Environmentally friendly construction method for in-situ cold recycling of foamed asphalt based on recycled materials.

Abstract

This invention discloses an environmentally friendly construction method for in-situ cold recycling of foamed asphalt based on recycled materials. It aims to solve the problems of unstable mixture performance and insufficient utilization of recycled materials caused by the diverse characteristics of recycled materials in traditional in-situ cold recycling processes. The method proposes a dynamically adaptable construction approach, the steps of which are as follows: first, the passing rate of the recycled material through 19mm and 0.075mm sieves and the penetration of the asphalt at 25°C are tested; then, the material is classified into three grades according to gradation and three degrees of aging; subsequently, the mix proportion, pre-wetting parameters of the bio-oil-based recycling agent, and the temperature at which the recycled material is added are dynamically adjusted according to the gradation; after verifying that the dry splitting strength and other indicators of the specimens meet the standards, batch construction is carried out. This method ensures the performance of the recycled mixture, improves the utilization rate of recycled materials, and combines environmental protection and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, and in particular to an environmentally friendly construction method for in-situ cold recycling of foamed asphalt based on recycled materials. Background Technology

[0002] Foamed asphalt in-situ cold recycling technology, as a green, environmentally friendly and economical road structure recycling technology, has been widely used in road maintenance and repair projects in recent years. This technology reuses old road surface milling and recycling materials, mixes, spreads and compacts them on site to form a new road base or subbase, effectively saving resources and reducing project costs.

[0003] However, in actual construction, due to differences in the structure and service life of old pavements, as well as the sources and performance fluctuations of different raw materials, the characteristics of milled and recycled old materials exhibit significant diversity and uncertainty. For example, key indicators such as the gradation composition and asphalt aging degree of old materials vary considerably. Traditional foamed asphalt in-situ cold recycling construction technology often adopts uniform empirical mix proportions and construction parameters, which leads to a disconnect between the performance of recycled mixtures and the characteristics of old materials. When the characteristics of old materials change significantly, if corresponding adjustments are not made, it may result in unstable performance of the recycled mixture, such as insufficient strength, poor water stability, and decreased low-temperature crack resistance, thereby affecting the service life and quality of the recycled pavement.

[0004] For example, an excessively high content of fine aggregates in the recycled material can lead to poor workability and compaction difficulties in the mixture; while an excessively high content of coarse aggregates may result in a loose skeleton structure in the mixture. The varying degrees of aging of asphalt in the recycled material can also affect the dosage and pre-wetting effect of the recycling agent. In addition, changes in the ambient temperature at the construction site can pose challenges to temperature control during pretreatment and mixing. These problems make it difficult for existing technologies to guarantee the performance stability and quality of foamed asphalt in-situ cold recycling mixtures when faced with complex and variable recycled material characteristics, thus limiting the further promotion and application of this technology. Therefore, how to dynamically adapt to the characteristics of the recycled material and optimize the construction process parameters to ensure that the performance of the recycled mixture meets the design requirements is a major challenge currently facing foamed asphalt in-situ cold recycling technology. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the existing foamed asphalt in-situ cold recycling construction process has the disadvantages of unstable performance of recycled mixture and insufficient utilization of old material resources when facing diverse old material characteristics. To this end, we propose an environmentally friendly construction method for foamed asphalt in-situ cold recycling based on old material recycling.

[0006] To achieve the above objectives, this application adopts the following technical solution: It provides an environmentally friendly construction method for in-situ cold recycling of foamed asphalt based on recycled materials, comprising the following steps:

[0007] S1: Recycled Material Characteristics Testing

[0008] Two core indicators were tested on the milled recycled material: the passing rate of 19mm and 0.075mm sieves, and the 25°C penetration of asphalt in the recycled material.

[0009] S2: Grading of Reclaimed Materials

[0010] Based on the test results of step S1, the recycled materials are divided into three categories according to their gradation characteristics: Grade 1, with a 19mm sieve pass rate ≥90% and a 0.075mm sieve pass rate ≤3%; Grade 2, with a 19mm sieve pass rate 80%~90% and a 0.075mm sieve pass rate 3%~5%; and Grade 3, with a 19mm sieve pass rate <80% and a 0.075mm sieve pass rate >5%. Simultaneously, the aging degree of the recycled materials is divided into light aging, moderate aging, and heavy aging according to the asphalt penetration at 25℃. Light aging corresponds to an asphalt penetration at 25℃ ≥50×0.1mm, moderate aging corresponds to an asphalt penetration at 25℃ 30-50×0.1mm, and heavy aging corresponds to an asphalt penetration at 25℃ <30×0.1mm.

