Method for producing self-hardening material

Abstract

To improve workability.SOLUTION: A method for producing a self-hardening material includes: a first step of subjecting a fly ash to treatment for removing an unburned carbon to produce an unburned carbon-removed fly ash; a second step of applying mechanochemical treatment to the unburned carbon-removed fly ash to activate a surface of the unburned carbon-removed fly ash; a third step of mixing a strong alkali solution with fine silicon powder to prepare a silicon mixture in which a silicon component is eluted into the strong alkali solution; and a fourth step of mixing the surface-activated unburned carbon-removed fly ash with the silicon mixture.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a self-hardening material.

Background Art

[0002] As self-hardening materials such as cement paste, mortar, and concrete, cement-based materials such as ordinary Portland cement are widely used. In addition, the development of self-hardening materials using coal ash (fly ash) as a base material has been carried out. For example, Patent Document 1 discloses that a highly dense self-hardening material can be obtained by mixing fly ash whose surface is activated by mechanochemical treatment, a mixture of a strong alkaline solution and silicon powder, and the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when manufacturing a self-hardening material using coal ash, there are problems in workability such as the improvement of fluidity being desired.

[0005] The present invention has been made in view of such problems, and an object thereof is to improve workability.

Means for Solving the Problems

[0006] The main invention for achieving the above object is a method for manufacturing a self-hardening material, comprising: a first step of subjecting fly ash to unburned carbon removal treatment to produce fly ash after unburned carbon removal treatment; a second step of subjecting the fly ash after unburned carbon removal treatment to mechanochemical treatment to activate the surface of the fly ash after unburned carbon removal treatment; a third step of mixing a strong alkali solution and silicon fine powder to prepare a silicon mixture in which a silicon component is eluted in the strong alkali solution; and a fourth step of mixing the fly ash after unburned carbon removal treatment with the surface activated and the silicon mixture.

[0007] Other features of the present invention will be clarified by the description in this specification and the accompanying drawings.

Advantages of the Invention

[0008] According to the present invention, workability can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0010] From the description in this specification and the attached drawings, at least the following matters become clear.

[0011] (Aspect 1) A first step of subjecting fly ash to an unburned carbon removal treatment to produce unburned carbon-removed fly ash, a second step of subjecting the unburned carbon-removed fly ash to a mechanochemical treatment to activate the surface of the unburned carbon-removed fly ash, a third step of mixing a strong alkali solution and fine silicon powder to prepare a silicon mixture in which a silicon component is eluted in the strong alkali solution, and a fourth step of mixing the unburned carbon-removed fly ash with the activated surface and the silicon mixture. A method for producing a self-hardening material, characterized by comprising:

[0012] According to the method for producing a self-hardening material of Aspect 1, the workability can be improved.

[0013] (Aspect 2) The method for producing a self-hardening material according to Aspect 1, wherein in the first step, it is desirable to make the content of the unburned carbon in the unburned carbon-removed fly ash 1% or less.

[0014] According to the method for producing a self-hardening material of Aspect 2, the flow (fluidity) after kneading can be improved.

[0015] (Aspect 3) The manufacturing method of the self-hardening material according to Aspect 1 or Aspect 2, wherein the unburned carbon removal treatment is preferably a heat treatment for heating the fly ash.

[0016] According to the manufacturing method of the self-hardening material of Aspect 3, unburned carbon can be easily removed (reduced) by heating the fly ash.

[0017] (Aspect 4) The manufacturing method of the self-hardening material according to Aspect 3, wherein the heat treatment is preferably within 1 hour using a heating device.

[0018] According to the manufacturing method of the self-hardening material of Aspect 4, unburned carbon in the fly ash can be removed (reduced).

[0019] (Aspect 5) The manufacturing method of the self-hardening material according to Aspect 3 or Aspect 4, wherein the temperature of the heat treatment is preferably 500°C or higher and 600°C or lower.

[0020] According to the manufacturing method of the self-hardening material of Aspect 5, the flowability can be improved.

[0021] (Aspect 6) The manufacturing method of the self-hardening material according to any one of Aspects 1 to 5, wherein the ratio of the strong alkali solution to the binder containing the fly ash after the unburned carbon removal treatment and the silicon fine powder is preferably 25% or more and 40% or less.

