Cement composition, alkali-silica reaction inhibitor, and method for inhibiting alkali-silica reaction

Abstract

To provide a cement composition capable of depressing alkali silica reaction, alkali silica reaction depressant and a depressing method for alkali silica reaction.SOLUTION: A cement composition in this invention includes a cement, aggregate, acetic acid or salt thereof and silica fume whose BET specific surface area is 5 m2 / g or more but less than 15 m2 / g. Besides, an alkali silica reaction depressant includes acetic acid or salt thereof, and the above silica fume. Further, a depressing method for alkali silica reaction of a cement composition includes adding acetic acid or salt thereof and the above silica fume in a process of producing a cement composition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cement composition, an alkali-silica reaction inhibitor, and a method for inhibiting alkali-silica reaction. [Background technology]

[0002] Alkali-silica reaction is a phenomenon in which alkali silica gel, produced by a chemical reaction between alkali metals, mainly supplied from cement, and amorphous silica in reactive aggregate, absorbs water and expands, causing cracks in concrete. As the reaction progresses, these cracks often occur throughout the concrete structure, leading to a decrease in the durability of the structure. Therefore, a technology that can suppress the alkali-silica reaction is desired.

[0003] A common method for suppressing alkali-silica reaction is to limit the total alkali content in concrete to 3.0 kg / m2 in Na2Oeq. 3 Examples of suitable aggregates include those containing blast furnace cement or fly ash cement, and aggregates that have been determined to be harmless based on JIS A1145 or JIS A1146 testing.

[0004] Patent Document 1 discloses a non-shrinkage mortar composition containing cement, an expansive agent, a fine pozzolan powder such as acidic silica fume, a foaming agent, a water-reducing agent, and fine aggregate, with the aim of obtaining concrete with improved fluidity that is suitable for use in areas with high radiation levels. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-93960 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned general suppression methods may not be able to control the total alkali content below a predetermined range due to the increasing use of high-strength concrete, or may be difficult to supply or obtain blast furnace slag, fly ash, or aggregates determined to be harmless due to increased demand.

[0007] Furthermore, the technology described in Patent Document 1 does not consider at all the suppression or control of the alkali-silica reaction.

[0008] Therefore, an object of the present invention is to provide a cement composition capable of inhibiting alkali-silica reaction, an alkali-silica reaction inhibitor, and a method for inhibiting alkali-silica reaction. [Means for solving the problem]

[0009] The present invention comprises cement, aggregate, acetic acid or a salt thereof, and silica fume, The BET specific surface area of ​​the silica fume is 5m 2 / g or more 15m 2 / g or less.

[0010] The present invention also relates to a method for producing a composition comprising acetic acid or a salt thereof and a compound having a BET specific surface area of ​​5 m 2 / g or more 15m 2 The present invention provides an alkali-silica reaction inhibitor for cement compositions, which contains silica fume having a silica fume content of less than 1000 ppm / g.

[0011] The present invention also relates to a method for producing a cement composition, comprising the steps of: mixing acetic acid or a salt thereof with a compound having a BET specific surface area of ​​5 m 2 / g or more 15m 2 The present invention provides a method for inhibiting alkali-silica reaction in cement compositions by adding silica fume having a silica content of less than 1 / g. [Effects of the Invention]

[0012] According to the present invention, the alkali-silica reaction can be suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a graph showing the results of the expansion rate of the cured products in Examples 1 to 4 and Comparative Example 1 over time. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention are described below. However, the present invention is not limited to the following embodiments. In the following description, when it is written "X to Y[Z]" (X and Y are arbitrary numerical values, and [Z] is a unit added as necessary), it means "X[Z] or more and Y[Z] or less" or "X or more and Y or less" unless otherwise specified.

[0015] The cement composition of the present invention contains cement, aggregate, acetic acid or a salt thereof, and silica fume having predetermined physical properties. In the following description, unless otherwise specified, the cement composition in this specification includes a powdered composition not containing water, a fluid before hardening that contains water as needed, or a hardened product of the composition, and the following description is applied appropriately depending on the context. In addition, when the cement composition is in the form of a fluid containing water, it includes both mortar containing only fine aggregate as an aggregate and concrete containing both fine and coarse aggregate.

