Method of manufacturing recycled asphalt mixture

Abstract

To provide a method of manufacturing a recycled asphalt mixture which can be implemented with no problems in terms of the environment or safety, can be manufactured without deteriorating productivity of an existing plant, and can secure sufficient quality even if a large amount of a recycled aggregate is used.SOLUTION: A method of manufacturing a recycled asphalt mixture includes a mixing step for mixing a new aggregate, a recycled aggregate, a foamed recycling additive and foamed asphalt.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a recycled asphalt mixture. [Background technology]

[0002] Asphalt pavement uses an asphalt mixture made by mixing aggregates such as crushed stone and sand with asphalt as a binder.

[0003] Conventionally, recycled aggregate has been produced by crushing and reusing waste asphalt mixtures used in the surface and base layers of asphalt pavements. This recycled aggregate is used as a material for asphalt mixtures, and is widely used in asphalt pavement construction by mixing it with new asphalt and new aggregate to produce asphalt mixtures.

[0004] However, recycled aggregate is made from old aggregate that has been discarded and is coated with old asphalt, and repeated recycling of this recycled aggregate causes the old asphalt to deteriorate due to reheating during production and ultraviolet rays during use, leading to an increase in recycled aggregate of inferior quality in recent years. This creates a problem of reduced performance for recycled asphalt mixtures made with recycled aggregate.

[0005] Therefore, it is known to include a recycling additive in the recycled asphalt mixture in order to restore the properties of the old asphalt attached to the recycled aggregate.

[0006] Recycled asphalt mixtures using recycled additives are produced by putting heated recycled aggregate, heated new aggregate, recycled additives, new asphalt, etc. into a mixer and stirring and mixing them.

[0007] Patent Document 1 discloses a method for producing such recycled asphalt mixtures, in which a recycling additive is added to and mixed with heated recycled aggregate, and then mixed with new aggregate and new asphalt. According to this method for producing asphalt mixtures, the recycling additive is added only to the recycled aggregate, and the entire amount of the recycling additive is mixed into the recycled aggregate, which is expected to effectively restore the properties of the old asphalt contained in the recycled aggregate and enable the production of high-quality recycled asphalt mixtures.

[0008] Patent Document 2 discloses a method for producing such a recycled asphalt mixture, in which a recycled additive is added to recycled aggregate, the recycled aggregate containing the recycled additive is cured, and then the cured recycled aggregate is mixed with new aggregate, new asphalt, etc.

[0009] Patent Document 3 discloses diffusing and spraying a slightly foamed recycling additive onto recycled aggregate. According to Patent Document 3, diffusing and spraying a slightly foamed recycling additive onto recycled aggregate promotes the improvement of the old asphalt contained in the recycled aggregate, making it possible to produce a high-quality recycled asphalt mixture. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-100996 [Patent Document 2] Japanese Patent Application Publication No. 2020-037798 [Patent Document 3] Patent Publication No. 2021-080743 Summary of the Invention [Problem to be solved by the invention]

[0011] The method described in Patent Document 1 requires a long mixing time, which reduces productivity when produced in an existing plant. Furthermore, the method described in Patent Document 2 may be difficult to implement in an existing plant due to environmental and safety considerations during curing, depending on the type of recycling additive. It has been found that the method described in Patent Document 3 may result in insufficient penetration of the recycling additive into the recycled aggregate when a large amount of recycled aggregate is used.

[0012] Therefore, the present invention provides a method for producing recycled asphalt mixtures that is environmentally and safety-friendly, can be produced without reducing the productivity of existing plants, and can ensure sufficient quality even when a large amount of recycled aggregate is used. [Means for solving the problem]

[0013] The present inventors have discovered that the above-mentioned problems can be solved by a method for producing a recycled asphalt mixture having the following features.

