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

Abstract

To provide a cement composition and an alkali silica reaction retardant capable of retarding alkali silica reaction.SOLUTION: A cement composition includes a cement, an aggregate, and a silica fume. The aggregate has an expansion coefficient at a material age of 26 weeks measured in accordance with JIS A1146:2017 of 0.05% or over. The silica fume has a BET specific surface area of 5 m2 / g or over and under 15 m2 / g. A content of the silica fume is preferably 1 pt.mass or over and 9 pts.mass or under with respect to 100 pts.mass of cement. The silica fume is preferably those recovered from an exhaust gas generated in production processes of an electromelting zirconia.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 the alkali-silica reaction. [Background technology]

[0002] The 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 aggregates, absorbs water and expands, causing cracks in concrete. These cracks often occur throughout the entire concrete structure as the reaction progresses, leading to a decrease in the structure's durability. Therefore, technologies that can suppress the alkali-silica reaction are desired.

[0003] A common method for suppressing alkali-silica reaction is, for example, to increase the total alkali content in concrete to 3.0 kg / m³ of Na2Oeq. 3 Examples include using blast furnace cement or fly ash cement, or using aggregates that have been determined to be harmless based on tests in JIS A1145 or JIS A1146.

[0004] Patent Document 1 discloses a non-shrink mortar composition comprising cement, an expansive agent, pozzolanic fine powder such as acidic silica fume, a foaming agent, a water-reducing agent, and fine aggregate, with the aim of obtaining concrete that has improved fluidity and can be suitably used in locations with high radiation levels. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-93960 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The general control methods described above may fail to control the total alkali content below a predetermined range due to the increased use of high-strength concrete, or the supply and availability of blast furnace slag, fly ash, or aggregates deemed harmless may become difficult as demand increases.

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

[0008] Therefore, the present invention aims to provide a cement composition and an alkali-silica reaction inhibitor that can suppress alkali-silica reactions. [Means for solving the problem]

[0009] The present invention comprises cement, aggregate, and silica fume. The expansion rate of the aggregate at 26 weeks of age, as measured in accordance with JIS A1146:2017, is 0.05% or more. The BET specific surface area of ​​the aforementioned silica fume is 5 m². 2 / g or more 15m 2 This invention provides a cement composition that is less than / g.

[0010] Furthermore, the present invention has a BET specific surface area of ​​5m². 2 / g or more 15m 2 Contains silica fume that is less than / g, This invention provides an alkali-silica reaction inhibitor for cement compositions, to be used in combination with aggregates whose expansion rate at 26 weeks of age, as measured in accordance with JIS A1146:2017, is 0.05% or higher.

[0011] Furthermore, the present invention relates to a process for producing a cement composition containing aggregate having an expansion rate of 0.05% or more at 26 weeks of age, as measured in accordance with JIS A1146:2017, wherein the BET specific surface area is 5 m². 2 / g or more 15m 2Provided is a method for suppressing the alkali-silica reaction of a cement composition by adding silica fume having a content of less than / g.

Advantages of the Invention

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

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a graph showing the results of the expansion rate of the hardened products in Example 1 and Comparative Examples 1 to 4 over time. [Figure 2] FIG. 2 is a graph showing the results of the expansion rate of the hardened products in Example 2 and Comparative Examples 1, 5, and 6 over time. [Figure 3] FIG. 3 is a graph showing the results of the expansion rate of the hardened products in Example 3 and Comparative Examples 1, 7, and 8 over time.

Embodiments for Carrying Out the Invention

[0014] Preferred embodiments of the present invention will be described below. Note that the present invention is not limited to the following embodiments. In the following description, when described as "X to Y [Z]" (X and Y are arbitrary numerical values, and [Z] is an optional unit), unless otherwise specified, it means "X [Z] or more and Y [Z] or less" or "X or more and Y or less".

