Filler for asphalt-paving mixture, method for manufacturing filler for asphalt-paving mixture, and asphalt-paving mixture

Abstract

To provide a filler for asphalt-paving mixture that can contribute to the reduction of CO2 in the natural environment.SOLUTION: A filler for asphalt-paving mixture has a calcium content of 37 mass% or less as an element, and satisfies at least one of the following conditions (1) to (4): (1) the particle size D50 of the filler for asphalt-paving mixture exceeds 20 μm; (2) the filler for asphalt-paving mixture has a mass percentage value of passing through a 600 μm sieve of 70% or more, a mass percentage value of passing through a 150 μm sieve of 45% or more, and a mass percentage value of passing through a 75 μm sieve of 30% or more; (3) the whiteness W(L*a*b*) of the filler for asphalt-paving mixture, measured by the CIE Lab method, is less than 95; and (4) the lightness index L* of the filler for asphalt-paving mixture, measured by the CIE Lab method, is less than 95.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a filler for asphalt mixtures, a method for producing a filler for asphalt mixtures, and an asphalt mixture. [Background technology]

[0002] Asphalt is generally used as an asphalt mixture mixed with a filler for asphalt mixtures, which is made from stone powder made from powdered limestone (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Japan Asphalt Association website (http: / / askyo.jp / knowledge / 06-1.html) "Basic knowledge of asphalt: Asphalt mixtures used for roads 6-1 What is asphalt mixture?" (Accessed May 1, 1994) Summary of the Invention [Problem to be solved by the invention]

[0004] Asphalt mixture fillers can be produced as particles containing calcium compounds such as calcium carbonate. Therefore, if asphalt mixture fillers could be produced by fixing CO2 present in the natural environment, such as the atmosphere, it would contribute to reducing CO2 in the natural environment. However, asphalt mixture fillers produced by fixing CO2 from the natural environment in this way have not yet been put to practical use.

[0005] Therefore, an object of the present disclosure is to provide a filler for asphalt mixtures, a method for producing a filler for asphalt mixtures, and an asphalt mixture that can contribute to reducing CO2 in the natural environment. [Means for solving the problem]

[0006] In order to achieve the above object, the filler for asphalt mixtures of the present disclosure is characterized in that the calcium content as an element is 37 mass% or less and satisfies at least one condition selected from the group consisting of the following conditions (1) to (4): (1) The particle diameter D50 of the filler for asphalt mixture exceeds 20 μm. (2) The filler for asphalt mixtures has a mass percentage passing through a sieve with a mesh size of 600 μm of 70% or more, a mass percentage passing through a sieve with a mesh size of 150 μm of 45% or more, and a mass percentage passing through a sieve with a mesh size of 75 μm of 30% or more. (3) The whiteness W (L * a * b * ) is less than 95. (4) The CIE Lab lightness index L of the asphalt mixture filler * is less than 95.

[0007] The method for producing a filler for asphalt mixtures of the present disclosure is characterized by comprising: a first step of obtaining a calcium-containing by-product from a calcination step for producing quicklime; a second step of reacting a substance containing the calcium-containing by-product with water to obtain a substance containing calcium hydrate; and a third step of reacting the substance containing calcium hydrate with CO2 to obtain a substance containing calcium carbonate, thereby fixing the CO2.

[0008] The asphalt mixture of the present disclosure is characterized by containing the filler for asphalt mixtures of the present disclosure and asphalt. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a filler for asphalt mixtures, a method for producing a filler for asphalt mixtures, and an asphalt mixture that can contribute to reducing CO2 in the natural environment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, the present disclosure will be described in more detail using examples, but the present disclosure is not limited to the following description.

[0011] [1. Filler for asphalt mixtures] As described above, the filler for asphalt mixtures of the present disclosure is characterized in that the calcium content as an element is 37 mass% or less and that it satisfies at least one condition selected from the group consisting of the following conditions (1) to (4): (1) The particle diameter D50 of the filler for asphalt mixture exceeds 20 μm. (2) The filler for asphalt mixtures has a mass percentage passing through a sieve with a mesh size of 600 μm of 70% or more, a mass percentage passing through a sieve with a mesh size of 150 μm of 45% or more, and a mass percentage passing through a sieve with a mesh size of 75 μm of 30% or more. (3) The whiteness W (L * a * b * ) is less than 95. (4) The CIE Lab lightness index L of the asphalt mixture filler * is less than 95.

[0012] In the asphalt mixture filler of the present disclosure, the calcium content as an element is a numerical value measured by the measurement method described in the Examples below. However, the measurement method for the calcium content is not limited to this, and measurement can also be performed by other measurement methods. In the present disclosure, the "calcium content as an element" is a concept that indicates the content (mass %, weight %) of calcium present as an element in a simple substance or compound such as Ca, CaO, Ca(OH)2, or CaCO3.

[0013] In the filler for asphalt mixtures of the present disclosure, the content of elemental calcium may be, for example, 5% by mass or more, 10% by mass or more, 15% by mass or more, 17% by mass or more, or 20% by mass or more, and may be, for example, 37% by mass or less, 36% by mass or less, 35% by mass or less, 34% by mass or less, 33% by mass or less, 32% by mass or less, 30% by mass or less, 28% by mass or less, or 25% by mass or less, for example, 5 to 37% by mass. In the filler for asphalt mixtures of the present disclosure, the content of elemental calcium is expected to be lower than that of general precipitated calcium carbonate, for example, by using a by-product discharged from a quicklime calcination process as a raw material, but is not limited to this.

