Method for producing cement composition

Abstract

To provide a method of manufacturing a cement composition with reduced time-dependent loss even in a high-strength compounding where a polycarboxylic acid-based admixture is used, and moreover, securing initial fluidity right after kneading.SOLUTION: A manufacturing method of a cement composition includes: a finishing step including pulverizing a clinker blend including at least one cement clinker selected from the group consisting of an early-strength Portland cement clinker and normal Portland cement clinker, and gypsum dihydrate by using a finishing mill, followed by controlling the hemihydration rate of the pulverized composition at the finishing mill to be under 50%; and a storage step including feeding the pulverized composition to an open type vessel, followed by dehydrating the gypsum dihydrate in the open type vessel and elevating the hemihydration rate of the pulverization composition by 10 points or over.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cement composition. [Background technology]

[0002] In order to reduce the environmental impact and production costs, a certain amount of waste materials is used as cement raw materials. Although there are many different types of waste, the selection and amount of waste used are limited to the extent that it does not affect the quality of the cement, and cement clinker is burned. Among the waste materials actively used as cement raw materials is coal ash (bottom ash and fly ash) from thermal power plants, whose chemical composition introduces a significant amount of Al2O3 into cement clinker. As a result, cement clinker is often designed with a high proportion of interstitial matter (C3A + C4AF). Non-Patent Document 1 cites examples of clinkers with an increased C3A content resulting in 19-24% interstitial matter, an equal increase in C3A and C4AF resulting in 20-26%, and an increased C4AF content resulting in 19-26% interstitial matter, compared to the standard bog composition of ordinary Portland cement clinker, where both C3A and C4AF are 9% and the interstitial matter is 18% (see Table 5 in Non-Patent Document 1).

[0003] As a result of this design with an increased proportion of voids, there is a concern that the initial fluidity immediately after mixing may not be ensured. As a countermeasure, Non-Patent Document 2 indicates that for compositions using highly porous cement clinker with C3A and C4AF contents of 11.0 and 12.7%, it is effective to increase the SO3 content of the cement from 2.0% to 3.5 and 5.0% (equivalent to gypsum-derived SO3 content of 1.34% to 2.84 and 4.34%), to increase the hemihydration rate from 0 to 50%, and to use a comb-type polymer dispersant (hereinafter referred to as a polycarboxylic acid-based dispersant). Furthermore, Non-Patent Document 3 uses a highly porous clinker with C3A and C4AF amounts of 11.6% and 8.8%, and adds less gypsum-derived SO3 than Non-Patent Document 2 (reduced to about 2.36%), and shows that a 10% replacement of limestone powder in cement with a hemihydrate rate of 50% can improve fluidity (see Fig. 2 in Non-Patent Document 3).

[0004] All of these documents share the common point that it is necessary to increase the amount of gypsum-derived SO3 by a certain amount in response to an increase in the interstitial material. Also, the form of gypsum hemihydrate is not specified, but it is generally thought to be the β form when it is produced by dehydration in air or when it is used as a reagent. On the other hand, there is some debate regarding the form of gypsum hemihydrate when cement is produced industrially. It is thought that the β-type will predominate if the cement is dehydrated by heating in air, but as described in Patent Document 1, grinding in a tube mill, which is the most common method for finishing cement grinding, requires the presence of steam due to ventilation and water spraying inside the mill, so that a certain proportion of the gypsum dihydrate added during finish grinding can transform to the α-type. Patent Document 1 also discloses a method for producing a cement composition with improved fluidity and viscosity, as well as good workability, in which the water content in the steam gas and the temperature immediately after grinding (at the finish mill outlet) are adjusted to 120 to 135°C. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-055008 [Non-patent literature]

[0006] [Non-Patent Document 1] Maruya et al., Material Design of Cement for Increasing Waste Use and Reducing CO2 Emissions, Journal of the Japan Society of Material Cycles and Waste Management, Vol. 20, No. 1, pp. 1-11, 2009 [Non-patent document 2] Nozaki et al., Optimization of sulfur trioxide (SO3) content in fluidity of cement with increased aluminate phase, Proceedings of the Cement and Concrete Journal, No. 60, pp. 2-8, 2006 [Non-patent document 3] Maruya et al., Fluidity and Hydration Properties of High-Aluminate Cement with Additives, Proceedings of the Cement and Concrete Society, No. 64, pp. 54-59, 2010 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a method for producing a cement composition in which loss over time is reduced even in a high-strength blend in which a polycarboxylic acid-based admixture is used, and in which initial fluidity immediately after mixing is ensured. [Means for solving the problem]