[0014] That is, the present invention has the following aspects: <<Aspect 1>> A method for producing a recycled asphalt mixture, comprising a mixing step of mixing new aggregate, recycled aggregate, foamed recycling additive, and foamed asphalt. <<Aspect 2>> The mixing step a first mixing step of mixing the recycled aggregate and the foamed recycling additive to obtain a first mixture; a second mixing step of mixing the first mixture with the new aggregate to obtain a second mixture; and A third mixing step in which the second mixture is mixed with the expanded asphalt to obtain a recycled asphalt mixture. 2. A method for producing an asphalt mixture according to claim 1, comprising: Aspect 3 The method for producing an asphalt mixture according to aspect 1, wherein the foamed regenerating additive is metered by a flow meter provided in a pipe. Aspect 4 The method for producing an asphalt mixture according to aspect 3, wherein the foamed regenerating additive is foamed by a foaming device, and the foaming device includes an in-line mixer on a downstream side of a pipe. Aspect 5 The method for producing an asphalt mixture according to aspect 1, wherein the rejuvenating additive is a mineral oil-based or vegetable oil-based rejuvenating additive. Aspect 6 A method for producing a recycled asphalt mixture according to aspect 1, wherein the mixing step further comprises mixing a workability improving agent containing a glycol ether compound or a fatty acid compound. Aspect 7 A method for producing a recycled asphalt mixture according to aspect 6, wherein recycled aggregate is used in an amount of 70% by mass or more based on the total amount of aggregate used. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for producing recycled asphalt mixtures that is environmentally and safety-friendly, can be produced without reducing the productivity of existing plants, and can ensure sufficient quality even when a large amount of recycled aggregate is used. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 illustrates one embodiment of a method for producing a recycled asphalt mixture. [Figure 2] Figure 2 shows a schematic diagram of a part of the recycled asphalt mixture manufacturing equipment. DETAILED DESCRIPTION OF THE INVENTION

[0017] <<Method for manufacturing asphalt mixture>> The method for producing an asphalt mixture of the present invention includes a mixing step of mixing new aggregate, recycled aggregate, a foamed regenerating additive, and foamed asphalt.

[0018] When a large amount of recycled aggregate is used, the amount of old asphalt adhering to the recycled aggregate increases, requiring time for the recycled additive to penetrate the recycled aggregate. However, with this manufacturing method, the recycled additive quickly penetrates the old asphalt in the recycled aggregate, allowing for highly productive production of asphalt mixtures. Furthermore, when a large amount of recycled aggregate is used, the amount of old asphalt increases, necessitating the addition of less new asphalt. In this case, it takes time to evenly adhere the new asphalt to the aggregate. In contrast, with this manufacturing method, the new asphalt is foamed and mixed, allowing for early and uniform adhesion of the new asphalt to the aggregate. Thus, by foaming and mixing both the recycled additive and asphalt, it has been found possible to provide a method for manufacturing recycled asphalt mixtures that can be produced without reducing the productivity of existing plants, even when a large amount of recycled aggregate is used, while still ensuring sufficient quality.

[0019] In the manufacturing method of the present invention, when a small amount of recycled aggregate is used, a recycled asphalt mixture of sufficient quality can be obtained even if the mixing time is shortened, thereby improving the productivity of existing plants.

[0020] Recycled asphalt mixtures are more prone to cracking than asphalt mixtures made with only virgin asphalt, and improvements in this area have been sought, but the recycled asphalt mixtures obtained using the method of this invention have been shown to offer exactly this improvement. Furthermore, with this manufacturing method, regardless of the type of recycling additive used, the recycling additive is handled entirely within the plant, allowing production in existing plants without any environmental or safety issues.

[0021] Preferably, the method for producing a recycled asphalt mixture includes a first mixing step in which heated recycled aggregate and a foamed regenerating additive are mixed to obtain a first mixture, a second mixing step in which the first mixture is mixed with new aggregate to obtain a second mixture, and a third mixing step in which the second mixture is mixed with foamed new asphalt to obtain a recycled asphalt mixture. Here, the first to third mixing steps can be performed in the same mixer. Furthermore, the total time for the first and second mixing steps can be longer than the time for the third mixing step. Furthermore, the third mixing step can be performed within 40 seconds.

[0022] By mixing the recycled aggregate with a foamed recycling additive before mixing the new aggregate with the recycled aggregate, the recycling additive can be effectively absorbed into the old asphalt adhering to the recycled aggregate. This is particularly advantageous when a large amount of recycled aggregate is used. However, if this were to be done in the same mixer at an existing plant using the same mixing time as the existing method, the total mixing time would be extremely long. If the mixing time in the mixer, which is the final process, were to be long, the asphalt mixture production capacity of the existing plant would be correspondingly reduced. Furthermore, since equipment other than the mixer is designed to match the production capacity of the existing plant, the longer mixing time in the mixer would also reduce the operating rate of the other equipment, resulting in an inefficient plant.

[0023] In response to this, by changing the mixing times for the first mixing step, in which heated recycled aggregate is mixed with foamed recycling additives, the second mixing step, in which the first mixture is mixed with new aggregate, and the third mixing step, in which the second mixture is mixed with foamed new asphalt, it is possible to provide a method for producing recycled asphalt mixtures that can be produced without reducing the productivity of existing plants and that can ensure sufficient quality, even when a large amount of recycled aggregate is used.