[0011] S3: Dynamic adjustment of mix proportions

[0012] Based on the old material type classified in step S2, a corresponding foamed asphalt in-situ cold recycled mixture mix proportion is matched. The mix proportion, by mass percentage, includes milled aggregate, 10-20mm coarse aggregate, 0-5mm fine aggregate, cement, foamed asphalt, and mixing water, wherein:

[0013] For Grade I recycled aggregate: Milled aggregate: 10-20mm coarse aggregate: 0-5mm fine aggregate = 70.0%: 10.0%: 19.0%, cement content 1.0%, foamed asphalt content 3.0%, and mixing water content is 80% of the optimum moisture content obtained from the compaction test;

[0014] For secondary recycled aggregate: milled aggregate: 10-20mm coarse aggregate: 0-5mm fine aggregate = 65.0%: 15.0%: 19.0%, cement content 0.8%, foamed asphalt content 2.6%, and mixing water content is 85% of the optimum moisture content obtained from the compaction test;

[0015] For grade III old aggregate: milled aggregate: 10-20mm coarse aggregate: 0-5mm fine aggregate = 60.0%: 20.0%: 19.0%, cement content 1.2%, foamed asphalt content 2.4%, and mixing water content is 90% of the optimum moisture content obtained from the compaction test.

[0016] S4: Dynamic Control of Recycled Material Pretreatment

[0017] The recycled material after grading in step S2 was pre-wetted using a bio-oil-based regenerator, and the temperature at which the recycled material was added was adjusted according to the ambient temperature during construction.

[0018] Pre-wetting parameters for regenerator: 0.3% regenerator dosage for lightly aged old materials and 2h pre-wetting time; 0.4% regenerator dosage for moderately aged old materials and 2.5h pre-wetting time; 0.5% regenerator dosage for heavily aged old materials and 3h pre-wetting time. Stir once every 15-30 minutes during the pre-wetting process.

[0019] Temperature control for adding recycled materials: When the ambient temperature is ≤15℃, the target temperature for adding recycled materials is 25~30℃. Use a hot air gun for preheating and measure the temperature every 5 minutes. When the ambient temperature is 15~30℃, the target temperature for adding recycled materials is 20~25℃. Transport the recycled materials to the construction area to achieve natural temperature equilibrium 12 hours in advance. When the ambient temperature is >30℃, the target temperature for adding recycled materials is 18~22℃. Use shading and spray cooling once every 1 hour.

[0020] S5: Field Performance Verification

[0021] Prepare mixture specimens according to the mix proportions in step S3 and the pretreatment parameters in step S4. Test the dry splitting strength, dry / wet splitting strength ratio, and low-temperature failure strain at -10℃ of the specimens. If the test results meet the preset standards, proceed with batch construction.

[0022] S6: Batch Construction

[0023] The old material pretreated in step S4 is mixed with new aggregate, cement and foamed asphalt according to the mix ratio in step S3. After paving and compaction, the in-situ cold recycling of foamed asphalt is completed.

[0024] The technical effects and advantages of this invention are as follows:

[0025] 1. This invention achieves dynamic adaptation of construction technology to the characteristics of recycled materials by detecting and classifying the core characteristics of recycled materials and dynamically adjusting the mix proportion and pretreatment parameters based on the classification results. This effectively solves the problem of unstable performance of the mixture caused by changes in the characteristics of recycled materials in traditional processes, and ensures that the various performance indicators of recycled mixtures, such as strength, water stability and low temperature crack resistance, always meet the design requirements, thereby significantly improving the quality and durability of recycled pavement.

[0026] 2. This invention provides refined mix proportions and recycling agent pre-wetting schemes for old asphalt with different gradations and aging degrees. For example, for grade III old asphalt with high fine aggregate content, the gradation defects are compensated by increasing the amount of coarse aggregate; for heavily aged old asphalt, the old asphalt is more fully activated by increasing the amount of recycling agent and extending the pre-wetting time. This allows old asphalt of different qualities to be used rationally and efficiently, maximizing the potential value of old asphalt, reducing the consumption of new materials, and having significant environmental and economic benefits. Attached Figure Description

[0027] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0028] Figure 1 This is a schematic diagram of the process for the environmentally friendly construction method of in-situ cold recycling of foamed asphalt based on recycled materials according to the present invention.