[0008] The present invention provides the following <1> ~ <4> to provide. <1> a finishing step of grinding a clinker mixture containing at least one cement clinker selected from the group consisting of high-early-strength Portland cement clinker and ordinary Portland cement clinker, and gypsum dihydrate, by a finishing mill to make the hemihydration rate of the ground composition output from the finishing mill less than 50%; an increasing step of introducing the ground composition into an open container and dehydrating the gypsum dihydrate in the open container to increase the hemihydration rate of the ground composition by 10 points or more; A method for producing a cement composition, comprising: The hemihydration rate is calculated by the following formula (1). Hemihydration rate (%) = amount of half-water SO3 / (amount of dihydrate SO3 + amount of half-water SO3) × 100 (1) In the formula (1), the amount of SO3 dihydrate represents the amount of converted SO3 derived from gypsum dihydrate in the pulverized composition and is calculated by multiplying the amount of gypsum dihydrate (mass%) in the pulverized composition by 80 / 172, and the amount of SO3 hemihydrate represents the amount of converted SO3 derived from gypsum hemihydrate in the pulverized composition and is calculated by multiplying the amount of gypsum hemihydrate (mass%) in the pulverized composition by 80 / 145.

[0009] <2> The semi-hydration rate of the ground composition obtained from the finishing mill is less than 40%. <1> A method for producing the cement composition described in claim 1. <3> Increase the semi-hydration rate of the ground composition in the open container by 20 points or more. <1> or <2> A method for producing the cement composition described in claim 1. <4> using a plurality of said finishing mills and cement coolers; The pulverized composition discharged from the finishing mill is charged into the open container without using the cement cooler in a charging step 1, and the pulverized composition discharged from the finishing mill is charged into the open container using the cement cooler in a charging step 2, which are carried out in parallel, thereby dehydrating the dihydrate gypsum in the open container and increasing the hemihydration rate of the pulverized composition. <1> ~ <3> 10. A method for producing a cement composition according to any one of the preceding claims. <5> The open vessel is a cement silo. <1> ~ <4> 10. A method for producing a cement composition according to any one of the preceding claims. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing a cement composition in which loss over time is reduced even in high-strength formulations in which polycarboxylic acid-based admixtures are used, and in which initial fluidity immediately after mixing is ensured. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph showing the relationship between the paste flow value and the hemihydration rate of an open-type cement paste immediately after mixing and an open-type cement paste 60 minutes after mixing in an example. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this specification, the expression "AA to BB" as a numerical range means "not less than AA and not more than BB."

[0013] In the past, when pumping concrete, pumps have sometimes become clogged with concrete. It has been found that the main causes of this are a phenomenon called arching, in which aggregates in the concrete clump together, and a phenomenon called paste blockage, in which the viscosity of the cement paste increases. As mentioned above, there has long been concern about compatibility issues, in which depending on the combination of cement and admixture, a decrease in fluidity (flow loss) occurs after mixing, and this compatibility issue is also one of the causes of poor pumping. Flow loss that occurs immediately after mixing cement and admixtures or after time has passed since mixing has not been able to improve fluidity even by adding more admixtures and water.

[0014] The mechanism behind these admixture compatibility issues has not yet been fully elucidated, but it is believed to be mainly caused by parameters related to the fineness of the cement, such as Blaine specific surface area and particle size distribution, parameters related to the initial amount of admixture adsorption, such as the pore mass (C3A, C4AF) in the cement clinker, the C3A / C4AF ratio in the pore mass, and alkali sulfate content, as well as the adsorption tendency of each admixture brand, and a certain degree of understanding has been achieved by combining these factors. Regarding the initial fluidity of cement and admixtures after mixing, the phenomenon of the amount of admixture required increasing immediately after mixing when there are no compatibility problems, and the phenomenon of the initial flow plateauing can be considered as follows from the perspective of the amount of adsorption to unhydrated cement and the amount of adsorption to cement hydrates.

[0015] (1) Specific surface area of ​​unhydrated cement The fluidity of cement paste using admixtures is achieved by mixing water and admixtures with cement, which causes the cement to begin to hydrate. As the admixtures are adsorbed onto the cement particles, they disperse, reducing viscosity. Increasing the specific surface area of ​​unhydrated cement by extending the finishing grinding time in cement production to ensure the initial strength of the cement increases the amount of admixture adsorbed to the unhydrated cement. This increases the amount of admixture required.

[0016] (2) Specific surface area of ​​initial cement hydrate Even if the specific surface area of ​​cement is not large, a large amount of hydrates can be formed after mixing cement with water and admixtures, resulting in an increase in the initial adsorption amount. This is due to the presence of a large amount of C3A and C4AF, known as interstitial materials, in cement clinker. This causes a large amount of unhydrated cement to react in the early stages, increasing the specific surface area of ​​the cement hydrates that react, and therefore the total amount of admixture adsorption. Cement hydrates are primarily ettringite phases, which have a high aspect ratio and tend to increase the specific surface area. As the amount of admixture adsorption increases, the amount of admixture required also increases.

