JP6766473B2 - Manufacturing method of coal ash mixed cement - Google Patents

Description

The present invention relates to a technique for producing a coal ash mixed cement that can effectively utilize coal ash generated in a coal-fired power plant.

Coal-fired power plants generate a large amount of coal ash, and it is difficult to dispose of it. As for the effective use of coal ash, the use as a raw material for cement, the use as fly ash for concrete, the use as earthwork materials, etc. are being promoted, but the amount of coal ash used is limited, and all coal ash can be used. It is not being used effectively.

In the use of coal ash as a raw material for cement, the use of clinker as a substitute raw material for clay sources has been promoted, but the amount of processing is also limited in order to maintain the quality of clinker. The use of coal ash as a mixture of fly ash cement is also being promoted, but the reality is that the demand for fly ash cement is low and the amount used is not increasing.

Coal ash can be used as a small amount of additive component (≤5% by mass) in ordinary Portland cement, which is in high demand, but when used as mortar or concrete, unburned carbon in coal ash floats black on the surface. Since it looks worse than ordinary Portland cement, which is generally available at present, its use was avoided. In addition, there is a problem that a black layer is formed at the concrete joint because the bleeding water at the time of concrete placement contains black suspended matter of unburned carbon.

As a technology that solves this problem of unburned carbon floating and enables the addition of fly ash to Portland cement, the ignition loss derived from fly ash in the cement composition should be 0.35% by mass or less. A coal ash mixed cement is disclosed in which a black layer is less likely to be formed in bleeding water 6 hours after production by mixing and crushing coal ash together with cement clinker and plaster (Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-196220

However, when coal ash and cement are simply mixed, even if the ignition loss in the cement composition derived from coal ash is controlled to 0.35% by mass or less, it depends on the source of coal ash and the type of coal. There was a problem that unburned carbon sometimes floated on the surface of the mortar and the joint, which spoiled the aesthetic appearance. Therefore, the amount of coal ash added had to be reduced more than necessary, which hindered the effective use of coal ash. In addition, in actual concrete construction, inspections are conducted at the time of acceptance at the site, so there is a demand for coal ash mixed cement in which the floating of unburned carbon is suppressed even in mortar and concrete that has just been kneaded.

The present invention solves the above-mentioned conventional problems, can easily evaluate the ease of floating of unburned carbon from coal ash in kneading mortar and concrete, and can be used for mortar and concrete using coal ash mixed cement. To provide a method for producing a coal ash mixed cement, which is excellent in surface aesthetics from immediately after production to after construction, is difficult to form a black layer at a joint, and can obtain concrete with stable quality. With the goal.

As a result of diligent studies on the above problems, the present inventors can easily evaluate the ease of floating of unburned carbon from coal ash by producing a cement composition and confirming its surface condition, and at the same time, the cement By adding a process to evaluate the ease of floating of unburned carbon in coal ash in the manufacturing process, and by selecting the coal ash to be used and setting the amount to be added based on this judgment result, unburned on the mortar and concrete surface We have found that it is possible to provide a coal ash mixed cement in which a black layer due to carbon is difficult to form, and have completed the present invention.