[0016] One of the characteristics of the cement composition of the present invention is that it contains acetic acid or a salt thereof. The coexistence of cement and an organic acid is likely to have an adverse effect on the strength of the resulting hardened product, such as concrete, and is therefore generally not adopted in this technical field from the perspective of developing and improving strength. The present inventors conducted extensive research into this point and unexpectedly discovered that by selecting and using acetic acid as the organic acid, it is possible to sufficiently reduce the adverse effect on the strength of the resulting hardened product, such as concrete, while suppressing the occurrence of alkali-silica reaction, which is one cause of concrete deterioration. Furthermore, since acetic acid or its salts are relatively inexpensive, it is also advantageous in that it can reduce the production cost of the cement composition.

[0017] Preferred examples of acetic acid or its salts include acetic acid itself, such as glacial acetic acid, and water-soluble salts of acetic acid. These may be anhydrides or hydrates. These may be used alone or in combination. Counter ions of acetic acid in water-soluble salts of acetic acid include, for example, non-metallic ions such as ammonium, alkali metal ions such as sodium and potassium, and alkaline earth metal ions such as calcium and magnesium. Among these, from the viewpoints of improving handleability, increasing concrete strength due to the supply of an alkali source, and effectively suppressing alkali-silica reaction, it is more preferable to use a water-soluble salt of acetic acid, even more preferable to use a salt of acetic acid with an alkaline earth metal, and even more preferable to use a salt of acetic acid with calcium or magnesium. Furthermore, from the viewpoint of reducing costs, it is preferable to exclude lithium acetate from the acetate salts.

[0018] The content of acetic acid or a salt thereof is preferably more than 0 and not more than 5 parts by mass, more preferably 0.5 to 3 parts by mass, and even more preferably 1 to 2.5 parts by mass, relative to 100 parts by mass of the total amount of cement and silica fume. By setting the content in this range, it is possible to sufficiently suppress the alkali-silica reaction without affecting the strength of the obtained hardened product. Note that the above content is a value calculated on an anhydrous basis.

[0019] The molar ratio of acetate ions to all alkali ions in the cement composition is preferably more than 0 and not more than 2.0, more preferably 0.1 to 1.5, even more preferably 0.2 to 1.2, even more preferably 0.3 to 1.0, and still more preferably 0.5 to 0.8. By keeping the molar ratio within this range, the resulting hardened product can exhibit sufficient strength while effectively suppressing alkali-silica reaction caused by aggregate expansion.

[0020] Cement composition 1m 3The total molar amount of alkali ions per unit area is preferably 20 to 300 mol, more preferably 40 to 250 mol, and even more preferably 60 to 170 mol. When the amount is within this range, the resulting cured product can exhibit sufficient strength. Total alkali ions can be measured using a powder obtained by pulverizing a hardened cement composition as the measurement target, using the measurement method described in JIS R5202:2010. If the amount of alkali in each material used in the cement composition is known, the total amount of alkali in each material can be calculated according to the description in Appendix B of JIS A5308:2019. In order to adjust the total amount of alkali ions to fall within the above range, for example, a method such as adding a metal hydroxide such as sodium hydroxide or potassium hydroxide can be used.

[0021] Cement composition 1m 3 The molar amount of acetate ions per unit mass is preferably 6 to 180 mol, more preferably 12 to 150 mol, and even more preferably 18 to 100 mol. By keeping the amount within this range, the strength development of the resulting cured product is less likely to be affected, and the alkali-silica reaction can be more effectively suppressed. Acetate ions can be measured by a measurement method such as ion chromatography using a powder obtained by finely pulverizing a hardened cement composition as the measurement object. To adjust the acetate ion concentration within the above range, for example, acetic acid or a salt thereof can be added together with other materials when mixing the cement composition, or acetic acid or a salt thereof can be injected into the hardened cement composition under pressure.

[0022] Another feature of the cement composition of the present invention is that it contains silica fume having a relatively low BET specific surface area. Silica fume is a powdered industrial waste material recovered from exhaust gases generated during the process of producing ferrosilicon, metallic silicon, electrofused zirconia, etc. in electric furnaces, and is commonly used in this technical field as an admixture to enhance the strength of hardened products. When using silica fume for concrete, the standard for its desirable quality is set forth in JIS A6207, and silica fume conforming to JIS A6207 is generally used. However, there is also a large amount of silica fume produced as industrial waste that does not meet the quality standards of JIS A6207, and so effective utilization of this silica fume is desirable.

