Asphalt mixture manufacturing method, asphalt mixture manufacturing plant, and carbon dioxide fixation agent

Abstract

The present invention provides a method for producing an asphalt mixture that effectively utilizes fixed carbon dioxide. [Solution] This is a method for producing an asphalt mixture, which includes an aggregate heating step, an aggregate transporting step, and a mixing step, and in at least one of the aggregate heating step, aggregate transporting step, and mixing step, the step is carried out in the presence of calcium hydroxide and carbon dioxide, thereby generating calcium carbonate through a reaction between calcium hydroxide and carbon dioxide, and immobilizing the carbon dioxide, and in the mixing step, mixing the generated calcium carbonate as a filler with aggregate and asphalt.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing an asphalt mixture, an asphalt mixture production plant, and a carbon dioxide fixation agent. [Background technology]

[0002] In view of the need to capture carbon dioxide in the atmosphere and exhaust gases, Patent Documents 1 and 2 disclose techniques for solidifying carbon dioxide in the production of asphalt mixtures. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-162682 [Patent Document 2] Japanese Patent Application Publication No. 2023-134985 Summary of the Invention [Problem to be solved by the invention]

[0004] The techniques of Prior Art Document 1 and Patent Document 2 have a problem in that they do not effectively utilize the fixed carbon dioxide.

[0005] Therefore, an object of the present disclosure is to provide a method for producing an asphalt mixture, an asphalt mixture production plant, and a carbon dioxide fixation agent that can effectively utilize fixed carbon dioxide. [Means for solving the problem]

[0006] In order to achieve the above object, the method for producing an asphalt mixture of the present disclosure comprises: The method includes an aggregate heating step, an aggregate conveying step, and a mixing step, The aggregate heating step is a step of heating aggregate, The aggregate transporting step is a step of transporting the heated aggregate to the mixing step, The mixing step is a step of mixing the aggregate, asphalt, and filler, At least one of the aggregate heating step, the aggregate transporting step, and the mixing step is carried out in the presence of calcium hydroxide and carbon dioxide, whereby calcium carbonate is produced by a reaction between the calcium hydroxide and carbon dioxide, and the carbon dioxide is immobilized; In the mixing step, the produced calcium carbonate is mixed as the filler with the aggregate and the asphalt. The manufacturing method.

[0007] The asphalt mixture manufacturing plant of the present disclosure comprises: The apparatus includes an aggregate heating section, an aggregate conveying section, and a mixing section, In the aggregate heating section, a step of heating the aggregate is carried out, In the aggregate transport section, a step of transporting the heated aggregate to the mixing section is carried out. In the mixing section, a step of mixing the aggregate, asphalt, and filler is carried out, In at least one of the aggregate heating section, the aggregate transport section, and the mixing section, each of the steps is carried out in the presence of calcium hydroxide and carbon dioxide, whereby calcium carbonate is produced by a reaction between the calcium hydroxide and carbon dioxide, and the carbon dioxide is immobilized; In the mixing section, the step of mixing the produced calcium carbonate as the filler with the aggregate and the asphalt is carried out. It is a manufacturing plant.

[0008] The carbon dioxide fixation agent of the present disclosure is a carbon dioxide fixation agent used in the method for producing an asphalt mixture of the present disclosure, The calcium hydroxide is included. It is a carbon dioxide fixation agent. [Effects of the Invention]

[0009] According to the present disclosure, immobilized carbon dioxide can be effectively utilized. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a configuration diagram showing an example of an asphalt mixture manufacturing plant according to the present disclosure. [Figure 2] FIG. 2 is a graph showing an example of carbon dioxide fixation according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] The asphalt mixture manufacturing method of the present disclosure further comprises a combustion step, The combustion process may be a process of burning fuel to generate heat, and the heat generated in the combustion process may be used to perform heating in at least the aggregate heating process, and carbon dioxide generated by the combustion in the combustion process may be used as the carbon dioxide in the reaction. In this embodiment, the number of the combustion steps may be one or more. In addition, the steps heated by the heat generated in the combustion step may be not only the aggregate heating step but also other steps such as the aggregate transport step, the mixing step, and the step of heating the asphalt before mixing.