That is, the present invention provides:
[1] A method for producing a coal ash mixed cement containing coal ash, cement clinker and gypsum, and confirming the surface condition of a cement composition obtained by kneading uncrushed coal ash, cement and water. The cement clinker is crushed using a closed-circuit ball mill and a sorting step of selecting the coal ash used for producing the coal ash mixed cement based on the test result of the quality test step. and grinding process, and the coal ash is sorted, and the cement clinker after the separators classification, mixing without milling the gypsum, or sorted the and coal ash, the cement clinker which is ground in grinding step A method for producing a coal ash mixed cement, which comprises a mixing step of mixing the gypsum and the plaster at a separator portion without crushing .
[2] The coal ash mixture according to [1], which comprises binarizing an image of the surface of the cement composition in the quality test step to confirm the surface state of the cement composition. How to make cement.
[3] The quality test step further includes a step of measuring the loss on ignition of coal ash and setting the addition rate of coal ash used for producing the coal ash mixed cement based on the result of the quality test. The method for producing a coal ash mixed cement according to [1] or [2].
[4] The method for producing a coal ash mixed cement according to any one of [1] to [3], further comprising a pulverization step of pulverizing the cement clinker.
[5] The cement clinker is crushed using a closed-circuit ball mill in the crushing step, and the cement clinker, the plaster, and the coal ash after separator classification are mixed in the mixing step. The method for producing a coal ash mixed cement according to [4].
[4] The total content of the cement clinker and gypsum in the coal ash mixed cement is 75 to 99.9% by mass, and the content of the coal ash is 0.1 to 25% by mass. , The method for producing a coal ash mixed cement according to any one of [1] to [3].
[5] In the quality test step, 5 to 600 parts by mass of fine aggregate is added to 100 parts by mass of the mixed cement in which 0.1 to 25% by mass of the coal ash and 75 to 99.9% by mass of the cement are mixed. The item according to any one of [1] to [4], wherein the cement composition is obtained by kneading a cement mortar having a water / powder mass ratio of 30 to 100% by mass. A method for producing coal ash mixed cement.
[6] The coal ash is characterized by including at least one of a classification treatment, a heat treatment, an electrostatic separation treatment, and a mixing treatment between coal ashes [1] to [5]. The method for producing a coal ash mixed cement according to any one of the above items.
[7] In any one of [1] to [6], a high shear mixer is used when the coal ash, the cement and the water are kneaded to obtain a cement composition in the quality test step. The method for producing a coal ash mixed cement according to the above.

According to the present invention, when placing concrete using coal ash mixed cement, it is difficult to form a black layer of unburned carbon floating at the joint, the surface of mortar or concrete is excellent in aesthetics, and the quality is stable. You can get the concrete.

An image of the surface of the level 2 cement paste taken with a digital camera (left) and an image obtained by binarizing the surface (right). This is an example of A evaluation when the floating state of unburned carbon on the surface is visually evaluated. This is an example of B evaluation when the floating state of unburned carbon on the surface is visually evaluated. This is an example of C evaluation when the floating state of unburned carbon on the surface is visually evaluated. This is an example of D evaluation when the floating state of unburned carbon on the surface is visually evaluated. This is an example of E evaluation when the floating state of unburned carbon on the surface is visually evaluated.

Hereinafter, preferred embodiments of the present invention will be described in detail.

An example of a method for producing a coal ash mixed cement according to the present invention will be described. According to the following production method, a coal ash mixed cement in which the floating of unburned carbon is suppressed can be produced.

The method for producing a coal ash mixed cement according to the present invention includes a coal ash quality test step, a coal ash sorting step, and a mixing step of mixing coal ash with cement clinker and gypsum. The method for producing a coal ash mixed cement according to the present invention includes a step of setting the addition rate of coal ash, a crushing step of crushing a cement clinker, and a classification treatment, a heat treatment, an electrostatic separation treatment, or coal of coal ash. At least one step of mixing the ash with each other can be further included.

The coal ash used in the present invention is a by-product generated when coal is burned in a coal-fired power plant or the like, and is a fly ash collected by an electrostatic precipitator, a cleaner ash deposited in the lower part of a boiler, and a bottom. For example, ash. In order to obtain stable quality coal ash mixed cement, it is preferable to use fly ash generated from a coal-fired power plant, and it is preferable to use fly ash specified in JIS A 6201 "Fly ash for concrete". More preferred.

The cement clinker used in the present invention is not particularly limited, but is manufactured using existing cement manufacturing equipment such as the SP method (multi-stage cyclone residual heat method) and the NSP method (multi-stage cyclone residual heat method with a calcining furnace). You can use things.

As the gypsum used in the present invention, gypsum specified in JIS R 9151 “Natural gypsum for cement”, dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum can be used. Portland cement can also be used in place of all or part of cement clinker and gypsum. Examples of Portland cement include ordinary Portland cement, early-strength Portland cement, ultra-early-strength Portland cement, low-heat Portland cement, moderate-heat Portland cement, and sulfuric acid-resistant Portland cement.