[0017] (3) Liquid phase composition in mixing water SO4 2- ion Next, as a phenomenon related to the effectiveness of admixtures, sulfate ions (SO4 2- ions) may be involved. When polycarboxylic acid based admixtures are used as admixtures, alkali sulfates in cement clinker are eluted and the SO4 2- The ion concentration may increase and remain high. In this case, the carboxyl group, which is the adsorption group of the admixture, competes with the sulfate ion (adsorption equilibrium) to produce SO4 2- This can lead to ion dominance, inhibiting the adsorption of admixtures to unhydrated cement and cement hydrates and suppressing the effectiveness (dispersion) of the admixtures. This increases the amount of admixture required and also suppresses the effectiveness of the admixture itself, making it impossible to resolve the decrease in initial flow.

[0018] Whether flow loss occurs or not, the amount of admixture adsorption increases over time, and once adsorption reaches a certain level, even greater flow loss may occur. This generally occurs when the admixture concentration reaches the equilibrium adsorption concentration, after which further significant flow loss occurs. More specifically, in concrete compositions with low W / C ratios that use a large amount of high-performance air-entraining water-reducing agent (known as high-strength flow mixes) and a target slump flow value exceeding 55 cm, the slump flow decreases over time, and the slump flow after a pressure bleeding test to evaluate pumpability decreases significantly.

[0019] The compatibility problem of admixtures that is specific to the use of cement made from high-porosity ordinary Portland cement clinker and polycarboxylic acid admixtures is thought to be related to the hydrates of the initial cement, as shown above in (2), which are mainly caused by an increase in the amount of C3A, which has high hydration activity. Furthermore, high-early-strength Portland cement has a high proportion of interstitial matter, similar to that of ordinary Portland cement, and is designed to contain a high proportion of C3S, has a high proportion of cement mineral phase, which is generally thought to have a high admixture absorption capacity, and has a higher Blaine specific surface area than other varieties in order to ensure compressive strength at short ages.For this reason, even in high-early-strength Portland cement, which has a slightly lower proportion of interstitial matter than ordinary Portland cement with high interstitial matter, the specific surface area of ​​the interstitial matter also increases when it is finely ground, so it is thought that both the specific surface area of ​​the unhydrated cement mentioned above (1) and the hydrates of the initial cement (2) are involved.

[0020] As disclosed in Non-Patent Document 1, the influence caused by an increase in interstitial components in cement clinker makes it particularly difficult to ensure fluidity immediately after mixing. Non-Patent Document 2 discloses that it is effective to increase the SO3 in cement to 3.5% or 5.0% using gypsum and to use a polycarboxylic acid-based admixture in combination. However, the current JIS R5210:2019 Portland cement regulations stipulate that the upper limit for sulfur trioxide (SO3) in ordinary Portland cement and high-early-strength Portland cement is 3.5%, so the lower limit of the range indicated as effective in this document is close to the upper limit specified in the JIS standard.

[0021] Similarly, Non-Patent Document 3 discloses that increasing the SO3 in cement with gypsum and adding 10% limestone powder is effective, but similarly, the current JIS standard limits the total amount of minor mixed components to 5%, so this falls outside the scope of the JIS standard. In the method for producing Portland cement disclosed in Patent Document 1, it is shown that cement with a higher proportion of alpha-type gypsum hemihydrate in the cement has good resistance to separation in a hardening test of a cement paste containing only water and cement, and in a cement paste containing water, cement, and a naphthalene sulfonic acid admixture, and that this method may enable a reduction in mixing time. However, given the recent demand for high-strength mixtures, it is not clear whether this production method is optimal for high-strength mixtures that use polycarboxylic acid admixtures.

[0022] Furthermore, the same CO2 emission reductions and energy conservation measures that are required in the cement industry are also being sought in the power generation industry, regardless of industry, and as a result, coal-fired power generation is expected to be replaced by other renewable energy sources. If the operation of thermal power plants is reduced, it is thought that obtaining the by-product, wastewater-decomposed gypsum dihydrate, will become difficult. Under such social circumstances, even if the upper limits on the amount of SO3 in cement and the amount of minor mixed components added are relaxed, it may become difficult to increase the gypsum-derived SO3 as in Non-Patent Documents 2 and 3 from the perspective of obtaining raw materials. This would increase the amount of gypsum required for the design of the cement composition as described above, and there is concern that the impact would be even greater due to the increased cost of the gypsum itself. Therefore, cement manufacturing methods that can reduce the amount of gypsum used and are optimized for the use of polycarboxylic acid admixtures are becoming increasingly important in an environment where energy conservation is required.