[0023] The present inventors have conducted extensive research into this issue and have unexpectedly found that the use of silica fume with a BET specific surface area lower than that specified in JIS A6207 effectively suppresses the occurrence of alkali-silica reaction, which is one cause of concrete deterioration, and also suppresses the progression of alkali-silica reaction over time. While the reason for this is unclear, the use of silica fume with a low BET specific surface area is thought to enhance the dispersibility of silica fume in the composition, resulting in the production of more hydrates that consume alkali during or after the composition hardens, resulting in a slower progression of alkali-silica reaction throughout the composition than usual. This is also advantageous in terms of the effective use of silica fume that does not conform to JIS A6207, reducing the environmental impact, and improving workability.

[0024] The BET specific surface area of ​​the silica fume is preferably 5 m 2 / g or more 15m 2 / g or less, more preferably 7 to 14m 2 / g, more preferably 9 to 12 m 2 / g. These BET specific surface areas are smaller than those specified in JIS A6207. By using silica fume with such a BET specific surface area, it is possible to effectively suppress the occurrence of alkali-silica reaction while maintaining the strength of the cured product, thereby reducing the environmental load. The BET specific surface area of ​​silica fume can be measured in accordance with the method described in JIS A6207.

[0025] As described above, silica fume is recovered from exhaust gas generated during the manufacturing process of metal silicon, fused zirconia, etc., and it is preferable to use silica fume recovered from exhaust gas generated during the manufacturing process of fused zirconia. By using silica fume of this origin, the occurrence of alkali-silica reaction can be more effectively suppressed. In addition, silica fume satisfying the above-mentioned BET specific surface area can be easily obtained without any special process, which is advantageous in terms of convenience.

[0026] The origin of silica fume can be determined, for example, by the presence or absence of zirconium in the constituent particles of the silica fume. If zirconium is contained in the silica fume particles, the silica fume is determined to have originated from the manufacturing process of electrofused zirconia. If zirconium is not contained in the silica fume particles, the silica fume is determined not to have originated from the manufacturing process of electrofused zirconia. The presence or absence and content of zirconium can be measured, for example, by ICP atomic emission spectrometry.

[0027] The silica fume preferably contains zirconium oxide (ZrO2). When the silica fume contains zirconium oxide, the content is preferably 1 to 8 mass%, more preferably 2 to 7 mass%, and even more preferably 3 to 6 mass%. By keeping the content within this range, the occurrence of alkali-silica reaction can be effectively suppressed. In addition, zirconium oxide has high toughness and low thermal conductivity, so it can improve the toughness of the hardened cement body and improve its fire resistance and heat insulation properties. The presence or absence of zirconium oxide and its content can be analyzed by, for example, ICP atomic emission spectrometry.

[0028] The Al2O3 content of silica fume is preferably 0.4 to 3 mass%, more preferably 0.6 to 2 mass%, even more preferably 0.8 to 1.2 mass%, and even more preferably 0.8 to 1 mass%. By keeping the Al2O3 content within this range, the occurrence of alkali-silica reaction can be more effectively suppressed. The Al2O3 content can be measured, for example, according to the method described in JIS R5202.

[0029] It is not clear why the use of silica fume that satisfies the above-mentioned Al2O3 content can suppress the alkali-silica reaction, but it is thought that the aluminum contained in the silica fume replaces the silicon in the calcium silicate hydrate present in the hardened material, forming a complex of calcium silicate hydrate and aluminum, and that the negatively charged aluminum ions in the complex ion-adsorb the alkali content in the hardened material, thereby reducing the occurrence of the alkali-silica reaction.

[0030] The pH of silica fume at 25° C. is preferably 1.0 to 5.0, more preferably 1.5 to 4.5, and even more preferably 2.0 to 4.0. By using silica fume having such a pH, the occurrence of alkali-silica reaction can be more effectively suppressed. The pH of silica fume was measured using a pH meter after adding 10 g of the silica fume to be measured to 100 mL of tap water at 25°C and stirring for 10 minutes with a stirrer.

[0031] The reason why the alkali-silica reaction can be suppressed by using silica fume, which has a relatively low pH, is not clear, but it is thought that a neutralization reaction with alkali occurs in the microscopic regions where silica fume particles exist in the composition before curing or in the cured product, adjusting the pH to the neutral or acidic side. In the microscopic regions where the pH is lowered, the alkali content decreases, making it difficult for the alkali-silica reaction to occur, and as a result, it is thought that the alkali-silica reaction is also difficult to occur in the composition as a whole.

