Aggregate manufacturing method

Abstract

This invention provides a method for manufacturing aggregates that increases their strength and is suitable for mass production. A method for manufacturing aggregate, comprising: a mixing step of mixing at least an alkali metal compound (K) with natural silica sand (SA) with a high silica content collected from a desert; a silica sand hardened body production step of placing the mixture (α1) obtained in the mixing step (S1) into a container (22), heating the entire container (22) to bind the natural silica sand and produce a silica sand hardened body (α2); a raw aggregate production step of crushing the silica sand hardened body to produce raw aggregate (α3) with uneven particle size; and a separation step (S4) of separating the raw aggregate according to particle size.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing aggregates.

Background Art

[0002] Generally, aggregates used for asphalt aggregates, concrete aggregates, roadbeds, subgrade materials, etc. are classified into coarse aggregates, medium aggregates, and fine aggregates according to the size of the particle diameter. Aggregates include natural sands and gravels existing in rivers, mountains, land, seas, etc., and artificial aggregates include blast furnace slag aggregates, artificial lightweight aggregates, recycled aggregates, etc.

[0003] Patent Document 1 discloses a technique for obtaining a cured body in which silicate-containing substances are directly joined by subjecting silicate-containing substances represented by sands and gravels to high-temperature treatment in an alcohol compound and an alkali metal compound or an alkaline earth metal compound.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a technique for joining silicate-containing substances to obtain a cured body by subjecting silicate-containing substances such as sands and gravels to high-temperature treatment, but does not disclose a technique for applying this cured body to aggregates such as coarse aggregates, medium aggregates, and fine aggregates. Moreover, when applying the technique of Patent Document 1 to the production of aggregates such as coarse aggregates, medium aggregates, and fine aggregates, there is a risk that the strength of the aggregates will be inferior. The present application aims to achieve the provision of a method for manufacturing aggregates that increases the strength of the aggregates and is suitable for mass production of the aggregates in order to solve the above problems. And, by extension, it contributes to supporting good connections between urban areas and local areas including the urban periphery. [Means for solving the problem]

[0006] One aspect of the present invention comprises a mixing step of mixing at least an alkali metal compound with natural silica sand with a high silica content collected from a desert; a silica sand hardened body production step of placing the mixture obtained in the mixing step into a container, heating the entire container, and bonding the natural silica sand to produce a silica sand hardened body; a raw aggregate production step of crushing the silica sand hardened body to produce raw aggregate with uneven particle size; and a separation step of separating the raw aggregate according to particle size. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for manufacturing aggregates that increases the strength of the aggregates and is suitable for mass production of aggregates. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing a silica sand hardening apparatus. [Figure 2] Figure 2 shows a crusher machine. [Figure 3] Figure 3 shows a crushing machine. [Figure 4] Figure 4 shows a sorting machine. [Figure 5] Figure 5 is a flowchart showing the method for manufacturing aggregate in Embodiment 1. [Figure 6] Figure 6 illustrates the reaction that leads to the formation of a hardened silica sand body. [Figure 7] Figure 7 illustrates the reaction that leads to the formation of a hardened silica sand body. [Figure 8] Figure 8 illustrates how silicic acid bonds. [Figure 9] Figure 9 shows a graph of the compressive strength of a hardened silica sand body. [Figure 10] Figure 10 shows a graph of the compressive strength of a hardened silica sand body. [Figure 11] Figure 11 shows an overview of the configuration used in the production of aggregate in Embodiment 2. [Figure 12] FIG. 12 is a flowchart showing a method for manufacturing an aggregate in Embodiment 2. [Figure 13] FIG. 13 is a diagram showing an outline of a configuration used for manufacturing an aggregate in Embodiment 3. [Figure 14] FIG. 14 is a flowchart showing a method for manufacturing an aggregate in Embodiment 3.

BEST MODE FOR CARRYING OUT THE INVENTION

[0009] (Embodiment 1) [1-1. Configuration] As shown in FIG. 1, the aggregate manufacturing apparatus of the present Embodiment 1 has a silica sand hardened body generator 2. The silica sand hardened body generator 2 mixes at least an alkali metal compound K and natural silica sand SA having a high silica content collected from the desert, heats the obtained mixture α1 as a whole, and bonds the natural silica sand SA to generate a silica sand hardened body.

[0010] Also, as shown in FIG. 2, the aggregate manufacturing apparatus has a crusher 34. The crusher 34 crushes the silica sand hardened body α2 generated by the silica sand hardened body generator 2 to generate raw aggregates α3 with uneven particle sizes. When generating raw aggregates α3 with uneven particle sizes, as shown in FIG. 3, a jaw crusher 31 may be used. The crusher 34 or the jaw crusher 31 constitutes a "raw aggregate generator".

[0011] As shown in FIG. 4, the aggregate manufacturing apparatus has a classifier 41. The classifier 41 includes three sieves 42A, 42B, and 42C having different meshes. The sieves 42A, 42B, and 42C classify the raw aggregates α3 by particle size.

[0012] [1-1-1. Configuration of Silica Sand Hardened Body Generator] FIG. 1 is a schematic diagram showing the silica sand hardened body generator 2. The silica sand hardened body generator 2 is a box-shaped thermostat. The silica sand hardened body generating device 2 houses a container 22. The silica sand hardened body generating device 2 is a tank-shaped heating device that heats the entire container 22. The silica sand hardened body generating device 2 is a constant temperature bath equipped with a heater (not shown) inside the main body wall surface and having the function of maintaining a constant temperature. The silica sand hardened body generating device 2 can at least adjust the temperature inside the silica sand hardened body generating device 2 within the range from normal temperature to 300 degrees Celsius. The silica sand hardened body generating device 2 may further be capable of heating at 300 degrees Celsius or higher. The silica sand hardened body generating device 2 may have the function of adjusting the pressure inside the silica sand hardened body generating device 2.

