JP2025127721A - Manufacturing method for recycled asphalt mixture - Google Patents

Abstract

The present invention provides a method for producing recycled asphalt mixtures that are environmentally and safety compliant, can be produced without reducing the productivity of existing plants, and has excellent properties such as fatigue resistance.
[Solution] The method for producing an asphalt mixture of the present invention comprises a first mixing step in which recycled aggregate and a recycling 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 new asphalt to obtain a recycled asphalt mixture, the first to third mixing steps being carried out in the same mixer, the total time for the first and second mixing steps being longer than the time for the third mixing step, and the third mixing step being carried out within 40 seconds.
[Selection diagram] None

Description

The present invention relates to a method for producing recycled asphalt mixtures.

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

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 an ingredient in asphalt mixtures, and is mixed with new asphalt and new aggregate to create asphalt mixtures that are widely used in asphalt-paved roads.

However, recycled aggregate is made from old, discarded aggregate coated with old asphalt. 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 the problem of reduced performance for recycled asphalt mixtures made with recycled aggregate.

It is therefore known that recycled asphalt mixtures contain recycling additives in order to restore the properties of the old asphalt attached to the recycled aggregate.

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.

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

Patent Document 2 discloses a method for producing such recycled asphalt mixtures, 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.

JP 2010-100996 A Japanese Patent Application Laid-Open No. 2020-037798

The method described in Patent Document 1 requires long mixing times, 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 concerns during curing, depending on the type of regeneration additive used.

The present invention therefore provides a method for producing recycled asphalt mixtures that are environmentally and safety-friendly, can be produced without reducing the productivity of existing plants, and has high properties such as fatigue resistance.

The inventors have discovered that the above-mentioned problems can be solved by a method for producing recycled asphalt mixtures having the following features:

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, 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.
Aspect 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 within 40 seconds, the second mixing step is carried out within 15 seconds, and the third mixing step is carried out within 30 seconds.
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.

The present invention provides a method for producing recycled asphalt mixtures that are environmentally and safety-friendly, can be produced without reducing the productivity of existing plants, and have excellent properties such as fatigue resistance.

FIG. 1 illustrates one embodiment of a method for producing a recycled asphalt mixture.

<<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 and a recycling 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 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.

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, longer mixer mixing times would also reduce the operating rate of equipment other than the mixer, resulting in an inefficient plant.

In response to this, the inventors have discovered a method for producing recycled asphalt mixtures of the present invention that, by varying the mixing times in the first mixing step, in which heated recycled aggregate is mixed with recycled 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 new asphalt, achieves 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 excellent 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.

Figure 1 illustrates one embodiment of a method for producing a recycled asphalt mixture. As shown in Figure 1, aggregates, including new aggregate and recycled aggregate, can be stored in stockyards or cold bins depending on their type.

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

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 mixing ratio. The aggregate supplied from the cold feeder can be sent to a cold elevator by an accumulation conveyor.

The method for producing recycled asphalt mixtures 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 respective proportions, or after performing this step for the various aggregates, the various aggregates can be mixed according to their respective proportions. For example, as shown in Figure 1, the aggregate can be sent to the dryer using a cold elevator.

The dryer has a burner that uses fuel such as heavy oil, and the flame can drive off the moisture contained in the aggregate. The dryer can be equipped with a dust collector, which collects the combustion gases and dust generated during drying and detoxifies them before discharging them. The dust collected by the dust collector can also be incorporated directly into the asphalt mixture as a filler.

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

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.

Classification devices include the trommel method, which rotates the sieve mesh itself, and the vibrating sieve method, which combines a sieve with mechanical vibration.

The method for producing recycled asphalt mixtures can include a dry mixing step in which various aggregates from hot bins 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.

The first mixing step, in which recycled aggregate and recycling additive are mixed, can be carried out within 60 seconds, 50 seconds, 40 seconds, 35 seconds, or 30 seconds, or within 10 seconds, 15 seconds, 20 seconds, or 25 seconds. For example, the first mixing step can be carried out within 10 to 60 seconds, 15 to 50 seconds, 20 to 40 seconds, or 25 to 35 seconds.

