Method for dispersing agglomeration of waste mixture through cooperation of mechanical shearing and surfactant

Abstract

The invention provides a waste mixture caking and dispersing method based on mechanical shearing in cooperation with a surfactant, and aims to solve the problem of performance degradation caused by caking in RAP regeneration, the method is based on the emulsification effect of the surfactant, and rapid stripping of aged asphalt and old aggregate is realized through pretreatment, mixing stirring and screening processes; the method specifically comprises the steps that RAP agglomerates are preheated and then mixed with a surfactant solution, emulsification and dispersion are completed under the specific temperature and stirring condition, and finally recycled aggregate and recyclable residual emulsion are recycled through screening, the technology breaks through the limitation of traditional mechanical crushing and chemical dissolving, the RAP agglomeration problem is solved, old asphalt is effectively stripped, and the recycling rate of the recycled aggregate is increased. The stability of the regenerated material is enhanced, and the cost is reduced; in addition, the method supports the reuse of the emulsion, reduces the environmental pollution, realizes the recycling of resources, and has important significance for improving the performance of the recycled asphalt pavement and promoting the sustainable development of the road construction industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycled waste asphalt utilization, and particularly relates to a method for agglomerating and dispersing waste mixtures by mechanical shearing in cooperation with surfactants. Background Art

[0002] In recent years, with the acceleration of urbanization and infrastructure construction, a large number of recycled asphalt pavements (RAP) have been generated and accumulated. These RAPs not only occupy a large amount of land resources but also cause serious environmental pollution. With the increase in the cost of pavement materials, the research on RAP recycling technology has received increasing attention. Generally, when the RAP utilization rate is between 5% and 15%, a 15 - 30% reduction in material costs can be achieved. The key factors hindering the application of high - content RAP materials in recycled asphalt pavements are the serious agglomeration phenomenon and the complexity of quality control during the construction process.

[0003] Increasing the percentage of RAP in pavement engineering has attracted great attention from researchers. However, one of the problems with using a large amount of RAP is the agglomeration effect. RAP agglomeration is considered to be due to the binding effect of the old asphalt, where fine RAP aggregates agglomerate into coarse RAP aggregates, which is the so - called RAP agglomeration. During the milling process of asphalt pavements, the use of the cold milling method inevitably leads to RAP agglomeration. Currently, the mix design of recycled hot - mix asphalt still based on the gradation of extracted RAP aggregates, which obviously does not take into account the influence of RAP agglomeration. Therefore, if high - dosage RAP is directly used, problems such as abnormal void ratio and decreased rutting resistance caused by agglomeration will significantly shorten the pavement life, instead increasing the full - life - cycle maintenance cost and forming a vicious cycle of "inefficient recycling - high - cost repair".

[0004] In order to achieve the effective recycling of RAP, the key lies in the full stripping of the old asphalt and old aggregates in RAP, which is an effective way to ensure the road - using performance of recycled pavements. For this reason, the industry urgently needs a green and low - cost medium - temperature separation technology to solve the problem of RAP agglomeration while avoiding secondary pollution and energy waste, and truly realizing the circular economy closed - loop of "turning waste into treasure". Summary of the Invention