[0012] The asphalt mixture manufacturing plant of the present disclosure may further include a combustion section and a gas delivery section, wherein a process of burning fuel to generate heat is carried out in the combustion section, a process of heating the aggregate in at least the aggregate heating section with the heat generated in the combustion section is carried out, and carbon dioxide generated by the combustion in the combustion section is delivered by the gas delivery section to at least one of the aggregate heating section, the aggregate transport section, and the mixing section where the reaction is carried out, and used as the carbon dioxide in the reaction. In this embodiment, the number of the combustion section and the gas supply section may be one or more. Furthermore, the section heated by the heat generated by combustion in the combustion section may be not only the aggregate heating section, but also other sections, such as the aggregate transport section, the mixing section, and a heating process for asphalt before mixing.

[0013] In the present disclosure, the reaction may be carried out in the presence of moisture. For example, water may be sprinkled or sprayed as the moisture at the location where carbon dioxide is immobilized. The moisture may also be moisture contained in the aggregate, such as moisture contained in sand.

[0014] In the present disclosure, the calcium hydroxide is not particularly limited and may be, for example, slaked lime, sludge (waste) of concrete, etc. The fixation reaction of carbon dioxide by calcium hydroxide is according to the following chemical reaction formula. Ca(OH)2+CO2→CaCO3+H2O

[0015] The slaked lime may be industrial slaked lime or highly reactive slaked lime for removing HCl and SOx from exhaust gas. Highly reactive slaked lime has a larger specific surface area and pore volume than ordinary slaked lime.

[0016] Furthermore, calcium hydroxide contained in waste materials, such as calcium hydroxide in sludge, may be used as the calcium hydroxide. Examples of sludge include concrete sludge.

[0017] Ready-mixed concrete plants produce cement-containing leftover concrete that is produced in excess of the ordered amount and not shipped, returned concrete that is not used by the supplier and returned, and dissolved products of these, as well as cleaning wastewater generated from cleaning equipment such as mixer trucks. In this disclosure, the ready-mixed concrete sludge produced in ready-mixed concrete plants can be used as calcium hydroxide.

[0018] Ready-mixed concrete sludge usually contains water, calcium components such as calcium hydroxide that dissolves in water, and sludge solids (mainly hydration products, aggregate fine particles, etc. (mainly metals such as silica, aluminum, and iron, and their inclusions, as well as calcium carbonate)). The solids are sometimes removed from the ready-mixed concrete sludge, and the sludge is separated into supernatant water containing calcium hydroxide and sludge water containing sludge solids (mainly hydration products, aggregate fine particles, etc.). In this case, both the supernatant water and the sludge water can be used as calcium hydroxide.

[0019] Regardless of whether the fresh concrete sludge water used as calcium hydroxide is the above-mentioned supernatant water or sludge water, the solids concentration in the fresh concrete sludge water is preferably 40 mass% or less, more preferably 20 mass% or less, even more preferably 10 mass% or less, and still more preferably 5 mass% or less.

[0020] As mentioned above, calcium hydroxide is present in the form of dissolved calcium hydroxide in ready-mixed concrete sludge water, but calcium hydroxide also exists as a solid due to its low solubility. Calcium also includes calcium carbonate and the like, which are present primarily as solids. Thus, ready-mixed concrete sludge water contains calcium hydroxide, calcium carbonate, and other calcium components as solids, as well as the solid components of the sludge (mainly including hydration products, aggregate particles, etc.), as mentioned above. These solid components, particularly calcium hydroxide contained as calcium, react with carbon dioxide to form calcium carbonate. Calcium carbonate contained in ready-mixed concrete sludge water can be used as a filler in the present disclosure.

[0021] From the viewpoint of promoting the production of calcium carbonate, the solids concentration in the fresh concrete sludge water is preferably 0.001 mass % or more, more preferably 0.0015 mass % or more, and even more preferably 0.002 mass % or more. From the same viewpoint, the particle size of the solid content in the fresh concrete sludge water is preferably 1000 μm or less, more preferably 100 μm or less, even more preferably 10 μm or less, still more preferably 1 μm or less, and particularly preferably 0.1 μm or less.

