Cement and its manufacturing method

Abstract

To provide a cement that can form a solidification-treated soil in which the selenium elution amount does not exceed the allowable amount even when it contains a large amount of clinker dust.SOLUTION: A method for producing cement includes a mixing step S3 of mixing cement clinker powder, gypsum powder and clinker dust to produce cement powder, a calculation step S4 of calculating the value[mg / l] of a regression equation {(value of 0.0014 or more and 0.0029 or less)×X1+(value of 0.00021 or more and 0.00034 or less)×X2+(value of 0.0020 or more and 0.0032 or less)} for the case in which the amount of selenium contained in the cement clinker powder in 1 kg of cement powder as X1[mg] and the amount of selenium contained in the clinker dust in 1 kg of cement powder as X2[mg], a determination step S5 of determining whether the value of the regression equation is equal to or less than a predetermined value, and an addition step S6 of adding clinker dust to the cement powder to produce cement when the value of the regression equation is determined to be equal to or less than the predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In ground improvement work, a cement-containing solidification material is spread and mixed into the soil (ground) to form a solidification-treated soil as a mixture of the soil and the solidification material, which can improve the strength of the ground. However, there is a risk that selenium derived from the cement will leach out from the solidification-treated soil formed using such a solidification material into the surrounding soil.

[0003] The following Patent Document 1 discloses a technique for producing cement by adding clinker dust to cement clinker powder. In this technique, it is proposed to limit the amount of selenium contained per kg of cement to 5.0 mg or less in order to reduce the amount of selenium eluted from solidified soil formed by spreading a solidification material containing cement on soil.

[0004] However, when the technology described in Patent Document 1 below is adopted, the amount of clinker dust that can be added to the cement clinker powder becomes very small in order to keep the amount of selenium contained per 1 kg of cement to 5.0 mg or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-254935 A Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a cement capable of forming a solidified treated soil from which the amount of selenium eluted does not exceed an allowable amount even if the solidified treated soil contains a large amount of clinker dust. [Means for solving the problem]

[0007] A method for producing cement according to a first aspect of the present invention includes a mixing step of mixing cement clinker powder, gypsum powder, and clinker dust to produce cement powder, a calculating step of calculating a value [mg / l] of a regression equation "(a value of 0.0014 or more and 0.0029 or less)×X1 + (a value of 0.00021 or more and 0.00034 or less)×X2 + (a value of 0.0020 or more and 0.0032 or less)" where X1 [mg] is the amount of selenium contained in the cement clinker powder per 1 kg of the cement powder and X2 [mg] is the amount of selenium contained in the clinker dust per 1 kg of the cement powder, a determining step of determining whether the value of the regression equation is a predetermined value or less, and an adding step of adding clinker dust to the cement powder to produce cement when it is determined that the value of the regression equation is the predetermined value or less.

[0008] According to the first item, by determining whether the value of the regression equation (i.e., the amount of selenium eluted from the solidified treated soil formed by spreading and mixing cement powder with soil in a selenium elution test) is equal to or less than a predetermined value, it is possible to accurately estimate whether the amount of selenium eluted from the solidified treated soil formed by actually spreading and mixing a solidification material containing this cement powder with soil does not exceed the allowable amount. If it is determined that the value of this regression equation is equal to or less than the predetermined value, clinker dust is added to the cement powder within the allowable range, so that cement can be produced in which the actual amount of selenium eluted from the solidified treated soil does not exceed the allowable amount even if it contains a large amount of clinker dust. The regression equation will be explained in detail in the test example described later.

[0009] The cement according to the second aspect of the present invention includes cement clinker powder, gypsum powder, and clinker dust. In this cement, when the amount of selenium contained in the cement clinker powder per 1 kg of the cement is X1 [mg] and the amount of selenium contained in the clinker dust per 1 kg of the cement is X2 [mg], the value [mg / l] of the regression equation "(a value of 0.0014 or more and 0.0029 or less) x X1 + (a value of 0.00021 or more and 0.00034 or less) x X2 + (a value of 0.0020 or more and 0.0032 or less)" is less than 0.01.