[0022] According to the manufacturing method of the self-hardening material of Aspect 6, the strength of the hardened body can be improved.

[0023] (Aspect 7) The manufacturing method of the self-hardening material according to any one of Aspects 1 to 6, wherein the ratio of the fly ash after the unburned carbon removal treatment in the binder is preferably 90% or more.

[0024] According to the manufacturing method of the self-hardening material of Aspect 7, the strength of the hardened body can be improved.

[0025] (Aspect 8) A method for manufacturing a self-hardening material according to any one of Aspects 1 to 7, wherein the silicon concentration in the fine silicon powder is desirably 40,000 PPM or more.

[0026] According to the method for manufacturing a self-hardening material of Aspect 8, the strength of the cured body can be improved.

[0027] (Aspect 9) A method for manufacturing a self-hardening material according to any one of Aspects 1 to 8, wherein the self-hardening material desirably does not contain cement.

[0028] According to the method for manufacturing a self-hardening material of Aspect 9, a cured body (cementless cured body) can be formed without using cement.

[0029] ===Embodiment=== Hereinafter, embodiments of the present invention will be described. The present inventors have proposed that by subjecting coal ash (fly ash) to a mechanochemical treatment, the surface of the coal ash is activated, and by allowing an alkaline solution to act thereon, the activated surface is dissolved and the surfaces are bonded to each other to produce a cementless self-hardening material using coal ash as a base material (see Patent Document 1). By this technique, it becomes possible to use industrial by-products (for example, coal ash generated when coal is burned in a thermal power plant) in the production of self-hardening materials. However, when manufacturing a self-hardening material using coal ash, there were problems in workability such as the desire to improve fluidity.

[0030] By the way, industrial by-product coal ash usually contains unburned carbon in a few percent (for example, about 5%) by weight.

[0031] Figure 1 is an electron microscope (SEM) image of unburned carbon in coal ash. As shown in the SEM image of Figure 1, there were scattered cases where coal ash particles were embedded in lumps of unburned carbon. Since it is presumed that this unburned carbon affects fluidity, in this application, we conceived of removing the unburned carbon contained in coal ash.

[0032] Figure 2 is a flowchart of the method for manufacturing the self-hardening material in this embodiment. Also, Figure 3 is a schematic diagram showing how the hardened body is formed.

[0033] In the material preparation process (S1), unburned carbon removal treatment (S11: corresponding to the first step) is performed on coal ash (fly ash). In the examples described later, as a method for removing unburned carbon in coal ash, heat treatment using a heating device (electric furnace) is employed. Note that in this embodiment, "removal" of unburned carbon does not mean completely removing unburned carbon from coal ash, but rather means reducing (lowering) the content rate of unburned carbon in coal ash. As will be described later, even in the coal ash after the unburned carbon treatment and removal process, a small amount of unburned carbon is still contained.

[0034] Next, a mechanochemical treatment (S12: corresponding to the second step) is performed to activate the surface of the coal ash (fly ash after unburned carbon removal treatment) after the unburned carbon treatment and removal process. Hereinafter, the mechanochemical treatment is also referred to as "MC treatment" or "grinding treatment". By this mechanochemical treatment, as shown in the center of Figure 3, reactivity is imparted to the surface of particles with poor reactivity (here, coal ash).

[0035] Note that mechanochemical treatment is a treatment that imparts chemical characteristics (reactivity) to a solid substance by subjecting it to mechanical treatments such as impact, shear, and friction. Also, particle pulverization can achieve component homogenization. Examples of devices capable of performing such treatments include mixing devices such as ball mills, vibration mills, planetary ball mills, and media stirring type mills, pulverizers such as ball media mills, roller mills, and mortars, and jet pulverizers. In the examples described later, a planetary ball mill is used.

[0036] In addition, in the material preparation process (S1), a pre-mixing process (S13: corresponding to the third step) is performed in which a strong alkali solution and silicon fine powder are mixed and slurried. Thereby, a silicon mixture (hereinafter also referred to as slurry) in which a silicon component is eluted in the strong alkali solution is produced. Note that the silicon fine powder and the strong alkali solution are for bonding fly ashes to each other. In the present embodiment, silica fume mainly composed of amorphous silica is used as the silicon fine powder, but it is not limited thereto, and any material that can supply dissolved silicon elements in the presence of an alkali may be used.