[0013] The container 22 includes an outer tank 23 with a lid and an inner tank 24.

[0014] The outer tank 23 is a so-called autoclave. The outer tank 23 is made of stainless steel, which is excellent in heat resistance and pressure resistance.

[0015] The inner tank 24 is an inner tank made of Teflon (registered trademark), which is excellent in chemical stability. A raw material container 25 is housed in the inner tank 24.

[0016] The raw material container 25 is made of, for example, a copper thin film or a stainless steel thin film. The raw material container 25 houses raw materials. The raw materials are natural silica sand and an alkali metal compound. Furthermore, the raw materials in Embodiment 1 include a solution of an alkali metal compound. The raw materials will be described in detail later.

[0017] The natural silica sand is a raw material with a high content of silicon dioxide (SiO2) collected from a desert. The natural silica sand is silica sand with a particle size of 250 μm or less. The larger the silicon dioxide content, the higher the quality of the aggregate produced.

[0018] The natural silica sand as a raw material is collected particularly from deserts in Kenya, Namibia, the Republic of South Africa, and the United Arab Emirates. Examples of deserts in Kenya include the Chalbi Desert and the Nili Desert. Examples of deserts in Namibia include the Namib Desert. Examples of deserts in South Africa include the Kalahari Desert. Examples of deserts in the United Arab Emirates include those in Dubai, Abu Dhabi, and Sharjah.

[0019] The natural silica sand obtained from these deserts is particularly suitable because it has a higher silica content compared to, for example, the natural silica sand from Japanese deserts.

[0020] The alkali metal compound is potassium hydroxide (KOH). Alkali metal compounds may also include alkaline earth metal compounds, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, cesium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, sodium fluoride, potassium fluoride, and cesium fluoride. Furthermore, alkali metal compounds and alkaline earth metal compounds may be used in combination of two or more types, rather than just one.

[0021] The solution is an alcohol compound. Examples of alcohol compounds include methanol or ethanol.

[0022] [1-1-2. Configuration of the raw aggregate generation device]

[0023] Figure 2 shows the crusher machine 34. The crusher machine 34 is a rotating device for crushing the silica sand hardened body α2. The crusher machine 34 is equipped with one or more rotating blades 35. The crusher machine 34 may be a single-shaft crusher equipped with one rotating blade and a fixed blade, or a twin-shaft crusher equipped with two rotating blades.

[0024] The crusher machine 34 crushes the silica sand hardened material α2 fed into the hopper with multiple rotating blades 35 to produce raw aggregate α3 with uneven particle sizes. The crusher machine 34 is particularly good at producing raw aggregate α3 that contains aggregates with small particle sizes.

[0025] When producing irregularly shaped raw aggregate α3, instead of the crusher machine 34, a threshing machine 31 may be used as an alternative, as shown in Figure 3. The threshing machine 31 comprises a vertically moving rammer 32 and a container stand 33.

[0026] The rammer 32 has a predetermined weight and, by dropping it from a predetermined height, strikes the container stand 33 and crushes the silica sand hardened material α2. The force striking the container stand 33 can be adjusted by adjusting the weight of the rammer 32 and the height from which it is dropped.

[0027] The container stand 33 holds the hardened silica sand α2. The hardened silica sand α2 contained in the container stand 33 is crushed by the rammer 32. The crushing machine 31 is particularly good at producing raw aggregate α3 containing aggregates with large particle sizes.

[0028] The crusher 34 described above is a more suitable crushing device than the mortar 31 when it is desired to adjust the particle size of the raw aggregate α3. The hardened silica sand α2 crushed by the mortar 31 may be further crushed by the crusher 34 to obtain the raw aggregate α3. In this way, the hardened silica sand α2 is crushed by the mortar 31 or the crusher 34, resulting in the production of raw aggregate α3 with uneven particle sizes.

[0029] [1-1-3. Configuration of the sorting machine] Figure 4 shows the sorting machine 41. As shown in Figure 4, the separator 41 is a so-called vibrating sieve. The separator 4 is equipped with three sieves 42A, 42B, and 42C, each having a predetermined mesh size that is different from the others. When crushed silica sand hardened material, i.e., raw aggregate, is introduced into the separator 41, the raw aggregate is separated by particle size by the three sieves 42A, 42B, and 42C.

[0030] The raw aggregate is separated into coarse aggregate with a particle size of 4.75 mm to 13.2 mm using sieve 42A, into medium aggregate with a particle size of 2.36 mm to 4.75 mm using sieve 42B, and into fine aggregate with a particle size of less than 2.36 mm using sieve 42C. The coarse aggregate can also be called No. 6 crushed stone. The medium aggregate can also be called No. 7 crushed stone. The fine aggregate can also be called coarse sand.

[0031] [1-2. Method for manufacturing aggregates] Figure 5 is a flowchart showing the method for manufacturing aggregate in Embodiment 1.

[0032] First, natural silica sand and alkali metal compounds are mixed (mixing step S1).

[0033] In mixing step S1, as shown in Figure 1, natural silica sand SA is immersed in a solution of alkali metal compound K in a raw material container 25. The mixture α1 of natural silica sand SA and alkali metal compound K is mixed in the raw material container 25. The particle size of natural silica sand is preferably less than 250 μm. In particular, it has been found that the particle size of natural silica sand collected from deserts in Kenya, Namibia, South Africa, and the United Arab Emirates is almost always less than 250 μm.

[0034] Regarding the alkali metal compound solution, the alkali metal compound or alkaline earth metal compound is present in an amount of 1 to 20 parts by weight, more preferably 13 to 20 parts by weight, per 100 parts by weight of natural silica sand.

