Hydraulic components and their blends

Abstract

To provide an admixture for a hydraulic composition useful for fixing carbon dioxide gas and capable of obtaining a hardened body with suppressed drying shrinkage strain, and to provide the hydraulic composition which includes the admixture for the hydraulic composition and which can obtain the hardened body with a high amount of carbon dioxide gas fixation and suppressed drying shrinkage strain.SOLUTION: An admixture for a hydraulic composition comprises a modified concrete powder which has a 50% particle size of 50 μm or less and is a reaction product of a recycled concrete powder and carbon dioxide gas, the modified concrete powder containing calcium carbonate and a silicate. The hydraulic composition comprising the admixture therefor is also provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to admixtures for hydraulic compositions and hydraulic compositions. [Background technology]

[0002] Portland cement, the main raw material for concrete, generates a large amount of carbon dioxide during its manufacturing process due to firing. Therefore, there is a need to suppress the total carbon dioxide emissions from hydraulic compositions such as concrete. One approach to address this is the effective utilization of demolished concrete rubble as a raw material for hydraulic compositions. Currently, concrete rubble obtained from demolishing concrete structures is reused as roadbed material, etc. However, given the limited demand for roads, it is clear that there will be a surplus in the future, and methods for recycling demolished concrete rubble are becoming a challenge.

[0003] Currently, attempts are being made to obtain recycled aggregate by crushing demolished concrete blocks. However, while it is possible to efficiently extract coarse aggregate with a particle size greater than 5 mm, extracting fine aggregate smaller than 5 mm requires excessive energy and is not efficient. Furthermore, there are no effective uses for the fine powder of demolished concrete (hereinafter also referred to as recycled concrete powder) remaining after the aggregate has been extracted. For this reason, although demolished concrete blocks are almost 100% recycled, the majority of the recycled material is used only as crushed material obtained by crushing demolished concrete blocks, as a low-cost material for backfilling, roadbed material, etc. On the other hand, at concrete manufacturing plants, a few percent of the concrete produced is disposed of as leftover concrete or returned concrete. Currently, when disposing of leftover concrete, the residue, which is mainly composed of cement-derived components after the aggregate has been removed, is dewatered and solidified before being disposed of. From the perspective of promoting the recycling of demolished concrete blocks, there is a desire to expand the uses of recycled concrete powder obtained from demolished concrete blocks.

[0004] As previously mentioned, cement generates a large amount of carbon dioxide during its production—specifically, 0.76 tons of carbon dioxide per ton—yet, cement waste is either used as a low-cost construction material or simply buried in landfills. Currently, no special consideration is given to the carbon dioxide sequestration capabilities of concrete itself, particularly demolished concrete blocks, and improvement is desired.

[0005] For the purpose of reusing recycled concrete powder, a method has been proposed in which, when recycling the fine powder generated as a by-product during the production of recycled aggregate from demolished concrete blocks as a cement raw material, a trace amount of waste concrete fine powder that contains almost no calcium hydroxide and preferably has undergone carbonation is added to cement clinker (see Patent Document 1).

[0006] Furthermore, one method aimed at reducing carbon dioxide emissions is to adsorb carbon dioxide into the hardened concrete itself, and various studies are being conducted on this method. A method for producing precast concrete has been proposed in which a hardened body is formed from a concrete mixture containing predetermined amounts of γ-C2S, one or two types of steelmaking slag powder, and Portland cement, with a water-cement ratio (W / C) of 80-250%, and then cured in a carbon dioxide atmosphere after demolding to adsorb a large amount of carbon dioxide (see Patent Document 2). Furthermore, a method has been proposed for recovering waste concrete powder by classifying the coarsely crushed waste concrete material, and then crushing, grinding, and classifying it to obtain carbonated waste concrete powder and uncarbonated waste concrete powder, with the uncarbonated waste concrete powder being used as a decarbonization raw material (see Patent Document 3). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2010-254503 [Patent Document 2] Japanese Patent Publication No. 2011-1684336 [Patent Document 3] Japanese Patent Publication No. 2012-17227 [Overview of the project] [Problems that the invention aims to solve]

[0008] The method described in Patent Document 1 attempts to expand the applications of cement clinker by adding fine powder obtained from concrete waste, particularly fine powder that has undergone significant carbon dioxide conversion, to cement clinker. However, the amount of waste concrete fine powder that replaces cement clinker is less than 5%, and the effective reuse of the fine powder has not been achieved. Although the concrete mixture and the hardened precast concrete body obtained therefrom described in Patent Document 2 use a powder selected for its carbon dioxide adsorption capacity, the method of curing the hardened precast concrete body with carbon dioxide gas has limitations in terms of the surface area of ​​the hardened body, and therefore there is still room for improvement in terms of the amount of carbon dioxide adsorbed. While Patent Document 3 describes waste concrete powder and its recovery method, it intends to differentiate uses based on the quality of the waste concrete powder. However, it merely considers uses for the crushed material by dividing it into decarbonated cement raw material, cement admixture, and ground improvement material based on particle size and degree of carbonation. This is insufficient from the perspective of expanding recycling, even for conventional uses of waste concrete. Furthermore, Patent Document 3 does not focus on actively increasing the added value of waste concrete powder, nor on modifying waste concrete powder for the purpose of increasing its added value.

[0009] An object of one aspect of this disclosure is to provide a hydraulic composition admixture that is useful for carbon dioxide fixation and can produce a hardened body with suppressed drying shrinkage strain. Another aspect of the present disclosure addresses the problem of providing a hydraulic composition admixture useful for carbon dioxide fixation, which can produce a hardened body with a high carbon dioxide fixation rate and suppressed drying shrinkage strain. [Means for solving the problem]

[0010] The solution to the above problems includes the following aspects. <1> It contains modified concrete powder which is a reaction product of recycled concrete powder and carbon dioxide gas, and has a particle size of 50 μm or less for 50% of the particles. The modified concrete powder is an admixture for a hydraulic composition containing calcium carbonate and silicate.