[0022] When the fresh concrete sludge water is the above-mentioned supernatant water, the calcium concentration contained in the fresh concrete sludge water is usually 100 mg / L or more, preferably 250 mg / L or more, more preferably 500 mg / L or more, and even more preferably 800 mg / L or more. The upper limit is preferably as high as possible, and is not particularly limited, but is usually 1500 mg / L or less. Furthermore, when the ready-mixed concrete sludge water is the above-mentioned sludge water, the calcium concentration contained in the ready-mixed concrete sludge water is usually 1,000 mg / L or more, preferably 10,000 mg / L or more, more preferably 100,000 mg / L or more, and even more preferably 300,000 mg / L or more. The upper limit is preferably as high as possible, and is not particularly limited, but is usually 3,000,000 mg / L or less.

[0023] Furthermore, the ready-mixed concrete sludge water can be obtained by removing the solids from a mixture of the above solids obtained from ready-mixed concrete sludge and water. The solids include calcium components such as calcium hydroxide, and the hydration products mainly contained in the solids include calcium hydroxide, calcium silicate hydrate, and other calcium components. Therefore, the mixture obtained by removing the solids still contains calcium that has dissolved from the solids into the water, making it possible to convert more calcium from the ready-mixed concrete sludge into calcium carbonate.

[0024] In the present disclosure, aggregate may be either new aggregate or recycled aggregate. For example, new aggregates include crushed stone, gravel, and sand. Recycled aggregates include recycled aggregates made from construction waste. Examples of the construction waste include asphalt pavement waste dug up during road construction and concrete waste (crushed stone) from demolished buildings.

[0025] Examples of crushed stone include single-grain crushed stone (No. 1 to No. 7), crusher run (C-20 to C-40), and adjusted-grain crushed stone (M-25 to M-40) as specified in JIS A5001:2008. Standardized products include crushed stone for concrete as specified in JIS A5005:2020. It is also possible to use non-standard crushed stone that is equivalent to these crushed stones.

[0026] Crushed sand includes, for example, crushed sand for concrete specified in JIS A5005: 2020. It is also possible to use non-standard crushed sand that is equivalent to crushed sand.

[0027] Examples of recycled aggregate include recycled aggregates for concrete H, M, and L, as specified in JIS A5021:2018, JIS A5022:2018, and JIS A5023:2018. It is also possible to use non-standard recycled aggregates that are equivalent to these recycled aggregates as recycled aggregate.

[0028] Examples of recycled crushed stone include the above-mentioned crushed stone, recycled crushed stone (for example, RC-40, etc.) using recycled material of particle-size-adjusted crushed stone, and recycled particle-size-adjusted crushed stone (for example, RM-30, etc.).

[0029] In the present disclosure, the filler is a fine particle aggregate, e.g., fine particles that pass through a 75 μm sieve. Examples of fillers include stone powder made from powdered limestone and igneous rock, hydrated lime, cement, and fly ash. The main component of stone powder is calcium carbonate, and in the present disclosure, calcium carbonate produced by fixing carbon dioxide can be used as a filler.

[0030] Next, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments. In the following drawings, the same parts are denoted by the same reference numerals. Furthermore, the descriptions of the embodiments can be mutually incorporated unless otherwise specified, and the configurations of the embodiments can be combined unless otherwise specified.

[0031] [Embodiment 1] FIG. 1 shows an example of the configuration of an asphalt mixture manufacturing plant according to the present disclosure. As shown in FIG. 1, the manufacturing plant of this example has as its main components a new aggregate dryer 11a, a recycled aggregate dryer 11b, a burner 15a, a burner 15b, a hot elevator 12, a mixer 13, a classifier 14, a filler hopper 16a, an asphalt storage tank 16b, a dust collection filter 17, and a chimney 18. The new aggregate dryer 11a and the burner 15a, and the recycled aggregate dryer 11b and the burner 15b, respectively, constitute two aggregate heating sections. The hot elevator is an aggregate transport section that transports heat-treated new aggregate to the classifier 14. Heat-treated recycled aggregate is also transported to the classifier 14 by an aggregate transport section (not shown). The mixer 13 is a mixing section that mixes aggregate supplied from the classifier 14, filler supplied from a filler hopper 16a, and asphalt supplied from an asphalt storage tank 16b. A portion of the exhaust gas discharged from the burner 15a is introduced into the new aggregate dryer 11a, and the other portion passes through a dust collection filter 17 and is discharged from a chimney 18. Similarly, a portion of the exhaust gas discharged from the burner 15b is introduced into the recycled aggregate dryer 11b by the exhaust gas section (indicated by an arrow in FIG. 1), and the other portion passes through a dust collection filter 17 and is discharged from a chimney 18. The exhaust gases from the new aggregate dryer 11a and the recycled aggregate dryer 11b also pass through a dust collection filter 17 and are discharged from a chimney 18.