[0032] The R2O content of silica fume is preferably 0.01 to 0.4 mass%, more preferably 0.02 to 0.3 mass%, and even more preferably 0.03 to 0.1 mass%. By keeping the R2O content within this range, the alkali content, which can be a factor in the occurrence of alkali-silica reaction, can be sufficiently reduced, reducing the occurrence of reaction with silica, thereby more effectively suppressing the occurrence of alkali-silica reaction. In addition, the adverse effects on cement setting can be reduced. The R2O content can be measured, for example, according to the method described in JIS R5202.

[0033] The average particle size of silica fume is preferably 0.3 to 4 μm, more preferably 0.6 to 3 μm, even more preferably 0.9 to 2 μm, and even more preferably 1.2 to 1.6 μm. By using silica fume having such a particle size, uniform dispersion in the composition can be improved, the occurrence of alkali-silica reaction can be effectively suppressed, and the environmental load can be reduced. The average particle size of silica fume is the weighted volume-based mean diameter (MV) measured and calculated using a laser diffraction / scattering particle size distribution analyzer.

[0034] The content of silica fume in the cement composition is preferably 1 to 9 parts by mass, more preferably 2 to 7 parts by mass, and even more preferably 3 to 5 parts by mass, per 100 parts by mass of the total amount of cement and silica fume. When silica fume is used primarily for the purpose of increasing the strength of the hardened product, it is generally used in an amount of about 10 to 20 parts by mass per 100 parts by mass of cement and silica fume. As mentioned above, the content of silica fume in the present invention is less than the amount normally used. By adding silica fume in this mass range, the occurrence of alkali-silica reaction can be more effectively suppressed.

[0035] The total content of acetic acid or its salt and silica fume is, for example, preferably more than 0 parts by mass and not more than 10 parts by mass, more preferably 3 to 8 parts by mass, and even more preferably 4 to 7 parts by mass, per 100 parts by mass of cement. This makes it possible to effectively suppress alkali-silica reaction caused by aggregate expansion. The above-mentioned content of acetic acid or its salt is a value calculated on an anhydride basis.

[0036] The content of acetic acid or a salt thereof is, for example, preferably more than 0 part by mass and not more than 100 parts by mass, more preferably 10 to 70 parts by mass, and even more preferably 20 to 50 parts by mass, relative to 100 parts by mass of silica fume. This makes it possible to effectively suppress alkali-silica reaction caused by expansion of the aggregate. The content of acetic acid or a salt thereof mentioned above is a value calculated on an anhydride basis.

[0037] Examples of cement that can be used include various types of Portland cement, such as ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement; blended cements, such as blast-furnace cement, silica cement, and fly ash cement; and special cements, such as ecocement and alumina cement. These may be used alone or in combination. Examples of cements that can be used include those specified in JIS R5210, JIS R5211, JIS R5212, JIS R5213, and JIS R5214.

[0038] The aggregate may be a fine aggregate or a coarse aggregate. Depending on the properties of the desired composition, the aggregate may be used in the form of mortar using only fine aggregate, or in the form of concrete using both fine and coarse aggregate.

[0039] Examples of fine aggregates include natural aggregates such as river sand, mountain sand, land sand, and sea sand, crushed sand, silica sand, blast furnace slag fine aggregate, ferronickel slag fine aggregate, and electric furnace oxidizing slag fine aggregate, as well as recycled fine aggregate. Fine aggregates specified in JIS A1102 can also be used as fine aggregates. These can be used alone or in combination. Examples of coarse aggregate include river gravel, sea gravel, mountain gravel, crushed stone, crushed slag stone, etc. Coarse aggregates specified in JIS A5005 can also be used. These can be used alone or in combination.

[0040] From the viewpoint of increasing the density and obtaining a hardened product with sufficient strength, the content of the fine aggregate is preferably 50 to 400 parts by mass, more preferably 100 to 300 parts by mass, and even more preferably 150 to 250 parts by mass per 100 parts by mass of the binder. From the same viewpoint, when coarse aggregate is contained, the content of the coarse aggregate is preferably 100 to 400 parts by mass, more preferably 150 to 350 parts by mass, and even more preferably 200 to 300 parts by mass per 100 parts by mass of the binder.