[0011] <2> A hydraulic composition containing a hydraulic binder, an admixture for a hydraulic composition containing modified concrete powder which is a reaction product of recycled concrete powder and carbon dioxide gas and has a particle size of 50 μm or less for 50% of the particles, and water. The modified concrete powder contains calcium carbonate and silicate, and the content of the admixture for the hydraulic composition is 5 to 60 parts by mass with respect to 100 parts by mass of the hydraulic binder.

[0012] <3> The hydraulic composition according to <2>, wherein the admixture for the hydraulic composition contains 10 to 40% by mass of calcium carbonate and 2 to 20% by mass of silicate with respect to the total amount of the admixture for the hydraulic composition. <4> The hydraulic composition according to <2> or <3>, wherein the maximum particle size of the modified concrete powder is 1.2 mm or less.

[0013] <5> The hydraulic composition according to any one of <2> to <4>, which contains 2 to 20% by mass of gypsum with respect to the admixture for the hydraulic composition.

Advantages of the Invention

[0014] According to one aspect of the present disclosure, it is possible to provide an admixture for a hydraulic composition that is useful for carbon dioxide fixation and can obtain a hardened body with suppressed drying shrinkage strain. According to another aspect of the present disclosure, it is possible to provide a hydraulic composition containing an admixture for a hydraulic composition useful for carbon dioxide fixation, having a high carbon dioxide fixation amount, and capable of obtaining a hardened body with suppressed drying shrinkage strain.

Embodiments for Carrying Out the Invention

[0015] The following describes in detail specific examples of admixtures for hydraulic compositions and hydraulic compositions of this disclosure. The following descriptions may be based on typical embodiments of this disclosure, but the following descriptions are illustrative and this disclosure is not limited to the following descriptions. In this disclosure, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the lower and upper limits, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, the term "process" includes not only independent processes but also any process that cannot be clearly distinguished from other processes, as long as its intended purpose is achieved. In this disclosure, unless otherwise specified, the particle size of aggregates and concrete powders refers to the following: Coarse aggregates are those that, when classified using a 5 mm sieve, fail to pass through at least 85% by mass; and fine aggregates are those that pass through a 10 mm sieve completely and contain at least 85% by mass of particles 5 mm or smaller. For aggregate size, the provisions of JIS A5022 (2016) "Recycled Aggregate Concrete M" or JIS A5023 (2016) "Recycled Aggregate Concrete L" shall be applied. For other powders, particle size refers to the 50% particle size.

[0016] In this disclosure, "recycled concrete powder" refers to unprocessed powder which is crushed waste concrete, and "modified concrete powder" refers to the reaction product of recycled concrete powder and carbon dioxide, which is powder that has adsorbed and immobilized carbon dioxide. In this disclosure, "recycled concrete powder" is obtained as residue remaining when waste concrete rubble such as demolished concrete is crushed, or when recycled aggregate is extracted from waste concrete. While waste concrete is largely composed of materials derived from demolished concrete, "recycled concrete powder" in this disclosure is not limited to recycled concrete powder derived from demolished concrete rubble. For example, recycled concrete powder originating from leftover concrete from ready-mixed concrete production, returned concrete, or sludge discharged when washing products at ready-mixed concrete plants is also included in "recycled concrete powder" in this disclosure.

[0017] <Admixture for hydraulic composition> The hydraulic composition admixture disclosed herein comprises modified concrete powder, which is a reaction product of recycled concrete powder and carbon dioxide, having a 50% particle size of 50 μm or less, wherein the modified concrete powder comprises calcium carbonate and silicate. Hereinafter, the admixtures for hydraulic compositions disclosed herein may be simply referred to as "the admixtures of this disclosure."

[0018] (Modified concrete powder) The admixture for hydraulic compositions disclosed herein has a 50% particle size of 50 μm or less, is a reaction product of recycled concrete powder and carbon dioxide, and contains modified concrete powder containing calcium carbonate and silicate. Recycled concrete powder contains approximately 40% by mass or more of cement components derived from waste concrete rubble, with the remainder being aggregate components derived from recycled aggregate mixed in during the crushing and classification of waste concrete rubble, also known as stone powder. The modified concrete powder contained in the admixture of this disclosure is a reaction product of recycled concrete powder and carbon dioxide, obtained by the reaction of cement-derived components in recycled concrete powder with carbon dioxide.

[0019] Modified concrete powder contains calcium carbonate and silicate, and when it reacts with recycled concrete powder and carbon dioxide, it effectively absorbs the carbon dioxide and fixes it within the powder. During this reaction, at least calcium hydroxide and calcium silicate hydrate (hereinafter also referred to as CSH) among the components contained in the cement-derived components are carbonated to produce calcium carbonate and silicate, and the modified concrete powder becomes a dense powder containing calcium carbonate and silicate. It is said that CSH has various compositions, and as an example, the following composition is shown, and the reaction in which CaO contained in CSH is carbonated is explained. Example of CSH: 1.7CaO·SiO2·2.17H2O The CaO contained in the above CSH reacts with carbon dioxide to produce calcium carbonate and silicon dioxide, as shown in the following equation. 1,7CaO·SiO2·2,17H2O → (Carbonation: CO2) →1.7CaCO3+SiO2+2.17H2O

[0020] From the viewpoint of improving the fluidity of the hydraulic composition containing the admixture, the admixture of this disclosure preferably contains 10% to 40% by mass of calcium carbonate and 2% to 20% by mass of silicate, and more preferably contains 17% to 35% by mass of calcium carbonate and 5% to 15% by mass of silicate, based on the total amount of the admixture. The silicic acid may be present in the form of silicon dioxide and silica gel, which is a hydrate of silicon dioxide. Furthermore, as mentioned above, modified concrete powder may contain stone powder derived from recycled aggregate. While the stone powder in modified concrete powder does not react with carbon dioxide, intentionally removing the stone powder through methods such as classification will also remove cement-derived components, resulting in a loss of cement-derived components. By using recycled concrete powder that still contains stone powder, the amount of cement-derived components recovered from concrete blocks can be improved. From the viewpoint of balancing the recovery rate of the modified concrete powder, energy consumption, and carbon dioxide fixation, the stone powder content in recycled concrete powder is preferably 60% by mass or less, and more preferably 50% by mass or less, relative to the total amount of modified concrete powder. It has been confirmed that if the modified concrete powder contains stone powder, the carbon dioxide fixation effect, which is the effect of this disclosure, is not impaired if the amount is 60% by mass or less.

