JP7529426B2 - Cement composition, its manufacturing method, and durability improving admixture - Google Patents

Description

The present disclosure relates to a cement composition and its manufacturing method, as well as a durability-improving admixture.

From the viewpoint of preventing global warming and reducing carbon emissions, it is desirable to increase the content of admixtures in cement compositions, instead of cement clinker, which emits a large amount of _CO2 during production. Inorganic powders that have excellent reactivity when used with cement compositions have been used as admixtures. These inorganic powders contain a lot of amorphous matter, and for example, blast furnace slag and fly ash are used. However, in order to further expand the use of admixtures, it is also desirable to expand the options of inorganic powders that can be used.

An example of an inorganic powder that has not been used much as an admixture is pulverized coal gasification slag. Coal gasification slag is an amorphous inorganic powder with a large amount of CaO, which is formed by melting and solidifying ash in coal after combustion in a coal gasification combined cycle power generation system. Coal gasification combined cycle power generation is more efficient than conventional coal-fired power generation and has less _CO2 emissions, so it is expected to become more widespread in the future. However, it is also necessary to consider effective utilization measures for the coal gasification slag that is produced as a by-product at the same time. Patent Document 1 discloses that a cement composition consisting of cement containing 40% by mass of belite and fly ash and/or coal gasification slag powder improves strength development and flow value at room temperature. However, strength development in a high-temperature environment when using coal gasification slag powder is not known.

In recent years, in relation to the durability of hardened cement bodies, delayed ettringite formation (DEF) in concrete structures and secondary products of steam curing under high temperature environments and the deterioration of hardened cement bodies due to DEF have become a problem (e.g., Non-Patent Document 1). DEF refers to the following phenomenon of regeneration of ettringite. First, the temperature inside the concrete rises significantly due to the initial high temperature curing and heat generation of the cement composition, causing decomposition of ettringite (a compound represented by 3CaO.Al ₂ O _{3.3CaSO 4.32H 2} O), which should have been generated in the initial stage. After that, the phenomenon of ettringite regeneration occurs due to the supply of moisture during the service of the concrete. It is also known that ettringite expands with crystallization, and the expansion of the hardened body structure due to DEF causes serious deterioration of the concrete, such as cracks.

As a measure to suppress DEF, Non-Patent Document 2 reports that adding 25% by mass of coal ash (fly ash) can suppress expansion even under conditions that tend to cause DEF. However, there are no documents that describe the effect on DEF of inorganic powders that contain a lot of amorphous matter , such as coal gasification slag powder, which are admixtures other than slag and fly ash.

Japanese Patent Application Publication No. 11-139860

Yuichiro Kawabata, Hiromichi Matsushita, "Study on DEF expansion in concrete cured at high temperature", Journal of the Japan Society of Civil Engineers E2 (Materials and Concrete Structures), 2011, Vol. 67, No. 4, pp. 549-563 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

The present disclosure aims to provide a cement composition and a method for producing the same that suppresses expansion associated with DEF and exhibits sufficient compressive strength in high-temperature environments, even when the admixture content is high. The present disclosure also aims to provide a durability-improving admixture that can be used to produce the above-mentioned cement composition.

One aspect of the present disclosure provides a cement composition comprising cement clinker, gypsum, and an admixture, the admixture comprising an inorganic powder containing an amorphous phase and limestone, the inorganic powder having a chemical composition containing CaO, SiO ₂ , and Al ₂ O ₃ , the CaO amount being 6.0 to 40.0 mass%, the SiO ₂ amount being 35.0 to 75.0 mass%, and the Al ₂ O ₃ amount being 14.0 to 25.0 mass% based on the total amount of the inorganic powder, the admixture content being 2.0 to 30.0 mass% based on the total amount of the cement clinker, the gypsum, and the admixture, the inorganic powder content being 1.0 to 29.0 mass%, and the limestone content being 1.0 to 10.0 mass%.

The above cement composition contains cement clinker, gypsum, inorganic powders having a specific chemical composition and containing an amorphous phase, and limestone in a specific mixture, so that although it contains admixtures, it is possible to prepare a hardened cement body that suppresses expansion associated with DEF and has excellent compressive strength in high-temperature environments.

The content of the inorganic powder may be 5.0 to 95.0% by mass based on 100% by mass of the admixture. By having the content of the admixture within the above range, it is possible to sufficiently achieve both the effect of reducing _CO2 during cement production and the compressive strength of the hardened cement body.

The chemical composition of the inorganic powder may further include MgO, and the amount of MgO based on the total amount of the inorganic powder may be 5.0 mass% or less. By having the amount of MgO within the above range, excellent strength expression can be obtained.

The chemical composition of the inorganic powder may further include SO ₃ , and the amount of SO ₃ based on the total amount of the inorganic powder may be 1.0 mass% or less. By having the amount of SO ₃ within the above range, expansion of the hardened cement body due to DEF can be suppressed.

The inorganic powder may have a Blaine specific surface area of 2000 to 10000 cm ² /g. When the Blaine specific surface area of the inorganic powder is within the above range, the expansion of the hardened cement body due to DEF can be further suppressed.

