JP2009040645A - Low hydration heat cement composition and its manufacturing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement composition which exhibits a reduced heat of hydration in the medium or long term (7 and/or 28 days in terms of material age), without deteriorating the basic properties such as setting and curing characteristics inherent in "all-purpose cements" such as normal Portland cement, and to provide its manufacturing process. <P>SOLUTION: The low hydration heat cement composition has a Se content of ≤0.8 mg/kg. The composition contains Portland cement clinker and the amount of SO<SB>3</SB>in the Portland cement clinker is 0.2-1.7 mass%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cement composition with reduced heat of hydration.

  The heat of hydration of ordinary Portland cement was determined by the Ministry of Construction in 1990 from the aspect of durability of concrete structures (age 7 days: 84 cal / g or less, age 28 days: 96 cal / g) Thereafter, the civil engineering specification of the Ministry of Land, Infrastructure, Transport and Tourism stipulates that the age of 7 days is 350 J / g or less and that the age of 28 days is 400 J / g or less. However, in recent years, there is a demand for higher strength and higher fluidity of concrete, and the amount of cement used per unit concrete is increasing as a condition of concrete distribution / mixing. Therefore, even if the above specified value is satisfied, depending on the amount of unit cement, there is a problem that the amount of increase in temperature inside the concrete structure due to cement hydration increases, causing cracks and lowering durability. It was.

  On the other hand, in cement production, the amount of waste treatment has been expanded for the purpose of social contribution, and in particular, the amount of waste containing a lot of Al, such as coal ash and construction generated soil, has been increased as a clinker material. I have done it. For this reason, as a composition of ordinary Portland cement clinker, it is necessary to increase the Al content, and as a result, the amount of clinker mineral containing Al having a large amount of hydration heat tends to increase slightly.

As a method for reducing the heat of hydration of cement, a method of controlling the main mineral composition (for example, increasing the amount of C ₂ S) such as moderately hot Portland cement clinker or low heat Portland cement clinker, , Blast furnace slag, fly ash, and pozzolana) may be added, but each method has a problem that the initial strength is delayed (Patent Document 1 and Non-Patent Document 1).

As described above, in “general-purpose cement” such as ordinary Portland cement, heat of hydration is reduced without changing the basic characters (main chemical composition, mineral composition, fineness, gypsum form and added amount, etc.) Although material design is desired, it has been difficult to obtain such materials with the prior art.
JP 61-097154 A "Common sense of cement" 2004 edition, Cement Association, p.11-17

  The problem of the present invention is that the heat of hydration can be achieved over the medium to long term (7 days and / or 28 days in terms of material age) without impairing the basic physical properties such as setting and hardening properties of “general purpose cement” such as ordinary Portland cement. An object of the present invention is to provide a cement composition and a method for producing the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that medium- and long-term (in terms of material age) without impairing the basic physical properties (condensation hardening characteristics) of “general-purpose cement” such as ordinary Portland cement. In order to reduce the heat of hydration on the 7th and / or the 28th), it has been found that it is effective to make the Se content not more than a predetermined value, and the present invention has been achieved.

  That is, the cement composition of the present invention is a low-hydration thermal cement composition having an Se content of 0.8 mg / kg or less.

The low-hydration thermal cement composition of the present invention preferably contains Portland cement clinker, and the amount of SO _{3 in the} Portland cement clinker is preferably 0.2 to 1.7% by mass.

The low-hydration thermal cement composition of the present invention contains Portland cement clinker and gypsum, and the amount of mineral contained in the low-hydration thermal cement composition is 50 to 65% by mass of C ₃ S, C ₃ It is preferable that A amount is 8-11 mass%.

  In addition, the heat of hydration of the low-hydration heat cement composition of the present invention with the Se content reduced to 0.8 mg / kg or less is 330 J / g or less at 7 days of age and / or 390 J / 28 at 28 days of age. g or less.

  Further, in order to reduce the Se content in the cement clinker to 0.8 mg / kg or less, in the cement firing apparatus including the suspension preheater part, the cement kiln from the suspension preheater part to the rotary kiln inlet hood part is used. A method for producing a low-hydration thermal cement composition, which includes performing extraction by extracting at least a part of the selenium-containing exhaust gas, can be used. Preferably, the temperature of the exhaust gas extracted at this time is 300 to 1300 ° C. Preferably, the extraction rate of the exhaust gas is 0.05 to 10% by volume.