[0029] Figure 2 This is a schematic diagram of the waste material characteristic detection method of the present invention;

[0030] Figure 3 This is a schematic diagram of the dynamic control method for pretreatment of recycled materials according to the present invention. Detailed Implementation

[0031] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0032] This invention provides an environmentally friendly construction method for in-situ cold recycling of foamed asphalt based on recycled materials, aiming to solve the problems of unstable performance and insufficient resource utilization of recycled mixtures caused by the diverse characteristics of recycled materials in existing technologies. This process ensures high quality of the recycled mixture and stability of the construction process by meticulously testing and grading the recycled materials, and then dynamically adjusting the mix proportions, pretreatment parameters, construction temperature control, and on-site performance verification.

[0033] Combination Figure 1 The process flow shown in this invention mainly includes the following steps:

[0034] S1: Recycled Material Characteristics Testing

[0035] Before carrying out in-situ cold recycling of foamed asphalt, the key characteristic indicators of the recycled material obtained by milling must be tested.

[0036] Specifically, two core indicators need to be tested:

[0037] Grading characteristics: The passing rate of the recycled aggregate through 19mm and 0.075mm sieves was measured. The passing rate through the 19mm sieve reflects the content of large-diameter coarse aggregates in the recycled aggregate, while the passing rate through the 0.075mm sieve reflects the content of fine aggregates, such as mineral powder and microparticles. These two indicators have a decisive influence on the skeleton structure, stability, and workability of the recycled aggregate.

[0038] In a preferred embodiment, such as Figure 2 As shown, the specific operation for the 19mm and 0.075mm sieve aperture pass rate test is as follows: Take a representative sample of the old material, with a sample mass ≥ 5kg. To ensure the accuracy of the test, crush the sample to a maximum particle size ≤ 26.5mm, then mix thoroughly. Divide the mixed sample into 3 parallel samples, with each parallel sample mass controlled at 1kg ± 0.02kg. Use a standard metal sieve for sieving, with a sieve aperture deviation of ± 0.3mm for the 19mm sieve and ± 0.005mm for the 0.075mm sieve. First, perform mechanical shaking sieving for 12min ± 1min to fully separate particles of different sizes. After mechanical shaking sieving, manually sieve the remaining particles on the sieve for 2min ± 0.5min to ensure thorough sieving. The pass rate calculation formula is: Pass rate = (mass of particles under sieve / total sample mass) × 100%. Calculate the pass rate for the 3 parallel samples. The error between parallel samples should be controlled at ≤ 1.0%. Finally, take the average value, accurate to 0.1%. The meticulous screening process ensures the accuracy of the gradation test for recycled materials.

[0039] Asphalt aging degree: The 25°C penetration of asphalt in old material is tested. Penetration is an important indicator for measuring the softness and viscosity of asphalt. The smaller the penetration, the harder the asphalt and the more serious the aging.

[0040] In a preferred embodiment, such as Figure 2As shown, the specific operation for the 25℃ penetration test of asphalt in recycled materials is as follows: First, recycled asphalt is extracted from the recycled materials using a toluene-ethanol mixed solvent with a volume ratio of 1:1 to obtain pure recycled asphalt. The extracted asphalt is heated to 135℃±5℃ to make it fluid, and then poured into a sample dish with a diameter of 55mm±1mm and a depth of 35mm±1mm. The sample dish containing asphalt is placed in a constant temperature water bath at 25℃±0.1℃ for 2h±5min to ensure that the asphalt reaches a stable test temperature. A standard needle is used for testing. The standard needle has a tip cone angle of 8°40′±2′ and a needle shaft diameter of 1.0mm±0.05mm. Under the strict conditions of a load of 50g±0.05g and a temperature of 25℃±0.1℃, the standard needle is allowed to freely penetrate the asphalt for 5s±0.1s, and the penetration depth is measured. Three parallel tests were conducted, with the error of each test controlled to ≤0.3mm. The final average value was taken, accurate to 0.1mm. Accurate penetration testing provides a reliable basis for subsequent judgment of the degree of asphalt aging.