[0014] In the present disclosure, "mass" and "weight" may be read interchangeably unless otherwise specified. For example, in the present disclosure, "mass%" and "wt%" may be read interchangeably unless otherwise specified.

[0015] In the asphalt mixture filler of the present disclosure, the values ​​of the conditions (1) to (4) are values ​​measured by the measurement method described in the Examples below. However, the measurement method of the values ​​of the conditions (1) to (4) is not limited to this, and they can also be measured by other measurement methods.

[0016] The particle diameter D50 of the asphalt mixture filler may be, for example, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, 42 μm or more, 45 μm or more, 47 μm or more, 50 μm or more, or 52 μm or more, and may be, for example, 500 μm or less, 250 μm or less, 120 μm or less, 100 μm or less, 95 μm or less, or 90 μm or less. From the viewpoint of ensuring watertightness, the particle diameter D50 of the asphalt mixture filler is preferably not too large or too small. Furthermore, if the D50 is too small, the amount of asphalt increases, which is economically undesirable. Therefore, it is desirable that the asphalt mixture filler of the present disclosure has a D50 that is neither too large nor too small, and has a moderate particle size distribution.

[0017] From the viewpoint of material specification regulations, the particle size of the asphalt mixture filler must satisfy the standard values, such that the mass percentage passing through a 600 μm sieve is 100%, the mass percentage passing through a 150 μm sieve is 90% or more, and the mass percentage passing through a 75 μm sieve is 75% or more. On the other hand, when evaluating from the viewpoint of mixture performance regulations, the above is not limiting, and the mass percentage passing through a 600 μm sieve may be, for example, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 97% or more. The upper limit of the mass percentage passing through a 600 μm sieve is not particularly limited, but is, for example, 100% or less. The filler for asphalt mixtures may have a passing mass percentage value through a sieve with a mesh size of 150 μm of, for example, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, or 75% or more, and may have a passing mass percentage value of, for example, 95% or less, 90% or less, or 85% or less. The filler for asphalt mixtures may have a passing mass percentage value through a sieve with a mesh size of 75 μm of, for example, 35% or more, 40% or more, 45% or more, 50% or more, or 55% or more, and may have a passing mass percentage value of, for example, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, or 60% or less.

[0018] The whiteness W (L * a * b * ) may be, for example, 90 or less, 85 or less, 80 or less, 75 or less, 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 45 or less, or 40 or less, and the lower limit is not particularly limited, but may be, for example, 0 or more or exceed 0. The CIE Lab lightness index L * may be, for example, 90 or less, 85 or less, 80 or less, 75 or less, 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 45 or less, or 40 or less, and the lower limit is not particularly limited, but may be, for example, 0 or more, or greater than 0.

[0019] The raw material for the filler for asphalt mixtures of the present disclosure is not particularly limited, but for example, calcium-containing materials discharged as by-products from the calcination process in the lime industry can be used.

[0020] In the calcination process for producing quicklime (CaO), coke is mixed with the main fuel and burned. During this process, dust containing ash from unburned coke is emitted as a by-product. Although this dust contains CaO and other calcium compounds, it has been discarded due to coloring and quality issues, and has not been used as a raw material for asphalt mixture fillers.

[0021] The present inventors have discovered that calcium-containing by-products, which are generated during the calcination process in the lime industry and which have traditionally been discarded, can be used as a raw material for asphalt mixture fillers. By using by-products that have traditionally been discarded, it is possible to expect benefits such as cost reduction and a reduction in the burden on the natural environment.

[0022] In the asphalt mixture filler disclosed herein, when a by-product generated in the calcination process for producing quicklime (CaO), i.e., dust containing ash such as unburned coke, is used as a raw material, the whiteness W(L) measured by CIE Lab is higher than that of general precipitated calcium carbonate. * a * b * ) tends to be low. Similarly, the CIE Lab lightness index L * tends to be a low value.

[0023] The asphalt mixture filler of the present disclosure may be, for example, an asphalt mixture filler that fixes CO2. The CO2 may or may not contain atmospheric CO2, and may or may not contain other CO2. The CO2 may be, for example, entirely atmospheric CO2. When the CO2 reacts with and fixes atmospheric CO2, the effect of reducing atmospheric CO2 can be achieved.

[0024] The color of the asphalt mixture filler of the present disclosure is not particularly limited, and may be, for example, any color selected from the group consisting of sand, chalk, natural, ivory, silver gray, brown gray, gray, Rikyu gray, lead, gray, soot bamboo, dark brown, ink, black, iron black, silver, ivory, sky gray, pearl gray, silver gray, ash gray, rose gray, gray, steel gray, straight gray, charcoal gray, lamp black, and black, as well as any of these colors modified with the terms "light," "strong," "dark," "light," "soft," "dull," "dark," "very light," "light grayish," "grayish," "dark grayish," "very dark," or "medium," as defined in Appendix 1 of Japanese Industrial Standards (JIS) Z 8102:2001 (Color Names of Object Colors).

[0025] Next, examples of general calcium carbonate and the filler for asphalt mixtures of the present disclosure will be described.

