JP2019172523A - Cement composition and manufacturing method therefor - Google Patents

Abstract

To provide a manufacturing method of a cement composition capable of effectively using a waste gypsum, and a cement composition capable of exhibiting excellent flowability.SOLUTION: The manufacturing method of a cement composition includes a heating process for supplying waste gypsum to a burning flame of a heating device, and a mixing process for obtaining a mixture containing regenerated anhydrous gypsum obtained through the heating process, cement clinker, and blast furnace slag. The cement composition contains the cement clinker, the blast furnace slag, and gypsum, at least a part of the gypsum is the regenerated anhydrous gypsum, the regenerated anhydrous gypsum has unburned carbon amount of 0.2 mass% or less and free lime amount of 0.2 mass% or less based on mass of the regenerated anhydrous gypsum.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a cementitious composition containing regenerated anhydrous gypsum and a method for producing the same.

  As the dismantling of houses and the like where gypsum boards are used increases year by year, the amount of waste gypsum generated has increased. Accordingly, there is an increasing need for technology for treating waste gypsum. For this reason, various studies have been made to effectively use waste gypsum.

  Waste gypsum usually contains paper and organic admixture together with dihydrate gypsum. For this reason, there is a concern that, if it is added as it is to a cement-based material, the strength development property is lowered or the setting property is fluctuated. Then, the method of carbonizing and decomposing | disassembling paper and an organic admixture by heating waste gypsum and collect | recovering gypsum content as anhydrous gypsum is proposed (refer patent documents 1-6). In addition, a method has also been proposed in which the recovered recycled anhydrous gypsum is mixed with a cement-based material and used as a soil solidification treatment or as an admixture for a high-strength cement composition (see Patent Documents 7 and 8).

Japanese Patent Laid-Open No. 10-036149 Japanese Patent No. 3108922 Japanese Patent No. 4567164 Japanese Patent No. 4735438 Japanese Patent No. 4777058 Japanese Patent No. 4838413 Japanese Patent No. 5737812 JP 2009-161377 A

  However, anhydrous gypsum obtained by heating waste gypsum contains components different from natural gypsum and chemical gypsum. Specifically, unburned carbon resulting from carbonization of paper and organic admixture and free lime (also referred to as “f.CaO” or “free lime”) resulting from partial decomposition of the gypsum component. Can be mentioned. In addition, there are many cases in which impurities such as mortar and earth and sand mixed in the process of collecting waste gypsum are contained in a trace amount. When such regenerated anhydrous gypsum is mixed with a cement-based material, there is a concern that the quality fluctuation of the obtained composition becomes large.

  An object of this indication is to provide the manufacturing method of the cementitious composition which can utilize waste gypsum effectively, and the cementitious composition which can express the outstanding fluidity | liquidity.

  The present inventors use regenerated anhydrous gypsum obtained by a manufacturing method invented in the past (Japanese Patent Laid-Open No. 2017-149619) and satisfying specific conditions as at least a part of gypsum. Even when used in combination with blast furnace slag, it has been found that a cementitious composition excellent in fluidity can be stably obtained, and the following invention has been completed.

  That is, a method for producing a cementitious composition according to the present disclosure includes a heating step of supplying waste gypsum toward a combustion frame of a heating device, a regenerated anhydrous gypsum obtained through the heating step, a cement clinker, and a blast furnace slag. And a mixing step to obtain a mixture. According to this production method, waste gypsum can be used effectively, and a sufficiently superior cementitious composition can be produced stably. A specific example of the heating device is a rotary kiln having a burner. This manufacturing method may further include a step of pulverizing the mixture.

