Old asphalt pavement cold regeneration construction process based on pressure-sensitive emulsified asphalt

Abstract

The application discloses a kind of old asphalt pavement cold regeneration construction process based on pressure-sensitive emulsified asphalt, belong to road engineering construction technical field.The process includes seven steps: old pavement milling and multi-stage crushing classification, realize old material 100% on-site use no external transport;Pressure-sensitive emulsified asphalt interface pre-spreading, mixing addition, three-stage accurate addition of surface layer supplementary spraying;Vibration mixing below demulsification threshold, evenly wrapped and not demulsification in advance;Continuous uniform paving;Initial pressure steady pressure, re-pressing vibration triggers demulsification, final pressure finishing three-stage variable parameter rolling, pressure and vibration force accurately match demulsification threshold;Real-time feedback closed-loop control of compaction degree, dynamic adjustment of rolling parameters;Early maintenance rapid opening traffic.The application controls demulsification process by rolling pressure initiative, does not rely on moisture evaporation, 2h strength after rolling is greater than or equal to 1.5MPa, 3d can open traffic, compaction degree is greater than or equal to 98%, old material 100% utilization, road performance meets the requirements of high-grade highway.

Description

Technical Field

[0001] This invention relates to the field of road engineering construction technology, specifically to a cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt. Background Technology

[0002] As my country's highway construction enters the maintenance and repair period, a large number of old asphalt pavements need to be renovated every year, generating hundreds of millions of tons of old asphalt pavement milling material.

[0003] Traditional cold recycling construction processes typically use ordinary slow-cracking emulsified asphalt, relying on the natural evaporation of moisture to achieve demulsification and molding. This presents the following technical problems: First, the demulsification speed is greatly affected by ambient temperature and humidity. High temperatures and dry conditions result in rapid demulsification but also lead to clumping, while low temperatures and humidity cause slow demulsification, requiring 7-14 days of curing before traffic can resume, resulting in a long construction period. Second, the compaction process uses fixed parameters, failing to adjust pressure and vibration according to the demulsification characteristics of the emulsified asphalt. Either the pressure is too low for sufficient demulsification and low strength, or too high for premature demulsification, leading to pushing and cracking, making it difficult to guarantee compaction quality. Third, the compaction process relies entirely on worker experience to judge compaction, frequently resulting in under-compaction or over-compaction and uneven compaction. Fourth, the milled material is not finely crushed and graded, with some oversized material being discarded, making 100% reuse of recycled material impossible and requiring the removal of waste and the addition of large amounts of new aggregate. Fifth, poor interlayer bonding and improper joint treatment during sectional construction easily lead to early defects such as interlayer slippage and joint cracking.

[0004] Based on this, the present invention provides a cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt. Summary of the Invention

[0005] This invention provides a cold recycling construction process for old asphalt pavements based on pressure-sensitive emulsified asphalt, which solves the technical problems of uncontrollable demulsification time, unreasonable compaction parameters, reliance on experience for compaction quality, low utilization rate of old materials, and low early strength in existing cold recycling construction processes.

[0006] The technical solution adopted by this invention to solve its technical problem is: a cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt, comprising the following steps: S1 Old Road Milling and Multi-stage Crushing and Grading: The old asphalt road surface is milled to the designed depth using a cold milling machine. The milled material is transported on-site to a multi-stage crushing and screening system. After crushing, grading and screening, it is divided into old materials of different particle sizes. All milled materials are 100% recycled on-site, and no waste is transported off-site. S2 pressure-sensitive emulsified asphalt is added in stages with precision: Based on the gradation and moisture content of the old material, pressure-sensitive emulsified asphalt is added in three stages: pre-spraying on the interface after milling, mixing and adding in the mixing drum, and surface spraying after paving. The pressure-sensitive emulsified asphalt is stable under static conditions and triggers demulsification under a set pressure threshold and vibration acceleration. S3 Vibration Mixing: Graded old material, cement, new aggregate, water and pressure-sensitive emulsified asphalt are fed into a twin-shaft vibration mixing tank and mixed for 60-90 seconds at the set vibration intensity to make the emulsified asphalt evenly coat the aggregate. The mixing vibration only initially activates the emulsified asphalt without premature demulsification. S4 paving: A cold recycling paver with a screed is used to spread the mixture evenly to the designed thickness. During the paving process, a continuous and uniform speed is maintained to avoid segregation. S5 staged pressure-triggered demulsification compaction: Compaction is carried out in three stages: initial pressure stabilization, intermediate pressure demulsification, and final pressure compaction. Different compaction pressures, vibration frequencies, amplitudes, and compaction speeds are used in different stages to precisely match the demulsification pressure threshold of pressure-sensitive emulsified asphalt. The emulsified asphalt is demulsified and solidified layer by layer through compaction pressure and vibration. S6 Real-time Compaction Feedback Closed-Loop Control: A real-time density monitoring sensor and a pressure sensor are installed on the roller. The road surface compaction and demulsification status are detected in real time after each rolling pass. The parameters for the next rolling pass are dynamically adjusted based on the detection results until the design compaction is achieved. S7 Early Maintenance: Early maintenance is carried out after compaction. Heavy vehicles are prohibited from passing during the maintenance period. Traffic is opened after the strength reaches the design requirements.