[0021] The raw material for the modified concrete powder is recycled concrete powder with a 50% particle size of 50 μm or less. The particle size of the modified concrete powder, which is a reaction product with carbon dioxide, maintains the particle size of the raw material modified concrete powder. Therefore, in this disclosure, the particle size of the recycled concrete powder and the particle size of the modified concrete powder are estimated to be the same. The modified concrete powder in this disclosure maintains a particle size of 50 μm or less at 50% particle size, which is larger than cement and smaller than fine aggregate. The 50% particle size of the modified concrete powder in this disclosure is the value measured by the following method. Approximately 0.05 g of recycled concrete fine powder was ultrasonically dispersed for 180 seconds using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII: manufactured by Microtrac-Bell Co., Ltd.) with ethanol as the solvent, and the 50% particle size value measured at room temperature (25°C) was adopted.

[0022] The particle size of the modified concrete powder is preferably 50% particle size of 50 μm or less, and more preferably 40 μm or less. Furthermore, the 50% particle size is, in other words, the median particle size of the modified concrete powder, and the modified concrete powder exists with a certain degree of particle size distribution. That is, the modified concrete powder is a mixture of powders with particle sizes smaller than the median of 50 μm and powders with particle sizes larger than that. From the viewpoint of further improving fluidity and strength through the addition of specific admixtures, it is preferable that the modified concrete powder does not contain any powder with a large particle size. More specifically, the maximum particle size of the modified concrete powder is preferably 1.2 mm or less, more preferably 600 μm or less, and even more preferably 150 μm or less.

[0023] There are no particular restrictions on the method for producing modified concrete powder. Modified concrete powder is a reaction product of recycled concrete powder with a 50% particle size of 50 μm or less and carbon dioxide. Therefore, it can be obtained by contacting recycled concrete powder obtained from waste concrete rubble with carbon dioxide and allowing it to react. More specifically, a method for obtaining modified concrete powder involves reacting recycled concrete powder with carbon dioxide at a concentration of 5% or more. The contact with carbon dioxide can be either a dry method, in which the recycled concrete powder is brought into contact with gaseous carbon dioxide, or a wet method, in which the recycled concrete powder is placed in a liquid such as water, and then carbon dioxide is blown into the liquid to bring it into contact. The following is an example of a method for producing modified concrete powder.

[0024] (Dry method) When the reaction between recycled concrete powder and carbon dioxide is carried out by a dry method, one method involves placing the recycled concrete powder in a closed space and then filling the closed space with carbon dioxide at a concentration of 5% or more to bring it into contact with the powder.

[0025] The temperature inside the enclosed space is preferably between 5°C and 200°C, and more preferably between 20°C and 100°C. For example, the carbonation treatment can also be performed in an enclosed space without specific temperature control, under a temperature atmosphere of 0°C to 40°C. The humidity in a closed space can be set to 30%RH to 90%RH, and preferably to 50%RH to 80%RH, from the viewpoint of improving carbonation efficiency.

[0026] The carbon dioxide concentration in the gas to be brought into contact is 5% or more, preferably 10% or more, and more preferably 50% or more. The carbon dioxide gas to be brought into contact may be 100% carbon dioxide. The carbon dioxide used in the carbonation process may be exhaust gas containing carbon dioxide. Examples of exhaust gas include exhaust gas emitted from heating furnaces and exhaust gas emitted from power engines, and there are no particular restrictions as long as it contains carbon dioxide at a concentration of 5% or more. In addition, recovered carbon dioxide emitted from factories, etc., may be used as a supply source. By using exhaust gas containing carbon dioxide in the carbonation treatment, it is possible to simultaneously reduce the amount of carbon dioxide in the exhaust gas and modify the recycled aggregate by adsorbing the carbon dioxide onto it. When the exhaust gas temperature exceeds 100°C, efficient carbonation treatment can be performed without heating a closed space, which has the advantage of simultaneously achieving reduced energy consumption and a reduction in carbon dioxide in the exhaust gas. Furthermore, in order to efficiently carbonate the recycled aggregate, a closed space may be pressurized and carbon dioxide may be supplied and brought into contact with the recycled aggregate.

[0027] The preferred processing time in the dry process is appropriately selected in relation to the carbon dioxide concentration and supply rate. For example, when using carbon dioxide at a concentration of 10% to 50%, the processing time can be 1 hour or more, preferably 24 hours or more, more preferably 2 days or more, even more preferably 5 days or more, and still more preferably 10 days or more. There is no particular upper limit to the processing time, but from the viewpoint of manufacturing efficiency, it can be 20 days or less. The preferred processing time can be appropriately selected depending on the condition of the aggregate and the physical properties of the modified recycled aggregate required. For example, if the amount of cement components adhering to the recycled aggregate is small, and if only the cement powder adhering to the surface and vicinity of the recycled aggregate is to be carbonated, the desired modified recycled aggregate can be obtained in a processing time of 1 to 2 hours. Furthermore, when the processing time in the dry process is 5 days or longer, it is preferable to stir the recycled aggregate, which has been left to stand in a closed space, at a frequency of once every few hours to 3 days, from the viewpoint of making the carbonation process more efficient. Stirring ensures more uniform contact between the recycled aggregate and carbon dioxide, and reduces the amount of unreacted areas, such as parts of the recycled aggregate or parts of individual recycled aggregates that are not carbonized.

[0028] Since the air contains approximately 0.03% by volume of carbon dioxide, one dry processing method involves storing recycled concrete powder in the atmosphere to fix carbon dioxide gas from the air into the recycled concrete powder, thereby obtaining modified concrete powder. When reacting recycled concrete powder with carbon dioxide in the atmosphere, the process can be carried out by placing the recycled concrete powder in an open space. When reacting with carbon dioxide in the atmosphere without temperature control, the reaction time is preferably 12 hours or more, and more preferably 24 hours or more. To increase the frequency of carbon dioxide contact with the recycled concrete powder, the recycled concrete powder may be mixed intermittently.

