Cement composition, method for producing cement composition, mortar composition, and concrete composition

Abstract

To improve the removability of hardened bodies from storage containers during long-term storage, while maintaining good compressive strength for a cement composition that can effectively utilize recycled gypsum recovered from waste gypsum.SOLUTION: A cement composition comprises cement clinker, gypsum containing recycled gypsum containing anhydrous gypsum, and limestone. The pH of a suspension containing 5.0 g of recycled gypsum and 100 mL of water is 10.0 to 13.0. The SO3 content of cement clinker is 0.3 to 1.6 mass% based on the mass of the cement clinker. The proportion of recycled gypsum in gypsum is 10 to 80 mass% based on the total mass of the gypsum, in SO3 equivalent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to cement compositions, methods for producing cement compositions, mortar compositions, and concrete compositions. [Background technology]

[0002] In order to effectively utilize waste gypsum, various methods for producing recycled gypsum from waste materials such as waste gypsum boards have been investigated (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-001567 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-146420 Summary of the Invention [Problem to be solved by the invention]

[0004] Cement compositions are sometimes stored in storage containers such as silos for long periods of time before use. When the cement composition is stored for a long period of time, the cement composition hardens strongly, making it difficult to extract the cement composition from the storage container. This difficulty in extraction has been a problem, particularly in the case of cement compositions containing gypsum dihydrate.

[0005] The present disclosure relates to a cement composition that can effectively utilize recycled gypsum recovered from waste gypsum, and to improving the ease of removal from a storage container during long-term storage while maintaining good compressive strength of the hardened body. [Means for solving the problem]

[0006] The present disclosure includes the following: [1] A cement composition comprising cement clinker, gypsum including recycled gypsum containing anhydrous gypsum, and limestone, The SO content of the cement clinker is 0.3 to 1.6 mass% based on the mass of the cement clinker; The pH of the suspension containing 5.0 g of the recycled gypsum and 100 mL of water is 10.0 to 13.0, The content of the gypsum is 0.50 to 2.9 mass% in terms of SO3 based on the mass of the cement composition, The proportion of the recycled gypsum in the gypsum is 10 to 80 mass% in terms of SO3 based on the total mass of the gypsum. Cement compositions. [2] The BET specific surface area of ​​the recycled gypsum is 3.0 to 9.0 m 2 / g of the cement composition according to [1]. [3] The cement composition according to [1] or [2], wherein the content of the recycled gypsum is 0.13 to 1.08 mass % in terms of SO3, based on the mass of the cement composition. [4] The cement composition according to any one of [1] to [3], wherein the content of the limestone is 1.0 to 15 mass % based on the mass of the cement composition. [5] The cement composition according to [1], wherein the mass of the recycled gypsum is reduced by 2.5 mass% or less when the recycled gypsum is heated at 700°C, based on the mass of the recycled gypsum before heating. [6] The SO content of the cement clinker is 0.3 to 0.7 mass% based on the mass of the cement clinker; The proportion of the recycled gypsum in the gypsum is 10 to 60 mass% in terms of SO3 based on the total mass of the gypsum. The cement composition according to any one of [1] to [5]. [7] The SO content of the cement clinker is more than 0.7% by mass and not more than 1.6% by mass, based on the mass of the cement clinker; The proportion of the recycled gypsum in the gypsum is 30 to 80 mass% in terms of SO3 based on the total mass of the gypsum. The cement composition according to any one of [1] to [5]. [8] A method for producing the cement composition according to any one of [1] to [7], The method includes mixing the cement clinker, the gypsum, and the limestone. [9] 1. A method for producing a cement composition, comprising mixing cement clinker, gypsum including recycled gypsum containing anhydrous gypsum, and limestone, The SO content of the cement clinker is 0.3 to 1.6 mass% based on the mass of the cement clinker; The pH of the suspension containing 5.0 g of the recycled gypsum and 100 mL of water is 10.0 to 13.0, The content of the gypsum is 0.50 to 2.9 mass% in terms of SO3 based on the mass of the cement composition, When the SO3 content of the cement clinker is 0.3 to 0.7 mass% based on the mass of the cement clinker, the proportion of the recycled gypsum in the gypsum is 10 to 60 mass% in terms of SO3 based on the total mass of the gypsum, When the SO3 content of the cement clinker is more than 0.7 mass% and not more than 1.6 mass% based on the mass of the cement clinker, the proportion of the recycled gypsum in the gypsum is 30 to 80 mass% in terms of SO3 based on the total mass of the gypsum.

