Method for producing self-hardening material

Abstract

[Problem] To improve workability. [Solution] This method comprises: a first step for subjecting fly ash to unburned carbon removal processing, thereby generating unburned carbon removal processed fly ash; a second step for subjecting the unburned carbon removal processed fly ash to mechanochemical processing and activating the surface of the unburned carbon removal processed fly ash; a third step for mixing a strong alkaline solution together with a silicon fine powder and preparing a silicon mixture in which a silicon component is eluted in the strong alkaline solution; and a fourth step for mixing the unburned carbon removal processed fly ash which has undergone surface activation together with the silicon mixture.

Description

Method for manufacturing self-hardening materials

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

[0002] Cement-based materials such as ordinary Portland cement are widely used as self-hardening materials for cement paste, mortar, concrete, etc. Furthermore, instead of cement-based materials, self-hardening materials using coal ash (fly ash) as a base material have been developed. For example, Patent Document 1 discloses that a highly dense self-hardening material can be obtained by mixing fly ash whose surface has been activated by mechanochemical treatment with a mixture of a strong alkaline solution and silicon powder.

[0003] Japanese Patent Application Laid-Open No. 2015-218070

[0004] However, when producing self-hardening materials using coal ash, there are issues with workability, such as the need to improve fluidity.

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

[0006] The main invention for achieving the above object is a method for producing a self-hardening material, comprising: a first step of treating fly ash to remove unburned carbon, thereby producing unburned-carbon-removed fly ash; a second step of mechanochemically treating the unburned-carbon-removed fly ash to activate the surface of the unburned-carbon-removed fly ash; a third step of mixing a strong alkaline solution with silicon fine powder to produce a silicon mixture in which silicon components are eluted into the strong alkaline solution; and a fourth step of mixing the surface-activated unburned-carbon-removed fly ash with the silicon mixture.

[0007] Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

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

[0009] FIG. 1 is an electron microscope (SEM) image of unburned carbon in coal ash. FIG. 2 is a flow diagram of a method for manufacturing a self-hardening material in this embodiment. FIG. 3 is a schematic diagram showing how a hardened body is formed. FIG. 4 is a diagram showing the relationship between heating temperature and the amount of unburned carbon. FIG. 5 is a diagram showing a list of test materials. FIG. 6 is a diagram showing the composition of a test specimen. FIG. 7A to FIG. 7F are diagrams showing the results of particle size distribution measurement. FIG. 7A are diagrams showing the results of pH measurement. FIG. 7B are diagrams showing the results of electrical conductivity measurement. FIG. 8 is a diagram showing the results of simplified flow measurement of a kneaded paste. FIG. 9A to FIG. 9E are diagrams showing the change in viscosity over time from kneading to solidification. FIG. 9E are diagrams showing the results of compressive strength measurement. FIG. 10 is a diagram showing the results of shape change rate measurement. FIG. 11A is a diagram showing the appearance of a test specimen.

[0010] At least the following matters will become clear from the description of this specification and the accompanying drawings.

[0011] (Aspect 1) A method for producing a self-hardening material, comprising: a first step of treating fly ash to remove unburned carbon, thereby producing unburned-carbon-removed fly ash; a second step of mechanochemically treating the unburned-carbon-removed fly ash to activate the surface of the unburned-carbon-removed fly ash; a third step of mixing a strong alkaline solution with silicon fine powder to produce a silicon mixture in which silicon components are eluted into the strong alkaline solution; and a fourth step of mixing the surface-activated unburned-carbon-removed fly ash with the silicon mixture.

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

[0013] (Aspect 2) In the method for producing a self-hardening material according to aspect 1, it is preferable that in the first step, the content of unburned carbon in the unburned carbon removal treated fly ash is set to 1% or less.

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

[0015] (Aspect 3) In the method for producing a self-hardening material according to Aspect 1 or Aspect 2, it is preferable that the unburned carbon removal treatment is a heat treatment in which the fly ash is heated.

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

[0017] (Aspect 4) In the method for producing a self-hardening material according to aspect 3, it is desirable that the heat treatment is carried out in a heating device for one hour or less.