In the quality test process, at least coal ash, cement and water are kneaded to produce a cement composition, and the surface condition thereof is confirmed. The cement composition includes cement paste obtained by kneading coal ash, cement and water, mortar obtained by kneading coal ash, cement, fine aggregate and water, and coal ash, cement and fine aggregate. Concrete obtained by kneading coarse aggregate and water can be mentioned, but cement paste or mortar is preferable in consideration of the time and effort of testing, and mortar is used from the viewpoint of producing more stable quality coal ash mixed cement. Most preferred. The exact reason is unknown, but it is thought that kneading fine aggregate and coal ash during mortar production will make the grain size of coal ash finer and make it easier for unburned carbon to float, so the conditions are simple but close to the actual product. Since it can be reproduced, it is possible to set the amount of coal ash added that can surely suppress the floating of unburned carbon while effectively using the coal ash.

The cement used in the quality test process is not particularly limited as long as it is cement used for coal ash mixed cement, and is ordinary Portland cement, early-strength Portland cement, moderate heat Portland cement, low heat Portland cement and the like. Further, instead of cement, crushed cement clinker may be mixed with coal ash, or coal ash and cement clinker may be mixed and crushed.

The cement composition used in the quality test step is, for example, 100 parts by mass of mixed cement in which 0.1 to 25% by mass of coal ash and 75 to 99.9% by mass of cement are mixed, and 5 to 600 parts by mass of fine aggregate. Can be produced by adding and kneading a cement mortar having a water / powder mass ratio = 30 to 100% by mass. As the fine aggregate, for example, standard sand for cement strength test can be used. Further, an operation of applying vibration to the obtained cement composition using a vibrator may be applied. Since the unburned carbon is easily floated by the vibrator treatment, it is possible to set the amount of coal ash added that can surely suppress the floating of the unburned carbon while effectively using the coal ash. The detailed method of kneading can be carried out according to JIS R 5201 “Physical test method for cement”.

The content of coal ash in the mixed cement is usually 0.1 to 25% by mass, preferably 0.2 to 15 parts by mass, and more preferably 0.3 to 5 parts by mass. The content of cement in the mixed cement is usually 75 to 99.9% by mass, preferably 85 to 99.8% by mass, and more preferably 95 to 99.7 parts by mass. The amount of the fine aggregate is usually 5 to 600 parts by mass, preferably 50 to 500 parts by mass, more preferably 100 to 400 parts by mass, and most preferably 200 to 200 parts by mass with respect to 100 parts by mass of the mixed cement. It is 300 parts by mass. The water / powder mass ratio is usually 30 to 100% by mass, preferably 40 to 80% by mass, and more preferably 45 to 55% by mass.

The mixer used for producing the cement composition in the quality test step is not particularly limited, and a hand mixer, a hovert mixer, or the like can be used. In order to produce coal ash mixed cement of more stable quality, it is preferable to use a high shear mixer such as a homomixer or a twin-screw mixer. It is thought that applying a high shearing force during kneading makes it easier for unburned carbon contained in coal ash to float, and the amount of coal ash added that can reliably suppress the floating of unburned carbon while making effective use of coal ash is set. It will be possible. The rotation speed of the mixer during kneading is not particularly limited, but in the case of a homomixer, for example, it is usually 2000 to 6000 rpm, preferably 3000 to 4000 rpm. By setting the rotation speed to 2000 rpm or more, the floating of unburned carbon is likely to occur on the surface of the cement composition, and the selection of coal ash that can suppress the floating of unburned carbon when the coal ash mixed cement is manufactured and used can be selected. It becomes easy to judge the amount of coal ash added. Here, "rpm" means "the number of revolutions per minute".

The surface condition of the produced cement composition can be judged from the amount and color of unburned carbon floating. The evaluator can evaluate with the naked eye, and the simplest method is to take a picture of the surface of the cement composition with a digital camera or the like and binarize the obtained image to calculate the area of the black part. To do. The binarization process is a process of converting an image with shading into two gradations. A certain threshold value is set, and the case where the value of each pixel exceeds the threshold value and the case where the value falls below the threshold value are replaced with different colors. .. Normally, white and black may be replaced based on the threshold value, but the present invention is not particularly limited. The threshold value of the binarization treatment may be appropriately set according to the target specifications of the coal ash mixed cement to be produced and the correspondence with the visual evaluation, and may be appropriately adjusted depending on the image shooting environment. As shown in Examples described later, since the area of the black portion tends to correspond to the visual evaluation, the judgment standard for each evaluator is calculated by binarizing the unburned carbon floating area. Since there is no deviation, the quality of the coal ash mixed cement to be produced is stable, and it becomes easy to sort the coal ash according to the specifications and targets of the coal ash mixed cement.

