Concrete composition

Abstract

To provide a concrete composition with a portion of aggregate thereof replaced with carbonate light aggregate, excellent in fresh characteristics and in post-curing strength and freeze damage resistance.SOLUTION: An aspect of the present invention relates to a concrete composition including (a) cement, (b) coarse aggregate, (c) fine aggregate, (d) granulated carbonate light aggregate of alkali earth metal, (e) and water, where the carbonate light aggregate has a cumulative pore volume of 0.06 mL / g or more, each pore having a pore size of 100 nm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to alkaline earth metal carbonate lightweight aggregates and concrete compositions containing same. [Background technology]

[0002] Technologies for storing and fixing carbon dioxide (CO2) are attracting attention as a way to realize a carbon-neutral society. If CO2 can be fixed as carbonates and these carbonates can be used as construction materials such as concrete, it is expected that large amounts of CO2 can be fixed, so there is a strong desire to establish practical and versatile technologies.

[0003] When carbonates are used as concrete materials, the appropriate blending amount and required properties differ depending on whether they are used as a powder admixture or as an aggregate. Since the majority of concrete's constituent materials are aggregates (fine or coarse aggregates), if the above carbonates could be used as aggregates, their contribution to CO2 fixation could be increased in light of the amount used. Furthermore, in order to popularize the use of such aggregates and contribute to a decarbonized society, it is preferable to use them in ordinary concrete rather than in secondary products or special-purpose concrete.

[0004] Patent Document 1 describes a concrete composition that contains water, a binder, a filler, and an aggregate, and that contains a predetermined amount of precipitated calcium carbonate as the filler. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-127648 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 does not conduct a detailed study on the light calcium carbonate used as aggregate, nor does it disclose granulated light carbonate aggregate.

[0007] An object of one aspect of the present disclosure is to provide a concrete composition containing granulated carbonate light aggregate, which can form concrete that has good fresh properties and is excellent in strength and frost resistance. [Means for solving the problem]

[0008] Preferred aspects of the present disclosure relate to the following:

[0009] 1. (a) Cement and (b) coarse aggregate; (c) fine aggregate; (d) granulated alkaline earth metal carbonate lightweight aggregate; (e) water; Including, A concrete composition, wherein the carbonate light aggregate has a cumulative pore volume of pores with diameters of 100 nm or less of 0.06 ml / g or more.

[0010] 2. The concrete composition according to item 1, wherein the volume ratio of the carbonate light aggregate to the total volume of the coarse aggregate, the fine aggregate, and the carbonate light aggregate is 1% or more and 45% or less.

[0011] 3. The concrete composition according to item 1 or 2, wherein the ratio of the volume of the carbonate light aggregate to the total volume of the fine aggregate and the carbonate light aggregate is 1% or more and 99% or less.

[0012] 4. The concrete composition according to any one of items 1 to 3, wherein the ratio of the volume of the carbonate light aggregate to the total volume of the fine aggregate and the carbonate light aggregate is 1% or more and 70% or less.

[0013] 5. The concrete composition according to any one of items 1 to 4, wherein the carbonate light aggregate has a total cumulative pore volume of 0.15 ml / g or more.

[0014] 6. The concrete composition according to any one of items 1 to 5, wherein the pore size distribution of the carbonate light aggregate has a maximum peak pore size of 100 nm or less.

[0015] 7. The concrete composition according to any one of items 1 to 6, wherein the carbonate light aggregate is derived from waste materials.

[0016] 8. The concrete composition according to any one of items 1 to 7, wherein the carbonate light aggregate is a stirred granulated product.

[0017] 9. The concrete composition according to any one of items 1 to 8, wherein the carbonate light aggregate has a water absorption rate of 15% or more.

[0018] 10. The concrete composition according to any one of items 1 to 9, wherein the carbonate light aggregate has a spherical shape.

[0019] 11. The density of the carbonate lightweight aggregate in bone dry state is 1.3 to 2.7 g / cm 3 11. The concrete composition according to any one of items 1 to 10,

[0020] 12. The concrete composition according to any one of items 1 to 11, wherein the alkaline earth metal carbonate light aggregate has a coarse particle ratio of 2.0 to 3.5.

[0021] 13. A hardened concrete composition according to any one of items 1 to 12.

[0022] 14. A granulated alkaline earth metal carbonate lightweight aggregate having a cumulative pore volume of 0.06 ml / g or more for pores with diameters of 100 nm or less.

[0023] 15. The granulated alkaline earth metal carbonate lightweight aggregate according to item 14, having a total cumulative pore volume of 0.15 ml / g or more.

[0024] 16. The granulated alkaline earth metal carbonate lightweight aggregate according to item 14 or 15, wherein the pore size at the maximum peak position of the pore volume in the pore size distribution is 100 nm or less. [Effects of the Invention]

[0025] According to one aspect of the present disclosure, it is possible to provide a concrete composition that has good fresh properties and exhibits excellent strength and frost resistance after hardening. Also, according to another aspect of the present disclosure, it is possible to provide a concrete composition that can reduce carbon dioxide emissions by using a carbonate light aggregate containing carbonate obtained by on-site immobilization of carbon dioxide from exhaust gas containing carbon dioxide. [Brief explanation of the drawings]

[0026] [Figure 1A] 1 is a graph showing the relationship between the pore diameter of aggregate and the cumulative pore volume. [Figure 1B] 1 is a graph showing the relationship between the pore diameter of an aggregate and the log differential pore volume. [Figure 2A] 1 is a photograph of one piece of granulated carbonate lightweight aggregate of the present disclosure. [Figure 2B] 1 is a photograph of granulated carbonate lightweight aggregates of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content. In the following description, when it is written "X to Y" (X and Y are arbitrary numbers), it means "X or more and Y or less" unless otherwise specified.

[0028] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in a composition such as a mixture means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0029] <Concrete composition> The concrete composition of the present disclosure (also simply referred to as "composition") comprises: (a) cement; (b) coarse aggregate; (c) fine aggregate; (d) Granulated alkaline earth metal carbonate light aggregate (also simply referred to as "carbonate light aggregate"); (e) water; Including, The carbonate light aggregate (d) has a cumulative pore volume of pores with a diameter of 100 nm or less of 0.06 ml / g or more. In this specification, the above components are also referred to as component (a), component (b), component (c), component (d), and component (e), respectively. The term "composition" may refer to the components before or after mixing, or to a mixture in which some components are premixed. The concrete composition of the present disclosure, containing component (d), exhibits good fresh properties and excellent strength and frost resistance after hardening. Examples of fresh properties include good slump and air content, and a reduced incidence of bleeding. In one aspect, the carbonate light aggregate of component (d) can be produced on-site from carbon dioxide-containing exhaust gas using carbonates that efficiently immobilize carbon dioxide, contributing to carbon neutrality.

[0030] Hereinafter, each component constituting the concrete composition of the present disclosure will be described. In this specification, "unit amount (kg / m 3 )" is 1m 3 The term "unit water volume" refers to the amount of each material used to produce concrete. 3 This refers to the amount of water used to produce concrete.

[0031] <(a) Cement> Examples of cement include ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, sulfate-resistant Portland cement, moderate-heat Portland cement, low-heat Portland cement, blast-furnace cement, fly ash cement, silica fume cement, alumina cement, etc. One type of cement may be used, or two or more types may be used in combination.