[0026] Common calcium carbonate is divided into two types, heavy calcium carbonate (stone powder) and light calcium carbonate (precipitated calcium carbonate), depending on the manufacturing method. Heavy calcium carbonate (stone powder) is produced by crushing limestone containing CaCO3. Therefore, the manufacturing process for heavy calcium carbonate does not involve CO2 absorption. In contrast, light calcium carbonate is produced by injecting CO2 into a saturated calcium hydroxide solution to cause a chemical reaction. Therefore, calcium carbonate that has absorbed CO2 for the purpose of reducing CO2 emissions is generally light calcium carbonate (precipitated calcium carbonate, which is reacted with CO2 in an aqueous solution) rather than heavy calcium carbonate (stone powder). The literature ("Ecotancal R (Light Calcium Carbonate) and Its Potential," Cement & Concrete No. 900, Feb. 2022, pp. 58-63) states that the light calcium carbonate described in the literature is precipitated calcium carbonate, stating that "it is produced by injecting CO2 into a saturated calcium hydroxide solution through a chemical reaction." Table 1 of the document lists precipitated calcium carbonate (registered trademark "Ecotancal") with the following physical properties:

[0027] [Table 1]

[0028] Additionally, an online article introducing Ecotancal (registered trademark) (https: / / www.ncic.co.jp / products / environment / ecocaco3.html) states, "It is produced by a chemical reaction, and no impurities are introduced during the production process, allowing for the provision of highly pure calcium carbonate. Its purity is 97-99%. It also provides high whiteness." Based on these facts, it can generally be said that light calcium carbonate (precipitated calcium carbonate) produced by absorbing CO2 has the properties listed below in 1) to 4). 1) It has "high whiteness." 2) Whiteness: 95% or more. 3) The CaCO3 content is 95% by mass or more (the Ca content as element is 38% by mass or more (95 / 100 × 40 = 38)). 4) The reaction that fixes CO2 is produced by a reaction in an aqueous solution.

[0029] In contrast, the filler for asphalt mixtures of the present disclosure differs from precipitated calcium carbonate in that the elemental Ca content is 37% by mass or less. The filler for asphalt mixtures of the present disclosure has, for example, one or more of the following properties 1) to 6), but these are merely examples and the properties of the filler for asphalt mixtures of the present disclosure are not limited thereto. 1) It is not white. 2) CIE Lab whiteness W(L * a * b * ): Less than 95. 3) The volume-based D50 measured by the laser diffraction / scattering method exceeds 20 μm. 4) The Ca content as an element is 37% by mass or less. 5) CO2 fixation can be achieved without reactions in aqueous solution. 6) Specific examples of colors include not white but gray, strong gray, weak gray, etc. Specific examples include sand, chalk, natural, ivory, silver gray, brown gray, gray, Rikyu gray, lead, gray, soot bamboo, dark brown, ink, black, iron black, silver, ivory, sky gray, pearl gray, silver gray, ash gray, rose gray, gray, steel gray, straight gray, charcoal gray, lamp black, black, etc., as specified in Appendix 1 of the Japanese Industrial Standards (JIS) Z 8102:2001 (Color Names of Object Colors). In addition, JIS Z 8102:2001 allows the addition of modifiers to the above conventional colors using the terms specified in 7.2 Table 3 and 7.3 Table 4 of the same specification, and includes colors modified by any of the above conventional color names with "bright," "strong," "dark," "light," "soft," "dull," "dark," "very light," "light grayish," "grayish," "dark grayish," "very dark," and "medium" as specified in JIS Z 8102:2001.7.2 Table 3 and 7.3 Table 4 (JIS Z 8102:2001.11.2 and 7.2 Table 3, 7.3 Table 4).

[0030] The properties of the filler for asphalt mixtures according to the present disclosure compared with those of common commercially available light calcium carbonate (precipitated calcium carbonate) and heavy calcium carbonate (stone powder) are, for example, as follows: However, these properties are merely examples, and the properties of the filler for asphalt mixtures according to the present disclosure, light calcium carbonate (precipitated calcium carbonate), and heavy calcium carbonate (stone powder) are not limited to these. Precipitated calcium carbonate (precipitated calcium carbonate): Produced by fixing CO2 Calcium carbonate content (95% by mass or more → Ca content 38% by mass or more) Whiteness: 95% ●Heavy calcium carbonate (stone powder): Cannot absorb (fix) CO2. Calcium carbonate content (90% by mass or more → Ca content 36% by mass or more) Whiteness: 93% Filler for asphalt mixtures disclosed herein: Manufactured by fixing CO2 ·Ca content 37% by mass or less ·50% particle size: D50: 20μm or more. Whiteness: Less than 95%

[0031] The method for producing the filler for asphalt mixtures of the present disclosure is not particularly limited, and for example, it can be produced by the above-mentioned method for producing a filler for asphalt mixtures of the present disclosure.

[0032] [2. Manufacturing method of filler for asphalt mixture] Next, the method for producing the filler for asphalt mixtures of the present disclosure will be described using an example.

[0033] As described above, the method for producing a filler for asphalt mixtures of the present disclosure is characterized by including a step of reacting a calcium hydrate-containing substance with CO2 to fix the CO2.