[0041] In this specification, the term "binder" refers to a powder substance that reacts with water and contributes to the development of strength in the hardened product. Specific examples of binders include the cement and silica fume that constitute the cement composition of the present invention, as well as water-reactive admixtures such as ground granulated blast furnace slag and fly ash that may be included as needed. Materials that do not react with water, such as aggregate, are also excluded from the term binder.

[0042] The aggregate contained in the cement composition preferably has an expansion coefficient within a predetermined range. Specifically, the expansion coefficient of the aggregate at an age of 26 weeks, measured in accordance with JIS A1146:2017, is preferably 0.05% or more, more preferably 0.05 to 5%, even more preferably 0.10 to 3%, even more preferably 0.20 to 2%, and even more preferably 0.40 to 1%. The expansion rate of the aggregate at an age of 13 weeks, measured in accordance with JIS A1146:2017, is preferably 0.05 to 5%, more preferably 0.10 to 3%, even more preferably 0.20 to 2%, and even more preferably 0.20 to 1%.

[0043] There is a correlation between a high expansion rate of aggregate and the frequency of alkali-silica reaction, and by using aggregate with an expansion rate that is deemed "not harmless" for alkali-silica reactivity according to the JIS standard (0.1% or more at 26 weeks of age), alkali-silica reaction can be sufficiently suppressed. Furthermore, while the expansion rate of aggregate can vary depending on the place of origin, time of collection, or raw materials used, this method eliminates the need for excessive time and cost in selecting the aggregate to be used and allows for efficient use of resources. From the viewpoint of suppressing alkali-silica reaction, it is preferable that at least the fine aggregate satisfies the above-mentioned expansion coefficient of the aggregate, and when coarse aggregate is used, it is more preferable that both the fine aggregate and the coarse aggregate satisfy the expansion coefficient.

[0044] The bone dry density of the fine aggregate is preferably 2.4 to 5 g / cm 3 , more preferably 2.5 to 4 g / cm 3 , more preferably 2.5 to 3 g / cm 3 When the fine aggregate has such a density, the alkali-silica reaction can be effectively suppressed, and the quality of the resulting cement composition and its hardened product can be improved. The bone dry density can be measured, for example, in accordance with JIS A1109.

[0045] The surface dry density of the fine aggregate is preferably 2.4 to 5 g / cm 3, more preferably 2.5 to 4 g / cm 3 , more preferably 2.6 to 3 g / cm 3 When the fine aggregate has such a density, the alkali-silica reaction can be effectively suppressed, and the quality of the resulting cement composition and its hardened product can be improved. The surface dry density can be measured, for example, in accordance with JIS A1109.

[0046] The lower the water absorption rate of the fine aggregate, the better. Preferably, it is greater than 0% and not greater than 4.0%, more preferably 0.5 to 3.0%, and even more preferably 1.0 to 2.0%. By using fine aggregate with such a water absorption rate, the moisture content, which is the medium for the alkali-silica reaction, can be reduced, thereby more effectively suppressing the occurrence of the alkali-silica reaction. This also improves the ease of handling of the cement composition during pouring and pumping, and improves the quality of the resulting cement composition and its hardened product. The water absorption rate can be measured, for example, in accordance with JIS A1109.

[0047] The fine aggregate has a particle size ratio of preferably 1.0 to 4.5, more preferably 1.5 to 4.0, even more preferably 2.0 to 3.5, and even more preferably 2.5 to 3.0. When the fine aggregate has such a particle size ratio, it is possible to effectively suppress the occurrence of alkali-silica reaction, and also to improve the workability of the cement composition when water is added. The particle size ratio can be measured, for example, in accordance with JIS A1102.

[0048] The cement composition of the present invention may further contain water depending on its purpose. In this case, the water may be any water commonly used in the technical field, such as tap water, well water, rainwater, distilled water, purified water, or ion-exchanged water, without any particular limitation.

[0049] When the cement composition further contains water, the water-to-binder ratio (ratio of the mass of water to the mass of binder) is preferably 0.3 to 0.6, more preferably 0.35 to 0.55, and even more preferably 0.4 to 0.55, from the viewpoint of further increasing the strength of the resulting hardened product.