[0007] Preferably, in step S1, the milling depth is 8-20cm, the milling speed is controlled at 6-10m / min, a small amount of water is sprayed during the milling process to reduce dust but without increasing the moisture content of the old material; the milled material undergoes two-stage crushing and three-stage screening, the maximum particle size after crushing does not exceed 31.5mm, and it is screened into three particle size ranges: 0-5mm, 5-15mm, and 15-31.5mm. It is then mixed back according to the design gradation requirements to achieve 100% utilization of the old material and no waste material is generated.

[0008] Preferably, in step S2, the total amount of pressure-sensitive emulsified asphalt is 3.5% to 5.0% of the mass of the recycled mixture, and it is added in three stages: the first stage is pre-spraying on the milled surface, accounting for 10% to 15% of the total amount, which is evenly sprayed on the cleaned surface of the underlying layer after milling to enhance interlayer bonding; the second stage is adding into the mixing tank, accounting for 75% to 85% of the total amount, and mixing it evenly with the aggregate; the third stage is surface finishing after paving, accounting for 5% to 10% of the total amount, which is evenly sprayed on the surface after initial compaction to seal surface voids.

[0009] Preferably, the vibration frequency of the biaxial vibration mixing in step S3 is 20-30Hz, and the vibration acceleration is 0.2-0.4g. This vibration intensity is lower than the demulsification threshold of pressure-sensitive emulsified asphalt and is only used to uniformly disperse and coat the aggregate with emulsified asphalt without triggering premature demulsification. The mixing sequence is as follows: first, dry mix the coarse aggregate, fine aggregate, and cement for 10s, then add water and 80% of the total amount of emulsified asphalt and mix for 40-60s, and finally add the remaining 20% ​​of emulsified asphalt and mix for 20s to avoid direct contact between the emulsified asphalt and cement, which may cause flocculation.

[0010] Preferably, the specific parameters for the staged compaction in step S5 are as follows: Initial compaction and stabilization stage: Use a double-drum roller for static compaction once, with a rolling speed of 2-3 km / h and a linear pressure of 10-15 MPa. Do not turn on the vibration. The purpose is to stabilize the paving layer and prevent pushing during the re-compaction. The secondary compaction and demulsification stage involves rolling the mixture 3-4 times with a single steel drum vibratory roller at a speed of 3-4 km / h, a vibration frequency of 30-50 Hz, an amplitude of 0.4-0.8 mm, a vibration acceleration of 0.5-1.0 g, and a linear pressure of 20-30 MPa. This pressure and vibration reach the demulsification threshold of the pressure-sensitive emulsified asphalt, triggering rapid demulsification of the emulsified asphalt and simultaneously compacting the mixture to a compaction degree of over 95%. Final compaction stage: Use a rubber-tired roller for static compaction 1 to 2 passes at a speed of 4 to 5 km / h and a tire ground pressure of 0.6 to 0.8 MPa. Do not turn on the vibration. The purpose is to smooth out the surface, eliminate wheel tracks, further compact the surface layer, and allow the demulsified emulsified asphalt on the surface to form a complete seal layer.

