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to cement compositions and methods for making cement compositions. [Background technology]

[0002] In recent years, even in Japan, delayed ettringite formation (DEF) in secondary products obtained by steam curing and the deterioration of hardened cement bodies due to DEF have become a problem. DEF refers to the regeneration phenomenon of expansive ettringite as described below. First, the temperature inside the concrete rises significantly due to initial high-temperature curing and heat generation from the cement composition, causing the decomposition of ettringite, which should have formed in the early stages. After that, when moisture is supplied to the concrete during its use, the regeneration of ettringite causes expansion in the hardened body structure, which leads to serious deterioration such as cracks in the concrete.

[0003] For example, Non-Patent Document 1 reports cases of expansion of secondary concrete products (precast concrete products) in Japan. In many cases, white cement with a high C3A content is used. When manufacturing secondary concrete products using cement with a high C3A content, steam curing is performed at high temperatures to increase the formwork turnover rate, and it has been reported that the thermal history at this time affects the DEF expansion of secondary concrete products.

[0004] Various measures to suppress DEF have been studied. Non-Patent Document 2 shows that expansion due to DEF is less likely to occur when low-heat Portland cement and moderate-heat Portland cement are used than when normal Portland cement and high-early-strength Portland cement are used. However, in the above cements that suppress DEF expansion, the C3A content is set low for the purpose of suppressing heat generation, etc., which causes a problem of reducing the amount of waste material used per unit amount of cement that can be added to the raw materials.

[0005] It is known that cement clinker, which is a raw material for cement, emits a large amount of CO2 during its manufacturing process. From the viewpoint of preventing global warming, it is desired to further increase the content of admixtures such as coal ash in the cement composition in order to reduce the cement content. As an admixture, for example, limestone is also known in addition to coal ash. From the viewpoint of limiting CO2 emissions, the incorporation of limestone is effective, but it has been reported that the addition of limestone promotes DEF (for example, Non-Patent Document 3).

[0006] In the production of secondary products, strength at the time of demolding after high-temperature curing is required to increase formwork turnover and improve yield. Patent Document 1 discloses a cement composition that sufficiently improves compressive strength at the time of demolding by adding chlorine bypass dust to the cement composition, and mortar and concrete prepared using the cement composition. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-176774 A [Non-patent literature]

[0008] [Non-Patent Document 1] Yuichiro Kawabata, Hiromichi Matsushita, "Study on DEF expansion in concrete cured at high temperature", Journal of the Japan Society of Civil Engineers, Vol. E2 (Materials and Concrete Structures), 2011, Vol. 67, No. 4, pp. 549-563 [Non-Patent Document 2] "Guidelines for Crack Control of Mass Concrete 2016", 2016, Japan Concrete Institute [Non-Patent Document 3] Shingo Asamoto et al., "Study on the effect of carbonate ions on delayed ettringite formation", Proceedings of the Japan Concrete Institute, 2016, Vol. 28, No. 1, pp. 819-824 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present disclosure is to provide a cement composition that can be produced with lower CO2 emissions than conventional cement compositions even when the C3A content is high, that suppresses DEF expansion in hardened cement bodies, and that has excellent compressive strength when demolded after high-temperature curing, and a method for producing the same. [Means for solving the problem]

[0010] One aspect of the present disclosure provides a cement composition comprising cement clinker having a C3S amount of 20.0 to 80.0 mass% and a C3A amount of 6.0 to 15.0 mass% calculated by the Bogue formula, gypsum, and an admixture, wherein the content of the admixture is 2.0 to 30.0 mass% when the total content of the cement clinker, the gypsum, and the admixture is taken as 100 mass%, and the C3S amount, the C3A amount, and the coal ash content relative to the total content of the cement clinker, the gypsum, and the admixture as 100 mass% satisfy the relationship: [C3S amount (mass%)]≦-3.3×[C3A amount (mass%)]+2.0×[coal ash content (mass%)]+β ... formula (1) [in the above formula (1), the above β represents a real number of 91.0 or less].

[0011] The above cement composition contains a specific cement clinker, gypsum, and admixtures in a predetermined amount, and thus can be produced with less CO2 emissions during cement production than before. In addition, by satisfying the relationship of the above formula (1) between the C3S amount and C3A amount in the cement clinker and the coal ash content, even if the C3A amount is large, DEF expansion is suppressed and the compressive strength at the time of demolding after high-temperature curing is excellent. Although the reason why the above-mentioned effect is obtained by satisfying the relationship of the above formula (1) is not clear, the inventors speculate that it is because the higher the C3S amount and C3A amount are, the more likely DEF is to occur, and the higher the coal ash content is, the more DEF is suppressed, so that the C3S amount needs to be adjusted according to the C3A amount and the coal ash content.

[0012] The cement clinker may contain SO3 and R2O, and the amount of SO3 may be 0.10 to 2.00 mass% and the amount of R2O may be 0.10 to 2.00 mass% in 100 mass% of the cement clinker. By having the above composition of the cement clinker, it is possible to obtain an appropriate pot life while suppressing DEF.

