Admixture for addition to cement composition, cement composition, cement hardened body, and method for suppressing elution of harmful element from cement hardened body

Abstract

To provide an admixture for addition to a cement composition, capable of suppressing elution of harmful elements from a cement hardened body finally obtained, without adversely affecting fresh properties of the cement composition.SOLUTION: The present invention relates to an admixture for addition to a cement composition, for suppressing elution of harmful elements from a cement hardened body obtained by hardening the cement composition, in which a particle size distribution D90 of the admixture falls within a range of 60 μm or more and 200 μm or less, and a composition of the admixture satisfies the following formulae: (i) 70 wt.%≤(Al2O3+SiO2) / (total mass of the admixture)≤95 wt.%, (ii) 4≤SiO2 / Al2O3 (mass ratio), and (iii) CaO≤5 wt.% and MgO≤2 wt.%. Further, the present invention provides the cement composition containing the admixture, the cement hardened body, and a method for suppressing the elution of the harmful elements from the cement hardened body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an admixture for addition to a cement composition, a cement composition containing the admixture, a hardened cement product, and a method for inhibiting the elution of harmful elements from the hardened cement product, and in particular to an admixture for addition to a cement composition that acts as an agent for inhibiting the elution of harmful elements from the hardened cement product, a cement composition containing the admixture, a hardened cement product formed by hardening the cement composition, and a method for inhibiting the elution of harmful elements from the hardened cement product. [Background technology]

[0002] At thermal power plants that use coal as fuel, large amounts of ash are produced during combustion. This ash has traditionally been treated as industrial waste, but the fine particles that are blown up with the combustion gases are collected by dust collectors. Fly ash is compatible with concrete, and when used as aggregate, it has been noted to improve durability, workability, and fluidity, and is therefore also mixed into cement compositions. However, not all of the fly ash generated at thermal power plants can be used in cement compositions, and a certain amount is currently discarded.

[0003] Therefore, in order to reduce the amount of fly ash that is disposed of, attempts have been made to increase the amount of fly ash mixed into cement compositions.

[0004] However, fly ash may contain harmful elements such as hexavalent chromium, arsenic, selenium, fluorine, boron, cadmium, mercury, and lead, and in such cases, increasing the amount of fly ash added to the cement composition will increase the concentration of these harmful elements in the resulting hardened cement paste. Therefore, there is a need for a method to prevent the elution of harmful elements from fly ash out of the hardened cement paste.

[0005] Non-Patent Document 1 discloses the treatment of large amounts of waste soil generated during civil engineering works, particularly excavated waste that is mostly rock fragments, with semi-burned dolomite (mainly composed of MgO and CaCO3). The semi-burned dolomite in Non-Patent Document 1 can insolubilize As (arsenic) and B (boron) in the excavated waste. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Tatsuro Naruse, Takeshi Kawashima, and Toshifumi Igarashi, "Reducing Arsenic Leaching from Excavated Sludge Using Semi-burnt Dolomite," Journal of the Japan Society of Civil Engineers, Vol. 70, No. 4, pp. 78-85, 2014 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, the semi-burned dolomite in Non-Patent Document 1 can insolubilize As (arsenic) and B (boron) in excavated muck, but the effectiveness of mixing it into a cement composition has not been confirmed. The inventors of the present application prepared a cement composition by kneading an insolubilizing agent for wastewater treatment and contaminated soil (product name: Metal Clear (registered trademark)-1000, manufactured by Yoshizawa Lime Industry Co., Ltd.) that contains semi-burned dolomite as its main component with cement and water, but found that the fresh properties of the resulting cement composition deteriorated, making it impossible to mold into the desired shape.

[0008] Therefore, there has been a demand for an admixture that can suppress the elution of harmful elements from hardened cement pastes and that does not adversely affect the fresh properties of the prepared cement composition.

[0009] The present invention was made in view of the above problems and aims to provide an admixture for cement compositions that, even when mixed with cement to prepare a cement composition, can suppress the elution of harmful elements from the final hardened cement product without adversely affecting the fresh properties of the cement composition. It is also an object of the present invention to provide a cement composition containing the admixture, a hardened cement product, and a method for suppressing the elution of harmful elements from a hardened cement product using the admixture. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to achieve the above object. As a result, they have found that the particle size of the admixture is within a predetermined range and the composition of the admixture satisfies the following formula: (i) 70wt%≦ (Al2O3+SiO2) / total mass of admixture ≦95wt% (ii) SiO2 / Al2O3 (mass ratio) 4≦ and (iii) CaO≦5wt% and MgO≦2wt% The present inventors have found that by satisfying the above requirements, it is possible to maintain the fresh properties of the cement composition at the same level as when no admixture is added, while suppressing the elution of harmful elements from the hardened cement composition after the cement composition has hardened, and have completed the present invention.