[0034] As described above, the manufacturing method of a filler for asphalt mixtures according to the present disclosure includes a first step of obtaining a calcium-containing by-product from a calcination step of producing quicklime, a second step of reacting a component of the calcium-containing by-product with water to obtain a component containing calcium hydrate, and a third step of reacting the component containing calcium hydrate with CO2 to obtain a component containing calcium carbonate, the third step being a step of fixing the CO2. Also, the filler for asphalt mixtures according to the present disclosure may be a filler for asphalt mixtures manufactured by a manufacturing method including a first step of obtaining a calcium-containing by-product from a calcination step of producing quicklime, a second step of reacting the component containing calcium-containing by-product with water to obtain a component containing calcium hydrate, and a third step of reacting the component containing calcium hydrate with CO2 to obtain a component containing calcium carbonate.

[0035] In the first step, for example, quicklime (CaO) is produced by calcining limestone (including calcium carbonate CaCO3). The calcium-containing by-product obtained in this first step includes, for example, calcium oxide CaO. The chemical reaction in the first step may be, for example, a chemical reaction represented by the following chemical reaction formula (1). In the second step, for example, CaO in the calcium-containing by-product reacts with water to obtain a calcium hydrate inclusion. The calcium hydrate may be, for example, calcium hydroxide Ca(OH)2. The chemical reaction in the second step may be, for example, a chemical reaction represented by the following chemical reaction formula (2). In the third step, as described above, the calcium hydrate inclusion is reacted with CO2 to obtain a calcium carbonate inclusion. The chemical reaction in the third step may be, for example, a chemical reaction represented by the following chemical reaction formula (3). CaCO3 → CaO + CO2(1) CaO + H2O → Ca(OH)2(2) Ca(OH)2+CO2→CaCO3+H2O (3)

[0036] Next, the calcium-containing by-product obtained in the first step will be described using an example. The production of quicklime (CaO) includes a step of calcining limestone. The reaction that occurs in this step is mainly the reaction shown in chemical reaction formula (1). Chemical reaction formula (1) is shown below. CaCO3 → CaO + CO2(1)

[0037] During this calcination process, calcium-containing waste (≒) and calcium-containing by-products are generated in the production of the finished quicklime. These calcium-containing waste (≒) and calcium-containing by-products include CaO. The calcination furnace used in this calcination process is not particularly limited, but vertical furnaces such as Maerz furnaces and Beckenbach furnaces, or horizontal furnaces such as rotary kilns, are commonly used. The following explanation refers to the reference "Establishment of Operating Technology for Beckenbach-Type Lime Calcination Kilns," Journal of the Society of Inorganic Materials, Japan 7, pp. 220-226 (2000)). In these calcination furnaces, for example, Beckenbach furnaces, coke co-firing was introduced to reduce fuel costs after the oil crisis. Coke is mixed with limestone and fed into the furnace for combustion. Problems with coke co-firing include dust retention in the furnace and coke sinking. These are discharged as calcium-containing dust or hearth discharge, as described below. The calcium-containing (retained) dust remains above the upper bridge. The calcium-containing ash is divided into those that adhere to the surface of the quicklime, those that disperse in the exhaust gas, and those that are emitted from the bottom of the furnace. Currently, these are treated industrially by separating them on the surface according to quality standards (quantitatively about 0.7%). These are discharged as waste (by-products) from the firing process. These contain CaO and can be the calcium-containing by-products obtained in the first step of the present disclosure. Reference: "Establishment of operating technology for Beckenbach lime kiln", Journal of the Society of Inorganic Materials, Japan 7, 220-226 (2000)).

[0038] Furthermore, although not mentioned in the reference, even when a rotary kiln is used, a substance called calcination dust, which contains unburned carbon and CaO, is collected by a dust collector. This calcination dust accounts for several percent of the total product. Thus, regardless of the calcination furnace used, waste products (by-products) are generated in the process of calcining limestone to produce CaO. These by-products contain CaO and can be the calcium-containing by-product obtained in the first step of the present disclosure.

[0039] Ordinary stone powder used in asphalt mixture fillers generally contains heavy calcium carbonate as the main component, with CaCO3 being 90% by weight or more (the elemental Ca content exceeds 36% by weight). Light calcium carbonate (precipitated calcium carbonate) contains 95% by weight or more of CaCO3, with an elemental Ca content of 38% by weight or more. In contrast, the asphalt mixture filler of the present disclosure differs from precipitated calcium carbonate (light calcium carbonate) in that the elemental Ca content is 37% by weight (mass%) or less. The asphalt mixture filler of the present disclosure is thought to have a low elemental Ca content of 37% by weight or less by using a calcium-containing by-product obtained from the calcination process for producing quicklime in the first step, for example.

[0040] The calcium content as an element in the calcium-containing by-product is not particularly limited, but may be, for example, 66% by mass or less, 65% by mass or less, 62% by mass or less, 60% by mass or less, 57% by mass or less, less than 57% by mass, 56% by mass or less, 55% by mass or less, 50% by mass or less, 48% by mass or less, 45% by mass or less, 40% by mass or less, or 35% by mass or less. The lower limit of the calcium content as an element is also not particularly limited, but a preferred lower limit is 5% by mass or more, 10% by mass or more, or 15% by mass or more, and more preferably 20% by mass or more, or 25% by mass or more.