[0013] The above cement composition has a Blaine specific surface area of ​​3000 to 6000 cm 2 When the Blaine specific surface area of ​​the cement composition is within the above range, the cement composition can exhibit both sufficient strength and appropriate heat of hydration.

[0014] The admixture may contain limestone, and the content of the limestone may be 2.0 to 22.5 mass% based on the total content of the cement clinker, the gypsum, and the admixture. By including a predetermined amount of limestone as an admixture, the hydration heat of the cement composition can be reduced and the demolding strength can be increased.

[0015] The admixture may contain limestone and coal ash, and the coal ash content may be 15.0 to 85.0 mass% based on the total amount of the admixture. By having the coal ash content within the above range, it is possible to suppress DEF expansion, reduce the heat of hydration of the cement composition, and increase the demolding strength.

[0016] The Blaine specific surface area of ​​the above coal ash is 3900 to 10000 cm 2 When the Blaine specific surface area of ​​the coal ash is within the above range, it is possible to suppress the DEF expansion and increase the strength.

[0017] The content of the gypsum may be 0.5% by mass or more and less than 1.8% by mass in terms of SO3, where the total content of the cement clinker, the gypsum, and the admixture is taken as 100% by mass. By having the content of the gypsum within the above range, it is possible to increase the strength while suppressing the DEF expansion.

[0018] The coal ash may have a 4 μm residue of 40 to 85% by volume and a 32 μm residue of 0 to 20.0% by volume. When the coal ash has the particle size distribution as described above, it is possible to increase the strength, suppress the DEF, and reduce the adiabatic temperature rise.

[0019] The cement composition may further contain a hardening accelerator, and the content of the hardening accelerator may be 0.1 to 20 parts by mass relative to 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture. By containing a predetermined amount of the hardening accelerator, it is possible to obtain appropriate workability while increasing the early strength.

[0020] One aspect of the present disclosure includes a step of mixing cement clinker having a C3S amount of 20.0 to 80.0 mass% and a C3A amount of 6.0 to 15.0 mass% calculated by the Bogue formula, with gypsum and an admixture, wherein in the step, the content of the admixture is 2.0 to 30.0 mass% when the total content of the cement clinker, the gypsum and the admixture is 100 mass%, and the C3S amount, the C3A amount, and the coal ash content relative to the total content of the cement clinker, the gypsum and the admixture being 100 mass% are: [C3S amount (mass%)]≦-3.3×[C3A amount (mass%)]+2.0×[coal ash content (mass%)]+β ... formula (1) [In the above formula (1), the above β represents a real number of 91.0 or less. The present invention provides a method for producing a cement composition, comprising adjusting the proportions of the cement clinker, the gypsum, and the admixture so as to satisfy the relationship:

[0021] The method for producing the cement composition can produce a cement composition with less CO2 emissions during cement production than before by adjusting the blending ratio of a specific cement clinker, gypsum, and admixtures to a specified ratio. The method for producing the cement composition can provide a cement composition that can suppress DEF expansion and produce a hardened cement body that has excellent compressive strength when demolded after high-temperature curing, even when the C3A content is high, by adjusting the blending ratio of admixtures, etc., so that the C3S content and C3A content in the cement clinker and the coal ash content satisfy the relationship of formula (1) above. Effect of the Invention

[0022] According to the present disclosure, it is possible to provide a cement composition that can reduce CO2 emissions during cement production compared to conventional methods, even when the C3A content is high, suppresses DEF expansion in the hardened cement body, and has excellent compressive strength when demolded after high-temperature curing, and a method for producing the same. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a graph showing the relationship between the mineral compositions of the cement clinker constituting the cement compositions used in the Examples and Comparative Examples. [Diagram 2] FIG. 2 is a graph showing the relationship between the mineral compositions of the cement clinker constituting the cement compositions used in the Examples and Comparative Examples. [Diagram 3] FIG. 3 is a graph showing the relationship between the mineral compositions of the cement clinker constituting the cement compositions used in the Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents. 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.

[0025] One embodiment of the cement composition includes a cement clinker in which the amount of C3S calculated by the Bogue formula is 20.0 to 80.0% by mass and the amount of C3A is 6.0 to 15.0% by mass, gypsum, and a mineral admixture. In the above cement composition, the content of the mineral admixture is 2.0 to 30.0% by mass based on the total content of the cement clinker, the gypsum, and the mineral admixture being 100% by mass.

[0026] In the above cement composition, the content of fly ash with respect to 100% by mass of the amount of C3S, the amount of C3A, and the total content of the cement clinker, the gypsum, and the mineral admixture satisfies the relationship of the following formula (1). The content of fly ash is 0 to 22.5% by mass based on the total content of the cement clinker, the gypsum, and the mineral admixture. [Amount of C3S (% by mass)] ≤ -3.3 × [Amount of C3A (% by mass)] + 2.0 × [Content of fly ash (% by mass)] + β... Formula (1)

[0027] In the above formula (1), β represents a real number of 91.0 or less (β ≤ 91.0), for example, it may preferably be 91.0, more preferably 81.0, and still more preferably 71.0.