[0050] The cement composition of the above-described embodiment can be produced by a process of adding and mixing cement, aggregate, acetic acid or a salt thereof, silica fume, and, if necessary, water in any order or simultaneously. When water is not contained, the cement composition obtained by this process is a powdery mixture. On the other hand, when water is contained, the cement composition obtained by this process is a composition consisting of a fluid, paste-like mixture. In either case, the mixer used to mix the raw materials is not particularly limited, and a chemical mixer, a mortar mixer, a twin-screw forced mixer, a pan mixer, a grout mixer, etc. can be used.

[0051] As long as the effects of the present invention are achieved, admixtures other than the above-mentioned cement, aggregate, acetic acid or a salt thereof, and silica fume may be added in any order or simultaneously, if necessary. Examples of other admixtures include water-reactive admixtures such as gypsum and ground granulated blast furnace slag that contribute to the development of strength in the hardened product in the presence of water, non-water-reactive admixtures such as calcium carbonate, limestone, or powder thereof, and chemical admixtures. Examples of chemical admixtures include those specified in JIS A6204, such as water-reducing agents, high-performance water-reducing agents, air-entraining agents, air-entraining water-reducing agents, antifoaming agents, shrinkage-reducing agents, fluidizing agents, thickeners, and hardening accelerators.

[0052] The cement composition of the above embodiment can suppress alkali-silica reaction and can exhibit strength in the resulting hardened product. Furthermore, since this composition contains acetic acid or a salt thereof for suppressing alkali-silica reaction and silica fume having predetermined physical properties, it is advantageous in that it can preventively suppress alkali-silica reaction. Furthermore, since acetic acid or a salt thereof and silica fume are used, it is advantageous in that it can simultaneously reduce environmental impact and production costs, and can easily suppress alkali-silica reaction.

[0053] As is clear from the above description, the present invention also provides an alkali-silica reaction inhibitor for cement compositions and a method for inhibiting the alkali-silica reaction of cement compositions. The alkali-silica reaction inhibitor contains the above-mentioned acetic acid or a salt thereof and silica fume having a predetermined BET specific surface area, and is used in combination with aggregate whose expansion rate at 26 weeks, measured in accordance with JIS A1146:2017, is 0.05% or more. The method for inhibiting alkali-silica reaction involves adding the above-mentioned acetic acid or a salt thereof and silica fume having a predetermined BET specific surface area in any step of the process for producing a cement composition containing aggregate whose expansion coefficient at 26 weeks, as measured in accordance with JIS A1146:2017, is 0.05% or more. The explanations regarding these methods are applicable to the above-mentioned embodiments as appropriate, and the embodiments can also be combined as appropriate. [Example]

[0054] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0055] [1. Materials used] The materials used are shown in Tables 1 and 2. In the following explanation, for the sake of convenience, evaluation is performed using mortar containing only fine aggregate as the aggregate, but similar results can be obtained with concrete. The bone dry density, surface dry density and water absorption of the aggregates listed in Table 1 are all values ​​measured according to JIS A1109, and the coarse particle ratio is a value measured according to JIS A1102. The physical properties and component contents of silica fume in Table 2 were measured according to methods such as JIS R5202. In Table 2, "%" means "% by mass."

[0056] [Table 1]

[0057] [Table 2]

[0058] [2. Mortar Mixture] The mix proportions for the cement composition (mortar) used in this test are shown in Table 3 below. The mix conformed to JIS A1146:2017. A mix containing no calcium acetate or silica fume was also prepared. Since the binders in this mix were cement and silica fume, the water-to-binder ratio was 0.5, and the ratio of aggregate to 100 parts by weight of binder was 225 parts by weight (see Table 3).

[0059] [3. Evaluation of Alkali-Silica Reactivity (Examples 1 to 4 and Comparative Example 1)] Using the cement compositions (Examples 1 to 4 and Comparative Example 1) prepared by mixing the above-mentioned materials in the proportions shown in Table 3 below, specimens were prepared according to the method described in JIS A1146:2017, and the expansion coefficients of the specimens (hardened products) were measured at ages of 2 to 21 weeks. The fine aggregate was used without adjusting its particle size. The test specimens were covered with absorbent paper, which kept the moisture constant to prevent the composition from leaking out, and then placed in a sealed plastic bag. The test specimens were cured in an environment with a temperature of 40±2°C and a relative humidity of 95% or higher until they reached the desired age. The smaller the expansion coefficient, the more the alkali-silica reaction is suppressed. The results are shown in Table 3 below and in Figure 1.