[0018] According to the method for producing a self-hardening material of aspect 4, it is possible to remove (reduce) unburned carbon in fly ash.

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

[0020] According to the method for producing a self-hardening material of aspect 5, flow (fluidity) can be improved.

[0021] (Aspect 6) In the method for producing a self-hardening material according to any one of Aspects 1 to 5, it is desirable that the ratio of the strong alkaline solution to the binder containing the fly ash from which unburned carbon has been removed and the silicon fine powder is 25% or more and 40% or less.

[0022] According to the method for producing a self-hardening material of aspect 6, the strength of the hardened body can be improved.

[0023] (Aspect 7) In the method for producing a self-hardening material according to any one of Aspects 1 to 6, it is desirable that the proportion of the fly ash from which unburned carbon has been removed in the binder is 90% or more.

[0024] According to the method for producing a self-hardening material of aspect 7, the strength of the hardened body can be improved.

[0025] (Embodiment 8) In the method for producing a self-hardening material according to any one of embodiments 1 to 7, the silicon concentration in the silicon fine powder is preferably 40,000 ppm or more.

[0026] According to the method for producing a self-hardening material of aspect 8, the strength of the hardened body can be improved.

[0027] (Aspect 9) In the method for producing a self-hardening material according to any one of Aspects 1 to 8, it is preferable that the self-hardening material does not contain cement.

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

[0029] Embodiments The following describes embodiments of the present invention. The present inventors have proposed that a cementless self-hardening material using coal ash as a base material can be produced by subjecting coal ash (fly ash) to a mechanochemical treatment to activate the surface of the coal ash, and then applying an alkaline solution to dissolve the activated surface and bond these surfaces together (see Patent Document 1). This technology makes it possible to use industrial by-products (e.g., coal ash generated when coal is burned in a thermal power plant) to produce self-hardening materials. However, when producing self-hardening materials using coal ash, there are issues with workability, such as the need to improve fluidity.

[0030] Incidentally, coal ash, which is an industrial by-product, usually contains a few percent (for example, about 5%) of unburned carbon 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, coal ash particles were occasionally found embedded in clumps of unburned carbon. Since this unburned carbon is presumed to affect fluidity, the present application conceived of removing the unburned carbon contained in the coal ash.

[0032] Fig. 2 is a flow diagram of the method for producing a self-hardening material in this embodiment, and Fig. 3 is a schematic diagram showing how a hardened body is formed.

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

[0034] Next, mechanochemical treatment (S12: corresponding to the second step) is performed to activate the surface of the unburned carbon-removed coal ash (unburned carbon-removed fly ash). Hereinafter, mechanochemical treatment will also be referred to as "MC treatment" or "grinding treatment." This mechanochemical treatment imparts reactivity to the surface of the less reactive particles (here, coal ash), as shown in the center of Figure 3.

[0035] Mechanochemical processing is a process in which a solid substance is subjected to mechanical processing such as impact, shear, or friction to impart chemical properties (reactivity) to the substance. It can also homogenize the components by pulverizing particles. Examples of equipment that can perform this type of processing include mixing devices such as ball mills, vibration mills, planetary ball mills, and media-agitated mills; grinders such as ball media mills, roller mills, and mortars; and jet grinders. In the examples described below, a planetary ball mill is used.

[0036] Furthermore, in the material preparation process (S1), a pre-mixing process (S13: corresponding to the third step) is performed in which a strong alkaline solution and silicon fine powder are mixed together to form a slurry. This produces a silicon mixture (hereinafter also referred to as a slurry) in which the silicon component is eluted into the strong alkaline solution. The silicon fine powder and the strong alkaline solution are used to bond the coal ash (fly ash) together. In this embodiment, silica fume, which is primarily composed of amorphous silica, is used as the silicon fine powder, but the present invention is not limited to this, and any powder that can provide dissolved silicon element in the presence of alkali may be used.

[0037] Next, in a mixing process of the materials (S2: corresponding to the fourth step), the surface-activated coal ash from which the unburned carbon has been removed is mixed with the silicon mixture (slurry).