[0023] In contrast, by using the method for producing a cement composition of the present invention, it is possible to produce ordinary Portland cement and high-early-strength Portland cement compositions that have reduced loss over time even in high-strength blends that use polycarboxylic acid admixtures and that also ensure initial fluidity immediately after mixing. The method for producing the cement composition of the present invention will be described in detail below.

[0024] <Method of manufacturing cement composition> The method for producing a cement composition of the present invention is characterized by comprising: a finishing step of grinding a mixture containing at least one cement clinker selected from the group consisting of high-early-strength Portland cement clinker and ordinary Portland cement clinker, and gypsum dihydrate, using a finishing mill, to reduce the hemihydration rate of the ground composition discharged from the finishing mill to less than 50%; and an increasing step of charging the ground composition into an open container, dehydrating the gypsum dihydrate in the open container, and increasing the hemihydration rate of the ground composition by 10 points or more. However, the hemihydration rate is calculated using the following formula (1). Hemihydration rate (%) = amount of half-water SO3 / (amount of dihydrate SO3 + amount of half-water SO3) × 100 (1) In formula (1), the amount of SO3 dihydrate represents the amount of converted SO3 derived from gypsum dihydrate in the ground composition and is calculated by multiplying the amount of gypsum dihydrate (mass%) in the ground composition by 80 / 172, and the amount of SO3 hemihydrate represents the amount of converted SO3 derived from gypsum hemihydrate in the ground composition and is calculated by multiplying the amount of gypsum hemihydrate (mass%) in the ground composition by 80 / 145.

[0025] Cement compositions are typically produced through a raw material process in which limestone, clay, etc. are mixed, crushed, and blended; a firing process in which the blended raw materials are fired in a rotary kiln to form clinker; and a finishing process in which gypsum dihydrate is added to the resulting clinker and pulverized in a finishing mill until the desired Blaine specific surface area is achieved. In the present invention, the finishing process is configured as described above, and the composition obtained by reducing the hemihydration rate of the ground composition discharged from the finishing mill to less than 50% and increasing the hemihydration rate by 10 points or more in an open container (e.g., a cement silo) is referred to as a cement composition.

[0026] [Finishing process] In the finishing step, a mixture containing gypsum dihydrate and at least one cement clinker selected from the group consisting of high-early-strength Portland cement clinker and ordinary Portland cement clinker is ground in a finishing mill to make the hemihydration ratio of the ground composition discharged from the finishing mill less than 50. The ground composition discharged from the finishing mill may be cooled using a cement cooler. In the finishing step, a plurality of finishing mills may be used, and in this case, the "hemihydration rate of the pulverized composition discharged from the finishing mill" is an average value. Furthermore, the "hemihydration ratio of the ground composition discharged from the finishing mill" refers to the hemihydration ratio of the ground composition after it is discharged from the finishing mill and before it is introduced into the open vessel for the ascending process. However, if other operations are performed on the ground composition after it is discharged from the finishing mill and before it is introduced into the open vessel for the ascending process, the "hemihydration ratio of the ground composition before it is introduced into the open vessel for the ascending process" refers to the hemihydration ratio of the ground composition before it is introduced into the open vessel for the ascending process. For example, if the ground composition discharged from the finishing mill is cooled using a cement cooler, the "hemihydration ratio of the ground composition after it is discharged from the finishing mill and before it is cooled in the cement cooler" is the "hemihydration ratio of the ground composition discharged from the finishing mill."

[0027] In addition to cement clinker and gypsum dihydrate, the mixture may further contain minor admixture components such as limestone, blast furnace slag, fly ash (Type I or Type II), and siliceous admixtures. If the hemihydration rate of the ground composition discharged from the finishing mill exceeds 50%, the content of gypsum dihydrate, which should be dehydrated in the open vessel, will be reduced, which is undesirable. Also, if the dehydration in the open vessel is excessive and the hemihydration rate exceeds 95%, the fluidity of cement paste, mortar, concrete, etc. immediately after mixing will be poor. Therefore, from the viewpoint of ensuring that there is enough gypsum dihydrate to undergo dehydration in the open vessel and ensuring a margin to prevent excessive dehydration in the open vessel, the hemihydration rate of the ground composition output from the finishing mill is preferably less than 40%, and from the viewpoint of preventing a significant decrease in grinding efficiency due to excessive suppression of the hemihydration rate in the finishing mill, the hemihydration rate is preferably 20% or more.