[0037] Next, in the mixing process (S2: corresponding to the fourth step) of each material, the surface-activated fly ash from which unburned carbon has been removed and the silicon mixture (slurry) are mixed.

[0038] Then, in the filling and curing process (S3), the mixture is filled into a mold and cured. As a result, as shown on the right side of FIG. 3, the fly ashes react with each other on the surface in the solution to form a cured body. Note that the silica fume in a dissolved state in the slurry has a role of filling the gaps between the fly ashes.

[0039] Thus, in the present embodiment, by performing the unburned carbon removal process (step S11), the unburned carbon contained in the fly ash is removed. Then, a mechanochemical process is performed using the fly ash after the unburned carbon removal process and mixed with the slurry. As a result, it was confirmed that the fluidity (flow) in the fresh state can be improved and the workability can be improved (see the examples described later).

[0040] <<<Examples>>> <<Regarding the relationship between heating temperature and unburned carbon amount>> As described above, in this example, heat treatment is adopted as a method for removing unburned carbon in coal ash. In order to understand the relationship between the removal rate of unburned carbon and the heating temperature, a heating test of coal ash was carried out using an electric furnace. As the coal ash, the coal ash from the Isozaki Thermal Power Plant (obtained in August 2018, the third time, hereinafter referred to as Isozaki 3) was used. Also, for the heat treatment, heating was carried out at a predetermined temperature using an electric furnace manufactured by Isuzu Manufacturing Co., Ltd. Note that the heating time is preferably 1 hour or less, and in this example, it was set to 1 hour.

[0041] Figure 4 is a diagram showing the relationship between the heating temperature and the amount of unburned carbon. The horizontal axis of the figure is the heating temperature (°C), and the vertical axis is the amount of unburned carbon (%: the content rate of unburned carbon).

[0042] In Figure 4, the amount of unburned carbon in the coal ash is about 4% when the heating temperature is 400°C or lower, but it changes (decreases) rapidly between 500°C and 600°C. Specifically, the amount of unburned carbon is about 1% at 500°C, about 0.3% at 550°C, and about 0.1% at 600°C.

[0043] Therefore, in this example, when preparing the test specimens, the heating conditions were varied between 400°C and 700°C, and also, as a comparative example, the condition of no unburned carbon removal treatment (no heating) was set (see Figure 6).

[0044] <<Preparation of Test Materials and Specimens>> Figure 5 is a diagram showing a list of test materials.

[0045] As shown in the figure, as the coal ash (fly ash), the dust collected from the Isozaki Thermal Power Plant (Isozaki 3) was used. Also, as the mixing water, a slurry (manufactured by Fujimi Incorporated) in which silica fume (SF) was semi-dissolved in a 3 mol / L potassium hydroxide (KOH solution: strong alkali solution) to make the dissolved silicon concentration 40,000 ppm was used. Note that it is more desirable that the silicon concentration is 40,000 ppm or more. Thereby, the strength of the hardened body of the self-hardening material is further improved.

[0046] Figure 6 shows the composition of the specimens. The heating temperature in the figure is the temperature in the unburned carbon removal treatment of coal ash (step S11: here it is the heat treatment). The heating device and heating time are the same as the conditions of the heating test (Figure 4) (heating for 1 hour using an electric furnace).

[0047] Although not shown in the figure, for each level, the conditions of the mechanochemical treatment (step S12) of coal ash were also carried out. The mechanochemical treatment was carried out dry using a planetary ball mill. A fritsch P-5 type planetary ball mill was used, and the rotation speed was set at 300 rpm. The grinding conditions (grinding time) were 0 hours (no grinding), 1 hour, 2 hours, 3 hours, 4 hours, and 6 hours (conventional conditions).

[0048] Specimens were prepared using paste hardened bodies with the composition shown in Figure 6. The ratio of mixing water to binder (W / B) is preferably 25% or more and 40% or less, and among these, 32.5% was used where a stable and high compressive strength was obtained. The binder (B) contains coal ash (fly ash) and silica fume (SF). The proportion of coal ash in the binder (B) is preferably 90% or more.