[0028] The Bogue formula is a formula widely used to calculate the content of main minerals in cement based on chemical composition. By using the Bogue formula shown below, the content of tricalcium silicate (3CaO·SiO2, denoted as C3S), dicalcium silicate (2CaO·SiO2, denoted as C2S), and tricalcium aluminate (3CaO·Al2O3, denoted as C3A) in the cement clinker can be calculated. Note that "%" in the following formula means "% by mass".

[0029] <Bogue formula> C3S [%] = (4.07 × CaO [%]) - (7.60 × SiO2 [%]) - (6.72 × Al2O3 [%]) - (1.43 × Fe2O3 [%]) - (2.85 × SO3 [%]) C2S[%]=(2.87×SiO2[%])-(0.754×C3S[%]) C3A[%]=(2.65×Al2O3[%])-(1.69×Fe2O3[%]) C4AF[%]=3.04×Fe2O3[%]

[0030] By designing the cement clinker so that it has a large amount of void phases such as C3A and C4AF, it is possible to make good use of materials derived from waste and by-products that contain a lot of Al and Fe, such as coal ash and slag, as cement clinker raw materials, thereby providing a cement composition that is desirable from the perspective of reducing the environmental impact.

[0031] The lower limit of the C3S content in the cement clinker is 20.0 mass% or more, preferably 30.0 mass% or more, more preferably 33.0 mass% or more, even more preferably 37.0 mass% or more, even more preferably 41.0 mass% or more, and particularly preferably 45.0 mass% or more. By the lower limit of the C3S content being within the above range, the decrease in early strength of the cement hardened body can be further suppressed. The upper limit of the C3S content in the cement clinker is 80.0 mass%, preferably 65.0 mass% or less, more preferably 60.0 mass% or less, even more preferably 54.0 mass% or less, and particularly preferably 48.0 mass% or less. By the upper limit of the C3S content being within the above range, the cement composition can be more easily produced.

[0032] The lower limit of the C3A content in the cement clinker is 6.0% by mass or more, preferably 8.0% by mass or more, more preferably 9.0% by mass or more, even more preferably 9.5% by mass or more, particularly preferably more than 10.0% by mass, and most preferably 10.3% by mass or more. By setting the lower limit of the C3A content within the above range, the content of the admixture in the cement composition can be increased, and the cement composition can be produced with a further reduction in CO2 emissions than before. The upper limit of the C3A content in the cement clinker is 15.0% by mass or less, preferably 14.0% by mass or less, more preferably 13.5% by mass or less, even more preferably 12.5% ​​by mass or less, and particularly preferably less than 10.5% by mass. By setting the upper limit of the C3A content within the above range, the increase in adiabatic temperature rise during hardening of the cement composition can be further reduced, and the expansion due to DEF can be further suppressed.

[0033] The C3A content and C3S content in this specification refer to values ​​calculated by the Bogue formula using chemical analysis values ​​of cement clinker measured in accordance with the method described in JIS R 5204 "Fluorescent X-ray analysis method for cement."

[0034] Cement clinker may contain SO3 and R2O.

[0035] The amount of RO in the cement clinker is preferably 0.10 to 2.00 mass%, more preferably 0.15 to 1.50 mass%, further more preferably 0.20 to 1.20 mass%, and particularly preferably 0.25 to 0.75 mass%, based on 100 mass% of the cement clinker. By keeping the amount of RO within the above range, it is possible to further increase the amount of waste material used during burning of the cement clinker, and it is possible to further suppress DEF in the hardened cement body obtained from the cement composition containing the cement clinker.

[0036] The amount of RO in cement clinker means a value calculated from the following formula using the chemical analysis value of cement clinker measured in accordance with the method described in JIS R 5204 "Method for fluorescent X-ray analysis of cement." The amount of RO is used in quality standards as the total amount of alkali in cement. In the formula below, "%" means "% by mass." R2O[%]=Na2O[%]+0.658×K2O[%]

[0037] The amount of SO3 in the cement clinker is preferably 0.10 to 2.00 mass%, more preferably 0.15 to 1.50 mass%, further more preferably 0.20 to 1.20 mass%, and particularly preferably 0.25 to 0.75 mass%, based on 100 mass% of the cement clinker. By keeping the amount of SO3 within the above range, it is possible to further increase the amount of waste material used during burning of the cement clinker, and it is possible to further suppress DEF in the hardened cement body obtained from the cement composition containing the cement clinker.

[0038] The amount of SO3 in the cement clinker means a chemical analysis value of the cement clinker measured in accordance with the method described in JIS R 5204 "Fluorescent X-ray analysis method for cement."