[0028] A finishing mill is a closed-system grinding machine also known as a ball mill, a tube mill, etc. A water spraying process is performed to control the temperature rise inside the finishing mill, and since the gypsum dihydrate is dehydrated in a closed space, the water vapor generated by the water spraying process and the dehydration of the gypsum dihydrate is not completely discharged outside the system from the finishing mill, and the water vapor content is maintained at around the water vapor content corresponding to the saturated water vapor pressure at the temperature inside the mill. The hemihydration rate of the pulverized composition obtained from the finishing mill can be adjusted by the temperature, grinding time, etc. when grinding a mixture containing cement clinker and gypsum dihydrate in a finishing mill. Alternatively, multiple finishing mills may be used to prepare pulverized compositions with different hemihydration rates, and the hemihydration rate may be adjusted by changing the mixing ratio of the pulverized compositions with different hemihydration rates.

[0029] In normal cement production, the temperature inside the finishing mill is maintained at at least 100°C or higher to prevent the ground composition from hydrating (weathering) by water spraying into the finishing mill. Therefore, gypsum dihydrate introduced into the finishing mill together with cement clinker is dehydrated due to the temperature rise, and particularly when the temperature inside the finishing mill is maintained at a high temperature of 130°C or higher, a significant proportion of the introduced gypsum dihydrate is dehydrated and becomes hemihydrate in a short period of time. The ground composition discharged from the finishing mill passes through a separator, where particles larger than a specified particle size are collected by a cyclone and returned to the finishing mill, while particles smaller than a specified particle size are sent to a cement cooler (to prevent further hemihydration).The material is cooled to around 50-80°C by heat exchange in the cement cooler, and is usually sent to a cement silo, which is an open container, except in cases where it is to be directly loaded onto a tanker for shipment.

[0030] [Rising process] In the raising step, the ground composition obtained through the finishing step is placed in an open container, and the dihydrate gypsum is dehydrated in the open container to raise the hemihydration rate of the ground composition by 10 points or more. For example, if the hemihydration rate of the ground composition at the finish mill is 30%, the gypsum dihydrate is dehydrated in an open container so that the hemihydration rate of the ground composition after the storage step is 40% or more. The increase in the hemihydration rate of the ground composition in the rising step is (i) A pulverized composition having a hemihydration rate of less than 50% [referred to as composition (a)] may be mixed with a pulverized composition having a hemihydration rate of 50% or more [referred to as composition (b)] obtained by dehydrating gypsum dihydrate in an open container, (ii) The composition (a) may be heated using a heating device or the like. (iii) When composition (a) is heated to a temperature higher than room temperature, simply storing composition (a) in an open container can promote dehydration of the pulverized composition, thereby increasing the hemihydration rate of the pulverized composition. (iv) It may be carried out by a combination of (i) to (iii). For example, composition (a) may be mixed with composition (b) heated to a temperature higher than that of composition (a), and composition (a) may be heated by the latent heat of composition (b) while adjusting the hemihydration rate.

[0031] If the increase in the hemihydration rate in the increasing step is less than 10 points, the fluidity of cement paste, mortar, concrete, etc. using the produced cement composition will not be excellent. The increase in the hemihydration rate of the ground composition after the rising step is preferably 20 points or more from the hemihydration rate of the ground composition as obtained by the finishing mill, and is preferably 60 points or less in order to prevent the hemihydration rate from becoming excessive.

[0032] The open container means a container that allows water vapor emitted from the pulverized composition placed in the container to be discharged from the container and allows ventilation, and may have a lid or not. Examples include a stainless steel tray, a cement silo, etc. Unlike finishing mills, cement silos have an open interior space, and the water vapor generated by the dehydration of gypsum dihydrate can easily escape from the cement silo. The cement brought into the cement silo carries latent heat depending on the temperature at the time of loading, so the temperature inside the silo rises above the outside air temperature. The environment inside the cement silo, such as the temperature and whether or not it is an atmosphere with water vapor, is thought to be related to the ventilation status inside the cement silo, and these conditions can be roughly classified into the following two and are thought to be affected. (1) A closed system that is airtight and maintains the temperature raised by the latent heat of the cement. (2) An open system in which water vapor is quickly transported outside the silo by ventilation and temperature increases due to latent heat are suppressed. However, in normal cement finishing facility operation, the cement is cooled sufficiently and is rarely maintained at temperatures above 80°C for long periods of time in the cement silo. Therefore, even in an open environment where hemihydration progresses more quickly when compared at the same temperature, the hemihydration rate does not increase significantly.