[0011] That is, the object is to provide an admixture for addition to a cement composition, The particle size distribution D90 of the admixture is in the range of 60 μm to 200 μm, The composition of the admixture is as follows: (i) 70wt%≦ (Al2O3+SiO2) / total mass of admixture ≦95wt% (ii) SiO2 / Al2O3 (mass ratio) 4≦ and (iii) CaO≦5wt% and MgO≦2wt% It has been found that the above object can be achieved by an admixture for suppressing the elution of harmful elements from a hardened cement body obtained by hardening the cement composition, which is characterized by satisfying the following.

[0012] The above object can also be achieved by a cement composition containing the admixture of the present invention, cement, water, and fly ash, and in particular, when the fly ash is present in the cement composition at a concentration of 500 kg / m 3 It is preferable that the amount is more than the above.

[0013] Furthermore, the above object can also be achieved by a hardened cement product obtained by hardening the cement composition of the present invention.

[0014] Furthermore, the above object can also be achieved by a method for suppressing the leaching of harmful elements from a hardened cement body obtained by hardening a cement composition containing harmful elements, which method comprises adding the admixture of the present invention to the cement composition. [Effects of the Invention]

[0015] According to the admixture for addition to a cement composition, the cement composition, the hardened cement body, and the method for inhibiting elution of harmful elements from the hardened cement body of the present invention, the fresh properties of the cement composition containing the admixture of the present invention can be maintained to the same level as when no admixture is added, and the elution of harmful elements from the obtained hardened cement body can be inhibited. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a distribution diagram showing the particle size distribution and the D90 values ​​of the admixtures according to the examples and comparative examples. [Figure 2] FIG. 1 is a schematic diagram showing a method for preparing a cement composition according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Admixture> The admixture of the present invention is an admixture for addition to a cement composition, The particle size distribution D90 of the admixture is in the range of 60 μm to 200 μm, The composition of the admixture is as follows: (i) 70wt%≦ (Al2O3+SiO2) / total mass of admixture ≦95wt% (ii) SiO2 / Al2O3 (mass ratio) 4≦ and (iii) CaO≦5wt% and MgO≦2wt% The cement composition satisfies the above requirements and is an admixture for suppressing elution of harmful elements from a hardened cement body obtained by hardening the cement composition.

[0018] Therefore, the admixture of the present invention is used in applications where it is added to cement compositions.

[0019] The admixture of the present invention has a particle size distribution D90 in the range of 60 μm to 200 μm, preferably in the range of 70 μm to 150 μm, and particularly preferably in the range of 80 μm to 120 μm.

[0020] If the D90 of the particle size distribution of the admixture is less than 60 μm, the fresh properties of the cement composition deteriorate when the admixture is added to the cement composition, making it difficult to form it into the desired shape. On the other hand, if the D90 of the particle size distribution of the admixture is more than 200 μm, the surface area of ​​the admixture becomes large, and the effect of insolubilizing harmful elements inside the hardened cement body becomes insufficient.

[0021] The particle size distribution of admixtures can be measured by various methods, such as sieving, laser diffraction / scattering, centrifugal sedimentation, particle trajectory analysis (particle tracking), dynamic light scattering, etc. Among these, it is preferable to measure the particle size distribution of admixtures by laser diffraction / scattering, from the viewpoint of accurately measuring particles with a particle size distribution D90 value in the range of 60 μm to 200 μm.

[0022] The composition of the admixture of the present invention is represented by the following formula: (i) 70wt%≦ (Al2O3+SiO2) / total mass of admixture ≦95wt%, and in particular, (i)' 80wt%≦ (Al2O3+SiO2) / total mass of admixture ≦90wt% It is preferable that the following is satisfied.

[0023] Furthermore, the composition of the admixture of the present invention is represented by the following formula: (ii) SiO2 / Al2O3 (mass ratio) is 4≦, and in particular, (ii)' It is preferable that 5≦SiO2 / Al2O3 (mass ratio) is satisfied.

[0024] Moreover, the composition of the admixture of the present invention is (iii) CaO≦5wt% and MgO≦2wt%, and in particular: (iii)' It is preferable that CaO≦4 wt% and MgO≦1 wt% are satisfied.