[10]

[11] A mortar composition comprising the cement composition according to any one of [1] to [7], fine aggregate, and water. A concrete composition comprising the cement composition according to any one of [1] to [7], fine aggregate, coarse aggregate, and water. [Effects of the Invention]

[0007] A cement composition containing recycled gypsum containing anhydrous gypsum recovered from waste gypsum can be improved in ease of removal from a storage container during long-term storage while maintaining good compressive strength of the hardened body. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention is not limited to the following examples.

[0009] In this specification, the SO3-equivalent content of each component in a cement composition refers to the content of compounds containing sulfur element in each component, calculated by assuming that all compounds containing sulfur element (sulfur oxides, etc.) contained in each component are SO3. The content and proportion of each component expressed in SO3 equivalent is a value calculated as the proportion of the SO3-equivalent content of each component.

[0010] An example of a cement composition according to the present disclosure includes cement clinker, gypsum including recycled gypsum, and limestone.

[0011] Recycled gypsum is a material derived from waste gypsum and includes anhydrous gypsum. Recycled gypsum including anhydrous gypsum is formed, for example, by firing waste gypsum recovered from used gypsum components. The used gypsum components may be, for example, waste gypsum board generated by the demolition of buildings. In other words, the recycled gypsum may be derived from waste gypsum board. The proportion of anhydrous gypsum in the recycled gypsum may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the mass of the recycled gypsum. It may also be 100% by mass or less.

[0012] Waste gypsum generally contains gypsum dihydrate and often further contains paper and organic admixtures. For example, particulate recycled gypsum containing anhydrous gypsum can be obtained by a method including pulverizing a material containing waste gypsum and firing the pulverized material. The firing temperature for forming the recycled gypsum may be, for example, 600 to 800°C or 650 to 750°C. Paper and the like may be removed from the pulverized material before firing.

[0013] The BET specific surface area of ​​recycled gypsum is 3.0 to 9.0 m 2 / g. Cement compositions containing recycled gypsum having a BET specific surface area in this range tend to be superior in terms of good compressive strength of the hardened body and ease of removal from a storage container after long-term storage. From the same perspective, the BET specific surface area of ​​recycled gypsum may be 3.5 m 2 / g or more, 4.0m 2 / g or more, or 4.5m 2 / g or more, and 2 / g or less, 8.0m 2 / g or less, 7.5m 2 / g or less, 7.0m 2 / g or less, 6.5m 2 / g or less, 6.0m 2 / g or less, 5.5m 2 / g or less, 5.0m 2 / g or less or 4.8m 2 / g or less. The BET specific surface area here refers to a value measured in accordance with the method described in JIS R 8830:2013 "Method for measuring specific surface area of ​​powder (solid) by gas adsorption," and may be a value measured by the method described in the Examples below. Recycled gypsum having a BET specific surface area within the above range can be obtained, for example, by adjusting the conditions for pulverizing the waste gypsum, the conditions for particle size adjustment, and the conditions for firing.

[0014] The pH of a suspension containing 5.0 g of recycled gypsum and 100 mL of water may be 10.0 to 13.0. Cement compositions containing recycled gypsum with a pH in this range tend to be easily removed from storage containers after long-term storage while maintaining good compressive strength of the hardened body. From the same perspective, the pH of the suspension may be 10.4 or more, 10.6 or more, 10.8 or more, or 11.0 or more, and may be 12.5 or less, 12.0 or less, or 11.5 or less. The pH of the suspension here is a value measured by a method in accordance with JIS R 9101:2018.