[0010] According to the second item, it is possible to provide cement that does not allow the amount of selenium eluted from solidified soil to exceed the allowable amount, even if the solidified soil contains a large amount of clinker dust. The "0.01" here is the maximum allowable amount of selenium eluted in a selenium elution test (the soil environmental standard value set by the Ministry of the Environment). Effect of the Invention

[0011] As described above, according to the present invention, it is possible to provide a cement that can form solidified treated soil from which the amount of selenium eluted does not exceed the allowable amount even if the solidified treated soil contains a large amount of clinker dust. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram for explaining the procedure of a method for producing cement according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a graph showing a test example for deriving a regression equation used in a method for producing cement according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A method for producing cement according to one embodiment of the present invention will be described in detail. In the following description, cement clinker powder refers to pulverized cement clinker recovered from a clinker cooler in a cement calcination apparatus (not shown). Clinker dust refers to dust obtained by extracting and collecting part of the gas flowing from the cement kiln to the preheater in the cement calcination apparatus. Clinker selenium refers to selenium contained in cement clinker powder. Dust selenium refers to selenium contained in clinker dust. Soil selenium refers to selenium that elutes from the soil itself when a solidification material containing cement powder is spread on and mixed with the soil to form solidified treated soil. The selenium elution test is a test specified in Notification No. 46 of the Environment Agency.

[0014] 1 is an explanatory diagram for explaining the procedure of this manufacturing method. This manufacturing method includes a first measurement step S1 for measuring the amount of selenium contained in cement clinker powder, a second measurement step S2 for measuring the amount of selenium contained in clinker dust, and a mixing step S3 for mixing cement clinker powder, gypsum powder, and clinker dust to manufacture cement powder. These measured values ​​of the amount of selenium are used to calculate X1 [mg] and X2 [mg] in a calculation step S4 described later.

[0015] Furthermore, this manufacturing method includes a calculation step S4 for calculating the value [mg / l] of the regression equation "a value of 0.0014 to 0.0029 x X1 + (a value of 0.00021 to 0.00034) x X2 + (a value of 0.0020 to 0.0032)" where the amount of clinker selenium per 1 kg of cement powder is X1 [mg] and the amount of dust selenium per 1 kg of cement powder is X2 [mg], and a judgment step S5 for judging whether the value of this regression equation is a predetermined value (e.g., 0.01) or less. The calculation step S4 and the judgment step S5 can be performed by either a human or a computer.

[0016] Here, the regression equation will be explained. "(value of 0.0014 or more and 0.0029 or less) x X1" in the regression equation is the amount of clinker selenium eluted in the selenium elution test [mg / L]. This coefficient "(value of 0.0014 or more and 0.0029 or less)" was derived by the present inventor from the test example described later.

[0017] The regression equation "(value between 0.00021 and 0.00034) x X2" represents the amount of dust selenium [mg / L] eluted in the selenium elution test. This coefficient "(value between 0.00021 and 0.00034)" was derived by the inventor from the test examples described later.

[0018] The "(value between 0.0020 and 0.0032)" in the regression equation indicates the amount of soil selenium eluted [mg / l] in the selenium elution test. This value was derived by the inventor from the test example described later.

[0019] In other words, the value of this regression equation indicates the total value of selenium eluted in the selenium elution test.

[0020] This manufacturing method also includes an adding step S6 of adding clinker dust to the cement powder to produce new cement powder when it is determined that the value of the regression equation is equal to or less than a predetermined value. Here, the amount of clinker dust to be added can be determined based on a previously recorded relationship between the value of the regression equation and the required amount of clinker dust to be added.

[0021] In the above embodiment, a step of measuring the amount of selenium contained in the cement powder may be provided. In this case, the amount of selenium contained in the cement clinker powder and the amount of selenium contained in the cement powder, or the amount of selenium contained in the clinker dust and the amount of selenium contained in the cement powder may be measured, and the values ​​of X1 and X2 may be calculated based on these measured values.

[0022] Next, a test example (selenium elution test) for deriving the regression equation used in the manufacturing method for cement according to one embodiment of the present invention will be described.