[0049] Regarding the preparation of the specimens, after step S1 in Figure 2, in step S2, coal ash (fly ash) and slurry were kneaded with a mixer for about 1 minute, and then in step S3, they were poured (filled) into a cylindrical mold (diameter 20 mm, height 40 mm). The placed paste was demolded after 2 days of sealed curing in a constant temperature machine at 40°C, and then dried and cured at 40°C for 5 days.

[0050] <<Test content and test method>> <Observation of the appearance and particle size distribution of coal ash after grinding treatment> A part of the coal ash after the grinding treatment (step S12) was taken out, and its appearance was observed and the particle size distribution was measured using an MT3000 manufactured by Microtrac Bel.

[0051] <Measurement of pH and electrical conductivity> With reference to the test method of the Japanese Geotechnical Society, the fly ash and ion-exchanged water were fixed at a solid-liquid ratio of 1:5, and the pH and electrical conductivity of the suspension were measured.

[0052] <Simple flow measurement of the paste immediately after mixing> A part of the paste immediately after mixing (immediately after step S2) was sampled, and a simple flow test was carried out. In this test, the paste was filled into an acrylic cell (inner diameter 28 mm, height 22 mm) for fixing the SEM observation material on a stainless steel plate. The acrylic cell was quickly lifted, and for the spreading situation of the paste, the major axis and minor axis were measured, and the average value was taken as the flow.

[0053] <Change in the fresh state after mixing> To grasp the fresh state from immediately after kneading, the change in the viscosity of the paste over time was measured using a rheometer (viscometer). The rheometer used was a rotational rheometer KINEXUS Lab+ manufactured by Malvern Panalytical. In the rheometer, the paste was sandwiched between a stainless steel disk with a diameter of 3 cm, the gap (paste thickness) was set to 1 mm, and a shear strain of 0.2% was applied at a frequency of 5 Hz, and the measurement was made from the response of the paste. The sampling interval was set to 10 seconds.

[0054] <Measurement of the compressive strength and dimensional change rate of the paste hardened body> The compressive strength was measured using specimens at an age of 7 days (sealed curing for 2 days and dry curing for 5 days). The number of specimens per level was set to 3. An autograph manufactured by Shimadzu Corporation was used for the compressive strength test.

[0055] The dimensional change rate was obtained with the diameter at an age of 2 days as the denominator and the difference between the age of 7 days and the age of 2 days (diameter at an age of 7 days - diameter at an age of 2 days) as the numerator. That is, when the dimensional change rate is negative, it means that the specimen has shrunk with curing, and when the dimensional change rate is positive, it means that the specimen has expanded with curing. Note that as the method for calculating the diameter, for the diameter in the circumferential direction of the specimen, the lengths at two orthogonal positions were measured, and the average was taken as the diameter.

[0056] <<Test Results>> <Observation of the Appearance and Particle Size Distribution of Coal Ash after Crushing Treatment> The coal ash was gray and changed to a bright yellowish-brown color when heated. Furthermore, the brown color tone became stronger due to the crushing treatment using a planetary ball mill.

[0057] Figures 7A to 7F are diagrams showing the measurement results of the particle size distribution. The horizontal axis of each figure is the particle diameter (μm), and the vertical axis is the frequency (%). Note that Figure 7A shows the particle size distribution in the case of non-heating (comparative example), Figure 7B shows 400 °C, Figure 7C shows 500 °C, Figure 7D shows 550 °C, Figure 7E shows 600 °C, and Figure 7F shows 700 °C. Also, in each figure (each heating temperature), the time of mechanochemical treatment (crushing treatment) is denoted as MC. For example, MC0H indicates no crushing, and MC1H indicates crushing for 1 hour (the same applies to the following figures).

[0058] In the figures, for ease of viewing, the values on the vertical axis for each level are shifted by 0.5% each (for example, at a particle diameter of 0.1 μm or 1000 μm, the values for each level are shifted by 0.5% each, but actually, they are all approximately the same).

[0059] As shown in Figure 7A, the coal ash without heating and without crushing (non-heating / MC0H) had a particle size distribution centered around a peak at a particle diameter of approximately 50 μm. However, with 1 hour of crushing, as the particles became finer, the peak shifted to approximately 4 μm, and in the case of 2 hours of crushing, in addition to approximately 3 μm, a new distribution with a peak at approximately 30 μm appeared. Thereafter, as the crushing time increased, the distribution with a peak at approximately 30 μm became larger.