The amount of the amorphous phase in 100% by mass of the inorganic powder may be 80.0 to 100.0% by mass. By having the amount of the amorphous phase in the inorganic powder within the above range, reactivity can be increased and excellent strength can be obtained.

The inorganic powder may contain pulverized coal gasification slag. By containing pulverized coal gasification slag in the inorganic powder, it is possible to obtain an effect of suppressing the expansion of the hardened cement body associated with DEF and excellent strength development.

The cement clinker may have a C ₃ S content of 35.0 to 75.0 mass % and a C ₃ A content of 8.0 to 15.0 mass % calculated by the Bogue formula. The cement clinker having the above mineral composition can increase the amount of waste used as a clinker raw material. In addition, the expansion of the hardened cement body caused by DEF can be suppressed.

The content of the gypsum may be 0.5 to 3.0 mass% in terms of the amount of SO ₃ based on the total amount of the cement clinker and the gypsum. By having the gypsum content within the above range, it is possible to suppress the generation of DEF while ensuring a sufficient pot life.

The cement clinker may contain _SO3 and _R2O , and the amount of _SO3 may be 0.10 to 2.0 mass% and the amount of _R2O may be 0.10 to 2.0 mass% in 100 mass% of the cement clinker. By having the amounts of _SO3 and _R2O in the cement clinker within the above ranges, it is possible to further increase the amount of waste material used during cement clinker burning, and DEF in the hardened cement body obtained from the cement composition containing the cement clinker can be further suppressed.

The cement composition may further contain a hardening accelerator, and the content of the hardening accelerator may be 0.1 to 20.0 parts by mass per 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture. By containing a hardening accelerator and having the content within the above range, the hardening acceleration effect can be fully exerted, and the promotion of setting and the decrease in fluidity can be suppressed.

Based on the total amount of the inorganic powder, the amorphous phase of the inorganic powder may have a CaO content of 6.0 to 40.0 mass%, a _SiO2 content of 35.0 to 75.0 mass%, and _{an Al2O3 content} of 14.0 to 25.0 mass%. When the inorganic powder has the chemical composition of the amorphous phase, it is possible to obtain an effect of suppressing the expansion of the hardened cement body associated with DEF and excellent strength development.

One aspect of the present disclosure provides a method for producing a cement composition, comprising the step of mixing cement clinker, gypsum, and an admixture, the admixture comprising an inorganic powder containing an amorphous phase and limestone, the inorganic powder having a chemical composition containing CaO, SiO ₂ , and Al ₂ O ₃ , and based on the total amount of the inorganic powder, the CaO amount is 6.0 to 40.0 mass%, the SiO ₂ amount is 35.0 to 75.0 mass%, and the Al ₂ O ₃ amount is 14.0 to 25.0 mass%, and in the step, the cement clinker, the gypsum, and the admixture are mixed such that the content of the admixture is 2.0 to 30.0 mass%, the content of the inorganic powder is 1.0 to 29.0 mass%, and the content of the limestone is 1.0 to 10.0 mass%, based on the total amount of the cement clinker, the gypsum, and the admixture.

The method for producing the above cement composition includes a process for preparing a specific mixture of cement clinker, gypsum, an inorganic powder having a specific chemical composition and containing an amorphous phase, and limestone, thereby producing a cement composition that contains admixtures but suppresses expansion associated with DEF and can produce a hardened cement body that has excellent compressive strength in high-temperature environments.

One aspect of the present disclosure provides a durability-improving admixture comprising an inorganic powder containing an amorphous phase and limestone, the inorganic powder having a chemical composition containing CaO, _SiO2 and _Al2O3 , and based on the total amount of the inorganic powder, the CaO amount is 6.0 to 40.0 mass%, the _SiO2 amount is 35.0 to 75.0 mass%, and _{the Al2O3 amount is} 14.0 to 25.0 mass%, and the durability-improving admixture is used by mixing with cement clinker and gypsum such that the content of the inorganic powder is 1.0 to 29 mass% and the content of the limestone is 1.0 to 10.0 mass%, relative to the total amount of cement clinker, gypsum, and the durability-improving admixture being 100 mass%.

The above-mentioned durability-improving admixture contains specific inorganic powders and limestone, and is mixed with cement clinker and gypsum in a specified ratio, making it easy to manufacture the above-mentioned cement composition.

According to the present disclosure, it is possible to provide a cement composition and a manufacturing method thereof that suppresses expansion associated with DEF and has sufficient compressive strength development in high-temperature environments even when the content of the admixture is high. According to the present disclosure, it is also possible to provide a durability-improving admixture that can be used to manufacture the above-mentioned cement composition.

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

One embodiment of the cement composition contains cement clinker, gypsum, and an admixture.

The content of the gypsum may be 0.5 to 3.5 mass% in terms of _SO3 , where the total content of the cement clinker, the gypsum, and the admixture is 100 mass%. By having the gypsum content within the above range, it is possible to further reduce the occurrence of DEF accompanying the hardening of the cement composition. Also, by having the gypsum content within the above range, it is possible to further improve the compressive strength of the hardened cement body prepared using the cement composition.

