METHOD FOR PROCESSING RECLAIMED ASPHALT PAVEMENT

Abstract

The present disclosure provides a method for processing a reclaimed asphalt pavement. The method includes: (a) providing a reclaimed asphalt pavement, wherein the reclaimed asphalt pavement includes aggregates and asphalt coating the aggregates; and (b) performing an asphalt stripping treatment on the reclaimed asphalt pavement, wherein the asphalt in the reclaimed asphalt pavement is at least partially separated from the aggregates by an asphalt stripping unit using water as a medium.

Description

This application claims the benefit of U.S. provisional application Ser. No. 63/797,193, filed Apr. 30, 2025, the disclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates to a method for processing reclaimed asphalt pavement, and more particularly to a method that is low energy consumption and enables the recycling of asphalt and aggregates.

BACKGROUND

Asphalt has become the mainstream material for road paving globally. With the rising awareness of global sustainable development, the recycling and reuse of reclaimed asphalt pavement (RAP) generated from road engineering has become an important issue. Reclaimed asphalt pavement is primarily composed of aggregate and aged asphalt binder coating the surface thereof. The aggregate includes crushed stone, sand, and the like.

Conventional asphalt recycling methods mostly utilize chemical technologies, such as organic solvents and thermal cracking, to process reclaimed asphalt pavement to extract the asphalt. However, although existing chemical technologies can separate asphalt from aggregate, there is still significant room for improvement in separation effectiveness. Furthermore, these technologies often require operation under specific high temperatures or complex conditions, resulting in considerably high energy consumption, making commercialization difficult and failing to align with current trends in sustainability and environmental protection.

Therefore, the development of low-energy processing technology capable of efficiently separating asphalt to achieve the resource utilization of reclaimed asphalt pavement is an urgent problem to be solved in the industry.

SUMMARY

The disclosure is directed to a method for processing a reclaimed asphalt pavement, for example, by separating asphalt and aggregates in the reclaimed asphalt pavement via a pretreatment unit and an asphalt stripping unit, and further screening out recycled stones and asphalt sands via a water-circulating screening and sorting processor unit.

According to some embodiments, the present disclosure provides a method for processing a reclaimed asphalt pavement. The method includes the following steps of: (a) providing a reclaimed asphalt pavement, wherein the reclaimed asphalt pavement comprises a plurality of aggregates and asphalt coating the aggregates; and (b) performing an asphalt stripping treatment on the reclaimed asphalt pavement, wherein the asphalt in the reclaimed asphalt pavement is at least partially separated from the aggregate by an asphalt stripping unit using water as a medium.

In order to have a better understanding of the above and other elements of the present disclosure, embodiments are given below and described in detail in conjunction with the accompanying drawings as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a step flowchart of a method for processing reclaimed asphalt pavement according to an embodiment of the present disclosure.

FIG. 1B is a schematic diagram illustrating the production of asphalt sand and recycled stone through a method for processing reclaimed asphalt pavement according to an embodiment of the present disclosure.

FIG. 1C is a schematic diagram illustrating the treatment of asphaltene using a biological agent according to an embodiment of the present disclosure.

FIG. 2 is a schematic diagram of a system for processing reclaimed asphalt pavement according to an embodiment of the present disclosure.

FIG. 3 is a schematic diagram illustrating processing elements included in a water-circulating screening and sorting processor unit for performing procedures such as screening and separation according to an embodiment of the present disclosure.

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

DETAILED DESCRIPTION

Various embodiments will be described in greater detail below in conjunction with the accompanying drawings. It should be understood that the descriptions and drawings are provided for illustrative purposes only and are not intended to be limiting. For the sake of clarity, some elements and/or symbols may be omitted in some drawings. In addition, elements in the drawings may not be drawn to scale. It is contemplated that elements and features in one embodiment can be advantageously incorporated into another embodiment without further recitation.

In the text, the phrase “a range between a first value and a second value” indicates that the range comprises the first value, the second value, and other values therebetween.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be understood that these terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the background or context of the present disclosure, and should not be interpreted in an idealized or overly formal sense unless specifically defined in the embodiments of the present disclosure.

FIG. 1A is a step flowchart of a method for processing reclaimed asphalt pavement (RAP) according to an embodiment of the present disclosure. FIG. 1B is a schematic diagram illustrating the production of asphalt sand SG1 and recycled stone SG2 through the method for processing reclaimed asphalt pavement RAP according to an embodiment of the present disclosure. FIG. 1C is a schematic diagram illustrating the treatment of asphaltenes ASN in reclaimed asphalt pavement RAP using a biological agent (BIO) according to an embodiment of the present disclosure.

The method of the present embodiment comprises sequential steps S11 to S17. It should be understood that the method may further comprise other steps and techniques, or certain steps may be omitted.

Please refer simultaneously to FIG. 1A and FIG. 1B. As shown in step S11, a reclaimed asphalt pavement RAP is provided. The reclaimed asphalt pavement RAP comprises aggregates AG and asphalt AS coating the surface of the aggregates AG. The aggregates AG may comprise sands and crushed stones, such as sands and stones with inconsistent particle sizes and irregular shapes.

As shown in step S13, a pretreatment is performed on the reclaimed asphalt pavement (RAP), wherein a biological agent (BIO) is applied to the reclaimed asphalt pavement (RAP) by a pretreatment unit 10 (as shown in FIG. 2) to form a first product. This step may be performed at room temperature. The range of room temperature may be 15 °C to 35 °C, for example, it may be 20 °C to 30 °C, or approximately 18 °C, 20 °C, 22 °C, 25 °C, 28 °C, 30 °C, 32 °C, etc., but the present disclosure is not limited thereto.