[0060] In the case of heating at 400 °C (Figure 7B), the tendency was almost the same as in Figure 7A.

[0061] In the case of heating at 500 °C (Figure 7C), a distribution with a peak at a particle diameter of approximately 2.5 μm appeared with 1 hour of crushing (MC1H). The same was true with an increase in the crushing time, and there was little change in the shape of the particle size distribution, with only a slight increase in the coarse particle fraction being observed.

[0062] At 550 °C heating (Figure 7D), the distribution with a peak particle size of approximately 2.5 μm is the same, but when the milling time is increased, the distribution of the 2.5-μm peak becomes smaller and a distribution with a peak particle size of approximately 30 μm appears.

[0063] At 600 °C and above, as shown in Figures 7E and 7F, the distribution with a peak particle size of approximately 30 μm was prominent.

[0064] Thus, as the content of unburned carbon decreases (in other words, as the heating temperature increases), the particle size distribution by milling changes, and at 550 °C and above, it becomes a particle size distribution different from that of unheated (non-heated) coal ash that has not removed unburned carbon.

[0065] The newly emerging peak (the peak around 30 μm) when the milling time is increased is considered to be due to the following reasons. That is, although the particles themselves become smaller in diameter by the milling of mechanochemical treatment, reactivity is imparted to the surface of particles with poor reactivity (here, coal ash), and it is considered that small-diameter particles with reactivity imparted to the surface aggregate to form large lumps.

[0066] <pH measurement results> Figure 8 is a diagram showing the pH measurement results. The horizontal axis of Figure 8 is the heating temperature (°C) of unburned treatment removal, and the vertical axis is the pH.

[0067] From Figure 8, it was found that coal ash treated at a higher heating temperature showed a higher pH value. Also, the longer the milling time, the greater the variation, but the pH tended to be lower.

[0068] <Electrical conductivity measurement results> Figure 9 is a diagram showing the electrical conductivity measurement results. The horizontal axis of Figure 9 is the heating temperature (°C) of unburned treatment removal, and the vertical axis is the electrical conductivity (mS / s).

[0069] In the case without milling, the coal ash heated at 600 °C had an electrical conductivity value approximately 25 mS / m lower than that of non-heated coal ash.

[0070] In the case of 1-hour milling treatment (MC1H), compared with "no milling", the electrical conductivity was generally lower and the difference in heating temperature became smaller.

[0071] When the milling treatment was 2 hours (MC2H) or more, the electrical conductivity was even lower than that of the 1-hour milling treatment, and regardless of the heating temperature and milling time, it became almost the same value.

[0072] <Measurement results of simple flow> Figure 10 is a diagram showing the measurement results of the simple flow of the paste after kneading. The horizontal axis in Figure 10 is the heating temperature (°C) for unburned treatment removal, and the vertical axis is the flow (mm). Also, the dotted line at 28 mm in the figure indicates the diameter of the container for flow measurement. Note that the paste with 6-hour milling treatment (MC6H) had extremely high viscosity, making it impossible to measure the flow and prepare the test specimen. Also, for the 1-hour milling treatment (MC1H) without heating and with heating at 400 °C, similarly, the viscosity was extremely high, making it impossible to measure the flow and prepare the test specimen.

[0073] Without milling, it had a high fluidity of 60 mm or more, and particularly showed a large value of 94.3 mm when heated at 600 °C. This is considered to be due to the fact that the coal ash has no binding property and the carbon (unburned carbon) content is extremely low due to high-temperature heat treatment.

[0074] When milling treatment was applied, the flow decreased, but when the heat treatment exceeded 400 °C, the flow increased and reached a maximum (peak) at about 550 °C. Note that when the heating temperature was 600 °C or higher, as the milling time increased, the flow size tended to decrease, and with 4-hour milling treatment, it almost had no fluidity.

[0075] From these results, it was confirmed that by setting the heating temperature for unburned carbon removal to about 550 °C (in other words, the unburned carbon amount to about 0.3%), the flow can be improved (workability can be enhanced). Note that since the flow is lower at 600 °C or higher than at 550 °C, it is considered that it is better to leave a little unburned carbon instead of removing all of it.