The quality test step can further measure the ignition loss of coal ash. As a measuring method, it can be measured according to JIS A 6201 "Measuring method of ignition loss of fly ash for concrete". By measuring the ignition loss of coal ash, it is possible to roughly estimate the amount of coal ash added, and the quality test can be carried out efficiently. That is, the method for producing a coal ash mixed cement according to the present invention can further include a step of setting the addition rate of coal ash.

In the sorting step, coal ash that can be used for producing the coal ash mixed cement is sorted based on the result of the quality test step.

In the step of setting the addition rate of coal ash, the addition rate of coal ash used for producing the coal ash mixed cement is set within a range in which floating due to unburned carbon can be suppressed based on the result of the quality test step. ..

In the mixing step, coal ash, cement clinker and gypsum are mixed. The cement clinker may be crushed. It is particularly preferable to mix the separator-classified cement clinker, gypsum and coal ash, or to mix the coal ash, cement clinker and gypsum at the separator portion from the viewpoint of suppressing the floating of unburned carbon.

The method for producing a coal ash mixed cement according to the present invention can further include a pulverization step. In the crushing step, the cement clinker is crushed. As a crushing method, various crushers such as a vertical mill and a ball mill can be used. It is most preferable to grind with a closed circuit type ball mill and classify with a separator.

In the method for producing a coal ash mixed cement according to the present invention, coal ash can be further classified, heat-treated, electrostatically separated, and mixed with each other.

In the classification process, the grain size of coal ash is adjusted with a separator or a sieve. For example, the strength development of the coal ash mixed cement can be enhanced by making the particle size of the coal ash finer, and the amount of unburned carbon in the coal ash can be adjusted by removing a specific particle size range.

In the heat treatment, coal ash is heated in a rotary kiln or a fluidized bed incinerator. The heating temperature is preferably 600 to 1200 ° C, more preferably 600 to 1000 ° C, and particularly preferably 700 to 900 ° C. If the temperature is lower than 600 ° C, the unburned carbon cannot be sufficiently reduced, and if the temperature exceeds 1200 ° C, coal ash may be fused.

In the electrostatic separation process, unburned carbon contained in coal ash is separated by electrostatic force. The method is not particularly limited, and may be an inductive charging type or a triboelectric charging type. Further, as the induction charging type, a method of dropping coal ash on the surface of the rotating drum electrode, a method of air transporting on the porous electrode, and the like can be used.

By mixing a plurality of types of coal ash, the floating and activity of unburned carbon can be adjusted. Coal ash to be mixed and its amount can be effectively used by selecting and setting the coal ash particularly from the results of the quality test process. Further, a plurality of types of coal ash may be substantially mixed, for example, another coal ash may be mixed with a mixture of coal ash and clinker, or a plurality of types of coal ash may be mixed and then mixed with clinker. Can be done.

The total content of cement clinker and gypsum in the coal ash mixed cement produced by the present invention is usually preferably 75 to 99.9% by mass. It is preferably 85 to 99.8% by mass, and more preferably 95 to 99.7 parts by mass. General cement may be used instead of cement clinker and gypsum, and examples of general cement include ordinary Portland cement, early-strength Portland cement, moderate heat Portland cement, and low heat Portland cement. Preferably, it is usually Portland cement.

The content of coal ash in the coal ash mixed cement produced by the present invention is usually 0.1 to 25% by mass. It is preferably 0.2 to 15% by mass, and more preferably 0.3 to 5% by mass.

Hereinafter, examples of the present invention will be shown. The present invention is not limited to the following examples.

