Method for manufacturing recycled asphalt mixture

Abstract

To provide a method for manufacturing a recycled asphalt mixture posing no problem in environment and safety, manufacturable without reducing productivity of an existing plant, and having properties excellent in fatigue resistance and the like.SOLUTION: This method for manufacturing an asphalt mixture comprises: a first mixing step of mixing recycled aggregate and a recycling additive to provide a first mixture; a second mixing step of mixing the first mixture and new aggregate to provide a second mixture; and a third mixing step of mixing the second mixture and new asphalt to provide a recycled asphalt mixture. The first to third mixing steps are executed in the same mixer, the total time of the first and second mixing steps is longer than the time of the third mixing step, and the third mixing step is executed within 40 seconds.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. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-100996 [Patent Document 2] Japanese Patent Application Publication No. 2020-037798 Summary of the Invention [Problem to be solved by the invention]

[0010] The method described in Patent Document 1 requires a long mixing time, which reduces productivity when produced in an existing plant. Also, 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 regeneration additive.

[0011] 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 has high properties such as fatigue resistance. [Means for solving the problem]

[0012] 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.

[0013] That is, the present invention has the following aspects: <<Aspect 1>> a first mixing step of mixing recycled aggregate and a recycling additive to obtain a first mixture; a second mixing step of mixing the first mixture with new aggregate to obtain a second mixture; and A third mixing step of mixing the second mixture with new asphalt to obtain a recycled asphalt mixture; A method for producing a recycled asphalt mixture, comprising: The first to third mixing steps are carried out in the same mixer, A method for producing a recycled asphalt mixture, in which the total time of the first mixing step and the second mixing step is longer than the time of the third mixing step, and the third mixing step is carried out within 40 seconds. <<Aspect 2>> 2. The method for producing a recycled asphalt mixture according to claim 1, wherein the first mixing step and the second mixing step are carried out within 50 seconds. Aspect 3 The method for producing a recycled asphalt mixture according to claim 1, wherein the first mixing step is carried out in 40 seconds or less, the second mixing step is carried out in 15 seconds or less, and the third mixing step is carried out in 30 seconds or less. Aspect 4 The method for producing a recycled asphalt mixture according to aspect 1, wherein the amount of recycled asphalt mixture produced at one time is in the range of 0.5 tons to 5.0 tons. [Effects of the Invention]

[0014] 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 has high properties such as fatigue resistance. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 illustrates one embodiment of a method for producing a recycled asphalt mixture. DETAILED DESCRIPTION OF THE INVENTION

[0016] <<Method for manufacturing asphalt mixture>> The method for producing an asphalt mixture of the present invention includes a first mixing step in which heated recycled aggregate is mixed with a recycling additive 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 new asphalt to obtain a recycled asphalt mixture. Here, the first to third mixing steps are performed in the same mixer, the total time of the first and second mixing steps is longer than the time of the third mixing step, and the third mixing step is performed within 40 seconds.

[0017] By mixing the recycled aggregate with a recycled additive before mixing the new aggregate with the recycled aggregate, the recycled additive can be effectively absorbed into the old asphalt adhering to the recycled aggregate. 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 reduced accordingly. Furthermore, because equipment other than the mixer was designed to match the production capacity of the existing plant, the longer the mixer's mixing time, the lower the operating rate of the equipment other than the mixer, resulting in an inefficient plant.

[0018] In response to this, the inventors discovered a method for producing recycled asphalt mixtures of the present invention. By varying the mixing times in the first mixing step (mixing heated recycled aggregate with recycled additives), the second mixing step (mixing the first mixture with new aggregate), and the third mixing step (mixing the second mixture with new asphalt), the method exhibits excellent properties such as fatigue resistance and can be produced without reducing the productivity of existing plants. Recycled asphalt mixtures are more prone to cracking than asphalt mixtures made with only new asphalt, and improvements in this area have been sought. The recycled asphalt mixtures obtained by the method of the present invention have been found to have improved performance in this area, providing significant advantages. Furthermore, regardless of the type of recycled additive used, this production method allows the recycled additives to be handled entirely within the plant, enabling production in existing plants without posing any environmental or safety issues.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The method for producing a recycled asphalt mixture can include a dry mixing step in which various aggregates from a hot bin and, if necessary, fillers such as stone powder are weighed and mixed in a mixer. This dry mixing step corresponds to the first and second mixing steps in the production method of the present invention.

[0028] The first mixing step of mixing the recycled aggregate and the 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.

[0029] 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.