[0005] The present invention aims to provide a method for agglomerating and dispersing waste mixtures by mechanical shearing in combination with surfactants to solve the key problems existing in traditional treatment technologies. Traditionally, waste asphalt mixtures are mainly treated by pure mechanical crushing. Due to the bonding characteristics of old asphalt, this method often leads to material agglomeration and incomplete dispersion. In the laboratory environment, the chemical dissolution method can remove the agglomeration phenomenon to a certain extent, but because toxic solvents such as trichloroethylene and acetone are used, it is neither environmentally friendly nor suitable for large-scale application. The technical solution proposed by the present invention is to combine a specific type of surfactant with waste asphalt mixtures, and through a series of treatment steps such as heating, stirring, and screening, finally obtain recycled aggregates that are completely dispersed and have different particle size specifications. This method not only effectively reduces the agglomeration effect of RAP materials, but also is more environmentally friendly and suitable for large-scale promotion and application. Therefore, the present invention successfully solves the limitations of the poor dispersion effect of the mechanical crushing method and the unsuitability for large-scale use of the chemical dissolution method in the prior art.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: A method for agglomerating and dispersing waste mixtures by mechanical shearing in combination with surfactants, comprising the following steps: (1) RAP pretreatment Place the agglomerated waste asphalt mixture in an oven at 110 - 120 °C for preheating for 0.5 h, and prepare a surfactant solution; (2) Emulsification and dispersion treatment Mix the preheated agglomerated waste asphalt mixture with the surfactant solution in proportion, and heat and stir for dispersion for a certain time. During this process, collect the asphalt foam on the upper layer of the emulsion surface; (3) Screening and recycling treatment After the experiment, separate the aggregates from the emulsion by screening; after standing, separate the emulsion from the sludge to obtain a reusable residual emulsion.

[0007] Further, the production process of the agglomerated waste asphalt mixture in step (1) is as follows: First, remove dust from the waste asphalt mixture, then heat it in an oven at a temperature of 110 - 120 °C for 1 h, then perform kneading and extrusion separation, and finally obtain agglomerated waste asphalt mixtures with different particle sizes after cooling.

[0008] Further, the agglomerated waste asphalt mixture in step (1) includes agglomerates with at least one of the following particle sizes: the particle size of the agglomerates is 13.2 - 16 mm, 9.5 - 13.2 mm, 4.75 - 9.5 mm, and 2.36 - 4.75 mm, and the concentration of the surfactant solution is 0 - 6 wt%.

[0009] Further, in the step (2), the mixing ratio of the surfactant solution to the agglomerated waste asphalt mixture is 1:2. The working condition parameters of heating and stirring include stirring speed, heating temperature, and time. The stirring speeds are 280 r / min, 700 r / min, and 1800 r / min, the heating temperatures are 60°C, 80°C, and 90°C, and the times are 0.5 h, 1 h, and 1.5 h.

[0010] Further, in the step (3), the aggregate is separated from the emulsion by the water sieve method, and the standing time is 0.5 - 1 h.

[0011] Further, in the step (3), for the recycled residual emulsion, the upper clear liquid after standing is taken and directly added with a certain amount of water and then used in a ratio of 1:2.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for dispersing the agglomerated waste mixture by mechanical shearing in cooperation with a surfactant, specifically a reusable surfactant for quickly separating the old asphalt and the old aggregate in the RAP agglomeration. The main function of this surfactant is to reduce the surface tension of the old asphalt. Under the action of mechanical stirring, the asphalt adhering to the surface of the RAP is eluted in the aqueous phase in the form of micrometers, thereby realizing the rapid separation of the old asphalt and the old aggregate. The emulsification and dispersion process significantly increases the activation energy of the ionic surfactant, which is completely ionized in the solution system and exists in the system in the form of ions. The surfactant molecules in ionic form are more conducive to reacting with the strong electrolytes in the asphalt, thus showing a solubilization effect. In addition, this surfactant can be miscible with water and the old asphalt to form an emulsion, which enables it to be evenly dispersed in the RAP, demonstrating simple and excellent process characteristics, and still maintaining high-performance even after multiple repeated uses. Therefore, the present invention realizes the effective separation of the old asphalt and the old aggregate in the RAP during the production process of recycled asphalt mixture, which has important engineering practical significance for improving the road performance of recycled asphalt pavement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation to the present invention. In the drawings: Figure 1 is a flow schematic diagram of the method for dispersing the agglomerated waste mixture based on the cooperation of mechanical shearing and surfactant in the embodiment of the present invention; Figure 2 is a method for pretreating RAP provided by the embodiment of the present invention; Figure 3 is the oil removal efficiency and gradation change of RAP and different surfactants in the test example of the present invention; Figure 4For the dispersion effect of RAP before and after emulsification and dispersion in the test examples of the present invention; Figure 5 For the dispersion effect of different particle sizes before and after extraction, emulsification and dispersion in the test examples of the present invention; Figure 6 For the influence of the number of residual emulsion recovery times on the oil removal efficiency in the test examples of the present invention; Figure 7 It is a comparison diagram of the appearance of RAP before and after dispersion. Detailed implementation manners

[0014] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0015] The present invention will be further described in detail below in conjunction with the embodiments.