[0023] In the test examples A1 to A5, cement clinker powder and dihydrate gypsum powder were mixed to produce cement powder, this cement powder was mixed with anhydrous gypsum powder to produce cement-based solidification material, this cement-based solidification material was mixed with sample soil (soil) to form solidified soil, and a test liquid was prepared from this solidified soil. The test liquid was prepared based on the method specified in the Environment Agency Notification No. 46.

[0024] Here, we will explain the detailed molding conditions of the solidified soil. The Blaine specific surface area of ​​the cement powder used is 3200 cm 2 / g or more 3300cm 2 / g or less. The SO3 content of the cement powder used was within the range of 2.4 mass% to 2.6 mass%. The cement-based solidification material used was for so-called general soft soil. The cement powder content of the cement-based solidification material used was 92 mass%. The anhydrous gypsum powder content of the cement-based solidification material used was 8 mass%. The sample soil used was Kuroboku collected from Koga city, Ibaraki prefecture. The wet density of the sample soil used was 1.447 g / cm 3 The water content was 86.4%. 3 The sample soil was mixed with 200 kg of the treated soil by the powder addition method. The age of the treated soil was 7 days.

[0025] Table 1 shows the mineral compositions (C3S content, C2S content, C3A content, and C4AF content) and selenium contents of the cement clinker powders A to E used in the test examples A1 to A5. The selenium contents are shown as the selenium content (mg) per kg of the cement clinker powder.

[0026] [Table 1]

[0027] Table 2 shows the type of cement clinker powder used in test examples A1 to A5, the clinker selenium content [mg] per 1 kg of cement powder, the total selenium content [mg] per 1 kg of cement powder, and the amount of selenium eluted [mg] per 1 L of test solution for each test example.

[0028] [Table 2]

[0029] In the test examples B1 to B8, cement clinker powder, clinker dust and dihydrate gypsum powder were mixed to produce cement powder, this cement powder was mixed with anhydrous gypsum powder to produce cement-based solidification material, this cement-based solidification material was mixed with sample soil (soil) to form solidified soil, and a test liquid was prepared from this solidified soil. The test liquid was prepared based on the method specified in the Environment Agency Notification No. 46.

[0030] Table 3 shows the type of cement clinker powder and type of clinker dust used in Test Examples B1 to B8, the clinker selenium content [mg] per 1 kg of cement powder, the dust selenium content [mg] per 1 kg of cement powder, the total selenium content [mg] per 1 kg of cement powder, and the amount of selenium eluted [mg] per 1 L of test solution for each test example. In Table 3, clinker dust X contains 310 mg of selenium per 1 kg, and clinker dust Y contains 280 mg of selenium per 1 kg.

[0031] [Table 3]

[0032] The cement powder used in Test Example B2 corresponds to the cement powder used in Test Example B1 with an increased amount of dust selenium. Similarly, the cement powders used in Test Examples B4, B6, and B8 correspond to the cement powders used in Test Examples B3, B5, and B7 with an increased amount of dust selenium, respectively.

[0033] Fig. 2 is a graph showing the relationship between the total selenium content and the amount of selenium eluted in each test example shown in Tables 2 and 3. In Fig. 2, the first line is drawn based on the plots for Test Examples A1 to A5. The second line is drawn based on the plots for Test Examples B1 and B2. The third line is drawn based on the plots for Test Examples B3 and B4. The fourth line is drawn based on the plots for Test Examples B5 and B6. The fifth line is drawn based on the plots for Test Examples B7 and B8.

[0034] The slope of the first line indicates the change in the amount of selenium eluted in the selenium elution test relative to the change in the total selenium content (corresponding to the clinker selenium content) per kg of cement powder. The slopes of the second to fifth lines indicate the change in the amount of selenium eluted in the selenium elution test relative to the change in the total selenium content (corresponding to the change in dust selenium content) per kg of cement powder.