The mineral composition of cement clinker can be calculated by the Bogue formula. Here, the Bogue formula is a formula that is widely used to calculate the content of major minerals in cement clinker from the content ratio of chemical composition. By using the Bogue formula shown below, the contents of tricalcium silicate (3CaO.SiO ₂ , represented by C ₃ S), dicalcium silicate (2CaO.SiO ₂ , represented by C ₂ S), and tricalcium aluminate (3CaO.Al ₂ O ₃ , represented by C3A) in cement clinker can be calculated. In addition, "%" in the following formula means "mass %". The chemical formula represents the content ratio (mass %) of each compound indicated by the chemical analysis value according to JIS R 5204 "Fluorescent X-ray analysis method for cement".

<Bogue Style>
C ₃ S [%] = (4.07 x CaO [%]) - (7.60 x SiO ₂ [%]) - (6.72 x Al ₂ O ₃ [%]) - (1.43 x Fe ₂ O ₃ [%]) - (2.85 x SO ₃ [%])
C ₂ S [%] = (2.87 x SiO ₂ [%]) - (0.754 x C ₃ S [%])
C ₃ A [%] = (2.65 x Al ₂ O ₃ [%]) - (1.69 x Fe ₂ O ₃ [%])
C ₄ AF [%] = 3.04 x Fe ₂ O ₃ [%]

The lower limit of the C ₃ S content in the cement clinker is preferably 35.0% by mass or more, more preferably 40.0% by mass or more, even more preferably 45.0% by mass or more, and particularly preferably 50.0% by mass or more. By the lower limit of the C ₃ S content being within the above range, the initial strength of the cement composition during hardening can be further improved. The upper limit of the C ₃ S content in the cement clinker is preferably 75.0% by mass or less, more preferably 70.0% by mass or less, even more preferably 65.0% by mass or less, even more preferably 60.0% by mass or less, and particularly preferably 55.0% by mass or less. By the upper limit of the C ₃ S content being within the above range, the heat generation during hardening of the cement composition can be further suppressed, the decomposition of ettringite can be suppressed, and the generation of DEF can be further suppressed. In addition, if the C ₃ S content exceeds 75.0% by mass, it becomes difficult to prepare the cement clinker.

The lower limit of the C ₃ A amount in the cement clinker is preferably 8.0% by mass or more, more preferably 9.0% by mass or more, even more preferably 9.5% by mass or more, and particularly preferably 10.0% by mass or more. By setting the lower limit of the C ₃ A amount within the above range, a cement composition can be produced in which the amount of waste and by-products such as coal ash used as the cement clinker raw material is increased. The upper limit of the C ₃ A amount in the cement clinker is 14.0% by mass or less, preferably 13.0% by mass or less, more preferably 12.0% by mass or less, even more preferably 11.0% by mass, and particularly preferably less than 10.5% by mass. The C ₃ A amount can be appropriately adjusted within the above range, and may be, for example, 8.0 to 14.0% by mass. By setting the upper limit of the _C3A content within the above range, the amount _of ettringite ( _a compound represented by _{3CaO.Al2O3.3CaSO4.32H2O} ) produced during hardening of the cement composition can be made appropriate. Also _, the increase in adiabatic temperature rise during hardening of the cement composition can be further reduced, and the decomposition of ettringite can be inhibited, and the expansion of the hardened cement body associated with DEF can be further inhibited.

The C ₃ A content and C ₃ S 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."

Cement clinker may contain _SO3 and _R2O .

The amount of SO ₃ in the cement clinker is preferably 0.10 to 2.00 mass%, more preferably 0.20 to 1.60 mass%, and even more preferably 0.30 to 0.70 mass%, based on 100 mass% of the cement clinker. By having the amount of _{SO 3} within the above range, it is possible to further increase the amount of waste material used during cement clinker burning, and DEF in the hardened cement body obtained from the cement composition containing the cement clinker can be further suppressed.

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".

The amount of R ₂ O in the cement clinker is preferably 0.10 to 2.00 mass%, more preferably 0.20 to 1.60 mass%, further preferably 0.25 to 1.25 mass%, and particularly preferably 0.30 to 0.70 mass%, based on 100 mass% of the cement clinker. By having the amount of R ₂ O 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.

The amount of R ₂ O in cement clinker means a value calculated from the following formula using the chemical analysis value of the cement clinker measured in accordance with the method described in JIS R 5204 "Method for fluorescent X-ray analysis of cement." The amount of R ₂ O is used as the total alkali amount in cement for quality standards, etc.
R ₂ O [%] = Na ₂ O [%] + 0.658×K ₂ O [%]

As the gypsum, for example, dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum can be used. One type of gypsum may be used alone, or a plurality of types may be used in combination. The content of gypsum in the cement composition is preferably 0.5 to 3.0 mass%, more preferably 0.7 to 2.5 mass%, further preferably 0.9 to 2.0 mass%, and particularly preferably 1.1 to 1.6 mass%, calculated as SO ₃ , with the total content of the cement clinker and the gypsum taken as 100 mass%. By the content of gypsum being within the above range, it is possible to sufficiently secure the pot life while suppressing the generation of DEF. By the content of gypsum being within the above range, it is possible to improve the compressive strength of the cement hardened body.