[0035] If the solution is an alcohol compound, the concentration of natural silica sand should be between 1 and 50 parts by weight per 100 parts by weight of the alcohol compound. Furthermore, a concentration of 90% or higher is preferable, and 100% is even more preferable.

[0036] Next, a mixture α1 of natural silica sand SA and alkali metal compound K is heated to bond the natural silica sand SA and produce a hardened silica sand body α2 (hardened silica sand body production step S2).

[0037] In the silica sand hardened body formation process S2, the mixture α1, along with the container 22, is heated by a heater (not shown) to bind the natural silica sand SA. The container 22 is heated when it is placed in the silica sand hardened body formation apparatus 2.

[0038] Figures 6 and 7 illustrate the formation reaction of silica sand hardened material α2. In each figure, the horizontal axis represents time [hour], and the vertical axis represents temperature [°C] and pressure [MPa]. Temperature changes are shown by dashed lines, and pressure changes are shown by solid lines. Furthermore, Figures 6 and 7 show the chemical reactions that occur within the period indicated by the double-headed arrows in the figures. In the examples shown in Figures 6 and 7, the natural silica sand SA is natural silica sand obtained from the Nili Desert with a silica content of 98.90%. The alkali metal compound is KOH, and the KOH concentration of the ethanol solution is 50 wt%. In this embodiment, the KOH concentration is a weight percentage [wt%] relative to ethanol.

[0039] Figure 6 shows the reaction when mixture α1 is heated to 150 degrees Celsius by a heater (not shown) in the silica sand hardening apparatus 2. When the mixture is heated to 150 degrees Celsius, the chemical reaction shown in the following reaction equation (1) occurs.

[0040] 2KOH + C2H5OH → K2CO3 + H2O…(1)

[0041] Reaction equation (1) shows the reaction in which potassium hydroxide and ethanol react to produce potassium carbonate and water. In this way, if the heating temperature of the silica sand hardening device 2 is not sufficiently high, the ethanol itself will react with potassium hydroxide. Therefore, since ethanol is consumed, the pressure will not rise.

[0042] Furthermore, when the mixture is released to the atmosphere after heating, the chemical reaction shown in the following reaction equation (2) occurs.

[0043] K2CO3 + H2O → 2K + +CO3 2- +H2O…(2)

[0044] The formation of potassium carbonate in reaction equation (1) is confirmed by the occurrence of deliquescence as shown in reaction equation (2).

[0045] Thus, if the heating temperature of the silica sand hardening apparatus 2 is not sufficiently high, the SiO2 will not react sufficiently, and the potassium carbonate will deliquesce, resulting in a silica sand hardening body with sufficient strength.

[0046] Figure 7 shows the reaction when mixture α1 is heated at 250 degrees Celsius using the silica sand hardening apparatus 2.

[0047] When mixture α1 is heated to 250 degrees Celsius, the chemical reactions shown in the following reaction equations (3) and (4) occur.

[0048] 2KOH + SiO2 → K2SiO3 + H2O…(3) C2H5OH → C2H4 + H2O…(4) In reaction equation (3), potassium hydroxide and silicic acid react to produce potassium silicate and water.

[0049] If the heating temperature is sufficiently high, ethanol is not consumed in reaction equation (3). Therefore, the pressure increases according to the vapor pressure of ethanol. If the temperature exceeds a certain level during the process, ethanol undergoes a dehydration reaction as thermal decomposition shown in reaction equation (4). This causes ethanol to decompose into ethylene and water. When the decomposition reaction of ethanol occurs, the pressure drops according to the vapor pressure of ethylene and water.

[0050] The inventors have found that pressure changes caused by ethanol appear similarly in blank tests. A blank test is a test in which heating is performed in the silica sand hardening apparatus 2 using only ethanol instead of mixture α1. Furthermore, the inventors have found that ethylene can be detected in container 22 after the silica sand hardening process S2 by gas chromatography analysis.

[0051] Figure 8 illustrates how silicic acid bonds. Figure 8(A) shows an electron microscope image of the silica sand hardened material α2. As shown in Figure 8(A), K2SiO3 is observed to be generated around SiO2 and to bond with SiO2. Figure 8(B) is a schematic diagram showing the state of the hardened silica sand body α2 in the initial stages of the reaction. Figure 8(C) is a schematic diagram showing the state of the hardened silica sand body α2 in the later stages of the reaction. The potassium silicate is generated in each grain of natural silica sand, causing the natural silica sand to bond together. As the heating time progresses, the potassium silicate grows. The voids in the hardened silica sand α2 that were present in the initial stages of the reaction are filled, improving the strength of the hardened silica sand α2 in the later stages of the reaction. The mixture α1 is heated for a predetermined time or longer until the porosity of the hardened silica sand falls below a predetermined value. The predetermined value is, for example, 15%. The predetermined time is, for example, 5 hours. Potassium silicate is an example of an alkali silicate.

[0052] Thus, if the heating temperature of the silica sand hardened body generating apparatus 2 is sufficiently high, a silica sand hardened body α2 with high strength can be obtained in the later stages of the reaction. Furthermore, the heating temperature in the silica sand hardened body formation step S2 is preferably between 200 and 240 degrees Celsius. This is because, in this temperature range, reaction equation (3) proceeds, allowing potassium silicate to grow easily and silicic acid molecules to bond with each other. This is because, above 240 degrees Celsius, the power consumption during heating increases significantly, so a temperature of 240 degrees Celsius or lower is preferable. Below 200 degrees Celsius, potassium carbonate grows according to the reaction equation (1) described above, weakening the bonds between silicic acid molecules. Furthermore, the heating temperature in the silica sand hardened body formation process S2 can be appropriately changed within the temperature range of 200 degrees Celsius to 1400 degrees Celsius. This is because if the temperature exceeds 1400 degrees Celsius, the silicic acid may melt, and reaction equation (3) may not proceed.