According to some embodiments, the biological agent (BIO) may be a microorganism screened from an environmental sample, and may be a single strain or a mixed strain. The strain may comprise bacteria belonging to the genus Bacillus, bacteria belonging to the genus Priestia, or a combination thereof. The bacteria belonging to the genus Bacillus may comprise, but are not limited to, Bacillus velezensis (BV), Bacillus subtilis, Bacillus toyonensis, Bacillus licheniformis, Bacillus paralicheniformis, Bacillus thuringiensis, and Bacillus pumilus. The bacteria belonging to the genus Priestia may comprise, but are not limited to, Priestia aryabhattai (PA), Priestia megaterium, Priestia flexa, Priestia filamentosa, and Priestia endophytica. It should be understood that the biological agent of the disclosure is not limited thereto. The Bacillus of the biological agent can produce endospores and has high-temperature resistance characteristics during the dormant period, with a tolerable temperature range of 60 °C to 90 °C. The biosafety level of the biological agent BIO belongs to Risk Group 1 (RG1), meaning the known risk to human, animal, and plant health and the environment is the lowest level.

Please refer to FIG. 1C. In the reclaimed asphalt pavement (RAP), the composition of the asphalt (AS) comprises asphaltenes (ASN). As the asphalt (AS) ages, the content of asphaltenes (ASN) increases and the degree of cross-linking increases, causing the viscosity of the asphalt (AS) to rise. By adding the biological agent (BIO) into the aged asphalt AS, the biological agent (BIO) secretes surfactants (not shown) to emulsify the asphaltenes (ASN), thereby decomposing the asphaltenes (ASN) and reduce the viscosity of the asphalt (AS) (i.e., reducing the bonding strength between the asphalt AS and the aggregate AG).

For example, the reclaimed asphalt pavement (RAP) has a first asphalt viscosity before performing step S13, and a first product formed after the reclaimed asphalt pavement (RAP) performs step S13 has a second asphalt viscosity, wherein the second asphalt viscosity is less than the first asphalt viscosity. According to an embodiment, a reduction percentage of the second asphalt viscosity relative to the first asphalt viscosity may be equal to or greater than 2%, such as equal to or greater than 5%, equal to or greater than 10%, etc., and for example, may be between 10% and 40%, such as between 15% and 35%, between 20% and 40%, etc., but the present disclosure is not limited thereto.

According to some embodiments, the biological agent (BIO) acts on the reclaimed asphalt pavement (RAP) in the form of a bacterial liquid. A weight ratio of the bacterial liquid to the reclaimed asphalt pavement is between 0.001 and 1 (i.e., the weight ratio of the bacterial liquid to the asphalt is between 0.2 and 30), for example, between 0.005 and 0.9, or between 0.01 and 0.8, but the present disclosure is not limited thereto. On the other hand, the concentration of the bacterial liquid (optical density, OD₆₀₀) may be between 1 and 3, for example, between 1.2 and 2.5, or between 1.2 and 1.4, but the present disclosure is not limited thereto.

Please refer to FIG. 1A and FIG. 1B again. As shown in step S15, an asphalt stripping treatment is performed on the first product, wherein an asphalt stripping unit 20 (as shown in FIG. 2) uses water as a medium to at least partially separate the asphalt (AS) in the first product (i.e., the reclaimed asphalt pavement (RAP) after the treatment of step S13, comprising the asphalt AS and the aggregates AG) from the aggregates (AG), and form a second product. The “at least partially separate” may represent that approximately at least 50%, at least 65%, at least 75%, at least 80% or at least 90% of the overall asphalt (AS) is separated from the aggregates (AG); however, the present disclosure is not limited thereto.

According to the asphalt stripping treatment of an embodiment of the present disclosure, the water is directly used as the medium without adding any organic solvent, which is very environmentally friendly. The water used in the present disclosure is, for example, the reverse osmosis water, deionized water, distilled water, mineral water, tap water or other suitable water.

Specifically, the asphalt stripping unit 20 (as shown in FIG. 2) immerses the first product in water and provides driving force through a water-phase assisted separation technology. That is, without using any organic solvent, water is used as a carrier to cause collisions among pieces of reclaimed asphalt pavement (RAP), so as to achieve the effect of separating the asphalt (AS) from the aggregates (AG). For example, the asphalt stripping treatment is performed in a drum reactor.

Since an embodiment of the present disclosure utilizes a drum reactor to perform the asphalt stripping treatment, rather than using a vertical reactor that requires rotation by blades, mass production can be performed, which is commercially feasible.

According to some embodiments, in the asphalt stripping treatment, a rotational tangential velocity of the drum reactor may be between 0.5 m/s and 2.5 m/s, such as between 0.75 m/s and 2.45 m/s, between 0.80 m/s and 2.4 m/s, or for example, may be between 0.82 m/s and 2.2 m/s, or between 0.86 m/s and 2.35 m/s, but the present disclosure is not limited thereto. A reaction temperature may be between 20 °C and 100 °C, such as between 30 °C and 95 °C, between 40 °C and 95 °C, between 50 °C and 95 °C, between 70 °C and 95 °C, between 90 °C and 95 °C, etc., but the present disclosure is not limited thereto. A reaction time may be between 20 minutes and 130 minutes, such as between 30 minutes and 120 minutes, between 40 minutes and 110 minutes, between 50 minutes and 100 minutes, between 60 minutes and 90 minutes, etc., but the present disclosure is not limited thereto.