[0032] <(b) Coarse aggregate> The coarse aggregate is not particularly limited, and a coarse aggregate commonly used in the production of ordinary concrete can be used. The coarse aggregate is an aggregate that retains 85% or more by mass on a 5 mm mesh sieve. Examples of coarse aggregate include crushed stone such as andesite, rhyolite, hard sandstone, and limestone, river gravel, mountain gravel, land gravel, blast furnace slag coarse aggregate, and recycled coarse aggregate. One type of coarse aggregate may be used alone, or two or more types may be used in combination. In this specification, carbonate light aggregate corresponding to component (d) is not considered to be coarse aggregate (b). Furthermore, when the carbonate light aggregate of component (d) is used as a coarse aggregate for ordinary concrete, for example, the average particle size of the carbonate light aggregate is preferably 7 to 32 mm or 8 to 31 mm, and more preferably 15 to 25 mm. The average particle size in this specification means the value measured by measuring the particle size distribution using the method described in JIS A 1102:2014 "Sieving test method for aggregates" and determining the particle size at which the calculated particle size accumulation curve is 50% of the mass fraction.

[0033] <(c) Fine aggregate> The fine aggregate is not particularly limited, and fine aggregates used in the production of ordinary concrete can be used. Fine aggregates are aggregates that pass 100% through a 10 mm sieve and 85% or more by mass through a 5 mm sieve. Examples of fine aggregates include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, lightweight fine aggregate, blast furnace slag fine aggregate, and limestone fine aggregate. Fine aggregates may be used alone or in combination. In this specification, carbonate light aggregates corresponding to component (d) are not considered to be fine aggregates (c). Furthermore, when the carbonate light aggregate of component (d) is used as a fine aggregate for ordinary concrete, for example, the average particle size of the carbonate light aggregate is preferably 0.4 to 1.2 mm, more preferably 0.6 to 1.0 mm.

[0034] <(d) Granulated alkaline earth metal carbonate lightweight aggregate> The concrete composition of the present disclosure contains granulated alkaline earth metal carbonate light aggregate (also simply referred to as "carbonate light aggregate"), and preferably the carbonate light aggregate has a cumulative pore volume of pores with a diameter of 100 nm or less of 0.06 ml / g or more.

[0035] The alkaline earth metal carbonate in the carbonate lightweight aggregate preferably includes a light carbonate (preferably light calcium carbonate) synthesized by chemical reaction. Examples of alkaline earth metals include magnesium and calcium, and calcium is preferred, with calcium being more preferred. The alkaline earth metal carbonate preferably includes MgCO3 (magnesium carbonate) and / or CaCO3 (calcium carbonate).

[0036] In one embodiment, the carbonate light aggregate is preferably a granulated product of a mixture containing an alkaline earth metal carbonate and a hydraulic material, and more preferably a granulated product of a mixture containing calcium carbonate and a hydraulic material.

[0037] The alkaline earth metal carbonate light aggregate used in the concrete composition of the present disclosure has pores, and the cumulative pore volume of pores with diameters of 100 nm or less may be preferably 0.06 mL / g or more, more preferably 0.08 mL / g or more, even more preferably 0.1 mL / g or more, or 0.12 mL / g or more. It may also be, but is not limited to, preferably 0.4 mL / g or less, more preferably 0.35 mL / g or less, even more preferably 0.3 mL / g or less, 0.27 mL / g or less, or 0.25 mL / g or less. Note that "pores" in this specification refer to pores measured by mercury intrusion porosimetry. The total pore volume and the cumulative pore volume of pores with a specific pore diameter range can be measured using a commercially available mercury porosimeter.

[0038] In the concrete composition of the present disclosure, the carbonate light aggregate may have a cumulative pore volume of pores with diameters of 50 nm or less, which is not limited to, but is preferably 0.05 mL / g or more, more preferably 0.07 mL / g or more, even more preferably 0.09 mL / g or more, or 0.10 mL / g or more, and may also preferably be 0.35 mL / g or less, more preferably 0.30 mL / g or less, and even more preferably 0.25 mL / g or less.

[0039] The carbonate light aggregate used in the concrete composition of the present disclosure tends to have a higher water absorption rate than artificial aggregates such as mesalite. Generally, the higher the water absorption rate, the lower the frost resistance. However, the inventors of the present disclosure have discovered that concrete with excellent frost resistance can be obtained by using a carbonate light aggregate with a cumulative pore volume of pores with a diameter of 100 nm or less or a cumulative pore volume of pores with a diameter of 50 nm or less within the above range. The carbonate light aggregate of the present disclosure has a large cumulative pore volume of small pores within the above range, which prevents water from entering the pores and therefore is less likely to affect frost resistance. It is believed that this results in improved frost resistance of the concrete.

[0040] In one embodiment, the pore size at the maximum peak position of the pore volume in the pore size distribution of the alkaline earth metal carbonate light aggregate is preferably 100 nm or less, more preferably 10 to 100 nm, and even more preferably 10 to 50 nm. When the pore size at the maximum peak position of the pore volume is within this range (particularly a pore size of 50 nm or less), water is less likely to freeze, and deterioration due to freeze-thaw cycles can be suppressed.

[0041] In one embodiment, the total cumulative pore volume of the alkaline earth metal carbonate light aggregate may be preferably 0.15 ml / g or more, or 0.18 ml / g or more, and preferably 0.4 ml / g or less, or 0.35 ml / g or less.

[0042] The differential pore volume of the maximum peak in the log differential pore volume (dV / d(logD)) of the carbonate light aggregate is not limited, but may be, for example, preferably 0.12 mL / g or more, more preferably 0.15 mL / g or more, and may be, for example, preferably 0.45 mL / g or less, more preferably 0.40 mL / g or less. The half-width of the maximum peak in the log differential pore volume of the carbonate light aggregate relative to the pore diameter is not limited, but is, for example, preferably 10 to 50 nm.

[0043] In one embodiment, the water absorption rate of the alkaline earth metal carbonate light aggregate is not limited, but is preferably 30% or less, more preferably 25% or less, and the lower limit may be 5% or more, 10% or more, or 15% or more. The water absorption rate can be determined in accordance with the methods described in JIS A 1109:2020 "Testing Method for Density and Water Absorption Rate of Fine Aggregate" and JIS A 1110:2020 "Testing Method for Density and Water Absorption Rate of Coarse Aggregate." The water absorption rate of the granulated carbonate light aggregate used in this embodiment tends to be higher than that of ordinary aggregate due to the greater amount of voids within the aggregate.

[0044] In one embodiment, the shape of the alkaline earth metal carbonate light aggregate is not limited, but is preferably spherical. In this specification, spherical may mean a perfect sphere, an approximately sphere, or an oval sphere. The sphericity of the carbonate light aggregate is preferably, for example, 0.80 or more, and more preferably 0.90 or more. The sphericity can be determined by image analysis of the carbonate light aggregate obtained using an optical microscope or a digital scope, using the [area of ​​the particle projected cross section (mm 2 The spherical shape of carbonate lightweight aggregate makes it easier to obtain good fresh properties for concrete compositions.

[0045] The bone dry density of the alkaline earth metal carbonate lightweight aggregate is not limited, but is, for example, 1.3 g / cm 3 It is preferable that the density is 1.5 g / cm or more. 3 The higher the bone dry density, the better the physical properties of the carbonate light aggregate can be improved in terms of reducing the water absorption rate. The upper limit of the bone dry density of the carbonate light aggregate is not limited, but is preferably 2.7 g / cm. 3 It may be less than 2.5 g / cm 3 It may be less than 2.3 g / cm 3 The bone dry density may be less than 100%. When the bone dry density is within this range, performance equivalent to that of artificial lightweight aggregate can be obtained. The bone dry density can be determined in accordance with the methods described in JIS A 1109:2020 "Testing methods for density and water absorption of fine aggregate" and JIS A 1110:2020 "Testing methods for density and water absorption of coarse aggregate."

