A method for improving the performance of foamed asphalt cold recycled mixture by using graphene

Abstract

The application relates to the technical field of regenerated pavement material research and development, and particularly discloses a method for improving the performance of foamed asphalt cold regeneration mixture by using graphene. The method comprises the following steps: 1) foaming after adding part of powdered graphene into asphalt; 2) adding another part of powdered graphene into mixture mixing water; and 3) mixing the cold regeneration mixture treated through steps 1) and 2) and shaping. The application aims at the problem that, under the action of adverse factors such as high temperature and heavy load, the regenerated pavement is damaged due to the poor performance of the cementing material of the foamed asphalt cold regeneration mixture; the graphene is used as an external additive to efficiently improve the performance of the foamed asphalt cold regeneration mixture, thereby prolonging the service life and application range of the regenerated pavement, promoting the development and application of the foamed asphalt cold regeneration technology, and having good economic and social benefits.

Description

Technical Field

[0001] This invention relates to the field of recycled pavement material research and development technology, and specifically discloses a method for improving the performance of foamed asphalt cold recycled mixture using graphene. Background Technology

[0002] Traditional asphalt pavement overhaul methods involve excavating and removing the damaged pavement structure before laying new materials. Practice has shown that traditional maintenance methods are time-consuming, costly, and disruptive to traffic. Furthermore, they generate over 5 million tons of pavement waste annually, accumulating land and polluting the environment. Additionally, paving new roads requires the extraction of new aggregates and asphalt, consuming resources. Therefore, traditional maintenance methods are detrimental to environmental and resource protection and do not align with my country's strategy of sustainable development and building a resource-conserving society.

[0003] To address the shortcomings of traditional road maintenance, and based on the concept of low-carbon, scientific management, a new approach to road maintenance—foamed asphalt cold recycling technology—characterized by low input, low consumption, high efficiency, high quality, and energy conservation, has been researched and applied both domestically and internationally. Foamed asphalt cold recycling technology involves milling, recycling, crushing, and screening old pavement materials, then mixing them with appropriate amounts of new aggregates, water, cement, and foamed asphalt to form a cold recycled mixture that meets design requirements. This mixture is then spread and compacted to create a pavement surface or base course with a certain load-bearing capacity.

[0004] Currently, foamed asphalt cold recycling technology is mostly used in the base course of medium- and light-traffic grade roads. However, with the development of this technology, the application scope of cold recycling layers is gradually shifting from the road base course to the lower layers, increasing the requirements for the shear resistance and water loss resistance of the cold recycled mixture. Furthermore, with global warming, continuously increasing traffic volume, and the rise of heavy-duty vehicles, foamed asphalt cold recycled pavements are prone to rutting and water loss due to insufficient high-temperature shear resistance and water loss resistance of the mixture under adverse external factors.

[0005] The strength of foamed asphalt cold recycled mixtures is mainly composed of aggregate interlocking force and binder ("spot-welded" asphalt mortar and cement mortar) cohesion. According to engineering practice and research, the failure path of recycled materials is mainly along the binder. Therefore, improving the performance of the binder is the key to improving the performance of foamed asphalt cold recycled mixtures.

[0006] Graphene is a novel carbon-based nanomaterial with excellent reactivity, a large specific surface area, and abundant polar oxygen-containing groups on its surface. In recent years, it has been increasingly applied in various fields. In improving asphalt, graphene can undergo physicochemical reactions with asphalt to form a dense layered structure, effectively preventing the volatilization of light components in the asphalt and preventing the intrusion of some oxygen and moisture. Simultaneously, graphene can increase the surface free energy of asphalt, improve the adhesion between asphalt and aggregates, and enhance the compactness and water stability of the mixture. In improving cement mortar, graphene, due to its inherent properties, can directly influence the cement hydration process, refining hydration products and ensuring the orderly growth and dense structure of the layered hydration products. This effectively prevents the formation of cracks and voids, thereby increasing the strength of the cement mortar.