[0015] The cement composition of the present invention includes cement, aggregate, and silica fume having predetermined physical properties. In the following description, unless otherwise specified, the cement composition in this specification includes a powdery composition that does not contain water, a fluid before curing that contains water as required, or a hardened product of the composition, and the following descriptions are appropriately applied according to the context. Also, when taking the form of a fluid containing water, both mortar containing only fine aggregate as aggregate and concrete containing both fine aggregate and coarse aggregate are included.

[0016] The cement composition of the present invention is characterized in that it contains silica fume having a relatively low BET specific surface area. Silica fume is a powdery industrial waste recovered from exhaust gas generated during the production of ferrosilicon, metallic silicon, electromelted zirconia, etc. in an electric furnace, and is generally used as a admixture for developing the strength of hardened products in this technical field. Also, when silica fume is used for concrete applications, the standards regarding its preferable quality are defined in JIS A6207, and those conforming to JIS A6207 are generally used. On the other hand, since there are many silica fumes produced as industrial waste that do not meet the quality conforming to JIS A6207, the effective utilization of these silica fumes is desired.

[0017] Regarding this point, when the present inventor earnestly studied, by using silica fume having a specific surface area lower than the BET specific surface area defined in JIS A6207, unexpectedly, it was found that the occurrence of alkali-silica reaction, which is one of the causes of concrete deterioration, can be effectively suppressed, and the progress of alkali-silica reaction with the passage of age can also be suppressed. The reason for this is not clear, but by using silica fume with a low BET specific surface area, the dispersibility in the composition of silica fume increases, and more hydrates that consume alkali components are generated during or after the hardening of the composition. Therefore, it is considered that the progress of alkali-silica reaction in the whole composition becomes slower than normal. Also, this is advantageous in terms of the effective utilization of silica fume that does not conform to JIS A6207 and the reduction of environmental load, and is also advantageous in terms of the convenience of work.

[0018] The BET specific surface area of silica fume is preferably 5 m 2 / g or more and less than 15 m 2 / g, more preferably 7 to 14 m 2 / g, still more preferably 9 to 12 m 2The BET specific surface area is / g. These BET specific surface areas are within a smaller range than those specified in JIS A6207. By using silica fume with such a BET specific surface area, the occurrence of alkali-silica reaction can be effectively suppressed while maintaining the strength of the cured product, thereby reducing the environmental burden. The BET specific surface area of ​​silica fume can be measured in accordance with the method described in JIS A6207.

[0019] As mentioned above, silica fume is recovered from exhaust gases generated during the manufacturing process of metallic silicon, fused zirconia, etc., and it is preferable to use silica fume recovered from exhaust gases generated during the manufacturing process of fused zirconia. By using silica fume of this origin, the occurrence of alkali-silica reaction can be suppressed more effectively. In addition, silica fume that satisfies the above-mentioned BET specific surface area can be easily obtained without going through any special processes, which is also advantageous in terms of convenience.

[0020] 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 present in the silica fume particles, the silica fume is determined to have originated from the electrofused zirconia manufacturing process. If zirconium is not present in the silica fume particles, the silica fume is determined not to have originated from the electrofused zirconia manufacturing process. The presence and content of zirconium can be measured, for example, by ICP emission spectrometry.

[0021] The silica fume preferably contains zirconium oxide (ZrO2). When the silica fume contains zirconium oxide, its content is preferably 1 to 8% by mass, more preferably 2 to 7% by mass, and even more preferably 3 to 6% by mass. This range effectively suppresses the occurrence of alkali-silica reactions. In addition, because zirconium oxide has high toughness and low thermal conductivity, it can improve the toughness of the hardened cement and enhance its fire resistance and heat insulation properties. The presence or absence of zirconium oxide and its content can be analyzed, for example, by ICP emission spectrometry.

[0022] The silica fume has an Al2O3 content of preferably 0.4 to 3% by mass, more preferably 0.6 to 2% by mass, even more preferably 0.8 to 1.2% by mass, and even more preferably 0.8 to 1% by mass. This range allows for more effective suppression of the alkali-silica reaction. The Al2O3 content can be measured, for example, according to the method described in JIS R5202.