[0025] Although the reason for this is not clear, it is thought that when the composition of the admixture satisfies all of the above formulas (i) to (iii), the balance of the CSH hardening system is improved and hardening proceeds compared to when a CaO-based admixture is used, in relation to the formulation of the cement composition, particularly the formulation of a cement composition to which a certain amount or more of fly ash has been added, and harmful elements are more easily absorbed into the hardened cement body, promoting the insolubilization of these harmful elements.

[0026] As the admixture of the present invention, for example, Aji stone powder can be suitably used, but any admixture can be used as long as it satisfies the requirements of the D90 of the particle size distribution and the requirements of the above formulas (i) to (iii).

[0027] The blending ratio of the admixture of the present invention in the cement composition is, for example, 0.5 to 10 mass %, preferably 1 to 6 mass %, based on the total mass of the powder raw materials in the cement composition.

[0028] If the mixing ratio of the admixture of the present invention is too high, the fresh properties of the cement composition will be reduced, and conversely, if the mixing ratio of the admixture of the present invention is too low, the insolubilization effect of harmful elements will be insufficient. Therefore, taking into account the advantages and disadvantages of both, the mixing ratio of the admixture of the present invention in the cement composition can be appropriately adjusted.

[0029] <Cement composition> The cement composition of the present invention contains the admixture of the present invention, cement, water, and fly ash. Of these, the admixture is the same as the admixture described above, so a description thereof will be omitted here.

[0030] [cement] Cement is an inorganic binder that hardens when mixed with water, and hydraulic cement is used in the present invention. As hydraulic cement, simple cement such as Portland cement (JIS R5210), hydraulic lime, Roman cement, or natural cement may be used, or mixed cement such as lime-blended cement or mixed Portland cement (JIS R5211, R5212, R5213) may be used.

[0031] [water] The water to be mixed into the cement composition is not limited to pure water, but tap water, river water, lake water, seawater (including artificial seawater) can also be used. From the viewpoint of improving the strength of the obtained hardened cement body and further insolubilizing harmful elements in the hardened cement body, it is preferable to use seawater as the water to be mixed into the cement composition. Metal ions (Mg 2+ , Na + It is presumed that these factors contribute to the improvement of the strength of hardened cement paste.

[0032] [Fly ash (coal ash)] Coal ash is ash particles generated by coal combustion, and is mainly produced at coal-fired power plants. Coal ash can be broadly divided into clinker, which is a porous mass of ash that melts and solidifies when coal is burned in a boiler and falls to the bottom of the boiler, and fly ash, which is fine spherical particles that are collected by an electric dust collector from ash floating with the combustion gas.

[0033] As already mentioned, fly ash may contain harmful elements such as hexavalent chromium, arsenic, selenium, fluorine, boron, cadmium, mercury, and lead, and the admixture of the present invention is added to the cement composition to insolubilize these harmful elements in the hardened cement after the cement composition has hardened.

[0034] The amount of fly ash blended in the cement composition may be any amount. However, from the viewpoint of reducing the amount of fly ash disposed of in coal-fired power plants, it is preferable that the amount of fly ash blended in the cement composition is 500 kg / m. 3 It is preferable that the amount of the compound is 800 kg / m or more. 3 It is more preferable that the amount is more than the above.

[0035] On the other hand, from the viewpoint of maintaining the fluidity of the cement composition, the fly ash is contained in the cement composition at a concentration of 1600 kg / m 3 It is preferable that the amount of the compound is 1300 kg / m 3 It is more preferable that the amount of the compound is as follows:

[0036] The cement composition may also contain aggregate as an optional component.

[0037] Aggregates are generally used in the production of concrete and are added to suppress heat generation due to the hydration reaction of the cement composition, suppress shrinkage, and reduce the amount of cement used to cut costs.Aggregates are divided into coarse aggregate and fine aggregate, with coarse aggregate being retained by 85% or more by mass on a 5mm sieve, and fine aggregate being passed through a 5mm sieve and 100% by mass passing through a 10mm sieve.

[0038] Examples of aggregate materials include river sand, mountain sand, sea sand, blast furnace slag, copper slag, etc. In the present invention, fly ash and the admixture of the present invention are not included in the aggregate.

[0039] Cement compositions containing the admixture of the present invention and a large amount of fly ash tend to have a low specific gravity. Therefore, when a hardened cement product is required that has a weight that can withstand tsunamis or ocean waves, it is preferable to add fine aggregate with a high specific gravity (copper slag, sand, gravel, etc.) to ensure a predetermined unit weight.