[0015] The unburned carbon content (C content) of the recycled gypsum may be 1.00% by mass or less, 0.50% by mass or less, or 0.30% by mass or less. A C content within the above range ensures excellent fluidity for cement paste and fresh concrete, while also preventing carbon from floating away from the recycled gypsum. The C content can be measured using a carbon-sulfur analyzer by non-dispersive infrared absorption spectroscopy.

[0016] The gypsum content in the cement composition may be 0.50 to 2.9 mass% in terms of SO3, based on the mass of the cement composition. If the gypsum content is 2.9 mass% or less, the cement composition containing anhydrous gypsum tends to exhibit a moderately long initial settling time. From the same viewpoint, the gypsum content in terms of SO3 may be 2.5 mass% or less, 2.2 mass% or less, 1.8 mass% or less, or 1.5 mass% or less. The gypsum content in terms of SO3 may be 1.0 mass% or more.

[0017] The percentage of mass loss when recycled gypsum is heated at 700°C (hereinafter sometimes referred to as "loss on ignition") may be 2.5% by mass or less based on the mass of the recycled gypsum before heating. When the loss on ignition is 2.5% by mass or less, better effects tend to be obtained in terms of fluidity as a cement paste or fresh concrete containing the cement composition. From the same perspective, the loss on ignition of the recycled gypsum may be 2.0% by mass or less, or may be 0.1% by mass or more, 0.5% by mass or more, or 1.0% by mass or more. The loss on ignition is a value measured in accordance with the method described in "5.2 For materials other than blast furnace cement and blast furnace slag" in "5. Method for determining loss on ignition" of JIS R 5202:2010.

[0018] The proportion of recycled gypsum in the gypsum contained in the cement composition may be 10 to 80 mass% in SO3 equivalent, based on the total mass of the gypsum. When the proportion of recycled gypsum is within this range, the cement composition containing recycled gypsum tends to be easy to remove from a storage container after long-term storage while maintaining good compressive strength of the hardened body. From the same perspective, the proportion of recycled gypsum may be 15 mass% or more, based on the total mass of the gypsum, in SO3 equivalent, and may be 75 mass% or less, 70 mass% or less, 65 mass% or less, 60 mass% or less, 55 mass% or less, 50 mass% or less, or 45 mass% or less. The proportion of recycled gypsum here refers to the ratio of the SO3 equivalent content of recycled gypsum to the SO3 equivalent content of gypsum.

[0019] The recycled gypsum content may be 0.13 to 1.08 mass% in SO3 equivalent, based on the mass of the cement composition. When the recycled gypsum content is within this range, the cement composition containing anhydrous gypsum tends to be easy to remove from a storage container after long-term storage while maintaining good compressive strength of the hardened body. From the same perspective, the recycled gypsum content may be 0.15 mass% or more, 0.20 mass%, 0.40 mass%, or 0.70 mass% or more, based on the mass of the cement composition, in SO3 equivalent, and may be 1.0 mass% or less, 0.95 mass% or less, or 0.90 mass% or less.

[0020] The limestone may be, for example, a powder containing calcium carbonate as its main component, such as commercially available limestone powder or kansui stone powder. The limestone may also include limestone conforming to the minor mixing components specified in JIS R 5210:2009 "Portland Cement." The Blaine specific surface area of ​​the cement composition can be adjusted by combining limestones with different particle size distributions.

[0021] The limestone content may be 1.0 to 15% by mass based on the mass of the cement composition. The limestone content may be 2.0% by mass or more, or 3.0% by mass or more, based on the mass of the cement composition, and may be 14% by mass or less, 13% by mass or less, 12% by mass or less, 11% by mass or less, 10% by mass or less, 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, or 5.0% by mass or less.

[0022] The cement clinker may be Portland cement clinker used to prepare various Portland cements specified in JIS R 5210:2003 "Portland Cement." Examples of the various Portland cements include ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement. The Portland cement clinker may be Portland cement clinker used to prepare ordinary Portland cement and high-early-strength Portland cement.