As shown in step S17, a vibratory screening and sorting step is performed on the second product (i.e., the reclaimed asphalt pavement RAP after being treated by step S15, comprising the asphalt AS and the aggregate AG) by a water-circulating screening and sorting processor unit 30 (as shown in FIG. 2) to sort out a third product and a fourth product, wherein the third product comprises a plurality of asphalt sands SG1, and the fourth product comprises a plurality of recycled stones SG2.

According to some embodiments, an average particle size of the asphalt sands SG1 may be less than 3 mm, such as 2 mm, 1.5 mm, 1 mm, etc., but the present disclosure is not limited thereto. On the other hand, based on a total weight of the asphalt sands SG1 (i.e., regarded as 100 wt %), a content of the asphalt AS may be greater than 6 wt %, such as 6.5 wt %, 7 wt %, 8 wt %, etc., but the present disclosure is not limited thereto. An average particle size of the recycled stones SG2 may be equal to or greater than 3 mm, such as 3.5 mm, 4 mm, 5 mm, etc., but the present disclosure is not limited thereto. On the other hand, when the total weight of the recycled stones SG2 is 100 wt %, the content of the asphalt AS may be less than 1 wt %, such as 0.75 wt %, 0.5 wt %, 0.25 wt %, etc., but the present disclosure is not limited thereto.

The recycled stones SG2 may comprise a first group of recycled stones, and an average particle size of the first group of recycled stones may be greater than 10 mm, such as 11 mm, 12 mm, 13 mm, etc., but the present disclosure is not limited thereto. On the other hand, when a total weight of the first group of recycled stones is 100 wt %, the content of the asphalt AS may be less than 0.2 wt %, such as 0.15 wt %, 0.1 wt %, 0.05 wt %, etc., but the present disclosure is not limited thereto.

The recycled stones SG2 may further comprise a second group of recycled stones, and an average particle size of the second group of recycled stones may be 3 mm to 10 mm, such as 5 mm, 7 mm, 9 mm, etc., but the present disclosure is not limited thereto. On the other hand, when a total weight of the second group of recycled stones is 100 wt %, the content of the asphalt AS may be less than 1 wt %, such as 0.75 wt %, 0.5 wt %, 0.25 wt %, etc., but the present disclosure is not limited thereto.

Since the water-circulating screening and sorting processor unit 30 may comprise a screening machine 31, a cyclone separator 33, a fine sand screening machine 35, a sedimentation tank 37, and a filter press-type dehydrator 39 (as shown in FIG. 3 and detailed below), step S17 may further comprise the following steps (i)-(iii):

(i) the screening machine 31 receives a first mixed liquid after the asphalt stripping treatment, the first mixed liquid comprising the asphalt AS, the aggregates AG, and water WR, and the screening machine 31 screens the first mixed liquid into a mixed liquid comprising the third product and a mixed liquid comprising the fourth product, wherein an average particle size of particles of the mixed liquid comprising the third product is less than 3 mm, and an average particle size of particles of the mixed liquid comprising the fourth product is greater than or equal to 3 mm;

(ii) further introducing the mixed liquid comprising the third product into the cyclone separator 33, circulating the mixed liquid with the fine sand screening machine 35, and collecting a second mixed liquid containing particles with an average particle size of less than 0.075 mm into the sedimentation tank 37 for standing, so as to form a sediment (a portion of the third product); and (iii) introducing the sediment into the filter press-type dehydrator 39 to remove moisture by pressing, and returning the supernatant in the sedimentation tank 37 after standing to the asphalt stripping unit for reuse.

According to other embodiments, the treatment method of reclaimed asphalt pavement RAP of the present disclosure may omit step S13 (not shown). That is, step S15 is performed after step S11 to directly perform the asphalt stripping treatment on the reclaimed asphalt pavement RAP, and the asphalt AS in the reclaimed asphalt pavement RAP is at least partially separated from the aggregates AG by the asphalt stripping unit 20 using water as a medium, without undergoing the pretreatment as shown in step S13. The steps S15 and S17 are the same as described above and will not be repeated here.

FIG. 2 illustrates a reclaimed asphalt pavement treatment system SY according to an embodiment of the present disclosure, for example, used for performing the steps as shown in FIGS. 1A-1C. FIG. 3 illustrates a water-circulating screening and sorting processor unit 30 according to an embodiment of the present disclosure.

Please refer to FIG. 2, the reclaimed asphalt pavement treatment system (SY) may comprise a pretreatment unit 10, an asphalt stripping unit 20, and a water-circulating screening and sorting processor unit 30. The pretreatment unit 10 is configured to apply a biological agent (BIO) to the reclaimed asphalt pavement (RAP) to form a first product. The asphalt stripping unit 20 is connected to the pretreatment unit 10 and the water-circulating screening and sorting processor unit 30, and is configured to receive the first product and perform an asphalt stripping treatment on the first product using water as a medium to at least partially separate the asphalt (AS) in the first product from the aggregates (AG) and form a second product. The water-circulating screening and sorting processor unit 30 is configured to receive the second product (i.e., the asphalt AS and the aggregates AG which have undergone the asphalt stripping treatment) and perform a vibratory screening and sorting step on the second product to sort out a third product and a fourth product, the third product comprising a plurality of asphalt sands SG1 and the fourth product comprising a plurality of recycled stones SG2. The water (WR) generated by the water-circulating screening and sorting processor unit 30 can be transmitted back to the asphalt stripping unit 20 for use in the asphalt stripping treatment. It can be seen that the water (WR) of the water-circulating screening and sorting processor unit 30 can be 100% reused, conforming to the concept of sustainable utilization.