[0024] The first mixing step of mixing the recycled aggregate with the foamed recycling additive can be carried out for 60 seconds or less, 50 seconds or less, 40 seconds or less, 35 seconds or less, or 30 seconds or less, or for 10 seconds or more, 15 seconds or more, 20 seconds or more, or 25 seconds or more. For example, the first mixing step can be carried out for 10 seconds or more to 60 seconds or less, 15 seconds or more to 50 seconds or less, 20 seconds or more to 40 seconds or less, or 25 seconds or more to 35 seconds.

[0025] The second mixing step in which the first mixture obtained in the first mixing step is mixed with new aggregate can be carried out within 20 seconds, 15 seconds, 12 seconds, or 10 seconds, or can be carried out for 3 seconds or more, 5 seconds or more, 8 seconds or more, or 10 seconds or more. For example, the second mixing step can be carried out within a range of 3 to 20 seconds, 5 to 15 seconds, or 8 to 12 seconds.

[0026] The first and second mixing steps can be performed for a total of 80 seconds or less, 70 seconds or less, 60 seconds or less, 50 seconds or less, 45 seconds or less, or 40 seconds or less, and can be performed for 15 seconds or more, 20 seconds or more, 25 seconds or more, or 30 seconds or more. For example, the dry mixing step can be performed for 15 seconds or more and 80 seconds or less, 20 seconds or more and 70 seconds or more, 25 seconds or more and 55 seconds or more, or 35 seconds or more and 45 seconds or less.

[0027] The ratio of the mixing time of the second mixing step to the first mixing step (second mixing step / first mixing step) can be 0.10 or more, 0.20 or more, or 0.30 or more, and can be 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. For example, this mixing time ratio can be 0.10 or more and 0.70 or less, 0.20 or more and 0.50 or less, or 0.30 or more and 0.40 or less.

[0028] The method for producing a recycled asphalt mixture can include a wet mixing step in which the mixture obtained in the dry mixing step is mixed with measured and foamed new asphalt. This dry mixing step corresponds to the first and second mixing steps in the above production method, and the wet mixing step corresponds to the third mixing step in the above production method.

[0029] The wet mixing step has traditionally been thought to require a time longer than 40 seconds, but in the manufacturing method of the present invention, the inventors have discovered that there is no problem even if the wet mixing time is 40 seconds or less.

[0030] The third mixing step, in which the second mixture obtained in the second mixing step is mixed with the foamed new asphalt, can be carried out for 40 seconds or less, 35 seconds or less, 30 seconds or less, or 25 seconds or less, or for 10 seconds or more, 15 seconds or more, 20 seconds or more, 22 seconds or more, or 25 seconds or more. For example, the third mixing step can be carried out for 10 seconds or more and 40 seconds or less, 15 seconds or more and 35 seconds or more, or 20 seconds or more and 30 seconds or more.

[0031] The ratio of the mixing time of the third mixing step to the total mixing time of the first and second mixing steps (third mixing step / first and second mixing steps) can be 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and can be 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, or 0.70 or less. For example, this mixing time ratio can be 0.20 or more and 0.90 or less, 0.30 or more and 0.85 or less, or 0.40 or more and 0.70 or less.

[0032] These mixing steps can be carried out when the recycled asphalt mixture is at a temperature of, for example, 80°C or higher, 100°C or higher, 120°C or higher, 130°C or higher, or 140°C or higher, or at a temperature of 170°C or lower, 160°C or lower, 150°C or lower, 140°C or lower, or 130°C or lower.

[0033] The dry mixing process and the wet mixing process can be carried out in the same mixer. A batch-mixing mixer with agitator blades, as is well known in the art, can be used. The recycled asphalt mixture does not need to be heated during these mixing processes, as long as it is brought to the above temperature by the heat of the aggregate received from the dryer.

[0034] The amount of recycled asphalt mixture that can be mixed in a mixer, i.e., the amount of recycled asphalt mixture produced at one time, can be 0.5 ton or more, 1.0 ton or more, 1.5 ton or more, or 2.0 tons or more, and can be 10 tons or less, 5.0 tons or less, or 3.0 tons or less. For example, the amount of recycled asphalt mixture produced at one time can be 0.5 tons or more and 10 tons or less, or 1.0 tons or more and 5.0 tons or less.

[0035] One embodiment of the method for producing recycled asphalt mixtures is illustrated in Figure 1. As shown in Figure 1, aggregates, including new aggregates and recycled aggregates, can be stored in stockyards or cold bins depending on their type.

[0036] The method for producing a recycled asphalt mixture can include a step of supplying various types of aggregate according to the mixing ratio using an aggregate supply device such as a cold feeder from an aggregate storage area such as a stockyard or cold bin.