[0040] On the other hand, in cases other than those intended for such applications, in order to reduce the weight and improve workability and transportability, it is preferable to include aggregate in an amount of 5% by mass or less, more preferably 1% by mass or less, based on the total mass of the cement composition, and it is particularly preferable to not add aggregate.

[0041] Furthermore, it may optionally contain admixtures such as air entraining agents (air entraining agents), water reducing agents (air entraining water reducing agents, water reducing agents, high performance air entraining water reducing agents, etc.), superplasticizers, setting and hardening regulators, accelerators, waterproofing agents, etc.

[0042] The cement composition of the present invention can be prepared, for example, by mixing the admixture of the present invention, cement, and fly ash in powder form, adding water and optionally an admixture to the powder mixture, kneading the mixture to form a paste, and then mixing with aggregate as needed and further kneading the mixture.

[0043] <Hardened cement> The hardened cement product of the present invention is a hardened cement product obtained by hardening the cement composition of the present invention.

[0044] The raw materials contained in the cement composition and their preparation are the same as those described above, and therefore, a description thereof will be omitted here.

[0045] The prepared cement composition is applied or sprayed onto an object or poured into a formwork, compacted, and cured until the required compressive strength is obtained, thereby obtaining the hardened cement product of the present invention.

[0046] Compaction is carried out to remove air bubbles from the cement composition that has been applied or poured into a formwork. Compaction is carried out by hitting the surface of the cement composition that has been applied or poured into a formwork with a tamper, poking it with a stick, or vibrating it with a vibrator. When a large amount of fly ash is contained in the cement composition (500 kg or more / 1 m of cement composition), compaction is carried out. 3 Since the fluidity of the cement composition decreases in the case of the above-mentioned compaction, it is preferable to use a table vibrator, a backhoe, or a backhoe with a special vibrating plate for compaction.

[0047] Curing can be carried out under conventionally known conditions such as air curing or underwater curing.

[0048] <Method for suppressing elution of harmful elements from hardened cement> The method of the present invention for suppressing the elution of harmful elements from hardened cement paste comprises adding the admixture of the present invention to a cement composition containing the harmful elements.

[0049] Examples of cement compositions containing harmful elements include, but are not limited to, cement compositions containing fly ash, such as the cement composition of the present invention. For example, not only fly ash (coal ash), but also biomass ash, gypsum, and contaminated soil may contain the harmful elements, and cement compositions containing these also fall under the category of cement compositions containing harmful elements.

[0050] The admixture of the present invention can be added to a cement composition containing harmful elements, for example, by adding the admixture of the present invention when mixing powder materials such as cement.

[0051] Thereafter, water is added to prepare a cement composition as described above, and the resulting cement composition is hardened to obtain a hardened cement product.

[0052] According to the present invention, an admixture for addition to a cement composition, a cement composition containing this admixture, a hardened cement product obtained by hardening this cement composition, and a method for suppressing elution of harmful elements from the hardened cement product, by adding the admixture of the present invention to a cement composition containing harmful elements, the fresh properties of the cement composition can be maintained to the same extent as when no admixture is added, and the elution of harmful elements from the finally obtained hardened cement product can be suppressed.

[0053] This is thought to be because, when the composition of the admixture satisfies all of the above formulas (i) to (iii), the balance of the CSH hardening system is improved and hardening proceeds compared to when a CaO-based admixture is used, in relation to the formulation of the cement composition, particularly the formulation of a cement composition to which a certain amount or more of fly ash has been added, and harmful elements are more easily absorbed into the hardened cement body, promoting the insolubilization of these harmful elements.

[0054] Furthermore, the hardened cement product obtained from the cement composition containing the admixture of the present invention has a higher compressive strength than the hardened cement product obtained from the cement composition not containing the admixture of the present invention.

[0055] Furthermore, when Aji stone powder is used as the admixture of the present invention, it is more economical than using commercially available admixtures, since Aji stone powder is generally obtained as industrial waste.

[0056] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the invention.

[0057] For example, the hardened cement product of the present invention is a hardened cement product obtained by hardening the cement composition of the present invention, but the hardened cement product may be so-called reinforced concrete containing steel.

[0058] The steel material includes a variety of materials such as reinforcing bars, steel frames, round steel bars, deformed steel bars, deformed reinforcing bars, PC steel materials, and molten wire mesh, and the material is not particularly limited.

[0059] In this case, the steel material is placed in a formwork in advance, and the cement composition is poured into the formwork. After hardening, the cement composition becomes a hardened cement body containing the steel material.