[0038] Then, in the filling and curing process (S3), the mixture is filled into a formwork and cured. As a result, the coal ash reacts with its surface in the solution to form a hardened body, as shown on the right side of Figure 3. The silica fume dissolved in the slurry serves to fill gaps in the coal ash.

[0039] In this embodiment, the unburned carbon removal process (step S11) is performed to remove unburned carbon from the coal ash. Then, the coal ash after the unburned carbon removal process is subjected to mechanochemical treatment and mixed with the slurry. This process improves the fluidity (flow) of the fresh coal ash, and it has been confirmed that this process improves workability (see Examples below).

[0040] <<<Example >>>> <<Regarding the Relationship Between Heating Temperature and the Amount of Unburned Carbon>> As described above, in this example, heat treatment is used as a method for removing unburned carbon from coal ash. In order to understand the relationship between the rate of unburned carbon removal and the heating temperature, a heating test of coal ash using an electric furnace was conducted. The coal ash used was coal ash from the Isogo Thermal Power Plant (obtained in August 2018 (third time), hereinafter referred to as Isogo 3). The heat treatment was carried out at a predetermined temperature using an electric furnace manufactured by Isuzu Corporation. The heating time is preferably one hour or less, and was set to one hour in this example.

[0041] 4 is a diagram showing the relationship between heating temperature and the amount of unburned carbon, where the horizontal axis represents heating temperature (° C.) and the vertical axis represents the amount of unburned carbon (%: content 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 less, but 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 as a comparative example, a condition without unburned carbon removal treatment (no heating) was also set (see Figure 6).

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

[0045] As shown in the figure, the coal ash (fly ash) used was collected dust ash (Isogo 3) from the Isogo Thermal Power Plant. Furthermore, the mixing water used was a slurry (manufactured by Fujimi Incorporated) in which silica fume (SF) was partially dissolved in potassium hydroxide (KOH solution: strong alkaline solution) with a concentration of 3 mol / L, resulting in a dissolved silicon concentration of 40,000 ppm. It is more desirable for the silicon concentration to be 40,000 ppm or higher. This further improves the strength of the hardened body of the self-hardening material.

[0046] Figure 6 shows the composition of the test specimen. The heating temperature in the figure is the temperature in the treatment for removing unburned carbon from the coal ash (step S11: heating treatment in this case). The heating device and heating time were the same as those in the heating test (Figure 4) (heating for 1 hour using an electric furnace).

[0047] Although not shown in the figure, the conditions for mechanochemical treatment (step S12) of the coal ash were also varied for each level. The mechanochemical treatment was carried out in a dry manner using a planetary ball mill. The planetary ball mill used was a P-5 type manufactured by Fritsch, and the rotation speed was set to 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] Test specimens were prepared using a hardened paste with the mix ratio shown in Figure 6. The ratio of mixing water to binder (W / B) is preferably between 25% and 40%, with 32.5% being selected as this ratio, which provides a stable and high compressive strength. The binder (B) contains coal ash (fly ash) and silica fume (SF). The proportion of coal ash in binder (B) is preferably 90% or more.

[0049] In preparing the specimen, after step S1 in Fig. 2, in step S2, coal ash (fly ash) and slurry were mixed in a mixer for about 1 minute, and then in step S3, the mixture was poured (filled) into a cylindrical formwork (diameter 20 mm, height 40 mm). The poured paste was sealed and cured in a thermostatic chamber at 40°C for 2 days, then removed from the formwork and dry-cured at 40°C for 5 days.

[0050] <<Test Contents and Test Method>> <Appearance Observation and Particle Size Distribution of Coal Ash After Grinding Treatment> A portion of the coal ash after the grinding treatment (step S12) was taken out, and its appearance was observed, and its particle size distribution was measured using an MT3000 manufactured by Microtrackbell.

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

[0052] <Simple flow measurement of paste immediately after kneading> A portion of the paste immediately after kneading (immediately after step S2) was sampled and subjected to a simple flow test. In this test, the paste was filled into an acrylic cell (inner diameter 28 mm, height 22 mm) for fixing epoxy resin to an SEM observation specimen placed on a stainless steel plate, and the acrylic cell was quickly lifted. The major and minor axes of the paste were measured to determine how it spread, and the average value was taken as the flow.