[0037] The location where the aggregate is supplied from the aggregate supply device may be a mixer, tank, hopper, silo, etc., or it may be an accumulation conveyor. Various types of aggregate may be supplied directly from the aggregate supply device to an accumulation conveyor and then supplied to the dryer. For example, as shown in Figure 1, various types of aggregate can be supplied from a stockyard by a cold feeder according to the blending ratio. The aggregate supplied from the cold feeder can be sent to a cold elevator by an accumulation conveyor.

[0038] The method for producing a recycled asphalt mixture can include a step of drying the aggregate in a dryer. As mentioned above, this step can be performed after mixing the various aggregates according to their mixing ratios, or after performing this step for the various aggregates, the various aggregates can be mixed according to their mixing ratios. For example, as shown in Figure 1, the aggregate can be sent to the dryer using a cold elevator.

[0039] The dryer has a burner that uses fuel such as heavy oil, and the flame can drive off the moisture contained in the aggregate. A dust collector can be attached to the dryer to collect the combustion gases and dust generated during drying and detoxify them before discharging them. The dust collected by the dust collector can also be added directly to the asphalt mixture as a filler.

[0040] Here, the recycled aggregate is stored in a stockyard separate from new aggregate, and can be supplied to the final mixer using a separate cold feeder and dryer.

[0041] The method for producing recycled asphalt mixtures can include a step of classifying the dried aggregate using a classifier and storing the aggregate in an aggregate storage device (or hot bin) according to particle size. In this case, a hot elevator can be used to transport the aggregate from the dryer to the classifier so as not to lower the temperature of the dried aggregate.

[0042] Examples of classifying devices include a trommel type in which the sieve mesh itself is rotated, and a vibrating sieve type in which a sieve and mechanical vibration are combined.

[0043] Fig. 2 is a schematic diagram of a portion of one embodiment of an apparatus for producing a recycled asphalt mixture, with the aggregate inlet and other components omitted from Fig. 2.

[0044] The recycled asphalt mixture is produced by mixing the new aggregate, recycled aggregate, foamed recycling additive, and foamed asphalt provided as described above in a mixer 10. As shown in FIG. 2, new asphalt is measured in a new asphalt tank 30, foamed in a foaming device 20, and then charged into the mixer 10. The foaming device 20 foams the asphalt by injecting water at high pressure into the asphalt using a high-pressure injector 20a. The foamed asphalt bubbles can then be refined using a static mixer 20b. This allows the bubbles to remain even after the recycled asphalt mixture is produced and transported to the construction site, improving workability at the construction site.

[0045] The amount of water used to foam the new asphalt may be, for example, 0.5 parts by mass or more, 1.0 parts by mass or more, 2.0 parts by mass or more, or 3.0 parts by mass or more, and may be 6.0 parts by mass or less, 5.0 parts by mass or less, 4.0 parts by mass or less, or 3.0 parts by mass or less, per 100 parts by mass of the new asphalt. For example, the amount of water used to foam the new asphalt may be 1.0 part by mass or more and 4.0 parts by mass or less.

[0046] The rejuvenating additive is supplied from a rejuvenating additive tank 40 and can be foamed by a foaming device 20 for foaming new asphalt, as shown in Figure 2. However, the rejuvenating additive can also be foamed using a second foaming device 21 separate from the foaming device 20 for foaming new asphalt, as shown in Figure 2. The second foaming device 21 can also be configured by combining a high-pressure injector 21a and a static mixer 21b.

[0047] The amount of water used to foam the regenerating additive may be, for example, 1.0 parts by mass or more, 2.0 parts by mass or more, 3.0 parts by mass or more, or 4.0 parts by mass or more, and may be 15.0 parts by mass or less, 10.0 parts by mass or less, 8.0 parts by mass or less, 6.0 parts by mass or less, or 5.0 parts by mass or less, relative to 100 parts by mass of the regenerating additive.

[0048] According to the investigations of the present inventors, it has been found that the foaming property can be significantly improved by heating the recycling additive before use. That is, the recycling additive can be heated to 50°C or higher, 80°C or higher, 100°C or higher, or 120°C or higher before use, and may also be heated to 240°C or lower, 200°C or lower, 180°C or lower, or 150°C or lower before use.

[0049] When the regeneration additive is a mineral oil-based or vegetable oil-based regeneration additive, for example, by heating it to 100°C or higher and 200°C or lower, and then using 2.0 parts by mass or higher and 10.0 parts by mass or lower of water per 100 parts by mass of the regeneration additive, very high foamability can be obtained.