[0060] However, if a large amount of fly ash is contained in the cement composition (500 kg or more / 1 m of cement composition), 3 In the case of concrete, the flowability of the steel material is low, and the position of the steel material placed in the formwork is unstable due to vibration during compaction, so it is preferable that the hardened cement body does not contain steel material.

[0061] Furthermore, the admixture of the present invention is an admixture for addition to cement compositions, but it may also be an admixture for addition to cement compositions that do not contain fly ash, and in view of the problem to be solved by the present invention, it may be an admixture for addition to cement compositions that contain harmful elements. Thus, for example, the admixture of the present invention may be an admixture for addition to cement compositions that contain biomass ash containing harmful elements or contaminated soil containing harmful elements as aggregate. [Example]

[0062] EXAMPLES The present invention will be specifically explained below by showing examples, but the present invention is not limited to these examples.

[0063] 1.Materials used In this example, the admixture used was powder of quarried Aji stone from Kagawa Prefecture, and the admixture used in the comparative example was an insolubilizing agent (product name: Metal Clear (registered trademark)-1000, manufactured by Yoshizawa Lime Industry Co., Ltd.) whose main component is semi-burned dolomite. The chemical formulas of the compounds contained in each admixture and their content (mass%) are shown in Table 1.

[0064] [Table 1]

[0065] Furthermore, the particle size distribution of each admixture was measured and the D90 value was determined. The results are shown in Figure 1. Figure 1 is a distribution diagram showing the particle size distribution of the admixtures according to the examples and comparative examples and their respective D90 values.

[0066] The particle size distribution was measured by a laser diffraction / scattering method using a Microtrac particle size distribution analyzer MT3300EX II (manufactured by Microtrac Bell Co., Ltd.) as the testing equipment. The conditions for the testing equipment are as follows:

[0067] (1) Device range: 0.1 to 700 μm (2) Dispersion medium: ethyl alcohol (3) Sample disperser: SDC-H (4) Measurement time: 30 seconds (5) Number of measurements: 2 As shown in the figure, the D90 value of the particle size distribution of the Aji stone powder was 96.0 μm, and the D90 value of the particle size distribution of Metal Clear (registered trademark)-1000 was 48.0 μm.

[0068] The density of the above admixtures (Aji stone powder, Metal Clear (registered trademark)-1000) and information on other materials used are shown in Table 2.

[0069] [Table 2]

[0070] Furthermore, as a preliminary study, the materials used, including cement (BB), coal ash (FA), Aji stone powder (SP), and Metal Clear (registered trademark)-1000 (MC), were tested for the amount of leaching of hazardous substances listed in Environment Agency Notification No. 46 (hexavalent chromium, arsenic, selenium, fluorine, boron, cadmium, total mercury, and lead). These eight hazardous elements are listed in the Japan Society of Civil Engineers' Concrete Library as items to be measured when used as civil engineering materials. The results are shown in Table 3.

[0071] [Table 3]

[0072] As shown in Table 3, in this example, it was confirmed that the amount of hazardous substances leached from coal ash (FA) exceeded the soil environmental standards set out in Environment Agency Notification No. 46. This shows that it is important to insolubilize the hazardous substances in coal ash (FA).

[0073] 2. Preparation of cement compositions containing the admixture of the present invention Next, the preparation of cement compositions containing admixtures will be described. Figure 2 is a schematic diagram showing a method for preparing cement compositions according to the examples. As shown in Figure 2, first, cement (BB), fly ash (FA), Aji stone powder (SP) or Metal Clear (registered trademark)-1000 (MC) were charged into a Hobart-type mortar mixer with a nominal capacity of 10 L and mixed for 15 seconds to powder mix, then water (W) was added and mixed for an additional 30 seconds, scraped off, and then mixed for an additional 90 seconds and discharged to obtain each cement composition.

[0074] The Vf20 value of the resulting cement composition was measured for its fresh properties. Specifically, a flow cone (JIS A 5201) was filled with the prepared cement composition and placed on a table vibrator. The flow cone was then gently lifted vertically. Only a cement composition with a diameter of 100 mm was placed on the table vibrator. The table vibrator was vibrated in this state for 20 seconds, after which the diameter of the cement composition was measured to the nearest 1 mm, and the measured value was taken as the Vf20 value.

[0075] Table 4 shows the blend amounts of cement (BB), fly ash (FA), Aji stone powder (SP), Metal Clear (registered trademark)-1000 (MC) and water (W) and the measured values ​​of Vf20.