[0007] Existing research indicates that graphene, due to its unique structure, can simultaneously improve the properties of asphalt and cementitious adhesives, theoretically making it a superior modifier for improving the properties of foamed asphalt cold recycled mixture adhesives. However, related research and applications have not yet been carried out domestically or internationally, and methods and processes for using graphene to improve the properties of foamed asphalt cold recycled mixtures are still lacking. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a method for improving the performance of foamed asphalt cold recycled mixtures using graphene.

[0009] The technical solution of the present invention is as follows:

[0010] A method for improving the properties of foamed asphalt cold recycled mixtures using graphene includes the following steps:

[0011] 1) A portion of powdered graphene is added to asphalt and then foamed;

[0012] 2) Another portion of the powdered graphene is added to the mixture and water;

[0013] 3) Mix the mixture after steps 1) and 2) together and shape it.

[0014] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, the amount of graphene powder added in step 1) is initially determined by the asphalt foaming performance index; the amount of graphene powder added in step 2) and the final amount of graphene powder added in step 1) are determined by the wet-dry splitting strength ratio (ITSR), dynamic stability at 60℃ (D), and the comprehensive index PIE = ITSR × DS.

[0015] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, the asphalt foaming performance indicators are an expansion rate ≥ 10 times and a half-life ≥ 8 s.

[0016] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, the ITSR ≥ 80% and DS ≥ 4000 times / mm are specified.

[0017] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, the graphene is graphene oxide powder.

[0018] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, step 1) includes the following process: heating the asphalt to be foamed to 150℃~160℃, adding graphene powder to the asphalt, and mixing it with a high-speed shear mixer for 15-60 minutes at a speed of 1000-5000 r / min; and foaming the graphene-infused asphalt using a foaming machine to obtain graphene foamed asphalt.

[0019] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, the amount of graphene powder added in step 1) is 0.5% to 2% of the amount of foamed asphalt, calculated by mass fraction.

[0020] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, step 2) includes the following process: adding graphene powder to the mixing water of the mixture and stirring evenly with a stirring rod; or stirring with a mixer for 3-10 minutes at a speed of 100-300 r / min.

[0021] Furthermore, in the above-mentioned method for improving the performance of foamed asphalt cold recycled mixture using graphene, the amount of graphene powder added in step 2) is 0.03% to 0.08% of the cement content, calculated by mass fraction.

[0022] Furthermore, this invention also discloses a design method for determining the production process of graphene-improved foamed asphalt cold recycled mixture. The method is characterized by, based on the preliminary mix proportion of the foamed asphalt cold recycled mixture completed with reference to the "Technical Specification for Recycling Asphalt Pavement of Highways" (JTG T5521-2019), determining graphene dosage 1 (added to the foamed asphalt) and graphene dosage 2 (added to the mixing water of the mixture), and excluding unsatisfactory graphene dosage groups based on the results of asphalt foaming performance tests, wet and dry splitting crack tests of the mixture, and rutting tests (60℃), then determining the optimal dosage group based on the comprehensive evaluation index PIE, thereby determining the production process of graphene-improved foamed asphalt cold recycled mixture.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention proposes a comprehensive method for determining the optimal graphene dosage, including "the foaming performance of graphene foamed asphalt (expansion rate and half-life), the dry-wet splitting strength ratio of foamed asphalt cold recycled mixture (ITS, %), the dynamic stability at 60℃ (DS, times / mm), and the comprehensive evaluation index PIE".

[0025] (1) Considering that foamed asphalt mortar plays a bonding and filling role in the mixture in an “electric welding” manner, the foaming characteristics of asphalt are more important. The foaming performance of graphene foamed asphalt with different dosages should meet the relevant requirements (expansion rate ≥ 10 times and half-life ≥ 8s).

[0026] (2) In order to improve the high temperature shear resistance and water loss resistance of the mixture, the dry-wet splitting strength ratio (ITSR, %) and dynamic stability at 60℃ (DS, times / mm) of foamed asphalt cold recycled mixture are selected as test sub-indicators to determine the optimal amount of graphene. The ITSR ≥ 80% and DS ≥ 4000 times / mm should be met.