  The production method according to the present disclosure may further include a step of measuring at least one of the amount of unburned carbon and the amount of free lime of the regenerated anhydrous gypsum discharged from the heating device. By measuring the amount of unburned carbon and / or free lime in the regenerated anhydrous gypsum discharged from the heating device, and grasping the fluctuations in these amounts, for example, the organic components contained in the waste gypsum that is the raw material will fluctuate. However, it is possible to stably and continuously produce an excellent quality cementitious composition by adjusting the amount of waste gypsum supplied to the heating device or changing the heating conditions. The amount of unburned carbon (total carbon amount) contained in the regenerated anhydrous gypsum is measured by the infrared absorption method of JIS R1603 “Chemical analysis method of fine silicon nitride powder for fine ceramics”. The amount of free lime (f.CaO amount) is measured by the Cement Association standard test method JCAS I-01 “Quantitative method of free calcium oxide”.

  For example, if the amount of unburned carbon in the regenerated anhydrous gypsum discharged from the heating device exceeds 0.2% by mass based on the mass of the regenerated anhydrous gypsum, the conditions are changed so that the temperature of the object to be heated in the heating device becomes high do it. If the amount of free lime in the regenerated anhydrous gypsum discharged from the heating device exceeds 0.2% by mass based on the mass of the regenerated anhydrous gypsum, the conditions should be changed so that the residence time of the object to be heated in the heating device is shortened. Good.

  The regenerated anhydrous gypsum discharged from the heating device preferably has an unburned carbon amount of 0.2% by mass or less and a free lime content of 0.2% by mass or less based on the mass of the regenerated anhydrous gypsum. By mixing a cementitious composition containing regenerated anhydrous gypsum that satisfies these conditions and water, a slurry having excellent fluidity can be obtained.

  The cementitious composition according to the present disclosure includes cement clinker, blast furnace slag, and gypsum, and at least a part of the gypsum is regenerated anhydrous gypsum, and the regenerated anhydrous gypsum is based on the mass of the regenerated anhydrous gypsum and is unburned. The amount of carbon is 0.2% by mass or less and the amount of free lime is 0.2% by mass or less. By mixing this cement composition and water, a slurry having excellent fluidity can be obtained. The regenerated anhydrous gypsum is, for example, a heated product of waste gypsum.

When the cement clinker content is 100 parts by mass, for example, the blast furnace slag content is 20 to 100 parts by mass, and the gypsum content is 5 to 25 parts by mass in terms of SO _3. It is. From the viewpoint of fluidity of the slurry containing the cementitious composition and effective utilization of the waste gypsum, the ratio of the regenerated anhydrous gypsum based on the total mass of the gypsum is, for example, 30 to 100% by mass.

  A slurry obtained by mixing the cement-based composition and water so that the ratio (w / c) of the mass w of water to the mass c of the cement-based composition according to the present disclosure is 0.6. It is preferable that the flow-down time measured using a Marsh Funnel viscometer and the temperature of the slurry is 35 ° C. or less is 35 seconds or less. One of the uses of the cementitious composition according to the present disclosure is a ground improvement solidified material.

  According to the present disclosure, a method for producing a cement-based composition that can effectively use waste gypsum and a cement-based composition that can exhibit excellent fluidity are provided.

FIG. 1 is a schematic view showing an example of a heating device for obtaining regenerated anhydrous gypsum from waste gypsum. FIG. 2 is a cross-sectional view taken along the line II-II of the heating apparatus shown in FIG. Fig. 3 (a) is a graph showing the change in the amount of unburned carbon (C amount) accompanying heating of the waste gypsum, and Fig. 3 (b) is the amount of free lime (f. CaO amount) accompanying heating of the waste gypsum. It is a graph which shows a change.

  Hereinafter, embodiments of the present disclosure will be described in detail. The present invention is not limited to the following embodiments.

<Method for producing cement-based composition>
The manufacturing method of the cementitious composition which concerns on this embodiment contains the heating process which supplies waste gypsum toward the combustion flame | frame of a heating apparatus, the regenerated anhydrous gypsum obtained through the heating process, cement clinker, and blast furnace slag. Mixing step to obtain a mixture. According to this production method, waste gypsum can be used effectively, and a sufficiently superior cementitious composition can be produced stably.