[0046] In one embodiment, the alkaline earth metal carbonate light aggregate is preferably derived from waste materials. The carbonate light aggregate of the present disclosure may be produced using exhaust gas containing carbon dioxide, as described below, and in particular, can be produced by immobilizing carbon dioxide on-site.

[0047] The particle size of the alkaline earth metal carbonate lightweight aggregate is not limited, but is preferably 2.0 to 3.5, and more preferably 2.4 to 3.0. When the particle size is within this range, excellent fresh properties are obtained. The particle size can be measured by a method in accordance with JIS A 1102:2014.

[0048] One embodiment of the method for producing alkaline earth metal carbonate light aggregate may include, but is not limited to, a carbonation step in which a raw material containing a basic compound having an alkaline earth metal (preferably Mg and / or Ca, etc.) as a constituent element is contacted with carbon dioxide in exhaust gas while stirring to obtain an alkaline earth metal carbonate (also referred to as "carbonate"), and a granulation step in which a mixture containing the carbonate and a hydraulic material is stirred and granulated to obtain an alkaline earth metal carbonate light aggregate (also referred to as "hardened carbonate"). Alternatively, in one embodiment, the carbonate may be commercially available or may be obtained by a method other than the carbonation step, and the granulation step may be performed using the carbonate. The carbonate light aggregate is obtained mainly in a particulate form, and the particulate form may be spherical.

[0049] (carbonation process) As a preferred example of the carbonation step, a process will be described in which a raw material containing a basic compound having an alkaline earth element as a constituent element is brought into contact with carbon dioxide in exhaust gas while being stirred, thereby obtaining an alkaline earth metal carbonate. This method makes it possible to efficiently immobilize carbon dioxide at the location where the carbon dioxide-containing exhaust gas is generated, i.e., on-site. The carbonate obtained in the carbonation step may, in some cases, be temporarily stored in a hopper or the like.

[0050] The exhaust gas containing carbon dioxide is not particularly limited as long as it contains carbon dioxide, and may be, for example, exhaust gas from a coal-fired power plant, a cement factory, an incineration plant, or the like. Since on-site fixation of carbon dioxide is possible, this method can be carried out at a coal-fired power plant, a cement factory, an incineration plant, or the like. The carbon dioxide content in the exhaust gas may be, for example, 1% by volume or more, 3 to 50% by volume, 5 to 40% by volume, or 8 to 30% by volume under standard conditions. Furthermore, these exhaust gases may be used directly, or highly concentrated (e.g., greater than 50% by volume) carbon dioxide recovered and concentrated from the exhaust gas may be used.

[0051] The raw material includes a basic compound having an alkaline earth metal (preferably calcium) such as calcium (Ca) or magnesium (Mg) as a constituent element, and may be composed of a basic compound having Ca as a constituent element. Examples of basic compounds having Ca as a constituent element include calcium oxide (CaO), calcium hydroxide (Ca(OH)2), calcium silicate (CaSiO3, Ca2SiO4, Ca3SiO5, etc.), and calcium aluminate (CaAl2O4, Ca3Al2O6, Ca 12 Al 14 O 33 Examples of basic compounds having Mg as a constituent element include magnesium hydroxide (Mg(OH)2). Two or more compounds may be used in combination as raw materials. Examples of raw materials containing these basic compounds include waste materials such as concrete sludge and waste concrete. The above waste materials can be used as they are, or can be prepared into calcium oxide or calcium hydroxide by chemical treatment, heat treatment, or the like. Furthermore, even in the case of waste materials that do not contain basic compounds, if they contain Ca, such as waste gypsum, basic compounds such as calcium oxide or calcium hydroxide can be prepared by chemical treatment, heat treatment, or the like, and these can be used.

[0052] The raw material may further contain other components in addition to the basic compound having an alkaline earth element such as Ca as a constituent element. The hydraulic material, binder, dispersant, and other additives described below can also be blended into the raw material as other components, provided they do not inhibit the fixation of CO2 during the carbonation process. In this case, the content of the hydraulic material and additives may be 64 parts by mass or less, or 50 parts by mass or less, based on 100 parts by mass of the dry mass of the raw material.

[0053] In the carbonation step, the raw materials preferably contain 15 to 40 parts by mass of water per 100 parts by mass of the dry mass. The raw materials can also be considered wet powders. When a long reaction time for carbonation can be ensured, a slurry state (e.g., 100 parts by mass or more of water per 100 parts by mass of the dry mass of the raw materials) is preferable. However, because the concentration of the raw materials in the slurry decreases and the diffusion of carbon dioxide is slow, the reaction rate may be insufficient when a short reaction time is required, such as in on-site carbon dioxide immobilization. Furthermore, while it is desirable to reduce the water content for on-site CO2 immobilization, the reaction sites for water-mediated carbonation are unevenly distributed. Therefore, stirring the raw materials can compensate for this and efficiently immobilize CO2 in a short time.

[0054] The water content of the raw material may be, for example, 17 parts by mass or more, 20 parts by mass or more, or 25 parts by mass or more, per 100 parts by mass of the dry mass of the raw material. By setting the lower limit of the water content of the raw material within the above range, the proportion of water present on the surface of the raw material increases, and the CO2 fixation rate can be further improved. The water content of the raw material may be, for example, 38 parts by mass or less, 37 parts by mass or less, or 35 parts by mass or less, per 100 parts by mass of the dry mass of the raw material. By setting the upper limit of the water content of the raw material within the above range, non-uniform carbon dioxide diffusion due to an increase in water in pores and a resulting decrease in the CO2 fixation rate can be suppressed. The water content of the raw material may be adjusted, for example, by directly adding water.

[0055] In the carbonation process, the raw material is brought into contact with carbon dioxide contained in the exhaust gas while being stirred. By stirring the raw material, it is possible to change the contact surface with carbon dioxide over time, which can further improve the efficiency of CO2 fixation. As mentioned above, in the carbonation process, the raw material needs to be used in the form of a wet powder from the perspective of on-site CO2 fixation. According to the inventors' studies, in the case of wet powder, it has been found that the CO2 fixation rate is significantly reduced when carbonation is attempted in a static state.

[0056] The means for stirring the raw materials is not particularly limited, and examples thereof include a stirring mixer (such as a ribbon mixer or a Nauta mixer), a container mixing mixer (such as a V-type mixer), a mixing transporter (such as a screw feeder), a moving bed reactor (such as a kiln type), and a stirring tank reactor.

[0057] In the carbonation step, the time during which the raw materials are in contact with the carbon dioxide may be adjusted depending on the carbon dioxide content in the exhaust gas, the shape and size of the vessel in which the carbonation step is performed, and the like. In the carbonation step, the time during which the raw materials are in contact with the carbon dioxide may be, for example, 3 minutes or more, 5 minutes or more, 6 minutes or more, or 7 minutes or more. By setting the lower limit of the time within the above range, the reaction time can be ensured and the CO2 fixation rate can be further improved. In the carbonation step, the time during which the raw materials are in contact with the carbon dioxide may be, for example, 20 minutes or less, 18 minutes or less, 15 minutes or less, or 12 minutes or less. Ensuring a long time requires a large reactor for fixating the continuously discharged exhaust gas, which is not suitable for on-site production and tends to increase the production costs of the carbonate cured material. Therefore, by setting the upper limit of the time within the above range, the carbonate cured material can be produced with more practical capital investment and operating costs. In the carbonation step, the time during which the raw material is in contact with the carbon dioxide may be adjusted within the above-mentioned range, and may be, for example, 3 to 20 minutes.