[0053] <Changes in fresh state after kneading> To understand the fresh state immediately after kneading, the change in 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 stainless steel disks with a diameter of 3 cm, a gap (thickness of the paste) was set to 1 mm, and a shear strain of 0.2% was applied at a frequency of 5 Hz to measure the response of the paste. The sampling interval was 10 seconds.

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

[0055] The dimensional change rate was calculated by taking the diameter at 2 days as the denominator and the difference between the diameter at 2 days and the diameter at 7 days (diameter at 7 days - diameter at 2 days) as the numerator. In other words, if the dimensional change rate is negative, it means that the specimen has shrunk as it hardens, and if the dimensional change rate is positive, it means that the specimen has expanded as it hardens. The diameter was calculated by measuring the length of two perpendicular points in the circumferential direction of the specimen, and taking the average of these measurements.

[0056] <<Test Results>> <Appearance and particle size distribution of coal ash after grinding> The coal ash was gray, and when heated it turned a light ochre color. Furthermore, grinding using a planetary ball mill deepened the brown color.

[0057] 7A to 7F are diagrams showing the results of particle size distribution measurements. The horizontal axis of each diagram is particle size (μm), and the vertical axis is frequency (%). Note that FIG. 7A shows particle size distributions without heating (comparative example), FIG. 7B shows particle size distributions at 400°C, FIG. 7C shows particle size distributions at 500°C, FIG. 7D shows particle size distributions at 550°C, FIG. 7E shows particle size distributions at 600°C, and FIG. 7F shows particle size distributions at 700°C. In addition, in each diagram (each heating temperature), the time of mechanochemical treatment (grinding treatment) is represented as MC. For example, MC0H indicates no grinding, and MC1H indicates grinding for 1 hour (the same applies to the following diagrams).

[0058] In the figure, for ease of viewing, the values ​​on the vertical axis for each level are shifted by 0.5% (for example, when the particle size is 0.1 μm or 1000 μm, the values ​​for each level are shifted by 0.5%, but in reality they are all almost the same).

[0059] As shown in Figure 7A, the particle size distribution of unheated and un-milled coal ash (unheated / MC0H) had a peak at about 50 μm. However, after 1 hour of milling, the particle size distribution shifted to about 4 μm as the particles became finer. After 2 hours of milling, a new distribution with a peak at about 30 μm appeared in addition to the peak at about 3 μm. Thereafter, the distribution with a peak at about 30 μm became larger as the milling time increased.

[0060] Heating at 400° C. (FIG. 7B) also showed a tendency similar to that shown in FIG. 7A.

[0061] When heated at 500°C (Fig. 7C), a particle size distribution peaking at approximately 2.5 μm appeared after 1 hour of milling (MC1H). The same was true with increasing milling time; the shape of the particle size distribution changed little, and a slight increase in the coarse particle content was observed.

[0062] When heated at 550°C (Fig. 7D), the distribution with a peak particle size of about 2.5 µm remained the same, but when the milling time was increased, the distribution with a peak particle size of about 2.5 µm became smaller, and a distribution with a peak particle size of about 30 µm appeared.

[0063] At temperatures above 600° C., as shown in FIGS. 7E and 7F, a distribution with a peak particle size of about 30 μm prevailed.

[0064] Thus, as the content of unburned carbon decreases (in other words, as the heating temperature increases), the particle size distribution due to grinding changes, and at 550°C or higher, the particle size distribution becomes different from that of coal ash from which unburned carbon has not been removed (unheated).

[0065] The reason for the new peak (peak at about 30 μm) that appears when the grinding time is increased is thought to be as follows: Although the particles themselves become smaller in diameter due to grinding in the mechanochemical treatment, reactivity is imparted to the surfaces of the less reactive particles (coal ash in this case), and the small particles with the reactivity imparted to their surfaces aggregate to form large agglomerates.

[0066] <pH Measurement Results> Fig. 8 is a diagram showing the pH measurement results, in which the horizontal axis represents the heating temperature (°C) for unburned matter removal, and the vertical axis represents pH.