  The low hydration heat cement composition of the present invention has a Se content of 0.8 mg / kg or less, so that the heat of hydration is 330 J / g or less at a material age of 7 days and 390 J / g or less at a material age of 28 days. Can be reduced.

  Hereinafter, the present invention will be described in detail.

  The cement composition of the present invention is a low-hydration thermal cement composition containing Portland cement clinker and gypsum, and having a Se content of 0.8 mg / kg or less. In order to ensure that the heat of hydration is low, the Se content is preferably 0.7 mg / kg or less.

  When the Se content in the cement composition exceeds the range of 0.8 mg / kg or less, the heat of hydration increases rapidly, and when used as concrete, the rise in the internal temperature of the structure increases, and cracks, etc. Causes the durability to decrease significantly. Therefore, in order to achieve the effect of the present invention, the Se content needs to be in the above range.

The low-hydration thermal cement composition of the present invention can be obtained by adding gypsum to a cement clinker and grinding it with a ball mill or the like. As for the amount of minerals contained in the low-hydration thermal cement composition of the present invention, C ₃ S is 50 to 65% by mass, preferably 50 to 60% by mass, and C ₃ A is preferably 8 to 11% by mass. In the region where C ₃ S and C ₃ A are below this range, the effect of reducing the heat of hydration due to the reduction of Se content is hardly observed. Conversely, if this range is exceeded, sufficient hydration is achieved even if the Se content is reduced. Heat generation cannot be reduced.

Although not particularly limited, the amount of mineral contained in the low-hydration thermal cement composition of the present invention is preferably 10 to 20% by mass of C ₂ S, 8 to 12% by mass of C ₄ AF, SO ₃ is 1.7 to 2.3 mass%, _{R 2} O content is 0.20 to 0.60% by weight, preferably from 0.30 to 0.55 wt%, Cl amount 0.005 to 0.030 % By mass, preferably 0.010 to 0.020% by mass, 30% to 95%, preferably 40% to 90%, and the fineness of gypsum in the cement composition is 2800 to 3700 cm ² / g, preferably 3100~3500cm ² / g.

Here, the content (mass%) of CaO, SiO ₂ , Al ₂ O ₃ and Fe ₂ O _{3 in} the cement is measured according to JIS R 5202: 1999 “Chemical analysis method of Portland cement”. Further, the C ₃ S amount, the C ₂ S amount, the C ₃ A amount, and the C ₄ AF amount are values calculated by the following Borg formulas (1), (2), (3), and (4).

C ₃ S amount (% by mass) = 4.07 × CaO amount (% by mass) −7.60 × SiO ₂ amount (% by mass) −6.72 × Al ₂ O ₃ amount (% by mass) −1.43 × Fe ₂ O ₃ amount (% by mass) -2.85 × SO ₃ amount (% by mass) (1)
C ₂ S amount (% by mass) = 2.87 × SiO ₂ amount (% by mass) −0.754 × C ₃ S amount (% by mass) (2)
C ₃ A amount (mass%) = 2.65 × Al ₂ O ₃ (mass%) − 1.69 × Fe ₂ O ₃ (mass%) (3)
C ₄ AF amount (mass%) = 3.04 × Fe ₂ O ₃ (mass%) (4)

Incidentally, SO ₃ amount of Portland cement clinker used for the preparation of the cement composition of the present invention is preferably from 0.2 to 1.7 wt%, more preferably 0.4 to 1.5 mass %, Particularly preferably 0.6 to 1.4% by mass.

In addition, although the action mechanism of the reduction of heat of hydration by Se content reduction is not clear, the following can be considered as a non-limiting hypothesis. The relationship between the Se content and the SO ₃ content of the Portland cement clinker is different before and after the specific Se content (0.8 mg / kg), and the heat of hydration tends to be different accordingly. In the region where the Se content in the Portland cement clinker is excessively increased, the correlation between the SO ₃ content and the Se content in the Portland cement clinker is disrupted as shown in FIG. This is thought to be because the production amount and hydration activity of clinker minerals (C ₃ S, C ₂ S, C ₃ A, C ₄ AF), water-soluble compounds (for example, alkali sulfate) and the like change.

≪Cement clinker manufacturing method≫
The manufacturing method of such a cement composition is as follows.

