JP2013184834A - Fly ash-mixing cement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fly ash-mixing cement containing large amount of fly ash and having stable quality.SOLUTION: In the fly ash-mixing cement, the content of an ordinary portland cement or a quick portland cement is not less than 50 mass% and less than 80 mass%, and a content of fly ash is more than 20 mass% and not more than 50 mass% and a content of Rb (rubidium) in 1 kg of the cement is 10 to 60 mg.

Description

  The present invention relates to a fly ash mixed cement that contains more fly ash than conventionally produced fly ash cement and is less susceptible to the influence of fluctuations in the chemical composition and the like of the fly ash.

  In fly ash cement, (i) fly ash and calcium hydroxide produced by hydration of the cement react to form a dense structure (pozzolanic reaction), so the strength increases over the long term and the water tightness of the concrete. (Ii) The heat of reaction of the pozzolanic reaction is less than the heat of hydration of the cement, so the heat of hydration of the fly ash cement as a whole is small. (Iii) Ball bearings of fly ash that are spherical fine particles Since the fluidity of the concrete is improved by the action, there is a feature that the unit water amount of concrete and drying shrinkage can be reduced. Taking advantage of these features, fly ash cement is used for foundation construction of building structures and mass concrete such as dams.

However, the production volume of fly ash cement is about 170,000 tons in 2010, which is only 0.3% of the total cement production volume. Moreover, the content rate of the fly ash in the produced fly ash cement stops at about 15 to 16% by mass. The reason why the production amount and the content of fly ash are low is that the quality of fly ash cement is likely to fluctuate due to variations in the quality of fly ash.
In other words, coal-fired power plants, which are the main sources of fly ash, have recently been using a variety of low-grade coal to reduce power generation costs, and in the summer when power demand increases, power generation efficiency has been reduced. As the combustion conditions are changed in order to increase the chemical composition, the variation in the chemical composition and particle size of fly ash is large, which affects the quality of fly ash cement.
Furthermore, recently, the amount of power generation at the nuclear power plant has drastically decreased due to the accident at the Fukushima Daiichi nuclear power plant, and the amount of power generation at the thermal power plant has increased rapidly nationwide to make up for this shortage. A large amount of fly ash with large fluctuations is expected to occur.
Therefore, it is expected that the amount of fly ash used can be increased if the influence on the fly ash cement due to the variation in the chemical composition and the like of the fly ash can be reduced.

In connection with this, a selection method of fly ash suitable for cement materials and a quality evaluation method thereof have been proposed.
For example, in Patent Document 1, the α obtained by the Rietveld analysis method has a BET specific surface area of 5.0 m ² / g or less as a cement mixture from one or more fly ash containing α-quartz. -A method of selecting fly ash having a lattice constant b of quartz of 0.4935 nm or less has been proposed. However, the method does not use fly ash having a BET specific surface area exceeding 5.0 m ² / g or α-quartz having a lattice constant b exceeding 0.4935 nm, thereby promoting the recycling of fly ash. From the point of view, it is insufficient.
In Patent Document 2, fly ash, cement, water reducing agent, and kneading water are mixed and stirred to prepare a suspension, and the suspension is allowed to stand for a predetermined time before sedimentation of suspended particles. A fly ash quality evaluation comprising: a placing step; a sediment volume measuring step for measuring a volume of the precipitate composed of the suspended particles; and an evaluation step for evaluating the quality of the fly ash from a change in the volume of the precipitate. Methods have been proposed. This method is intended to stabilize the quality of the concrete by preliminarily evaluating the quality fluctuation caused by the water reducing agent adsorption capacity of fly ash by simple means and reflecting the evaluation in the modification of the concrete composition. , Not necessarily directly related to the high volume use of fly ash.

JP 2011-20867 A JP 2010-43933 A

  Therefore, the present invention is intended for mass use of fly ash, and specifically, an object of the present invention is to provide a fly ash mixed cement containing a large amount of fly ash and having a stable quality.

  As a result of intensive studies to achieve the above object, the present inventor has found that fly ash mixed cement having a specific content of Rb (rubidium) has a stable quality even if it contains a large amount of fly ash. And the present invention was completed.