[0023] The reason why using silica fume that satisfies the aforementioned Al2O3 content can suppress the alkali-silica reaction is not clear, but it is presumed that the aluminum contained in the silica fume substitutes for the silicon in the calcium silicate hydrate present in the hardened product, forming a composite of calcium silicate hydrate and aluminum, and that the negatively charged aluminum ions in the composite ionically adsorb the alkali in the hardened product, thereby reducing the occurrence of the alkali-silica reaction.

[0024] The silica fume has a pH of preferably 1.0 to 5.0, more preferably 1.5 to 4.5, and even more preferably 2.0 to 4.0 at 25°C. By using silica fume with such a pH, the occurrence of alkali-silica reactions can be more effectively suppressed. The pH of silica fume was measured using a pH meter on a mixture prepared by adding 10 g of the silica fume to 100 mL of tap water at 25°C and stirring with a stirrer for 10 minutes.

[0025] The reason why using silica fume with a relatively low pH can suppress the alkali-silica reaction is not clear, but it is thought that in the composition before curing or in the cured product, a neutralization reaction with the alkali occurs in the microscopic region where silica fume particles are present, adjusting the pH to neutral or acidic. Then, in the microscopic region where the pH is lower, the alkali content decreases, making it less likely for the alkali-silica reaction to occur, and as a result, the alkali-silica reaction becomes less likely to occur in the composition as a whole.

[0026] The silica fume has an R2O content of preferably 0.01 to 0.4% by mass, more preferably 0.02 to 0.3% by mass, and even more preferably 0.03 to 0.1% by mass. This range sufficiently reduces the alkali content, which can be a factor in the occurrence of alkali-silica reaction, thereby reducing the reaction with silica and more effectively suppressing the alkali-silica reaction. In addition, it reduces the adverse effects on cement setting. The R2O content can be measured, for example, according to the method described in JIS R5202.

[0027] 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 with such particle sizes, the uniform dispersibility in the composition can be improved, the occurrence of alkali-silica reactions can be effectively suppressed, and the environmental burden can be reduced. The average particle size of silica fume is the weighted volume-based average diameter (MV) measured and calculated by a laser diffraction / scattering particle size distribution analyzer.

[0028] The silica fume content 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 cement. When silica fume is used primarily to enhance the strength of a hardened material, it is generally used in a mass ratio of approximately 10 to 20 parts by mass of silica fume per 100 parts by mass of cement. However, as described above, the silica fume content in this invention is less than the amount typically used. By adding silica fume within this mass range, the occurrence of alkali-silica reaction can be suppressed more effectively.

[0029] The cement used can include various types of Portland cement such as ordinary Portland cement, rapid-hardening Portland cement, ultra-rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, and sulfate-resistant Portland cement, as well as blended cements such as blast furnace cement, silica cement, and fly ash cement, and special cements such as eco-cement and alumina cement. These can be used individually or in combination. As these cements, for example, cements specified in JIS R5210, JIS R5211, JIS R5212, JIS R5213, and JIS R5214 can also be used.

[0030] Examples of aggregates include fine aggregate and coarse aggregate. Depending on the properties of the desired composition, these aggregates can be used in the form of mortar using only fine aggregate, or in the form of concrete using both fine and coarse aggregate.

[0031] Examples of fine aggregates include natural aggregates such as river sand, mountain sand, land sand, and sea sand; artificial aggregates such as crushed sand, silica sand, blast furnace slag fine aggregate, ferronickel slag fine aggregate, and electric furnace oxidized slag fine aggregate; and recycled fine aggregates. Fine aggregates specified in JIS A1102 can also be used. These can be used individually or in combination. Examples of coarse aggregates include river gravel, sea gravel, mountain gravel, crushed stone, and crushed slag. Coarse aggregates specified in JIS A5005 can also be used. These can be used individually or in combination.