[0076] <Change in fresh state> Figures 11A to 11E are diagrams showing the change in viscosity over time from after kneading to solidification. The horizontal axis of each figure is time (minutes), and the vertical axis is viscosity η (Pa·s). Note that Figure 11A shows the case of 1 hour of grinding treatment, Figure 11B shows the case of 2 hours of grinding treatment, Figure 11C shows the case of 3 hours of grinding treatment, Figure 11D shows the case of 4 hours of grinding treatment, and Figure 11E shows the case of 6 hours of grinding treatment.

[0077] In the case of 1 hour of grinding treatment (Figure 11A), non-heating and heating at 400 °C (the ones with a large content of unburned carbon) caused strong swelling immediately after kneading and could not be measured. In the other pastes (heating at 500 to 700 °C), the viscosity tended to decrease as the heating temperature increased.

[0078] In the case of 2 hours of grinding treatment (Figure 11B), compared with 1 hour of grinding treatment (Figure 11A), the viscosity was generally lower. For non-heating and heating at 400 °C, the viscosity was high immediately after kneading and reached a cured state in about 5 minutes. For heating at 500 °C or higher, the viscosity gradually decreased as the heating temperature increased, and at 600 °C and 700 °C, the viscosity showed almost the same change over time for about 20 minutes after kneading.

[0079] In the case of 3 hours of grinding treatment (Figure 11C), compared with 2 hours of grinding treatment (Figure 11B), the viscosity tended to decrease further overall.

[0080] In the case of 4 hours of grinding treatment (Figure 11D), although a decrease in viscosity was observed at heating temperatures of 500 °C or lower, at heating temperatures above that, the viscosity showed almost the same change over time as in the case of 3 hours of grinding treatment (Figure 11C).

[0081] In the case of 6 hours of grinding treatment (Figure 11E), compared with 4 hours of grinding treatment (Figure 11D), the viscosity was generally higher. Especially in the case of heating at 600 °C, the viscosity was high immediately after kneading, making it difficult to pour into the mold.

[0082] From these results, it can be said that the time for the grinding process is too long at 6 hours (conventional conditions), and 3 hours is appropriate. Also, by performing heating at 500°C or higher (in other words, reducing the unburned carbon content to 1% or less), it was confirmed that the time until the paste hardens can be greatly extended (workability can be improved) compared to the case without heating.

[0083] <Measurement Results of Compressive Strength> Figure 12 is a diagram showing the measurement results of compressive strength. The horizontal axis of Figure 12 is the heating temperature (°C) of the unburned carbon removal treatment, and the vertical axis is the compressive strength (N / mm 2 ).

[0084] The compressive strength of the specimen without grinding was maximized at 17 N / mm without heating 2 and remained at a maximum of 10 N / mm even with heating 2 .

[0085] In the case of 1-hour grinding treatment (MC1H), the viscosity of the paste was very high without heating (non-heating) and at 400°C heating, making it difficult to prepare specimens.

[0086] The fly ashes added with other grinding treatments (MC2H~4H) all showed almost the same compressive strength. Specifically, the compressive strength was slightly less than 50 N / mm without heating 2 . As the heating temperature increased, the compressive strength slightly decreased, and when it exceeded 500°C, it decreased rapidly, reaching 30 N / mm at 600°C and 700°C 2 . Note that the compressive strength (20 N / mm 2 ) required for use as a construction material was ensured.

[0087] <Measurement Results of Dimensional Change Rate> Figure 13 is a diagram showing the measurement results of the shape change rate (dimensional change rate). The horizontal axis of Figure 13 is the heating temperature (°C) of the unburned carbon removal treatment, and the vertical axis is the dimensional change rate (%).

[0088] Note that when the value of the vertical axis (shape change rate) in the figure is positive (greater than 0), it indicates that the specimen has expanded, and when it is negative (less than 0), it indicates that the specimen has contracted.

[0089] From the figure, it was found that for coal ash heated at 500°C or higher, shrinkage could be suppressed by applying grinding treatment. In particular, in the range of 550°C to 600°C, the coal ash with a grinding treatment time of 3 hours showed a result that the shape change rate changed from negative (shrinkage) to positive (expansion).