[0050] In particular, under the foaming conditions described above, when the reclaiming additive is a mineral oil-based or vegetable oil-based reclaiming additive, the reclaiming additive can be foamed relatively easily using the foaming device 20 for foaming new asphalt. Even when foaming such a reclaiming additive, the bubbles can be refined using the static mixer 20b. Furthermore, the reclaiming additive and / or asphalt can be foamed using a foaming assistant. This allows the foam to remain even after the reclaimed asphalt mixture is produced and transported to the construction site, improving workability at the construction site. By using a common foaming device 20 for foaming new asphalt and a foaming device 20 for the reclaiming additive, the manufacturing method of the present invention can be implemented as is in existing plants without major equipment modifications.

[0051] When a foaming aid is used, it can be added directly to the regenerating additive tank 40, the new asphalt tank 30 or the mixer 10.

[0052] The rejuvenating additive can be metered using a flow meter 41 attached to pipe A and introduced into the mixer 10, or it can be provided to the new asphalt tank 30 through pipe B and metered in the new asphalt tank 30 and introduced into the mixer 10. Furthermore, when the rejuvenating additive is foamed using a second foaming device 41 separate from the foaming device 20 for foaming the new asphalt, the rejuvenating additive can be metered and introduced into the mixer 10 using a flow meter 42 attached to pipe C used for that purpose. Alternatively, after the rejuvenating additive is metered using the flow meter 41 attached to pipe A, the rejuvenating additive can be foamed using the second foaming device 21 and introduced into the mixer 10.

[0053] The recycled asphalt mixture obtained in this way can be loaded onto a dump truck or the like, kept warm, and transported to the construction site, as shown in Figure 1.

[0054] <asphalt> The new asphalt newly added in the method of the present invention is not particularly limited, and foamed asphalt commonly used in this field can be used. For example, various asphalts can be used. Examples include straight asphalt, which is petroleum asphalt for paving, as well as modified asphalt and foamed asphalt. Modified asphalts include blown asphalt and asphalt modified with polymeric materials such as thermoplastic elastomers and thermoplastic resins.

[0055] The amount of new asphalt to be foamed and added to the recycled asphalt mixture may be 0.5 parts by mass or more, 1.0 parts by mass or more, 1.5 parts by mass or more, 2.0 parts by mass or more, 3.0 parts by mass or more, 4.0 parts by mass or more, or 5.0 parts by mass or more, relative to 100 parts by mass of the total amount of new aggregate and recycled aggregate used. It may also be 10 parts by mass or less, 8.0 parts by mass or less, 6.0 parts by mass or less, 5.0 parts by mass or less, 4.0 parts by mass or less, 3.0 parts by mass or less, or 2.0 parts by mass or less. When referring to the amount of recycled aggregate in this specification, this means the amount excluding the amount of old asphalt adhering to the recycled aggregate.

[0056] <aggregate> The recycled aggregate used in the method of the present invention is obtained by crushing waste asphalt mixtures used in the surface and base layers of asphalt pavement. The recycled aggregate contains aggregate and old asphalt.

[0057] The recycled aggregate used in the method of the present invention may be aged recycled aggregate that has been reused. Such aged recycled aggregate usually deteriorates the properties of the recycled asphalt mixture, but the recycled asphalt mixture produced by the method of the present invention can obtain excellent properties even when using aged recycled aggregate.

[0058] The deteriorated recycled aggregate may have a penetration index of 25 or less, 20 or less, or 18 or less. Here, the penetration index is measured as described in "A041 Penetration Test Method" in the "Pavement Inspection and Testing Methods Handbook (Japan Road Association)" (JIS K 2207:1996).

[0059] The novel aggregate used in the method of the present invention is not particularly limited, and any aggregate commonly used in this field can be used. Examples of aggregate include those commonly used in paving, such as crushed stone, slag, and sand. Aggregates of different particle sizes are usually used in combination.

[0060] The recycled aggregate may account for 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 70% by mass or more, or 80% by mass or more of the total aggregate, or 100% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less. For example, the recycled aggregate may account for 5% by mass or more and 100% by mass or less, or 50% by mass or more and 90% by mass or less of the total aggregate. In the method of the present invention, even when recycled aggregate is used in an amount of 50% by mass or more, 60% by mass or more, or 70% by mass or more of the total aggregate, production can be performed without reducing productivity and sufficient quality can be obtained.

[0061] The content of aggregate, including recycled aggregate and new aggregate, in the recycled asphalt mixture obtained by the method of the present invention may be 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, or 90% by mass or more, or 97% by mass or less, 95% by mass or less, 93% by mass or less, 90% by mass or less, or 85% by mass or less.

[0062] <Recycling additives> The reclamation additive used in the method of the present invention is not particularly limited, and any of those commonly used in this field can be used. The reclamation additive is not particularly limited as long as it is a substance that can restore the properties of old asphalt, but examples include the reclamation additives described in Patent Documents 1 and 2, asphalt-based additives, petroleum lubricant oil-based additives, mineral-based additives, animal oil-based additives, vegetable oil-based additives, and asphalt emulsion-based additives, and in particular, mineral oil-based or vegetable oil-based reclamation additives can be used.