[0041] Next, the second step and the third step will be described. The main chemical reaction in the second step can be expressed, for example, by the chemical reaction formula (2). The main chemical reaction in the third step can be expressed, for example, by the chemical reaction formula (3). The chemical reaction formulas (2) and (3) are shown again below. The reaction conditions for the second step are not particularly limited, but may be similar to or equivalent to, for example, a general hydration step. The reaction conditions for the third step are not particularly limited, but may be similar to or equivalent to, for example, a general carbonation step. Hereinafter, the second step may be referred to as the "hydration step," and the third step may be referred to as the "carbonation step." CaO + H2O → Ca(OH)2(2) Ca(OH)2+CO2→CaCO3+H2O (3)

[0042] The second step (hydration step) and the third step (carbonation step) can be carried out in the same manner as or in accordance with the general hydration step and general carbonation step described below, respectively. A document ("Preparation of Granular Slaked Lime by Hydration of Quicklime," Gypsum & Lime No. 234, pp. 306-314 (1991)) describes a hydration step in which water is sprayed onto CaO powder from above, the mixture is stirred with a scrubber, and Ca(OH)2 is produced by the hydration reaction of CaO. A document ("On the Slake of Limestone," Inorganic Materials Society, Gypsum and Lime, Vol. 1957, No. 29, pp. 1434-1335 (1957)) describes the hydration step and the carbonation step as follows: Specifically, the document notes that the majority of small and medium-sized Japanese industries use a method of depositing CaO on the floor or in a container and then pouring water over it to hydrate it; that there are many mechanical methods for hydrating CaO, such as an Anker-type automatic hydrator; and that CaO naturally hydrates when exposed to moisture in the air. CaO naturally absorbs moisture from the air to produce Ca(OH)2, which then absorbs CO2 from the air to produce CaCO3. Therefore, hydration and carbonation reactions can also occur through natural weathering. The document ("Research Trends in Lime," Inorganic Materials, Vol. 1, No. 252, pp. 370-381 (1994)) also notes that much research has been done on the carbonation process. Furthermore, Patent Publication No. 07282338 describes a vending machine equipped with a CO2 adsorbent. The hydration and carbonation processes can be carried out using these known methods or a combination of them. As described in the above-mentioned documents, the hydration reaction and / or the carbonation reaction can be carried out even in a non-aqueous solution.

[0043] Known calcium carbonate, which is generally sold as precipitated calcium carbonate (precipitated calcium carbonate), is produced, for example, as follows: First, CaO is suspended in an aqueous solution and reacted with water to cause a hydration reaction of CaO + HO → Ca(OH). After this reaction, CO is blown into the aqueous solution to cause a carbonation reaction, and the precipitated calcium carbonate is dehydrated and recovered. In Japan, precipitated calcium carbonate was commercially produced and sold using this method by Koji Shiraishi in 1909. In the method for producing a filler for asphalt mixtures disclosed herein, it is possible to cause a Ca-containing by-product obtained from the calcination process for producing quicklime to undergo a hydration reaction in an aqueous solution, or to cause a carbonation reaction in an aqueous solution.

[0044] [3. Asphalt mixture] As described above, the asphalt mixture of the present disclosure is characterized by containing the filler for asphalt mixtures of the present disclosure and asphalt.

[0045] The asphalt mixture of the present disclosure may or may not contain any components other than the asphalt mixture filler of the present disclosure and asphalt. The asphalt mixture of the present disclosure may or may not contain, for example, stone (crushed stone). The asphalt mixture of the present disclosure may or may not contain, for example, sand.

[0046] The composition of the asphalt mixture of the present disclosure is not particularly limited, and may be the same as the composition of a general asphalt mixture, for example, except that all or part of the filler for asphalt mixtures in a general asphalt mixture is replaced with the filler for asphalt mixtures of the present disclosure.

[0047] In the asphalt mixture of the present disclosure, the filler for asphalt mixtures of the present disclosure may be used alone as the filler for asphalt mixtures, or a general filler for asphalt mixtures (for example, stone powder) may be used in combination with the filler for asphalt mixtures of the present disclosure. When stone powder and the filler for asphalt mixtures of the present disclosure are used in combination, the content of the filler for asphalt mixtures of the present disclosure in the entire filler for asphalt mixtures is not particularly limited and can be selected as appropriate. The higher the content of the filler for asphalt mixtures of the present disclosure, the greater the effect of the present disclosure, which can contribute to reducing CO2 in the natural environment.

[0048] In the asphalt mixture of the present disclosure, the content of the filler for asphalt mixtures is not particularly limited and can be selected appropriately depending on the application of the asphalt mixture, etc. For example, it may be the same as or equivalent to the content of the filler for asphalt mixtures in general asphalt mixtures. The filler content in general new asphalt mixtures is often about 5 to 6% by mass. However, in special asphalt mixtures for bridge surfaces, the filler content may exceed 25% by mass, for example. In addition, in recycled asphalt mixtures, for example, if the replacement (use) rate of recycled aggregate (asphalt mixture once used in roads that has been crushed and grading adjusted) is 50% by mass, the amount of newly used filler can be, for example, about 2.5 to 3% by mass, half that of new asphalt mixtures.