(Heating process)
A heating process is a process of supplying waste gypsum toward the combustion flame | frame of a heating apparatus. Various types of waste plaster can be used regardless of the location of the waste.For example, waste materials generated at gypsum board manufacturing plants, gypsum board scraps generated at new construction sites, waste materials generated at demolition sites, etc. Can be used. However, since waste materials generated at the demolition work site are mixed with inorganic building waste materials other than gypsum, it is preferable to remove them as much as possible. From the viewpoint of the quality of the regenerated anhydrous gypsum obtained after the heat treatment, the content of inorganic building waste other than gypsum in the waste gypsum is preferably less than 10% by mass.

  The particle size of the waste gypsum is preferably such that it does not clog during the heating process and can be easily discharged from a silo or tank. The particle size of the waste gypsum is preferably 50 mm or less, more preferably 10 mm or less, and still more preferably 5 mm or less. If the particle size of the waste gypsum is about this level, it can be easily fed into a heating device, and handling properties can be secured.

  The heating device is not limited in shape and type as long as it has a burner and can directly put waste gypsum into its frame, but a co-current type rotary kiln is easy to feed and discharge and homogeneous heating Is preferable. The burner fuel can be any of gas (city gas, etc.), liquid (heavy oil, etc.), and solid (pulverized coal, etc.).

  In the present embodiment, it is important that the waste gypsum contacts the combustion frame by supplying the waste gypsum toward the combustion frame. As a result, paper and organic admixture burn in an extremely short time, and efficiently produce regenerated anhydrous gypsum with an unburned carbon content of 0.2% by mass or less and a free lime content of 0.2% by mass or less. it can.

  FIG. 1 is a schematic view showing an example of a heating device for obtaining regenerated anhydrous gypsum from waste gypsum. The heating device 100 includes a burner 12, and includes a cocurrent rotary kiln 10 that heats the waste gypsum 30 to reform it to anhydrous gypsum 32, and a supply unit 20 that supplies the waste gypsum 30 to the cocurrent rotary kiln 10. .

  The co-current rotary kiln 10 is provided with a kiln hood 11, a drum body 17, and a settling chamber 14 in communication from the upstream side to the downstream side. A burner 12 is attached to the kiln hood 11 of the parallel flow rotary kiln 10. A fuel supply unit for supplying fuel is connected to the burner 12 (not shown). As the fuel, any of gaseous fuel (such as city gas), liquid fuel (such as heavy oil), and solid fuel (such as pulverized coal) may be used. From the viewpoint of easy handling, a liquid fuel that generates less dust is preferable.

  The shape and size of the cocurrent rotary kiln 10 are not particularly limited. The length L of the drum main body 17 along the rotation axis direction is preferably 1 to 10 m, more preferably 2 to 6 m, from the viewpoint of achieving both a reduction in size of the heating device and sufficient production capacity. The inner diameter φ of the drum body 17 of the cocurrent rotary kiln 10 is, for example, 1 to 3 m. From the viewpoint of allowing anhydrous gypsum to be discharged in a short time, it is preferable that the inclination angle of the drum body 17 with respect to the horizontal plane is 0.5 to 8 ° and the rotation speed is 1 to 10 rpm. From the same viewpoint, it is more preferable that the tilt angle is 1 to 5 ° and the rotation speed is 2 to 7 rpm.

  The supply part 20 is comprised by piping, for example. The pipe is inserted into the co-current rotary kiln 10 from the upper wall surface of the kiln hood 11, and the tip thereof is disposed inside the drum body 17. The waste gypsum 30 flows through the piping that forms the supply unit 20 and is supplied into the co-current rotary kiln 10 from the opening at the tip of the piping. The supply unit 20 supplies waste gypsum toward the combustion frame 16 in the drum body 17. The supply unit 20 may be configured to supply the waste gypsum toward the combustion frame 16 by dropping the gypsum by gravity, or to supply the waste gypsum toward the combustion frame 16 by discharging the waste gypsum together with the flowing gas. It may be configured to.