[0063] The amount of recycling additive used in the recycled asphalt mixture obtained by the method of the present invention may be 0.01 parts by mass or more, 0.05 parts by mass or more, 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, relative to 100 parts by mass of the total amount of new aggregate and recycled aggregate used, or may be 2.0 parts by mass or less, 1.5 parts by mass or less, 1.0 parts by mass or less, 0.8 parts by mass or less, or 0.5 parts by mass or less.

[0064] <Workability improver> Workability improvers are usually used to make it easier to spread and level the surface at the construction site, but glycol ether compounds and fatty acid compounds are not only used for this purpose; they also refine the bubbles in the foamed asphalt, allowing the fine bubbles to last longer in the asphalt mixture. This allows the bubbles to remain even after the recycled asphalt mixture is produced and transported to the construction site, improving workability at the construction site.

[0065] The amount of the workability improving agent used may be 0.001 part by mass or more, 0.005 part by mass or more, 0.01 part by mass or more, 0.03 part by mass or more, or 0.05 part by mass or more, relative to 100 parts by mass of the total amount of new aggregate and recycled aggregate used, or may be 0.20 parts by mass or less, 0.15 parts by mass or less, 0.10 parts by mass or less, 0.08 parts by mass or less, or 0.05 parts by mass or less.

[0066] <Workability improver - glycol ether compound> Examples of the glycol ether compound include glycol ether compounds represented by the following formula (I): R 1 -O-(AO)nH····(I)

[0067] In the formula, R 1 represents a linear, branched or cyclic hydrocarbon group having 1 to 24 carbon atoms which may have a substituent; AO represents a linear or branched oxyalkylene group having 2 to 4 carbon atoms; and n represents the number of moles of oxyalkylene groups added and is a number from 1 to 30.

[0068] In formula (I), R 1 is preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 2 to 6 carbon atoms. AO is preferably an oxyethylene group. n is preferably 2 to 20, more preferably 3 to 10.

[0069] Examples of glycol ether compounds represented by general formula (I) include (poly)ethylene glycol methyl ether, (poly)ethylene glycol ethyl ether, (poly)ethylene glycol propyl ether, (poly)ethylene glycol butyl ether, (poly)ethylene glycol hexyl ether, and (poly)ethylene glycol octyl ether.

[0070] <Workability improver - fatty acid compound> The fatty acid compound is preferably a compound represented by the following formula (II). R 11 -COO-(AO)mR 12 (II)

[0071] In the formula, R 11 is a linear, branched or cyclic hydrocarbon group having 1 to 24 carbon atoms which may have a substituent; R 12 represents a hydrogen atom or a methyl group, AO represents a linear or branched oxyalkylene group having 2 to 4 carbon atoms, and m represents the number of moles of oxyalkylene groups added and is a number of 0 or 1 to 30.

[0072] In formula (II), R 11 The number of carbon atoms in the formula (II) is preferably 6 to 24, more preferably 8 to 20, still more preferably 10 to 18, and particularly preferably 12 to 16. In formula (II), m is preferably 0 or 1 to 25, more preferably 0 or 1 to 20, and still more preferably 0 or 1 to 15. In formula (II), AO is preferably an oxyethylene group.

[0073] The fatty acid compound may have an iodine value of, for example, 50 to 110, 60 to 100, or 70 to 90. These may be a combination of multiple fatty acid compounds, in which case the iodine value refers to the value of the fatty acid compound in which multiple compounds are combined. The iodine value of the fatty acid compound is measured in accordance with JIS K0070-1992.

[0074] The fatty acid compound represented by formula (II) is preferably a fatty acid, a fatty acid alkyl ester, a fatty acid polyoxyalkylene alkyl ester, or a polyoxyalkylene fatty acid ester, and these can be used alone or in combination of two or more selected from these.

[0075] The molecular weight (g / mol) of the fatty acid compound may be, for example, 100 or more, 150 or more, 200 or more, 250 or more, 270 or more, or 280 or more, or 500 or less, 450 or less, 400 or less, 350 or less, 330 or less, or 320 or less. When a fatty acid compound is used in combination with multiple compounds, these molecular weights may be weight-average molecular weights.

[0076] The compound represented by formula (II) includes fatty acids: R 11 COOH, fatty acid methyl ester: R 11 COOCH3, fatty acid (poly)oxyethylene methyl ester: R 11 COO(CH2CH2O) m CH3, (poly)oxyethylene fatty acid ester: R 11 COO(CH2CH2O m Examples include H.