[0041] S2: Grading of Reclaimed Materials

[0042] Based on the test results of step S1, the recycled material is graded, which is key to achieving dynamic adaptation. The recycled material is mainly graded based on two dimensions: gradation characteristics and asphalt aging degree.

[0043] Classification by gradation characteristics:

[0044] Grade 1 recycled material: its 19mm sieve pass rate is ≥90% and its 0.075mm sieve pass rate is ≤3%. This type of recycled material has a high coarse aggregate content, a moderate fine aggregate content, and a relatively good gradation, which is close to an ideal skeleton structure.

[0045] Secondary recycled material: its 19mm sieve pass rate is 80%–90% and its 0.075mm sieve pass rate is 3%–5%. This type of recycled material has a gradation between primary and tertiary grades and may require appropriate adjustments.

[0046] Grade III recycled material: Its 19mm sieve pass rate is <80% and its 0.075mm sieve pass rate is >5%. This type of recycled material usually has insufficient coarse aggregate or too much fine aggregate, resulting in poor gradation, requiring significant adjustments to meet the requirements.

[0047] Classification by asphalt aging degree:

[0048] Mild aging: Corresponds to a penetration of ≥50×0.1mm in asphalt at 25℃. This indicates that the old asphalt has a low degree of aging and still has good ductility.

[0049] Moderate aging: Corresponds to a penetration of 30-50 × 0.1 mm in asphalt at 25℃. This indicates that the old asphalt has undergone a certain degree of aging.

[0050] Severe aging: corresponds to a penetration of asphalt at 25℃ <30×0.1mm. This indicates that the old asphalt has hardened severely, has a high degree of aging, and requires stronger recycling capabilities.

[0051] S3: Dynamic adjustment of mix proportions

[0052] Based on the type of recycled material classified in step S2, the corresponding foamed asphalt in-situ cold recycling mix proportion is matched. This step ensures that recycled materials with different characteristics can be mixed in the most suitable way, thereby ensuring the performance of the recycled mixture. The mix proportion is based on the mass percentage, and the main components include milled material, 10-20mm coarse aggregate, 0-5mm fine aggregate, cement, foamed asphalt, and mixing water.

[0053] For primary aggregate: milled aggregate: 10-20mm coarse aggregate: 0-5mm fine aggregate = 70.0%: 10.0%: 19.0%. Due to the good gradation of primary aggregate, its proportion in the mixture can be relatively high. Cement content is 1.0%, providing early strength and water stability; foamed asphalt content is 3.0%, ensuring sufficient bonding performance. The mixing water content is 80% of the optimum moisture content obtained from the compaction test, slightly lower than the optimum moisture content, to facilitate compaction and avoid water damage.

[0054] For secondary aggregate: milled aggregate: 10-20mm coarse aggregate: 0-5mm fine aggregate = 65.0%: 15.0%: 19.0%. Compared to primary aggregate, secondary aggregate has a slightly lower proportion of milled aggregate, and the gradation is optimized by increasing the amount of 10-20mm coarse aggregate. The cement content is 0.8%, and the foamed asphalt content is 2.6%. The mixing water content is 85% of the optimum moisture content obtained from the compaction test.

[0055] For Class III recycled aggregate: milled aggregate: 10-20mm coarse aggregate: 0-5mm fine aggregate = 60.0%: 20.0%: 19.0%. Class III recycled aggregate has poor gradation, with milled aggregate having the lowest proportion. The gradation is improved by significantly increasing the amount of 10-20mm coarse aggregate, thus constructing a stable skeleton structure. The cement content is 1.2%, and the foamed asphalt content is 2.4%. The mixing water content is 90% of the optimum moisture content obtained from the compaction test.

[0056] In a preferred embodiment, the compaction test is performed and the optimum moisture content is determined as follows:

[0057] Compaction Test Procedure: Take the mixture corresponding to the mix proportion in step S3, with a mass ≥ 10 kg, and load it into the compaction cylinder in 4 layers. The compaction cylinder has a volume of 2177 cm³ ± 2 cm³, an inner diameter of 152 mm ± 1 mm, and a height of 116 mm ± 1 mm. Compaction is performed using a compaction hammer with a mass of 4.5 kg ± 0.05 kg and a drop height of 450 mm ± 5 mm. Each layer is compacted 50 ± 1 times. During compaction, the hammer must be kept vertically lowered without deviation to ensure uniform compaction.