[0049] In the asphalt mixture of the present disclosure, the asphalt content is not particularly limited and can be appropriately selected depending on the application of the asphalt mixture, and may be the same as or equivalent to the asphalt content in a general asphalt mixture. In a general new asphalt mixture, the asphalt content is, for example, approximately 4.5 to 6.5 mass%. In a recycled asphalt mixture, if the replacement (use) rate of recycled aggregate is 50 mass%, the amount of new asphalt used is, for example, approximately 2.2 to 3.5 mass%. As the proportion of recycled aggregate used increases, the amount of new asphalt used tends to decrease. In the asphalt mixture of the present disclosure, it is preferable that the asphalt content is not too high to prevent a decrease in flow resistance and an increase in rutting. In the asphalt mixture of the present disclosure, it is preferable that the asphalt content is not too low to prevent a decrease in the gripping force between the aggregate and asphalt, resulting in reduced shattering resistance and bending strength at low temperatures.

[0050] The asphalt mixture of the present disclosure may or may not contain coarse aggregate, and may or may not contain fine aggregate. The content of coarse aggregate and fine aggregate in the asphalt mixture of the present invention is not particularly limited and may be the same as or equivalent to the content of coarse aggregate and fine aggregate in a typical asphalt mixture. Varying the ratio of coarse aggregate to fine aggregate can produce asphalt mixtures with various characteristics. For example, the new dense-graded asphalt mixture used on typical roads can have a composition of 55% coarse aggregate by mass, 35% fine aggregate by mass, 5.5% filler by mass, and 5.5% asphalt by mass. Furthermore, for example, the high-performance Type II (formerly known as drainage pavement), which is a type of pavement that drains water and is found on expressways, can have a composition of 75% coarse aggregate by mass, 15% fine aggregate by mass, 5% filler by mass, and 5% asphalt by mass. In the case of recycled dense-graded asphalt mixtures, which have been widely used in recent years, the amount of coarse aggregate and fine aggregate used varies depending on the replacement (use) rate of recycled aggregate. For example, if the replacement rate of recycled aggregate is 50% by mass, the composition can be 24% by mass of coarse aggregate, 24% by mass of fine aggregate, 2% by mass of filler, 2% by mass of new asphalt, and 50% by mass of recycled aggregate (particle size 13-0 mm).In this way, the amount of coarse aggregate and fine aggregate can be changed (the mixture can be changed) depending on the application location and use of the asphalt mixture.

[0051] The method for producing an asphalt mixture of the present disclosure is not particularly limited, and may be the same as a method for producing a general asphalt mixture, for example, except that all or part of the filler for asphalt mixtures in a general asphalt mixture is replaced with the filler for asphalt mixtures of the present disclosure. The asphalt mixture of the present disclosure can also be produced, for example, by simply mixing the components that make up the asphalt mixture of the present disclosure (for example, the filler for asphalt mixtures of the present disclosure, crushed stone, sand, and asphalt). [Example]

[0052] Next, examples of the present disclosure will be described, but the present disclosure is not limited to the following examples.

[0053] In the following Reference Examples, Examples, and Comparative Examples, the number of parts (relative amount used) of each substance is in parts by mass (parts by weight) unless otherwise specified.

[0054] [Example 1: Production of filler for asphalt mixture] The filler for asphalt mixtures of this example (Example 1) was produced as follows.

[0055] (1) First step First, in a calcination step of producing quicklime from limestone in a Beckenbach furnace, a calcium-containing by-product was obtained as calcined dust from the Beckenbach furnace. This calcium-containing by-product contains CaO. This step corresponds to the "first step" in the method for producing a filler for asphalt mixtures of the present disclosure. The elemental calcium content in the asphalt mixture filler produced from this calcium-containing by-product is as described below. The elemental calcium content in the calcium-containing by-product can be estimated from the elemental calcium content in the produced asphalt mixture filler using chemical reaction formulas (2) and (3). For example, if the elemental calcium content in the produced asphalt mixture filler is 37% by mass, the elemental calcium content in the calcium-containing by-product can be estimated to be around 60% by mass (approximately 62% by mass) using chemical reaction formulas (2) and (3).

[0056] (2) Second process Next, water was sprayed onto the calcium-containing by-product obtained in the first step, causing a reaction (hydration reaction) between the calcium-containing by-product and water to obtain a product containing calcium hydrate. This step corresponds to the "second step" in the method for producing a filler for asphalt mixtures of the present disclosure.

[0057] (3) The third step Next, the calcium hydrate-containing product obtained in the second step was placed in a cylindrical tube, and air was passed through it to react with CO2 in the air. Through this reaction, the calcium hydrate in the calcium hydrate-containing product reacted with CO2 to produce calcium carbonate (CaCO3), and a filler for asphalt mixtures according to the present disclosure containing the produced calcium carbonate was obtained. This step corresponds to the "third step" in the method for producing a filler for asphalt mixtures according to the present disclosure.

[0058] In this manner, the filler for asphalt mixtures of this example was produced.

[0059] [Examples 2 to 6: Production of filler for asphalt mixture] The fillers for asphalt mixtures of Examples 2 to 6 were produced using the same production method as in Example 1. The calcium-containing by-product obtained in the "first step" is calcined dust, as described above. Therefore, the composition, physical properties, etc. of the calcium-containing by-product vary depending on the production lot, and even within the same production lot, depending on the collection location. Therefore, even when fillers for asphalt mixtures are produced using the same production method, the composition, physical properties, etc. of the produced fillers for asphalt mixtures vary depending on the calcium-containing by-product used. The analysis results of the composition, physical properties, etc. of the fillers for asphalt mixtures will be described later.

[0060] In the hydration reaction (second step) and the carbonation reaction (third step) in Examples 1 to 6, reactions in aqueous solutions were not utilized.