  The cement clinker is either (1) a method of controlling the amount of waste containing a large amount of Se in the clinker raw material preparation step, or (2) a high temperature containing a high concentration of Se using an extraction bypass facility. The amount of Se is controlled to be equal to or less than a predetermined amount by any method of extracting gas, but the method (2) is more preferable.

  The method (1) for controlling the amount of waste containing a large amount of Se to a predetermined amount or less is used when using a cement firing device not equipped with an extraction bypass facility or when the extraction capability of the extraction bypass facility is small. It is useful, and the total amount of waste having an Se content of 5.0 mg / kg or more is 140 kg / t-cl ′ or less in basic unit, and the Se content is 0.2 to 0.8 mg / kg or less, preferably 0 It is also possible to obtain the same effect by manufacturing at 2 to 0.7 mg / kg or less. Here, “kg / t-cl ′” is a raw material necessary for producing 1 ton of clinker. In addition, examples of the waste having a Se content of 5.0 mg / kg or more include coal ash, converter furnace, and copper tangles. In particular, it is effective to reduce the basic unit of coal ash.

  The method (2) uses a cement calciner equipped with a suspension pre-heater unit and a bleed-off bypass facility, and uses a cement kiln from the suspension pre-heater unit to the rotary kiln inlet hood (kiln bottom). In this method, the Se content in the cement clinker is reduced by extracting at least a part. Hereinafter, the method (2) will be described more specifically.

  Generally, the cement clinker is manufactured by the SP method (multistage cyclone preheating method) or the NSP method (multistage cyclone preheating method equipped with a calcining furnace). In these production methods, when a waste material containing a large amount of chloride such as sewage treatment sludge generated at a sewerage treatment facility or municipal waste incineration ash is used as a raw material, a large amount of chloride is taken into the cement clinker. On the other hand, since chloride corrodes the reinforcing bars and steel materials of concrete structures, the content in the cement is regulated. For this reason, as a workaround when using waste containing a large amount of chloride, the chloride is volatilized by high-temperature heat treatment in the kiln firing zone, and backflowed to the raw material preheating part along the flow of combustion gas, In a system that cools, condenses and recirculates by heat exchange, the kiln exhaust gas containing chloride in a volatilized state during the process from the inlet to the raw material preheating section to the inlet to the rotary kiln is used. A method of extracting and separating a part (bleeding), collecting dust after cooling and condensation is effective. Since the substance obtained by collecting from the exhaust gas (extracted gas) extracted by such a method is mainly a cement clinker component, this substance is referred to as “extracted clinker” in this specification.

  As an apparatus used in the above method, there is an extraction gas facility such as a chlorine bypass facility or an alkali bypass facility. As an example, an extraction gas facility generally used for a cement kiln will be described based on a chlorine bypass facility shown in FIG.

  In FIG. 3, 1 is a cement firing kiln, 1a is a firing burner, 2 is a clinker cooler for cooling the clinker fired in the cement firing kiln 1, and 3 is a cement raw material supply side of the cement firing kiln 1 The attached cross section is a substantially rectangular kiln inlet hood, and the kiln inlet hood 3 constitutes a kiln exhaust gas passage and a part of the calcined raw material receiving passage at the kiln kiln bottom. 5 is a suspension preheater (SP) provided with a calcining furnace 5b, 5a is the lowermost cyclone of the suspension preheater 5 and 5c is a raw material supply pipe for supplying raw materials to the preheater 5, 4 is a kiln. It is a rising duct (rising pipe) for connecting the upper end of the inlet hood part 3 and the suspension preheater part 5 to supply the kiln exhaust gas to the suspension preheater part 5 via the calcining furnace 5b.

  6 is an exhaust fan of the suspension pre-heater section 5, and 7 is connected to the lower part of the lowermost cyclone 5a, and the lower end is connected to the lower part of the side wall of the kiln inlet hood 3 that intersects the side wall of the cement firing kiln 1 side. A chute for feeding high-temperature cement raw material (hereinafter referred to as “calcined raw material”), which has been opened and preheated by the suspension preheater 5 and then calcined in the calcining furnace 5b, to the cement firing kiln 1 , 8 are ducts for feeding the exhaust gas of the clinker cooler 2 to the calcining furnace 5b.