That is, the present invention provides the following [1] and [2]. Unless otherwise indicated, “%” means “mass%”.
[1] A fly ash mixed cement in which the content of ordinary Portland cement or early-strength Portland cement is 50% or more and less than 80%, and the fly ash content is more than 20% but not more than 50%, and 1 kg of the cement The fly ash mixing cement whose content of Rb (rubidium) in it is 10-60 mg.
[2] The fly ash mixed cement according to [1], wherein the mass ratio of the amount of SO ₃ derived from hemihydrate gypsum / the total amount of SO ₃ contained in the fly ash mixed cement is 0 to 0.8.

  The fly ash mixed cement of the present invention contains more fly ash than the conventional fly ash cement, and the cement quality is stable even if the fly ash quality varies.

As described above, the present invention is a fly ash mixed cement in which the content of ordinary Portland cement or early strong Portland cement is 50% or more and less than 80%, and the fly ash content is more than 20% but 50% or less. , Fly ash mixed cement or the like in which the content of Rb in 1 kg of the cement is 10 to 60 mg.
Hereinafter, the fly ash mixed cement of the present invention: 1. Normal or early strength Portland cement and fly ash content 2. Rb content, _3. Mass ratio of hemihydrate gypsum-derived SO ₃ amount / total SO ₃ amount; The method will be described in detail according to the manufacturing method of fly ash mixed cement.

1. Ordinary or early strength Portland cement and fly ash content In the fly ash mixed cement according to the present invention, the ordinary Portland cement or early strength Portland cement content is 50% or more and less than 80%, and the fly ash content is 20%. And 50% or less. Here, the total content of ordinary Portland cement or early-strength Portland cement and fly ash is 100%.
If the fly ash content is less than 20%, the fly ash content in the conventionally produced fly ash cement is almost the same, and the purpose of mass use of fly ash in the present invention cannot be achieved. When the content is 50% or more, the strength development of the cement tends to decrease.
In addition, the content of the fly ash is preferably 25 to 48%, more preferably 30 to 47%, and still more preferably 32 to 45% in consideration of a balance between mass use of fly ash and strength development.

The fly ash used in the present invention is fly ash type I, type II, type III, type IV, or a pulverized product thereof as defined in JIS A 6201.
Also, the Blaine specific surface area of the fly ash is preferably at least 1500 cm ² / g, more preferably 2000~12000cm ² / g, more preferably ^{2500~11000cm 2 / g, 3000~10000cm 2 /} g is particularly preferred. If the Blaine specific surface area is less than 1500 cm ² / g, the strength development of the fly ash mixed cement is small.
As a pulverization method for fly ash, fly ash may be pulverized alone, but in order to increase the pulverization efficiency, a pulverization aid may be added to the fly ash for pulverization. Examples of the grinding aid include diethylene glycol, triethanolamine, and triisopropanolamine. Among these, triisopropanolamine is more preferable because it improves the strength development of the cement. The addition amount of these grinding aids is preferably 0.01 to 1 part by mass with respect to 100 parts by mass of fly ash. Examples of the pulverizer include a ball mill.

2. Content of Rb The lower limit of the content of Rb in 1 kg of the fly ash mixed cement of the present invention is 10 mg, preferably 12 mg, more preferably 15 mg, while the upper limit of the content is 60 mg, preferably 55 mg. 50 mg is more preferable. When the content of Rb is in the range of 10 to 60 mg, the fly ash mixed cement is hardly affected by the quality fluctuation of fly ash, and a large amount of fly ash can be used. If the Rb content in the cement is less than 10 mg, the cement is less susceptible to the effects of fly ash quality fluctuations, but the production of the cement becomes difficult and the cost is increased.

Generally, the content of Rb in ordinary Portland cement or early-strength Portland cement is approximately 90 mg or more per kg of cement, and the content of Rb in fly ash is approximately 30 to 120 mg per kg of fly ash. Therefore, in order to adjust the Rb content in the fly ash mixed cement within the above range, the Rb content in the fly ash is preferably 100 mg or less, more preferably 90 mg or less per kg of fly ash, and the clinker The Rb content is preferably 1 to 35 mg, more preferably 2 to 30 mg, and even more preferably 3 to 25 mg per kg of clinker.
When the content of Rb in the clinker exceeds the above range, a clinker raw material having a low Rb content may be selected, or a method of volatilizing and removing Rb in the clinker firing step may be selected. Examples of the removal method include a chlorination volatilization method and a reduction firing method.

