JP7850400B2 - Method for manufacturing a binder, and method for manufacturing a hydraulic composition - Google Patents

Description

This invention relates to a method for producing a binder and a method for producing a hydraulic composition.

Fly ash, a type of coal ash, is produced in large quantities as waste from thermal power plants, and its utilization has been considered.
Fly ash contains many spherical particles mainly composed of silicon and aluminum, and its surface is covered with a glassy structure. This glassy structure is chemically stable. For this reason, fly ash has been considered difficult to use in its unprocessed state due to its poor chemical reactivity.

In recent years, it has become clear that subjecting fly ash to strong grinding processes allows it to acquire chemical reactivity. One of the acquired reactivity properties is bonding, specifically the polymerization of silicon. Therefore, the application of ground fly ash as a binder in hydraulic compositions such as concrete is being considered (see, for example, Patent Documents 1 and 2).

Japanese Patent Publication No. 2015-218070 Japanese Patent Publication No. 2016-222528

Hydraulic compositions using fly ash that has undergone intense grinding as a binder have been found to have low fluidity. Therefore, such hydraulic compositions have been difficult to use in applications requiring high fluidity.

The present invention aims to provide a method for producing a binder used to manufacture a highly fluid hydraulic composition, and a method for producing a hydraulic composition containing said binder.

To solve the aforementioned problems, the inventors of the present invention investigated the mechanism by which hydraulic compositions harden. Hydraulic compositions harden mainly through the polymerization reaction of silicon in the binder. In this process, it is thought that aluminum in the binder exists by substituting for silicon atoms that have polymerized to form a chain-like structure.
Therefore, the inventors considered that the proportion of aluminum is related to the fluidity of the hydraulic composition and focused on the ratio of silicon to aluminum. As a result, they discovered that by increasing the proportion of aluminum, a binder capable of producing a highly fluid hydraulic composition could be obtained, leading to the completion of the present invention.

To achieve the above objective, one aspect of the present invention is characterized by mechanochemical treatment of a mixture of fly ash and alumina.
To achieve the above objective, another aspect of the present invention is characterized by mechanochemically treating a mixture of fly ash and alumina and adding an alkaline solution containing a silicon source.

Furthermore, in the method for producing the binder of the present invention, the mass ratio of silicon to aluminum in the mixture (silicon/aluminum) is preferably 0.75 to 2.5.
In the method for producing the hydraulic composition of the present invention, it is preferable that the alkaline solution containing the silicon source is a potassium hydroxide solution containing silica fume.

According to the present invention, it is possible to provide a method for producing a binder used to manufacture a highly fluid hydraulic composition, and a method for producing a hydraulic composition containing said binder.

Figure 1A shows the pH measurement results for Examples 1-1 to 1-3 and Comparative Example 1. Figure 1B shows the pH measurement results for Examples 2-1 to 2-4 and Comparative Example 2. Figure 1C shows the pH measurement results for Examples 3-1 to 3-2 and Comparative Example 3. Figure 2A shows the measurement results of the electrical conductivity for Examples 1-1 to 1-3 and Comparative Example 1. Figure 2B shows the measurement results of the electrical conductivity for Examples 2-1 to 2-4 and Comparative Example 2. Figure 2C shows the measurement results of the electrical conductivity for Examples 3-1 to 3-2 and Comparative Example 3. Figure 3A shows the measurement results of the particle size distribution after one hour of mechanochemical treatment for Examples 1-1 to 1-3 and Comparative Example 1. Figure 3B shows the measurement results of the particle size distribution after one hour of mechanochemical treatment for Examples 2-1 to 2-4 and Comparative Example 2. Figure 3C shows the measurement results of the particle size distribution after one hour of mechanochemical treatment in Examples 3-1 to 3-2 and Comparative Example 3. Figure 4A shows the measurement results of the particle size distribution after mechanochemical treatment for Examples 1-1 to 1-3 and Comparative Example 1 for 3 hours. Figure 4B shows the measurement results of the particle size distribution after mechanochemical treatment for Examples 2-1 to 2-4 and Comparative Example 2 for 3 hours. Figure 4C shows the measurement results of the particle size distribution after mechanochemical treatment for Examples 3-1 to 3-2 and Comparative Example 3 for 3 hours. Figure 5A shows the measurement results of the particle size distribution after 6 hours of mechanochemical treatment for Examples 1-1 to 1-3 and Comparative Example 1. Figure 5B shows the measurement results of the particle size distribution after 6 hours of mechanochemical treatment for Examples 2-1 to 2-4 and Comparative Example 2. Figure 5C shows the measurement results of the particle size distribution after 6 hours of mechanochemical treatment in Examples 3-1 to 3-2 and Comparative Example 3.

(Method of manufacturing the binder)
One embodiment of the present invention involves a method for producing a binder, which involves mechanochemical treatment of a mixture. The mixture contains fly ash and alumina, and may further contain other components as needed.