  The burner 12 may be a variable burner capable of arbitrarily adjusting the direction of the combustion frame 16. By adjusting the direction of the frame to the optimum position according to the particle size of the waste gypsum 30, it becomes easy to find the optimum heating condition. As a result, it can be more efficiently modified to anhydrous gypsum. As an example of the variable burner, there is one in which the tip of the burner is bent with respect to the axis of the burner tube main body, and the direction of the combustion frame can be changed by rotating the burner tube main body around the axis. The variable burner is not limited to such a form, and is not particularly limited as long as the direction of the combustion frame 16 can be changed.

  The supply unit 20 supplies waste gypsum 30 toward the combustion frame 16 of the burner 12. Most of the waste gypsum 30 supplied into the co-current rotary kiln 10 contacts the combustion frame 16 before contacting the inner wall surface of the co-current rotary kiln 10. The waste gypsum 30 may be supplied so as to pass through the combustion frame 16. However, it is not essential that all of the supplied waste gypsum 30 contacts the combustion frame 16 or passes through the combustion frame 16.

  The waste gypsum 30 supplied toward the combustion frame 16 of the burner 12 is heated at a sufficiently high heating rate. As a result, the paper and the organic admixture contained in the waste gypsum 30 in contact with the combustion frame 16 of the burner 12 are quickly carbonized and decomposed. And most of the dihydrate gypsum contained in the waste gypsum 30 is promptly modified into anhydrous gypsum. These reactions can be completed before the gypsum decomposes. Therefore, it is considered that dihydrate gypsum can be efficiently modified to anhydrous gypsum while suppressing the generation of SOx generated with the decomposition of gypsum.

  2 is a cross-sectional view taken along line II-II of the heating apparatus 100 shown in FIG. A combustion frame 16 is formed in the vicinity of the center in the radial direction on the upstream side of the drum body 17 of the parallel flow rotary kiln 10. The waste gypsum 30 supplied from the supply unit 20 toward the combustion frame 16 passes through the combustion frame 16 and accumulates near the bottom on the upstream side of the drum body 17.

  The waste gypsum 30 that has passed through the combustion frame 16 is exposed to the high temperature of the combustion frame 16 until it has left the periphery of the combustion frame 16 even after being deposited near the bottom of the drum body 17. Waste gypsum 30 that does not come into contact with the combustion frame 16 is also deposited near the bottom of the drum body 17 and then exposed to the high temperature of the combustion frame 16 around the combustion frame 16. By being exposed to high temperature in this way, carbonization and decomposition of paper and organic admixture and reforming to anhydrous gypsum proceed rapidly.

  The drum body 17 continuously rotates in the direction P. Since the rotation axis of the drum body 17 is inclined by 0.5 to 8 ° with respect to the horizontal plane, the upstream side is higher than the downstream side. For this reason, the waste gypsum 30 gradually moves to the downstream side of the drum body 17 while being agitated by the rotation of the drum body 17 of the cocurrent rotary kiln 10.

  The external flame of the combustion flame | frame 16 has the temperature of 1200 degreeC or more which is a gypsum decomposition temperature, for example. Since the decomposition reaction of gypsum does not occur instantaneously, the carbonization and decomposition of the paper and the organic admixture contained in the waste gypsum 30 in contact with the external flame and the waste gypsum 30 that has passed through the vicinity of the external flame can be rapidly advanced. . The waste gypsum 30 is supplied toward the combustion frame 16 by the supply unit 20. For this reason, even if the waste gypsum 30 contains fine particles, the fine particles are suspended by the air flow in the drum body 17 and are sufficiently prevented from being discharged as dust in the exhaust gas without contacting the combustion frame 16. be able to. The fine particles are instantly reformed by coming into contact with the combustion flame 16 or passing through the vicinity of the combustion flame 16.