[0053] From the above, it is clear that ethanol does not directly participate in the chemical reaction between SiO2 and KOH. Therefore, the solution of the alkali metal compound or alkaline earth metal compound can be changed as appropriate, and is not limited to alcohol compounds.

[0054] In the silica sand hardened body production process S2, the mixture α1 is placed in the raw material container 25, and the entire container 22 containing the raw material container 25 is heated. Since the raw material container 25 is placed on the inner bottom of container 22, as in Patent Document 1, the bottom of container 22 can be partially heated under fixed high-pressure conditions. However, in this case, an equilibrium reaction occurs in which the alcohol compound dehydrates the silicic acid, producing tetraalkoxysilane, which is an organosilicon compound. When the bottom of container 22 is partially heated, the entire mixture α1 is not heated by the atmosphere, so the temperature of mixture α1 does not rise sufficiently, making it easy for tetraalkoxylane to be produced. Also, in this case, although the SiO2 molecules are directly bonded to each other due to repeated breaking and regeneration of the chemical bonds of SiO2, the bond strength of SiO2 is weak, and the strength of the hardened silica sand is weak.

[0055] Unlike the case where the container 22 is partially heated under fixed high-pressure conditions, in this embodiment, the entire container 22 is heated by the silica sand hardened material generating device 2. Therefore, the temperature inside the container 22 is raised more appropriately than in the case of partial heating, and the silica is bonded together by potassium silicate. As a result, a high-strength silica sand hardened material α2 is obtained, and consequently, a high-strength aggregate α4 is obtained.

[0056] Here, we performed a process to obtain a hardened silica sand body under two conditions: partially heating the bottom of the container 22 and heating the entire container 22. The compressive strength [MPa] of the hardened silica sand body was then evaluated. Figure 9 shows a graph of the compressive strength of a hardened silica sand body. The vertical axis of the graph in Figure 9 represents compressive strength.

[0057] Comparative Example 1 is a structural concrete corresponding to the conventional material. The compressive strength of the conventional material in Comparative Example 1 is 18 MPa. The compressive strength of the conventional material in Comparative Example 1 is the literature value in "JASS 5 Reinforced Concrete Works" in the Architectural Institute of Japan's Standard Specifications for Building Construction, and corresponds to the design standard strength (short term) of structural concrete. Comparative Examples 2 to 5 are silica sand hardened bodies obtained by partially heating the container 22 with the mixture α obtained in the mixing step S1.

[0058] In Comparative Example 2, the concentration of the KOH ethanol solution is 7.5 wt%. In Comparative Example 3, the concentration of the KOH ethanol solution is 12.5 wt%. In Comparative Example 4, the concentration of the KOH ethanol solution is 25 wt%. In Comparative Example 5, the concentration of the KOH ethanol solution is 50 wt%.

[0059] Examples 1 and 2 are silica sand hardened bodies obtained in the mixing step S1 and the silica sand hardened body production step S2. In other words, Examples 1 and 2 are silica sand hardened bodies obtained by heating the entire container 22.

[0060] Furthermore, the silica content of the natural silica sand used in Comparative Examples 2 to 5 was 84.70%. The silica content of the natural silica sand used in Examples 1 and 2 was 98.90%. The weight of the natural silica sand used in Comparative Examples 2 to 5, and in Examples 1 and 2, was 15g.

[0061] The compressive strength of all samples except Comparative Example 1 was evaluated using a Shimadzu universal testing machine (UH-1000kN) with a loading speed of 0.6kN / min and a silica sand hardened specimen size of 20φ × 200mm.

[0062] The compressive strength of Comparative Example 2 was 1.9 MPa, the compressive strength of Comparative Example 3 was 3.8 MPa, the compressive strength of Comparative Example 4 was 6.4 MPa, and the compressive strength of Comparative Example 5 was 8.2 MPa. Thus, Comparative Examples 2 through 5 had lower compressive strengths than the design standard strength of the structural concrete in Comparative Example 1, indicating that the strength of the silica sand hardened body was inferior.

[0063] On the other hand, the compressive strength of Example 1 was 14.2 MPa, and the compressive strength of Example 2 was 47 MPa. The compressive strength of Example 1 is lower than that of the conventional material, but higher than that of Comparative Examples 2 to 5. The compressive strength of Example 2 is higher than that of Comparative Examples 1 to 5, and also higher than that of Example 2.

[0064] In this way, by heating the entire container 22, a hardened silica sand body with high strength can be obtained. Furthermore, the silica content of natural silica sand is preferably 80% or more, and more preferably 85% or more. More preferably, the silica content of natural silica sand is 90% or more.

[0065] If the silica content is less than 85%, the potassium silicate shown in reaction equation (3) will not grow sufficiently, or the silicate molecules will not bond sufficiently with the grown potassium silicate, making the material unsuitable. In particular, this case is considered to correspond to the hardened silica sand materials of Comparative Examples 2 to 5.

[0066] The higher the silica content, the stronger the bonds between silica particles due to potassium silicate, resulting in improved strength of the resulting aggregate.

[0067] Here, the weight and KOH concentration of the KOH ethanol solution were varied, and the container 22 was heated to 240 degrees Celsius to obtain a hardened silica sand body. The compressive strength [MPa] of the hardened silica sand body was then evaluated. Figure 10 is a graph showing the relationship between the weight of a KOH ethanol solution and its compressive strength.

[0068] The silica sand hardened body of Example 3 had a KOH ethanol solution weighing 5.5 g and a KOH concentration of 25 wt%. The silica sand hardened body of Example 4 had a KOH ethanol solution weighing 8.5 g and a KOH concentration of 25 wt%. The silica sand hardened body of Example 5 had a KOH ethanol solution weighing 11 g and a KOH concentration of 25 wt%.