[0035] The first straight line is represented by the regression equation "(amount of selenium eluted in selenium elution test) = 0.00212 × (clinker selenium content per kg of cement powder) + 0.00248." Here, by substituting 0 for "clinker selenium content per kg of cement powder," the amount of selenium eluted from soil in the selenium elution test (0.00248 mg) is calculated as the "amount of selenium eluted in selenium elution test." In addition, "0.00212 × (clinker selenium content per kg of cement powder)" indicates the amount of selenium eluted from clinker in the selenium elution test.

[0036] The slopes of the second to fifth lines were in the range of 0.00021 or more and 0.00034 or less. As described above, the slopes of the second to fifth lines indicate the change in the amount of eluted selenium in the selenium elution test relative to the change in the dust selenium content per kg of cement powder. Therefore, "(a value of 0.00021 or more and 0.00034 or less) x (dust selenium content per kg of cement powder)" indicates the amount of eluted dust selenium in the selenium elution test.

[0037] From the above, the regression equation of the above embodiment is derived: "(amount of selenium eluted in selenium elution test) = 0.00212 × (clinker selenium content per kg of cement powder) + (value equal to or greater than 0.00021 and equal to or less than 0.00034) × (dust selenium content per kg of cement powder) + 0.00248."

[0038] Here, the "0.00212" in this regression equation is taken from the slope of the first line shown in Figure 2, but even if the first line in Figure 2 is drawn based on the five plots, the slope of the first line is thought to have a range depending on how it is drawn. For this reason, it is preferable to give the "0.00212" in this regression equation a range such as "a value of 0.0014 or more and 0.0029 or less." Furthermore, since the "0.00248" in this regression equation is thought to differ depending on the location where the soil (sample soil) is collected, it is preferable to give it a range such as "a value of 0.0020 or more and 0.0032 or less."

[0039] By determining whether the value of this regression equation is equal to or less than a predetermined value, it is possible to accurately estimate whether the amount of selenium eluted from the solidified treated soil will exceed the allowable amount. If it is determined that the value of this regression equation is equal to or less than the predetermined value, it is possible to produce cement in which the actual amount of selenium eluted from the solidified treated soil will not exceed the allowable amount, even if it contains a large amount of clinker dust, by adding clinker dust to the cement powder.

[0040] The regression equation is particularly suitable for use in the case of producing cement using the same cement clinker powder as that used in this test example. In other words, it is preferable that the mineral composition and selenium content of the cement clinker powder used as the material for cement are as follows. As shown in Table 1, the C3S content is 58.9 mass% or more and 63.2 mass% or less, the C2S content is 13.7 mass% or more and 18.4 mass% or less, the C3A content is 9.7 mass% or more and 10.6 mass% or less, the C4AF content is 8.7 mass% or less and 9.4 mass% or less, and the selenium content is 0.19 mg / kg or more and 1.64 mg / kg or less.

[0041] By using this regression equation, it is possible to produce the following cement: This cement contains cement clinker powder, gypsum powder, and clinker dust. The mineral composition and selenium content of this cement clinker powder are as described above, and the value of the regression equation for this cement is less than 0.01 (and even less than 0.0060 as shown in Table 3). In other words, it is possible to produce cement in which the actual amount of selenium eluted from the solidified soil does not exceed the allowable amount, even if the cement contains a large amount of clinker dust. [Explanation of symbols]

[0042] S1 1st measurement process S2 2nd measurement process S3 Mixing process S4 calculation process S5 Judgment process S6 addition process

Claims

[Claim 1] A mixing step of mixing cement clinker powder, gypsum powder and clinker dust to produce cement powder; a calculation step of calculating a value [mg / l] of a regression equation "(a value of 0.0014 or more and 0.0029 or less) x X1 + (a value of 0.00021 or more and 0.00034 or less) x X2 + (a value of 0.0020 or more and 0.0032 or less)" in a case where the amount of selenium contained in the cement clinker powder per 1 kg of the cement powder is X1 [mg] and the amount of selenium contained in the clinker dust per 1 kg of the cement powder is X2 [mg]; a determining step of determining whether the value of the regression equation is equal to or less than a predetermined value; and if it is determined that the value of the regression equation is equal to or less than the predetermined value, an adding step of adding clinker dust to the cement powder to produce cement.

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