1. 1. Raw materials used The following materials were used as raw materials. At some levels, unburned carbon was separated from the following coal ash by an electrostatic separator (electrostatic), and the following coal ash was heat-treated at 800 ° C. for 30 minutes in an electric furnace (electrostatic). (Heating), or the following coal ash was pre-crushed with a ball mill to a brain specific surface area of 5500 ± 150 cm ² / g (separate crushing). The ignition loss (ig. Loss) of coal ash was measured according to JIS A 6201 "Measuring method of ignition loss of fly ash for concrete".
・ Ordinary Portland cement ・ Coal ash 1 (ig.loss = 10.5% by mass)
-Coal ash 2 (ig. Loss = 3.54% by mass)
-Coal ash 3 (ig. Loss = 2.6% by mass)
-Coal ash 4 (ig. Loss = 5.83% by mass)
・ Standard sand for cement strength test (Cement Association)

2. Preparation of mortar and cement paste (1) Mortar Ordinary Portland cement was mixed with coal ash so as to have the content shown in Table 1. At some levels, ordinary Portland cement and coal ash were mixed and then pulverized with a ball mill so that the brain specific surface area was 3100 ± 50 cm ² / g (mixed pulverization). To 450 g of the mixture of coal ash and ordinary Portland cement thus obtained, 1350 g of standard sand and tap water were added so that the water powder ratio was 50% by mass, and kneaded with a hovert mixer. , The vibrator treatment was performed while the sample was poured into a mold for making a specimen. The detailed procedure for kneading and the vibrator conformed to JIS R 5201 “Physical test method for cement”.

(2) Cement paste Coal ash and ordinary Portland cement are mixed so that the coal ash content is 5% by mass, tap water is added so that the water powder ratio is 50% by mass, and a hand mixer or homomixer is used. Kneaded with. The kneading time was 2 minutes, and the rotation speed of the homomixer was 4000 rpm.

3. 3. Evaluation of floating state of unburned carbon In the case of mortar, the floating state of unburned carbon was evaluated by visually confirming the surface state immediately after pouring it into a mold and performing a vibrator treatment for 120 seconds. In the case of cement paste, put the kneaded cement paste in a plastic container, apply vibration for 120 seconds using an ultrasonic cleaner, and immediately visually check the surface condition to check the floating state of unburned carbon. evaluated. In addition, the surface of both samples was photographed with a digital camera, and the images were binarized to calculate the floating area of unburned carbon. Note that FIG. 1 shows an image of the surface of the level 2 cement paste taken with a digital camera and an image of the surface after the binarization process. The visual evaluation of the floating state of unburned carbon is a five-grade evaluation from A to E, and each criterion is A: No floating of unburned carbon is confirmed (Fig. 2), B: Very pale black floating matter. Can be confirmed (Fig. 3), C: Many pale black floating substances can be confirmed (Fig. 4), D: Black floating substances can be confirmed sparsely (Fig. 5), E: Many black floating substances can be confirmed (Fig. 5). FIG. 6). A or B has no aesthetic problem, C has unburned carbon floating but is rarely a problem, and D or E is a state in which the aesthetic appearance is clearly spoiled by the unburned carbon floating.

4. Results (1) Mortar Table 1 shows the results of the floating test of unburned carbon in mortar to which coal ash was added. When the ignition loss derived from coal ash exceeds 0.35% by mass (levels 1, 2, 5), a large amount of unburned carbon was confirmed on the surface of the mortar. On the other hand, it was confirmed that unburned carbon may float on the surface of the mortar even when the loss on ignition in the cement derived from coal ash is sufficiently small (0.35% by mass or less) (levels 3, 6, and 7). , 8, 11). From the above, by mixing coal ash, cement and water to prepare a cement composition and observing its surface, a strong heat loss derived from coal ash is generated in coal ash mixed cement with a small amount of 0.35% by mass or less. It was found that the floating of unburned carbon can be discovered and evaluated. Therefore, a large amount of coal ash can be effectively used as compared with the conventional production method while suppressing the floating of unburned carbon.

Furthermore, when the area of the unburned carbon that floated was calculated by binarizing the image of the surface of the mortar, the floating of the unburned carbon could be easily quantitatively evaluated, and a tendency that generally corresponds to the visual evaluation was obtained. It was. Therefore, by binarizing the image of the mortar surface and evaluating the floating of unburned carbon, the floating of unburned carbon generated in the coal ash mixed cement can be easily determined without causing a judgment deviation by the evaluator. be able to.