[0069] The silica sand hardened body of Example 6 had a KOH ethanol solution weighing 5.5 g and a KOH concentration of 50 wt%. The silica sand hardened body of Example 7 had a KOH ethanol solution weighing 8.5 g and a KOH concentration of 50 wt%. The silica sand hardened body of Example 8 had a KOH ethanol solution weighing 11 g and a KOH concentration of 50 wt%.

[0070] The compressive strength of Example 3 was 6.3 MPa, the compressive strength of Example 4 was 6.2 MPa, and the compressive strength of Example 5 was 14.2 MPa. The compressive strength of Example 6 was 13.4 MPa, the compressive strength of Example 7 was 14.2 MPa, and the compressive strength of Example 8 was 47.0 MPa.

[0071] From the above, it can be concluded that the higher the KOH concentration in the ethanol solution, the greater the compressive strength of the hardened silica sand. Also, the greater the weight of the KOH in the ethanol solution, the greater the compressive strength of the hardened silica sand.

[0072] Therefore, from the above, it can be concluded that if the amount of KOH is large and the container 22 is heated as a whole, the strength of the resulting silica sand hardened body will improve, and consequently the strength of the aggregate will improve.

[0073] Next, the obtained silica sand hardened body α2 is crushed to obtain raw aggregate α3 (see Figure 2) (raw aggregate production process S3).

[0074] In the raw aggregate generation process S3, the silica sand hardened body α2 is crushed by the crusher machine 34 or crusher machine 31 described above, and raw aggregate α3 with uneven particle size is generated.

[0075] Next, the obtained raw aggregate α3 is separated to obtain aggregate α4 (see Figure 4) (separation step S4).

[0076] The raw aggregate is separated by the sorting machine 41 into the coarse aggregate α4A, medium aggregate α4B, and fine aggregate α4C as aggregate α4.

[0077] Any aggregate α4 that is not properly separated can be collected, finely crushed, and used again as a raw material to produce hardened silica sand.

[0078] By using the aggregate manufacturing method described above, high-quality aggregate α4 can be obtained by using natural silica sand SA, which has a high silica content and is obtained from deserts, as a raw material. The asphalt pavement using aggregate α4 obtained under the superheating conditions shown in Figure 7 has a Marshall stability of 7.9 kN, a flow value of 2.6 mm, and a DS (dynamic stability) value of 1968 cycles / mm.

[0079] In Japan, the standard values ​​for Marshall stability are 4.9 kN or higher, the flow value is 2.0 to 4.0 mm, and the actual DS value is 800 to 1000 cycles / mm. Asphalt pavements using this aggregate all exceed the standard or actual values ​​for Marshall stability, flow value, and DS value, indicating that the quality of this aggregate α4 is high.

[0080] While natural silica sand SA obtained from deserts has a nearly spherical shape, the aggregate obtained by this disclosure has more angular and irregular shapes compared to natural silica sand SA, making it suitable for actual use in asphalt paving. Furthermore, the aggregate manufacturing method of this disclosure allows for the adjustment of the aggregate's shape and particle size, making it possible to comprehensively manufacture the types of aggregate particle sizes required for aggregate α4 as a product.

[0081] (Embodiment 2) [2-1. Structure] Figure 11 shows an overview of the configuration used in the production of aggregate in Embodiment 2.

[0082] Figure 11(A) is a schematic diagram showing the mixing machine 61. The kneading machine 61 comprises a mixing tank 62 and a kneading section 63 for kneading the inside of the mixing tank 62. Alkali metal compound K and natural silica sand SA are added to the mixing tank 62. The mixing unit 63 is equipped with stirring blades 64 and mixes the contents of the mixing tank 62. The mixing unit 63 may also be an air pump. Liquid does not necessarily have to be introduced into the mixing tank 62.

[0083] Figure 11(B) is a schematic diagram showing the formwork 101. The compound β1 obtained from the mixing machine 61 is poured into the mold 101. Compound β1 is an example of a mixture.

[0084] The formwork 101 is a box-shaped member with an open top. The formwork 101 has multiple projections 103 that taper upwards from the bottom 102. When the formwork 101 is viewed from above, the projections 103 are arranged in a grid pattern. The projections 103 can also be described as comb-shaped partitions.

[0085] The height of the tip of the projection 103 is formed lower than the upper end of the side wall 104 of the formwork 101.

[0086] The shape of the poured mixture β1 can be changed by altering the shape of the protrusions 103 and the spacing between them. The mold 101 is, for example, 3m square and 0.5m high.

[0087] Figure 11(C) is a schematic diagram showing the press device 71. The press device 71 forms a strip-shaped molded body β2 by pressing the mold 101 and the kneaded material β1 inside the mold 101. The press device 71 presses, for example, at 3 MPa for 10 seconds. The pressing conditions of the press device 71 are set so that the strip-shaped molded body β2 hardens to the extent that it can be removed from the mold 101.

[0088] Since the tip of the projection 103 is formed lower than the upper end of the side wall 104, the press device 71 does not touch the tip of the projection 103. As a result, the strip-shaped molded body β2 pressed by the press device 71 can be formed into a single strip-shaped mass.

[0089] Figure 11(D) is a schematic diagram showing the heating furnace 81. The heating furnace 81 is a continuous furnace comprising a conveyor section 82 and a heating section 83.

[0090] The heating furnace 81 heats the strip-shaped molded body β2. Heating in the heating furnace 81 generates the silica sand hardened body β3. The heating furnace 81 is, for example, an electric furnace. The heating conditions are, for example, a temperature of 200 degrees Celsius, a heating time of 2.8 hours, and a heating path of 35 meters. The heating conditions can be changed as appropriate.