The admixture contains at least an inorganic powder containing an amorphous phase and limestone. The inclusion of the inorganic powder as an admixture contributes to suppressing the expansion of the hardened cement body caused by DEF and improving the compressive strength after long-term high-temperature curing. The inclusion of limestone as an admixture contributes to reducing _CO2 emissions during cement production and improving the compressive strength of the hardened cement body after high-temperature curing.

The total content of the admixture in the cement composition is preferably high from the viewpoint of low carbonization, 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 in the cement composition is 2.0 to 30.0 mass% based on the total amount of the cement clinker, the gypsum, and the admixture, but is preferably 4.0 to 25.0 mass%, more preferably 5.5 to 20 mass%, even more preferably 6.5 to 15.0 mass%, and particularly preferably 7.5 to 12.5 mass%. By having the content of the admixture within the above range, it is possible to sufficiently achieve both the effect of reducing CO ₂ during cement production and the compressive strength of the hardened cement body.

The inorganic powder has a chemical composition including CaO, SiO ₂ , and Al ₂ O _3. The chemical composition of the inorganic powder may further include, for example, MgO and SO ₃ in addition to CaO, SiO ₂ , and Al ₂ O _3. The chemical composition of the inorganic powder is, based on the total amount of the inorganic powder, 6.0 to 40.0 mass% CaO, 35.0 to 75.0 mass% SiO ₂ , and 14.0 to 25.0 mass% Al ₂ O _3. The above composition provides an excellent DEF suppression effect and sufficient compressive strength during high-temperature curing.

The amount of CaO is preferably 7.0 to 35 mass%, more preferably 8.0 to 30.0 mass%, even more preferably 10.0 to 25.0 mass%, even more preferably 12.0 to 20.0 mass%, and particularly preferably 14.0 to 18.0 mass%, based on the total amount of the inorganic powder.

The amount of _SiO2 is preferably 40.0 to 70.0 mass%, more preferably 45.0 to 65.0 mass%, and even more preferably 50.0 to 60.0 mass%, based on the total amount of the inorganic powder.

The amount of Al ₂ O ₃ is preferably 15.0 to 24.0 mass%, more preferably 16.0 to 22.0 mass%, still more preferably 17.0 to 21.0 mass%, and particularly preferably 18.0 to 20.0 mass%, based on the total amount of the inorganic powder.

When MgO is included in the chemical composition of the inorganic powder, the amount of MgO is preferably 5.0% by mass or less, more preferably 0.2 to 4.5% by mass, even more preferably 0.4 to 4.0% by mass, and particularly preferably 0.6 to 2.0% by mass, based on the total amount of the inorganic powder.

When SO ₃ is contained in the chemical composition of the inorganic powder, the amount of SO ₃ is preferably 1.0 mass% or less, more preferably 0.8 mass% or less, still more preferably 0.6 mass% or less, and particularly preferably 0.4 mass% or less, based on the total amount of the inorganic powder. From the viewpoint of suppressing DEF, it is better for the amount of SO ₃ in the inorganic powder to be low.

It is more preferable that the inorganic powder contains a large amount of amorphous matter. The amount of amorphous phase in 100% by mass of the inorganic powder is preferably 80.0 to 100.0% by mass, more preferably 85.0 to 100.0% by mass, even more preferably 90.0 to 100.0% by mass, and particularly preferably 95.0 to 100.0% by mass. The above-mentioned chemical composition is preferably the composition in the amorphous phase.

The Blaine specific surface area of the inorganic powder is preferably 2000 to 10000 cm ² /g, more preferably 3000 to 10000 cm ² /g, still more preferably 3500 to 8000 cm ² /g, and particularly preferably 4000 to 6000 cm ² /g. If the Blaine specific surface area of the inorganic powder is low, the DEF suppression effect is low, and if the Blaine specific surface area is too high, handling may be poor. The Blaine specific surface area can be adjusted, for example, by classifying and crushing the inorganic powder. It may also be adjusted by mixing the crushed inorganic powder and the classified inorganic powder. The classification of the inorganic powder can be performed, for example, by air classification, electrostatic classification, sieve classification, gravity field classification, and centrifugal field classification. The method of pulverizing the inorganic powder is not particularly limited, and for example, equipment such as a ball mill, a jet mill, a rod mill, a blade mill, and a vertical mill can be used.

In this specification, "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."

As the inorganic powder, for example, pulverized coal gasification slag discharged from a coal-fired power plant can be suitably used. Coal gasification slag is amorphous inorganic particles with a large amount of CaO formed by melting and solidifying ash in coal after combustion in a coal gasification combined cycle power generation. The coal gasification slag can be pulverized using, for example, a ball mill, a jet mill, a rod mill, a blade mill, a vertical mill, or the like, and a coal gasification slag powder can be obtained by pulverizing. The coal gasification slag can be pulverized simultaneously with limestone, cement clinker, or the like, or can be pulverized separately.