Please refer to FIG. 3, the water-circulating screening and sorting processor unit 30 may comprise a screening machine 31, a cyclone separator 33, a fine sand screening machine 35, a sedimentation tank 37, and a filter press-type dehydrator 39.

According to an embodiment of the present disclosure, the screening machine 31 can receive a first mixed liquid after the asphalt stripping treatment, the first mixed liquid comprising the asphalt (AS), the aggregates (AG), and water (WR), and the screening machine 31 screens the first mixed liquid into a mixed liquid comprising the third product and a mixed liquid comprising the fourth product, wherein an average particle size of particles of the mixed liquid comprising the third product is less than 3 mm, and an average particle size of particles of the mixed liquid comprising the fourth product is greater than or equal to 3 mm. The cyclone separator 33 can operate cyclically with the fine sand screening machine 35 to collect particles with a particle size between 0.075 mm and 3 mm, and simultaneously collect particles with a particle size of less than 0.075 mm to the sedimentation tank 37 for standing and settling to the bottom. For example, the cyclone separator 33 can collect a second mixed liquid containing particles with an average particle size of less than 0.075 mm into the sedimentation tank 37 for standing to form a sediment (a portion of the third product). The sediment is pressed by the filter press-type dehydrator 39 to remove moisture, and a clear supernatant (e.g., water WR) after standing in the sedimentation tank 37 is returned to the asphalt stripping unit 20 for cyclic use.

In order to make the above and other objects, features, and advantages of the present invention more comprehensible, several embodiments are given below and described in detail as follows:

1. Pretreatment Unit—Impact Assessment of the Biological Agent

In order to test the impact of the biological agent on the viscosity of asphalt, embodiments and comparative examples were used to conduct the evaluation of the following experiments. It should be noted that although the following experiments use Bacillus velezensis (BV) and/or Priestia aryabhattai (PA) as representatives of the bacterial species contained in the biological agent, the biological agent in the disclosure is not limited to these two species. Users can select suitable single species or mixed species according to requirements, and the mixing ratio of mixed species can also be adjusted according to actual needs.

1-1 Experiment 1

Embodiment 1 is asphalt treated with the biological agent, and the bacterial species in the biological agent is Bacillus velezensis (BV). The bacterial liquid concentration (OD₆₀₀) used is 1.2 to 1.4, and the weight ratio of the bacterial liquid to the asphalt is about 2.86 (i.e., weight of bacterial liquid:weight of asphalt=2.86:1). Comparative Example 1 is original asphalt without treatment with the biological agent.

Embodiment 1 and Comparative Example 1 were treated at room temperature (25 °C) for 1 to 7 days. During this period, the asphalt viscosities of Embodiment 1 and Comparative Example 1 on each day were tested, and the test results of Embodiment 1 and Comparative Example 1 were used to calculate the asphalt viscosity reduction percentage according to the following Formula 1:

$\begin{array}{cc}\mathrm{VP}=\frac{\left(V0-V1\right)}{V0}\times 100\%& \mathrm{Formula}1\end{array}$

In Formula 1, V0 represents the initial asphalt viscosity of Comparative Example 1, V1 represents the respective viscosities of the asphalt of Embodiment 1 after being treated with the biological agent for 1 to 7 days, and VP represents the asphalt viscosity reduction percentage. The analysis results are shown in Table 1.

	TABLE 1
	treatment duration of the biological agent (days)
	1	2	3	4	5	6	7
asphalt	2.3%	6.0%	10.0%	10.5%	10.7%	11.1%	11.5%
viscosity
reduction
percentage
(%)

As shown in Table 1, using a single bacterial species BV alone can reduce asphalt viscosity, and the viscosity reduction can reach 10% on the third day of the reaction, and the viscosity reduction effects on the subsequent fourth to seventh days are all greater than 10%.

1-2 Experiment 2

Embodiment 2-1 and Embodiment 2-2 are both asphalts treated with the biological agent. The bacterial species in the biological agent of Embodiment 2-1 is Bacillus velezensis (BV), and the bacterial species in the biological agent of Embodiment 2-2 is Priestia aryabhattai (PA). The bacterial liquid concentration (OD₆₀₀) used is 1.2 to 1.4, and the weight ratio of the bacterial liquid to the asphalt is about 8.3 (i.e., weight of bacterial liquid:weight of asphalt=8.3:1). Comparative Example 2 is original asphalt without treatment with the biological agent.

Regarding the treatment temperature, asphalt viscosity testing, and calculation of asphalt viscosity reduction percentage used in Experiment 2, they are all performed in an operation manner similar to that of the above Experiment 1, and will not be repeated here.

After one week of treatment, the asphalt viscosity reduction percentages of Embodiment 2-1 and Embodiment 2-2 relative to Comparative Example 2 are shown in Table 2.

	TABLE 2
		Embodi-	Embodi-
	group	ment 2-1	ment 2-2
	asphalt viscosity	28.9%	19.8%
	reduction
	percentage (%)

As shown in Table 2, using a single bacterial species, whether it is BV or PA, has a significant effect of reducing asphalt viscosity by nearly 20% or even nearly 30% after one week.