[0058] Determining the optimal moisture content: Prepare at least 5 parallel samples with different moisture contents, controlling the difference between adjacent samples within 1.5% ± 0.2%. After compacting each sample, measure its wet density to an accuracy of 0.01 g / cm³, and calculate its dry density. The formula for calculating dry density is: Dry density = Wet density / (1 + Moisture content / 100). Plot the moisture content-dry density curve, and take the moisture content corresponding to the peak value of the curve as the optimal moisture content. The dry density calculation is accurate to 0.01 g / cm³, and the moisture content is accurate to 0.1%. Accurately determining the optimal moisture content through compaction tests provides a scientific basis for controlling the amount of mixing water, ensuring that the recycled mixture reaches the optimal compaction state.

[0059] S4: Dynamic Control of Recycled Material Pretreatment

[0060] This step involves dynamic control of the pretreatment process based on the aging degree of the recycled materials and the ambient temperature during construction, to ensure the effective use of the recycling agent and the smooth progress of the construction.

[0061] Pre-wetting parameters for the regenerator: The waste material after grading in step S2 is pre-wetted using a bio-oil-based regenerator, such as... Figure 3 As shown. The rejuvenator can effectively replenish the lightweight components in aged asphalt and restore its properties. The pre-wetting parameters are adjusted according to the degree of aging of the old asphalt:

[0062] Slightly aged old materials: 0.3% regenerator dosage, 2 hours pre-wetting time. Due to the light aging, less regenerator is required, and the pre-wetting time is also relatively short.

[0063] Moderately aged recycled materials: 0.4% regenerator dosage, 2.5h pre-wetting time. For moderately aged materials, appropriately increase the regenerator dosage and pre-wetting time.

[0064] Severely aged asphalt: 0.5% recycling agent dosage, 3-hour pre-wetting time. Severe aging requires a higher recycling agent dosage and a longer pre-wetting time to ensure full penetration and activation of the old asphalt.

[0065] During the pre-wetting process, the material is stirred every 15-30 minutes to ensure sufficient contact and uniform penetration of the regenerant with the old material. This stirring frequency is dynamically adjusted according to the aging degree of the old material. In a preferred embodiment, the stirring frequency during the regenerant pre-wetting process is as follows: lightly aged old material is stirred once every 30 minutes, moderately aged old material is stirred once every 25 minutes, and heavily aged old material is stirred once every 15 minutes. This means that the more severe the aging, the more frequently the material is stirred to accelerate the penetration and uniform mixing of the regenerant.

[0066] Furthermore, the bio-oil-based regenerator meets the following performance requirements: it can replenish the light components of aged asphalt in the old material, and the low-temperature failure strain of the old material after pre-wetting treatment is increased by ≥12% compared with the untreated old material. This quantitative indicator ensures the effectiveness of the selected regenerator.

[0067] Temperature control for adding recycled materials: The target temperature for adding recycled materials is adjusted according to the ambient temperature of the construction environment to meet the construction needs under different seasons and climatic conditions.

[0068] When the ambient temperature during construction is ≤15℃: the target temperature for adding recycled materials is 25~30℃. At this time, the recycled materials need to be preheated using equipment such as a hot air gun, and the temperature should be measured every 5 minutes to ensure that the temperature meets the requirements and to avoid low temperature affecting the activation of the recycling agent and the adhesion of the asphalt.

[0069] When the ambient temperature during construction is 15~30℃: the target temperature for adding the old material is 20~25℃. At this temperature, the ambient temperature is suitable, and the old material can be transported to the construction area 12 hours in advance to allow it to naturally reach temperature equilibrium with the environment.

[0070] When the ambient temperature during construction is >30℃: the target temperature for adding the recycled material is 18~22℃. If the ambient temperature is too high, the recycled material needs to be cooled by covering it with shade and spraying it with water every hour. During spray cooling, the droplet diameter should be ≥0.5mm to avoid the bio-oil-based regenerator evaporating or being lost due to excessive spraying. This measure of controlling the droplet diameter prevents the loss of the regenerator and ensures the regeneration effect.

[0071] S5: Field Performance Verification

[0072] Before the start of mass construction, this invention introduces an on-site performance verification process, which verifies the effectiveness of process parameters in advance by making and testing mixture specimens.