[0091] The hardened silica sand body β3 obtained by heating in the heating furnace 81 takes on a shape that conforms to the formwork 101.

[0092] Figure 11(E) is a schematic diagram showing the rotary drum 91. The rotary drum 91 is an example of a sorting and crushing machine.

[0093] The silica sand hardened body β3 has a notch C1 formed in it, corresponding to the shape of the projection 103 of the formwork 101. The innermost part of the notch C1 corresponds to the tip of the projection 103 of the formwork 101. At this point, the silica sand hardened body β3 is thinner and easily crushed. The silica sand hardened body β3 is crushed by being agitated by the rotation of the rotary drum 91, resulting in raw aggregate with uneven particle size.

[0094] Figure 11(F) is a view of the rotary drum 91 from the axial direction. The rotary drum 91 is equipped with three drum screens 92. The mesh size of the drum screens 92A, 92B, and 92C decreases as you move radially outward. Figure 11(G)(H)(I) is a schematic diagram showing the aggregates to be separated. The innermost drum screen 92A separates the coarse aggregate β4A shown in Figure 11(G), the central drum screen 92B separates the medium aggregate β4B shown in Figure 11(H), and the outermost drum screen 92C separates the fine aggregate β4C shown in Figure 11(I).

[0095] In this way, the rotary drum 91 crushes the silica sand hardened body β3 having the notched portion C1 to produce raw aggregate, and then separates it into different particle sizes to produce aggregate β4.

[0096] [2-2. Method for manufacturing aggregates] Figure 12 is a flowchart showing the method for manufacturing aggregate in Embodiment 2. First, natural silica sand and alkali metal compounds are mixed (mixing step S21).

[0097] The mixing process S21 is carried out by putting alkali metal compounds and natural silica sand into the kneader 61. In mixing step S21, a component analysis of the natural silica sand may be performed. In mixing step S21, the mixing time is set appropriately according to the weight of the alkali metal compound, the concentration of the alkali metal compound, the type of solution, and the type of natural silica sand. The pH inside the kneader 61 may also be set as appropriate.

[0098] Next, the mixture β1 of natural silica sand and alkali metal compound is poured into the mold 101 (pouring process S22).

[0099] Next, the kneaded material β1 is pressed by the press device 71 to form a strip-shaped molded body β2 (molding process S23).

[0100] Next, the strip-shaped molded body β2 is heated in a heating furnace 81 to produce a silica sand hardened body β3 having a notched portion C1 (silica sand hardened body production step S24).

[0101] In the silica sand hardening process S24, the chemical reaction shown in the following reaction formula (3) occurs, similar to Embodiment 1. Although potassium is given as an example of an alkali metal, it can be substituted with other alkali metals or alkalinity-type metals. 2KOH + SiO2 → K2SiO3 + H2O…(3)

[0102] Next, the hardened silica sand body β3 obtained is crushed and separated using a rotary drum 91 to obtain aggregate β4 (aggregate production process S25).

[0103] In the aggregate generation process S25 of Embodiment 2, raw aggregate α3 is generated and aggregate α4 is manufactured by separating the raw aggregate α3. The aggregate generation process S25 is an example of a raw aggregate generation process and a separation process.

[0104] (Embodiment 3) [3-1. Structure] Figure 13 shows an overview of the configuration used in the production of aggregate in Embodiment 3. In the production of aggregate α4 in Embodiment 3, natural silica sand SA is used as the raw material to create aggregate α4, similar to Embodiments 1-2. Components similar to those in Embodiments 1-2 are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0105] Figure 13(A) is a schematic diagram showing the mixing machine 61. The mixing machine 61 has the same configuration as in Embodiment 2. Alkali metal compounds and natural silica sand are added to the mixing tank 62. Water or an alcohol compound is also added to the mixing tank 62 to facilitate the molding of the compound γ1 into pellets. Compound γ1 is an example of a mixture.

[0106] Figure 13(B) is a schematic diagram showing the pellet molding machine 111. The pellet molding machine 111 comprises a pair of adjacent rotating drums 112. The rotating drums 112 have multiple circular holes formed in them. The compound γ1 is introduced onto the boundary between a pair of rotating drums 112. Once the compound γ1 is drawn into the pair of rotating drums 112, it is discharged from the holes. This forms a pelletized body γ2.

[0107] Furthermore, the pellet molding machine 111 may be configured to include a rotating blade. Also, the holes in the rotating drum 112 do not need to be of a constant diameter in order to create pellet molded bodies γ2 of different diameters. Moreover, multiple pellet molding machines 111 may be provided in the aggregate manufacturing system 3000. This makes it possible to produce pellet molded bodies with different shapes from each other.

[0108] Figure 13(C) is a schematic diagram showing the rotary kiln 121. The rotary kiln 121 is equipped with a rotary heating unit 122. The rotary kiln 121 is configured by adding the rotary heating unit 122 to the rotary drum 91 of Embodiment 2. In other words, the rotary kiln 121 is an example of a crushing device and a sorting machine, and also an example of a heating device.

[0109] Heating in the rotary kiln 121 hardens the pelletized body γ2, transforming it into a hardened silica sand body γ3.

[0110] Furthermore, the stirring by the rotary kiln 121 causes the hardened silica sand γ3 to have its corners C2 crushed, resulting in raw aggregate α3. As a result, the raw aggregate α3 has uneven particle size and is rounded in shape. Furthermore, the rotary kiln 121 separates the raw aggregate α3 into coarse aggregate, medium aggregate, and fine aggregate.

[0111] [3-2. Method for manufacturing aggregates] Figure 14 is a flowchart showing the method for manufacturing aggregate in Embodiment 3.