[0061] [Reference example] A commercially available filler for asphalt mixtures (manufactured by Chichibu Sekki Kogyo Co., Ltd., trade name TA149) was used as the filler for asphalt mixtures in the reference example.

[0062] The analytical values ​​and physical properties of the fillers for asphalt mixtures produced in Examples 1, 2, and 3 and the fillers for asphalt mixtures were measured, and the results were as follows.

[0063] [Component analysis values] The compositions of the components of the fillers for asphalt mixtures produced in Examples 1, 2, and 3 were analyzed by semi-quantitative composition analysis using fluorescent X-ray analysis. The fluorescent X-ray analysis was carried out under the following conditions. The results are shown in Table 2 below. (Conditions for semi-quantitative composition analysis using X-ray fluorescence analysis) The measurement device used was a scanning X-ray fluorescence analyzer (product name: ZSX PrimusIV) manufactured by Rigaku Corporation. To prepare the sample, an appropriate amount of sample was dispensed into a vinyl chloride sample holder and pressed under a pressure of approximately 20 tons. The test method was to quantify elements from boron (5B) to uranium (92U) using semi-quantitative analysis.

[0064] [Table 2]

[0065] The calcium content as an element for the fillers for asphalt mixtures of Examples 1 to 3 shown in Table 2 was calculated and is shown in Table 3. In all cases, the calcium content as an element was 37 mass % or less.

[0066] [Table 3]

[0067] The fillers for asphalt mixtures of Examples 1 to 6 were tested for peeling resistance using the measurement method of Japan Road Association A0014 Stone Powder Peeling Resistance Test, and all of Examples 1 to 6 showed good results with a peeling resistance of 0%.

[0068] [Particle size D50] The particle diameter D50 (Median diameter) was measured using the following device and conditions. As a result, the particle diameter D50 of the filler for asphalt mixtures in Example 1 was 71.6 μm and in Example 2 was 55.75 μm. Equipment used: Microtrac MT3300EX laser diffraction particle size distribution analyzer manufactured by Microtrac Bell Measurement conditions: refractive index 1.66, particle shape non-spherical, solvent ethanol, ultrasonic irradiation time 30 seconds twice.

[0069] [Percentage of mass passing through sieve openings] For the filler for asphalt mixtures of Example 4, which was produced in the same manner as in Example 1, the mass percentage passing through a sieve with a mesh size of 600 μm, the mass percentage passing through a sieve with a mesh size of 150 μm, and the mass percentage passing through a sieve with a mesh size of 75 μm were measured, and the results were as shown in Table 4 below.

[0070] [Table 4]

[0071] [Color measurement results] The color of the fillers for asphalt mixtures of Examples 5 and 6, which were manufactured by the same manufacturing method as Example 1, was measured. The measurement was carried out using a spectrophotometer SE7700 (product name) manufactured by Nippon Denshoku Industries Co., Ltd., with reflection, light source / viewing field = C / 2, and filling into a Φ58 mm round cell. More specifically, the lightness index L according to CIE Lab was used. * , CIE Lab color coordinate a * , b * CIE Lab measured the L * The value of a * The value of b * and the whiteness W(L * a * b * The relationship between the values ​​of ( ) is given by the following formula: The results are shown in Table 5 below.

[0072]

number

[0073] [Table 5]

[0074] [Example 7: Asphalt mixture] An asphalt mixture was produced by mixing 0.057 kg of the filler for asphalt mixtures of Example 1, Example 2, or Reference Example, 0.601 kg of coarse aggregate (manufactured by Auris Co., Ltd., product name: No. 6 crushed stone, manufactured by Auris Co., Ltd., product name: No. 7 crushed stone), 0.476 kg of fine aggregate (manufactured by Auris Co., Ltd., product name: crushed sand, manufactured by Aoki Building Materials Industry Co., Ltd., product name: coarse sand, manufactured by Hokuso Kogyo Co., Ltd., product name: fine sand), and 0.066 kg of asphalt (manufactured by Idemitsu Kosan Co., Ltd., product name: Straight Asphalt 60 / 80). Similarly, an asphalt mixture was also produced in which 50 mass% of the filler for asphalt mixtures of the Reference Example was replaced with the filler for asphalt mixtures of Example 1 or Example 2. Furthermore, in a similar manner, an asphalt mixture was also produced in which only 50% by mass of the asphalt was replaced with recycled material (used asphalt mixture). The evaluation results (test results) of these physical property values ​​are summarized in Table 6 below. Of these asphalt mixtures, those containing the filler for asphalt mixtures of Example 1 or Example 2 as a filler correspond to the asphalt mixtures of the present disclosure. Furthermore, of these asphalt mixtures, those containing only the filler for asphalt mixtures of the Reference Example as a filler but not the filler for asphalt mixtures of the Examples correspond to the asphalt mixtures of the Reference Example.

[0075] In Table 6 below, the Marshall stability test was conducted by submerging the test piece in water at 60°C for 30 minutes. In the residual stability test, the test piece was submerged in water at 60°C for 48 hours, and the strength after immersion for 30 minutes was compared with the strength after immersion for 48 hours to evaluate water resistance.

[0076] [Table 6]

[0077] As can be seen from Table 6, all of the asphalt mixtures of the Examples and Reference Examples exhibited good physical property values ​​that met the standard values. As can be seen from this, it was confirmed that the asphalt mixture filler of the present disclosure exhibits good properties comparable to those of general asphalt mixture fillers.