[0032] In the manufacturing plant of this example, the production of an asphalt mixture is carried out, for example, as follows. First, new aggregate (crushed stone, gravel, sand, etc.) and calcium hydroxide (slaked lime, etc.) are charged into new aggregate dryer 11a and heated by burner 15a. At this time, exhaust gas from burner 15a is introduced into new aggregate dryer 11a. Inside new aggregate dryer 11a, the new aggregate is dried by heating, and carbon dioxide in the exhaust gas reacts with calcium hydroxide to produce calcium carbonate. The calcium carbonate produced in new aggregate dryer 11a is supplied to classifier 14 together with the dried new aggregate by hot elevator 12. Next, recycled aggregate and calcium hydroxide (slaked lime, etc.) are charged into recycled aggregate dryer 11b and heated by burner 15b. At this time, exhaust gas from burner 15b is introduced into recycled aggregate dryer 11b. Inside the recycled aggregate dryer 11b, the recycled aggregate is dried by heating, and carbon dioxide in the exhaust gas reacts with calcium hydroxide to produce calcium carbonate. The calcium carbonate produced in the new aggregate dryer 11b is supplied to a classifier 14 together with the dried recycled aggregate by an aggregate conveying unit (not shown). The new aggregate, recycled aggregate, and calcium carbonate supplied to the classifier 14 are classified and then supplied to a mixer 13. Filler (stone powder, etc.) is supplied to the mixer 13 from a filler hopper 16a as needed. Asphalt is supplied to the mixer 13 from an asphalt storage tank 16b. In the mixer 13, the new aggregate, recycled aggregate, calcium carbonate (filler), and asphalt are mixed to produce an asphalt mixture. The produced asphalt mixture is loaded onto a dump truck and delivered to a road construction site, etc. The exhaust gas from the burners 15a and 15b passes through a dust collection filter 17 and is released into the atmosphere through a chimney 18, but the exhaust gas has carbon dioxide recovered from it.

[0033] In the present disclosure, the method of adding calcium hydroxide is not particularly limited, and may be, for example, added manually or automatically using a machine. Furthermore, when added in a state of being dispersed in water, it may be added by sprinkling or spraying.

[0034] In the present disclosure, the carbon dioxide to be immobilized is not particularly limited, and may be, for example, carbon dioxide generated during combustion in a burner or carbon dioxide in the atmosphere.

[0035] In the present disclosure, the location where carbon dioxide is fixed is not particularly limited, and may be any of the aggregate heating section, aggregate transport section, and mixing section, or may be fixed at a location other than these.

[0036] [Embodiment 2] This embodiment is an experimental example in which carbon dioxide is immobilized using calcium hydroxide.

[0037] A carbon dioxide measuring device and a calcium hydroxide sample were placed in a plastic bag and the bag was then sealed. Three types of samples were used: fresh concrete sludge, industrial hydrated lime, and highly reactive hydrated lime. Air was removed from the sealed plastic bag using a syringe. A carbon dioxide-containing gas was introduced into the air-removed plastic bag. The carbon dioxide-containing gas had a carbon dioxide gas concentration of 3 vol% and a nitrogen gas concentration of 97 vol%. The plastic bag with the carbon dioxide-containing gas introduced was placed in a shaker and shaken at a shaking amplitude of 50 mm and 200 rpm, and the carbon dioxide concentration inside the plastic bag was measured. The results are shown in the graph in Figure 2.

[0038] In Figure 2, graph A shows sludge, graph B shows industrial slaked lime, and graph C shows highly reactive slaked lime. As shown in the graphs in Figure 2, the carbon dioxide concentration decreased over time in all three types of samples, confirming the fixation of carbon dioxide by the sample. When highly reactive slaked lime was used as the sample, the carbon dioxide concentration decreased rapidly. Furthermore, a decrease in carbon dioxide concentration was confirmed even when sludge was used as the sample. Meanwhile, the generation of calcium carbonate was confirmed in all samples.