[0039] For example, gypsum dihydrate, hemihydrate, and anhydrous gypsum can be used. One type of gypsum may be used alone, or a combination of two or more types may be used. The content of gypsum in the cement composition is preferably 0.5% by mass or more and less than 1.8% by mass, more preferably 0.7% by mass or more and less than 1.7% by mass, and even more preferably 1.1 to 1.6% by mass, calculated as SO3, based on the total content of the cement clinker, the gypsum, and the admixture being 100% by mass. By setting the content of gypsum within the above range, it is possible to further suppress the decrease in compressive strength at the time of demolding when the cement composition is cured at high temperature, and to further suppress DEF in the hardened cement body.

[0040] The cement composition may contain the above-mentioned cement clinker and the above-mentioned gypsum as a base cement that has been mixed and ground in advance.

[0041] The Blaine specific surface area of ​​the base cement is preferably 3000 to 5000 cm 2 / g, and more preferably 3100 to 4500 cm 2 / g, and more preferably 3150 to 4000 cm 2 When the Blaine specific surface area is within the above range, the compressive strength of the hardened cement body when demolded can be improved, the initial heat of hydration of the cement composition can be reduced, and the DEF in the hardened cement body can be further suppressed.

[0042] 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 test methods for cement."

[0043] Examples of the admixture include limestone and coal ash. It is preferable to use coal ash and limestone in combination as the admixture. By using coal ash and limestone in combination, it is possible to reduce the amount of CO2 generated in the production of the cement composition and to further improve the compressive strength of the hardened cement body obtained by high-temperature curing of the cement composition.

[0044] The content of the admixture is preferably high from the viewpoint of low carbonization including reduction in CO2 generation in the production of the cement composition, while being low from the viewpoint of improving the physical properties (e.g., compressive strength, etc.) of the hardened cement body. The content of the admixture is 2.0 to 30.0 mass%, preferably 2.5 to 27.5 mass%, more preferably 3.0 to 20.0 mass%, even more preferably 4.0 to 15.0 mass%, and particularly preferably more than 5.0 mass% and 12.5 mass% or less, based on 100 mass% of the total content of the cement clinker, the gypsum, and the admixture.

[0045] When the admixture contains other components (e.g., limestone) in addition to coal ash, the coal ash content is preferably 15.0 to 85.0 mass% based on the total amount of the admixture, more preferably 25.0 to 75.0 mass%, further preferably 35.0 to 60.0 mass%, and particularly preferably 45.0 to 55.0 mass%. By setting the coal ash content in the admixture within the above range, the DEF expansion in the hardened cement body can be further suppressed, and the compressive strength of the hardened cement body obtained by high-temperature curing of the cement composition can be further improved.

[0046] The coal ash may be, for example, coal ash discharged from a coal-fired power plant. The above-mentioned mixture may contain other components in addition to coal ash and limestone. For example, ash obtained when coal, which is the main fuel, and biomass fuel derived from wood chips, coconut shells, sewage sludge, etc. are charged and mixed as a power generation boiler fuel in a coal-fired power plant can also be used as the mixture.

[0047] The Blaine specific surface area of ​​the coal ash is preferably 3900 to 10000 cm 2 / g, and more preferably 4200 to 8000 cm 2 / g, and more preferably 4500 to 6500 cm 2 / g, and even more preferably 5000 to 6000 cm 2 / g. The Blaine specific surface area of ​​coal ash can be adjusted, for example, by classification, crushing, etc. of coal ash. The Blaine specific surface area of ​​coal ash may also be adjusted by mixing coal ashes having different Blaine specific surface areas, or by mixing crushed coal ash with classified coal ash. Examples of the classification method of coal ash include air classification, electrostatic classification, sieve classification, gravity field classification, and centrifugal field classification. Examples of the pulverization method of coal ash include a method using equipment such as a ball mill, a jet mill, a rod mill, and a blade mill.

[0048] The particle size of the coal ash is preferably 40 to 85 volume % of 4 μm residue and 0 to 20.0 volume % or less of 32 μm residue, more preferably 65 to 80 volume % of 4 μm residue and 10.0 volume % or less of 32 μm residue, and even more preferably 70.5 to 77.5 volume % of 4 μm residue and 5.0 volume % or less of 32 μm residue. By having the 4 μm residue of the coal ash be 40 volume % or more, the content of fine coal ash particles can be reduced and the deterioration of handleability can be suppressed. By having the 4 μm residue of the coal ash be 40 volume % or more, the increase in adiabatic temperature rise during hardening of the cement composition can be further suppressed, and the DEF suppression effect can be maintained for a longer period of time. By keeping the 32 μm residue of the coal ash at 20.0 volume % or less, the content of coarse particles in the coal ash is low, which suppresses a decrease in pozzolanic reactivity and further suppresses a decrease in the strength of the hardened cement body (e.g., compressive strength, etc.) and a decrease in the DEF inhibitory effect.