[0030] The dry mixing process, including the first and second mixing processes, can be carried out 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 carried out for 15 seconds or more, 20 seconds or more, 25 seconds or more, or 30 seconds or more. For example, the dry mixing process can be carried out 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.

[0031] 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.

[0032] 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 a measured amount of new asphalt. This wet mixing step corresponds to the third mixing step in the production method of the present invention.

[0033] 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.

[0034] The third mixing step, in which the second mixture obtained in the second mixing step is mixed with 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] <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.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] 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, or 60% 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 20% by mass or more and 80% by mass or less of the total aggregate.

[0045] 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.

[0046] <Recycling additives> The regeneration 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 regeneration additive is not particularly limited as long as it is a substance that can restore the properties of old asphalt, and examples thereof include the regeneration 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.

[0047] <asphalt> The new asphalt newly added in the method of the present invention is not particularly limited, and any 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. Examples of modified asphalt include blown asphalt, asphalt modified with polymeric materials such as thermoplastic elastomers and thermoplastic resins.

[0048] The content of new asphalt in the recycled asphalt mixture obtained by the method of the present invention may be 2.0% by mass or more, 3.0% by mass or more, 4.0% by mass or more, or 5.0% by mass or more, or 20% by mass or less, 15% by mass or less, 10% by mass or less, 8.0% by mass or less, 5.0% by mass or less, or 4.0% by mass or less.

[0049] <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.

[0050] The recycled asphalt mixture obtained by the method of the present invention may contain no other components than aggregate, asphalt, and warming agent. For example, the asphalt mixture may contain no more than 50% by mass, 40% by mass, 30% by mass, 20% by mass, 10% by mass, 5% by mass, 1% by mass, or 0.1% by mass of other components.

[0051] The present invention will be explained in more detail in the following examples, but the present invention is not limited thereto. [Example]

[0052] <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.

[0053] As an example, the composition and aggregate gradation of the recycled asphalt mixture (13) produced at the Yamanashi Plant are shown below.

[0054] [Table 1]

[0055] 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.

[0056] 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.

[0057] The mixing conditions, such as mixing time, for the recycled asphalt mixture (13) produced at the three plants are shown in the table below.

[0058] [Table 2]

[0059] "test" The various physical properties of the recycled asphalt mixture obtained in this manner were measured using the following measurement methods.

[0060] <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)."

[0061] <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.

[0062] 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."

[0063] 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."

[0064] "result" These results are shown in Table 3.

[0065] [Table 3]

[0066] Looking at the results from each plant, compared to the comparative example recycled asphalt mixture, the recycled asphalt mixtures of each example showed a 10-40% improvement in crack resistance (SCB test) at room temperature (25°C).Furthermore, the fatigue resistance improved by 20-50% at low temperature (10°C) and 15-70% at high temperature (40°C).

[0067] Furthermore, Examples 1 to 3 tended to be superior to Comparative Examples 1 and 2 in terms of the splitting strength ratio and high-temperature cantabloid loss ratio.

[0068] Comparing the mixing times of Examples 1 to 3, Example 2, in which the first mixing step was 40 seconds, gave generally good results. Furthermore, comparing the mixing times of Examples 4 to 7, 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.

[0069] The results of each example were almost equivalent to those of the recycled asphalt mixture produced using 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.

[0070] 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 of the Examples were generally equivalent to or better than those of the Comparative Examples. [Industrial Applicability]

[0071] The manufacturing method of the present invention is environmentally and safety compliant, can be produced without reducing the productivity of existing plants, and can produce recycled asphalt mixtures with excellent properties such as fatigue resistance, making it highly industrially applicable.

Claims

1. a first mixing step of mixing recycled aggregate and a recycling additive to obtain a first mixture; a second mixing step of mixing the first mixture with new aggregate to obtain a second mixture; and A third mixing step of mixing the second mixture with new asphalt to obtain a recycled asphalt mixture; A method for producing a recycled asphalt mixture, comprising: The first to third mixing steps are carried out in the same mixer, A method for producing a recycled asphalt mixture, wherein the total time of the first mixing step and the second mixing step is longer than the time of the third mixing step, and the third mixing step is carried out within 40 seconds.

2. The method for producing a recycled asphalt mixture according to claim 1, wherein the first mixing step and the second mixing step are carried out within 50 seconds.

3. 2. The method for producing a recycled asphalt mixture according to claim 1, wherein the first mixing step is carried out within 40 seconds, the second mixing step is carried out within 15 seconds, and the third mixing step is carried out within 30 seconds.

4. The method for producing a recycled asphalt mixture according to claim 1, wherein the amount of recycled asphalt mixture produced at one time is in the range of 0.5 tons to 5.0 tons.

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