An example of an inorganic powder other than crushed coal gasification slag is ash obtained when coal, the main fuel, is mixed with biomass fuels derived from wood chips, coconut shells, sewage sludge, etc., as fuel for the power generation boilers of coal-fired power plants. Other examples include natural pozzolans such as volcanic ash, clinker ash, and chlorine bypass dust.

Even if a material cannot be used alone, it may be used if the components are adjusted by mixing and grinding, etc., to satisfy the requirements of the inorganic powder. For example, even if a material such as coal gasification slag powder, biomass combustion ash, natural pozzolan, clinker ash, chlorine bypass dust, coal ash, and blast furnace slag powder cannot be used alone as the inorganic powder, it can be used as an inorganic powder by mixing and grinding and adjusting the components.

The lower limit of the content of the inorganic powder is preferably 5.0% by mass or more, more preferably 12.5% by mass or more, even more preferably 35.0% by mass or more, and particularly preferably 60.0% by mass or more, based on 100% by mass of the admixture. The upper limit of the content of the inorganic powder is preferably 95.0% by mass or less, more preferably 92.5% by mass or less, even more preferably 90.0% by mass or less, and particularly preferably 87.5% by mass or less, based on 100% by mass of the admixture. The content of the inorganic powder can be appropriately adjusted within the above-mentioned range, and may be, for example, 5.0 to 95.0% by mass, based on 100% by mass of the admixture. The content of the inorganic powder is within the above-mentioned range, and the DEF suppression effect can be improved by including a large amount of the inorganic powder. The inclusion of an appropriate amount of limestone contributes to improving the strength after high-temperature curing.

The content of the inorganic powder is 1.0 to 29.0% by mass, based on the total amount of the cement clinker, the gypsum, and the admixture, but is preferably 3.0 to 20.0% by mass, more preferably 5.5 to 15.0% by mass, and even more preferably 5.0 to 9.0% by mass.

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

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

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 1.0 to 10.0 mass% based on the total amount of the cement clinker, the gypsum, and the admixture, but is preferably 2.0 to 9.0 mass%, more preferably 2.4 to 12.5 mass%, and even more preferably .5 to 10.0 mass%. By having the limestone content within the above range, the heat generated by the hydration of the cement composition can be reduced, the decomposition of ettringite can be further suppressed, and the strength of the cement hardened body can be further enhanced. 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.

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. Mortar and concrete formed using the above-mentioned cement composition can exhibit excellent adiabatic temperature rise suppression, strength enhancement, and DEF suppression effects.

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. One type of fine aggregate may be used alone, or a combination of two or more types may be used. The content of the fine aggregate in the above-mentioned cement composition may be, for example, 50 to 500 parts by mass per 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture.

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 50 to 500 parts by mass per 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture.

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

Examples of admixtures include air entraining agents, water reducing agents, air entraining water reducing agents, high performance water reducing agents, high performance air entraining water reducing agents, superplasticizers, antifoaming agents, shrinkage reducing agents, setting accelerators, setting retarders, and thickeners. Depending on the required performance, the admixtures 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 per 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture.

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, C-S-H nanoparticles, and calcium thiocyanate. Hardening accelerators may be used alone or in combination.

The content of the hardening accelerator in the above-mentioned cement composition is preferably 0.1 to 20.0 parts by mass, more preferably 3.0 to 15.0 parts by mass, and even more preferably 6.0 to 10.0 parts by mass or less, per 100 parts by mass of the total amount of the cement clinker, the gypsum, and the admixture. By having the content of the hardening accelerator within the above-mentioned range, the hardening acceleration effect can be fully exerted, and the promotion of setting and the decrease in fluidity can be suppressed.

The Blaine specific surface area of the above cement composition is preferably 3000 to 5000 cm ² /g, more preferably 3100 to 4500 cm ² /g, and even more preferably 3150 to 4000 cm ² /g. When the Blaine specific surface area is 3000 cm ² /g or more, the strength development at the time of demolding is improved, and when it is 5000 cm ² /g or less, the initial heat of hydration is reduced, and DEF can be further suppressed.

The admixture in the above-mentioned cement composition can be used to improve the durability of the cement hardened body by itself, and can also be called a durability-improving admixture. The durability-improving admixture includes an inorganic powder containing an amorphous phase and limestone. The inorganic powder has a chemical composition containing CaO, SiO ₂ , and Al ₂ O ₃ , and the CaO content is 6.0 to 40.0 mass%, the SiO ₂ content is 35.0 to 75.0 mass%, and the Al ₂ O ₃ content is 14.0 to 25.0 mass%, based on the total amount of the inorganic powder. The durability-improving admixture is mixed with the cement clinker and gypsum so that the content of the inorganic powder is 1.0 to 29 mass%, and the content of the limestone is 1.0 to 10.0 mass%, based on the total amount of the cement clinker, gypsum, and the durability-improving admixture, which is 100 mass%.