[0032] From the viewpoint of obtaining a hardened product with increased density and sufficient strength, the content of 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 binder. From a similar viewpoint, if coarse aggregate is included, 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 binder.

[0033] In this specification, "binder" refers to a general term for powders that react with water and contribute to the development of strength in the hardened product. Specific examples of binders include cement and silica fume that constitute the cement composition of the present invention, as well as water-reactive admixtures such as blast furnace slag powder and fly ash, which may be included as needed. Materials that do not react with water, such as aggregates, are excluded from the definition of a binder.

[0034] The aggregate contained in the cement composition preferably has an expansion rate within a predetermined range. Specifically, the expansion rate of the aggregate at 26 weeks of age, as 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%. Furthermore, the aggregate expansion rate at 13 weeks of age, 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%.

[0035] There is a correlation between the high expansion rate of aggregate and the frequency of alkali-silica reaction. With this expansion rate, alkali-silica reaction can be sufficiently suppressed even when using aggregate with an expansion rate that is considered "not harmless" according to the JIS standard (0.1% or more at 26 weeks of age). Furthermore, since the expansion rate of aggregate can vary depending on its origin, harvesting time, or the raw materials used, this eliminates the need to spend excessive time and cost on selecting the aggregate to be used, and allows for the efficient use of resources. The aforementioned aggregate expansion rate is preferably met in at least the fine aggregate from the viewpoint of suppressing alkali-silica reaction, and more preferably in both the fine and coarse aggregate when coarse aggregate is used.

[0036] The oven-dry density of the fine aggregate is preferably 2.4 to 5 g / cm³. 3 More preferably 2.5 to 4 g / cm³ 3 More preferably 2.5-3 g / cm³ 3 This density of fine aggregate effectively suppresses the alkali-silica reaction and improves the quality of the resulting cement composition and its hardened product. The oven-dry density can be measured, for example, in accordance with JIS A1109.

[0037] The surface-dry density of the fine aggregate is preferably 2.4 to 5 g / cm³. 3 More preferably 2.5 to 4 g / cm³ 3 More preferably 2.6-3 g / cm³ 3 This density of fine aggregate effectively suppresses the alkali-silica reaction and improves the quality of the resulting cement composition and its hardened product. The surface-dry density can be measured, for example, in accordance with JIS A1109.

[0038] The water absorption rate of the fine aggregate is preferable as low as possible, but preferably it is greater than 0% and 4.0% or less, more preferably 0.5 to 3.0%, and even more preferably 1.0% to 2.0%. Having such a water absorption rate in the fine aggregate reduces the amount of water, which is the medium for the alkali-silica reaction, thus more effectively suppressing the occurrence of the alkali-silica reaction. Furthermore, it improves the handling of the cement composition during placement 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.

[0039] The coarseness ratio of the fine aggregate is 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. Having such a coarseness ratio of fine aggregate effectively suppresses the occurrence of alkali-silica reaction and improves the workability of the cement composition when water is added. The coarseness ratio can be measured, for example, in accordance with JIS A1102.

[0040] The cement composition of the present invention may further contain water, depending on its purpose. In this case, the water can be any water commonly used in the art, such as tap water, well water, rainwater, distilled water, purified water, or deionized water, without any particular limitations.

[0041] When the cement composition further contains water, from the viewpoint of further increasing the strength of the resulting hardened product, the water-to-binder ratio (ratio of water mass to binder mass) is preferably 0.3 to 0.6, more preferably 0.35 to 0.55, and even more preferably 0.4 to 0.55.

[0042] The cement composition of the above-described embodiment can be manufactured by mixing cement, aggregate, silica fume, and, if necessary, water, in any order or simultaneously. If water is not included, the cement composition obtained through this process is a powdered mixture. On the other hand, if water is included, the cement composition obtained through this process is a composition consisting of a fluid paste-like mixture. In any case, the mixer used for mixing the raw materials is not particularly limited, and chemical mixers, mortar mixers, twin-shaft forced mixers, pan mixers, grout mixers, etc., can be used.