  The extraction gas facility 10 for a cement kiln has an exhaust gas extraction port 3a opened on a side wall located on the kiln side of the rising portion of the kiln inlet hood 3 and an exhaust gas which is connected to the inside and fixedly attached to the side wall. The exhaust gas extraction pipe 11 also serving as a cooling means, the lump removal device (chamber) 12 connected to the exhaust gas outlet of the exhaust gas extraction tube 11, the exhaust gas outlet of the lump removal device 12 and the exhaust gas duct 13a communicate the exhaust gas inlet. The bag filter (dust collecting means) 15, the exhaust fan 16 communicated with the exhaust gas outlet of the bag filter 15 via the duct 13 b, the gas outlet of the exhaust fan 16 and the exhaust gas of the clinker cooler 2 to the calcining furnace 5 b On the exhaust gas inlet of the bag filter 15 of the exhaust gas duct 13a and the exhaust gas exhaust duct 13c for connecting the duct 8 to be sent A cool air inlet tube 14 with a damper 14a which is connected to a position, and a cooling fan 11a of the exhaust gas extraction pipe 11 connected with an air supply duct.

  Note that the extraction gas exhaust duct 13c can exhaust the extraction gas by connecting the gas outlet of the exhaust fan 16 and the duct 8 for sending the cooler exhaust gas to the calcining furnace 5b. Further, instead of this mode, a mode in which the gas outlet of the exhaust fan 16 and the calcining furnace 5b are directly connected, a mode in which the gas outlet of the exhaust fan 16 and the rising duct 4 are connected, and a cooling fan of the clinker cooler 2 are further provided. The mode may be returned to 2a.

  On the other hand, a lower hopper 15 a, an extraction clinker discharging screw conveyor 15 b, a cushion hopper 21, and a double butterfly damper 22 are provided at the lower part of the bag filter 15, and constitute an extraction clinker storage / dispensing facility 20. The bleed clinker delivered from the bleed clinker storage / delivery facility 20 is received by the bleed clinker carry-out vehicle (bulk car) 23 and then carried out to the bleed clinker storage receiving hopper 33. Thus, the extraction clinker collected and collected by the bag filter 15 of the extraction gas facility 10 and received by the extraction clinker storage receiving hopper 33 is conveyed to the classifier 32 of the cement finishing mill facility 30 and classified, and the coarse powder is The fine powder is returned to the ball mill 31 and collected as a cement product together with the classified cement fine powder.

The present inventors use this kiln exhaust gas extraction technology not only to remove chlorides in the raw material, but also to be effective for extraction of volatile heavy metals, particularly for extraction and separation of selenium. I found it. That is, in the extracted gas, in addition to the generally known chlorine, potassium, sulfur, and the like, heavy metals such as selenium, cadmium, lead, molybdenum, fluorine, and zinc are included in the form of gas. it is conceivable that. Further, the extracted gas may contain a cement raw material or a calcined raw material thereof. The selenium content remaining in the extraction clinker varies depending on the flow of gas unique to each cement kiln, the site to be extracted, and the ratio of the extracted gas. When gas containing selenium is extracted, a portion with a high selenium content in the exhaust gas is suitable for the extraction position. Specifically, the part from the suspension preheater part 5 to the rotary kiln inlet hood part 3 of the cement firing device is preferable. When the existing extraction gas equipment is used as it is, the rising duct 4 part or the kiln inlet hood is used. Part 3 is preferred. In addition, considering the vaporization temperature of SeO ₂ at 1 atm of about 320 ° C., the upper stage part of the suspension preheater part where the extraction gas temperature is lowered, more specifically, from the viewpoint of heat loss of the kiln due to the high temperature gas extraction. More preferably, an exhaust gas extraction port is newly provided at each of the cyclone junction ducts 5f between the lower cyclone 5a and the exhaust fan 6, particularly the outlet 5g of the uppermost cyclone 5e where the gas temperature is close to 300 ° C. . When the extraction gas temperature is low, the cooling part for protecting the extraction pipe from heat is unnecessary, and the shape of the external air, which is a feature of the conventional chlorine bypass equipment, flows as a swirl flow on the inner wall of the extraction pipe (as shown in FIG. 3 Or a double tube shape in which a portion through which the cooling gas passes is provided around the bleed tube, it can be a simple cylindrical bleed tube.