1-3 Experiment 3

Embodiment 3-1, Embodiment 3-2, and Embodiment 3-3 are asphalts treated with different biological agents. The bacterial species in the biological agent of Embodiment 3-1 is Bacillus velezensis (BV); the bacterial species in the biological agent of Embodiment 3-2 is Priestia aryabhattai (PA); and the bacterial species in the biological agent of Embodiment 3-3 is a mixed bacterial species composed of Bacillus velezensis (BV) and Priestia aryabhattai (PA) in a mixing ratio of 1:1. The bacterial liquid concentration (OD₆₀₀) used is 1.2 to 1.4, and the weight ratio of the bacterial liquid to the asphalt is about 3.75 (i.e., weight of bacterial liquid:weight of asphalt=3.75:1). Comparative Example 3 is original asphalt without treatment with the biological agent.

Regarding the treatment temperature, asphalt viscosity testing, and calculation of asphalt viscosity reduction percentage used in Experiment 3, they are all performed in an operation manner similar to that of the above Experiment 1, and will not be repeated here.

After one month of treatment, the asphalt viscosity reduction percentages of Embodiment 3-1, Embodiment 3-2, and Embodiment 3-3 relative to Comparative Example 3 are shown in Table 3.

	TABLE 3
		Embodi-	Embodi-	Embodi-
	group	ment 3-1	ment 3-2	ment 3-3
	asphalt viscosity	36.6%	21.1%	23.4%
	reduction
	percentage (%)

As shown in the results of Table 3, whether using a single bacterial species (BV or PA) or using a mixed bacterial species of BV and PA, there is a significant effect of reducing asphalt viscosity by at least 20% or even greater than 30% after one month.

On the other hand, the contents (%) of four components in the asphalt of Embodiment 3-1 (treated with single bacterial species BV) and the asphalt of Comparative Example 3 are compared as shown in Table 4. The viscosities of the four components from low to high are respectively saturates, aromatics, resins, and asphaltenes.

	TABLE 4
		Comparative	Embodi-
	contents (%)	Example 3	ment 3-1
	saturates	3.62	4.41
	aromatics	13.04	12.62
	resins	64.31	65.12
	asphaltenes	19.03	17.84

As shown in Table 4, compared to Comparative Example 3, after the asphalt of Embodiment 3-1 reacts with the bacterial liquid, the proportion of high-viscosity asphaltenes decreases, while the proportion of low-viscosity saturates increases, which achieved an effect of assisting the decrease of viscosity characteristics.

1-4 Experiment 4

Embodiment 4 is a reclaimed asphalt pavement (as shown in steps S11 and S13) treated with the biological agent having a bacterial species of Bacillus velezensis (BV) for one month, followed by performing an asphalt stripping treatment (as shown in step S15) and subsequently testing the asphalt content thereof. Comparative Example 4 is an original reclaimed asphalt pavement (as shown in step S11) subjected to an asphalt stripping treatment (as shown in step S15), followed by testing the asphalt content thereof; the difference from Embodiment 4 is that Comparative Example 4 did not undergo treatment with the biological agent (i.e., step S13 was not performed).

The asphalt content of the above-mentioned original reclaimed asphalt pavement RAP (i.e., the percentage occupied by asphalt based on the total weight of the reclaimed asphalt pavement RAP (100%)) is 4.35%, and the asphalt viscosity is 300,000 Poise (P, 1 P=1 g/(cm·s)). The bacterial liquid used in Embodiment 4 is a single bacterial species BV; the weight ratio of the bacterial liquid to the reclaimed asphalt pavement is 0.0125 (i.e., weight of bacterial liquid:weight of reclaimed asphalt pavement=1:80); the weight ratio of the bacterial liquid to the asphalt is 0.286 (i.e., weight of bacterial liquid:weight of asphalt=1:3.5); and the bacterial liquid concentration (OD₆₀₀) is 1.6 to 2. The particle sizes of the reclaimed asphalt pavement RAP tested in Comparative Example 4 and Embodiment 4 are consistent.

In the subsequently performed asphalt stripping treatment, the reclaimed asphalt pavements of Comparative Example 4 and Embodiment 4 are added into a reactor, and water is added, with the temperature maintained at 90 °C to 93 °C and a reaction time of 30 minutes. After the asphalt stripping treatment is completed, the asphalt contents of Comparative Example 4 and Embodiment 4 are respectively detected, as shown in Table 5.

	TABLE 5
	Comparative	Embodi-
	Example 4	ment 4
	asphalt	1.99	1.21
	contents
	(%)

As shown in Table 5, compared to Comparative Example 4, after the asphalt stripping treatment under the same conditions, the magnitude of the decrease in asphalt content of Embodiment 4 is more significant. In addition, the asphalt viscosity measured in Embodiment 4 is 200,000 Poise (P, 1 P=1 g/(cm·s)), and the asphalt viscosity reduction percentage calculated according to the above Formula 1 is about 33%.

Further, an asphalt stripping rate SR of Comparative Example 4 and Embodiment 4 after the asphalt stripping treatment is calculated according to the following Formula 2.

$\begin{array}{cc}\mathrm{SR}=\frac{\left(C0-C1\right)}{C0}\times 100\%& \mathrm{Formula}2\end{array}$

In Formula 2, C0 represents the asphalt content of the original reclaimed asphalt pavement RAP, and C1 represents the residual amount of asphalt after the asphalt stripping treatment.