  Without contact with the combustion flame 16, the time required for carbonization and decomposition of the paper and organic admixture tends to be longer. When the time for heating becomes longer, the decomposition reaction of gypsum tends to proceed. For this reason, it is preferable that the waste gypsum 30 contacts the combustion frame 16.

  As the heating time in the heating step is shorter, productivity can be improved while suppressing decomposition of gypsum. From such a viewpoint, the heating time is preferably 20 minutes or less, more preferably less than 10 minutes, further preferably less than 7 minutes, and particularly preferably less than 5 minutes. Although there is no restriction | limiting in particular in the minimum of heating time, From a viewpoint of fully progressing the modification | reformation to an anhydrous gypsum, it is preferable that it is 1 minute or more, and it is more preferable that it is 2 minutes or more.

  After the waste gypsum 30 comes into contact with the combustion frame 16, the kiln bottom temperature in the cocurrent rotary kiln 10 is preferably 500 to 1000 ° C. in order to sufficiently dehydrate the gypsum in the cocurrent rotary kiln 10. The cocurrent rotary kiln 10 preferably has a structure capable of maintaining the above-described heating time and kiln bottom temperature.

  The anhydrous gypsum 32 (waste gypsum 30) deposited on the bottom of the drum body 17 on the upstream side moves to the downstream side of the drum body 17 while being stirred. As shown in FIG. 1, the anhydrous gypsum 32 generated by heating in the drum body 17 is discharged to the outside of the cocurrent rotary kiln 10 via the settling chamber 14 connected to the downstream side of the drum body 17. . In this way, anhydrous gypsum can be produced. This anhydrous gypsum is classified as type II anhydrous gypsum.

  The manufacturing method according to the present embodiment may further include a step of measuring at least one of the amount of unburned carbon and the amount of free lime of the regenerated anhydrous gypsum discharged from the heating device. By measuring the amount of unburned carbon and / or free lime in the regenerated anhydrous gypsum discharged from the heating device, and grasping the fluctuations in these amounts, for example, the organic components contained in the waste gypsum that is the raw material will fluctuate. Even if the amount of waste gypsum supplied to the heating device is adjusted or the heating conditions (for example, heating temperature and residence time) are changed, an excellent quality cementitious composition can be produced stably and continuously. Can be manufactured.

  In the present embodiment, it is important that the amount of unburned carbon in the regenerated anhydrous gypsum is 0.2% by mass or less and the amount of free lime is 0.2% by mass or less. According to the study by the present inventors, by using a regenerated anhydrous gypsum satisfying these conditions as at least a part of gypsum to produce a cement-based composition, the cement-based composition has stable and excellent fluidity. Show. This mechanism is thought to result from the amount of organic impurities in the regenerated anhydrous gypsum and the reactivity of the gypsum itself. That is, when waste gypsum is heated, the amount of unburned carbon is an indicator of the degree of decomposition of organic matter, and the amount of free lime is an indicator of the degree of decomposition of gypsum, so the above conditions are good while suppressing impurities in regenerated anhydrous gypsum This is considered to be an index of the optimum heating condition for ensuring a good reactivity. Such an index is based on the inventors' unique knowledge, and is useful when reclaimed anhydrous gypsum for cement-based materials is obtained by heating waste gypsum.

  Fig. 3 (a) is a graph showing the change in the amount of unburned carbon (C amount) accompanying heating of the waste gypsum, and Fig. 3 (b) is the amount of free lime (f. CaO amount) accompanying heating of the waste gypsum. It is a graph which shows a change. As shown in these graphs, as the heating temperature increases, unburned carbon decreases in a short time, whereas free lime tends to increase rapidly. By optimizing the heating temperature and heating time (residence time of the object to be heated in the heating device), the amount of unburned carbon is 0.2% by mass or less and the amount of free lime is 0.2% by mass or less. Gypsum can be obtained. In addition, the temperature 600 degreeC, 700 degreeC, and 800 degreeC in FIG. 3 (a) and FIG.3 (b) is the kiln bottom temperature in a cocurrent type rotary kiln.