[0058] In the carbonation step, the amount of the basic compound per mole of carbon dioxide may be, for example, 2 moles or less, 1.7 moles or less, or 1.5 moles or less in terms of calcium oxide (or magnesium oxide). By setting the upper limit of the supply amount of the basic compound within the above range, an excessive increase in the amount of the basic compound used can be suppressed, and an increase in operating costs can be suppressed. In the carbonation step, the amount of the basic compound per mole of carbon dioxide may be, for example, 1 mole or more in terms of calcium oxide. By setting the lower limit of the supply amount of the basic compound within the above range, CO2 fixation can be more sufficient, and the amount of calcium carbonate can be increased. In the carbonation step, the amount of the basic compound per mole of carbon dioxide may be adjusted within the above range, and may be adjusted to, for example, 1 to 2 moles, 1 to 1.7 moles, or 1 to 1.5 moles in terms of calcium oxide (or magnesium oxide).

[0059] In one embodiment, the carbonate obtained in the carbonation step may include calcium carbonate and calcium hydroxide. In another embodiment, the carbonate may include magnesium carbonate and magnesium hydroxide. The carbonate may further include components contained in the raw material (e.g., calcium oxide, magnesium oxide, etc.).

[0060] In one embodiment, in the granulation step, a mixture containing the carbonate obtained in the carbonation step and a hydraulic material is stirred and granulated to prepare a carbonate light aggregate (also referred to as a "carbonate hardened material"). The carbonate may be the carbonate obtained in the carbonation step, a carbonate obtained by another method, or a commercially available carbonate. Note that, although the following description may be given in the form of using calcium carbonate as the carbonate, the invention of the present disclosure is not limited thereto, and some or all of the carbonate may be a carbonate of another alkaline earth metal (such as magnesium carbonate).

[0061] The amounts of calcium carbonate, calcium hydroxide, and hydraulic material in the mixture may be adjusted to improve the strength of the carbonate hardened product. In the mixture, the total dry mass of the calcium carbonate, calcium hydroxide, and hydraulic material is 100 parts by mass. For example, the calcium carbonate content may be 31 to 55 parts by mass, the calcium hydroxide content may be 5 to 19 parts by mass, and the hydraulic material content may be 26 to 64 parts by mass. Preferably, the calcium carbonate content may be 35 to 50 parts by mass, the calcium hydroxide content may be 5 to 17 parts by mass, and the hydraulic material content may be 33 to 60 parts by mass. More preferably, the calcium carbonate content may be 40 to 50 parts by mass, the calcium hydroxide content may be 10 to 16 parts by mass, and the hydraulic material content may be 34 to 50 parts by mass. By adjusting the amounts of calcium carbonate, calcium hydroxide, and hydraulic material in the mixture to fall within the above ranges, the carbonate content can be maintained sufficiently high, while the mechanical strength of the carbonate hardened product obtained in the process described below can be further improved. The carbonate hardened material thus obtained is more suitable as an aggregate for ordinary concrete.

[0062] Hydraulic materials are materials that harden through a hydration reaction to form a hardened body. Examples of hydraulic materials include blast furnace slag and pozzolanic substances. Examples of pozzolanic substances include fly ash and siliceous admixtures. Blast furnace slag is a suitable hydraulic material because it is relatively inexpensive and emits little CO2 when produced. Cement compositions containing cement clinker, etc., are also hydraulic materials, but it may be desirable not to use commercially available products because they emit a lot of CO2 when produced. When using a cement composition as the hydraulic material in the present disclosure, it is desirable that the cement composition be recovered from an unnecessary hardened cement body or the like and reused.

[0063] In addition to the carbonate and hydraulic material, the mixture used in the granulation step may further contain other materials, such as water, a binder to promote granulation, and a dispersant.

[0064] By adopting agitation granulation as the granulation method, the resulting carbonate light aggregate (carbonate hardened material) has excellent mechanical strength. Generally, wet granulation and dry granulation are known as granulation methods. Wet granulation methods include agitation granulation, tumbling granulation, fluidized bed granulation, and coating granulation. The reason why agitation granulation produces a hardened material with superior mechanical strength compared to other granulation methods is not entirely clear, but the inventors speculate as follows: (1) First, when a mixture of carbonate and hydraulic material is granulated, the carbonate itself does not undergo a hydration reaction, making it more difficult to ensure mechanical strength than when only the hydraulic material is granulated. In this case, it is believed that the condition for excellent mechanical strength is that the carbonate particles and the hydraulic material particles are thoroughly mixed and in close contact with each other. (2) Among wet granulation methods, tumbling granulation, fluidized bed granulation, and coating granulation are thought to produce a layered structure in the hardened material obtained by stacking multiple layers. During this granulation process, voids tend to form between layers, making it difficult for the carbonate particles and hydraulic material particles to come into close contact. This can lead to the formation of mechanically weak defects between some layers, potentially reducing the mechanical strength of the hardened product. (3) On the other hand, among wet granulation methods, agitation granulation involves agitating the mixture of raw materials for the hardened product and applying centrifugal compression while homogenizing the system. This makes it difficult for a layered structure to form, and the carbonate particles and hydraulic material particles tend to be thoroughly mixed and come into close contact. Therefore, it is believed that the strength of the hardened product obtained by agitation granulation can be improved.

[0065] As described above, agitation granulation can produce dense granules and their hardened products, and allows for continuous production, making it suitable for on-site production of carbonate light aggregate. As an alternative to granulation, a method can be considered in which sufficient water is added to the mixture, followed by casting and crushing after hardening to produce aggregate. However, in this case, a large amount of water is likely to be added to homogenize the material, making it difficult to obtain high mechanical strength.

[0066] In the granulation process, the mixture may contain water. The water may be derived from the carbonate or hydraulic material, or may be added externally. In this specification, the water content of the mixture refers to the total amount of both. As mentioned above, the raw materials used in the carbonation process contain 15 to 40 parts by mass of water per 100 parts by mass of dry mass. However, some of this water may evaporate due to heat generated by the carbonation reaction. The water vaporized by this evaporation is not included in the water content of the mixture. The lower limit of the water content may be, for example, 10 parts by mass or more, 12 parts by mass or more, 15 parts by mass or more, or 17 parts by mass or more per 100 parts by mass of dry mass of the mixture. By keeping the lower limit of the water content within the above range, the setting reaction of the hydraulic material can proceed more sufficiently. The upper limit of the water content may be, for example, 35 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, or 24 parts by mass or less per 100 parts by mass of dry mass of the mixture. By setting the upper limit of the water content within the above range, it is possible to shorten the time required for stirring and granulation, and to more stably prepare a hardened carbonate material. The water content may be adjusted within the above range, for example, to 10 to 35 parts by mass of water per 100 parts by mass of the dry mass of the mixture.