The extraction gas temperature of the exhaust gas extraction port 3a is preferably 300 to 1300 ° C. If the extraction gas temperature is less than 300 ° C., only a part of selenium may be volatilized. If the extraction gas temperature exceeds 1300 ° C., it is necessary to install a refractory brick or the like to ensure the heat resistance of the extraction port portion. . Since the temperature at which SeO ₂ vaporizes at 1 atm is about 320 ° C., the extraction gas temperature is more preferably 320 to 1200 ° C., further preferably 700 to 1200 ° C. By setting it as such a temperature range, Se content in the cement clinker used as the raw material of a cement composition can be reduced, and Se content in a cement composition can be controlled to 0.8 mg / kg or less. From the viewpoint of preventing heat loss of the kiln due to high temperature gas extraction, the upper limit temperature of the extraction gas temperature can be set to 800 ° C.

The extraction rate when extracting a part of the exhaust gas is preferably 0.05 to 10% by volume. Here, the extraction rate is the percentage (volume%) of the extraction amount (m ³ ) extracted from the cement firing device using the extraction gas equipment with respect to the exhaust gas amount (m ³ ) passing through the kiln inlet hood 3. Say. If it is less than 0.05% by volume, gas containing selenium cannot be sufficiently extracted, and if it exceeds 10% by volume, the fuel consumption deteriorates, the productivity deteriorates due to excessive intake of the calcined raw material, and the incorporated raw material or calcined raw material Is required. The extraction rate is more preferably 0.1 to 7% by volume. Note that, as conventionally performed, the extraction rate is controlled from the kiln by the opening of a damper installed upstream of the exhaust fan 16 with respect to the air volume at the extraction position calculated from the theoretical value and the actual measurement value. The amount of the exhaust gas flowing into the exhaust gas extraction port 3a (extraction amount) is adjusted.

  Further, the bleed gas is cooled to 350 ° C. or less, preferably 320 ° C. or less, more preferably 300 ° C. or less, and particularly preferably 250 ° C. or less in the part removing device 12. If it exceeds 350 ° C., the selenium contained in the exhaust gas is not sufficiently cooled and is not sufficiently taken into the extraction clinker. The extraction gas is cooled by mixing the cooling air from the cooling fan 11a with the extraction gas in the exhaust gas extraction pipe 11, and sequentially measuring the mixed gas temperature with a thermometer installed in the vicinity of the exhaust gas extraction port 3a. Also adjust the amount.

  The selenium-containing substance (extracted clinker) condensed and solidified by cooling the selenium-containing exhaust gas is collected by the bag filter 15 of the extracted gas equipment. The extracted gas from which selenium and other heavy metals are collected and removed is returned to the calcining furnace 5b through the duct 13c. Further, the extracted clinker containing the collected selenium and other heavy metals is extracted through the cushion hopper 21, the double butterfly damper 22 and the extracted clinker carry-out vehicle (bulk vehicle) 23 of FIG. It is carried out to 33.

  As the selenium collection method, in addition to the above method, a method of extracting a part of the calcined raw material from the lowest cyclone 5a where selenium is relatively easily condensed can be used. The extraction amount in this case is 0.05 to 5% by mass, preferably 0.1 to 1% by mass with respect to the amount of raw material fed. If the amount is less than 0.05% by mass, selenium cannot be sufficiently collected. If the amount exceeds 5% by mass, the productivity deteriorates due to excessive extraction of high-temperature gas, and processing of the incorporated calcined raw material is required.

≪Method for producing cement composition≫
In the cement composition manufacturing method, using cement clinker fired by reducing the basic unit of waste with high Se content, or using cement clinker with reduced Se content using extraction bypass equipment, together with gypsum, etc. A low-hydration heat cement composition having a Se content of 0.8 mg / kg or less is produced by pulverization using a ball mill.

  In addition, the low-hydration heat cement composition contains a cooled aggregate of high-temperature gas extracted (including raw materials entrained during extraction and a part of the calcined raw material) or water-soluble components from the cooled aggregate. It is also possible to add solid residues.

  The cement composition of the present invention may contain one or more selected from blast furnace granulated slag, limestone, and fly ash as other components.

  Examples of the gypsum to be added include natural gypsum, drainage gypsum, fluoric acid gypsum, phosphate gypsum, and the like, and these forms may be any of dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum.

  When this cement is used as concrete, the ratio of water cement as in high-strength concrete is as small as 30 to 35%, and even if the amount of cement used per unit concrete is as large as 400 to 550 kg, the concrete structure due to cement hydration Expansion cracks due to temperature rise inside the body can be suppressed.

  In addition, expansion cracks due to a temperature rise associated with heat of hydration can be suppressed even in concrete having a relatively large cross section such as mass concrete.