[0049] In this specification, the particle size of coal ash means a value determined by a laser diffraction particle size distribution analyzer. In this specification, the 4 μm residue of coal ash means the content ratio of particles having a particle diameter of 4 μm or more to the total amount of coal ash, and the 32 μm residue of coal ash means the content ratio of particles having a particle diameter of 32 μm or more to the total amount of coal ash.

[0050] A larger coal ash content is desirable from the viewpoint of suppressing DEF, while a smaller coal ash content is desirable from the viewpoint of improving the physical properties (e.g., compressive strength) of the hardened cement body. The coal ash content is preferably 0 to 22.5 mass%, more preferably 1.0 to 17.0 mass%, still more preferably 1.5 to 12.5 mass%, and particularly preferably 2.5 to 7.5 mass%, based on the total content of the cement clinker, the gypsum, and the admixture.

[0051] As the limestone, for example, powders mainly composed of calcium carbonate, such as limestone powder that is generally available on the market, and kansui stone powder, can be used. The limestone preferably includes those conforming to the minor mixing components described in JIS R 5210 "Portland cement".

[0052] The Blaine specific surface area of ​​limestone is preferably 2500 to 10000 cm 2 / g, and more preferably 4000 to 9000 cm 2 / g, and more preferably 6000 to 8000 cm 2 / g. The Blaine specific surface area of ​​limestone is 2500 cm 2 / g or more, the reactivity of the cement composition can be improved. 2 / g or less, deterioration of handleability can be suppressed.

[0053] The limestone content is preferably low from the viewpoint of suppressing DEF, while being high from the viewpoint of low carbonization including reducing the amount of CO2 generated in the production of the cement composition. The limestone content is preferably 2.0 to 22.5 mass%, more preferably 2.2 to 17.0 mass%, more preferably 2.5 to 12.5 mass%, and even more preferably more than 2.5 mass% and 10.0 mass% or less, based on the total content of the cement clinker, the gypsum, and the admixture. By having the limestone content within the above range, the heat of hydration can be further reduced and the strength of the cement hardened body can be further improved. By having the limestone content within the above range, the initial and long-term strength development of the cement hardened body can be further improved.

[0054] A mortar composition or a concrete-forming composition can be produced by adding fine aggregate, coarse aggregate, water and / or admixtures, hardening accelerators, etc. to the above-mentioned cement composition. The cement composition containing fine aggregate is suitable for forming mortar, and may be referred to as a mortar-forming composition or simply as a mortar composition. The cement composition containing coarse aggregate is suitable for forming concrete, and may be referred to as a concrete-forming composition. The mortar and concrete formed using the above-mentioned cement composition can exhibit excellent adiabatic temperature rise suppression, strength enhancement, and DEF suppression effects.

[0055] The fine aggregate may be one specified in JIS A 5005 "Crushed Stone and Crushed Sand for Concrete". Examples of fine aggregate include river sand, land sand, sea sand, crushed sand, silica sand, hard blast furnace slag fine aggregate, blast furnace slag fine aggregate, copper slag fine aggregate, and electric furnace oxidized slag fine aggregate. The fine aggregate may be used alone or in combination. The content of the fine aggregate in the above-mentioned cement composition may be, for example, 150 to 350 parts by mass with respect to 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture.

[0056] The coarse aggregate may be one specified in JIS A 5005 "Crushed Stone and Crushed Sand for Concrete". Examples of the coarse aggregate include gravel, crushed stone, blast furnace slag coarse aggregate, and electric furnace oxidized slag coarse aggregate. One type of coarse aggregate may be used alone, or a combination of two or more types may be used. The content of the coarse aggregate in the above-mentioned cement composition is preferably 150 to 350 parts by mass relative to 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture.

[0057] Examples of water include tap water, distilled water, and deionized water. The content of water in the above-mentioned cement composition is preferably 20 parts by mass or more and 60 parts by mass or less with respect to 100 parts by mass of the total amount of the above-mentioned cement clinker, the above-mentioned gypsum, and the above-mentioned admixture. By setting the content of water in the cement composition within the above-mentioned range, it is possible to sufficiently ensure the predetermined fresh properties (fluidity, air content, etc.) and moldability, and also to sufficiently suppress the decrease in the compressive strength and durability of the obtained cement hardened body.

[0058] Examples of the admixture include AE ​​agents, water reducing agents, AE water reducing agents, high performance water reducing agents, high performance AE water reducing agents, superplasticizers, antifoaming agents, shrinkage reducing agents, setting accelerators, setting retarders, and thickeners. Depending on the required performance, the admixture may be used alone or in combination. The content of the admixture in the above-mentioned cement composition is preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture.

[0059] Examples of hardening accelerators include potassium sulfate, sodium sulfate, lithium sulfate, anhydrous gypsum, quicklime, slaked lime, calcium nitrite, calcium nitrate, calcium chloride, alkali aluminate, alkali carbonate, triethanolamine, triisopropanolamine, methyldiethanolamine, diethanolisopropanolamine, calcium formate, maleic anhydride, calcium rhodanate, CSH nanoparticles, and calcium thiocyanate. The hardening accelerator may be used alone or in combination. The content of the hardening accelerator in the above-mentioned cement composition is preferably 0.1 to 20 parts by mass, more preferably 3.0 to 15 parts by mass, and even more preferably 6.0 to 10 parts by mass or less, relative to 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture. By the content of the hardening accelerator being within the above-mentioned range, the hardening acceleration effect can be fully exhibited, and the promotion of setting and the decrease in fluidity can be suppressed.