[0029] (wet method) The wet method involves immersing recycled concrete powder in water and supplying carbon dioxide to the water until the water's pH reaches 6-8. More specifically, it involves filling a container with water containing recycled concrete powder to immerse the recycled aggregate in water, and then bubbling carbon dioxide into the water. There are no particular restrictions on the water used for immersion. From the viewpoint of treatment efficiency, it is preferable that the water used contains few impurities that form salts when in contact with carbon dioxide. As water, for example, industrial water, tap water, or deionized water can be used.

[0030] When using the wet method, the carbon dioxide concentration supplied to the water can be 5%. There is no particular upper limit on the carbon dioxide concentration supplied in the wet method, and the carbon dioxide concentration may be 100%. A higher carbon dioxide concentration leads to better carbonation efficiency of recycled aggregate, allowing for shorter processing times. The supplied carbon dioxide may be exhaust gas containing carbon dioxide, similar to the dry method. When exhaust gas is used as the carbon dioxide source, the carbon dioxide concentration depends on the amount of carbon dioxide contained in the exhaust gas. Even when using exhaust gas, it is preferable that the carbon dioxide concentration in the exhaust gas be 5% or higher.

[0031] The amount of carbon dioxide supplied to the water in which the recycled aggregate is immersed, and the rate at which the carbon dioxide of the above concentration is supplied, can be appropriately selected according to the purpose. By optimizing the total amount and rate of carbon dioxide supply and blowing it in, contact between the recycled aggregate immersed in water and the carbon dioxide is efficiently achieved, and the carbonation of the recycled aggregate progresses. Furthermore, the solubility of carbon dioxide in water increases at lower water temperatures. Therefore, the water temperature does not need to be specifically controlled. Furthermore, when exhaust gas is used as the source of carbon dioxide, the water temperature may rise depending on the temperature of the exhaust gas, but the water temperature will not reach 100°C, so it is not expected to affect the progress of the carbonation treatment of the recycled aggregate.

[0032] There are no particular restrictions on the water temperature in the wet process, and it can be carried out at room temperature. Furthermore, when exhaust gas is used to supply carbon dioxide, the water temperature may rise to, for example, around 90°C due to the temperature and supply rate of the exhaust gas, but the carbonation process can still be performed under these temperature conditions.

[0033] There are no particular restrictions on the processing time using the wet method. The processing time can be, for example, 5 minutes to 10 hours, and preferably 30 minutes to 6 hours. As the carbonation of cement-derived components in recycled aggregate progresses due to contact with carbon dioxide, the pH of the water tends to decrease. Therefore, the end point of the carbonation treatment may be set when the pH of the water reaches 6 to 8. It is preferable to continue the treatment by the wet method until the pH of the water reaches 6.5 to 7.0, and more preferably until the pH reaches 6.5 to 6.8. It is even more preferable to continue the treatment for a further 30 to 90 minutes after the pH of the water reaches the target value, for example, when the pH of the water reaches 6.5 to 7.0. The pH of water in a wet treatment can be measured using a known pH meter. In this disclosure, the values ​​used are those measured with a glass electrode type hydrogen ion concentration indicator (TPX-999Si) from Toko Chemical Research Institute Co., Ltd., at a liquid temperature of 20°C.

[0034] The method for producing modified concrete powder is not limited to the above. Modified concrete powder can be obtained by contacting recycled concrete powder with carbon dioxide in some way, and the obtained recycled concrete powder can be suitably used as an admixture in this disclosure.

[0035] The admixtures in this disclosure are not particularly limited, except that they include recycled concrete powder. The admixtures in this disclosure may consist only of recycled concrete powder, or they may contain recycled concrete powder in addition to other known admixtures.

[0036] The admixtures of this disclosure are suitably used in hydraulic compositions described later. The admixtures of this disclosure, when incorporated into hydraulic compositions such as cement compositions, have the advantage of further improving the fluidity of the hydraulic composition due to the function of the modified concrete powder, and further enhancing the strength development of the hardened body of the hydraulic composition.

[0037] <Hydraulic composition> The hydraulic composition disclosed herein comprises a hydraulic binder, an admixture for hydraulic compositions containing modified concrete powder which is a reaction product of recycled concrete powder and carbon dioxide and has a 50% particle size of 50 μm or less, and water, wherein the modified concrete powder contains calcium carbonate and silicate, and the content of the admixture for hydraulic compositions is 5 to 60 parts by mass per 100 parts by mass of the hydraulic binder.

[0038] Although the mechanism of action of the hydraulic composition disclosed herein is not clear, the inventors believe it to be as follows. The modified concrete powder contained in the hydraulic composition of this disclosure has a higher degree of fineness compared to cement particles, which are hydraulic binders, and is supplied as carbon dioxide-fixed powder, which is a concrete material effective for decarbonization in which carbon dioxide is fixed. While modified concrete powder cannot be expected to be as reactive as cement, its 50% particle size is 50 μm or less, and because it contains both hard calcium carbonate and hydrophilic silicate, it is thought that it can reduce voids larger than 50 nm, which are said to affect strength development. Furthermore, by including modified concrete powder in the hydraulic composition, the amount of powder with smaller particle sizes increases, and water is distributed around the modified concrete powder. Therefore, in the case of hydraulic compositions with the same water / binder ratio, it is presumed that the amount of water distributed around the cement particles will decrease, resulting in a locally smaller water / binder ratio. Consequently, water separation is less likely to occur, and the resistance to separation during mixing of the hydraulic composition is expected to increase, making it possible to realize a low-heat, high-flow concrete. It is generally said that as the amount of powder added increases, the voids in the hardened body of a hydraulic composition increase, and the strength of the hardened body decreases. However, in the hydraulic composition disclosed herein, we believe that the reduction in strength is suppressed while maintaining fluidity due to the above-mentioned effect of the modified concrete powder.