The above-mentioned cement composition can be produced, for example, by the following method. One embodiment of the method for producing a cement composition includes a step of mixing cement clinker, gypsum, and an admixture (mixing step). The admixture includes an inorganic powder containing an amorphous phase and limestone, the inorganic powder has a chemical composition including CaO, SiO ₂ and Al ₂ O ₃ , and based on the total amount of the inorganic powder, the CaO amount is 6.0 to 40.0 mass%, the SiO ₂ amount is 35.0 to 75.0 mass%, and the Al ₂ O ₃ amount is 14.0 to 25.0 mass%, and in the above process, the cement clinker, the gypsum and the admixture are mixed so that the content of the admixture is 2.0 to 30.0 mass%, the content of the inorganic powder is 1.0 to 29.0 mass%, and the content of the limestone is 1.0 to 10.0 mass%, based on the total amount of the cement clinker, the gypsum and the admixture.

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 manufacturing method may include a mixing step in which the cement clinker, gypsum, and admixture are fed into a grinder and mixed and ground. By mixing and grinding the cement clinker, gypsum, and admixture in the mixing step, a cement composition having a superior DEF suppression effect can be manufactured.

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

Although several embodiments have been described above, the present disclosure is in no way limited to the above-mentioned embodiments. Furthermore, the contents of the descriptions of the above-mentioned embodiments can be mutually applied.

The contents of this disclosure will be described in more detail below with reference to examples and comparative examples. However, this disclosure is not limited to the following examples.

[Preparation of base cement (mixture of cement clinker and gypsum)]
Table 1 shows the base cements (NC1 to NC3) used in the Examples and Comparative Examples described later. Each of the base cements (NC1 to NC3) was prepared by adding gypsum dihydrate to cement clinker without adding any small amount of additive admixture, and then pulverizing with a ball mill so that the Blaine specific surface area was 3300±100 ^cm2 /g. The amount of gypsum dihydrate was adjusted and added so that the total _SO3 content in the base cement was 1.9% by mass±0.1% by mass.

Table 1 shows the Blaine specific surface area and chemical components of the base cement, and the mineral composition of the cement clinker calculated by the Bogue formula. The Blaine specific surface area of the base cement was determined 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 the X-ray fluorescence analysis method of JIS R 5204 "X-ray fluorescence analysis method for cement". Simultix 12 manufactured by Rigaku Corporation was used for the X-ray fluorescence analysis.

[Inorganic powder (IGCC slag)]
The inorganic powders (IG1 and IG2) used in the examples and comparative examples described later are shown in Tables 2 and 3. The inorganic powders were prepared by pulverizing the same coal gasification slag collected from a thermal power plant using a ball mill.

[Limestone]
Table 2 shows the limestone (CC) used in the examples and comparative examples described later. The limestone used was a 325 mesh product (passing 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, a calcium carbonate content of 90 mass% or more, and an aluminum oxide content of 1.0 mass% or less, and conformed to the minor mixing components of JIS R 5210:2019 "Portland cement".

[Grained blast furnace slag]
The ground granulated blast furnace slag (BS) used in the examples and comparative examples described below are shown in Tables 2 and 3. As the ground granulated blast furnace slag (BS), a commercially available ground granulated blast furnace slag (Blaine specific surface area: 4180 cm ² /g) was used.

Table 2 shows the Blaine specific surface area and chemical composition of the admixtures (inorganic powder, limestone, and ground granulated blast furnace slag). The Blaine specific surface area was determined based on JIS R 5201 "Physical test method for cement". The chemical composition was analyzed based on the X-ray fluorescence analysis method of JIS R 5204 "X-ray fluorescence analysis method for cement". Simultix 12 manufactured by Rigaku Corporation was used for the X-ray fluorescence analysis.

Table 3 shows the amorphous mass of the admixture (inorganic powder and ground granulated blast furnace slag) and the ratio of chemical composition in the amorphous phase based on the total amount of the admixture. Since no peak corresponding to crystalline matter was observed in the X-ray diffraction measurement of the inorganic powder (coal gasification slag), it was determined that the entire amount was amorphous (amorphous mass was 100% by mass). Since no peak other than that of gypsum dihydrate was observed in the X-ray diffraction measurement of the ground granulated blast furnace slag, it was assumed that all _SO3 components were derived from gypsum dihydrate, and the amorphous mass was calculated by subtracting the mass ratio of gypsum dihydrate. The X-ray diffraction apparatus used was a D2PHASER (Bruker AXS).

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

(Examples 1 to 6, Comparative Examples 1 to 6, and Reference Example 1)
Cement, inorganic powder (coal gasification slag), limestone, and ground granulated blast furnace slag were mixed and pulverized in the proportions (mass %) shown in Table 4 to prepare cement compositions.

DEF tests and compressive strength measurements were performed using each cement composition prepared in the examples and comparative examples.