[0016] As Figure 1 shown, Specific Embodiment 1 of the method for dispersing agglomerated waste mixtures by mechanical shearing in cooperation with a surfactant provided by the present invention: The method for dispersing agglomerated waste mixtures by mechanical shearing in cooperation with a surfactant includes the following steps: (1) RAP pretreatment First, the waste asphalt mixture is dusted, then heated in an oven at a temperature of 110 - 120 °C for 1 h, then kneaded and extruded for separation, and after cooling, agglomerated waste asphalt mixtures with different particle sizes are obtained (see Figure 2 ).

[0017] (2) Emulsification and dispersion treatment When performing emulsification and dispersion, the agglomerated waste asphalt mixture is preheated in an oven at 110 - 120 °C for another 0.5 h, and a surfactant solution is prepared with a concentration of 0 - 6 wt%. The agglomerated waste asphalt mixture and the surfactant solution are mixed at a ratio of 1:2, and their oil removal efficiency is studied. Heat and stir for a certain period of time, and during this process, collect the asphalt foam on the upper layer of the emulsion surface to prevent them from adhering to the aggregates again; by changing the heating temperature, time, and stirring speed, study the influence of different process conditions on the dispersion effect of RAP. Specifically, the working condition parameters of heating and stirring include stirring speed, heating temperature, and time. The stirring speeds are 280 r / min, 700 r / min, and 1800 r / min, the heating temperatures are 60 °C, 80 °C, and 90 °C, and the times are 0.5 h, 1 h, and 1.5 h. Test the changes in asphalt content and gradation before and after fractional emulsification, dispersion, and extraction, and use the agglomeration rate (PL) and fineness modulus ratio (FMR) to measure the gradation changes. Emulsify and disperse the RAP agglomerates with different particle sizes after pretreatment respectively, and study the treatment effects of different particle sizes by the emulsification and dispersion method.

[0018] The calculation formula for the fineness modulus ratio is as follows: (1) (2) In the formula: is the fineness modulus; , , , , are the cumulative sieve residue percentages of each sieve of 13.2 mm, 9.5 mm, 4.75 mm, 2.36 mm, <2.36 mm respectively. In this study, the separation of RAP above 2.36 mm is mainly studied, so directly takes 100%. is the fineness modulus ratio; is the fineness modulus of the aggregate after the extraction test of RAP; is the fineness modulus of RAP after emulsification and dispersion.

[0019] Calculate the total agglomeration degree by adding the difference in the loss rate of each particle size before and after extraction and emulsification and dispersion: (3) (4) (5) Among them, PL i1 is the loss rate (%) of the i-th particle size after extraction, and p i is the cumulative sieve residue of the i-th sieve after extraction. PL i2 is the loss rate (%) of the i-th particle size after emulsification and dispersion, and Ci It is the cumulative sieve residue of the i-th sieve after emulsification and screening. The sieve hole size of the i-th sieve is not less than 2.36 mm, where PL is the degree of agglomeration (%) of RAP particles.

[0020] (3)Screening and recycling treatment After the experiment, the aggregate and the emulsion are separated by the water sieve method; after standing for 0.5 - 1 h, the emulsion and the sludge are separated to obtain the reusable residual emulsion. Water is directly added to the residual emulsion and it is continued to be mixed with the untreated RAP in a ratio of 1:2 for use.