[0023] The mineral composition of Portland cement clinker can be calculated by the Bogue formula. Here, the Bogue formula is a widely used formula for calculating the content ratio of the main minerals in Portland cement clinker from the content ratio of the chemical composition. By using the Bogue formula shown below, the contents of tricalcium silicate (3CaO·SiO2, denoted as C3S), dicalcium silicate (2CaO·SiO2, denoted as C2S), and tricalcium aluminate (3CaO·Al2O3, denoted as C3A) in Portland cement clinker can be calculated. Note that "%" in the following formula means "mass %". The chemical formula represents the content ratio (mass %) of each compound shown by the chemical analysis values according to JIS R 5204:2019 "Fluorescent X-ray analysis method for cement". <Bogue formula> C3S [%] = (4.07 × CaO [%]) - (7.60 × SiO2 [%]) - (6.72 × Al2O3 [%]) - (1.43 × Fe2O3 [%]) - (2.85 × SO3 [%]) C2S [%] = (2.87 × SiO2 [%]) - (0.754 × C3S [%]) C3A [%] = (2.65 × Al2O3 [%]) - (1.69 × Fe2O3 [%]) C4AF [%] = 3.04 × Fe2O3 [%]

[0024] In an example of cement clinker, the amount of C3S is 50 mass % or more and 64 mass % or less. The amount of C3S may be 52.0 mass % or more, 54.0 mass % or more, 56.0 mass % or more, 58.0 mass % or more, or 60.0 mass % or more, and may also be 63.0 mass % or less, 62.0 mass % or less, or 61.0 mass % or less. When the amount of C3S is large, the initial strength of the hardened body of the concrete composition or mortar composition tends to be more improved. When the amount of C3S is small, the heat generation accompanying the hardening of the concrete composition or mortar composition tends to be suppressed.

[0025] In one example of cement clinker, the C3A content is 9.0% by mass or more and 12% by mass or less. The C3A content may be 9.5% by mass or more or 10% by mass or more, or 11% by mass or less or 10.4% by mass or less. A high C3A content allows for increased utilization of waste and by-products such as coal ash as raw materials for cement clinker. A low C3A content tends to inhibit the regeneration of ettringite (a compound represented by 3CaO·Al2O3·3CaSO4·32H2O). A low C3A content tends to make it difficult for the adiabatic temperature of the hardened concrete or mortar composition to increase.

[0026] In one example of cement clinker, the C2S content may be 5.0% by mass or more and 65.0% by mass or less. The C2S content may be 10.0% by mass or more or 15.0% by mass or more, or 50.0% by mass or less, 40.0% by mass or less, 30.0% by mass or less, or 25.0% by mass or less. A high C2S content tends to improve the strength of the hardened concrete composition or mortar composition after a long period of time. A low C2S content tends to improve the early strength of the hardened concrete composition or mortar composition.

[0027] In one example of cement clinker, the C4AF content may be 7.0% by mass or more, 8.0% by mass or more, or 9.0% by mass or more. A high C4AF content can increase the amount of waste and by-products, such as coal ash, used as raw materials for cement clinker. The C4AF content may be 14.0% by mass or less, 12.0% by mass or less, 11.0% by mass or less, 10.5% by mass, or 10.0% by mass or less. A low C4AF content tends to suppress heat generation associated with hardening of the concrete composition or mortar composition.

[0028] The SO3 content of the cement clinker may be 0.3 to 1.6% by mass, with the mass of the cement clinker being 100% by mass. When the SO3 content of the cement clinker is within this range, even if the proportion of recycled gypsum in the gypsum increases, the ease of removal from a storage container during long-term storage tends to be improved while maintaining good compressive strength of the hardened body. In addition, the ability to fill a formwork can also be improved. The SO3 content of the cement clinker may be 0.5% by mass or more, 0.7% by mass or more, 0.9% by mass or more, or 1.1% by mass or more, or 1.4% by mass or less.