Through calculation, the asphalt stripping rate of Comparative Example 4 is about 54%, and the asphalt stripping rate of Embodiment 4 is about 72%. Compared to Comparative Example 4, Embodiment 4 can improve the asphalt stripping effectiveness by at least 18%. It is evident that the biological agent treatment can enhance the asphalt stripping effect.

2. Asphalt Stripping Unit—Influence of Different Reaction Conditions

2-1 Experiment 5

Embodiments 5-1 to 5-4 show the asphalt content of feedstocks composed of reclaimed asphalt pavement RAP with different particle sizes (as shown in step S11), which do not pass through the pretreatment unit 10 (as shown by not performing step S13), but are directly treated by the asphalt stripping unit 20 (as shown in step S15) and the water-circulating screening and sorting processor unit 30, showing the influence of different particle sizes on the stripping effect.

In Embodiments 5-1 to 5-4, the weights of the reclaimed asphalt pavement are all 60 kg, and the asphalt contents are all 4% to 5.5%. The particle size of the reclaimed asphalt pavement of Embodiment 5-1 is between 100 mm and 120 mm; the particle size of the reclaimed asphalt pavement of Embodiment 5-2 is between 50 mm and 100 mm; the particle size of the reclaimed asphalt pavement of Embodiment 5-3 is between 9.5 mm and 25 mm; and the particle size of the reclaimed asphalt pavement of Embodiment 5-4 is less than 9.5 mm.

First, the reclaimed asphalt pavements of Embodiments 5-1 to 5-4 are added into a reactor (e.g., a drum reactor) to perform an asphalt stripping treatment (as shown in step S15). The reactor contains water and the reaction is performed according to specific conditions, wherein, in Embodiments 5-1 to 5-2 and 5-4, the reaction temperatures are all between 90 °C and 100 °C, and the rotational tangential velocity of the reactor is 0.86 m/s; in Embodiment 5-3, the reaction temperature is about 70 °C, and the rotational tangential velocity of the reactor is 2.3 m/s. The reaction times of Embodiments 5-1 to 5-4 are 120 minutes, 90 minutes, 90 minutes, and 60 minutes, respectively.

Next, the reclaimed asphalt pavement after the asphalt stripping treatment is subjected to vibratory screening and sorting, and is screened into a first group of recycled stones, a second group of recycled stones, and asphalt sands with different particle sizes. The particle size of the screened first group of recycled stones is about 12.5 mm; the particle sizes of the second group of recycled stones are about 4.75 mm and 9.52 mm; and the particle sizes of the asphalt sands are about 1.18 mm and 2.36 mm.

The asphalt contents of Embodiments 5-1 to 5-4 are shown in Table 6, wherein “-” represents no data.

TABLE 6
	Embodi-	Embodi-	Embodi-	Embodi-
group	ment 5-1	ment 5-2	ment 5-3	ment 5-4
asphalt	first group	0.28~0.84	0.31~0.76	0.063~0.29	0.46
contents	of recycled
(%)	stones
	second group	0.98	1.52	0.97	1.47
	of recycled
	stones
	asphalt sands	—	—	10.27	—

As shown in Table 6, after performing the asphalt stripping treatment, the asphalt contents of Embodiments 5-1 to 5-4 all significantly decreased. It can be seen that different feedstock particle sizes all possess an asphalt stripping effect.

2-2 Experiment 6

Embodiments 6-1 to 6-3 show the asphalt contents after the reclaimed asphalt pavement RAP is treated in the asphalt stripping unit 20 (as shown in step S15) at different reaction temperatures, showing the influence of reaction temperature on the stripping effect.

In Embodiments 6-1 to 6-3, the weights of the reclaimed asphalt pavement are all 60 kg, the particle sizes of the feedstocks are all between 9.5 mm and 25 mm, the asphalt contents are all 4% to 5.5%, the rotational tangential velocities of the reactor are all 2.3 m/s, and the reaction times are all 90 minutes. The reaction temperatures of Embodiments 6-1 to 6-3 are 90 °C to 100 °C, 70 °C, and room temperature (e.g., 20 °C to 25 °C), respectively. The subsequent particle size division through the vibratory screening and sorting step is as described above.

The asphalt contents of Embodiments 6-1 to 6-3 are shown in Table 7, wherein “-” represents no data.

TABLE 7
	Embodi-	Embodi-	Embodi-
group	ment 6-1	ment 6-2	ment 6-3
asphalt	first group	0.086~0.45	0.063~0.29	0.46~0.97
contents	of recycled
(%)	stones
	second group	1.08~1.54	0.97	1.2
	of recycled
	stones
	asphalt sands	10.36	10.27	—

As shown in Table 7, after performing the asphalt stripping treatment (step S15), the asphalt contents of Embodiments 6-1 to 6-3 all significantly decreased. It can be seen that different reaction temperatures all possess an asphalt stripping effect. Specifically, when the reaction temperature is equal to or greater than 70 °C, the asphalt stripping effect is better.

2-3 Experiment 7

Embodiments 7-1 to 7-3 show the asphalt contents after the reclaimed asphalt pavement RAP is reacted under different conditions of the rotational tangential velocity through the asphalt stripping treatment (as shown in step S15), showing the influence of the rotational tangential velocity on the stripping effect.