[0060] The Blaine specific surface area of ​​the above-mentioned cement composition is preferably 3000 to 6000 cm 2 / g, and more preferably 3050 to 5000 cm 2 / g, and more preferably 3100 to 4500 cm 2 / g, and even more preferably 3150 to 4000 cm 2 / g, and particularly preferably 3200 to 3800 cm 2When the Blaine specific surface area is within the above range, the compressive strength of the hardened cement body when demolded can be improved, the initial heat of hydration of the cement composition can be reduced, and the DEF in the hardened cement body can be further suppressed.

[0061] 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 (mixing step) of mixing cement clinker having a C3S content of 20.0 to 80.0 mass% and a C3A content of 6.0 to 15.0 mass% calculated by the Bogue formula, gypsum, and an admixture.

[0062] In the above manufacturing method, in the above step, the total content of the cement clinker, the gypsum, and the admixture is taken as 100 mass%, the content of the admixture is taken as 2.0 to 30.0 mass%, and the blending of the cement clinker, the gypsum, and the admixture is adjusted so that the content of the coal ash relative to 100 mass% of the total content of the cement clinker, the gypsum, and the admixture satisfies the relationship of the following formula (1): [C3S amount (mass%)]≦-3.3×[C3A amount (mass%)]+2.0×[coal ash content (mass%)]+β…Formula (1)

[0063] In the above formula (1), β represents a real number of 91.0 or less (β≦91.0), and may be, for example, preferably 91.0, more preferably 81.0, and even more preferably 71.0.

[0064] The order of mixing the various components in the mixing step may be adjusted as appropriate. For example, the cement clinker and gypsum may be mixed first to prepare a base cement, and then the admixture may be mixed, or the cement clinker, gypsum, and admixture may be mixed at once. The mixing step may also serve as a grinding step for grinding the various components. For example, the above-mentioned production method may include a mixing step in which the cement clinker, gypsum, and admixture are put into a grinder and mixed and ground. By mixing the cement clinker, gypsum, and admixture in the mixing step, a cement composition having a superior DEF suppression effect can be produced.

[0065] The mixing of the various components in the mixing step may be carried out using a mixer such as a pan mixer, a tilting mixer, or a ribbon mixer.

[0066] Although several embodiments have been described above, the present disclosure is not limited to the above-described embodiments. In addition, the descriptions of the above-described embodiments can be mutually applied. EXAMPLES

[0067] The present disclosure will be described in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

[0068] [Preparation of base cement (mixture of cement clinker and gypsum)] Table 1 shows the base cements (NC1 to NC8) used in the examples and comparative examples described below. The base cements (NC1 to NC8) were all made by adding gypsum dihydrate to cement clinker without adding any small amount of additives, and the Blaine specific surface area was 3300±100 cm 2 / g. The amount of gypsum dihydrate was adjusted and added so that the total amount of SO3 in the base cement was 1.9% by mass ± 0.1% by mass.

[0069] Table 1 shows the Blaine specific surface area value of the base cement, its chemical components, and the mineral composition of the cement clinker calculated by the Bogue formula. The Blaine specific surface area of ​​the base cement was calculated based on JIS R 5201 "Physical testing methods for cement." The chemical composition of the base cement and the mineral composition of the cement clinker were analyzed based on JIS R 5204 "Fluorescent X-ray analysis method for cement." The Simultix12 manufactured by Rigaku Corporation was used for the fluorescent X-ray analysis.

[0070] [Table 1]

[0071] [Coal ash (fly ash)] The coal ash (F1) used in the examples and comparative examples described later is shown in Table 2. Coal ash (FA1) was prepared by classifying coal ash collected from a thermal power plant using a swirling air separator (Turbo Classifier, manufactured by Nisshin Engineering Inc.) at 3000 rpm to remove coarse particles, and further classifying the resulting fine powder fraction at 6000 rpm to remove very fine particles and adjust the particle size before use.

[0072] The Blaine specific surface area and particle size of coal ash are shown in Table 2. The Blaine specific surface area of ​​coal ash was determined based on JIS R 5201 "Physical Testing Methods for Cement." The particle size distribution of coal ash was measured by dispersing the coal ash in ethanol using a laser diffraction particle size distribution analyzer SALD2200 manufactured by Shimadzu Corporation.

[0073] [Table 2]

[0074] [Limestone] The limestone (CC) used in the examples and comparative examples described below was a 325 mesh product (passed through a 45 μm sieve) manufactured by Ube Material Industries, Ltd. The 325 mesh product had a Blaine specific surface area of ​​7470 cm 2 / g, calcium carbonate content of 90 mass% or more, aluminum oxide content of 1.0 mass% or less, and conforming to the minor mixed components of JIS R 5210:2019 "Portland cement" were used.