Here, the chlorination volatilization method is a method in which heavy metals such as Rb contained in the clinker raw material are volatilized and removed in the form of chlorides having a low boiling point. Specifically, in this method, a chlorine source such as calcium chloride is added to a clinker raw material containing heavy metal, and is fired using a firing furnace such as a rotary kiln, and the generated heavy metal chloride is volatilized and removed. It is.
In the reduction firing method, heavy metals such as Rb contained in the clinker raw material are reduced and volatilized and removed in the form of a metal having a low boiling point. Specifically, in the method, the clinker raw material containing heavy metal is reduced in a reducing atmosphere and / or added with a reducing agent, and baked using a baking kiln such as a rotary kiln to reduce the heavy metal, and this reduction is performed. Heavy metals are volatilized and removed.

3. Hemihydrate gypsum from the SO ₃ content / total SO ₃ content of the mass ratio the fly ash SO ₃ from hemihydrate gypsum mixture contained in cement content / total SO ₃ content mass ratio is preferably from 0 to 0.8, 0.2-0.8 is more preferable, 0.4-0.8 is still more preferable, and 0.6-0.7 is especially preferable. If the ratio is in the range of 0 to 0.8, even if the fly ash quality (chemical composition, etc.) varies, the effect on the quality (strength development, etc.) of the cement mixed with the fly ash is smaller. .

4). Manufacturing method of fly ash mixed cement The manufacturing method includes (1) a clinker raw material preparation step, (2) a firing step, (3) a finishing step, and (4) a fly ash mixing step. In the following, each process will be described separately.
(1) Clinker raw material preparation step In this step, cement raw materials such as calcium raw material, silicon raw material, aluminum raw material, and iron raw material are used as the cement mineral composition range of ordinary Portland cement clinker or early strong Portland cement clinker (C ₃ S but 55.0 to 75.0% _{C 2} S is 7.0-20.0% _{C 3} A is from 8.0 to 12.0%, and _C 4 AF are from 8.0 to 12.0%) The clinker raw material is prepared by blending as follows. Moreover, in this process, it is preferable to prepare the clinker raw material so that the content of Rb in the clinker is in the range of 1 to 35 mg per 1 kg of the clinker exemplified above. Here, limestone, quicklime, slaked lime, and the like are used as the calcium material, silica and clay are used as the silicon material, clay is used as the aluminum material, and iron cake and iron cake are used as the iron material.

As the raw material, in addition to natural raw materials, industrial waste, general waste, and / or waste such as construction generated soil can be used as part of the raw material.
Examples of the industrial waste include various sludges such as coal ash, ready-mixed concrete sludge, construction sludge, and iron sludge, boring waste soil, various incineration ash, foundry sand, rock wool, blast furnace secondary ash, construction waste, and concrete waste. Etc. Examples of the general waste include purified water sludge, sewage sludge, sewage sludge dry powder, municipal waste incineration ash, shells, and sewage sludge incineration ash. Furthermore, as the construction generated soil, soil or residual soil generated from a construction site or a construction site can be cited.
In addition, when it is necessary to adjust the fineness of a clinker raw material, it adjusts by grind | pulverizing until it becomes predetermined | prescribed fineness with raw material grinders, such as a ball mill.

The composition (content ratio) of the cement mineral is calculated using the following Borg formulas (i) to (iv).
C ₃ S (%) = 4.07 × CaO (%) − 7.60 × SiO ₂ (%) − 6.72 × Al ₂ O ₃ (%) − 1.43 × Fe ₂ O ₃ (%) − 2.85 × SO ₃ (%) (i)
C ₂ S (%) = 2.87 × SiO ₂ (%) − 0.754 × C ₃ S (%) (ii)
C ₃ A (%) = 2.65 × Al ₂ O ₃ (%) − 1.69 × Fe ₂ O ₃ (%) (iii)
C ₄ AF (%) = 3.04 × Fe ₂ O ₃ (%) (iv)
(The chemical formula in the formula represents the content of the compound represented by the chemical formula in the clinker raw material or in the clinker.)

(2) Firing step This step is a step of firing the clinker raw material to obtain an ordinary Portland cement clinker or an early strength Portland cement clinker.
1000-1450 degreeC is preferable and the baking temperature of this process has more preferable 1200-1400 degreeC. When the temperature is in the range of 1000 to 1450 ° C., a highly mineral cement mineral is likely to be generated. Moreover, 30-120 minutes are preferable and, as for the baking time of this process, 40-60 minutes are more preferable. If the time is less than 30 minutes, firing may not be sufficient, and if it exceeds 120 minutes, productivity is lowered.
In addition, when the content of Rb in the clinker exceeds the range of 1 to 35 mg per 1 kg of the clinker exemplified above, in order to reduce the content of Rb, the chloride volatilization method, the reduction firing method, etc. It is preferable to use the Rb removal method in combination.