[0011] Preferably, the compaction sensor used in step S6 is a nucleus-free density meter or an accelerometer, installed on the vibratory wheel of the roller. Compaction data is collected every 0.5m and transmitted to the control system in real time. When the compaction degree is detected to reach 93%, the amplitude and vibration force of the next rolling pass are reduced. When the compaction degree reaches the design value (≥98%) for two consecutive detection points, rolling is automatically stopped to avoid over-pressure causing asphalt film detachment or aggregate breakage. At the same time, the ground pressure of the roller is monitored by a pressure sensor. When the pressure exceeds the upper limit of the demulsification threshold, the rolling speed is automatically reduced to ensure uniform demulsification.

[0012] Preferably, after milling in step S1, the surface of the underlying layer is treated with interface treatment: the dust on the milled surface is cleaned by a sweeper, the loose parts are removed, and then the pressure-sensitive emulsified asphalt pre-sprayed in the first stage is sprayed at a rate of 0.3-0.5 kg / m². After demulsification, a tack coat is formed to ensure the bonding strength between the recycled layer and the underlying layer, and the interlayer shear strength is ≥0.4 MPa.

[0013] Preferably, the joint treatment during construction is as follows: longitudinal joints are treated with echelon-style hot jointing, leaving a 10-15cm width uncompacted during compaction as an elevation reference surface for subsequent paving. After subsequent paving is completed, the joints are compacted together across the joint. Transverse joints are treated with flat jointing, using a transverse compaction method. First, the compaction is carried out on the already compacted pavement, gradually advancing towards the new paved layer, advancing 10-15cm laterally each time, until the entire new paved layer is compacted. Then, longitudinal compaction is switched to ensure that the joint is dense and flat, with the compaction degree at the joint being 1%-2% higher than the design value.

[0014] Preferably, the early curing time in step S7 is 24-72 hours. During the curing period, the road surface is kept moist. When the ambient temperature is above 20℃, light traffic can be opened after 24 hours of curing. When the ambient temperature is 10-20℃, traffic can be opened after 48 hours of curing. When the ambient temperature is below 10℃, traffic can be opened after 72 hours of curing. Before opening to traffic, the road surface strength is tested, requiring an early strength of ≥1.5MPa at 2 hours, a strength of ≥3.0MPa at 24 hours, a strength of ≥4.5MPa at 3 days, a compaction degree of ≥98%, and a smoothness of ≤3mm / m.

[0015] Preferably, the ambient temperature during construction is not lower than 10℃, and construction is prohibited on rainy days or when it is about to rain; the time from mixing to the end of compaction of the mixed material does not exceed 4 hours, and the paving temperature is not lower than 10℃; the demulsification pressure threshold of pressure-sensitive emulsified asphalt is 0.4~0.6MPa, the demulsification vibration acceleration threshold is 0.4~0.6g, the emulsion is stable when it is below the threshold, and rapidly demulsifies and solidifies within 1~2 minutes when it is above the threshold; the unconfined compressive strength of the cold recycled layer after molding is ≥5MPa, the freeze-thaw splitting strength ratio (TSR) is ≥85%, and the dynamic stability is ≥5000 times / mm.

[0016] The advantages of this invention are: 1. This invention actively triggers the demulsification of pressure-sensitive emulsified asphalt through rolling pressure and vibration, without relying on water evaporation. The strength is ≥1.5MPa 2 hours after rolling, and traffic can be opened in 3 days. It shortens the construction period by more than 70% compared with traditional cold recycling and is less affected by ambient temperature and humidity.

[0017] 2. The present invention uses three-stage compaction parameters to precisely match the demulsification process, and dynamically adjusts the parameters in real time. The compaction degree is ≥98%, and the compaction uniformity is significantly improved. It avoids under-compaction and over-compaction, and eliminates defects such as pushing, cracking, and whitening. The milled material is crushed and graded on-site, and accurately mixed back according to the gradation. There is no waste material transported out. The amount of new aggregate used is reduced by more than 50% compared with traditional processes, the project cost is reduced by 20% to 30%, and carbon emissions are reduced by more than 40%.

[0018] 3. This invention involves the addition of emulsified asphalt in three stages, with tack coat pre-sprayed at the interface. The interlayer shear strength is ≥0.4MPa, the 7-day strength after molding is ≥5MPa, the TSR is ≥85%, the dynamic stability is ≥5000 cycles / mm, and the high-temperature stability and water stability meet the requirements of expressways and first-class highways. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the overall process of cold recycling construction according to the present invention. Figure 2 This is a schematic diagram of the process parameters for staged pressure-triggered demulsification and compaction. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: A major overhaul project of an old asphalt pavement on a highway. The pavement structure consists of an 18cm old asphalt surface layer. The process of this invention is used for in-situ cold recycling, and the recycled layer is 18cm thick.