(1) Manufacture of cement clinker and cement composition Se content is changed by changing waste unit of Se content 5mg / kg or more in the range of 60-140kg / t-cl 'and whether or not extraction bypass equipment is in operation. 17 types of Portland cement clinker were prepared by adjusting the amount. In addition, No. Nos. 1 to 4 are cements having a Se content of 5 mg / kg or more and 140 kg / t-cl ′ or less, and a Se content reduced to 0.2 to 0.4 mg / kg or less. 5-6 is the cement which extracted Se using the extraction bypass equipment, and reduced Se content to 0.6-0.7 mg / kg or less. At this time, the operating conditions of the extraction bypass facility were an extraction rate of 0.1 to 10.0% and an extraction gas temperature of 900 to 1200 ° C.

Further, by adding gypsum, blast furnace slag and / or limestone in a total amount of 5.0% by mass or less to the obtained cement clinker and pulverizing with a ball mill, the Blaine specific surface area is 3100-3500 cm ² / g, SO ₃ amount Produced a cement composition of 1.75-2.25% by weight. In addition, the grinding | pulverization temperature of a finishing mill was controlled so that the semi-waterification rate of the gypsum in a cement composition might be 40 to 90%.

  The obtained cement composition was analyzed for Se content, and a cement composition having a Se content in the range of 0.2 to 1.3 mg / kg was obtained.

(2) Method for measuring selenium content in cement composition The method for quantifying the selenium (Se) content in cement clinker, cement composition, etc. is determined by the Cement Association standard test method JCAS I-52: 2000 “ICP emission spectroscopy and The sample was dissolved in accordance with “Method for Quantifying Cement Trace Elements by Electric Heating Atomic Absorption Spectrometry”, and then quantified by hydride generation ICP method.

The ICP emission spectroscopic analyzer was quantified using SPS3000 manufactured by Seiko Instruments Inc., and the hydride generator was also THG-1200 manufactured by Seiko Instruments Inc. In addition, Table 1 shows Se measurement conditions by the ICP emission spectroscopic analyzer.

In addition, the calculation of the lower limit of quantification is performed after obtaining the lower limit of quantification of the apparatus according to the appendix “ICP emission spectroscopic analyzer use determination item” in JIS K 0116: 1995 “General Rules of Emission Spectrometry” (Sample basis) The lower limit of quantification was calculated. The lower limit of Se quantification in the powder of this test method thus obtained is 0.2 mg / kg, and it is confirmed that there is sufficient accuracy to determine the Se content of 0.8 mg / kg or less of the present invention. It was done. The calculation method of the quantitative lower limit of the apparatus and the powder quantitative lower limit is shown below.
・ Calculation method of apparatus quantification lower limit value Apparatus quantification lower limit value (μg / L) = detection lower limit value (μg / L) × 3.3 (6)
Lower limit of determination of apparatus (μg / L) = 0.10 (μg / L) × 3.3 = 0.33 (μg / L)
・ Calculation method of powder (sample base) quantification lower limit value Powder quantification lower limit value (mg / kg) = quantitative lower limit value (μg / L) / balance (g) × constant volume (mL) / sorting ( mL) x constant volume (mL) x 1/1000 (unit conversion) (7)
Lower limit of powder quantification (mg / kg) = 0.33 (μg / L) /0.5 (g) × 250 (mL) / 100 (mL) × 100 (mL) × 1/1000 = 0.2 ( mg / kg)

(3) Method of measuring heat of hydration of cement composition The method of measuring heat of hydration of Portland cement was measured according to JIS R 5203: 1995 “Method of measuring heat of hydration of cement (heat of solution method)”.

Table 2 shows the SO ₃ content of the manufactured cement clinker and the mineral composition calculated by the Borg equation. Table 3 shows the SO ₃ content, the total alkali content (R ₂ O content), the Cl content, the Blaine specific surface area, and the Borg formula mineral composition of the cement composition produced using the cement clinker of Table 2.

(4) Test results Table 4 shows the Se content and heat of hydration of the test cement. As shown in Table 4, the cement composition No. in which the Se content in the cement composition is as high as 0.9 to 1.3 mg / kg. 7 to 17 had high heats of hydration at ages 7 and 28 at 332 to 340 J / g and 393 to 407 J / g, respectively.