In Embodiments 7-1 to 7-3, the weights of the reclaimed asphalt pavement are all 60 kg, the particle sizes of the feedstocks are all between 9.5 mm and 25 mm, the asphalt contents are all 4% to 5.5%, the reaction times are all 30 minutes, and the reaction temperatures are all 90 °C to 100 °C. The rotational tangential velocities of Embodiments 7-1 to 7-3 are 2.3 m/s, 1.8 m/s, and 0.86 m/s, respectively. The subsequent particle size division through the vibratory screening and sorting step is as described above.

The asphalt contents of Embodiments 7-1 to 7-3 are shown in Table 8, wherein “-” represents no data.

TABLE 8
	Embodi-	Embodi-	Embodi-
group	ment 7-1	ment 7-2	ment 7-3
asphalt	first group	0.086~0.45	0.79	0.46
contents	of recycled
(%)	stones
	second group	1.08~1.54	1.2-2.9	1.47
	of recycled
	stones
	asphalt sands	10.36	—	—

As shown in Table 8, after performing the asphalt stripping treatment, the asphalt contents of Embodiments 7-1 to 7-3 all significantly decreased. Specifically, as the rotational tangential velocity increases, the asphalt stripping effect becomes better.

It should be understood that the settings of the above parameters (such as reaction temperature and tangential speed) and the product particle sizes will be adjusted according to the immediate needs of the actual field operation.

In the method of the prior art (e.g., reference JP5979532B2), after the reclaimed asphalt pavement RAP undergoes a primary treatment (performed with a heating and crushing device at a reaction temperature of 100 °C), the asphalt is extracted by a first-stage treatment device (reaction temperature 60-90 °C), a second-stage treatment device (reaction temperature 60-90 °C), and a third-stage treatment device (reaction temperature 100-300 °C). Its heating and crushing device is a vertical reactor, which performs treatment by blade stirring, and the resulting asphalt stripping efficiency is about 80-85%. In another prior art, the reclaimed asphalt pavement RAP is only treated by physical methods (e.g., heating and crushing) without treatment with a biological agent, and the resulting asphalt stripping efficiency is about 50-75%. According to the asphalt stripping method of the present disclosure (as shown in FIG. 1A), the resulting asphalt stripping efficiency can reach exceed 92%. It can be seen that compared to the prior art, the asphalt stripping method provided by the present disclosure can not only significantly improve stripping efficiency, but the obtained products can also retain good particle sizes and shapes and can be directly used, and water resources can be further recycled, which is environmentally friendly.

Through the method for treating asphalt according to some embodiments of the present disclosure, the obtained recycled stones (e.g., asphalt content less than 1 wt. %, particle size greater than 3 mm) are tested to comply with relevant quality requirements for new or recycled coarse aggregates (e.g., Republic of China National Standards CNS 15308 and CNS 1240; American Society for Testing and Materials standards ASTM-D692M-15 and ASTM-C33), and can be used as a source of aggregates for graded materials applied in asphalt concrete (AC) and reinforced concrete (RC).

In terms of asphalt concrete applications, the recycled stones of an embodiment of the present disclosure can be used together with asphalt sands as graded aggregates, and a 100% recycling rate can be achieved. Asphalt concrete specimens meeting the requirements are successfully prepared, showing that the product obtained by the method of the present disclosure has the benefits of increasing the resource utilization ratio of reclaimed pavement materials, reducing the usage of natural aggregates, and decreasing waste stream flow.

In terms of reinforced concrete applications, the recycled stones of an embodiment of the present disclosure are used to replace coarse aggregates; under the condition of maintaining the same compressive strength, the amount of cementitious material can be reduced by about 12% to 25%. Therefore, it not only reduces the cost of cementitious materials and carbon emissions but also simultaneously enhances the technical efficacy of resource recycling efficiency.

On the other hand, the asphalt sands obtained in an embodiment of the present disclosure (e.g., asphalt content greater than 9 wt %, particle size less than 3 mm) have a high asphalt content and thus can be directly used as a recycled graded material for asphalt concrete. The asphalt sands can be directly returned to paving material preparation and repaving projects. Since the asphalt sands contain usable asphalt, they can be mixed into asphalt concrete to reduce the demand for new asphalt, and are expected to provide an asphalt replacement amount greater than or equal to 50%. Compared to hot-mix operations using entirely new materials, the asphalt sand products of the present disclosure can be fully reused, effectively reducing the input amount of new asphalt and reducing carbon emissions caused by the manufacturing and transportation of asphalt materials. Therefore, it can not only increase the resource utilization ratio of reclaimed asphalt pavement but also possesses the comprehensive benefits of asphalt saving and carbon reduction.

In summary, the present disclosure provides an improved method for processing a reclaimed asphalt pavement, which can separate asphalt in a low-energy-consumption and high-efficiency manner. The present disclosure performs the asphalt stripping treatment using water as a medium without the need to introduce any organic solvents, possessing the advantage of being environmentally friendly. In addition, the water generated during the treatment process can be recycled, and the recycled stones and asphalt sands obtained from screening have excellent quality and high reuse value. Therefore, the consumption of aggregates and asphalt can be significantly saved, achieving the dual effects of environmental sustainability and carbon reduction.

Although the present disclosure has been disclosed as above through embodiments, they are not intended to limit the present disclosure. Any person having ordinary knowledge in the technical field to which the present disclosure belongs may make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be determined by the scope defined by the appended claims.