[0075] [Fine aggregate] In the DEF test and compressive strength measurement, standard sand for cement strength testing from the Cement Association (Inc.) was used as fine aggregate.

[0076] (Examples 1 to 12 and Comparative Example 4) Cement compositions were prepared by mixing and pulverizing base cement, coal ash, and limestone in the mixing ratio (mass%) shown in Table 3. Graphs showing the relationship between the mineral composition of the cement clinker constituting the cement composition used for the cement compositions shown in Table 3 were created and shown in Figures 1, 2, and 3. The area below the straight line in the figures shows the case where β is 91.0 in formula (1), and the area below the dotted line shows the case where β is 81 in formula (1).

[0077] [Table 3]

[0078] [DEF test and compressive strength measurement] (Preparation of mortar composition) Each composition prepared in the Examples and Comparative Examples was mixed with standard sand for cement strength testing by the Japan Cement Association (Inc.) as fine aggregate, and water to prepare a mortar composition in accordance with the method described in JIS R 5201:2015 "Physical Testing Methods for Cement." The composition of the mortar composition is shown in Table 4.

[0079] [Table 4]

[0080] (DEF Test) The DEF test was carried out on the above-mentioned mortar specimens under conditions conducive to the generation of DEF by adding potassium sulfate as a hardening accelerator, adjusting the total amount of SO3 in the mixed cement to 6.2% by mass, and pre-curing at a high temperature of 90°C. This is because, in the absence of high-temperature curing and an increase in the amount of SO3, expansion due to DEF may not occur, and the above adjustments were made to make observation easier.

[0081] More specifically, the hardening accelerator was added to the mortar composition, and the mixture was mixed and molded. The mold was then sealed and placed in a thermostatic chamber, cured at 20°C for 4 hours, heated to 90°C for 2 hours, and held at 90°C for 12 hours. After 12 hours, the temperature was lowered to 20°C for 4 hours, and cured at 20°C for 2 hours. The mixture was then demolded to obtain a hardened mortar.

[0082] Three hardened mortar bodies were prepared in the same manner as described above. Two of the three were used in the DEF test. The prepared hardened mortar bodies were cured underwater in a thermostatic chamber at 20°C, and the length change of each hardened mortar body was measured. The length change was measured using a dial gauge in accordance with the description of JIS A 1129-3:2010 "Method of measuring length change in mortar and concrete". The length change was measured by taking the hardened mortar body out of the water on the 7th, 14th, and 28th days after the underwater curing age and every 28 days thereafter, with the base length at the time of removal from the form as the time of removal. The length change was measured at four points on the front and back of the two hardened mortar bodies, and the average value was taken as the length change of the target hardened mortar body. The value obtained by dividing the length change by the interval (100 mm) of the strain gauge was taken as the expansion coefficient of the hardened mortar body, and the degree of DEF suppression of the hardened mortar body after 112 days of underwater curing was evaluated according to the following criteria. The results are shown in Table 5. A: The expansion coefficient of the hardened mortar is 0.03% or less. B: The expansion coefficient of the hardened mortar is greater than 0.03% and less than 0.10%. C: The expansion coefficient of the hardened mortar is greater than 0.10% and less than 1.00%. D: The expansion rate of the hardened mortar exceeds 1.00%.

[0083] (Measurement of compressive strength when demolded) The compressive strength was measured when demolded 24 hours after mixing. The compressive strength was measured according to the method described in JIS R 5201:2015 "Physical Test Methods for Cement." The measurement was performed on one of the three pieces, and the average value obtained from two measurements was taken as the compressive strength when demolded, and was evaluated according to the following criteria. The results are shown in Table 5. A: Compressive strength is 35MPa or more. B: The compressive strength is 30 MPa or more and less than 35 MPa. C: The compressive strength is 27 MPa or more and less than 30 MPa. D: The compressive strength is 23 MPa or more and less than 27 MPa. E: The compressive strength is 20 MPa or more and less than 23 MPa. F: Compressive strength is less than 20 MPa.

[0084] [Table 5]

[0085] As shown in Table 5, by comparing the mortar compositions of Examples 1 to 3 prepared without using coal ash with the compositions of Comparative Examples 1 to 3, it was confirmed that the cement compositions satisfying the formula (1) can suppress the expansion rate and are also superior in terms of compressive strength when demolded.

[0086] As shown in Table 5, a comparison of the mortar compositions of Examples 4 to 10, which contain 5% by mass of coal ash, with the composition of Comparative Example 4 confirmed that the cement composition satisfying formula (1) can suppress the expansion rate and is also excellent in terms of compressive strength at the time of demolding. In particular, the composition of Comparative Example 1 and the mortar composition of Example 7, and the composition of Comparative Example 2 and the mortar composition of Example 8 each contain the same cement clinker, but it was confirmed that by increasing the coal ash content so as to satisfy formula (1), it is possible to achieve both a high level of DEF expansion suppression effect and a high level of compressive strength at the time of demolding.