In addition, the floating of unburned carbon worsened in the separated and crushed coal ash (levels 2 and 11). Therefore, as a method of adding coal ash in the cement manufacturing process, when cement is manufactured by a closed circuit mill, unburned carbon is further floated by throwing it into the separator part or the cement refined after separator classification instead of in the ball mill. Can be reduced. Further, it is preferable to put it in the separator from the viewpoint of controlling the particle size, and when putting it in the fine powder of cement, the powderiness of coal ash is confirmed in advance, and the specific surface area of the brain is preferably 5000 cm ² / g or more. It is preferable to select and input coal ash.

Further, by subjecting the coal ash to electrostatic separation treatment or heat treatment, the floating of unburned carbon was significantly improved (levels 3, 4, 7, 12, 13).

(2) Cement paste Table 2 shows the results of the floating test of unburned carbon in the paste to which coal ash was added. As in the case of mortar, the floating of unburned carbon in coal ash mixed cement can be evaluated in the case of paste, and the floating of unburned carbon can be evaluated even when the loss on ignition derived from coal ash is as small as 0.35% by mass or less. Was found and evaluated (levels 19, 20, 24).

Further, when the image of the surface of the cement paste was binarized and the floating area of the unburned carbon was calculated, a tendency that generally corresponded to the visual evaluation was obtained as in the case of the mortar. Furthermore, it was possible to reflect the difference between the mixers, which is difficult to visually discriminate, that the floating area of unburned carbon becomes larger when kneaded with a homomixer having a high shearing force (levels 15 and 20). Therefore, by combining kneading with a homomixer and binarization of the cement paste surface image, more coal ash can be used while reliably suppressing the floating of unburned carbon while being a simple test process. It becomes possible to do. In the case of coal ash separated and pulverized, the floating of unburned carbon deteriorated as in the case of mortar (levels 16 and 24).

Further, by subjecting the coal ash to electrostatic separation treatment or heat treatment, the floating of unburned carbon could be suppressed to a level where there was no problem in terms of quality (levels 17, 18, 21, 25).

Claims (7)

A method for producing a coal ash mixed cement containing coal ash, cement clinker and gypsum.
A quality test process for confirming the surface condition of the cement composition obtained by kneading uncrushed coal ash, cement and water, and
Based on the test results of the quality test step, a sorting step of sorting the coal ash used for producing the coal ash mixed cement and a sorting step
A crushing step of crushing the cement clinker using a closed circuit ball mill, and
And sorted the coal ash, and separators classification after the cement clinker are mixed without grinding the gypsum, or, with the coal ash is sorted, and the cement clinker which is ground in the grinding step, and plaster It is characterized by including a mixing step of mixing in a separator portion without crushing .
A method for producing coal ash mixed cement. In the quality test step, an image of the surface of the cement composition is binarized to confirm the surface state of the cement composition.
The method for producing a coal ash mixed cement according to claim 1. The ignition loss of coal ash was further measured in the quality test step.
It is characterized by including a step of setting the addition rate of coal ash used for producing the coal ash mixed cement based on the result of the quality test.
The method for producing a coal ash mixed cement according to claim 1 or 2. The total content of the cement clinker and gypsum in the coal ash mixed cement is 75 to 99.9% by mass, and the content of the coal ash is 0.1 to 25% by mass.
The method for producing a coal ash mixed cement according to any one of claims 1 to 3 . In the quality test step, 5 to 600 parts by mass of fine aggregate is added to 100 parts by mass of the mixed cement in which 0.1 to 25% by mass of the coal ash and 75 to 99.9% by mass of the cement are mixed, and water is added. The cement composition is obtained by kneading a cement mortar having a powder mass ratio of 30 to 100% by mass.
The method for producing a coal ash mixed cement according to any one of claims 1 to 4 . It is characterized by including a step of performing at least one of a classification treatment, a heat treatment, an electrostatic separation treatment, and a mixing treatment of coal ash with respect to the coal ash.
The method for producing a coal ash mixed cement according to any one of claims 1 to 5 . In the quality test step, a high shear mixer is used when the coal ash, the cement and the water are kneaded to obtain a cement composition.
The method for producing a coal ash mixed cement according to any one of claims 1 to 6.