  On the other hand, the Se content in the cement composition was 0.8 mg / kg or less. 1 to 6 are cement compositions having a heat of hydration of 323 to 326 J / g or less at 7 days of age, 386 to 390 J / g or less at 28 days of age, and a Se content of 0.8 mg / kg or more. 6-17 J / g could be reduced compared to the product.

  FIG. 1 shows the relationship between the Se content in the cement composition and the heat of hydration. The heat of hydration tends to increase when the Se content is 0.8 mg / kg or more. It was found that the heat of hydration can be stably reduced by setting the Se content in the composition to 0.8 mg / kg or less. Therefore, the cement composition of the present invention having a Se content of 0.8 mg / kg or less reduces the heat of hydration to 330 J / kg or less at 7 days of age and / or 390 J / kg or less at 28 days of age. Is possible.

  Table 5 shows the test results of setting and mortar compressive strength of the test cement. As shown in Table 5, the cement compositions of the present invention with reduced Se content in the cement composition (Examples 1 to 6) showed strength development properties and setting properties equivalent to those of Comparative Examples 1 to 11, The technology of the present invention was effective in reducing the heat of hydration without adversely affecting the basic physical properties (condensation and strength development properties).

Further, Comparative Example 12 (reduced C ₃ S and C ₃ A) and Comparative Example 13 (added fly ash as a mixed material so as to be 17% by mass in the cement composition) produced using the conventional technique, Although the heat of hydration can be reduced, the mortar compressive strength at the age of 3 to 7 days is remarkably reduced, and the initial strength is clearly inferior to the technique of the present invention.

It is the figure which showed the relationship between Se content and the heat of hydration. It is a diagram showing the relationship between Se content and the SO ₃ content of clinker. It is a figure which shows the systematic diagram of one Embodiment which bleeds selenium using an extraction gas installation.

Explanation of symbols

1: Kiln for cement firing 1a: Burner for firing 2: Clinker cooler 2a: Cooling fan for clinker cooler 3: Kiln inlet hood part 3a: Exhaust gas extraction port 4: Rising duct 5: SP (suspension preheater part)
5a: lowermost cyclone 5b: calcining furnace 5c: raw material supply pipe 5e: uppermost cyclone 5f: cyclone junction duct 5g: uppermost cyclone outlet 6: exhaust fan 7: chute 8: cooler exhaust gas supply duct 10: extraction gas equipment 11: Exhaust gas extraction pipe 11a: Cooling fan 12: Lump removal devices 13a, 13b, 13c: Exhaust gas duct 14: Cold air intake pipe 14a: Damper 15: Bag filter (dust collector)
15a: Bag filter lower hopper 15b: Extraction clinker discharge screw conveyor 16: Exhaust (attraction) fan 20: Extraction clinker storage / discharge facility 21: Cushion hopper 22: Butterfly damper 23: Extraction clinker unloading vehicle 30: Finishing mill facility 31: Ball mill 32: Classifier 33: Extraction clinker storage receiving hopper 34: Washing treatment tank 35: Filter 36: Reaction tank 1
37: Reaction tank 2
38: Settling tank 1
39: Precipitation tank 2
40: Dehydration tank

Claims (7)

  A low-hydration thermal cement composition having a Se content of 0.8 mg / kg or less. The low-hydration thermal cement composition according to claim 1, wherein the low-hydration thermal cement composition contains Portland cement clinker, and the amount of SO _{3 in the} Portland cement clinker is 0.2 to 1.7% by mass. And a Portland cement clinker and gypsum, _{C 3} S content is 50 to 65 mass%, _{C 3} A content is 8 to 11 wt%, according to claim 1 or 2 lower heat of hydration cement composition.   The low hydration heat cement composition according to claim 1, wherein the heat of hydration is 330 J / g or less at 7 days of age and / or 390 J / g or less at 28 days of age.   Reduction of the Se content in the cement clinker is performed by extracting at least a part of the selenium-containing exhaust gas from the cement kiln from the suspension preheater to the rotary kiln inlet hood in a cement firing apparatus having a suspension preheater. The manufacturing method of the low hydration heat | fever cement composition of Claims 1-4 characterized by the above-mentioned.   The method for producing a cement composition according to claim 5, wherein the temperature of the exhaust gas extracted is 300 to 1300 ° C.   The method for producing a cement composition according to claim 5 or 6, wherein an extraction rate of the exhaust gas is 0.05 to 10% by volume.

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