[DEF test]
(Preparation of mortar composition)
First, standard sand for cement strength testing by the Cement Association (Inc.) as fine aggregate and water were mixed with each of the cement compositions prepared in the Examples and Comparative Examples to prepare mortar compositions in accordance with the method described in JIS R 5201:2015 "Physical test methods for cement". The formulations of the mortar compositions are shown in Table 5.

(DEF test)
The DEF test was carried out under conditions that facilitate the occurrence of DEF by adding potassium sulfate as a hardening accelerator to the above-mentioned mortar composition, adjusting the total _SO3 content in the cement composition to 6 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-mentioned adjustment was made to facilitate observation.

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

The mortar hardened bodies prepared by the above method were cured underwater in a thermostatic chamber at 20°C, and the length change of three mortar hardened bodies was measured for each level. 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 of mortar and concrete". The length change was measured by taking the mortar hardened bodies out of the water on the 7th, 14th, and 28th days of underwater curing 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 six points on the front and back of the three mortar hardened bodies, and the average value was taken as the length change of the target mortar hardened 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 mortar hardened body, and the degree of expansion suppression of the mortar hardened body due to DEF and DEF was evaluated for the mortar hardened bodies on the 112th day of underwater curing according to the following criteria. The results are shown in Tables 6 and 7.
A: The expansion coefficient of the hardened mortar is 0.05% or less.
B: The expansion coefficient of the hardened mortar body is more than 0.05% and not more than 0.10%.
C: The expansion coefficient of the hardened mortar body is more than 0.10% and not more than 0.25%.
D: The expansion coefficient of the hardened mortar exceeds 0.25%.

(Compressive strength measurement)
The compressive strength of each mortar hardened body was measured in accordance with the description of JIS R 5201:2015 "Physical test method for cement". The mortar hardened body for compressive strength measurement was prepared by first mixing the mortar composition prepared according to the formulation in Table 3 and Table 4 as mortar in a constant temperature room at 35 ° C. and filling the mold, storing the mold in a humidity box and curing for 24 hours. After curing for 24 hours, the mold was removed to obtain a mortar hardened body. The obtained mortar hardened body was cured in water in a constant temperature room at 35 ° C. until the material age of 28 days, and then the compressive strength was measured. Each mortar hardened body was evaluated according to the following criteria. The results are shown in Tables 6 and 7.
A: Compressive strength is 55 MPa or more.
B: The compressive strength is 53 MPa or more and less than 55 MPa.
C: Compressive strength is 52 MPa or more and less than 53 MPa.
D: Compressive strength is 50 MPa or more and less than 52 MPa.
E: The compressive strength is less than 50 MPa.

As shown in Table 6, it was confirmed that by satisfying the requirements of the cement composition according to the present disclosure, it is possible to practically achieve both the effect of suppressing expansion associated with DEF and compressive strength. First, the compositions of Comparative Examples 1 to 3 shown in Table 6 and the mortar compositions of Examples 1 to 3 have the same base cement of NC1 and the same total content of admixtures of 10 mass%, as shown in Table 5. On the other hand, the compositions of Comparative Examples 1 to 3 and the mortar compositions of Examples 1 to 3 differ in the type and composition ratio of admixtures. As shown in Table 6, from the results of the compositions of Comparative Examples 1 to 3 and the mortar compositions of Examples 1 to 3, it was confirmed that if the admixture is only limestone, the expansion associated with DEF cannot be suppressed (Comparative Example 2), and if the admixture is only inorganic powder, the compressive strength decreases (Comparative Example 3), and it was confirmed that it is necessary to use inorganic powder and limestone in combination as an admixture. The results of Comparative Example 1 and Example 2 confirm that by including an inorganic powder with a specific chemical composition as an admixture, it is possible to practically achieve both the effect of suppressing the expansion associated with DEF and compressive strength.

As shown in Table 7, even when the base cement is NC2, it was confirmed that the same tendency was observed as when the base cement was NC1. When comparing samples with different base cements using the same mixture (for example, comparisons between Comparative Examples 2 and 6, or Examples 1 and 4), it was confirmed that the expansion rate associated with DEF differs depending on the type of base cement, and that the larger the _C3S and _C3A amounts of the base cement, the higher the expansion rate associated with DEF. In addition, the larger the _C3A amount, the lower the compressive strength at 35°C. From this, it was confirmed that it is desirable to adjust the mix depending on the type of base cement, depending on the desired degree of suppression effect of expansion associated with DEF and compressive strength.

Comparative Example 4 was a sample that contained 5% limestone by mass, simulating ordinary Portland cement as specified in JIS R 5201, but had a large expansion rate due to DEF. Furthermore, when the limestone was increased to 10% by mass, or when blast furnace slag powder was added to 5% by mass of limestone, an increase in the expansion rate due to DEF was observed. In contrast, it was confirmed that all of the samples in the examples had a high DEF suppression effect and sufficient compressive strength.

Comparing Reference Example 1 and Example 2, the cement clinker and the composition are the same, but the expansion rate associated with DEF differs depending on the coal gasification slag used. It was confirmed that the higher the Blaine specific surface area of the coal gasification slag, the smaller the expansion rate associated with DEF.