<Mechanochemical Treatment>
Mechanochemical treatment is a process that applies mechanical energy to a substance through impact, compression, grinding, crushing, mixing, etc., to induce mechanochemical phenomena.
Mechanochemical phenomena are those in which the physicochemical and chemical properties of a substance and its surroundings change when mechanical energy is applied to it through processes such as impact, compression, grinding, crushing, or mixing. A substance that has undergone mechanochemical phenomena is also called a substance in a mechanochemical state.

When a material is subjected to impact, it generates mechanical energy that creates a high-energy state in an extremely short time, from that moment to ^10⁻⁷ to ^10⁻⁸ seconds. After that, the energy quickly dissipates. It is believed that a portion of this energy remains as structural irregularities due to inelastic deformation and accumulates within the material, changing its physical properties, which is then observed as a mechanochemical phenomenon.

Mechanical energy generated by grinding or other processes breaks the bonds between molecules within a material. The resulting new surface contains tangling bonds—bonds that have lost their coupling. These tangling bonds are in an unstable and active state, searching for bonding partners. The new surface can attract and aggregate other particles, adsorb, or directly react with other substances. This type of effect is called a mechanochemical effect. Mechanochemical effects are particularly known to occur during the grinding and grinding of fine powders.

There are no particular restrictions on the method of applying mechanical energy; it can be appropriately selected depending on the purpose. Examples include impact treatment using a ball mill and grinding treatment.
There are no particular restrictions on the shape of the ball mill, and it can be selected as appropriate depending on the purpose, but a planetary type is preferred because it allows for efficient mechanochemical processing. This is because using a planetary ball mill results in a grinding process that breaks up the nearly spherical fly ash.

There are no particular restrictions on the size of the ball mill; it can be selected appropriately according to the purpose.
There are no particular restrictions on the material of the ball mill; it can be appropriately selected according to the purpose, for example, iron, zirconia, etc.

There are no particular restrictions on conditions such as rotational speed during the grinding process; they can be appropriately selected according to the purpose.

<<Fly Ash>>
Fly ash is essentially coal ash, an industrial waste generated at coal-fired power plants.
Fly ash contains a large amount of silica ( _SiO₂ ) and _alumina ( _Al₂O₃ ), as well as iron oxide, magnesium oxide, and calcium oxide.
According to JIS standards, there are four types of fly ash (Type I to Type IV). In this invention, any of these types can be used.

<<Alumina>>
Alumina is included to improve the fluidity of the hydraulic composition described later.
There are no particular restrictions on the shape and size of the alumina; they can be selected as appropriate depending on the purpose.

- Mass ratio (silicon/aluminum) -
The mass ratio of silicon to aluminum in the mixture (silicon/aluminum) is preferably 0.75 to 2.5, and more preferably 0.75 to 1.5, from the viewpoint of the fluidity of the hydraulic composition.

<<Other ingredients>>
Other components are not particularly limited as long as they do not inhibit the effects of the present invention, and can be appropriately selected depending on the purpose.

(Method for producing hydraulic compositions)
Another aspect of the present invention involves adding an alkaline solution containing a silicon source to the binder described above in order to produce a hydraulic composition.

<Alkaline solution containing silicon source>
The alkaline solution containing the silicon source plays a role in adding silicon to the hydraulic composition and in acting as mixing water when preparing the hydraulic composition.
Hydraulic compositions harden through the polymerization reaction of silicon. Therefore, if the silicon content is insufficient, the hardening reaction may not occur adequately. To prevent this, an alkaline solution containing a silicon source is used as the mixing water, rather than just water alone.

<<Silicon Source>>
There are no particular restrictions on the silicon source, and it can be appropriately selected depending on the purpose. Examples include sodium silicate and silica fume. In the alkaline solution containing the silicon source, the silicon may be completely dissolved or may remain as a slurry.

<<Alkaline solution>>
The solute in the alkaline solution is not particularly limited as long as it exhibits basic properties and can be appropriately selected according to the purpose. Examples include sodium hydroxide and potassium hydroxide.
There are no particular restrictions on the solvent, and it can be selected as appropriate depending on the purpose, but water is one example.
There are no particular restrictions on the concentration of the alkaline solution; it can be selected appropriately depending on the purpose.

The following describes examples of the disclosed technology, but the disclosed technology is not limited to these examples.

Table 1 shows the results of X-ray fluorescence analysis of the coal ash (fly ash) used as a raw material in the examples.

(Examples 1-1 to 3-2, Comparative Examples 1 to 3)
Each type of coal ash was mixed with alumina (Fujifilm Wako Pure Chemical Industries, Ltd.) in the amounts shown in Table 2. The mixture was ground using a planetary ball mill (P-5, manufactured by Fritsch Japan Co., Ltd.) to obtain a binder. The grinding time was 1 hour, 3 hours, and 6 hours.