[0029] The cement composition may satisfy either of the following conditions (1) and (2). (1) The SO3 content of the cement clinker is 0.3 to 0.7 mass% based on the mass of the cement clinker, and the proportion of recycled gypsum in the gypsum is 10 to 60 mass% converted to SO3 based on the total mass of the gypsum. (2) The SO3 content of the cement clinker is more than 0.7 mass% and not more than 1.6 mass% based on the mass of the cement clinker, and the proportion of recycled gypsum in the gypsum is 30 to 80 mass% converted to SO3 based on the total mass of the gypsum.

[0030] When the cement composition satisfies condition (1), the cement composition tends to be easier to extract from a storage container after long-term storage while maintaining better compressive strength of the hardened body. From a similar perspective, the proportion of recycled gypsum may be 30% by mass or more, or 35% by mass or more, calculated as SO3, based on the total mass of the gypsum, and may be 50% by mass or less, less than 50% by mass, or 45% by mass or less.

[0031] When a cement composition satisfies condition (2), the hardened body maintains good compressive strength, particularly while using a large amount of recycled gypsum, and tends to be easier to extract from a storage container after long-term storage. From a similar perspective, the proportion of recycled gypsum, calculated as SO3 based on the total mass of gypsum, may be 30% by mass or more, 40% by mass or more, 50% by mass or more, more than 50% by mass, or 55% by mass or more, or may be 75% by mass or less, 70% by mass or less, or 65% by mass or less.

[0032] The cement composition may further contain other components as necessary in addition to cement clinker, gypsum, and limestone. Examples of other components include calcium hydroxide, silica powder, calcium-containing powder (excluding gypsum and limestone), concrete water reducers, accelerators, and retarders.

[0033] The cement compositions exemplified above can be produced by a method including mixing cement clinker, gypsum, and limestone. The mixing ratio of each component may be adjusted so that it falls within the range of the content or ratio exemplified for each component. The cement clinker, gypsum, and limestone may be mixed and pulverized at the same time. A mixture containing recycled gypsum containing anhydrous gypsum can be easily pulverized, making it easy to form a cement composition with a large specific surface area. The cement clinker, gypsum, and limestone may be pulverized separately as necessary and then mixed.

[0034] In the method for producing a cement composition, the proportion of recycled gypsum may be determined based on the SO content of the cement clinker. For example, when the SO content of the cement clinker is 0.3 to 0.7 mass% based on the mass of the cement clinker, the proportion of recycled gypsum in the gypsum may be adjusted so that the above condition (1) is satisfied, and when the SO content of the cement clinker is more than 0.7 mass% and not more than 1.6 mass% based on the mass of the cement clinker, the proportion of recycled gypsum in the gypsum may be adjusted so that the above condition (2) is satisfied.

[0035] The cement composition can be used to prepare a mortar composition or a concrete composition. The mortar composition includes the cement composition, fine aggregate, and water. The concrete composition includes the cement composition, fine aggregate, coarse aggregate, and water.

[0036] The fine aggregate may be a fine aggregate specified in JIS A 5005:2020 "Crushed Stone and Crushed Sand for Concrete." The fine aggregate may include, for example, river sand, land sand, mountain sand, sea sand, crushed sand, silica sand, limestone aggregate, blast furnace slag fine aggregate, copper slag fine aggregate, electric furnace oxidizing slag fine aggregate, or a combination thereof. The mass ratio (sand-cement ratio) of the content of the fine aggregate to the content of the cement composition in the mortar composition may be, for example, 0.5 or more and 10.0 or less, 0.8 or more and 5.0 or less, or 1.0 or more and 3.0 or less. The content of the fine aggregate to the content of the cement composition in the concrete composition is, for example, 200 kg / m based on the volume of the concrete composition. 3 More than 1500kg / m 3 It may be the following:

[0037] Coarse aggregate is specified in JIS A 5005:2020 "Crushed stone and crushed sand for concrete" The concrete composition may contain coarse aggregate, such as gravel, crushed stone, limestone aggregate, blast furnace slag coarse aggregate, electric furnace oxidizing slag coarse aggregate, or a combination thereof. The content of the coarse aggregate in the concrete composition is, for example, 200 kg / m based on the volume of the concrete composition. 3 More than 1500kg / m 3 It may be the following:

[0038] The water constituting the mortar composition or concrete composition may be, for example, tap water, distilled water, or deionized water. The mass ratio of the water content to the cement composition content (water-cement ratio) may be, for example, 0.10 to 5.00, 0.20 to 3.00, 0.30 to 1.00, or 0.40 to 0.60. [Example]

[0039] The present invention is not limited to the following examples.