[0033] As described above, in the raising step, the hemihydration rate of the pulverized composition in the cement silo can be increased by 10 points or more by controlling the temperature of the pulverized composition introduced into the cement silo. For example, by using a plurality of finishing mills and cement coolers, and carrying out in parallel a charging step 1 in which the pulverized composition discharged from the finishing mill is charged into a cement silo without using a cement cooler, and a charging step 2 in which the pulverized composition discharged from the finishing mill is charged into the cement silo using the cement cooler, it is possible to dehydrate the dihydrate gypsum in the cement silo and increase the hemihydration rate of the pulverized composition.

[0034] Below, an example of the operation of the finishing mill and cement cooler in the finishing step and the control of the temperature and hemihydration rate of the pulverized composition fed into the cement silo in the rising step will be described based on a specific embodiment.

[0035] [Embodiment 1] (One low-temperature mill) When grinding is performed using a single finishing mill, the hemihydration process can be promoted in the cement silo by intermittently repeating the steps below, which involve introducing latent heat by grinding at high temperatures and suppressing an increase in the hemihydration rate by grinding at low temperatures. This allows the average hemihydration rate of the cement output from the finishing mill to be kept below 50% and also promotes the dehydration of gypsum dihydrate in the cement silo. In the latent heat carrying-in step, high-temperature grinding operation (finishing mill outlet temperature of 120°C or higher) is performed in the finishing mill, and the ground composition is charged into a cement silo without using a cement cooler. In the step of suppressing an increase in the finishing mill hemihydration rate, low-temperature grinding operation is performed in the finishing mill, and the ground composition is charged into a cement silo using a cement cooler. An embodiment of the above-mentioned configuration is shown in Table 1. The mill capacity is 10 t / hour.

[0036] [Table 1]

[0037] Stably repeating the above-described high-temperature grinding operation and low-temperature grinding operation while periodically fluctuating between them requires a large temperature difference between the high-temperature grinding and the low-temperature grinding, and requires a greater cooling capacity from the cement cooler than during normal operation. For these reasons, it is difficult to achieve this in plants with large production capacities where it is not possible to quickly change operating conditions. For this reason, when multiple mills can be used for finish grinding, it is desirable to operate them in the manner as in the second embodiment.

[0038] [Embodiment 2] (Multiple mills) If multiple finishing mills can be used, the progress of hemihydration in the cement silo becomes easier. By using multiple finishing mills, the average hemihydration rate of the cement composition output from the multiple finishing mills can be kept below 50%, and the dehydration of gypsum dihydrate in the cement silo can be promoted.

[0039] (1) In the latent heat carrying finishing mill, high temperature grinding is performed in the finishing mill (finishing mill outlet temperature of 140°C or higher), and the ground composition is poured into a cement silo without using a cement cooler. (2) In the finishing mill for suppressing an increase in the hemihydration rate, low-temperature grinding is carried out in the finishing mill, and the ground composition is poured into a cement silo using a cement cooler. As an example, as shown in Table 2, by operating two mills (1) with a mill outlet temperature of 140°C and three cement coolers (2) with a cement cooler outlet temperature of 80°C, it is expected that the mixture will be brought into the cement silo at around 100°C.

[0040] [Table 2]

[0041] By monitoring the cement temperature at the finishing mill and the cement temperature in the silo and operating as described above, it is possible to keep the average hemihydration rate of the cement at the finishing mill low and to promote hemihydration in the cement silo. The rate at which dehydration and semi-hydration progress varies depending on the holding temperature and the presence or absence of steam, but in the case of dehydration in an open system such as dehydration in a silo, the process progresses quickly above 110°C, but becomes extremely slow below 70°C. [Example]

[0042] <Raw materials for cement compositions> Base cement: High-early-strength Portland cement (produced in a commercial plant, sampled and cooled before being poured from the finishing mill into the cement silo). The chemical composition is shown in Tables 3 and 4.

[0043] [Table 3]

[0044] [Table 4]

[0045] Open system dehydration cement (semi-hydrated rate 99%): Dehydration in an environment where water vapor is quickly released The base cement was placed in a stainless steel tray measuring 580 x 420 x 110 mm at a height of about 3 cm and kept at 140°C for one day to dehydrate. Closed system dehydration cement (semi-hydrated rate 91%): Dehydration in an environment where water vapor remains within the system 500 g of base cement was sealed in a 500 mL plastic bottle and dehydrated by keeping it in a dryer at 100°C for 5 days.

[0046] The mineral compositions of the base cement, closed-system dehydrated cement, and open-system dehydrated cement are shown in Table 5.