According to the present disclosure, it is possible to provide a cement composition and a manufacturing method thereof that can suppress the expansion associated with DEF and provide a hardened cement body that has excellent compressive strength in a high-temperature environment, even when the content of the admixture is high. According to the present disclosure, it is also possible to provide a durability-improving admixture that can be used to manufacture the above-mentioned cement composition.

Claims (13)

Cement clinker;
Plaster and
and
The admixture comprises an inorganic powder having an amorphous phase and limestone;
The inorganic powder has a chemical composition including CaO, SiO ₂ , and Al ₂ O ₃ , and based on the total amount of the inorganic powder, the CaO amount is 6.0 to 40.0 mass%, the SiO ₂ amount is 35.0 to 75.0 mass%, and the Al ₂ O ₃ amount is 14.0 to 25.0 mass%,
The amount of the amorphous phase in 100% by mass of the inorganic powder is 80.0 to 100.0% by mass,
Based on the total amount of the cement clinker, the gypsum and the admixture,
The content of the admixture is 2.0 to 30.0 mass %,
The content of the inorganic powder is 1.0 to 29.0 mass%, and
The cement composition, wherein the limestone content is 1.0 to 10.0 mass%. The cement composition according to claim 1, wherein the content of the inorganic powder is 5.0 to 95.0% by mass based on 100% by mass of the admixture. The chemical composition of the inorganic powder further includes MgO;
3. The cement composition according to claim 1, wherein the amount of MgO is 5.0 mass% or less based on the total amount of the inorganic powder. The chemical composition of the inorganic powder further comprises _SO3 ;
The cement composition according to any one of claims 1 to 3, wherein the amount of SO ₃ based on the total amount of the inorganic powder is 1.0 mass% or less. The cement composition according to any one of claims 1 to 4, wherein the inorganic powder has a Blaine specific surface area of 2000 to 10000 cm ² /g. The cement composition according to any one of claims 1 to 5, wherein the inorganic powder contains pulverized coal gasification slag. The cement composition according to any one of claims 1 to 6, wherein the cement clinker has a C ₃ S content of 35.0 to 75.0 mass % and a C ₃ A content of 8.0 to 14.0 mass %, as calculated by the Bogue formula. The cement composition according to any one of claims 1 to 7, wherein the content of the gypsum is 0.5 to 3.0 mass% in terms of SO ₃ based on the total amount of the cement clinker and the gypsum. The cement clinker comprises _SO3 and _R2O ;
The cement composition according to any one of claims 1 to 8, wherein the amount of _SO3 is 0.10 to 2.00 mass% in 100 mass% of the cement clinker, and the amount of _R2O indicates a total amount of alkali, and the total amount of alkali calculated by _R2O [%] = _Na2O [%] + 0.658 × _K2O [%] is 0.10 to 2.00 mass%. Further containing a curing accelerator,
The cement composition according to any one of claims 1 to 9, wherein the content of the hardening accelerator is 0.1 to 20.0 parts by mass relative to 100 parts by mass of a total amount of the cement clinker, the gypsum, and the admixture. _The cement composition according to any one of claims 1 to 10, wherein the amount of CaO in the amorphous phase of the inorganic powder is 6.0 to 40.0 mass%, the amount of _SiO2 is 35.0 to 75.0 mass%, and the amount of _Al2O3 is 14.0 to 25.0 mass%, based on the total amount of the inorganic powder. The method includes a step of mixing cement clinker, gypsum, and an admixture,
The admixture comprises an inorganic powder having an amorphous phase and limestone;
The inorganic powder has a chemical composition including CaO, SiO ₂ , and Al ₂ O ₃ , and based on the total amount of the inorganic powder, the CaO amount is 6.0 to 40.0 mass%, the SiO ₂ amount is 35.0 to 75.0 mass%, and the Al ₂ O ₃ amount is 14.0 to 25.0 mass%,
The amount of the amorphous phase in 100% by mass of the inorganic powder is 80.0 to 100.0% by mass,
In the step, the cement clinker, the gypsum, and the admixture are mixed so that the content of the admixture is 2.0 to 30.0 mass%, the content of the inorganic powder is 1.0 to 29.0 mass%, and the content of the limestone is 1.0 to 10.0 mass%, based on the total amount of the cement clinker, the gypsum, and the admixture. A durability improving admixture comprising an inorganic powder having an amorphous phase and limestone,
The inorganic powder has a chemical composition including CaO, SiO ₂ , and Al ₂ O ₃ , and based on the total amount of the inorganic powder, the CaO amount is 6.0 to 40.0 mass%, the SiO ₂ amount is 35.0 to 75.0 mass%, and the Al ₂ O ₃ amount is 14.0 to 25.0 mass%,
The amount of the amorphous phase in 100% by mass of the inorganic powder is 80.0 to 100.0% by mass,
The durability improving admixture is used by mixing with cement clinker and gypsum so that the content of the inorganic powder is 1.0 to 29 mass% and the content of the limestone is 1.0 to 10.0 mass% with respect to the total amount of the cement clinker, gypsum, and the durability improving admixture being 100 mass%.