[0023] The construction process is as follows: S1 Existing Road Milling and Multi-Stage Crushing and Grading: A Wirtgen W2000 cold milling machine was used, with a milling depth of 18cm and a milling speed of 8m / min. A small amount of dust was sprayed during the milling process. The milled material was conveyed by belt to the supporting multi-stage crushing and screening station, where it underwent two-stage crushing by a jaw crusher and an impact crusher. Then, it was screened by a three-layer vibrating screen into three particle size ranges: 0-5mm, 5-15mm, and 15-31.5mm. According to the design gradation requirements: 0-5mm accounts for 35%, 5-15mm accounts for 40%, and 15-31.5mm accounts for 25%, which is automatically metered and mixed back into the aggregate. All milled material is 100% utilized, with no waste transported out. Only 1.5% cement is added as an active filler, and no new aggregate is added.

[0024] S2 pressure-sensitive emulsified asphalt is added in stages with precision: Pressure-sensitive cationic emulsified asphalt with a pressure threshold of 0.5 MPa and a vibration acceleration threshold of 0.5 g is used, with a total dosage of 4.2% of the mixture mass. Stage 1: After cleaning the milled surface, pre-spray 0.5 kg / m² of emulsified asphalt (12% of the total dosage) as a tack coat. Stage 2: Add 80% of the total dosage to the mixing tank and mix with the aggregate. Stage 3: After initial compaction, apply a final layer of 0.2 kg / m² of emulsified asphalt (8% of the total dosage) to seal the surface.

[0025] S3 Vibration Mixing: A twin-shaft vibration mixing plant is used. During mixing, the three types of old materials with cement are first dry-mixed for 10 seconds, then water and 80% of the emulsified asphalt are added and mixed for 50 seconds at a vibration intensity of 25Hz and 0.3g. Finally, the remaining 20% ​​of the emulsified asphalt is added and mixed for 20 seconds, with a total mixing time of 80 seconds. During the mixing process, the vibration intensity is lower than the demulsification threshold, and the emulsified asphalt is evenly coated with the aggregate without clumping.

[0026] S4 paving: Uses Vogele S1800 cold recycling paver with a paving speed of 4m / min, a loose paving factor of 1.25, a paving thickness of 22.5cm, and a continuous and uniform paving speed. The paver's auger spreader is embedded in the mixture to avoid segregation.

[0027] S5 staged pressure-triggered demulsification compaction: Initial compaction uses a Dynapac CC6200 double-drum roller for one pass of static compaction at a speed of 2.5 km / h and a linear pressure of 12 MPa, without vibration. After compaction stabilization, there is no significant displacement of the paved layer. Secondary compaction uses a Dynapac CA610 single-drum vibratory roller for four passes of compaction at a speed of 3.5 km / h, a vibration frequency of 40 Hz, an amplitude of 0.6 mm, a vibration acceleration of 0.7 g, and a linear pressure of 25 MPa. These parameters meet the demulsification threshold of pressure-sensitive emulsified asphalt. During compaction, the emulsified asphalt can be observed to gradually demulsify and change color, with the asphalt changing from brown to black. Final compaction uses an XCMG XP303 rubber-tired roller for two passes of static compaction at a speed of 4.5 km / h and a tire ground pressure of 0.7 MPa to eliminate wheel tracks and form a tight sealing layer on the surface.

[0028] S6 Real-time Compaction Feedback Closed-Loop Control: An accelerometer-type compaction sensor is installed on the single-drum roller, collecting compaction data every 0.5m and transmitting it to the cab control system in real time. After the first pass of compaction, the compaction degree reaches 92%; the second pass reaches 96%; the third pass reaches 98.2%; and after the fourth pass, the compaction degree at each continuous monitoring point is ≥98%. The system then indicates that compaction is complete and automatically stops compaction to avoid over-compaction.

[0029] S7 Early curing: After compaction, cover with geotextile and spray with water for curing at an ambient temperature of 25℃. After 24 hours of curing, test the strength: 1.9MPa at 2 hours, 3.6MPa at 24 hours, 5.0MPa at 3 days, 98.5% compaction degree, and 2.2mm / m flatness. Light traffic can be opened at this time. Full traffic can be opened after 7 days.