(3) Finishing step This step is performed by adding gypsum to the ordinary Portland cement clinker or early strength Portland cement clinker obtained in the firing step, and pulverizing it using a pulverizer such as a ball mill or a rod mill. This is a process for obtaining Portland cement. As a pulverization / mixing method, in addition to the above-described mixed pulverization (simultaneous pulverization), the clinker and gypsum may be separately pulverized and then mixed.

  In the above pulverization operation, the clinker and gypsum may be pulverized as they are, but preferably, a pulverization aid is added for pulverization in order to increase the pulverization efficiency. Examples of the grinding aid include diethylene glycol, triethanolamine, and triisopropanolamine. Among these, triisopropanolamine is more preferable because the strength development of cement is improved. As for the addition ratio of these grinding | pulverization adjuvants, 0.01-1 mass part is preferable with respect to 100 mass parts of clinker.

The content of the gypsum is preferably 1.5 to 5.0 parts by mass, more preferably 2.0 to 4.0 parts by mass in terms of SO ₃ with respect to 100 parts by mass of the clinker. When the value is in the range of 1.5 to 5.0 parts by mass, strength development is high and fluidity is also good.
Here, examples of the gypsum include at least one selected from natural dihydrate gypsum, flue gas desulfurization gypsum, phosphate gypsum, titanium gypsum, hydrofluoric gypsum, refined gypsum, hemihydrate gypsum, and anhydrous gypsum. . However, it is preferable to mix the gypsum so that the mass ratio of the amount of SO ₃ derived from hemihydrate gypsum contained in the fly ash mixed cement / the total amount of SO ₃ falls within the range of 0 to 0.8 exemplified above.
Moreover, 2000-10000 cm < ² > / g is preferable and, as for the brane specific surface area of gypsum, 3000-9000 cm < ² > / g is more preferable. When the value is out of the range of 2000 to 10000 cm ² / g, there is a possibility that strength development is reduced and heat of hydration is increased.

(4) Fly ash mixing step This step is a step of mixing the normal Portland cement or early strong Portland cement and fly ash to obtain fly ash mixed cement. Here, examples of the mixing device include a Henschel mixer and a tumbler mixer. In addition, although the fly ash used in this process can use the Rb content of 30 to 120 mg per kg of fly ash exemplified above, from the viewpoint of reducing the Rb content in the fly ash mixed cement, It is preferable to use fly ash having an Rb content of 100 mg or less (more preferably 90 mg or less).
Fineness of the fly ash mixed cement according to the present invention, strength development, in view of workability and cost, is preferably 3000~5000cm ² / g in Blaine specific surface area, more preferably 3100~4800cm ² / g, 3200 More preferably, ˜4500 cm ² / g.
In addition, the fly ash mixed cement according to the present invention may further include blast furnace slag, coal ash, silica fume, silica powder, limestone powder, and the like within a range where the effects of the present invention are exhibited.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
1. Production of ordinary Portland cement clinker Limestone, clay, iron slag, three types of fly ash having a chemical composition shown in Table 1 (Brain specific surface area of 3000 to 3200 cm ² / g) and two types of sewage sludge having different chemical compositions Used to prepare the clinker raw material. Since Rb is mainly contained in fly ash and sewage sludge, the mixing ratio of fly ash and sewage sludge was adjusted so that the content of Rb in the clinker was within the above range in the above preparation.
Next, the clinker raw material is fired by using a small rotary kiln and adjusting the firing time so that the firing temperature is 1450 ° C. and the amount of free lime (f-CaO) in the clinker is 0.2 ± 0.2%. I went. Cement mineral composition of the obtained ordinary Portland cement clinker 1 to 3 has C ₃ S of 59 ± 1%, C ₂ S of 18 ± 1%, C ₃ A of 9.5 ± 0.5%, and C ₄ The AF was 9.5 ± 0.5, and the variation in chemical composition among the three types of clinker was small.