[0039] (Admixture for hydraulic composition) The hydraulic composition disclosed herein includes the admixture for the hydraulic composition disclosed herein. In other words, the hydraulic composition of the present disclosure contains modified concrete powder, which is a reaction product of recycled concrete powder and carbon dioxide, with a 50% particle size of 50 μm or less. The content of the admixture of the present disclosure in the hydraulic composition of the present disclosure is 5 to 60 parts by mass, preferably 10 to 55 parts by mass, and more preferably 20 to 50 parts by mass, per 100 parts by mass of the hydraulic binder.

[0040] The inventors focused on the fact that the cement-derived components contained in recycled concrete powder have high carbon dioxide fixation capabilities. Compared to conventional methods of adsorbing carbon dioxide onto hardened concrete, recycled concrete powder, which has a high degree of fineness and a large surface area, can fix a large amount of carbon dioxide when it reacts with carbon dioxide. The resulting modified concrete powder contains calcium carbonate and silicates produced by the carbonation of calcium hydroxide and CSH contained in the recycled fine aggregate. Furthermore, silicic acid may be included in modified and recycled aggregate in the form of silicon dioxide, or in the form of silica gel, which is a hydrate of silicon dioxide. The admixtures of the present disclosure contained in the hydraulic compositions of the present disclosure are the same as the admixtures of the present disclosure, and the preferred examples are also the same.

[0041] Generally, calcium hydroxide accounts for only about 20% by mass of the cement-derived components. Therefore, simply carbonating calcium hydroxide to obtain calcium carbonate is insufficient for modifying recycled concrete powder, and the amount of carbon dioxide that can be solidified is limited. On the other hand, CSH accounts for about 50% by mass of the cement components. Therefore, the modified concrete powder in this disclosure contains not only calcium carbonate but also silicates, resulting in better fluidity when mixed with the hydraulic composition compared to the recycled concrete powder before modification. This makes it less likely for fine voids, which are one of the factors that reduce the strength of the hardened hydraulic composition, to form. As a result, a high-strength hardened body can be obtained using the hydraulic composition in this disclosure. Furthermore, it becomes possible to solidify a larger amount of carbon dioxide.

[0042] From the viewpoint of improving the fluidity of the hydraulic composition, the admixture contained in the hydraulic composition of this disclosure preferably contains 10% to 40% by mass of calcium carbonate and 2% to 20% by mass of silicate, and more preferably contains 20% to 30% by mass of calcium carbonate and 5% to 15% by mass of silicate, based on the total amount of the admixture.

[0043] (Quantitative determination of calcium carbonate) The calcium carbonate content in modified concrete powder can be determined by thermal analysis. In this disclosure, the calcium carbonate content is calculated from the weight loss at 600°C to 800°C using a thermal analyzer TG-DTA (Rigaku Thermo plus EVO2 TG-DTA8122).

[0044] (Quantitative determination of silicon dioxide) The silicate content in modified concrete powder can be determined by emission spectroscopy. Since silica gel, a silicate, is a hydrated form of silicon dioxide, its content is measured based on the Si element. Modified concrete powder is dissolved in an HCl(1+4) aqueous solution prepared by mixing reagent-grade hydrochloric acid (concentration approximately 35% by mass) with pure water in a volume ratio of 1:4. Undissolved components are further dissolved with 0.2N KOH, and the Si content in the resulting solution is measured using an inductively coupled plasma (ICP) emission spectrometer to confirm the SiO2 gel content. In this disclosure, the values ​​used are those measured using the SPECTROBLUE® EOP ICP emission spectrometer manufactured by Hitachi High-Tech Science Corporation.

[0045] The particle size of the modified concrete powder is preferably 50% particle size of 50 μm or less, and more preferably 45 μm or less. From the viewpoint of further improving the fluidity of the hydraulic composition and the strength of the resulting hardened body, it is preferable that the modified concrete powder does not contain any powder with a large particle size. More specifically, the maximum particle size of the modified concrete powder is preferably 1.2 mm or less, more preferably 600 μm or less, and even more preferably 150 μm or less.

[0046] As previously mentioned, the particle size of modified concrete powder is specified to be 50 μm or less for the 50% particle size. However, the 50% particle size is the median particle size of the modified concrete powder, and the modified concrete powder exists with a certain degree of particle size distribution. In other words, the modified concrete powder is a mixture of powders with particle sizes smaller than the median of 50 μm and powders with particle sizes larger than that. When using the admixtures of this disclosure in a hydraulic composition, the fluidity of the hydraulic composition is improved if the modified concrete powder does not contain large particles, specifically, if the maximum particle size of the modified concrete powder is 1.2 mm or less, more preferably 600 μm or less, and even more preferably 150 μm or less. Furthermore, by not containing particles of the above size, fine voids are less likely to form in the hardened hydraulic composition, resulting in a better strength improvement effect on the hardened body, which is preferable.

[0047] The content of the admixture of this disclosure, which includes modified concrete powder, in the hydraulic composition can be the same as the content of admixtures for general hydraulic compositions. Specifically, it is preferable that the hydraulic binder described later contains 5% to 60% by mass of the admixture of this disclosure, and more preferably 10 to 55 parts by mass.

[0048] (Hydraulic binder) The hydraulic compositions disclosed herein include hydraulic binders such as Portland cement. In this disclosure, the term "hydraulic binder" is used to mean a binder that can be mixed with water to form a hardened body and is included as a main component in the hydraulic composition. Examples of hydraulic binders include concrete, mortar, and grout, and mixed cements in which a portion is replaced with blast furnace slag powder, fly ash, silica fume, etc. are also included in the hydraulic binders of this disclosure.

[0049] The following description will use Portland cement, which is commonly used in concrete compositions, as an example of a hydraulic binder; however, the hydraulic binder in this disclosure is not limited to Portland cement.

[0050] There are no particular restrictions on Portland cement used as a hydraulic binder; it can be appropriately selected from various types of cement depending on the intended use of the hydraulic composition. Portland cement, which is one form of hydraulic binder, includes rapid-hardening Portland cement, ordinary Portland cement, moderate-heat Portland cement, and low-heat Portland cement.

[0051] The content of the hydraulic binder in the hydraulic composition disclosed herein is appropriately selected considering the initial curability, initial strength, long-term strength, and the intended use of the cured hydraulic composition. Typically, the hydraulic binder is included in the hydraulic composition constituting the cured body in a total amount of 270 kg / m³. 3 ~650kg / m 3 Preferably, it should contain 320 kg / m³. 3 ~530 kg / m 3 It is even more preferable to include it.