[0030] Performance testing: After molding, the recycled layer has an unconfined compressive strength of 5.8 MPa after 7 days, a freeze-thaw splitting strength ratio (TSR) of 88%, a dynamic stability of 6200 cycles / mm, and an interlayer shear strength of 0.48 MPa. All indicators meet the requirements for highway base courses. The utilization rate of old materials is 100%, there is no waste material transported out, and the construction period is shortened by 5 days compared with the traditional process.

[0031] Example 2: A mid-level highway repair project with a recycled layer thickness of 10cm, using a plant-mixed cold recycling process.

[0032] The construction process differs from Example 1 in the following ways: milling depth is 10cm, maximum particle size after crushing is 19mm, total amount of pressure-sensitive emulsified asphalt is 3.8%, secondary compaction is performed at 30Hz and 0.5mm amplitude, with 3 passes, and traffic is allowed after 48 hours of curing. Testing showed a 2-hour strength of 1.7MPa, a 24-hour strength of 3.3MPa, a 3-day strength of 4.7MPa, a compaction degree of 98.2%, a TSR of 86%, and a dynamic stability of 5600 cycles / mm, meeting the performance requirements for Class I highways.

[0033] Comparative Example 1: The same road section was used for comparison, with the same pressure-sensitive emulsified asphalt, but the traditional fixed-parameter compaction process was adopted: single steel wheel vibratory compaction for 5 passes, vibration frequency 50Hz, amplitude 0.8mm, speed 2km / h, without real-time feedback control.

[0034] Test results: Obvious pushing and cracking occurred in the first two passes of compaction due to excessive pressure and premature demulsification; the compaction degree was uneven, with the lowest point only reaching 93%, and the aggregate was broken at the over-compacted areas; the 2-hour strength was only 0.8 MPa, and the 7-day strength only reached 3.5 MPa, requiring 7 days before traffic could be opened; the interlayer bonding was poor, with local loosening, and the performance was significantly worse than the process of this invention.

[0035] Comparative Example 2: It uses ordinary slow-cracking emulsified asphalt, traditional construction techniques, fixed parameter compaction, and a pressureless demulsification design.

[0036] Test results: slow demulsification, not completely demulsified even 24 hours after compaction, strength of only 0.4 MPa after 2 hours, requiring 10 days of curing before traffic can be opened; compaction degree 95%, TSR=76%, dynamic stability 3200 times / mm, old material utilization rate only 80%, and 20% of oversized material was discarded and transported off-site.

[0037] The results of the above embodiments show that the present invention, through staged pressure-triggered demulsification and compaction and real-time feedback control, fully utilizes the characteristics of pressure-sensitive emulsified asphalt, and achieves rapid molding, high quality, and 100% reuse of old materials in cold recycling construction. The road performance and construction efficiency are significantly better than those of traditional processes.

[0038] It is important to note that the constructions and arrangements of this application shown in several different exemplary embodiments are merely illustrative. Although only a few embodiments are described in detail in this disclosure, those who consult this disclosure will readily understand that many modifications are possible (e.g., changes in the size, dimensions, structure, shape, and proportions of various elements, as well as parameter values ​​(e.g., temperature, pressure, etc.), installation arrangements, use of materials, color, orientation, etc.) without substantially departing from the novel teachings and advantages of the subject matter described in this application. For example, an element shown as integrally formed may be composed of multiple parts or elements, the position of elements may be inverted or otherwise changed, and the nature or number or position of discrete elements may be altered or changed. Therefore, all such modifications are intended to be included within the scope of the invention. The order or sequence of any process or method steps may be changed or rearranged according to alternative embodiments. In the claims, any device-plus-function clause is intended to cover the structure described herein for performing the function, and not only structurally equivalent but also equivalent in structure. Other substitutions, modifications, alterations, and omissions may be made in the design, operation, and arrangement of the exemplary embodiments without departing from the scope of the invention. Therefore, the present invention is not limited to the specific embodiments, but extends to various modifications that still fall within the scope of the appended claims.

[0039] Furthermore, in order to provide a concise description of exemplary embodiments, not all features of actual embodiments (i.e., those features that are not relevant to the best mode of carrying out the invention as currently considered, or those features that are not relevant to implementing the invention) may be omitted.