[0047] [Table 5]

[0048] The chemical compositions of the base cements shown in Tables 3 and 4 were analyzed by the glass bead method using an X-ray fluorescence analyzer (PRIMUS IV, manufactured by Rigaku Corporation) in accordance with JIS R 5204:2019 "Method for X-ray fluorescence analysis of cement." The mineral compositions of the base cements shown in Tables 3 and 4 were calculated from the mass proportions of CaO, SiO2, Al2O3, and Fe2O3 obtained using the Borg formula below. C3S=(4.07×CaO)-(7.60×SiO2)-(6.72×Al2O3)-(1.43×Fe2O3) C2S = (2.87 × SiO2) - (0.754 × C3S) C3A=(2.65×Al2O3)-(1.69×Fe2O3) C4AF = 3.04 × Fe2O3

[0049] The Blaine specific surface area of ​​the base cement shown in Table 4 was measured in accordance with JIS R 5201:2015 "Physical testing methods for cement."

[0050] The mineral composition of each cement shown in Table 5 was determined by powder X-ray diffraction measurement and Rietveld analysis. The powder X-ray diffractometer used was a D8 Advance (manufactured by Bruker AXS). The measurement conditions and Rietveld analysis conditions are described below. (Measurement conditions) X-ray tube:Cu Tube voltage: 40kV Tube current: 40mA Measurement range of diffraction angle 2θ: start angle 5°, end angle 70° Step width: 0.025° / step Counting time: 60 sec. / step

[0051] Rietveld analysis conditions Rietveld analysis software: TOPAS Ver. 4.2 (Bruker AXS) Zero point correction: None Sample surface height correction: Yes

[0052] Regarding the measurement and analysis of the hemihydration rate (when the quantification of cement minerals is not required), the quantification of gypsum dihydrate and gypsum hemihydrate in cement and the calculation of the hemihydration rate can be performed by known means. Accurate quantification can also be performed by TG / DTA using a sealed aluminum pan with holes or DSC measurement using a sealed aluminum pan with holes and a water vapor supply means.

[0053] <Preparation of cement with various hemihydration rates> According to the mixing ratios shown in the "Open Mixing" column of Table 6, the base cement and open dehydrated cement were weighed and mixed by dry mixing at low speed for about 1 minute using a Hobart mixer to prepare cements with hemihydration rates of 40%, 59%, and 81%. According to the mixing ratios shown in the "Closed System Mixing" column of Table 6, the base cement and closed system dehydrated cement were weighed and mixed by dry mixing at low speed for about 1 minute using a Hobart mixer to prepare cements with semi-hydration rates of 40%, 58%, and 80%. In this manner, a closed-system dehydration cement simulating dehydration in a finishing mill and an open-system dehydration cement simulating dehydration in a cement silo were prepared.

[0054] <Preparation of cement paste> A total of seven cement pastes were prepared using the base cement, the three prepared open-system dehydration cements, and the three prepared closed-system dehydration cements. Specifically, water was added to 300 g of cement so that the water-to-cement ratio (W / C) was 30% by mass and the admixture-to-cement ratio (SP / C) was 2.4% by mass, and mixing was then started immediately. After mixing for 60 seconds at low speed, 30 seconds of scraping, and 90 seconds at high speed, the paste was subjected to a paste flow test. The admixture (SP) used was a polycarboxylic acid-based high-performance air-entraining water-reducing agent manufactured by BASF Pozzolith, trade name "Rheobuild SP8SV (standard type)."

[0055] <Evaluation> The prepared cement paste was subjected to a cement paste test using a cylindrical acrylic pipe flow cone with an inner diameter of 50 mm and a height of 51 mm (internal volume ≈ 100 mL) to evaluate the flow immediately after mixing and the flow over time. The flow immediately after mixing and the flow over time were evaluated as follows. The results are shown in Table 6.

[0056] (Flow immediately after mixing) Immediately after mixing, the cement paste was poured into the flow cone, and after 1 minute (4 minutes after the start of mixing), the flow cone was raised and the flow value was measured.

[0057] (Age-dependent material flow) The cement paste in the mixing bowl was homogenized by stirring it with a spoon for 30 seconds 90 seconds before the material reached its aged age, and immediately after homogenization, the cement paste was poured into the flow cone. After 1 minute, the flow cone was lifted and the flow value was measured.

[0058] [Table 6]

[0059] From the results shown in Table 6, the flow values ​​of the open-mixed cement paste of the example and the closed-mixed cement paste of the comparative example can be considered as follows.

[0060] (Open mixed system) The flow value immediately after mixing for cement paste using cement with a hemihydration rate of 79% is almost the same as that for cement paste using base cement, while cement pastes using cement with hemihydration rates of 39% and 59% have better fluidity than cement paste using base cement.