[0027] (3) A comprehensive evaluation index PI E = I TSR × DS is proposed. The graphene doping amount corresponding to the maximum value of PI E is the optimal doping amount group. If there are multiple dependent variables in addition to the graphene doping amount, an orthogonal experiment can be set up.

[0028] The method for determining the optimal graphene addition amount proposed in this invention does not merely emphasize orthogonal experiments, but rather a comprehensive, graded method for determining the optimal graphene dosage, encompassing "graphene foamed asphalt foaming performance (expansion rate and half-life), wet-dry splitting strength ratio (ITSR, %), dynamic stability at 60℃ (DS, cycles / mm), and the comprehensive evaluation index PIE." The comprehensive evaluation index PIE proposed in this invention is specifically designed for evaluating the water stability and high-temperature stability of the mixture.

[0029] 1. Compared with general modifiers, graphene can improve the performance of both foamed asphalt mortar and cement mortar simultaneously, with higher efficiency.

[0030] 2. The method of batch incorporation of graphene proposed in this patent can simultaneously improve the performance of foamed asphalt and cement mortar, resulting in a more significant improvement in the performance of the mixture.

[0031] 3. Using powdered graphene as a modifier is simple to add and has no special requirements for the construction environment and machinery.

[0032] 4. To comprehensively evaluate the high-temperature shear resistance and water loss resistance of foamed asphalt cold recycled mixtures, the comprehensive evaluation index proposed in this patent can quantitatively evaluate the improvement effect of graphene, and the quality of the improved mixture is controllable.

[0033] 5. It can effectively solve the problem of pavement damage caused by poor binder performance in foamed asphalt cold recycled mixtures, extend the service life and application range of recycled pavement, and has good economic and social benefits. Attached Figure Description

[0034] Figure 1 The specific production process for improving foamed asphalt cold recycled mixtures using graphene;

[0035] Figure 2 For test group 2 Marshall specimens;

[0036] Figure 3 The control group consists of Marshall specimens (without graphene doping). Detailed Implementation

[0037] Graphene Improves the Production Process of Foamed Asphalt Cold Recycled Mixture

[0038] Based on the preliminary mix design of foamed asphalt cold recycled mixture according to the "Technical Specification for Recycling Asphalt Pavement of Highways" (JTG T5521-2019), graphene dosage 1 (added to foamed asphalt) and graphene dosage 2 (added to the mixing water of the mixture) were determined. According to the results of asphalt foaming performance tests, wet and dry splitting crack tests, and rutting tests (60℃), graphene dosage groups that did not meet the requirements were eliminated. Then, the optimal dosage group was determined based on the comprehensive evaluation index PIE, thus determining the production process of graphene-improved foamed asphalt cold recycled mixture. For the detailed production process flow of graphene-improved foamed asphalt cold recycled mixture, please refer to [link to relevant documentation]. Figure 1 .

[0039] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0040] Example

[0041] Raw materials for foamed asphalt cold recycled mixtures that meet the requirements of the "Technical Specification for Recycling Asphalt Pavement of Highway" (JTG T5521-2019) were selected, and a preliminary mix design was carried out. It was assumed that the optimal asphalt foaming conditions were: foaming temperature: 160℃, foaming water content: 2.5%; optimal foamed asphalt content: 2.6%; cement content: 1.8%.

[0042] The base asphalt used is Zhenhai brand AH-70# asphalt, the cement is PO42.5 ordinary Portland cement, the mixing water is ordinary tap water, and the new and old aggregates are from a major repair project. The performance of all the above materials meets the relevant specifications.

[0043] Select qualified graphene oxide powder produced by a certain company, with specific quality meeting the relevant requirements in Table 1.