[0043] To the extent that the effects of the present invention are achieved, other admixtures other than the cement, aggregate, and silica fume described above may be added in any order or simultaneously as needed. Other admixtures include, for example, water-reactive admixtures that contribute to the strength development of the hardened product in the presence of water, such as gypsum and blast furnace slag powder; water-nonreactive admixtures such as calcium carbonate, limestone or its powder; and chemical admixtures. Examples of chemical admixtures include those specified in JIS A6204, specifically water-reducing agents, high-performance water-reducing agents, air-entraining agents, air-entraining water-reducing agents, defoaming agents, shrinkage-reducing agents, fluidizing agents, thickeners, and hardening accelerators.

[0044] The cement compositions of the above embodiments can suppress alkali-silica reactions and achieve the strength of the resulting hardened product. Furthermore, since these compositions contain silica fume having predetermined physical properties for suppressing alkali-silica reactions, they are advantageous in that they can suppress alkali-silica reactions proactively. In addition, because silica fume is used, environmental impact and manufacturing costs are reduced simultaneously, and alkali-silica reactions can be suppressed easily, which is also advantageous.

[0045] Furthermore, 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 silica fume having the specified BET specific surface area described above and is used in combination with aggregate having an expansion rate of 0.05% or more at 26 weeks of age, as measured in accordance with JIS A1146:2017. The alkali-silica reaction suppression method involves adding silica fume having the predetermined BET specific surface area described above during one of the steps in the process of manufacturing a cement composition containing aggregate whose expansion rate at 26 weeks of age, as measured in accordance with JIS A1146:2017, is 0.05% or more. The descriptions of these methods are made by applying the descriptions of the embodiments described above as appropriate, and it is also possible to combine the embodiments as appropriate. [Examples]

[0046] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

[0047] [1. Materials used] The materials used are shown in Tables 1 and 2 below. For the sake of evaluation, the following explanation uses mortar containing only fine aggregate; however, similar results can be obtained with concrete. The absolute dry density, surface dry density, and water absorption rate of the aggregates listed in Table 1 were all measured according to JIS A1109, and the coarseness ratio was measured according to JIS A1102. Furthermore, the physical properties of silica fume and the content of each component in Table 2 were measured using methods such as JIS R5202. In Table 2, "%" means "mass percent," and columns marked with "-" indicate that the measurement was not performed.

[0048] [Table 1]

[0049] [Table 2]

[0050] [2. Mortar Mix Design] The cement composition (mortar) used in this test is shown in Table 3 below. The composition conforms to JIS A1146:2017. In addition, a silica fume-free version was also prepared separately. In this composition, the binders are cement and silica fume, so the water-to-binder ratio was 0.5, and the ratio of aggregate to 100 parts by mass of binder was 225 parts by mass (see Table 3).

[0051] [3. Evaluation of alkali-silica reactivity (Examples 1-3 and Comparative Examples 1-8)] Cement compositions (Examples 1-3 and Comparative Examples 1-8) were prepared by blending the above-mentioned materials in the proportions shown in Table 3 below. Test specimens were prepared according to the method described in JIS A1146:2017, and the expansion rate of the test specimens (hardened material) at 2-26 weeks of age was measured. The fine aggregate was used without adjusting its particle size. Curing was carried out by covering the test specimens with absorbent paper that constantly retains moisture to prevent the composition from leaking out, placing them in a sealed plastic bag, and maintaining an environment with a temperature of 40±2℃ and a relative humidity of 95% or higher until the desired age was reached. A smaller expansion coefficient indicates that the alkali-silica reaction is suppressed. The results are shown in Table 3 and Figures 1 to 3 below.