[0087] As shown in Table 5, it was confirmed that the mortar compositions of Examples 11 and 12, which contain 10 mass% coal ash, have a low expansion rate and excellent compressive strength at the time of demolding by satisfying formula (1). In particular, the compositions of Comparative Examples 3 and 4 and the mortar composition of Example 12 each contain the same cement clinker, but it was confirmed that by increasing the coal ash content so as to satisfy formula (1), it is possible to achieve both a high level of DEF expansion suppression effect and a high level of compressive strength at the time of demolding. [Industrial Applicability]

[0088] According to the present disclosure, even when the C3A content is high, it is possible to produce cement with less CO2 emissions than before, and it is possible to provide a cement composition that suppresses DEF expansion and has excellent demolding strength after high-temperature curing, and a method for producing the same.

Claims

1. C calculated by the Bogue formula ３ The amount of S is 20.0 to 80.0 mass%, and C ３ Cement clinker having an A content of 6.0 to 15.0 mass%; Plaster and and The admixture includes coal ash, The coal ash has a 4 μm residue of 65 to 80 vol. % and a 32 μm residue of 0 to 10.0 vol. %; The content of the admixture is 2.0 to 30.0% by mass, with the total content of the cement clinker, the gypsum, and the admixture being 100% by mass; Said C ３ S amount, the above C ３ The relationship between the amount of A, and the amount of the coal ash relative to the total amount of the cement clinker, the gypsum, and the admixture being 100% by mass, is [C ３ S content (mass %)] ≤ -3.3 × [C ３ A content (mass %)] + 2.0 × [coal ash content (mass %)] + β ... Formula (1) [In the formula (1), β represents a real number of 91.0 or less.] A cement composition which satisfies the relationship:

2. The cement clinker is SO ３ and R ２ Contains O, The SO ３ The amount is 0.10 to 2.00% by weight, and R ２ The amount of O indicates the total amount of alkali, and R ２ O [%] = Na ２ O[%]+0.658×K ２ The cement composition according to claim 1, wherein the total alkali content calculated in terms of O [%] is 0.10 to 2.00 mass%.

3. Blaine specific surface area is 3000 to 6000 cm ２ The cement composition according to claim 1 or 2, wherein the Cement content is 1 / g.

4. the admixture comprises limestone; The content of the limestone is 2.0 to 22.5 mass% based on the total content of the cement clinker, the gypsum and the admixture. The cement composition according to any one of claims 1 to 3.

5. The admixture comprises limestone and coal ash; The cement composition according to any one of claims 1 to 4, wherein the coal ash content is 15.0 to 85.0 mass% based on the total amount of the admixture.

6. The Blaine specific surface area of ​​the coal ash is 3900 to 10000 cm ２ The cement composition according to any one of claims 1 to 5, wherein the Cementitious Agent is Cr, Mn, MnO ...

7. The content of the gypsum is expressed as follows: ３ The cement composition according to any one of claims 1 to 6, wherein the content is 0.5% by mass or more and less than 1.8% by mass.

8. Further containing a curing accelerator, the hardening accelerator is at least one selected from the group consisting of potassium sulfate, sodium sulfate, lithium sulfate, quicklime, slaked lime, calcium nitrite, calcium nitrate, calcium chloride, alkali aluminate, alkali carbonate, triethanolamine, triisopropanolamine, methyldiethanolamine, diethanolisopropanolamine, calcium formate, maleic anhydride, calcium rhodanate, C-S-H nanoparticles, and calcium thiocyanate; The cement composition according to any one of claims 1 to 7, wherein the content of the hardening accelerator is 0.1 to 20 parts by mass relative to 100 parts by mass of a total amount of the cement clinker, the gypsum, and the admixture.

9. C calculated by the Bogue formula ３ The amount of S is 20.0 to 80.0 mass%, and C ３ The method includes a step of mixing cement clinker having an A content of 6.0 to 15.0 mass%, gypsum, and an admixture, The mixture contains coal ash, and the coal ash has a 4 μm residue of 65 to 80 vol % and a 32 μm residue of 0 to 10.0 vol %, In the above step, the content of the admixture is set to 2.0 to 30.0 mass%, with the total content of the cement clinker, the gypsum and the admixture being 100 mass%, and ３ S amount, the above C ３ The relationship between the amount of A, and the amount of the coal ash relative to the total amount of the cement clinker, the gypsum, and the admixture being 100% by mass, is [C ３ S content (mass %)] ≤ -3.3 × [C ３ A content (mass %)] + 2.0 × [coal ash content (mass %)] + β ... Formula (1) [In the formula (1), β represents a real number of 91.0 or less] The method for producing a cement composition is characterized in that the proportions of the cement clinker, the gypsum, and the admixture are adjusted so as to satisfy the relationship.

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