The binders from Examples 1-1 to 3-2 and Comparative Examples 1 to 3 were mixed with deionized water in a solid-liquid ratio of 1:5. After decantation, the water was separated. The pH and electrical conductivity of the separated water were measured. pH and electrical conductivity (EC) were measured using a pH meter (product name: HM-20J, manufactured by Toa DKK Co., Ltd.). Electrical conductivity is considered an indicator of whether a mechanochemical state has been reached. A mechanochemical state can be determined if the electrical conductivity is 40 mS/m or less. The pH measurement results are shown in Table 3 and Figures 1A to 1C, and the electrical conductivity measurement results (mS/m) are shown in Table 4 and Figures 2A to 2C.

pH measurement results clearly showed that grinding lowers the pH.
Furthermore, electrical conductivity measurements revealed that the mixture enters a mechanochemical state after six hours of grinding. Therefore, the grinding treatment applied to the mixture is a mechanochemical treatment.
Furthermore, in Figure 2B, after 3 hours of mechanochemical treatment, the mechanochemical state was not reached when the Si/Al ratio was 2.6 (Comparative Example 2: no alumina added), whereas the mechanochemical state was reached when the Si/Al ratio was 2.5 or less. From these results, it is clear that the mechanochemical state is reached more quickly when the Si/Al ratio is 2.5 or less.

Furthermore, the particle size distribution of the binder was measured using a particle size analyzer (Microtrac MT3000EX II, manufactured by Microtrac-Bell Co., Ltd.). Figures 3A-C show the particle size distribution after 1 hour of mechanochemical treatment, Figures 4A-C show the results after 3 hours of mechanochemical treatment, and Figures 5A-C show the results after 6 hours of mechanochemical treatment.

Comparing Comparative Examples 1-3 in Figures 3A-C with Comparative Examples 1-3 in Figures 5A-C, Comparative Examples 1-3 in Figures 5A-C show a generally smoother particle size distribution (broader particle size curve) than Comparative Examples 1-3 in Figures 3A-C, where grinding has barely progressed. This is likely because some particles became aggregated as grinding progressed. Therefore, it can be said that as grinding progresses and particles become mechanochemically processed, the particle size distribution curve becomes broader.

Next, in Figure 3A, the particle size distribution peaks are broader in Examples 1-1 to 1-3 than in Comparative Example 1. In Figure 4A, the particle size distribution peaks are broader in Examples 1-1 to 1-3 than in Comparative Example 1. In Figure 5, the particle size distribution peaks for the Comparative Example and Examples 1-1 to 1-3 are broad and double. This trend was similar in Figures 3B to 5B and 3C to 5C. From these findings, it became clear, even from the perspective of particle size distribution, that a smaller Si/Al value (higher Al content) leads to reaching the mechanochemical state more quickly.

<Preparation of hydraulic compositions>
Hydraulic compositions (pastes) were prepared using the binders of Examples 1-1 to 3-2 and Comparative Examples 1 to 3. As the alkaline solution containing the silicon source, a KOH solution in which silica fume was partially dissolved (KOH concentration: 3 mol/L, Si concentration: 40,000 ppm, manufactured by Fujimi Incorporated Co., Ltd.) was used.
The ratio (W/B) of the alkaline solution containing the silicon source to the binder was set to 32.5%.
Each binder and an alkaline solution containing a silicon source were kneaded for 120 seconds to form a paste, thereby obtaining a hydraulic composition.

<Flow>
The flow of the obtained hydraulic composition was measured immediately after mixing. The hydraulic composition was poured into an acrylic cylindrical container (mold used: inner diameter 28 mm, height 22 mm) placed on a stainless steel plate until the liquid level reached the top of the container. Immediately after pouring, the cylindrical container was gently lifted upwards and removed. The spread length of the paste on the stainless steel plate was measured at two points: the maximum length and the minimum length. The average of these lengths was calculated and used as the flow measurement result. The flow measurement results are shown in Table 5. The units of the values in the table are mm. If there is no data in Table 5, it indicates that the viscosity of the hydraulic composition was too high and measurement was not possible because it could not be demolded from the container.

The results from the examples and comparative examples clearly showed that the flow rate increased with increasing aluminum content, i.e., with decreasing Si/Al ratio. In particular, the increase in flow rate was significant when the grinding treatment time was 3 hours or longer. These results suggest that the manufacturing method of the present invention can improve the fluidity of hydraulic compositions and reduce the amount of water-reducing agent used.

Claims (3)

A method for producing a binder, characterized by mechanochemical treatment of a mixture of fly ash and alumina ,
A method for producing a binder, wherein the mass ratio of silicon to aluminum (silicon/aluminum) in the mixture is 0.75 to 1.00 . A method for producing a hydraulic composition, characterized by mechanochemically treating a mixture of fly ash and alumina and adding an alkaline solution containing a silicon source,
A method for producing a hydraulic composition in which the mass ratio of silicon to aluminum (silicon/aluminum) in the mixture is 0.75 to 1.00 . The method for producing a hydraulic composition according to claim 2, wherein the alkaline solution containing the silicon source is a potassium hydroxide solution containing silica fume.