[0044] Table 1 Quality Requirements for Graphene Oxide Powder

[0045] project Quality Standards Appearance Brown, fluffy powder (color varies depending on oxygen content). Loose packing density <![CDATA[≤0.3g / cm 3 ]]> purity ≥95 Particle size (D50) ≤50μm Carbon-oxygen ratio 2.0-2.5 grayscale ≤5wt% pH value / aqueous dispersion ＞3

[0046] The base asphalt to be foamed was heated to 155℃, and graphene asphalt with graphene content of 0.5%, 1.0%, 1.5%, and 2.0% was prepared respectively. Foaming tests were then conducted (foaming temperature: 160℃, foaming water content: 2.5%), and the results are shown in Table 2. According to the test results, the graphene content of 0.5% and 2.0% did not meet the relevant requirements, and subsequent tests were not conducted.

[0047] Table 2 Foaming Test Results

[0048] Graphene doping percentage Expansion rate (times) Half-life (s) 0.5 24 7.1 1.0 19 11.7 1.5 11 18.6 2.0 6 22.7

[0049] Graphene powder with mass fractions of 0.03%, 0.05%, and 0.08% of cement (graphene content 2) was weighed out and thoroughly mixed with mixing water. Based on the combinations of graphene content 1 and graphene content 2, foamed asphalt cold recycled mixtures were prepared, and dry and wet splitting crack tests and rutting tests were conducted. The test results are shown in Table 3.

[0050] Table 3 Results of Mixture Tests

[0051]

[0052] Based on the experimental results, experimental groups 1, 3, and 6 did not meet the requirements of the sub-indicators and were therefore excluded. However, according to traditional sub-indicators, it is impossible to comprehensively determine the optimal combination from experimental groups 2, 4, and 5. Based on the comprehensive evaluation index FIE proposed in this patent, which integrates ITSR and DS indicators, it can be intuitively determined that experimental group 2 (graphene content 1 = 1.0%, graphene content 2 = 0.05%) is the optimal content group. By comparing the appearance of the Marshall specimens from experimental group 2 and the blank control group, it can be intuitively demonstrated that the addition of an appropriate amount of graphene can effectively improve the performance of foamed asphalt mortar and cement mortar in foamed asphalt cold recycled mixtures, and improve the integrity and density of the mixture specimens.

[0053] The above examples illustrate specific methods for using graphene to improve the performance of foamed asphalt cold recycled mixtures.

[0054] Meanwhile, to further demonstrate the superiority of the proposed "batch incorporation of graphene (partial graphene added to foamed asphalt, partial graphene added to the mixing water)" in this invention, based on the optimal graphene content combination A (graphene content 1 = 1.0%, graphene content 2 = 0.05%) obtained in the above experiments, control group B (all graphene from group A was added to foamed asphalt) and control group C (all graphene from group A was added to the mixing water) were set up. Foamed asphalt cold recycled mixtures were prepared respectively, and dry and wet splitting crack tests and rutting tests were conducted. The test results are shown in Table 4.

[0055] Table 4. Results of the mixture test

[0056]

[0057] Based on the test results, the method of batch incorporation of graphene proposed in this patent is superior. This method can improve the performance of foamed asphalt mortar and cement mortar to a greater extent, thereby improving the compactness and high-temperature stability of cold recycled mixtures.

[0058] As can be seen from the above embodiments, the present invention proposes a complete set of methods for determining the optimal graphene dosage, including "the foaming performance of graphene foamed asphalt (expansion rate and half-life), the dry-wet splitting strength ratio of foamed asphalt cold recycled mixture (ITS, %), the dynamic stability at 60℃ (DS, times / mm), and the comprehensive evaluation index PIE".

[0059] (1) Considering that foamed asphalt mortar plays a bonding and filling role in the mixture in an “electric welding” manner, the foaming characteristics of asphalt are more important. The foaming performance of graphene foamed asphalt with different dosages should meet the relevant requirements (expansion rate ≥ 10 times and half-life ≥ 8s).

[0060] (2) In order to improve the high temperature shear resistance and water loss resistance of the mixture, the dry-wet splitting strength ratio (ITSR, %) and dynamic stability at 60℃ (DS, times / mm) of foamed asphalt cold recycled mixture are selected as test sub-indicators to determine the optimal amount of graphene. The ITSR ≥ 80% and DS ≥ 4000 times / mm should be met.