[0040] 1. Cement clinker Clinkers A and B were prepared with the mineral compositions shown in Table 1. Clinkers A and B were ordinary Portland cement clinkers. In accordance with JIS R 5204:2019, chemical component values ​​were determined by X-ray fluorescence analysis using a calibration curve with glass beads, and the mineral composition was calculated from these chemical component values ​​using the Bogue formula. The SO3 content shown in Table 1 is the chemical component value determined by X-ray fluorescence analysis.

[0041] [Table 1]

[0042] 2. Gypsum 2-1. Preparation Gypsum A Flue gas desulfurized gypsum (gypsum dihydrate) generated from a cement manufacturing facility was dried at 100°C for 48 hours to obtain gypsum hemihydrate. The gypsum dihydrate before drying was uniformly mixed with the gypsum hemihydrate obtained by drying in a 1:1 mass ratio to obtain gypsum A containing gypsum dihydrate and gypsum hemihydrate.

[0043] Gypsum B Gypsum B containing gypsum dihydrate and gypsum hemihydrate was prepared in the same manner as Gypsum A, except that flue gas desulfurized gypsum generated from a cement manufacturing facility different from the flue gas desulfurized gypsum used to prepare Gypsum A was used.

[0044] Gypsum C The waste gypsum board was crushed to a size of 9 mm or less. Some of the paper in the crushed material was removed. The crushed material was then fired in a dedicated kiln at a temperature of approximately 700°C for approximately 4.5 minutes to obtain Gypsum C, a recycled gypsum containing mainly anhydrous gypsum. The proportion of anhydrous gypsum in Gypsum C was 92% by mass based on the mass of Gypsum C.

[0045] Reagent anhydrous gypsum A commercially available reagent, anhydrous gypsum (Fujifilm Wako Pure Chemical Industries, Ltd.: calcium sulfate, anhydrous, 99%), was prepared.

[0046] 2-2.Analysis The prepared gypsum A to C were analyzed by the following method. The results are shown in Table 2.

[0047] Ignition loss (ig.loss) Each gypsum sample was heated at 700°C until it reached a constant weight. The mass of the sample lost by heating was taken as the loss on ignition.

[0048] Chemical composition values The chemical composition values ​​of each gypsum were determined using fluorescent X-ray analysis with a calibration curve in accordance with JIS R 5204:2019.

[0049] pH The pH of the gypsum was measured according to JIS R 9101:2018. 5.0 g of the gypsum sample was added to 100 mL of water in a beaker, and the mixture was stirred to form a suspension. A pH electrode was immersed in the suspension, and the pH was measured 5 minutes after the sample was added.

[0050] BET specific surface area A Microtrac-Bel specific surface area measuring device (BELSORP MAX X) was used. Each gypsum sample, pretreated by heating, was placed in the adsorption chamber of the measuring device. The amount of nitrogen adsorption was measured using the BET method with nitrogen over a relative pressure range of 0.05 to 0.30. The BET surface area was calculated from the measurement data.

[0051] Unburned carbon amount (C amount) The amount of unburned carbon (C amount) in each gypsum was measured by non-dispersive infrared absorption method using a carbon-sulfur analyzer (CS744) manufactured by Leco.