[0052] As shown in Table 3 and Figures 1 to 3, the expansion rate of each example was smaller than that of Comparative Example 1, which did not contain silica fume, at all ages, indicating that alkali-silica reaction can be suppressed. Furthermore, comparing the results of the examples and comparative examples with the same silica fume content, it can be seen that in all combinations of Example 1 and Comparative Examples 2-4, Example 2 and Comparative Examples 5-6, and Example 3 and Comparative Examples 7-8, the degree of increase in the expansion rate of each example is smaller than that of each comparative example, indicating that alkali-silica reaction and its progression can be suppressed even as the age of the material increases. This is also evident from the significant difference in the expansion rates between Example 2 and Comparative Examples 5-6 at 17, 21, and 26 weeks of age, and between Example 3 and Comparative Examples 7-8 at 26 weeks of age. Furthermore, even when using fine aggregate (see Table 1) that was judged as "not harmless" in the alkali-silica reactivity test, each example shows a further reduction in expansion rate, indicating excellent inhibitory effect on alkali-silica reaction.

[0053] [Table 3]

Claims

1. Containing cement, aggregate and silica fume, The expansion rate of the aggregate at 26 weeks of age, as measured in accordance with JIS A1146:2017, is 0.05% or more and 5% or less. The BET specific surface area of ​​the aforementioned silica fume is 5 m². ２ / g or more 15m ２ Less than / g, The zirconium oxide content of the silica fume is 1% by mass or more and 8% by mass or less. The Al₂O₃ content of the silica fume is 0.4% by mass or more and 3% by mass or less. The pH of the silica fume at 25°C is 1.0 or higher and 5.0 or lower. The R₂O content of the silica fume is 0.01% by mass or more and 0.4% by mass or less. The average particle size of the silica fume is 0.3 μm or more and 4 μm or less. A cement composition in which the silica fume content is 1 part by mass or more and 9 parts by mass or less per 100 parts by mass of cement.

2. The cement composition according to claim 1, wherein the silica fume is recovered from exhaust gas generated during the manufacturing process of electrofused zirconia.

3. comprising silica fume, An alkali-silica reaction inhibitor for cement compositions, used in combination with aggregate having an expansion rate of 0.05% or more and 5% or less at 26 weeks of age, as measured in accordance with JIS A1146:2017, The BET specific surface area of ​​the silica fume is 5 m² / g or more and less than 15 m² / g. The zirconium oxide content of the silica fume is 1% by mass or more and 8% by mass or less. The Al₂O₃ content of the silica fume is 0.4% by mass or more and 3% by mass or less. The pH of the silica fume at 25°C is 1.0 or higher and 5.0 or lower. The R₂O content of the silica fume is 0.01% by mass or more and 0.4% by mass or less. The average particle size of the silica fume is 0.3 μm or more and 4 μm or less. An alkali-silica reaction inhibitor for a cement composition, used such that the silica fume content in the cement composition is 1 part by mass or more and 9 parts by mass or less per 100 parts by mass of cement contained in the cement composition.

4. A method for suppressing alkali-silica reaction in a cement composition, comprising adding silica fume in one of the steps of manufacturing a cement composition containing aggregate having an expansion rate of 0.05% or more and 5% or less at 26 weeks of age, as measured in accordance with JIS A1146:2017, The BET specific surface area of ​​the silica fume is 5 m² / g or more and less than 15 m² / g. The zirconium oxide content of the silica fume is 1% by mass or more and 8% by mass or less. The Al₂O₃ content of the silica fume is 0.4% by mass or more and 3% by mass or less. The pH of the silica fume at 25°C is 1.0 or higher and 5.0 or lower. The R₂O content of the silica fume is 0.01% by mass or more and 0.4% by mass or less. The average particle size of the silica fume is 0.3 μm or more and 4 μm or less. A method for suppressing alkali-silica reaction in a cement composition, wherein the amount of silica fume added is 1 part by mass or more and 9 parts by mass or less per 100 parts by mass of cement contained in the cement composition.

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