[0090] From the above results, by heating coal ash to 500 - 600°C (in other words, reducing unburned carbon to 1% - 0.1%), the flow immediately after kneading increased, and especially when heated at 550°C, the flow became maximum. Also, in the time-dependent change of viscosity, the time until hardening could be extended compared to non-heated cases. Therefore, it was confirmed that improving workability can be achieved by removing unburned carbon from coal ash.

[0091] It was also confirmed that shrinkage can be suppressed by applying heating at 500 - 600°C and grinding treatment.

[0092] It was also confirmed that the grinding treatment time is preferably about 3 hours (the grinding time can be shortened compared to the conventional method).

[0093] Also, Fig. 14 is a diagram showing the appearance of the prepared specimen. It is black without heating (without unburned carbon removal treatment), a change to a lighter color tone is seen with a heat treatment at 550°C, and at 600°C, it becomes a color tone close to almost white. Thus, by removing unburned carbon through heat treatment (unburned carbon removal treatment), the hardened body becomes closer to white, so that the degree of freedom in coloring and the like can also be obtained.

[0094] ===Regarding Other Embodiments=== The above embodiments are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. It goes without saying that the present invention can be changed and improved without departing from its gist, and equivalents of the present invention are included therein.

[0095] In the foregoing embodiment, the treatment using a planetary ball mill as the mechanochemical treatment was exemplified. However, as long as the surface of the coal ash can be activated, the treatment is not limited thereto.

[0096] Also, in the foregoing embodiment, a potassium hydroxide solution was used as the strong alkali solution. However, the solution is not limited thereto, and a sodium hydroxide solution obtained by dissolving sodium hydroxide in water may also be used. Further, the concentration of the strong alkali solution is not limited to 3 mol / L.

[0097] Also, with respect to the self-hardening material, fine aggregate may be added to form mortar, or fine aggregate and coarse aggregate may be added to form concrete (cementless concrete).

[0098] Also, in the step (step S2) of mixing coal ash (fly ash) and a silicon mixture (slurry), other materials (for example, a water reducing agent or a retarder for adjusting the time until hardening, a shrinkage reducing agent for preventing cracking, etc.) may be further mixed.

Claims

1. A first step of subjecting fly ash to unburned carbon removal treatment to produce fly ash after unburned carbon removal treatment; A second step of subjecting the fly ash after unburned carbon removal treatment to mechanochemical treatment to activate the surface of the fly ash after unburned carbon removal treatment; A third step of mixing a strong alkaline solution and silicon fine powder to produce a silicon mixture in which a silicon component is eluted in the strong alkaline solution; A fourth step of mixing the fly ash after unburned carbon removal treatment with an activated surface and the silicon mixture; A method for producing a self-hardening material, characterized by comprising the above steps.

2. The method for producing a self-hardening material according to Claim 1, wherein in the first step, the content of the unburned carbon in the fly ash after unburned carbon removal treatment is made 1% or less. A method for producing a self-hardening material, characterized by the above.

3. The method for producing a self-hardening material according to Claim 1, wherein the unburned carbon removal treatment is a heat treatment for heating the fly ash. A method for producing a self-hardening material, characterized by the above.

4. The method for producing a self-hardening material according to Claim 3, wherein the heat treatment is within 1 hour using a heating device. A method for producing a self-hardening material, characterized by the above.

5. The method for producing a self-hardening material according to Claim 3, wherein the temperature of the heat treatment is 500°C or higher and 600°C or lower. A method for producing a self-hardening material, characterized by the above.

6. The method for producing a self-hardening material according to Claim 1, wherein the ratio of the strong alkaline solution to the binder containing the fly ash after unburned carbon removal treatment and the silicon fine powder is 25% or more and 40% or less. A method for producing a self-hardening material, characterized by the above.

7. The method for producing a self-hardening material according to Claim 6, wherein the proportion of the fly ash after unburned carbon removal treatment in the binder is 90% or more. A method for producing a self-hardening material, characterized by the above.

8. The method for producing a self-hardening material according to Claim 1, wherein the silicon concentration in the silicon fine powder is 40,000 PPM or more. A method for producing a self-hardening material, characterized by the above.

9. The method for producing a self-hardening material according to any one of Claims 1 to 8, wherein the self-hardening material does not contain cement. A method for producing a self-hardening material, characterized by the above.

Images