[0052] In this disclosure, the hydraulic binder content refers to the content of Portland cement when only Portland cement is used as the hydraulic binder, and to the total content of multiple hydraulic binders when a mixed cement is used in which a portion of the Portland cement is replaced with blast furnace slag powder, fly ash, etc.

[0053] (water) The hydraulic composition disclosed herein contains water. There are no particular restrictions on the water used in the hydraulic composition; tap water or similar can be used. The water content in the hydraulic composition can be appropriately selected according to the fluidity of the hydraulic composition and the desired properties of the hardened hydraulic composition, which is the cured product of the hydraulic composition. The water / hydraulic binder content ratio is 18 N / mm², which is the compressive strength of the final hardened hydraulic composition. 2 It is preferable to maintain a range that exhibits the above strength. Furthermore, from the viewpoint of suppressing the carbonation reaction with carbon dioxide in the atmosphere and protecting the reinforcing bars placed within the hardened hydraulic composition from corrosion, the water / hydraulic binder content is preferably 60% or less by mass, and more preferably 50% or less. In hydraulic compositions for forming hardened bodies, the strength and physical properties of the hardened body can be adjusted not only by adjusting the ratio of water to cement, but also by adjusting the aggregate content, and further by adjusting the content of various materials such as admixtures and hardening accelerators, which are optional components.

[0054] (Other ingredients) The hydraulic compositions disclosed herein may further contain, in addition to the hydraulic binder, the binder for hydraulic compositions, and water described above, other components as needed, provided that the effects are not impaired. Other components include aggregates such as fine aggregate and coarse aggregate, and various additives used in hydraulic compositions, such as gypsum, admixtures, reaction modifiers, water-reducing agents, air-entraining agents, defoaming agents, hardening accelerators, setting retarders, shrinkage-reducing agents, thickeners, preservatives, rust inhibitors, and fast-setting admixtures.

[0055] (plaster) The hydraulic compositions disclosed herein may further contain gypsum. The hydraulic composition of this disclosure preferably contains 2% to 20% by mass of gypsum in addition to the admixture of this disclosure described above. If the hydraulic composition of the present disclosure contains gypsum, the gypsum content is more preferably 2% to 20% by mass, and even more preferably 10% to 15% by mass, relative to the admixture of the present disclosure described above. Furthermore, if the hydraulic composition contains gypsum, the gypsum content is preferably 1% to 30% by mass, more preferably 3% to 20% by mass, and even more preferably 5% to 15% by mass, relative to the total amount of the hydraulic binder and the modified concrete powder. By containing the specified amount of gypsum in the hydraulic composition disclosed herein, initial expandability is imparted to the hardened hydraulic composition, reducing drying shrinkage that causes cracking of the hardened body, thereby minimizing the decrease in compressive strength.

[0056] There are no particular restrictions on the gypsum that can be used in the hydraulic composition of this disclosure, and known gypsums can be used. For example, any of the following gypsums may be used: dihydrate gypsum, anhydrous gypsum, etc., and one or more of these may be used. As gypsum, recycled gypsum produced from the SO3 component derived from cement contained in demolished concrete rubble may also be used. In particular, from the viewpoint of having a better effect in suppressing drying shrinkage of the hardened hydraulic composition obtained from the hydraulic composition, dihydrate gypsum and anhydrous gypsum are preferred.

[0057] (aggregate) The hydraulic compositions disclosed herein may optionally contain aggregates such as fine aggregates and coarse aggregates. There are no particular restrictions on the aggregates that can be used in hydraulic compositions. Depending on the desired size and physical properties of the hardened body, known fine aggregates and coarse aggregates can be used, and the content can be arbitrarily selected within a range that does not impair the effect, similar to hydraulic compositions such as general concrete compositions. Recycled fine aggregate and recycled coarse aggregate obtained from demolished concrete blocks may be used as fine aggregate and coarse aggregate, respectively. Depending on the intended use of the hardened material, aggregate may not be required, in which case the hydraulic composition can be prepared without using aggregate.

[0058] (Fine aggregate) Fine aggregates used include high-quality, hard natural sand, crushed sand, and processed sand. The type and content of fine aggregates should be appropriately selected according to the target strength of the hardened hydraulic composition. When using crushed or processed sand, it is also acceptable to use sand with treated edges or adjusted particle size. Furthermore, recycled fine aggregate obtained by crushing and classifying demolished concrete blocks may be used to replace some or all of the conventional aggregate. When fine aggregate with a high SiO2 content is used, the components of the fine aggregate react, albeit slightly, during high-temperature curing, which is considered effective in increasing the strength of the hardened hydraulic composition. From this perspective, fine aggregate containing 70% or more SiO2, such as rhyolite or quartz-based fine aggregate, is preferred.

[0059] (coarse aggregate) When using coarse aggregate in addition to fine aggregate, it is preferable to use high-quality, hard coarse aggregate. The maximum particle size of the coarse aggregate must be 20 mm or less, and preferably 15 mm or less. As for the rock type, it can be appropriately selected from common types such as hard sandstone, andesite, and rhyolite, depending on the target strength. Including coarse aggregate in the concrete composition further improves the strength of the resulting hydraulic composition hardened body. As coarse aggregate, recycled coarse aggregate obtained by crushing and classifying demolition concrete blocks may be used to replace some or all of the regular aggregate.

[0060] The hydraulic composition can be prepared by known methods. For example, one method involves mixing at least the hydraulic binder described above, and other additives such as gypsum and reaction modifiers as needed, in a mixer, thoroughly mixing them, and then adding water and the admixture of this disclosure and mixing them. If the hydraulic composition contains aggregate as needed, the amount of aggregate to be added is appropriately selected considering the intended use of the hardened body, economic efficiency, handling, etc. Typically, for example, the amount of coarse aggregate with a size of 5 mm or larger is preferably in the range of 25 to 45 parts per 100 parts per volume of the hydraulic composition. The amount of fine aggregate with a size of 5 mm or smaller is preferably in the range of 50 to 100 parts per 100 parts per volume of the hydraulic composition. The mixing time for the hydraulic composition after adding each component is typically about 1 to 3 minutes. In this way, a hydraulic composition for forming a hardened body is prepared.