[0077] Specific examples include palmitic acid, palmitic acid methyl ester, palmitic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene palmitic acid ester (average number of moles added: 1 to 15), stearic acid, stearic acid methyl ester, stearic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene stearic acid ester (average number of moles added: 1 to 15), oleic acid, oleic acid methyl ester, oleic acid (poly)oxyethylene methyl ester ester (average number of moles added: 1 to 15), (poly)oxyethylene oleate ester (average number of moles added: 1 to 15), linoleic acid, linoleic acid methyl ester, linoleic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene linoleate ester (average number of moles added: 1 to 15), linolenic acid, linolenic acid methyl ester, linolenic acid (poly)oxyethylene methyl ester (average number of moles added: 1 to 15), (poly)oxyethylene linolenate ester (average number of moles added: 1 to 15).

[0078] <Foaming aid> In the method of the present invention, a foaming aid can be used to assist in foaming of the asphalt and / or the reclaiming additive. The glycol ether compounds and fatty acid compounds used as the above-mentioned workability improving agents can also be used as such foaming aids, but other foaming aids include surfactants, inorganic compounds, etc.

[0079] Examples of surfactants include cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants, with anionic surfactants and nonionic surfactants being particularly preferred. The anionic surfactants are not particularly limited as long as they can achieve the above-mentioned effects, and examples include carboxylic acid surfactants, sulfonic acid surfactants, sulfate ester surfactants, and phosphate ester surfactants, with phosphate ester surfactants being particularly preferred. Furthermore, examples of nonionic surfactants that can be used include polyoxyalkylene alkyl ethers and polyoxyalkylene alkylates.

[0080] Examples of inorganic compounds include sodium bicarbonate, fluorosulfonic acid, sodium sulfide, hexafluorosilicic acid, ammonium iodide, magnesium hydroxide, potassium fluoride, potassium cyanate, zinc sulfate, calcium oxide, potassium permanganate, ammonium perchlorate, hydrobromic acid, aluminum bromide, and silicon carbide.

[0081] <others> The recycled asphalt mixture obtained by the method of the present invention may contain other components than those described above that are commonly used in this field. For example, the recycled asphalt mixture obtained by the method of the present invention may contain a filler such as stone powder.

[0082] The recycled asphalt mixture obtained by the method of the present invention may contain no other components than aggregate, asphalt, and the rejuvenating additive. For example, the asphalt mixture may contain no more than 50% by weight, 40% by weight, 30% by weight, 20% by weight, 10% by weight, 5% by weight, 1% by weight, or 0.1% by weight of other components.

[0083] The present invention will be explained in more detail in the following examples, but the present invention is not limited thereto. [Example]

[0084] <Production example> Recycled asphalt mixture (13) was produced at three existing plants in Yamanashi, Sakaide, and Morioka. The raw materials were obtained from nearby production areas and factories, and recycled aggregates with different penetration strengths were used.

[0085] As an example, the composition and aggregate gradation of the recycled asphalt mixture (13) produced at the Yamanashi Plant are shown below.

[0086] [Table 1]

[0087] To obtain the recycled asphalt mixture (13) with this composition, the new aggregate was heated in a dryer to 200°C ± 10°C, the recycled aggregate was heated to 160°C ± 10°C, and the asphalt was heated to 160°C ± 10°C and mixed in a mixer to produce a mixture at a temperature of 165°C ± 10°C. The weight of the mixture produced in one batch was 2,000 kg.

[0088] The recycled asphalt mixtures (13) produced in Sakaide and Morioka were changed to use 60% and 70% recycled aggregate by mass, respectively. Instead, the amount of new aggregate used was reduced compared to the recycled asphalt mixture (13) produced at the Yamanashi Plant. On the other hand, the amounts of asphalt and recycled additives used were kept at the same level as those at the Yamanashi Plant. The multiple types of recycled asphalt mixtures (13) produced at each plant had the same composition.

[0089] The mixing conditions, such as mixing time, for the recycled asphalt mixture (13) produced at the three plants are shown in the table below.

[0090] [Table 2]

[0091] "test" The various physical properties of the recycled asphalt mixture obtained in this manner were measured using the following measurement methods.

[0092] <Crush strength ratio> The split strength ratio was measured according to the method described in "B006 Split Test Method" in the "Pavement Survey and Test Method Handbook (Japan Road Association)."

[0093] <High temperature cantabro loss rate> The high-temperature cantablo loss rate was measured according to the method described in "B010 Cantablo Test Method" in the "Pavement Survey and Test Method Handbook (Japan Road Association)." The test conditions were a specimen temperature of 60°C, a temperature inside the Los Angeles tester of 30°C, and a drum rotation speed of 300 rpm.