[0112] First, natural silica sand and alkali metal compounds are mixed (mixing step S31). The mixing process S31 is carried out by putting an alkali metal compound, natural silica sand, and water or an alcohol compound into a kneader 61.

[0113] In mixing step S31, a component analysis of the natural silica sand SA may be performed. In mixing step S31, the mixing time is set appropriately according to the weight of the alkali metal compound, the concentration of the alkali metal compound, the type of solution, and the type of natural silica sand SA. The pH inside the kneader 61 may also be set as appropriate.

[0114] Next, the mixed material γ1 is fed into the pellet molding machine 111, and the pelletized body γ2 is molded (pellet molding process S32). The pellet molding process S32 in Embodiment 3 is an example of the "silica sand hardened body production process".

[0115] Next, the pelletized body γ2 is fed into the rotary kiln 121 (aggregate production process S33).

[0116] In the aggregate formation process S33, the chemical reaction shown in the following reaction equation (3) occurs, similar to Embodiment 1. Although potassium is given as an example of an alkali metal, it can be substituted with other alkali metals or alkalinity-type metals. 2KOH + SiO2 → K2SiO3 + H2O…(3)

[0117] Furthermore, in the aggregate production process S33, the pelletized body is heated to become a silica sand hardened body γ3, the corners C2 are crushed to become raw aggregate, and then separated to manufacture the aggregate. In Embodiment 3, the aggregate generation process S33 is an example of a "raw aggregate generation process" and a "sorting process".

[0118] [4. Other Embodiments] The embodiments described above are merely examples and can be modified and applied as needed.

[0119] As described above, the method for producing aggregate comprises a mixing step of mixing at least an alkali metal compound with natural silica sand with a high silica content collected from deserts. This mixing step may be carried out inside the container 22, as in Embodiment 1, or in a kneader 61, as in Embodiments 2-3.

[0120] Furthermore, the aggregate manufacturing method includes a raw aggregate production step in which the mixture obtained in the mixing step is combined with natural silica sand to produce a silica sand hardened body, and the silica sand hardened body is crushed to produce raw aggregate with uneven particle size. The raw aggregate production process includes a raw aggregate production step, as described in Embodiment 1-3, which involves crushing a hardened silica sand body to produce the raw aggregate. Furthermore, the method for manufacturing aggregate includes a separation step to obtain aggregate by separating the raw aggregate according to particle size. This separation step may be performed simultaneously with the raw aggregate production step, as in Embodiment 3.

[0121] [5. Configurations supported by the above embodiment] The above embodiment supports the following configuration:

[0122] (Configuration 1) A method for manufacturing aggregate, comprising: a mixing step of mixing at least an alkali metal compound with natural silica sand with a high silica content collected from a desert; a silica sand hardened body production step of placing the mixture obtained in the mixing step into a container, heating the entire container, and bonding the natural silica sand to produce a silica sand hardened body; a raw aggregate production step of crushing the silica sand hardened body to produce raw aggregate with uneven particle size; and a separation step of separating the raw aggregate according to particle size. According to Configuration 1, natural silica sand with a high silica content collected from deserts is heated in its entirety within a container, causing the natural silica sand to bond together to form a hardened silica sand body. This hardened silica sand body is then crushed to produce aggregate. Thus, it is possible to provide an aggregate manufacturing method that increases the strength of the aggregate and is suitable for mass production of aggregate.

[0123] (Configuration 2) A method for manufacturing aggregate, comprising: a mixing step of mixing at least an alkali metal compound with natural silica sand with a high silica content collected from a desert; a silica sand hardened body production step of forming the mixture obtained in the mixing step into a notched strip-shaped molded body, heating the molded body, and bonding the natural silica sand to produce a notched silica sand hardened body; a raw aggregate production step of crushing the silica sand hardened body at the notched portions to produce raw aggregate with uneven particle sizes; and a sorting step of sorting the raw aggregate according to particle size. According to configuration 2, the hardened silica sand is easily crushed by the notches, making it easy to produce raw aggregate. Therefore, it is possible to provide an aggregate manufacturing method that increases the strength of the aggregate and is suitable for mass production of aggregate.

[0124] (Configuration 3) A method for manufacturing aggregate, comprising: a mixing step of mixing at least an alkali metal compound with natural silica sand with a high silica content collected from a desert; a silica sand hardened body production step of forming the mixture obtained in the mixing step into a pellet-shaped molded body, heating the molded body, and bonding the natural silica sand to produce a pellet-shaped silica sand hardened body; a raw aggregate production step of crushing the silica sand hardened body to produce raw aggregate with uneven particle size; and a separation step of separating the raw aggregate according to particle size. According to configuration 3, the mixture is molded into pellets before becoming a hardened silica sand body or raw aggregate, making it easy to produce raw aggregate. This provides a method for manufacturing aggregate that increases the strength of the aggregate and is suitable for mass production.

[0125] (Composition 4) The method for producing aggregate according to any one of Compositions 1 to 3, wherein the natural silica sand has a silica content of 80% or more. According to configuration 4, the strength of the aggregate can be further increased.

[0126] (Configuration 5) The method for producing aggregate according to Configuration 4, wherein the natural silica sand has a silica content of 85% or more. According to configuration 5, the compressive strength of the silica sand hardened body can be improved, thereby increasing the strength of the aggregate.

[0127] (Configuration 6) The method for producing aggregate according to any one of Configurations 1 to 5, wherein the silica sand hardening step is heated to a temperature at which the alkali metal compound and the silicic acid react to produce an alkali silicate. According to composition 6, the silicic acid contained in natural silica sand is bonded by alkali silicates, thereby increasing the strength of the hardened silica sand body and, consequently, the strength of the aggregate.