[0067] 8, the results show that the higher the heating temperature of the coal ash, the higher the pH value. Also, the longer the grinding time, the lower the pH value, although there was a large variation.

[0068] <Measurement Results of Electrical Conductivity> Fig. 9 is a diagram showing the measurement results of electrical conductivity, in which the horizontal axis represents the heating temperature (°C) for unburned material removal, and the vertical axis represents electrical conductivity (mS / s).

[0069] Without grinding, the coal ash heated to 600°C had an electrical conductivity that was approximately 25 mS / m lower than that of unheated coal ash.

[0070] After 1 hour of milling (MC1H), the electrical conductivity was lower overall and the difference in heating temperature was smaller than in the case of "no milling."

[0071] When the milling treatment was carried out for 2 hours or more (MC2H), the electrical conductivity was further decreased compared to when the milling treatment was carried out for 1 hour, and remained at approximately the same value regardless of the heating temperature or milling time.

[0072] <Simple Flow Measurement Results> Figure 10 shows the results of simple flow measurement of the paste after kneading. The horizontal axis of Figure 10 is the heating temperature (°C) for unburned treatment removal, and the vertical axis is flow (mm). The 28 mm dotted line in the figure indicates the diameter of the container used for flow measurement. The paste subjected to 6 hours of grinding treatment (MC6H) had such high viscosity that it was impossible to measure the flow or prepare a test specimen. Similarly, the pastes without heating and those subjected to 1 hour of grinding treatment (MC1H) with heating at 400°C also had such high viscosity that it was impossible to measure the flow or prepare a test specimen.

[0073] The coal ash without grinding had high fluidity of 60 mm or more, and showed a particularly large value of 94.3 mm when heated at 600°C. This is thought to be due to the fact that the coal ash does not have binding properties and the carbon (unburned carbon) content is extremely low due to the high-temperature heat treatment.

[0074] When milling treatment was added, the flow decreased, but when the heating treatment exceeded 400° C., the flow increased, reaching a maximum (peak) at approximately 550° C. At heating temperatures of 600° C. or higher, the magnitude of the flow tended to decrease as the milling time increased, and after 4 hours of milling treatment, the material had almost no fluidity.

[0075] These results confirmed that the flow can be improved (the workability can be improved) by setting the heating temperature for unburned carbon removal to about 550°C (in other words, the amount of unburned carbon to about 0.3%). Note that since the flow is lower at 600°C or higher than at 550°C, it is thought that it is better not to remove all of the unburned carbon but to leave some.

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

[0077] In the case of the pastes that were not heated or heated to 400°C (high content of unburned carbon) after 1 hour of grinding (Fig. 11A), the viscosity of the pastes that were not heated or heated to 400°C (high content of unburned carbon) became stiff immediately after mixing, making it impossible to measure. In the other pastes (heated to 500 to 700°C), the viscosity tended to decrease as the heating temperature increased.

[0078] After 2 hours of milling (FIG. 11B), the viscosity was generally lower than after 1 hour of milling (FIG. 11A). When not heated or heated to 400°C, the viscosity was high immediately after kneading and reached a hardened state in about 5 minutes. When heated to 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 until about 20 minutes after kneading.

[0079] After 3 hours of grinding (FIG. 11C), the viscosity tended to decrease overall even more compared to after 2 hours of grinding (FIG. 11B).

[0080] In the case of 4 hours of milling treatment (FIG. 11D), a decrease in viscosity was observed when heated to 500° C. or less, but at higher heating temperatures the viscosity change over time was almost the same as in the case of 3 hours of milling treatment (FIG. 11C).

[0081] After 6 hours of grinding (FIG. 11E), the viscosity was higher overall than after 4 hours of grinding (FIG. 11D). In particular, after heating at 600°C, the viscosity was high immediately after kneading, making it difficult to pour the mixture into a mold.

[0082] These results suggest that a grinding time of 6 hours (conventional conditions) is too long, and that a more appropriate time is around 3 hours. It was also confirmed that heating at 500°C or higher (in other words, keeping the unburned carbon content below 1%) significantly extends the time it takes for the paste to harden (improving workability) compared to when no heating is performed.