[0076] In Table 4, Examples show cement compositions using Aji stone powder (SP) as an admixture, Comparative Examples show cement compositions using Metal Clear (registered trademark)-1000 (MC) as an admixture, and Reference Examples show cement compositions containing no admixture.

[0077] The mixing volume of each cement composition was 3 L.

[0078] [Table 4]

[0079] 3. Testing of hardening properties 3-1. Manufacturing of hardened cement paste and measurement of its compressive strength Each cement composition obtained in 2. Preparation of cement compositions containing the admixture of the present invention was filled into a formwork (inner diameter 5 cm x height 10 cm) and compacted for 60 seconds using a table vibrator (vibration frequency: 60 Hz). Each compacted cement composition was subjected to standard underwater curing to obtain a hardened cement composition.

[0080] The compressive strength of each hardened specimen was measured on the 7th and 28th days in accordance with JIS A 1108:2018 "Testing method for compressive strength of concrete." The results are shown in Table 5.

[0081] [Table 5]

[0082] 3-2. Measurement of the amount of leaching of harmful substances The amount of leaching of harmful substances (hexavalent chromium, arsenic, selenium, fluorine, boron, cadmium, total mercury, and lead) from the 28-day-old hardened cement paste obtained in the above 3-1. Manufacturing of hardened cement paste and measurement of its compressive strength was measured.

[0083] The test solution was prepared in accordance with the appendix of Environment Agency Notification No. 46. The hardened cement paste was roughly crushed using a jaw crusher, then pulverized in a mortar, and then used to prepare the test solution.

[0084] The results are shown in Table 6.

[0085] [Table 6]

[0086] 4. Results and Discussion As shown in Table 6, in both the comparative example, which used Metal Clear (registered trademark)-1000, an insolubilizing treatment agent for contaminated soil, as an admixture, and the example, which used Aji stone powder as an admixture, the amount of harmful substances leaching from the hardened cement body was reduced compared to the reference example, which did not contain these admixtures, and the soil environmental standards of the Environment Agency Notification No. 46 were met.

[0087] This is thought to be the result of harmful substances derived from fly ash (coal ash) blended into the cement composition being insolubilized by the admixture. Furthermore, as shown in Table 5, the hardened cement products of the Examples and Comparative Examples both exhibited greater compressive strength than the hardened cement product of the Reference Example, which did not contain any admixture.

[0088] However, as shown in Table 4, the cement compositions of the Examples exhibited fresh properties (Vf values) equivalent to those of the Reference Examples containing no admixture, while the Vf20 values ​​of the cement compositions of the Comparative Examples were significantly reduced and fell below the lower limit of the moldable range.

[0089] Therefore, by using the admixture of the present invention as an admixture for a cement composition, the fresh properties of the cement composition can be maintained to the same extent as when no admixture is added, and the leaching of harmful elements from the final hardened cement body can be suppressed. [Industrial Applicability]

[0090] The admixture of the present invention can be used as an additive to cement compositions. Furthermore, a hardened cement product obtained by hardening a cement composition containing the admixture of the present invention, and a hardened cement product obtained by the method of suppressing elution of harmful elements from a hardened cement product of the present invention, can be used for, for example, backfilling of seawalls and revetment construction, road and parking lot bases, agricultural land foundation materials, embankment construction for residential land, industrial land, green parks, etc., as well as secondary products such as wave-dissipating foot protection blocks and tetrapods.

Claims

1. 1. An admixture for addition to a cement composition, comprising: The particle size distribution D90 of the admixture is in the range of 60 μm or more and 200 μm or less, The composition of the admixture is as follows: (i) 70wt%≦(Al ２ O ３ +SiO ２ ) / total mass of admixture ≦95wt% (ii) 4≦SiO ２ / Al ２ O ３ (mass ratio) and (iii) CaO≦5 wt% and MgO≦2 wt% characterized in that An admixture for inhibiting the elution of harmful elements from a hardened cement body obtained by hardening the cement composition.

2. A cement composition comprising the admixture of claim 1, cement, water, and fly ash.

3. The fly ash is present in the cement composition at a concentration of 500 kg / m ３ 3. The cement composition according to claim 2, wherein the above amounts are blended.

4. A hardened cement product obtained by hardening the cement composition according to claim 2 or 3.

5. A method for suppressing elution of harmful elements from a hardened cement product obtained by hardening a cement composition containing harmful elements, comprising adding the admixture according to claim 1 to the cement composition.

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