  If the amount of unburned carbon in the regenerated anhydrous gypsum discharged from the heating device exceeds 0.2% by mass based on the mass of the regenerated anhydrous gypsum, the conditions should be changed so that the temperature of the object to be heated in the heating device becomes high. Good. If the amount of free lime in the regenerated anhydrous gypsum discharged from the heating device exceeds 0.2% by mass based on the mass of the regenerated anhydrous gypsum, the conditions should be changed so that the residence time of the object to be heated in the heating device is shortened. Good.

  In addition, even if the heating temperature and / or residence time of the article to be heated in the heating device are adjusted, the regenerated anhydrous gypsum having an unburned carbon content of 0.2% by mass or less and a free lime content of 0.2% by mass or less. For example, if the contact time between the waste gypsum and the combustion flame is adjusted, or waste gypsum that is heat-treated is mixed with waste gypsum with less organic components such as organic admixtures. Then, regenerated anhydrous gypsum satisfying the above conditions can be produced by diluting the organic component.

  The regenerated anhydrous gypsum discharged from the heating device preferably has an unburned carbon amount of 0.2% by mass or less and a free lime content of 0.2% by mass or less based on the mass of the regenerated anhydrous gypsum. By mixing a cementitious composition containing regenerated anhydrous gypsum that satisfies these conditions and water, a slurry having excellent fluidity can be obtained.

(Mixing process)
A mixing process is a process of obtaining the mixture containing the regenerated anhydrous gypsum obtained through the heating process, and other gypsum as needed, cement clinker, and blast furnace slag. The production method according to the present embodiment preferably further includes a step of pulverizing the mixture in terms of controlling the fineness. In the step of mixing the obtained regenerated anhydrous gypsum, cement clinker and blast furnace slag, and the step of pulverizing the mixture, the type of apparatus to be used is not particularly limited. Further, it can be pulverized after mixing or mixed after pulverization. For example, pulverization and mixing can be simultaneously performed using a ball mill or the like.

  As the cement clinker, a cement clinker such as an ordinary cement clinker, an early-strength cement clinker, a medium heat cement clinker, a low heat cement clinker, and an oil well cement clinker can be used. Among these, ordinary cement clinker and early-strength cement clinker can be preferably used in consideration of strength characteristics and availability.

  The blast furnace slag is not particularly limited as long as it is commercially available, and blast furnace slag fine powder defined in JIS A 6206 “Blast furnace slag fine powder for concrete” can be used. When the content of the cement clinker in the cement-based composition is 100 parts by mass, the content of the blast furnace slag is preferably 20 to 100 parts by mass, more preferably 25 to 80 parts by mass, and 30 to 30 parts by mass. More preferably, it is 70 mass parts. When the content of the blast furnace slag is in the above range, the slurry containing the cement-based composition has excellent fluidity and can achieve excellent strength characteristics when the cement-based composition is used as a ground improvement solidifying material. .

The content of gypsum in the cement-based composition (total of regenerated anhydrous gypsum and other gypsum) is preferably 5 to 25 parts by mass in terms of SO _{3 when} the content of cement clinker is 100 parts by mass, More preferably, it is 7-23 mass parts, and it is still more preferable that it is 10-20 mass parts. When the gypsum content is in the above range, the slurry containing the cement-based composition has excellent fluidity, and excellent strength characteristics can be achieved when the cement-based composition is used as a ground improvement solidifying material.