[0021] In this embodiment, since the main function of the surfactant is to soften the asphalt, if their oil removal rate is the highest under the same conditions, it indicates that their effect is the best and the agglomeration dispersion effect of RAP is better. Therefore, only the change in asphalt content is used to measure the dispersion effect. Through preliminary experimental exploration, the whole RAP is selected as the research object. Under the same treatment conditions of a rotation speed of 1800 r / min, 80 °C and 1 h, three different anionic surfactants, namely sodium dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfate (SDS) and sodium methyl ester sulfonate (MES), are selected to study the effect of different concentrations (0 - 6 wt%) of surfactants on the asphalt content after emulsification and dispersion.

[0022] The method for agglomeration dispersion of waste mixtures based on the synergy of mechanical shear and surfactant includes the following steps: (1)Transfer 1000 parts by weight of SDBS, MES, and SDS solutions with different concentrations to a stirring container, and place the container on an electric hot plate heating device. (2)Start stirring, control the rotation speed at 1800 r / min, and gradually add 2000 parts by weight of RAP agglomerates, and control the temperature at 80 °C. (3)Flip and stir the RAP agglomerates every 10 min. After stirring for 1 h, separate the RAP agglomerates and the residual emulsion. Air-dry the RAP aggregates at room temperature, weigh the masses of different particle sizes to obtain their gradation, and then perform extraction to obtain their asphalt content.

[0023] Through conventional extraction tests, the asphalt content of the original RAP is 4.81%. As Figure 3 shown in (a), the asphalt contents of the recycled aggregates treated with different concentrations of surfactants are different. Although some old asphalt can be eluted without adding a solvent, the effect is better when the surfactant plays a role. The effect of SDBS with a concentration of 2 wt% is the best, and the asphalt content is reduced by 50%. The effects of MES and SDS are relatively poor, and the concentration needs to be increased to achieve the corresponding effect. The emulsification dispersion and extraction gradation curves are as Figure 3 shown in (b). The integral area between the curves is 64.58, and their gradations are basically the same, indicating that the emulsification dispersion effect is extremely close to the extraction effect.

[0024] Specific Example 2 of the method for dispersing agglomerated waste mixture by mechanical shearing and surfactant provided by the present invention: In this example, the orthogonal experiment method was used to study the influence of different process parameters on the agglomeration of RAP. The rotational speed (i.e., 280, 700, 1800 r / min), temperature (i.e., 60, 80, 90 °C), and rotation time (i.e., 0.5, 1, 1.5 h) all affect the separation efficiency of agglomeration. Therefore, the fineness modulus ratio (FMR) and the degree of agglomeration (PL) were used as evaluation criteria to determine the optimal process parameters for emulsion separation. The separation effect of RAP under three process parameters was studied by a three-factor and three-level orthogonal experiment.

[0025]

[0026] As Figure 4 shown, when the dosage of SDBS surfactant is 2 wt%, the ratio of emulsion to RAP is 1:2, the rotation time is 1 h, the temperature is controlled at about 80 °C, and the rotational speed is determined to be 1800 r / min, the separation effect is the best. Its asphalt content drops to 2.24, the PL has dropped to 26.9, and the FMR is 0.89.

[0027] Specific Example 3 of the method for dispersing agglomerated waste mixture by mechanical shearing and surfactant provided by the present invention: In this example, since the shearing and collision effects have a significant impact on the separation effect of RAP particles with different particle sizes during the mixing process, after determining the relevant experimental parameters, the separation effect of RAP particles with different particle sizes was refined. Pretreated RAP agglomerates with different particle sizes (13.2 - 16 mm, 9.5 - 13.2 mm, 4.75 - 9.5 mm, 2.36 - 4.75 mm) were selected for emulsification dispersion experiments. As Figure 2 shown, it is the production process of agglomerated waste asphalt mixtures with different particle sizes.