[0067] In the granulation step, the average particle size of the carbonate light aggregate may be adjusted to, for example, 0.4 mm or more. The average particle size may also be adjusted depending on the intended use of the carbonate hardened product. In a preferred embodiment of the concrete composition of the present disclosure, a portion of the coarse aggregate and / or fine aggregate is preferably substituted with (d) an alkaline earth metal carbonate light aggregate. For example, when a portion of the fine aggregate for ordinary concrete is substituted with a carbonate light aggregate, the average particle size of the carbonate hardened product is preferably 0.4 to 1.2 mm, more preferably 0.6 to 1.0 mm. When the carbonate hardened product is used as a coarse aggregate for ordinary concrete, the average particle size of the carbonate hardened product is, for example, preferably 7 to 32 mm or 8 to 31 mm, more preferably 15 to 25 mm. By adjusting the average particle size of the carbonate hardened product to such values, for example, a portion of the fine aggregate or coarse aggregate for ordinary concrete can be substituted with the carbonate hardened product.

[0068] The average particle size in this specification means the value measured by measuring the particle size distribution using the method described in JIS A 1102:2014 "Sieving test method for aggregates" and determining the particle size at which the calculated particle size accumulation curve is 50% of the mass fraction.

[0069] The method for producing a hardened carbonate material may include other steps in addition to the carbonation step and the granulation step, such as a step of adjusting the composition of the mixture, a step of analyzing exhaust gases and carbonates, a step of curing the hardened carbonate material, and a step of adjusting particle size.

[0070] The step of adjusting the composition of the mixture may be a step of adjusting the composition of the carbonate obtained in the carbonation step. The step of adjusting the composition of the mixture is preferably carried out after the carbonation step and before the granulation step. In the adjustment step, at least the hydraulic material may be added to the carbonate to prepare a mixture having a calcium carbonate content of 31 to 55 parts by mass, a calcium hydroxide content of 5 to 19 parts by mass, and a hydraulic material content of 26 to 64 parts by mass, where the total dry mass of calcium carbonate, calcium hydroxide, and hydraulic material is 100 parts by mass. In the preparation step, the above-mentioned composition may be adjusted by adjusting the blending amounts of the carbonate and hydraulic material, or by adding at least one of calcium carbonate and calcium hydroxide from an external source. For example, the composition of the carbonate obtained in the carbonation step may be analyzed to determine the contents of calcium carbonate and calcium hydroxide in the carbonate, and the blending ratio may be adjusted based on these values.

[0071] <(e)Water> There are no particular restrictions on the water used in the concrete composition, and any water that does not affect the strength development or fluidity of the concrete, such as tap water, treated sewage water, or supernatant water from ready-mixed concrete, can be used.

[0072] <Blend amount> The amount of cement (a) in the concrete composition is not limited, but is preferably 180 kg / m 3 More preferably, 200 kg / m 3 The amount of cement (a) in the concrete composition is not limited, but is preferably 500 kg / m 3 may be less than 450 kg / m 3 It may be the following: Alternatively, when the cement composition is used in the region of high strength concrete and the carbonate light aggregate according to the present invention is used, the upper limit of the amount of cement (a) to be blended is, for example, 700 kg / m 3 may be less than 600 kg / m 3 It may be the following:

[0073] The amount of water (e) in the concrete composition is not limited, but is preferably 120 kg / m 3 in terms of unit water amount. 3 More preferably, 130 kg / m 3 or more, and preferably 185 kg / m 3 Less than or equal to 175 kg / m 3 The following is the result.

[0074] The water-to-binder ratio (W / C, sometimes referred to as "water-to-cement ratio") in a concrete composition is not limited, but may be, for example, 20% or more, 30% or more, 40% or more, 50% or more, or 60% or more, and may be 65% or less, or 60% or less. In this specification, "water-to-binder ratio (W / C)" refers to the mass ratio (W / C) of the binder, including water (W) of component (e) and cement (C) of component (a), expressed as a percentage (%). When the composition contains an expansive agent as a binder, the total mass of the cement and expansive agent is used as C in calculating W / C. A water-to-binder ratio within this range facilitates the production of concrete with good strength and fluidity.

[0075] In the concrete composition, the amount of (b) coarse aggregate mixed is, for example, preferably 400 kg / m 3 More preferably, 500 kg / m 3More preferably, 600 kg / m 3 or more, and preferably 1300 kg / m 3 or less, more preferably 1200 kg / m 3 or less, more preferably 1100 kg / m 3 or less, or 950 kg / m 3 It may be the following:

[0076] In the concrete composition, the amount of (c) fine aggregate mixed is, for example, preferably 50 kg / m 3 More preferably, 100 kg / m 3 More preferably, 200 kg / m 3 or more than 300 kg / m 3 or more, and preferably 1300 kg / m 3 or less, more preferably 1200 kg / m 3 Below 1000kg / m 3 Below 900kg / m 3 Below 700kg / m 3 It may be the following:

[0077] The amount of alkaline earth metal carbonate light aggregate (d) in the concrete composition is not limited, but is preferably 100 kg / m 3 More preferably, 120 kg / m 3 More preferably, it is 300 kg / m or more. 3 The amount of alkaline earth metal carbonate light aggregate (d) in the concrete composition is not limited, but is preferably 1200 kg / m 3 in terms of unit amount. 3 Less than 1000 kg / m 3 or less, more preferably 800 kg / m 3 may be less than 700 kg / m 3 Below 500kg / m 3 or less, or 450 kg / m 3 It may be the following:

[0078] In the concrete composition of the present disclosure, it is preferable that a portion of the coarse aggregate and / or fine aggregate is replaced with (d) alkaline earth metal carbonate light aggregate, and it is more preferable that at least a portion of the fine aggregate is replaced with (d) alkaline earth metal carbonate light aggregate. In this specification, "replacement" of aggregate refers to the use of (d) alkaline earth metal carbonate light aggregate in place of normal coarse aggregate and / or normal fine aggregate.

[0079] In one embodiment, a portion of the fine and coarse aggregates in the concrete composition is preferably replaced with carbonate light aggregate. The volume ratio of carbonate light aggregate to the total aggregate volume (the total volume of coarse aggregate, fine aggregate, and carbonate light aggregate) (also referred to as the "volume replacement ratio of carbonate light aggregate to total aggregate") is not limited, but may be preferably 1% or more, 10% or more, 20% or more, or 25% or more, and may be preferably 45% or less, 44% or less, 42% or less, 40% or less, 35% or less, 30% or less, or 25% or less. When the volume replacement ratio of carbonate light aggregate to total aggregate is within the above range, concrete can be formed that has good fresh properties and excellent strength and frost resistance after hardening.

[0080] The mass ratio of carbonate light aggregate to the mass of all aggregates (total mass of coarse aggregate, fine aggregate, and carbonate light aggregate) (also referred to as "mass replacement rate of carbonate light aggregate to all aggregates") is not limited, but may be preferably 1% or more, 5% or more, and may be preferably 37% or less, more preferably 36% or less, 30% or less, 25% or less, or 17% or less.