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

[0084] The compressive strength of the unground specimen was 17 N / mm ２ With heating, the maximum is 10N / mm ２ It remained at that level.

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

[0086] The other coal ashes that had been subjected to the grinding treatment (MC2H to MC4H) all showed almost the same compressive strength. ２ The compressive strength is weak, and as the heating temperature increases, the compressive strength decreases slightly. When the heating temperature exceeds 500°C, the compressive strength decreases sharply, reaching 30 N / mm at 600°C and 700°C. ２ In addition, the compressive strength (20 N / mm) required for use as a construction material is ２ ) has been secured.

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

[0088] In addition, when the value on the vertical axis (shape change rate) of the graph 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 shrunk.

[0089] The figure shows that shrinkage can be suppressed by grinding coal ash heated to 500°C or higher. In particular, coal ash heated to 550°C to 600°C and ground for three hours showed a change in shape from negative (shrinkage) to positive (expansion).

[0090] The above results show that heating coal ash to 500-600°C (in other words, reducing the unburned carbon content to 1%-0.1%) increases the flow immediately after mixing, with the flow reaching its maximum when heated to 550°C. Furthermore, the time until hardening could be extended compared to when not heated, in terms of the change in viscosity over time. Therefore, it was confirmed that workability can be improved by removing the unburned carbon from coal ash.

[0091] It was also confirmed that shrinkage could be suppressed by heating at 500 to 600°C and grinding.

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

[0093] 14 shows the appearance of the prepared specimen. It was black when not heated (no unburned carbon removal treatment), but after heating at 550°C, it changed to a lighter color, and at 600°C, it became almost white. By removing the unburned carbon through heating (unburned carbon removal treatment), the hardened body becomes nearly white, which allows for greater freedom in coloring, etc.

[0094] ===Regarding Other Embodiments=== The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and it goes without saying that the present invention includes equivalents thereof.

[0095] In the above embodiment, a treatment using a planetary ball mill was exemplified as the mechanochemical treatment, but the treatment is not limited to this as long as it can activate the surface of the coal ash.

[0096] In the above embodiment, a potassium hydroxide solution is used as the strong alkaline solution, but this is not limiting and a sodium hydroxide solution in which sodium hydroxide is dissolved in water may also be used. Furthermore, the concentration of the strong alkaline solution is not limited to 3 mol / L.

[0097] Furthermore, with regard 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] In addition, in the process of mixing the coal ash (fly ash) with the silicon mixture (slurry) (step S2), other materials (for example, a water-reducing agent or retarder for adjusting the time until hardening, a shrinkage-reducing agent for preventing cracking, etc.) may be further mixed.

Claims

1. A method for producing a self-hardening material, comprising: a first step of treating fly ash to remove unburned carbon, thereby producing 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 alkaline solution with silicon fine powder to produce a silicon mixture in which silicon components are eluted into the strong alkaline solution; and a fourth step of mixing the surface-activated fly ash that has been treated to remove unburned carbon with the silicon mixture.

2. A method for producing a self-hardening material as described in claim 1, characterized in that in the first step, the content of unburned carbon in the fly ash from which the unburned carbon removal treatment has been performed is set to 1% or less.

3. A method for producing a self-hardening material according to claim 1, characterized in that the unburned carbon removal treatment is a heat treatment for heating the fly ash.

4. A method for producing a self-hardening material according to claim 3, characterized in that the heat treatment is performed in a heating device for one hour or less.

5. A method for producing a self-hardening material according to claim 3, characterized in that the temperature of the heat treatment is 500°C or higher and 600°C or lower.

6. A method for producing a self-hardening material as described in claim 1, characterized in that the ratio of the strong alkaline solution to the binder containing the fly ash from which unburned carbon has been removed and the silicon micropowder is 25% or more and 40% or less.

7. A method for producing a self-hardening material according to claim 6, characterized in that the proportion of the fly ash from which unburned carbon has been removed in the binder is 90% or more.

8. A method for producing a self-hardening material according to claim 1, characterized in that the silicon concentration in the silicon fine powder is 40,000 ppm or more.

9. A method for producing a self-hardening material according to any one of claims 1 to 8, characterized in that the self-hardening material does not contain cement.

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