  Based on the total mass of gypsum in the cementitious composition (total of regenerated anhydrous gypsum and other gypsum), the ratio of regenerated anhydrous gypsum is preferably 30 to 100% by mass, and preferably 40 to 100% by mass. More preferably, it is 50-100 mass%, More preferably, it is 60-100 mass%. The larger the amount of regenerated anhydrous gypsum used, the more excellent the fluidity of the slurry containing the cementitious composition, and the better the strength characteristics when the cementitious composition is used as a ground improvement solidifying material.

  As gypsum other than regenerated anhydrous gypsum, normally available dihydrate gypsum (exhaust dihydrate gypsum, phosphate dihydrate gypsum, etc.) and hemihydrate gypsum (heated dihydrate gypsum, etc.) Anhydrous gypsum obtained by baking water gypsum, natural anhydrous gypsum, hydrofluoric acid anhydrous gypsum, and the like can be arbitrarily used.

  According to the method for producing a cement composition according to the above embodiment, even if regenerated anhydrous gypsum whose quality tends to fluctuate in accordance with changes in the types and properties of waste gypsum as a raw material, a specific component (amount of unburned carbon) And the amount of free lime) can be efficiently and stably obtained by a simple operation of controlling the amount of free lime). A slurry obtained by mixing the cement-based composition and water so that the ratio (w / c) of the weight w of water to the weight c of the cement-based composition is 0.6, and the target is a Marsh funnel. The flow-down time measured using a viscometer and the temperature of the slurry at 35 ° C. is preferably 35 seconds or less, and may be 10 to 34 seconds or 15 to 33 seconds.

  Hereinafter, the present disclosure will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited to a following example.

[Materials used]
The waste gypsum board was crushed to 4 mm or less, and a portion of the paper was removed to obtain waste gypsum samples (granular) of the quality shown in Table 1.

[Heating waste gypsum]
The waste gypsum sample was put into a small cocurrent rotary kiln (φ1.4 m × L4.0 m, inclination 5%) and subjected to heat treatment. Recycled heavy oil was used as the fuel, and the kiln bottom temperature was set at 680 ° C. Here, the amount of the sample fed was 1.1 t / h and was directly put into the combustion flame (see FIG. 2).

  Table 2 shows the quality and physical properties of the regenerated anhydrous gypsum obtained by the heat treatment. The amount of free lime (f.CaO amount) was quantified by Cement Association standard test method JCAS I-01 “Quantification method of free calcium oxide”. As shown in Table 2, the carbon content (unburned carbon content) and free lime content of the regenerated anhydrous gypsum were both 0.2% by mass or less.

<Examples 1-4 and Comparative Example 1>
[Preparation of cementitious composition]
Cement clinker, blast furnace slag fine powder (manufactured by Chiba Riverment), and gypsum (SO ₃ equivalent) are mixed at a mass ratio shown in Table 3 to prepare cement-based compositions according to Examples and Comparative Examples. did. That is, each material was put into a test ball mill (LA-PO1, manufactured by Ito Seisakusho, pot inner diameter 10 cm), and pulverization and mixing were simultaneously performed. The brane specific surface area of the cementitious composition was generally constant in the range of 4410 to 4510 cm ² / g. In Examples 1 to 4, the above regenerated anhydrous gypsum and drained dihydrate gypsum (produced by Chugoku Electric Power New Onoda Power Plant) were used in combination as gypsum. Suigetsu (manufactured by Shinden Onoda Power Plant, Chugoku Electric Power Company) was used alone.

[Evaluation of fluidity of cementitious composition]
Using a Marsh funnel viscometer (manufactured by Maruto Co., Ltd., model number: SF-1013), fluidity was evaluated by measuring the flow time of the slurry containing the cementitious compositions according to Examples and Comparative Examples. In this measurement, the shorter the flow-down time, the lower the viscosity and the better the fluidity. The measurement slurry is prepared by adding water to the cementitious composition and mixing with a mixer for 3 minutes so that the ratio (w / c) of the mass w of water to the mass c of the cementitious composition is 0.6. Obtained by. The flow-down time was measured under the condition of a slurry temperature of 35 ° C., and the slurry after 15 minutes from the preparation was used as a measurement target. Table 3 shows the results.