[0081] In one embodiment, a portion of the fine aggregate in the concrete composition is preferably replaced with carbonate light aggregate, and more preferably with carbonate light aggregate with an average particle size of less than 5 mm. In the concrete composition, the volume ratio of carbonate light aggregate to the total volume of fine aggregate and carbonate light aggregate (also referred to as the "volume replacement ratio of carbonate light aggregate to fine aggregate") is not limited, but may be preferably 1% or more, 10% or more, 20% or more, or 25% or more, and may be preferably 99% or less, 90% or less, 80% or less, 75% or less, 70% or less, 60% or less, 55% or less, or 50% or less. In one embodiment, the volume replacement ratio of carbonate light aggregate to fine aggregate is preferably 20% or more and 60% or less, more preferably 25% or more and 50% or less. When the volumetric replacement ratio of carbonate light aggregate to fine aggregate is within the above range, concrete having good fresh properties and excellent strength and frost resistance can be formed. In one embodiment, for example, in the concrete composition, the volumetric replacement ratio of carbonate light aggregate to fine aggregate is 20% or more and 75% or less, and the blending amount of fine aggregate is 200 to 700 kg / m 3 The blending amount of carbonate light aggregate is 100 to 500 kg / m 3 It is preferable that:

[0082] When a portion of the fine aggregate is replaced with carbonate light aggregate, the mass ratio of the carbonate light aggregate to the total mass of the fine aggregate and carbonate light aggregate (also referred to as the "mass substitution ratio of carbonate light aggregate to fine aggregate") is not limited, but may be preferably 1% or more, 10% or more, 20% or more, or 25% or more, and may be preferably 99% or less, 90% or less, 80% or less, less than 75%, 70% or less, 60% or less, 55% or less, or 50% or less. In one embodiment, the mass substitution ratio of carbonate light aggregate to fine aggregate is preferably 20% or more and 50% or less.

[0083] When a portion of the coarse aggregate is replaced with carbonate light aggregate, the mass ratio of the carbonate light aggregate to the total mass of the coarse aggregate and carbonate light aggregate (also referred to as the "mass replacement rate of carbonate light aggregate to coarse aggregate") is not limited, but may be preferably 1% or more, 10% or more, 20% or more, or 25% or more, and may be preferably 99% or less, 90% or less, 80% or less, less than 75%, 70% or less, 60% or less, 55% or less, or 50% or less.

[0084] <Other ingredients> The concrete composition may contain other components (additives) to the extent that the effects of the present invention are not impaired. Examples of other components include inorganic fine powders such as gypsum and fly ash, thickeners, antifoaming agents, water-reducing agents, high-performance air-entraining water-reducing agents, air-entraining agents, inks, pigments, dispersants, set adjusters, expansive agents, and shrinkage-reducing agents. Air-entraining water-reducing agents and air-entraining agents are chemical admixtures specified in JIS A 6204:2011.

[0085] <Method of manufacturing concrete composition> A concrete composition is produced by mixing components (a) to (e) and, if necessary, other additives to a predetermined mixing ratio and kneading the mixture. The mixing order of the components is not limited, and they may be mixed in any order. Examples of kneading machines used for mixing include tilting barrel mixers, twin-shaft mixers, hand mixers, and Hobart mixers. The temperature of the concrete composition after mixing is preferably adjusted to, for example, about 10°C to 40°C, more preferably about 15°C to 35°C, but this is not limited thereto. The longer the mixing time of the composition, the greater the flow, which then saturates and becomes almost constant. The mixing time is preferably 3 minutes or more in an environment of 20°C or higher. Furthermore, in a low-temperature environment below 20°C, the mixing time of the concrete composition is preferably 5 minutes or more, more preferably 6 minutes or more.

[0086] <Cured product> One aspect of the present disclosure relates to a hardened product of the above concrete composition. The method for producing the hardened product is not limited, but may include a step of molding the mixed concrete composition to obtain a molded body (molding step), and a step of curing the molded body (curing step). The molding method is not particularly limited, and may involve, for example, pouring the concrete composition into a mold (such as a metal or plastic mold). Deaeration may be performed using a vibrator, if necessary. The concrete composition is placed in the mold and left to stand for, for example, about 1 to 5 days to obtain a molded body. When using a core material such as reinforcing bars or steel frames, the core material may be placed in the mold before pouring the concrete composition.

[0087] In the curing step, the molded body obtained in the molding step is cured. The molded body may be demolded before curing. The curing method is not particularly limited, and may be any curing method such as sealed curing or underwater curing. Curing is preferably carried out until the concrete composition solidifies.

[0088] The hardened concrete composition of the present embodiment can be used for a variety of purposes, including but not limited to, building materials and wave-dissipating blocks. [Example]

[0089] The present disclosure will be described in more detail below with reference to Examples, Comparative Examples, Production Examples, and Reference Examples, although the present disclosure is not limited to the following Examples.

[0090] <Materials used> The materials used in the following examples and their abbreviations are shown below. Cement (C): Blast-furnace cement type B (manufactured by UBE Mitsubishi Cement Corporation, density: 3.04 g / cm 3 ) Fine aggregate (S1): Mountain sand (produced in Kimitsu City, Chiba Prefecture, bone dry density: 2.55 g / cm 3 ) and crushed limestone sand (Hachinohe City, Aomori Prefecture, bone dry density: 2.68 g / cm 3 ) mixed sand (mountain sand: crushed limestone sand (mass ratio) = 7:3), fine aggregate (S1) total bone dry density: 2.58 g / cm 3 Carbonate light aggregate (S2): Calcium carbonate light aggregate produced in Production Example 1 described later Fine aggregate (S3): Mesalite (artificial lightweight fine aggregate, manufactured by Nippon Mesalite Kogyo Co., Ltd., bone dry density: 1.68 g / cm 3 , water absorption rate: 13.0%, coarse particle ratio: 2.79, fine particle content: 7.47%) Coarse aggregate (G1): Limestone crushed stone 2005 (Hachinohe City, Aomori Prefecture, bone dry density: 2.67 g / cm 3 , Actual rate: 61%) Coarse aggregate (G2): Limestone crushed stone 2005 (Mine City, Yamaguchi Prefecture, bone dry density: 2.68 g / cm 3 , Actual rate: 61%) Water (W): Tap water (chemical admixture) AE water reducer (AD): Chupol EX60T (Takemoto Oil & Fat Co., Ltd.) Air-entraining agent (AE): AE-300 (Takemoto Oil & Fat Co., Ltd.) Antifoaming agent (AF): Master Air 404 (Pozzolith Solutions, Inc.)

[0091] <Production Example 1: Production of carbonate light aggregate (S2)> As an example of carbonate, a mixture of calcium carbonate (light, manufactured by New Lime Co., Ltd.) and calcium hydroxide (slaked lime, special edition, manufactured by Ube Materials Co., Ltd.) was prepared, and blast furnace slag (trade name: Riverment Gx, manufactured by Chiba Riverment Co., Ltd.) was added as a hydraulic material, to prepare a mixture in which the mass ratio of calcium carbonate, calcium hydroxide, and hydraulic material was 44:11:45.

[0092] 100 parts by mass of the above mixture was weighed out and placed in a 118 L high-speed mixer (FS100, manufactured by EarthTechnica Co., Ltd.) and mixed for 1 minute under conditions of an agitator rotation speed of 140 rpm and a chopper rotation speed of 1500 rpm. 25 parts by mass of tap water was then weighed out and placed in the same high-speed mixer and mixed for 3 minutes under conditions of an agitator rotation speed of 200 rpm and a chopper rotation speed of 1500 rpm. The chopper rotation speed was then increased to 3500 rpm, and the mixture was stirred and granulated for 4.5 minutes to obtain a calcium carbonate hardened product. This calcium carbonate hardened product was used as carbonate light aggregate (S2).

[0093] Carbonate lightweight aggregate (S2) has an oven-dry density of 1.59 g / cm 3 The water absorption rate was 23.4%, the coarse particle rate was 2.46%, the fine particle content was 7.95%, and the average particle size was 0.63 mm. For the concrete composition described below, evaluation was performed when a portion of the fine aggregate S1 was replaced with carbonate light aggregate (S2). The bone-dry density and water absorption rate were determined according to JIS A 1109:2020, the coarse particle rate was determined according to JIS A 1102:2014, and the fine particle content was determined according to JIS A 1103:2014. Figures 2A and 2B are photographs of the carbonate light aggregate (S2) observed with an optical microscope (Figure 2A shows one particle, and Figure 2B shows multiple particles). The granulated carbonate light aggregate (S2) was nearly spherical.