[0039] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate. [Industrial Applicability]

[0040] According to the present disclosure, immobilized carbon dioxide can be effectively utilized as a filler for asphalt mixtures. According to the present disclosure, for example, by making simple improvements to existing asphalt mixture manufacturing plants, it is possible to fix and effectively utilize carbon dioxide. According to the present disclosure, for example, it is possible to fix carbon dioxide generated in asphalt mixture manufacturing plants, and further, it is possible to fix and effectively utilize carbon dioxide in the atmosphere and carbon dioxide contained in exhaust gases from other factories. Therefore, the asphalt mixture manufacturing method and the like disclosed herein are useful, for example, for reducing carbon dioxide emissions and making effective use of resources. [Explanation of symbols]

[0041] 1. Asphalt mixture manufacturing plant 11a New aggregate dryer 11b Recycled aggregate dryer 12 Hot Elevator 13 Mixer 14 Classifier 15a, 15b burner 16a Filler hopper 16b Asphalt storage tank 17 Dust collection filter 18 Chimney

Claims

1. The process includes an aggregate heating process, an aggregate transport process, a mixing process, and a combustion process. The aggregate heating step is a step of heating aggregate, The aggregate transporting step is a step of transporting the heated aggregate to the mixing step, The mixing step is a step of mixing the aggregate, asphalt, and fine aggregate, In the aggregate heating step, calcium hydroxide is added and the step is carried out in the presence of carbon dioxide, whereby calcium carbonate is produced by a reaction between the calcium hydroxide and carbon dioxide, and the carbon dioxide is immobilized; The combustion step is a step of burning fuel to generate heat, Heating is performed at least in the aggregate heating step using the heat generated in the combustion step, Carbon dioxide generated by the combustion in the combustion step is used as the carbon dioxide in the reaction, In the mixing step, the produced calcium carbonate is mixed as a filler with the aggregate, the asphalt, and the fine particle aggregate. Method for manufacturing asphalt mixture.

2. The method for producing an asphalt mixture according to claim 1, wherein the reaction is carried out in the presence of water.

3. The method for producing an asphalt mixture according to claim 2, wherein the water content is water contained in the aggregate.

4. The calcium hydroxide is slaked lime. A method for producing the asphalt mixture according to claim 1.

5. The system includes an aggregate heating section, an aggregate transport section, a mixing section, and a combustion section. In the aggregate heating section, a step of heating the aggregate is carried out, In the aggregate transport section, a step of transporting the heated aggregate to the mixing section is carried out. In the mixing section, a step of mixing the aggregate, asphalt, and fine aggregate is carried out, In the aggregate heating section, calcium hydroxide is introduced, and the above steps are carried out in the presence of carbon dioxide, whereby calcium carbonate is produced by a reaction between the calcium hydroxide and carbon dioxide, and the carbon dioxide is immobilized. In the combustion section, a step of burning fuel to generate heat is carried out, a step of heating the aggregate in at least the aggregate heating section with the heat generated in the combustion section is carried out; Carbon dioxide generated by the combustion in the combustion section is used as the carbon dioxide in the reaction, In the mixing section, the step of mixing the produced calcium carbonate as a filler with the aggregate, the asphalt, and the fine particle aggregate is carried out. Asphalt mixture manufacturing plant.

6. Further, the gas delivery unit is included. The gas sending section sends carbon dioxide generated by the combustion in the combustion section to the aggregate heating section where the reaction is carried out, and the carbon dioxide is used as the carbon dioxide in the reaction. A plant for producing the asphalt mixture according to claim 5.

7. The reaction is carried out in the presence of moisture. A plant for producing the asphalt mixture according to claim 5.

8. The moisture is the moisture contained in the aggregate. A plant for producing the asphalt mixture according to claim 7.

9. The calcium hydroxide is slaked lime. A plant for producing the asphalt mixture according to claim 5.

10. A carbon dioxide fixative used in the method for producing an asphalt mixture according to claim 1, A carbon dioxide fixation agent comprising the calcium hydroxide.

11. The calcium hydroxide includes slaked lime. The carbon dioxide fixation agent according to claim 10.

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