[0060] As shown in Table 3 and FIG. 1, the expansion coefficient of each example was smaller than that of Comparative Example 1, which did not contain calcium acetate or silica fume, at any age, demonstrating that the alkali-silica reaction could be suppressed. Furthermore, in each example, even when fine aggregate that was judged to be "not harmless" in the alkali-silica reactivity assessment (see Table 1) was used, the expansion coefficient was further reduced, indicating that the example has an excellent effect of suppressing alkali-silica reactivity.

[0061] [Table 3]

Claims

1. Contains cement, aggregate, acetate and silica fume The BET specific surface area of ​​the silica fume is 5 m ２ / g or more 15m ２ / g or less, The zirconium oxide content of the silica fume is 1% by mass or more and 8% by mass or less, The silica fume has an Al 2 O 3 content of 0.4% by mass or more and 3% by mass or less, The R 2 O content of the silica fume is 0.01% by mass or more and 0.4% by mass or less, The silica fume has a pH of 1.0 or more and 5.0 or less at 25°C, The average particle size of the silica fume is 0.3 μm or more and 4 μm or less, The content of the silica fume is 1 part by mass or more and 9 parts by mass or less per 100 parts by mass of the total amount of the cement and the silica fume, The cement composition, wherein the R 2 O content is the total alkali content.

2. The cement composition according to claim 1, wherein the aggregate has an expansion coefficient of 0.05% or more at a 26-week age measured in accordance with JIS A1146:2017.

3. 3. The cement composition according to claim 1, wherein the content of the acetate salt in terms of anhydride is more than 0 parts by mass and not more than 5 parts by mass per 100 parts by mass of the total amount of the cement and the silica fume.

4. The cement composition according to any one of claims 1 to 3, wherein the molar ratio of acetate ions to total alkali ions is greater than 0 and not greater than 2.

0.

5. The cement composition according to any one of claims 1 to 4, wherein the acetate salt comprises a salt of acetic acid and an alkaline earth metal.

6. 6. The cement composition according to claim 1, wherein the silica fume is recovered from exhaust gas generated in the process of producing electrofused zirconia.

7. Acetate and BET specific surface area 5m ２ / g or more 15m ２ An alkali-silica reaction inhibitor for cement compositions, comprising silica fume having a silica fume content of less than 1 / g, The zirconium oxide content of the silica fume is 1% by mass or more and 8% by mass or less, The silica fume has an Al 2 O 3 content of 0.4% by mass or more and 3% by mass or less, The R 2 O content of the silica fume is 0.01% by mass or more and 0.4% by mass or less, The silica fume has a pH of 1.0 or more and 5.0 or less at 25°C, The average particle size of the silica fume is 0.3 μm or more and 4 μm or less, The content of the silica fume in the cement composition is 1 part by mass or more and 9 parts by mass or less per 100 parts by mass of the total amount of cement and the silica fume contained in the cement composition, The alkali-silica reaction inhibitor for cement compositions, wherein the R 2 O content is a total alkali amount.

8. 8. The alkali-silica reaction inhibitor according to claim 7, wherein the acetate comprises a salt of acetic acid and an alkaline earth metal.

9. In the process for producing the cement composition, acetate and a cement having a BET specific surface area of ​​5 m ２ / g or more 15m ２ A method for inhibiting alkali-silica reaction in a cement composition, comprising adding silica fume having a silica fume content of less than 1 / g, The zirconium oxide content of the silica fume is 1% by mass or more and 8% by mass or less, The silica fume has an Al 2 O 3 content of 0.4% by mass or more and 3% by mass or less, The R 2 O content of the silica fume is 0.01% by mass or more and 0.4% by mass or less, The silica fume has a pH of 1.0 or more and 5.0 or less at 25°C, The average particle size of the silica fume is 0.3 μm or more and 4 μm or less, The silica fume is added so that the content of the silica fume is 1 part by mass or more and 9 parts by mass or less relative to 100 parts by mass of the total amount of the cement and the silica fume contained in the cement composition; The method for inhibiting alkali-silica reaction in a cement composition, wherein the R 2 O content is a total alkali amount.

Images