[0052] [Table 2]

[0053] 3. Cement composition Cement clinker, gypsum, and limestone were charged into a ball mill, and cement compositions No. 1 to 10 were prepared by grinding the mixture. Table 3 shows the amount of gypsum and limestone in each cement composition. The amount of gypsum is expressed as an SO3 equivalent value (mass %) based on the total mass of the cement composition. The remainder after excluding gypsum and limestone from the cement composition is the amount of cement clinker. The content of cement clinker in each cement composition was 0.54 to 1.17 mass % in SO3 equivalent based on the total mass of the cement composition. In the table, the proportion of gypsum C is the proportion of the mass of gypsum C in SO3 equivalent based on the total mass of gypsum in SO3 equivalent. Of the prepared cement compositions Nos. 1 to 10, cement compositions Nos. 2 to 4 and 7 to 9 satisfy the requirements that the gypsum content is within the range of 0.50 to 2.9 mass% in terms of SO3, and the proportion of recycled gypsum in the gypsum is 10 to 80 mass%. The Blaine value of each cement composition was measured by a method in accordance with JIS R 5201:2015. The results are also shown in Table 3.

[0054] [Table 3]

[0055] 4. Evaluation 4-1. Packet Set Index (PSI) Test 100 g of the cement composition was placed in a 200 mL Erlenmeyer flask with a circular bottom, and the Erlenmeyer flask was gently shaken to level the cement composition. The Erlenmeyer flask was then vibrated for 15 seconds with a table vibrator to compact the cement composition on the bottom of the Erlenmeyer flask. The Erlenmeyer flask containing the cement composition was then left to stand in a dryer adjusted to 80°C for 2 weeks.

[0056] A rubber stopper was attached to the neck of the Erlenmeyer flask removed from the dryer. The Erlenmeyer flask was attached to a funnel tester with its bottom facing vertically. The Erlenmeyer flask was rotated 180 degrees around the central axis of the bottom at a speed of 40 rotations per minute using the funnel tester. The number of rotations required for the cement composition compacted on the bottom of the flask to completely disintegrate was recorded as PSI. A small PSI means that the cement composition that has hardened after being left standing for a long period of time disintegrates easily and can be easily removed from the container.

[0057] 4-2.Compression strength The compressive strength of hardened specimens formed from each cement composition at 3, 7, or 28 days was measured using 40 × 40 × 160 mm mortar specimens according to JIS R 5201:2015, "Physical Testing Methods for Cement." The mass ratio of water to cement composition (W / C) was 0.50, and the mass of standard sand (JIS R5201 strength test standard sand) to cement composition was 3.00. Mortar compositions for forming mortar specimens were prepared by kneading these without adding any admixtures. The "compressive strength ratios" shown in Table 4 are the ratios of cement compositions 2 to 5 to the compressive strength of cement composition 1 at the same age, and the ratios of cement compositions 7 to 10 to the compressive strength of cement composition 6 at the same age.

[0058] 4-3.First train time The initial release time of the cement composition was measured using a Vicat needle device in accordance with JIS R 5201:2015 "Physical Testing Methods for Cement." The initial release time refers to the time until the material is sufficiently self-supporting without sagging or other deformation.

[0059] [Table 4]

[0060] 4-4. Crushing test Clinker A, gypsum A, gypsum C, or reagent anhydrous gypsum, and limestone were placed in a test mill and ground at 1,080 revolutions per minute to obtain a cement composition. The blending ratio was adjusted so that the amount of gypsum was 1.35 mass% SO3 equivalent and the amount of limestone was 4 mass% based on the total mass of the mixture (cement composition). The Blaine values ​​of the resulting cement compositions were measured using a method in accordance with JIS R 5201:2015. As shown in Table 5, the cement composition containing gypsum C, which is recycled gypsum, had the largest surface area. In other words, it was confirmed that the mixture containing recycled gypsum had good grindability.

[0061] [Table 5]

[0062] From the above evaluation results, it was confirmed that, for example, cement compositions Nos. 2 to 4 have improved properties in terms of ease of removal from storage containers during long-term storage compared to cement composition No. 1. Similarly, it was confirmed that cement compositions Nos. 7 to 9 have improved properties in terms of ease of removal from storage containers during long-term storage compared to cement composition No. 6. Furthermore, it was confirmed that cement compositions Nos. 2 to 4 and 7 to 9 can form hardened bodies having good compressive strength almost equivalent to that of cement composition No. 1 or 6, which contains only gypsum derived from flue gas desulfurization gypsum.