[0061] The hydraulic composition disclosed herein exhibits improved fluidity in the fresh state after mixing, due to the appropriate interaction of the admixture described herein with the hydraulic binder, and can be easily injected into formwork even at low water / binder ratios. Furthermore, due to the function of the modified concrete powder in the admixture of the disclosed herein, the resulting hardened hydraulic composition has fewer fine voids and good strength.

[0062] The hydraulic compositions described herein have good fluidity, and therefore can be easily injected into formwork. Furthermore, according to the hydraulic composition of this disclosure, in the manufacturing process, the modified concrete powder contained in the admixture of this disclosure can immobilize a large amount of carbon dioxide when it reacts with carbon dioxide, and the hardened hydraulic composition obtained has high strength, so it is expected that the recycling of demolished concrete will be promoted and the environmental burden will be reduced. [Examples]

[0063] The following will describe in detail, with specific examples, the admixtures for hydraulic compositions, hydraulic compositions, and methods for producing the same as disclosed herein. However, the following examples are merely illustrative, and various modifications can be made in accordance with the spirit of this disclosure.

[0064] <Manufacturing of modified concrete powder> The concrete blocks generated during the demolition of the building were crushed to obtain fragments smaller than 40 mm. The obtained pulverized material was classified to separate recycled coarse aggregate and recycled fine aggregate, and the resulting powder was recovered as recycled concrete powder. The 50% particle size of the recycled concrete powder measured by the method described above was 27 μm.

[0065] (wet method) The recycled concrete powder obtained above and distilled water were added to a 20L bottle and allowed to stand for 60 minutes. The slurry concentration was 125 g / L. Carbon dioxide gas was supplied into the bottle at a rate of 30 L / min, and while stirring with a stirrer, the supply of carbon dioxide gas was continued until the pH of the slurry fell to 6.8 or below. After that, it was allowed to stand for 60 minutes, and the water was removed to recover the modified concrete powder A.

[0066] (Dry method) The recycled concrete powder obtained above was uniformly placed to a thickness of 5 cm in a tank with an ambient temperature of 20°C, humidity of 60% RH, and carbon dioxide concentration of 10%, and exposed to carbon dioxide for 9 days. The recycled concrete powder was stirred every two days to ensure that the entire powder was in contact with carbon dioxide, thereby obtaining modified concrete powder B.

[0067] (Evaluation of concrete powder) 1.50% particle size Approximately 0.05 g of powder was ultrasonically dispersed for 180 seconds using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII: manufactured by Nikkiso Co., Ltd.) with ethanol as the solvent, and then the 50% particle size was measured at room temperature (25°C). 2. Density The density was measured by gas-phase displacement method in accordance with JIS R1620 (1995), taking into account the possibility of dissolution in water by the Archimedes method.

[0068] 3. Calcium carbonate and silicate content (Calcium carbonate) The amount of calcium carbonate in the obtained modified concrete powder was determined by the TG-DTA apparatus described above, by weight loss at 600°C to 800°C. The mass at 100°C was used as the reference. (Silicate) The silicate content was quantified in terms of Si elements using the following method. Concrete powder was dissolved in an HCl(1+4) aqueous solution prepared by mixing reagent-grade hydrochloric acid (concentration approximately 35% by mass) with pure water in a volume ratio of 1:4. Undissolved components were further dissolved with 0.2N KOH, and the Si content in the resulting solution was measured using an inductively coupled plasma (ICP) emission spectrometer to confirm the SiO2 gel content. The SPECTROBLUE® EOP ICP emission spectrometer, manufactured by Hitachi High-Tech Science Corporation, was used.

[0069] 4. Carbon dioxide content The amount of carbon dioxide (CO2) contained in the powder was calculated from the calcium carbonate content of the powder.

[0070] 5. Content of stone powder The content of the concrete powder was measured with the undissolved portion after dissolving KOH as described above as the insoluble residue, that is, the stone powder derived from the aggregate.

[0071] Furthermore, the same measurement and evaluation were also carried out on the untreated recycled concrete powder that had not reacted with carbon dioxide gas. The results are shown in Table 1 below.

[0072]

Table 1

[0073] From the above results, the modified concrete powder, which is the reaction product of the recycled concrete powder and carbon dioxide gas, showed a density similar to or higher than that of the unreacted recycled concrete powder. Also, in the modified concrete powder, the contents of calcium carbonate and silica gel, which is siliceous, were more than those in the recycled concrete powder. In particular, in the treatment by the wet method, it was found that the adsorbability of carbon dioxide gas and the calcium carbonate content were higher.

[0074] 〔Examples 1 to 4, Comparative Examples 1 to 2〕 (Preparation of mortar composition) A mortar composition was prepared according to the following formulation and the contents in Table 2. The hydraulic binder, fine aggregate, and modified concrete powder (or recycled concrete powder) used for the preparation of the mortar composition are as follows. 1. Hydraulic binder * Ordinary Portland cement (density: 3.16 g / cm 3 , specific surface area: 3140 cm 2 / g) 2. Fine aggregate * Fine aggregate: No. 4 silica sand (2.64 g / cm 3 ), No. 5 silica sand (2.63 g / cm 3 ), and No. 6 silica sand (2.63 g / cm 3A mixture of ) in a mass ratio of 0.3:0.5:0.2. 3. Modified concrete powder *Modified concrete powder A (dry method, density: 2.53 g / cm³) 3 ) *Modified concrete powder B (wet method, density: 2.58 g / cm³) 3 ) 4. Recycled concrete powder Control example: Untreated recycled concrete powder that has not been reacted with carbon dioxide (density: 2.51 g / cm³) 3 ) In the tables below, modified concrete powder A, modified concrete powder B, and recycled concrete powder may be abbreviated as modified powder A, modified powder B, and recycled powder, respectively. In Table 2 below, F represents recycled powder or modified powder, C represents Portland cement (a hydraulic binder), W represents water, and S represents fine aggregate.