[0128] (Configuration 7) The method for producing aggregate according to Configuration 6, wherein the silica sand hardening step is heated at a temperature of 200 degrees Celsius or higher and 1400 degrees Celsius or lower as the temperature at which the alkali silicate is produced. According to configuration 7, a lower temperature increases the number of points where silicic acid contained in natural silica sand is bonded by compounds other than alkali silicates, which can reduce the strength of the hardened silica sand. Conversely, a higher temperature can prevent the silicic acid from melting and becoming unable to bond with alkali silicates. Therefore, the strength of the aggregate can be increased.

[0129] (Configuration 8) The method for producing aggregate according to Configuration 7, wherein the silica sand hardening step is to heat the silica sand at a temperature of 200 degrees Celsius or higher and 240 degrees Celsius or lower as the temperature at which the alkali silicate is produced. According to configuration 8, in addition to the effects achieved by configuration 7, the power consumption when producing the silica sand hardened body can be reduced.

[0130] (Configuration 9) The method for producing aggregate according to any one of Configurations 1 to 8, wherein the separation step separates the raw aggregate into coarse aggregate with a particle size of 4.75 mm or more and 13.2 mm or less, medium aggregate with a particle size of 2.36 mm or more and 4.75 mm or less, and fine aggregate with a particle size of less than 2.36 mm. According to configuration 8, aggregates can be separated according to particle size, which is particularly suitable for their intended use. [Explanation of Symbols]

[0131] 2...Silica sand hardened body generating device, 22...Container, 23...Outer tank, 24...Inner tank, 25...Raw material container, 31...Crusher, 32...Rammer, 33...Container stand, 34...Crusher machine, 35...Rotating blade, 41...Separator, 61...Mixer, 62...Mixing tank, 63...Mixing section, 64...Agitator blade, 71...Pressing device, 81...Heating furnace, 82...Conveyor section, 83...Heating section, 91...Rotary drum, 92A, 92B, 92C...Drum screen, 101...Mold, 102...Bottom, 103...Protrusion, 104...Side wall, 111...Pellet molding machine, 112...Rotating drum, 121...Rotary kiln, 122...Rotary heating section, C1...Notch, C2...Corner, S1 ...Mixing process, S2...Silica sand hardened body production process, S3...Raw aggregate production process, S4...Fractional process, S21...Mixing process, S22...Pouring process, S23...Molding process, S24...Silica sand hardened body production process, S25...Aggregate production process (raw aggregate production process, fractional process), S31...Mixing process, S32...Pellet molding process, S33...Aggregate production process (raw aggregate production process, fractional process), K...Alkali metal compound, SA...Natural silica sand, α1...Mixture, α2...Silica sand hardened body, α3...Raw aggregate, α4...Aggregate, β1...Mixed product, β2...Strip-shaped molded body (strip-shaped molded body), β3...Silica sand hardened body, γ1...Mixed product, γ2...Pellet-shaped molded body (pellet-shaped molded body), γ3...Silica sand hardened body.

Claims

1. A method for manufacturing aggregate, A mixing process in which at least an alkali metal compound is mixed with natural silica sand with a high silica content collected from the desert, A silica sand hardened body production step involves placing the mixture obtained in the above mixing step into a container, heating the entire container, and bonding the natural silica sand to produce a silica sand hardened body, A raw aggregate production step involves crushing the aforementioned hardened silica sand to produce raw aggregate with uneven particle size, The system includes a sorting step for separating the raw aggregate according to particle size, Method for manufacturing aggregates.

2. A method for manufacturing aggregate, A mixing process in which at least an alkali metal compound is mixed with natural silica sand with a high silica content collected from the desert, A silica sand hardened body production step involves forming a notched strip-shaped molded body from the mixture obtained in the mixing step, heating the molded body, and bonding the natural silica sand to produce a notched silica sand hardened body, The process involves crushing the hardened silica sand at the notched portion to produce raw aggregate with uneven particle size, and The system includes a sorting step for separating the raw aggregate according to particle size, Method for manufacturing aggregates.

3. A method for manufacturing aggregate, A mixing process in which at least an alkali metal compound is mixed with natural silica sand with a high silica content collected from the desert, A silica sand hardened body production step involves molding the mixture obtained in the mixing step into a pellet-shaped molded body, heating the molded body, and bonding the natural silica sand to produce a pellet-shaped silica sand hardened body, A raw aggregate production step involves crushing the hardened silica sand body to produce raw aggregate with uneven particle size, The system includes a sorting step for separating the raw aggregate according to particle size, Method for manufacturing aggregates.

4. The aforementioned natural silica sand has a silica content of 80% or more. A method for manufacturing aggregate according to any one of claims 1 to 3.

5. The aforementioned natural silica sand has a silica content of 85% or more. The method for producing aggregate according to claim 4.

6. The silica sand hardened body production step is as follows: The alkali metal compound and the silicic acid are heated to a temperature at which they react to produce an alkali silicate. A method for manufacturing aggregate according to any one of claims 1 to 3.

7. The silica sand hardened body production step is as follows: The temperature at which the alkali silicate is produced is set to a temperature of 200 degrees Celsius or higher and 1400 degrees Celsius or lower. The method for producing aggregate according to claim 6.

8. The silica sand hardened body production step is as follows: The temperature at which the alkali silicate is produced is set to a temperature of 200 degrees Celsius or higher and 240 degrees Celsius or lower. The method for producing aggregate according to claim 7.

9. The aforementioned sorting process is, The raw aggregate is separated into coarse aggregate with a particle size of 4.75 mm or more and 13.2 mm or less, medium aggregate with a particle size of 2.36 mm or more and 4.75 mm or less, and fine aggregate with a particle size of less than 2.36 mm. A method for manufacturing aggregate according to any one of claims 1 to 3.

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