[0073] Prepare the mixture specimens according to the mix proportions determined in step S3 and the pretreatment parameters determined in step S4. Test the dry splitting tensile strength, dry / wet splitting tensile strength ratio, and low-temperature failure strain at -10℃ of the specimens.

[0074] The preset standard is:

[0075] Specimens corresponding to Grade I recycled materials: dry splitting strength ≥ 0.7 MPa, dry / wet splitting strength ratio ≥ 91.6%, and low-temperature failure strain at -10℃ ≥ 1500 με.

[0076] Specimens corresponding to Grade II recycled materials: dry splitting strength ≥ 0.6 MPa, dry / wet splitting strength ratio ≥ 88%, and low-temperature failure strain at -10℃ ≥ 1300 με.

[0077] Specimens corresponding to Grade III recycled materials: dry splitting strength ≥ 0.5 MPa, dry / wet splitting strength ratio ≥ 85%, and low-temperature failure strain at -10℃ ≥ 1200 με.

[0078] Batch construction can only proceed when the test results meet the preset standards for the corresponding type of recycled material. This step is the final checkpoint to ensure project quality and prevents substandard mixtures from being used.

[0079] S6: Batch Construction

[0080] Once all preliminary testing and verification work is completed and the performance meets the requirements, batch construction can begin.

[0081] The pretreated old material from step S4 is mixed with new aggregate, cement, and foamed asphalt in a cold recycling machine according to the mix proportions determined in step S3. The mixing of the mixture is completed simultaneously using the cold recycling machine, with the mixing temperature controlled at room temperature to ensure the stability of the asphalt foam and the activity of the recycling agent. After uniform mixing, the mixture is laid and compacted, ultimately completing the in-situ cold recycling of foamed asphalt. During compaction, the initial compaction speed is ≤3 km / h, and the secondary compaction speed is 1.5–2.5 km / h to achieve the best compaction effect.

[0082] In a preferred embodiment, the foaming parameters of the foamed asphalt are: foaming temperature 170~190℃, foaming water content 3.0%~3.5%, and the theoretical expansion rate of the foamed asphalt ≥10% and half-life >8s. These parameters ensure that the foamed asphalt has good foaming performance, can uniformly coat the aggregate, and improve the performance of the mixture.

[0083] In addition, after the completion of S6 construction, the recycled layer is naturally cured for ≥7 days to allow the mixture strength to fully develop. During the curing period, the moisture content of the recycled layer is maintained at 80%–90% of the optimum moisture content in step S3 to ensure a suitable curing environment. Asphalt seal is applied promptly after curing to protect the recycled layer and provide initial abrasion resistance and waterproofing.

[0084] Taking a highway maintenance project as an example, the following core data of the milled old material were obtained by performing characteristic testing according to step S1 of the present invention:

[0085] 19mm sieve aperture: 75.2%, meeting the requirement of <80% for grade III recycled materials;

[0086] 0.075mm sieve aperture: 7.0%, meeting the requirement of >5% for grade III recycled materials;

[0087] The penetration of asphalt at 25℃ is 28.3×0.1mm, which meets the requirement of <30×0.1mm for heavy aging.

[0088] According to the grading standard, the old material is classified as Grade III heavily aged old material, and the mixing ratio scheme corresponding to Grade III old material and the pretreatment parameters of heavily aged old material need to be matched.

[0089] The construction parameter scheme for milling the old material in this project is as follows:

[0090] Mix proportions: 60.0% milling aggregate, 20.0% 10-20mm coarse aggregate, 19.0% 0-5mm fine aggregate, 1.2% cement, and 2.4% foamed asphalt;

[0091] The compaction test determined the optimum moisture content to be 6.8%, therefore the mixing water content is 6.8% × 90% = 6.1%.

[0092] Pretreatment parameters: bio-oil-based regenerator dosage 0.5%, pre-wetting time 3h, stirring once every 15min; construction ambient temperature 25℃, target temperature for old material addition 22℃;

[0093] Foamed asphalt parameters: foaming temperature 180℃, foaming water content 3.2%, theoretical expansion rate 12%, half-life 10s.

[0094] Three sets of parallel specimens were prepared according to the above parameters. After testing in step S5, the core performance indicators are as follows:

[0095]

[0096] The errors of the three parallel samples were all ≤1.5%, and the test results were stable and fully met the preset standards.