[0075] [Table 2]

[0076] Of the aforementioned materials, Portland cement, modified or recycled powder, and fine aggregate were dry-mixed in a forced twin-screw mixer for 30 seconds, then water was added and mixed for 2 minutes to obtain a mortar composition. The water / binder ratio was set to 50.0% by mass.

[0077] (Evaluation of mortar composition) 1. Flow value Flow values ​​were measured in accordance with JIS R5201 (2015). 2. Compressive strength In accordance with JIS A1108 (2018), drying shrinkage strain at 4 weeks (28 days) of age was measured. Samples were used that had been demolded for 1 day and then subjected to simple thermal insulation curing. The formwork dimensions were set to a diameter of 50 mm and a length of 100 mm. 3. Drying shrinkage The compressive strength at 4 weeks of age was measured in accordance with JIS A1129 (2009). The formwork dimensions were set to 40mm x 40mm x 160mm. The results are shown in Table 3 below.

[0078] [Table 3]

[0079] As is clear from Table 3, the mortar compositions of Examples 1 to 4 using the modified concrete powder contained in the admixture of this disclosure had flow values ​​equivalent to or better than those of the mortar compositions of Comparative Examples 1 and 2, which contained recycled concrete powder that had not reacted with carbon dioxide, and the fluidity was at a level that posed no practical problems. The hardened bodies obtained from the mortar compositions of Examples 1 to 4 all exhibited a compressive strength of 40 N / mm², which is acceptable for practical use. 2 This significantly exceeded the previous result. Furthermore, it was found that the hardened bodies obtained from the mortar compositions of Examples 1 to 4 had equivalent compressive strength to those obtained from the mortar compositions of Comparative Examples 1 and 2, and exhibited even greater suppression of drying shrinkage strain.

[0080] [Examples 5-16, Comparative Examples 3-4] (Preparation of mortar composition) Mortar compositions were prepared according to the following formulation, in accordance with the mass ratios of each component listed in Table 4. The hydraulic binder, fine aggregate, gypsum, admixtures, and modified concrete powder (or recycled concrete powder) used in the preparation of the mortar composition are as follows: 1.Hydraulic binder *Ordinary Portland cement (density: 3.16 g / cm³) 3 , Specific surface area: 3140cm 2 / g) 2. Fine aggregate *Fine aggregate: Silica sand No. 4 (2.64g / cm³) 3 ), silica sand No. 5 (2.63g / cm³) 3 ), and silica sand No. 6 (2.63 g / cm³) 3 A mixture of ) in a mass ratio of 0.3:0.5:0.2. 3. Modified concrete powder (same as the powder used in Examples 1 to 4) *Modified concrete powder A (dry method, density: 2.45 g / cm³) 3 ) *Modified concrete powder B (wet method, density: 2.57 g / cm³) 3 ) 4. Recycled concrete powder (same powder as in Comparative Examples 1 and 2) Control example: Untreated recycled concrete powder that has not been reacted with carbon dioxide (density: 2.465 g / cm³) 3 ) 5.Gypsum *Gypsum dihydrate (density 2.31g / cm 3 )

[0081] In Table 4 below, F represents recycled or modified powder, C represents Portland cement (a hydraulic binder), W represents water, S represents fine aggregate, and P represents gypsum.

[0082] [Table 4]

[0083] Of the aforementioned materials, Portland cement, modified powder, or recycled powder, fine aggregate, and optionally used gypsum were dry-mixed in a forced twin-screw mixer for 30 seconds, then water was added and mixed for 2 minutes to obtain a mortar composition. The water / binder ratio was set to 50.0% by mass.

[0084] (Evaluation of mortar composition) Flow value, compressive strength, and drying shrinkage strain were evaluated in the same manner as in Example 1. The results are shown in Table 5. The compressive strength of the hardened mortar composition was measured using a 28-day-old sample that had undergone simple thermal insulation curing after demolding for one day. The evaluation results for flow value, compressive strength of the hardened body, and drying shrinkage strain are shown in Table 5 below.

[0085] [Table 5]

[0086] As is clear from Table 5, the mortar compositions of Examples 5 to 16, which contained modified concrete powder, all showed flow values ​​that were practically acceptable. Furthermore, the compressive strength at 4 weeks of age is 40 N / mm², which is a practically acceptable value. 2 It surpassed that. In all of the examples, drying shrinkage strain was improved compared to Comparative Examples 3 and 4, which contained equal amounts of untreated recycled concrete powder. In particular, the hardened mortar compositions of Examples 6 and 7, which contain modified concrete powder and gypsum, were found to exhibit better drying shrinkage strain compared to the hardened mortar composition of Example 5, which does not contain gypsum at the same level.

Claims

1. A hydraulic binder, an admixture for hydraulic compositions containing modified concrete powder which is a reaction product of recycled concrete powder and carbon dioxide, with a 50% particle size of 50 μm or less, and containing water, The aforementioned modified concrete powder contains calcium carbonate and silicate, The content of the calcium carbonate in the total amount of the admixture for the hydraulic composition is 10% by mass to 40% by mass. The content of the siliceous admixture for hydraulic compositions relative to the total amount is 2% by mass to 20% by mass. The content of the admixture for the hydraulic composition is 30 parts by mass to 60 parts by mass based on 100 parts by mass of the hydraulic binder.

2. The hydraulic composition according to claim 1, wherein the maximum particle size of the modified concrete powder is 1.2 mm or less.

3. The hydraulic composition according to claim 1 or claim 2, comprising 2% to 20% by mass of gypsum with respect to the total solid content of the hydraulic composition.

4. An admixture for hydraulic compositions containing modified concrete powder, which is a reaction product of recycled concrete powder and carbon dioxide, with a 50% particle size of 50 μm or less. The maximum particle size of the modified concrete powder is 1.2 mm or less. The aforementioned modified concrete powder contains calcium carbonate and silicate, The content of the calcium carbonate in the total amount of the admixture for the hydraulic composition is 10% by mass to 40% by mass. The admixture for hydraulic compositions wherein the content of the siliceous substance relative to the total amount of the admixture for hydraulic compositions is 2% by mass to 20% by mass.

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