2. Manufacture of fly ash mixed cement According to the formulation in Table 2, the clinker 1 to 3 and gypsum (2-water gypsum and hemihydrate gypsum) were simultaneously pulverized with a small ball mill, and the brain specific surface area was 3200 ± 100 cm ² / g. A normal Portland cement containing 1.5% of gypsum in terms of SO ₃ was obtained.
Next, 60% of the cement and 40% fly ash listed in Table 1 were mixed to produce fly ash mixed cements (Examples 1 to 5 and Comparative Examples 1 to 3). The mass ratio of SO ₃ weight / total SO ₃ content derived from hemihydrate gypsum of the fly ash mixed cement was adjusted to 0.3 to 0.55 by adjusting the dihydrate gypsum weight and hemihydrate gypsum weight.
For reference, a fly ash mixed cement (Reference Examples 1 and 2) in which 60% of commercially available ordinary Portland cement and 40% of fly ash in Table 1 were mixed was also produced.

3. Effect of mass ratio of SO ₃ amount / total SO ₃ amount derived from hemihydrate gypsum on cement quality In order to examine the effect of the title, hemihydrate gypsum was further added to the fly ash mixed cements of Examples 1 to 3 Then, fly ash mixed cement (Examples 6 to 8) having a mass ratio of 0.6 to 0.7 was manufactured.

3. Measurement of Flow Value A mortar was prepared using the fly ash mixed cement, and the flow value immediately after kneading and after 30 minutes from kneading was measured to determine the fluidity of the cement. In particular,
(I) Mortar with fine aggregate / cement ratio = 2.0, water / cement ratio = 0.35, and water reducing agent (in terms of solid content) / cement ratio = 0.007 using the cement Was kneaded using a Hobart mixer for 2.5 minutes at low speed followed by 3 minutes at high speed. The fine aggregate used was standard sand specified in JIS R 5201, and the water reducing agent used was a polycarboxylic acid-based high-performance AE water reducing agent (trade name: Leobuild SP8N [registered trademark], manufactured by BASF Pozzolith).
(Ii) When the prepared mortar was put into a steel slump cone (mini slump cone) defined in JIS A 1171: 2000 “Testing method for polymer cement mortar”, the slump cone was removed upward. Mortar spread (flow value) was measured. The results are shown in Table 2.

4). Setting time and compressive strength The setting time and compressive strength of the cement were measured according to JIS R 5201 and JIS R 5203, respectively. These measurement results are shown in Table 2.
Table 3 shows the difference (magnitude of fluctuation) between the maximum value and the minimum value of each physical property value described in Table 2.

As shown in Table 2 and Table 3, the fluctuation range of the compressive strength of Comparative Examples 1 to 3 and Reference Examples 1 and 2 in which the Rb content is 65 mg / kg or more is 3.8 N / year at the age of 3 days, respectively. mm ² and ^{4.3N / mm 2, 4.8N / mm} 2 and 3.3N / mm ² at the age of 7 days, the large and 6.0N / mm ² and 3.7N / mm ² at the age of 28 days contrast, in examples 1 to 8 the content of Rb is less than 47mg / kg, 0.9N / mm ² 3 days the age, at the age 7 days 1.2 N / mm ^2, at age of 28 days It is remarkably small at 2.3 N / mm ² .
Therefore, the fly ash mixed cement of the present invention having a Rb content in the range of 10 to 60 mg / kg contains a large amount of fly ash having a large chemical composition as shown in Table 1 in spite of a large amount. It can be seen that the fluctuation of is small.
Among the examples 1 to 8, in particular, variations in the compressive strength of Examples 6-8 in which the mass ratio of SO ₃ weight / total SO ₃ content derived from hemihydrate gypsum is in the range of 0.6 to 0.7 width, 0.3 N / mm ² 3 days the age, 0.4 N / mm ² at an age of 7 days, and 0.6 N / mm ² at an age of 28 days, and the corresponding values in examples 1-5 Compared to this, it is even smaller.

In addition, regarding the flow value and the setting time, similarly to the case of the compressive strength, the fluctuation range of Examples 1 to 8 is smaller by about 1/2 to 2/3 than the fluctuation range of Comparative Examples 1 to 3.
Therefore, the fly ash mixed cement of the present invention is less affected by the variation in the quality of fly ash, and therefore can contain a larger amount of fly ash than conventional fly ash cement.

Claims (2)

  A fly ash mixed cement in which the content of ordinary Portland cement or early strong Portland cement is 50% by mass or more and less than 80% by mass, and the fly ash content is more than 20% by mass and 50% by mass or less, The fly ash mixing cement whose content of Rb (rubidium) in 1 kg is 10-60 mg. The fly ash mixed cement according to claim 1, wherein a mass ratio of the amount of SO ₃ derived from hemihydrate gypsum / the total amount of SO ₃ contained in the fly ash mixed cement is 0 to 0.8.