[0040] It should be understood that numerous specific implementation decisions can be made during the development of any actual implementation method, and in any engineering or design project. Such development efforts may be complex and time-consuming, but for those of ordinary skill in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0041] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt, characterized in that, Includes the following steps: S1 Old Road Milling and Multi-stage Crushing and Grading: The old asphalt road surface is milled to the designed depth using a cold milling machine. The milled material is transported on-site to a multi-stage crushing and screening system. After crushing, grading and screening, it is divided into old materials of different particle sizes. All milled materials are 100% recycled on-site, and no waste is transported off-site. S2 pressure-sensitive emulsified asphalt is added in stages with precision: Based on the gradation and moisture content of the old material, pressure-sensitive emulsified asphalt is added in three stages: pre-spraying on the interface after milling, mixing and adding in the mixing drum, and surface spraying after paving. The pressure-sensitive emulsified asphalt is stable under static conditions and triggers demulsification under a set pressure threshold and vibration acceleration. S3 Vibration Mixing: Graded old material, cement, new aggregate, water and pressure-sensitive emulsified asphalt are fed into a twin-shaft vibration mixing tank and mixed for 60-90 seconds at the set vibration intensity to make the emulsified asphalt evenly coat the aggregate. The mixing vibration only initially activates the emulsified asphalt without premature demulsification. S4 paving: A cold recycling paver with a screed is used to spread the mixture evenly to the designed thickness. During the paving process, a continuous and uniform speed is maintained to avoid segregation. S5 staged pressure-triggered demulsification compaction: Compaction is carried out in three stages: initial pressure stabilization, intermediate pressure demulsification, and final pressure compaction. Different compaction pressures, vibration frequencies, amplitudes, and compaction speeds are used in different stages to precisely match the demulsification pressure threshold of pressure-sensitive emulsified asphalt. The emulsified asphalt is demulsified and solidified layer by layer through compaction pressure and vibration. S6 Real-time Compaction Feedback Closed-Loop Control: A real-time density monitoring sensor and a pressure sensor are installed on the roller. The road surface compaction and demulsification status are detected in real time after each rolling pass. The parameters for the next rolling pass are dynamically adjusted based on the detection results until the design compaction is achieved. S7 Early Maintenance: Early maintenance is carried out after compaction. Heavy vehicles are prohibited from passing during the maintenance period. Traffic is opened after the strength reaches the design requirements.

2. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: In step S1, the milling depth is 8-20cm, and the milling speed is controlled at 6-10m / min. A small amount of water is sprayed during the milling process to reduce dust but without increasing the moisture content of the old material. The milled material undergoes two-stage crushing and three-stage screening. After crushing, the maximum particle size does not exceed 31.5mm. It is screened into three particle size ranges: 0-5mm, 5-15mm, and 15-31.5mm. The old material is recycled in proportion according to the design gradation requirements to achieve 100% utilization of the old material and no waste material is generated.

3. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: In step S2, the total amount of pressure-sensitive emulsified asphalt is 3.5% to 5.0% of the mass of the recycled mixture, and it is added in three stages: the first stage is pre-spraying on the milled surface, accounting for 10% to 15% of the total amount, and is evenly sprayed on the cleaned surface of the underlying layer after milling to enhance the interlayer bonding. In the second stage, 75% to 85% of the total amount is added to the mixing tank and mixed evenly with the aggregate. In the third stage, 5% to 10% of the total amount is sprinkled on the surface after paving and is evenly sprayed on the surface after the initial compaction to seal the surface voids.

4. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: In step S3, the vibration frequency of the biaxial vibration mixing is 20-30 Hz, and the vibration acceleration is 0.2-0.4 g. This vibration intensity is lower than the demulsification threshold of pressure-sensitive emulsified asphalt and is only used to uniformly disperse and coat the aggregate with emulsified asphalt without triggering premature demulsification. The mixing sequence is as follows: first, dry mix the coarse aggregate, fine aggregate, and cement for 10 seconds, then add water and 80% of the total amount of emulsified asphalt and mix for 40-60 seconds, and finally add the remaining 20% ​​of emulsified asphalt and mix for 20 seconds to avoid direct contact between the emulsified asphalt and cement, which may cause flocculation.

5. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: The specific parameters for the staged compaction in step S5 are as follows: Initial compaction and stabilization stage: Use a double-drum roller for static compaction once, with a rolling speed of 2-3 km / h and a linear pressure of 10-15 MPa. Do not turn on the vibration. The purpose is to stabilize the paving layer and prevent pushing during the re-compaction. The secondary compaction and demulsification stage involves rolling the mixture 3-4 times with a single steel drum vibratory roller at a speed of 3-4 km / h, a vibration frequency of 30-50 Hz, an amplitude of 0.4-0.8 mm, a vibration acceleration of 0.5-1.0 g, and a linear pressure of 20-30 MPa. This pressure and vibration reach the demulsification threshold of the pressure-sensitive emulsified asphalt, triggering rapid demulsification of the emulsified asphalt and simultaneously compacting the mixture to a compaction degree of over 95%. Final compaction stage: Use a rubber-tired roller for static compaction 1 to 2 passes at a speed of 4 to 5 km / h and a tire ground pressure of 0.6 to 0.8 MPa. Do not turn on the vibration. The purpose is to smooth out the surface, eliminate wheel tracks, further compact the surface layer, and allow the demulsified emulsified asphalt on the surface to form a complete seal layer.

6. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: In step S6, the density sensor used is a nucleus-free density meter or an accelerometer, which is installed on the vibratory wheel of the roller. Compaction data is collected every 0.5m and transmitted to the control system in real time. When the compaction degree is detected to reach 93%, the amplitude and vibration force of the next rolling pass are reduced. When the compaction degree reaches the design value (≥98%) for two consecutive detection points, rolling is automatically stopped to avoid over-pressure that could cause asphalt film to fall off or aggregate to break. At the same time, the ground pressure of the roller is monitored by a pressure sensor. When the pressure exceeds the upper limit of the demulsification threshold, the rolling speed is automatically reduced to ensure uniform demulsification.

7. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: After milling in step S1, the surface of the underlying layer is treated: the dust on the milled surface is cleaned with a sweeper, the loose parts are removed, and then the pressure-sensitive emulsified asphalt pre-sprayed in the first stage is sprayed at a rate of 0.3-0.5 kg / m². After demulsification, a tack coat is formed to ensure the bonding strength between the recycled layer and the underlying layer, with an interlayer shear strength ≥ 0.4 MPa.

8. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: Joint treatment during construction: Longitudinal joints are treated with echelon-style hot jointing. During compaction, a 10-15cm width is left uncompacted as an elevation reference surface for subsequent paving. After subsequent paving is completed, the joints are compacted together. Transverse joints are treated with flat jointing. During compaction, a transverse compaction method is used. First, the compacted pavement is driven on, and then the compaction is gradually advanced towards the new paved layer, advancing 10-15cm laterally each time, until the entire new paved layer is compacted. Then, longitudinal compaction is switched to ensure that the joint is dense and flat, and the compaction degree at the joint is 1%-2% higher than the design value.

9. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: Step S7: Early curing time is 24–72 hours. During the curing period, the road surface should be kept moist. When the ambient temperature is above 20℃, light traffic can be opened after 24 hours of curing. When the ambient temperature is between 10 and 20℃, traffic can be opened after 48 hours of curing. When the ambient temperature is below 10℃, traffic can be opened after 72 hours of curing. Before opening to traffic, the road surface strength should be tested. The requirements are: 2-hour early strength ≥ 1.5 MPa, 24-hour strength ≥ 3.0 MPa, 3-day strength ≥ 4.5 MPa, compaction degree ≥ 98%, and smoothness ≤ 3 mm / m.

10. The cold recycling construction process for old asphalt pavement based on pressure-sensitive emulsified asphalt according to claim 1, characterized in that: During construction, the ambient temperature shall not be lower than 10℃, and construction shall not be carried out in rainy weather or when it is about to rain; the time from mixing to the end of compaction of the mixed material shall not exceed 4 hours, and the paving temperature shall not be lower than 10℃; the demulsification pressure threshold of pressure-sensitive emulsified asphalt is 0.4~0.6MPa, the demulsification vibration acceleration threshold is 0.4~0.6g, the emulsion is stable when it is below the threshold, and rapidly demulsifies and solidifies within 1~2 minutes when it is above the threshold; the unconfined compressive strength of the cold recycled layer after molding shall be ≥5MPa after 7 days, the freeze-thaw splitting strength ratio (TSR) shall be ≥85%, and the dynamic stability shall be ≥5000 times / mm.

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