[0061] Compared to the cement paste of base cement, the flow value over time was large for all cement pastes using cement with hemihydration rates of 39%, 59% and 79%, and the paste flow value was high after 30 minutes of aging, the fluidity was good, and no flow loss was observed. From the above results, it can be seen that since fluidity is good if the increase in hemihydration rate from the base cement is 21, 41 or 61 points, sufficient effects can also be expected from cement with a hemihydration rate of 20 or 40 points increased from a base cement with a hemihydration rate of 50%. In other words, it is recognized that an increase of around 0.53 or 1.06 points in the amount of SO3 hemihydrate due to open system dehydration will have a significant effect.

[0062] Figure 1 is a graph showing the relationship between paste flow and hemihydration rate for open-system cement paste immediately after mixing and for open-system cement paste 60 minutes after mixing. As shown in Figure 1, the plot shows that open-system dehydration has a significant effect when the hemihydration rate increases in 20-point increments. A 10-point increase in hemihydration rate from a hemihydration rate of less than 50% is expected to be sufficient to produce a significant effect, while an increase from less than 50% to around 70% is expected to maintain the current level. Therefore, even if the base cement hemihydration rate is somewhat high, around 50%, open-system dehydration can be used to improve fluidity by securing a margin of 10 to 15 points in production at a cement manufacturing plant.

[0063] (Closed mixed system) The flow values ​​immediately after mixing were higher for all cement pastes using cement with hemihydration rates of 39%, 58%, and 79% than for the cement paste with base cement, and the fluidity was good. However, the flow values ​​over time were lower than for the cement paste with base cement. All cement pastes using cement with hemihydration rates of 39%, 58%, and 79% showed flow loss immediately after mixing after 30 minutes. After 60 minutes, the flow increased slightly, but was smaller than the flow value of the base cement.

[0064] From the above results, it can be seen that the method for producing a cement composition of the present invention makes it possible to produce a cement composition with reduced loss over time in a cement production facility equipped with a finishing mill and a cement silo. It also makes it possible to produce a cement composition with reduced gypsum consumption or required admixtures.

Claims

1. a finishing step of grinding a mixture containing at least one cement clinker selected from the group consisting of high-early-strength Portland cement clinker and ordinary Portland cement clinker and gypsum dihydrate by a finishing mill to make the hemihydration rate of the ground composition output from the finishing mill less than 50%; an increasing step of introducing the pulverized composition into an open container and dehydrating the gypsum dihydrate in the open container to increase the hemihydration rate of the pulverized composition by 10 points or more and increasing the amount of SO 3 equivalent derived from the gypsum hemihydrate in the pulverized composition by 0.53 points; The method for producing a cement composition, wherein the rising step is carried out by any one of the following (i) to (iv): (i) The pulverized composition having a hemihydration rate of less than 50% obtained in the finishing step is mixed with a pulverized composition having a hemihydration rate of 50% or more obtained by dehydrating gypsum dihydrate in the open container. (ii) The pulverized composition having a semi-hydration rate of less than 50% obtained in the finishing step is heated by a heating device. (iii) storing the ground composition having a semi-hydration rate of less than 50% obtained in the finishing step in the open container; (iv) A combination of (i) to (iii) The hemihydration rate is calculated by the following formula (1). Hemihydrate rate (%) = hemihydrate SO ３ Quantity / (SO₂ dihydrate) ３ Quantity + half water SO ３ (Quantity) × 100 (1) In the formula (1), the dihydrate SO ３ The amount is the converted SO 2 from gypsum dihydrate in the ground composition. ３ The amount of gypsum dihydrate in the ground composition (% by mass) is calculated by multiplying the amount by 80 / 172. ３ The amount of converted SO 2 from gypsum hemihydrate in the ground composition ３ The amount represents the amount of gypsum hemihydrate in the ground composition (% by mass) × 80 / 145.

2. 2. The method for producing a cement composition according to claim 1, wherein the hemihydration rate of the ground composition obtained by the finishing mill is less than 40%.

3. 3. The method for producing a cement composition according to claim 1, wherein the hemihydration rate of the pulverized composition in the open vessel is increased by 20 points or more.

4. using a plurality of said finishing mills and cement coolers; 4. The method for producing a cement composition according to any one of claims 1 to 3, wherein a charging step 1 of charging the pulverized composition obtained by the finish milling into the open container without using the cement cooler and a charging step 2 of charging the pulverized composition obtained by the finish milling into the open container using the cement cooler are carried out in parallel, thereby dehydrating gypsum dihydrate in the open container and increasing the hemihydration rate of the pulverized composition.

5. The method for producing a cement composition according to any one of claims 1 to 4, wherein the open container is a cement silo.

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