[0028] As Figure 5 shown in (a) and (b), when emulsifying and dispersing RAP agglomerates with different particle sizes. Calculate the integral area between the emulsification dispersion gradation curve and the extraction gradation curve. The treatment effect of 9.5 mm RAP is the best, with an area of 50.31, the asphalt content is reduced by more than 60%, and the PL is only 3.85. The area of 2.36 mm RAP is 139.21, the asphalt content is reduced by 20%, and the PL is 29.86. From the FMR, the FMR of those larger than 4.75 mm is basically greater than 0.9, and the dispersion effect is excellent.

[0029] Specific Example 4 of the method for dispersing agglomerated waste mixture by mechanical shearing and surfactant provided by the present invention: In this embodiment, RAP is mixed with the upper-layer transparent emulsion after the first treatment, and water is added to the residual emulsion so that the ratio of the emulsion to RAP in each experiment is 1:2. The following experimental steps are the same as those in the emulsification and dispersion experiment. Then, the residual emulsion is collected again for the next recycling experiment, and the emulsion recycling experiment is repeated six times.

[0030] As Figure 6 shown, as the number of emulsification cycles increases, the asphalt content of the aggregate is about 1.7%, with little change. This indicates that the main function of the emulsion is to reduce the viscosity of RAP and promote the formation of bubbles. Therefore, the emulsion collected during the RAP emulsification and dispersion process can be reused in the system to achieve zero emissions.

[0031] It should be noted that in this article, terms such as "including", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such a process, method, article or device.

[0032] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for agglomerating and dispersing waste mixtures by mechanical shearing and surfactant, characterized in that: The following steps are involved: (1) RAP pretreatment The waste asphalt mixture is agglomerated and placed in a 110-120°C oven for preheating for 0.5 h, and a surfactant solution is prepared; (2) Emulsification and dispersion treatment The preheated waste asphalt mixture agglomerates and the surfactant solution are mixed in proportion, and heated, stirred and dispersed for a certain period of time, during which the asphalt foam on the upper layer of the emulsion surface is collected; (3) Screening and recovery After the experiment, the aggregate was separated from the emulsion by screening; after standing, the emulsion was separated from the sludge to obtain reusable residual emulsion.

2. The method for agglomerating and dispersing waste mixed materials by mechanical shearing and surfactant according to claim 1, characterized in that: The production process of the waste asphalt mixture agglomerates in step (1) is as follows: first, the waste asphalt mixture is dusted, then heated in an oven at 110-120° C. for 1 hour, then kneaded and extruded for separation, and finally cooled to obtain waste asphalt mixture agglomerates of different particle sizes.

3. The method for agglomerating and dispersing waste mixed materials by mechanical shearing and surfactant according to claim 1, characterized in that: In the step (1), the waste asphalt mixture agglomerates include agglomerates of at least one of the following particle sizes: 13.2-16 mm, 9.5-13.2 mm, 4.75-9.5 mm, and 2.36-4.75 mm, and the concentration of the surfactant solution is 0-6 wt%.

4. The method for agglomerating and dispersing waste mixed materials by mechanical shearing and surfactant according to claim 1, characterized in that: In the step (2), the mixing ratio of the surfactant solution to the waste asphalt mixture agglomerate is 1:2, and the working condition parameters of the heating and stirring include stirring speed, heating temperature and time. The stirring speed is 280r / min, 700r / min and 1800r / min, the heating temperature is 60°C, 80°C and 90°C, and the time is 0.5h, 1h and 1.5h.

5. The method for agglomerating and dispersing waste mixed materials by mechanical shearing and synergistic surfactant according to claim 1, characterized in that: In the step (3), the recycled aggregate is separated from the emulsion by a water screening method, and the standing time is 0.5 to 1 hour.

6. The method for agglomerating and dispersing waste mixed materials by mechanical shearing and synergistic surfactant according to claim 5, characterized in that: The residual emulsion reused in step (3) is taken as the upper clear liquid after standing, and a certain amount of water is directly added to continue to be used in a ratio of 1:2.

Images