[0078] The present disclosure can be described, for example, as in the following supplementary notes: However, the supplementary notes below are examples, and the present disclosure is not limited to these forms.

[0079] (Appendix 1) A filler for asphalt mixtures, characterized in that the content of elemental calcium is 37 mass % or less and the filler satisfies at least one condition selected from the group consisting of the following conditions (1) to (4): (1) The particle diameter D50 of the filler for asphalt mixture exceeds 20 μm. (2) The filler for asphalt mixtures has a mass percentage passing through a sieve with a mesh size of 600 μm of 70% or more, a mass percentage passing through a sieve with a mesh size of 150 μm of 45% or more, and a mass percentage passing through a sieve with a mesh size of 75 μm of 30% or more. (3) The whiteness W (L * a * b * ) is less than 95. (4) The CIE Lab lightness index L of the asphalt mixture filler * is less than 95. (Appendix 2) 2. The asphalt mixture filler of claim 1, comprising calcium carbonate. (Appendix 3) A filler for asphalt mixtures according to appendix 1 or 2, in which CO2 is fixed. (Appendix 4) The asphalt mixture filler according to any one of Appendixes 1 to 3, wherein the color of the asphalt mixture filler is any one of the colors selected from the group consisting of sand, chalk, natural, ivory, silver gray, brown gray, gray, Rikyu gray, lead, gray, soot bamboo, dark brown, ink, black, iron black, silver, ivory, sky gray, pearl gray, silver gray, ash gray, rose gray, gray, steel gray, straight gray, charcoal gray, lamp black, and black, as defined in Appendix 1 of Japanese Industrial Standards (JIS) Z 8102:2001 (Color names of objects), and colors modified by the terms "light," "strong," "dark," "light," "light gray," "gray," "dark gray," "very dark," or "medium." (Appendix 5) A first step of obtaining a calcium-containing by-product from a calcination process for producing quicklime; a second step of reacting the calcium-containing by-product content with water to obtain a calcium hydrate content; and a third step of reacting the calcium hydrate-containing material with CO2 to obtain a calcium carbonate-containing material, thereby fixing the CO2. (Appendix 6) 6. The manufacturing method according to claim 5, wherein the filler for asphalt mixtures manufactured is a filler for asphalt mixtures manufactured according to any one of claims 1 to 4. (Appendix 7) A filler for asphalt mixtures produced by the production method described in Appendix 5 or 6. (Appendix 8) An asphalt mixture comprising the filler for asphalt mixtures according to any one of appendices 1 to 4 and 7, and asphalt. [Industrial Applicability]

[0080] As explained above, according to the present disclosure, it is possible to provide a filler for asphalt mixtures, a method for producing a filler for asphalt mixtures, and an asphalt mixture that can contribute to reducing CO2 in the natural environment.In addition to being able to contribute to reducing CO2 in the natural environment, the filler for asphalt mixtures, a method for producing a filler for asphalt mixtures, and an asphalt mixture of the present disclosure can be used for all the same applications as general asphalt, and therefore have great industrial utility value.

Claims

1. A filler for asphalt mixtures, characterized in that the content of calcium as an element is 37 mass% or less and satisfies at least one condition selected from the group consisting of the following conditions (1) to (4): (1) The particle diameter D50 of the filler for asphalt mixture exceeds 20 μm. (2) The filler for asphalt mixtures has a mass percentage passing through a sieve with a mesh size of 600 μm of 70% or more, a mass percentage passing through a sieve with a mesh size of 150 μm of 45% or more, and a mass percentage passing through a sieve with a mesh size of 75 μm of 30% or more. (3) The whiteness W (L) of the asphalt mixture filler according to CIE Lab ＊ a ＊ b ＊ ) is less than 95. (4) The CIE Lab lightness index L of the asphalt mixture filler ＊ is less than 95.

2. 2. The filler for asphalt mixtures according to claim 1, which contains calcium carbonate.

3. CO ２ 2. The filler for asphalt mixtures according to claim 1, wherein the above-mentioned is fixed.

4. The color of the asphalt mixture filler is any one of the colors specified in Appendix 1 of Japanese Industrial Standards (JIS) Z 8102:2001 (Color Names of Object Colors), including sand, chalk, natural, ivory, silver gray, brown gray, gray, Rikyu gray, lead, gray, soot bamboo, black tea, ink, black, iron black, silver, ivory, sky gray, pearl gray, silver gray, ash gray, rose gray, gray, steel gray, straight gray, charcoal gray, lamp black, and black, as well as any of these colors modified with the terms "light," "strong," "dark," "light," "soft," "dull," "dark," "very light," "light grayish," "grayish," "dark grayish," "very dark," or "medium." The asphalt mixture filler according to claim 1,

5. a first step of obtaining a calcium-containing by-product from a calcination process for producing quicklime; a second step of reacting the calcium-containing by-product content with water to obtain a calcium hydrate content; The calcium hydrate content and CO ２ and reacting the CO ２ and a third step of fixing the filler for asphalt mixtures.

6. The method according to claim 5, wherein the filler for asphalt mixtures produced is the filler for asphalt mixtures according to any one of claims 1 to 4.

7. An asphalt mixture comprising the filler for asphalt mixtures according to any one of claims 1 to 4 and asphalt.

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