[0063] In the case of cement compositions Nos. 6 to 10, which contain clinker B with a relatively low SO3 content, the absolute compressive strength was high, but the compressive strength ratio tended to decrease slightly when the proportion of recycled gypsum (gypsum C) was high. On the other hand, in the case of cement compositions Nos. 1 to 5, which contain clinker A with a relatively high SO3 content, the compressive strength ratio did not decrease even in cement compositions Nos. 2 to 4, which contain recycled gypsum, compared to cement composition No. 1, which does not contain recycled gypsum. These results also confirmed that when the SO3 content of cement clinker is high, the high strength of the hardened body tends to be more easily maintained when a large proportion of gypsum dihydrate and gypsum hemihydrate is substituted.

Claims

1. A cement composition comprising cement clinker, gypsum including recycled gypsum containing anhydrous gypsum, and limestone, The cement clinker SO ３ The content is 0.3 to 1.6% by mass based on the mass of the cement clinker, the pH of the suspension containing 5.0 g of recycled gypsum and 100 mL of water is 10.0 to 13.0; The content of the gypsum is based on the mass of the cement composition, and ３ converted to 0.50 to 2.9 mass%; The proportion of the recycled gypsum in the gypsum is SO ３ converted to 10 to 80 mass%. Cement compositions.

2. The BET specific surface area of ​​the recycled gypsum is 3.0 to 9.0 m ２ The cement composition of claim 1, wherein the SiO 2 content is 1 / g.

3. The content of the recycled gypsum is based on the mass of the cement composition, and ３ The cement composition according to claim 1, wherein the content is 0.13 to 1.08 mass% in terms of the total mass of the cement.

4. 2. The cement composition according to claim 1, wherein the content of the limestone is 1.0 to 15% by mass based on the mass of the cement composition.

5. 2. The cement composition according to claim 1, wherein the percentage of mass reduction when the recycled gypsum is heated at 700°C is 2.5 mass% or less based on the mass of the recycled gypsum before heating.

6. The cement clinker SO ３ The content is 0.3 to 0.7% by mass based on the mass of the cement clinker, The proportion of the recycled gypsum in the gypsum is SO ３ converted to 10 to 60 mass%. The cement composition of claim 1.

7. The cement clinker SO ３ The content is more than 0.7% by mass and not more than 1.6% by mass based on the mass of the cement clinker, The proportion of the recycled gypsum in the gypsum is SO ３ converted to 30 to 80 mass%. The cement composition of claim 1.

8. A method for producing the cement composition according to any one of claims 1 to 7, comprising: The method includes mixing the cement clinker, the gypsum, and the limestone.

9. 1. A method for producing a cement composition, comprising mixing cement clinker, gypsum including recycled gypsum containing anhydrous gypsum, and limestone, The cement clinker SO ３ The content is 0.3 to 1.6% by mass based on the mass of the cement clinker, the pH of the suspension containing 5.0 g of recycled gypsum and 100 mL of water is 10.0 to 13.0; The content of the gypsum is based on the mass of the cement composition, and ３ converted to 0.50 to 2.9 mass%; The cement clinker SO ３ When the content is 0.3 to 0.7 mass% based on the mass of the cement clinker, the proportion of the recycled gypsum in the gypsum is set to SO 4 based on the total mass of the gypsum. ３ Converted to 10 to 60 mass %, The cement clinker SO ３ When the content is more than 0.7 mass% and 1.6 mass% or less based on the mass of the cement clinker, the proportion of the recycled gypsum in the gypsum is set to SO 4 based on the total mass of the gypsum. ３ The amount of the hydroxyl group is converted to 30 to 80 mass %.

10. A mortar composition comprising the cement composition according to any one of claims 1 to 7, fine aggregate, and water.

11. A concrete composition comprising the cement composition according to any one of claims 1 to 7, fine aggregate, coarse aggregate and water.

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