[0061] (3) A comprehensive evaluation index PI E = I TSR × DS is proposed. The graphene doping amount corresponding to the maximum value of PI E is the optimal doping amount group. If there are multiple dependent variables in addition to the graphene doping amount, an orthogonal experiment can be set up.

[0062] The method for determining the optimal graphene addition amount proposed in this invention does not merely emphasize orthogonal experiments, but rather highlights the comprehensive, graded method for determining the optimal graphene dosage based on the "graphene foam asphalt foaming performance (expansion rate and half-life), wet-dry splitting strength ratio (ITSR, %), and 60℃ dynamic stability (DS, cycles / mm) comprehensive evaluation index PI E". The comprehensive evaluation index PI E proposed in this invention is specifically designed for the comprehensive evaluation of the water stability and high-temperature stability of the mixture.

[0063] The scope of protection of this application is not limited to the dimensions and materials mentioned above. Furthermore, improving the performance of foamed asphalt cold recycled mixtures by simply adding graphene to foamed asphalt or simply adding graphene to the mixing water is also within the scope of this patent protection.

[0064] The above are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any simple equivalent changes and modifications made in accordance with the claims and contents of the present invention shall still fall within the scope of protection of the present invention patent application.

Claims

1. A method for improving the performance of foamed asphalt cold recycled mixtures using graphene, characterized in that, Includes the following steps: 1) A portion of powdered graphene is added to asphalt and then foamed; 2) Another portion of the powdered graphene is added to the mixture and water; 3) Mix the materials processed in steps 1) and 2) together and shape them; The amount of graphene powder added in step 1) was initially determined by the asphalt foaming performance index; The amount of graphene powder added in step 2) and the final amount of graphene powder added in step 1) are determined by graded based on the wet-dry splitting strength ratio (ITSR), dynamic stability at 60℃ (DS), and comprehensive index (PIE = ITSR × DS). The asphalt foaming performance indicators are an expansion rate ≥ 10 times and a half-life ≥ 8 s; The required ITSR is ≥80%, and DS is ≥4000 times / mm.

2. The method for improving the performance of foamed asphalt cold recycled mixtures using graphene according to claim 1, characterized in that, The graphene is graphene oxide powder.

3. The method for improving the performance of foamed asphalt cold recycled mixtures using graphene according to claim 1, characterized in that, Step 1) includes the following process: heating the asphalt to be foamed to 150℃~160℃, adding graphene powder to the asphalt, and stirring with a high-speed shear mixer for 15-60 minutes at a speed of 1000-5000 r / min; and foaming the asphalt mixed with graphene using a foaming machine to obtain graphene foamed asphalt.

4. A method for improving the performance of foamed asphalt cold recycled mixtures using graphene according to claim 1, characterized in that, Calculated by mass fraction, the amount of graphene powder added in step 1) accounts for 0.5% to 2% of the amount of foamed asphalt.

5. A method for improving the performance of foamed asphalt cold recycled mixtures using graphene according to claim 1, characterized in that, Step 2) includes the following process: adding graphene powder to the mixing water and stirring evenly with a stirring rod; or stirring with a mixer for 3-10 minutes at a speed of 100-300 r / min.

6. A method for improving the performance of foamed asphalt cold recycled mixtures using graphene according to claim 1, characterized in that, Calculated by mass fraction, the amount of graphene powder added in step 2) accounts for 0.03%~0.08% of the cement content.

7. A design method for determining the production process of graphene-improved foamed asphalt cold recycled mixture, characterized in that, Based on the preliminary mix proportion of foamed asphalt cold recycled mixture completed with reference to the "Technical Specification for Recycling of Highway Asphalt Pavement" (JTG T5521-2019), the graphene dosage 1 to be incorporated into the foamed asphalt and the graphene dosage 2 to be incorporated into the mixing water of the mixture were determined. According to the results of asphalt foaming performance test, dry and wet splitting test and rutting test of the mixture, under the condition of 60℃, the graphene dosage group that does not meet the requirements was eliminated. Then, the optimal dosage group was determined according to the comprehensive evaluation index PIE, thereby determining the production process of graphene-improved foamed asphalt cold recycled mixture.

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