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 within 3 seconds, 5 seconds, 8 seconds, or 10 seconds. For example, the second mixing step can be carried out within 3 to 20 seconds, 5 to 15 seconds, or 8 to 12 seconds.

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 also 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.

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.

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.

The wet mixing process 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 with a wet mixing time of 40 seconds or less.

The third mixing step, in which the second mixture obtained in the second mixing step is mixed with new asphalt, can be carried out within 40 seconds, 35 seconds, 30 seconds, or 25 seconds, or within 10 seconds, 15 seconds, 20 seconds, 22 seconds, or 25 seconds. For example, the third mixing step can be carried out within 10 to 40 seconds, 15 to 35 seconds, or 20 to 30 seconds.

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.

These mixing processes 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.

The dry mixing process and the wet mixing process can be carried out in the same mixer. The mixer can be a batch mixer with agitating blades, as is well known in the art. The recycled asphalt mixture does not need to be heated during these mixing processes; it only needs to be brought to the above temperature by the heat of the aggregate received from the dryer.

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

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 tonnes or more, 1.0 tonnes or more, 1.5 tonnes or more, or 2.0 tonnes or more, and can be 10 tonnes or less, 5.0 tonnes or less, or 3.0 tonnes or less. For example, the amount of recycled asphalt mixture produced at one time can be 0.5 tonnes or more and 10 tonnes or less, or 1.0 tonnes or more and 5.0 tonnes or less.

<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.

The recycled aggregate used in the method of the present invention may be aged recycled aggregate that has been reused. Such aged recycled aggregate normally reduces the properties of recycled asphalt mixtures, but the recycled asphalt mixture produced by the method of the present invention can achieve excellent properties even when using aged recycled aggregate.

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

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. It is common to use a mixture of multiple types of aggregate with different particle sizes.

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, 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.

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.

<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.

<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.

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 may be 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.

<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.

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

The present invention will be further explained in detail in the following examples, but the present invention is not limited thereto.

<Production example>
Recycled asphalt mixture (13) was produced at three existing plants in Yamanashi, Sakaide, and Morioka. Each raw material was obtained from a production area or factory near the plant, and recycled aggregates with different penetration strengths were used.

As an example, the details of the composition and aggregate particle size of the recycled asphalt mixture (13) produced at the Yamanashi Plant are shown below.

To obtain 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.

The recycled asphalt mixtures (13) produced in Sakaide and Morioka had the amount of recycled aggregate changed to 60% and 70% by mass, respectively. Instead, the amount of new aggregate used was reduced compared to the recycled asphalt mixture (13) produced at the Yamanashi plant. Meanwhile, 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.

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

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

<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)."

<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.

<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."

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 described in "Masahiro Ando and four others, 'Research on evaluation methods for the mechanical properties of recycled asphalt mixtures,' Japan Society of Civil Engineers, Proceedings E1 (Pavement Engineering), vol. 78, No. 1, pp. 12-27, 2022."

"result"
The results are shown in Table 3.

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

Furthermore, Examples 1 to 3 tended to be superior to Comparative Examples 1 and 2 in terms of splitting strength ratio and high-temperature cantabro loss rate.

When comparing the mixing times of Examples 1 to 3, Example 2, in which the first mixing step was 40 seconds, produced better results overall. Furthermore, when comparing the mixing times of Examples 4 to 7, Examples 5 and 6, in which the first mixing step was 20 or 30 seconds, produced better results overall. It was found that if the first mixing step was too long, no improvement in physical properties was observed.

The results of each example were nearly 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 recycling additive to penetrate deeper into the recycled aggregate, thereby improving the crack resistance, fatigue resistance, etc. of the recycled mixture.

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 Examples were generally equivalent to or better than those for the Comparative Examples.

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 high properties such as fatigue resistance, making it highly applicable to industry.

Claims (4)

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. 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. The method for producing a recycled asphalt mixture described in 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. 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.