  As shown in Table 3, the flow-down time was 36 seconds in Comparative Example 1 which did not contain regenerated anhydrous gypsum as a gypsum, whereas Comparative Examples 1 to 4 which contained regenerated anhydrous gypsum as at least a part of gypsum The flow time was shorter than 1, and good fluidity was obtained. Furthermore, it was found that as the proportion of regenerated anhydrous gypsum in the gypsum increases, the flow-down time becomes shorter and the fluidity becomes better.

  From the above, according to the present disclosure, even when regenerated anhydrous gypsum produced from waste gypsum is used for a cement-based composition, stable and excellent fluidity can be secured. This can contribute to the construction of a recycling system for waste gypsum, which is a social problem.

DESCRIPTION OF SYMBOLS 10 ... Cocurrent type rotary kiln, 12 ... Burner, 16 ... Combustion flame, 30 ... Waste gypsum, 32 ... Anhydrous gypsum, 100 ... Heating apparatus

Claims (12)

A heating process for supplying waste gypsum toward the combustion frame of the heating device;
A mixing step of obtaining a mixture containing the regenerated anhydrous gypsum obtained through the heating step, a cement clinker, and a blast furnace slag;
The manufacturing method of the cementitious composition containing this.   The method for producing a cementitious composition according to claim 1, further comprising a step of measuring at least one of an unburned carbon amount and a free lime amount of the regenerated anhydrous gypsum discharged from the heating device.   When the amount of unburned carbon of the regenerated anhydrous gypsum exceeds 0.2% by mass based on the mass of the regenerated anhydrous gypsum, the method further includes a step of changing conditions so that the temperature of the heated object in the heating device is increased. The manufacturing method of the cementitious composition of Claim 2.   When the amount of free lime of the regenerated anhydrous gypsum exceeds 0.2% by mass on the basis of the mass of the regenerated anhydrous gypsum, it further includes a step of changing the conditions so that the residence time of the object to be heated in the heating device is shortened. The manufacturing method of the cementitious composition of Claim 2 or 3.   The regenerated anhydrous gypsum according to any one of claims 1 to 4, wherein the amount of unburned carbon is 0.2% by mass or less and the amount of free lime is 0.2% by mass or less, based on the mass of the regenerated anhydrous gypsum. A method for producing a cementitious composition according to one item.   The manufacturing method of the cementitious composition as described in any one of Claims 1-5 which further includes the process of grind | pulverizing the said mixture.   The said heating apparatus is a manufacturing method of the cementitious composition as described in any one of Claims 1-6 which is a rotary kiln which has a burner. A cement-based composition comprising cement clinker, blast furnace slag, and gypsum,
At least a portion of the gypsum is regenerated anhydrous gypsum,
The regenerated anhydrous gypsum is a cement-based composition having an unburned carbon content of 0.2% by mass or less and a free lime content of 0.2% by mass or less, based on the mass of the regenerated anhydrous gypsum. The content of the blast furnace slag is 20 to 100 parts by mass when the content of the cement clinker is 100 parts by mass, and the content of the gypsum is 5 to 25 parts by mass in terms of SO _3. The cementitious composition as described in 2.   The cementitious composition of Claim 8 or 9 whose ratio of the said reproduction | regeneration anhydrous gypsum is 30-100 mass% on the basis of the total mass of the said gypsum. The slurry is obtained by mixing the cement-based composition and water so that the ratio (w / c) of the mass w of water to the mass c of the cement-based composition is 0.6.
The cementitious composition according to any one of claims 8 to 10, wherein a flow-down time measured using a Marsh funnel viscometer and a temperature of the slurry of 35 ° C is 35 seconds or less.   The cementitious composition as described in any one of Claims 8-11 which is a ground improvement solidification material.

Images