[0097] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A foamed asphalt cold-in-place recycling environment-friendly construction method based on old material recycling, characterized in that, Comprising the following steps: S1. Old material property detection: Detect two core indicators of milling and reclamation material, respectively detect 19mm, 0.075mm screen passing rate, and detect the 25℃ penetration of asphalt in old material; S2. Old material type classification: According to the detection results of step S1, the old material is classified into three categories according to the grading characteristics: first level, 19mm screen passing rate ≥ 90% and 0.075mm screen passing rate ≤ 3%; second level, 19mm screen passing rate 80%-90% and 0.075mm screen passing rate 3%-5%; third level, 19mm screen passing rate < 80% and 0.075mm screen passing rate > 5%; At the same time, according to the 25℃ penetration of asphalt, the aging degree of old material is divided into mild aging, moderate aging and severe aging, wherein mild aging corresponds to 25℃ penetration of asphalt ≥ 50×0.1mm, moderate aging corresponds to 25℃ penetration of asphalt 30-50×0.1mm, and severe aging corresponds to 25℃ penetration of asphalt < 30×0.1mm; S3. Dynamic adjustment of mix proportion: According to the type of old material classified in step S2, the mix proportion of foam asphalt cold in-place recycling mixture is matched, which comprises milling material, 10-20mm coarse aggregate, 0-5mm fine aggregate, cement, foam asphalt and mixing water, wherein: For first level old material: milling material: 10-20mm coarse aggregate: 0-5mm fine aggregate = 70.0%:10.0%:19.0%, cement content 1.0%, foam asphalt content 3.0%, and mixing water amount is 80% of the optimal water content obtained by compaction test; For second level old material: milling material: 10-20mm coarse aggregate: 0-5mm fine aggregate = 65.0%:15.0%:19.0%, cement content 0.8%, foam asphalt content 2.6%, and mixing water amount is 85% of the optimal water content obtained by compaction test; For third level old material: milling material: 10-20mm coarse aggregate: 0-5mm fine aggregate = 60.0%:20.0%:19.0%, cement content 1.2%, foam asphalt content 2.4%, and mixing water amount is 90% of the optimal water content obtained by compaction test; S4. Dynamic regulation of old material pretreatment: The old material classified in step S2 is pretreated with bio-oil-based regenerant, and the old material addition temperature is regulated according to the construction environment temperature, wherein: Regenerant pretreatment parameters: mild aging old material regenerant content 0.3%, pretreatment time 2h, moderate aging old material regenerant content 0.4%, pretreatment time 2.5h, severe aging old material regenerant content 0.5%, pretreatment time 3h, and turn over every 15-30min during pretreatment; Old material mixing temperature regulation: when the construction environment temperature is ≤15℃, the target temperature of old material mixing is 25~30℃, the hot air gun is used for preheating and the temperature is measured every 5 minutes; when the construction environment temperature is 15~30℃, the target temperature of old material mixing is 20~25℃, the old material is transported to the construction area 12 hours in advance to balance the temperature naturally; when the construction environment temperature is >30℃, the target temperature of old material mixing is 18~22℃, the sunshade is covered and the temperature is sprayed every 1 hour; S5. Field performance verification: the mixture specimen is prepared according to the mixing proportion of step S3 and the pretreatment parameters of step S4, the dry splitting strength, dry / wet splitting strength ratio and-10℃ low temperature damage strain of the specimen are detected, and if the detection results meet the preset standard, batch construction is carried out; S6. Batch construction: the old material pretreated in step S4 is mixed with new aggregate, cement and foamed asphalt according to the mixing proportion of step S3, and after paving and rolling, the foamed asphalt cold in-place recycling construction is completed.

2. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, In step S1: 19mm, 0.075mm sieve hole passing rate detection: take representative sample of old material, sample mass ≥5kg, crush the sample to a maximum particle size of ≤26.5mm, then mix evenly, divide into 3 parallel samples, each parallel sample mass is 1kg±0.02kg; use standard metal sieve, the 19mm sieve hole has a deviation of ±0.3mm, the 0.075mm sieve hole has a deviation of ±0.005mm, first mechanically shake the sieve for 12min±1min, then manually supplement the sieve for 2min±0.5min; calculate the passing rate, the passing rate calculation formula is passing rate=(sieve under particle mass / sample total mass)×100%, parallel sample error ≤1.0%, take the average value, the average value is accurate to 0.1%; Old material asphalt 25℃ penetration detection: extract asphalt from old material by toluene-ethanol mixed solvent, heat the asphalt to 135℃±5℃ to flow state, pour into a sample dish, the sample dish has a diameter of 55mm±1mm and a depth of 35mm±1mm, keep it in a constant temperature water bath at 25℃±0.1℃ for 2h±5min; use a standard needle, the standard needle has a conical angle of 8°40′±2′ at the tip and a diameter of 1.0mm±0.05mm at the shaft, under the conditions of load 50g±0.05g and temperature 25℃±0.1℃, let the needle penetrate the asphalt freely for 5s±0.1s, measure the penetration depth, detect 3 times, single error ≤0.3mm, take the average value, the average value is accurate to 0.1mm.

3. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, In step S3: Compaction test operation: take the mixture corresponding to the mixing proportion of step S3, mixture mass ≥10kg, divide into 4 layers and load into the compaction cylinder, the compaction cylinder has a volume of 2177cm³±2cm³, an inner diameter of 152mm±1mm and a height of 116mm±1mm; use a compaction hammer, the compaction hammer has a mass of 4.5kg±0.05kg and a drop distance of 450mm±5mm, each layer is compacted for 50 times±1 time, keep the hammer body vertical during compaction without deviation; Optimal moisture content determination: at least 5 groups of different moisture content parallel samples are prepared, the moisture content difference between adjacent groups is 1.5%±0.2%; after compaction of each group of samples, the wet density is measured, the wet density is accurate to 0.01g / cm³, and the dry density is calculated, the dry density calculation formula is dry density=wet density / (1+moisture content / 100); the moisture content corresponding to the peak value of the moisture content-dry density relationship curve is taken as the optimal moisture content, wherein the dry density is calculated to 0.01g / cm³, and the moisture content is accurate to 0.1%.

4. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, In step S4, the performance of the bio-oil-based regenerant meets the requirements that it can supplement the light components of aged asphalt in old materials, and the low-temperature failure strain of the old materials after pre-wetting treatment is increased by more than 12% compared with that of untreated old materials.

5. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, In step S5, the preset standards are: for first-grade old materials, the dry splitting strength of the test piece is greater than or equal to 0.7 MPa, the dry / wet splitting strength ratio is greater than or equal to 91.6%, and the low-temperature failure strain at-10 DEG C is greater than or equal to 1500με; for second-grade old materials, the dry splitting strength of the test piece is greater than or equal to 0.6 MPa, the dry / wet splitting strength ratio is greater than or equal to 88%, and the low-temperature failure strain at-10 DEG C is greater than or equal to 1300με; for third-grade old materials, the dry splitting strength of the test piece is greater than or equal to 0.5 MPa, the dry / wet splitting strength ratio is greater than or equal to 85%, and the low-temperature failure strain at-10 DEG C is greater than or equal to 1200με.

6. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, The droplet diameter used for spray cooling is greater than or equal to 0.5 mm to avoid volatilization or loss of the bio-oil-based regenerant due to excessive spraying.

7. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, The mixing of the mixture is completed synchronously by a cold recycling machine, and the mixing temperature is controlled at room temperature. The initial compaction speed during the rolling process is less than or equal to 3 km / h, and the recompaction speed is 1.5-2.5 km / h.

8. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, The turning frequency of the regenerant pre-wetting process is adjusted according to the aging degree of the old materials: the old materials with slight aging are turned every 30 minutes, the old materials with moderate aging are turned every 25 minutes, and the old materials with severe aging are turned every 15 minutes.

9. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, The foaming parameters of the foamed asphalt are: foaming temperature 170-190 DEG C, water amount for foaming 3.0%-3.5%, and the theoretical expansion rate of the foamed asphalt is greater than or equal to 10%, and the half-life period is greater than 8s.

10. The old material-based foamed asphalt cold-in-place recycling environment-friendly construction method according to claim 1, characterized in that, After the construction in step S6 is completed, the recycled layer is naturally cured for more than or equal to 7 days, the moisture content of the recycled layer during the curing period is maintained at 80%-90% of the optimal moisture content in step S3, and the asphalt chip seal coating construction is carried out in time after the curing.

Images