[0094] SCB Test The SCB test was conducted in accordance with the TP124-18 standard of the American Association of State Highway and Transportation Officials (AASHTO). Details of this test are described in "Masahiro Ando and four others, 'Study on Evaluation Methods for the Mechanical Properties of Reclaimed Asphalt Mixtures,' Journal of the Japan Society of Civil Engineers, Vol. 78, No. 1, pp. 12-27, 2022."

[0095] Fatigue fracture test Fatigue fracture tests were performed in accordance with the NAT-SCB test and two-point cyclic bending test (BS EN12697-249). Details of these tests are also provided in "Masahiro Ando and four others, 'Study on evaluation methods for the mechanical properties of recycled asphalt mixtures,' Journal of the Japan Society of Civil Engineers, E1 (Pavement Engineering), vol. 78, No. 1, pp. 12-27, 2022."

[0096] "result" These results are shown in Table 3.

[0097] [Table 3]

[0098] Looking at the results from each plant, compared to the comparative example recycled asphalt mixture, the crack resistance (SCB test) of each reference example recycled asphalt mixture was improved by approximately 10 to 40% at room temperature (25°C).Furthermore, fatigue resistance was improved by approximately 20 to 50% at low temperature (10°C) and approximately 15 to 70% at high temperature (40°C).

[0099] Furthermore, Reference Examples 1 to 3 also tended to be superior to Comparative Examples 1 and 2 in terms of the splitting strength ratio and high-temperature cantabloid loss rate.

[0100] Comparing the mixing times of Reference Examples 1 to 3, Reference Example 2, in which the first mixing step was 40 seconds, gave generally good results. Furthermore, comparing the mixing times of Reference Examples 4 to 7, Reference Examples 5 and 6, in which the first mixing step was 20 or 30 seconds, gave generally good results. It was found that if the first mixing step was too long, no improvement in physical properties was observed.

[0101] The results of each reference example were almost equivalent to those of the recycled asphalt mixture produced by the method described in Patent Document 2. It is believed that the manufacturing method of the present invention has the effect of allowing the recycled additive to penetrate deeper into the recycled aggregate, thereby improving the crack resistance, fatigue resistance, etc. of the recycled mixture.

[0102] In addition to the results shown in Table 3, Marshall density tests, Marshall stability tests, wheel tracking tests, etc. were also conducted on these recycled asphalt mixtures, and the results for the Reference Examples were generally equivalent to or better than those for the Comparative Examples.

[0103] In the above example, similar advantageous effects can be obtained even when the new asphalt and the regenerating additive are foamed and mixed. In this case, the mixing times of the first mixing step (dry 1) and the third mixing step (wet) can be relatively short, and similar advantageous effects can be obtained even when the amount of recycled aggregate used is high. [Industrial Applicability]

[0104] This provides a method for producing recycled asphalt mixtures that is environmentally and safety-friendly, can be produced without reducing the productivity of existing plants, and can ensure sufficient quality even when using a large amount of recycled aggregate, making it highly industrially applicable. [Explanation of symbols]

[0105] 10...Mixer 20, 21...Foaming device 20a, 21a...High-pressure injector 20b, 21b...Static mixer 30...New asphalt tank 40...Regeneration additive tank 41,42…Flowmeter A,B,C…Piping

Claims

1. A method for producing a recycled asphalt mixture, comprising a mixing step of mixing new aggregate, recycled aggregate, foamed recycling additive, and foamed asphalt.

2. The mixing step a first mixing step of mixing the recycled aggregate and the foamed recycling additive to obtain a first mixture; a second mixing step of mixing the first mixture with the new aggregate to obtain a second mixture; and A third mixing step in which the second mixture is mixed with the expanded asphalt to obtain a recycled asphalt mixture. The method for producing the asphalt mixture according to claim 1, comprising:

3. The method for producing an asphalt mixture according to claim 1, wherein the foamed regenerating additive is metered by a flow meter provided in a pipe.

4. The method for producing an asphalt mixture according to claim 3 , wherein the foamed regenerating additive is foamed by a foaming device, and the foaming device includes an in-line mixer on a downstream side of a pipe.

5. The method for producing an asphalt mixture according to claim 1, wherein the rejuvenating additive is a mineral oil-based or vegetable oil-based rejuvenating additive.

6. The method for producing a recycled asphalt mixture according to claim 1, wherein a workability improver containing a glycol ether compound or a fatty acid compound is further mixed in the mixing step.

7. The method for producing a recycled asphalt mixture according to claim 6, wherein recycled aggregate is used in an amount of 70% by mass or more relative to the total amount of aggregate used.

Images