[0094] <Production Example 2: Production of carbonate light aggregate> A raw material was prepared by measuring 100 parts by mass of dust generated in a limestone calciner (manufactured by Ube Material Industries, Ltd., quicklime content 48.1% by mass) and 50 parts by mass of distilled water and mixing them in a 4.7 L Hobart mixer (manufactured by Hobart Japan Co., Ltd., N50). Carbon dioxide (carbonic acid gas) was then passed through 100 parts by mass of dust at a flow rate of 10 L / min for 15 minutes to obtain carbonate. During the carbonation process, the raw material was stirred to maintain a dynamic state. The stirring speed was 139 rpm.

[0095] The carbonate obtained as described above was transferred to a plastic tray and dried at 105°C for 24 hours.

[0096] 55 parts by mass of the carbonate obtained above and 45 parts by mass of blast furnace slag as a hydraulic material were weighed out and placed in an 11 L high-speed mixer (FS10, manufactured by EarthTechnica Co., Ltd.) and mixed for 1 minute under conditions of an agitator rotation speed of 310 rpm and a chopper rotation speed of 3000 rpm. 25 parts by mass of tap water was then weighed out per 100 parts by mass of the dry mass of the obtained mixture and placed in the same high-speed mixer. The mixture was stirred and granulated for 4.5 minutes under conditions of an agitator rotation speed of 310 rpm and a chopper rotation speed of 3000 rpm, yielding a carbonate light aggregate.

[0097] <Bulking of components in concrete composition> The blending ratio of each component in the preparation of the concrete composition is shown in Table 1. The blending ratio is expressed in units of unit amount (kg / m 3 ) The mixing amounts (wt%) of AD, AE, and AF are the mass ratios of each component to the amount of cement used (a). The W / C, s / a, and replacement rates of each aggregate listed in Table 1 are values ​​calculated as follows.

[0098] W / C(%) = 100 x unit amount of W / unit amount of C It was calculated by:

[0099] In addition, the total volume ratio (s / a) of fine aggregate and carbonate light aggregate in the total aggregate was calculated using the following formula. s / a (%) = 100 × (total volume of S1 and S2 (or S3)) / (total volume of S1, S2 (or S3), G1, and G2)

[0100] Volume replacement rate of S2 to fine aggregate (%) = 100 × volume of S2 / (volume of S1 + volume of S2) Volume replacement rate of S3 to fine aggregate (%) = 100 × volume of S3 / (volume of S1 + volume of S3) Volume replacement rate of S2 to total aggregate (%) = 100 × volume of S2 / (volume of S1 + volume of S2 + volume of G1 + volume of G2) Volume replacement rate of S3 to total aggregate (%) = 100 × volume of S3 / (volume of S1 + volume of S3 + volume of G1 + volume of G2) Mass replacement rate of S2 to total aggregate (%) = 100 × mass of S2 / (mass of S1 + mass of S2 + mass of G1 + mass of G2) Mass replacement rate of S3 to total aggregate (%) = 100 × mass of S3 / (mass of S1 + mass of S3 + mass of G1 + mass of G2)

[0101] [Table 1]

[0102] <Evaluation of fresh properties> Cement, fine aggregate, coarse aggregate, and carbonate light aggregate S2 (or fine aggregate S3) were charged into a horizontal biaxial forced mixing mixer to obtain the mix proportions shown in Table 1, and after 30 seconds of dry mixing, water, air-entraining water-reducing agent, air-entraining agent, and antifoaming agent were added and mixed for 120 seconds, and then allowed to stand for 5 minutes to prepare fresh concrete. The concrete composition was mixed in a constant temperature and humidity chamber at a temperature of 20±2°C and a relative humidity of 60±5%. The fresh properties of the concrete composition immediately after mixing were measured using the following test methods: slump, air content, and bleeding rate.

[0103] (slump) The slump of the concrete composition was measured in accordance with JIS A 1101:2020 "Test method for slump of concrete." The target slump value was 12±2.5 cm. The results are shown in Table 2.

[0104] (air volume) The air content of the concrete composition was measured in accordance with JIS A 1128 "Pressure testing method for air content of fresh concrete - Air chamber pressure method." The target value for air content was 4.5±1.5%. The results are shown in Table 2.

[0105] (Concrete temperature) The temperature of the concrete composition after mixing was measured in accordance with JIS A 1156 2006 "Method for measuring temperature of fresh concrete." The results are shown in Table 2.

[0106] (Bleeding rate) The bleeding rate of concrete compositions was measured in accordance with JIS A 1123:2012 "Test method for bleeding of concrete." Bleeding water is the water that rises to the surface of fresh concrete after it is poured. The amount of bleeding water relative to the total amount of water in the sample, expressed as a percentage, was taken as the "bleeding rate." The smaller the bleeding rate, the better. The results are shown in Table 2.

[0107] [Table 2]

[0108] As shown in Table 2, Examples 1-2 to 1-4 achieved the target values ​​for slump and air content. Furthermore, compared to Comparative Examples 2-1 and 2-2, which used mesalite, Example 1-3 showed that it was possible to significantly suppress the occurrence of bleeding, despite the use of carbonate light aggregate (S2), which has a high water absorption rate.

[0109] <Strength evaluation> For the samples of Reference Example 1-1, Examples 1-2 to 1-4, and Comparative Example 1-5 (W / C ratio 55%), cylindrical specimens measuring 100 mm (diameter) x 200 mm (height) were prepared in accordance with JIS A 1132:2020 "Method of preparing specimens for concrete strength tests." The specimens were cured at standard curing conditions until the test age (28 days), and the compressive strength, static modulus of elasticity, and splitting tensile strength were measured using the methods described below. Three specimens were prepared for each sample, and their average values ​​were calculated. The results are shown in Table 3.

[0110] (Compressive strength) The compressive strength of the above-mentioned 28-day-old specimens was measured in accordance with JIS A 1108 "Testing method for compressive strength of concrete."

[0111] (Static elastic modulus) The static elastic modulus of the above-mentioned 28-day-old specimen was calculated in accordance with JIS A 1149:2017 "Test method for static elastic modulus of concrete."

[0112] (splitting tensile strength test) The splitting tensile strength of the above-mentioned 28-day-old specimens was measured according to the method in accordance with JIS A 1113:2018 "Test method for splitting tensile strength of concrete."

[0113] [Table 3]

[0114] As the volumetric replacement rate of S2 to fine aggregate increased, the compressive strength, static modulus of elasticity, and splitting tensile strength tended to decrease. However, Examples 1-2 to 1-4 exhibited good compressive strength, and Examples 1-2 and 1-3 exhibited particularly good compressive strength. On the other hand, Comparative Example 1-5 exhibited low compressive strength. Therefore, it was found that replacing a portion of the fine aggregate with carbonate light aggregate S2 can exhibit good strength after hardening.