Claims

1. A method for processing a reclaimed asphalt pavement, comprising the steps of:

(a) providing a reclaimed asphalt pavement, wherein the reclaimed asphalt pavement comprises a plurality of aggregates and asphalt coating the aggregates; and

(b) performing an asphalt stripping treatment on the reclaimed asphalt pavement, wherein the asphalt in the reclaimed asphalt pavement is at least partially separated from the aggregates by an asphalt stripping unit using water as a medium.

2. The method for processing a reclaimed asphalt pavement according to claim 1, further comprising:

prior to step (b), performing a pretreatment on the reclaimed asphalt pavement, wherein a biological agent is applied to the reclaimed asphalt pavement by a pretreatment unit to form a first product.

3. The method for processing a reclaimed asphalt pavement according to claim 2, further comprising:

in step (b), at least partially separating the asphalt in the first product from the aggregates by the asphalt stripping unit using the water as the medium to form a second product.

4. The method for processing a reclaimed asphalt pavement according to claim 3, further comprising:

(c) performing a vibratory screening and sorting treatment on the second product by a water-circulating screening and sorting processor unit to sort out a third product and a fourth product, wherein the third product comprises a plurality of asphalt sands, and the fourth product comprises a plurality of recycled stones.

5. The method for processing a reclaimed asphalt pavement according to claim 4, wherein the water-circulating screening and sorting processor unit comprises a screening machine, a cyclone separator, a fine sand screening machine, a sedimentation tank, and a filter press-type dehydrator.

6. The method for processing a reclaimed asphalt pavement according to claim 5, wherein the screening machine receives a first mixed liquid after the asphalt stripping treatment, the first mixed liquid comprising the asphalt, the aggregates, and the water, and the screening machine screens the first mixed liquid into a mixed liquid comprising the third product and a mixed liquid comprising the fourth product, wherein an average particle size of particles of the mixed liquid comprising the third product is less than 3 mm, and an average particle size of particles of the mixed liquid comprising the fourth product is greater than or equal to 3 mm.

7. The method for processing a reclaimed asphalt pavement according to claim 6, further comprising providing the mixed liquid containing the third product into the cyclone separator, and collecting a second mixed liquid containing particles with an average particle size of less than 0.075 mm into the sedimentation tank for standing to form a sediment.

8. The method for processing a reclaimed asphalt pavement according to claim 7, further comprising introducing the sediment into the filter press-type dehydrator to remove moisture by pressing, and returning the supernatant in the sedimentation tank after standing to the asphalt stripping unit for reuse.

9. The method for processing a reclaimed asphalt pavement according to claim 4, wherein a content of the asphalt is greater than 6 wt % when a total weight of the asphalt sands is 100 wt %.

10. The method for processing a reclaimed asphalt pavement according to claim 4, wherein a content of the asphalt is less than 1 wt % when a total weight of the recycled stones is 100 wt %.

11. The method for processing a reclaimed asphalt pavement according to claim 4, wherein the recycled stones comprise a first group of recycled stones, an average particle size of the first group of recycled stones is greater than or equal to 10 mm, and a content of the asphalt is less than 0.2 wt % when a total weight of the first group of recycled stones is 100 wt %.

12. The method for processing a reclaimed asphalt pavement according to claim 4, wherein the recycled stones comprise a second group of recycled stones, an average particle size of the second group of recycled stones is 3 mm to 10 mm, and a content of the asphalt is less than 1 wt % when a total weight of the second group of recycled stones is 100 wt %.

13. The method for processing a reclaimed asphalt pavement according to claim 2, wherein a bacterial species of the biological agent comprises a bacteria belonging to genus Bacillus, a bacteria belonging to genus Priestia, or a combination thereof.

14. The method for processing a reclaimed asphalt pavement according to claim 13, wherein the bacteria belonging to the genus Bacillus comprises Bacillus velezensis, Bacillus subtilis, Bacillus toyonensis, Bacillus licheniformis, Bacillus paralicheniformis, Bacillus thuringiensis, Bacillus pumilus or a combination thereof, and the bacteria belonging to the genus Priestia comprises Priestia aryabhattai, Priestia megaterium, Priestia flexa, Priestia filamentosa, Priestia endophytica or a combination thereof.

15. The method for processing a reclaimed asphalt pavement according to claim 2, wherein the biological agent is applied to the reclaimed asphalt pavement in the form of a bacterial liquid, a weight ratio of the bacterial liquid to the reclaimed asphalt pavement is between 0.001 and 1, and a concentration (OD600) of the bacterial liquid is between 1 and 3.

16. The method for processing a reclaimed asphalt pavement according to claim 2, wherein the reclaimed asphalt pavement has a first asphalt viscosity before applying the biological agent, the first product has a second asphalt viscosity, and the second asphalt viscosity is less than the first asphalt viscosity.

17. The method for processing a reclaimed asphalt pavement according to claim 1, wherein in step (b), the asphalt stripping treatment is performed in a drum reactor.

18. The method for processing a reclaimed asphalt pavement according to claim 17, wherein a rotational tangential velocity of the drum reactor is between 0.5 m/s and 2.5 m/s.

19. The method for processing a reclaimed asphalt pavement according to claim 1, wherein in step (b), a reaction temperature of the asphalt stripping treatment is between 20 °C and 100 °C.

20. The method for processing a reclaimed asphalt pavement according to claim 1, wherein in step (b), a reaction time of the asphalt stripping treatment is between 20 minutes and 130 minutes.