[0115] <Freeze resistance test (freeze-thaw test)> Freeze-thaw tests were conducted using specimens (rectangular columns measuring 100 mm long x 100 mm wide x 400 mm high) obtained from the concrete compositions of Example 1-3 and Comparative Example 2-1. The freeze-thaw tests were conducted in accordance with the "underwater freeze-thaw test method" (Method A) specified in JIS A 1148:2010, "Freeze-thaw Test Method for Concrete." The specimens were placed in a container so that the entire surface was covered with water, and the freeze-thaw cycle was repeated. The primary resonance frequency of the flexural vibration according to JIS A 1127 was measured at predetermined cycles. The primary resonance frequency was used to calculate the relative dynamic modulus of elasticity. The results after 0 cycles and 30 cycles are shown in Table 4. In Table 4, the "relative value of the relative dynamic modulus of elasticity" indicates the ratio of the dynamic modulus of elasticity after each cycle for Example 1-3 and Comparative Example 2-1, relative to the relative dynamic modulus of elasticity at 0 cycles for Reference Example 1-1 (where the substitution ratio of carbonate light aggregate S2 and mesalite S3 to the fine aggregate was 0%), taken as 100%.

[0116] [Table 4]

[0117] Compared with Comparative Example 2-1, which used mesalite, Example 1-3, which used carbonate light aggregate, showed a large relative dynamic modulus of elasticity and excellent frost resistance. The inventors discovered that the carbonate light aggregate of the present invention has a large amount of pores of 100 nm or less, particularly 50 nm or less, as described below. This is presumably why the concrete obtained from the composition of the present invention has excellent frost resistance. The results of measuring the pore diameter of the aggregate are shown below.

[0118] <Aggregate pore size distribution> The pore size distribution was measured for the calcium carbonate light aggregate and Mesalite S3 prepared in Production Example 2. Specifically, the pore size range of 500,000 to 5.5 nm was measured using a mercury intrusion porosimeter (Shimadzu Corporation, Autopore IV9500 series).

[0119] FIG. 1A shows the relationship between pore size and cumulative pore volume (the cumulative value (cumulative value) of the volume of each pore, starting from the largest pore size). The horizontal axis of the graph in FIG. 1A represents pore size (nm), and the vertical axis represents cumulative pore volume (mL / g). FIG. 1B shows the relationship between pore size and log differential pore volume (dV / d(logD)). The horizontal axis of the graph in FIG. 1B represents pore size (nm), and the vertical axis represents dV / d(logD) (mL / g). Here, dV represents the differential pore volume, and d(logD) represents the logarithmic differential value of pore size D. The calculation results of the cumulative pore volume for pore sizes of 100 nm or less and 50 nm or less are shown in Table 5 below.

[0120] [Table 5]

[0121] The value at the left end of the graph in Figure 1A is the total pore volume for each sample. For both the carbonate light aggregate of Production Example 2 and mesalite, the pore volume ranged from 0.2 to 0.3 mL / g, with no significant difference observed. However, in Figures 1A and 1B, the pore size distribution of the carbonate light aggregate showed a significant increase near 20 to 30 nm, while the pore size distribution of mesalite was spread across the entire pore size distribution, with no significant peak below 100 nm. Furthermore, when the pore size distribution of the carbonate light aggregate obtained in Production Example 1 was also measured, a similar trend to that observed for the carbonate light aggregate of Production Example 2 was observed.

[0122] The more pores in concrete with sizes greater than 100 to approximately 750 nm, the lower its frost resistance tends to be. On the other hand, the carbonate light aggregate used in the present invention has a large number of pores of 100 nm or less (particularly 50 nm or less) as described above, which is thought to prevent water from entering the pores and therefore has little effect on frost resistance. Therefore, although the carbonate light aggregate in the present disclosure has a total cumulative pore volume similar to that of mesalite, it is presumed that its large number of pores of 50 nm or less allows it to exhibit excellent frost resistance.

[0123] Furthermore, carbonate light aggregates obtained by stirring and granulating raw materials, as in Production Examples 1 and 2, tend to have a high water absorption. The reason why carbonate light aggregates can exhibit excellent frost resistance despite having a higher water absorption than mesalite and the like is thought to be due to the large amount of pores of 100 nm or less (especially 50 nm or less) as described above.

[0124] In the above examples, the carbonate light aggregate was used to replace part of the fine aggregate, but it is believed that similar results can be obtained even if part of the coarse aggregate is replaced with the carbonate light aggregate.

[0125] While preferred embodiments of the present invention are described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only, and that various modifications, changes, and substitutions may be made by those skilled in the art without departing from the invention. It should be understood that various alternative embodiments of the invention described herein may be used in practicing the invention. Furthermore, the contents of all publications, including patents and patent applications, referenced herein should be construed as incorporated by reference as if expressly set forth herein. [Industrial Applicability]

[0126] According to one aspect of the present disclosure, by using granulated alkaline earth metal carbonate light aggregate as part of the aggregate, it is possible to provide a concrete composition that has excellent fresh properties and excellent strength and frost resistance after hardening. In one aspect, the carbonate light aggregate used in the concrete composition of the present disclosure can be obtained by efficiently immobilizing carbon dioxide on-site from carbon dioxide-containing exhaust gas, which can contribute to the realization of a carbon-neutral society.

Claims

1. (a) cement; (b) coarse aggregate; (c) fine aggregate; (d) granulated alkaline earth metal carbonate lightweight aggregate; (e) water; Including, A concrete composition, wherein the carbonate light aggregate has a cumulative pore volume of pores with diameters of 100 nm or less of 0.06 ml / g or more.

2. 2. The concrete composition according to claim 1, wherein a volume ratio of the alkaline earth metal carbonate light aggregate to a total volume of the coarse aggregate, the fine aggregate, and the carbonate light aggregate is 1% or more and 45% or less.

3. 3. The concrete composition according to claim 1, wherein a ratio of the volume of the alkaline earth metal carbonate light aggregate to the total volume of the fine aggregate and the carbonate light aggregate is 1% or more and 99% or less.

4. 3. The concrete composition according to claim 1, wherein a ratio of the volume of the alkaline earth metal carbonate light aggregate to the total volume of the fine aggregate and the carbonate light aggregate is 1% or more and 70% or less.

5. 3. The concrete composition according to claim 1, wherein the carbonate light aggregate has a total cumulative pore volume of 0.15 ml / g or more.

6. 3. The concrete composition according to claim 1, wherein the carbonate light aggregate has a pore size distribution in which the pore size at the maximum peak position of the pore volume is 100 nm or less.

7. 3. The concrete composition according to claim 1, wherein the carbonate light aggregate is derived from waste materials.

8. The concrete composition according to claim 1 or 2, wherein the carbonate light aggregate is an agitated granulated product.

9. 3. The concrete composition according to claim 1, wherein the carbonate light aggregate has a water absorption rate of 15% or more.

10. 3. The concrete composition according to claim 1, wherein the carbonate light aggregate has a spherical shape.

11. The bone dry density of the carbonate light aggregate is 1.3 to 2.7 g / cm ３ 3. The concrete composition according to claim 1 or 2, wherein

12. 3. The concrete composition according to claim 1, wherein the alkaline earth metal carbonate light aggregate has a coarse particle ratio of 2.0 to 3.

5.

13. A hardened concrete composition according to claim 1 or 2.

14. A granulated alkaline earth metal carbonate lightweight aggregate having a cumulative pore volume of pores with diameters of 100 nm or less of 0.06 ml / g or more.

15. 15. The granulated alkaline earth metal carbonate light aggregate according to claim 14, wherein the total cumulative pore volume is 0.15 ml / g or more.

16. 16. The granulated alkaline earth metal carbonate light aggregate according to claim 14 or 15, wherein the pore size at the position of the maximum peak of the pore volume in the pore size distribution is 100 nm or less.

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