A method and system for healing asphalt pavement by microwave intermittent pulse heating

Abstract

The application discloses a kind of asphalt pavement microwave intermittent pulse heating healing method and system.The method comprises: applying calibration pulse to pavement material and fitting cooling curve to obtain characteristic thermal relaxation time constant τ ;with τ As control variable, intermittent pulse microwave heating is carried out on the healing area, and the pulse intermittent time t r Satisfies 1.5 τ ≤ t r ≤ 3 τ , and the maximum temperature monitored by infrared temperature measurement during heating does not exceed the safety threshold.The microwave self-healing heating system automatically completes τ Calibration and calculation of subsequent intermittent duration.The present application utilizes the hysteresis conduction intersection effect of wave-absorbing aggregate residual heat during the intermittent period, and under the same total heating energy, the maximum temperature deviation is reduced by more than 55%, the cycle healing rate is increased by more than 38%, and the asphalt thermal oxidative aging index is reduced by more than 47%.

Description

Technical Field

[0001] This invention relates to the field of road engineering maintenance technology, specifically to a method and system for self-healing asphalt pavement using microwave intermittent pulse heating based on thermal relaxation time constant. Background Technology

[0002] Microwave heating self-healing technology utilizes microwave-absorbing materials incorporated into asphalt mixtures, such as steel slag, ferrite, and magnetite, to convert microwave energy into heat energy. This raises the temperature of the asphalt at the cracks above its softening point, allowing the cracks to self-heal through viscoelastic flow. Compared to traditional milling and resurfacing, this technology offers advantages such as speed, energy efficiency, and no traffic disruption, and has received widespread attention in recent years. However, research has identified the following technical challenges associated with microwave heating self-healing:

[0003] (1) In asphalt mixtures containing isolated, point-distributed microwave-absorbing aggregates such as steel slag, microwave energy is excessively captured at the interface of the microwave-absorbing aggregates, causing the asphalt temperature near the interface to rapidly exceed the thermo-oxidative aging limit, while the mortar area far from the aggregates remains below the healing threshold. Extending the heating time can expand the healing coverage but at the same time exacerbates overheating damage, forming an irreconcilable contradiction.

[0004] (2) After continuous heating stops, the high-temperature residual heat accumulated in the microwave-absorbing aggregate will diffuse to the surrounding low-temperature area through conduction. In the high-dosage system, the hysteretic heat waves emitted by multiple steel slag particles converge and superimpose in the central area, which can significantly raise the temperature of the originally heating blind zone. In addition, in the system with uniformly dispersed micro-powder, the matrix exhibits isothermal lock-in characteristics after shutdown, and the heat is mainly lost at the interface between the aggregate and the mortar. These heat transfer kinetic laws during the cooling period indicate that the time period after shutdown contains valuable opportunities for heat redistribution, but this resource is wasted in the continuous heating mode.

[0005] (3) A few studies have proposed surface temperature-triggered intermittent heating, but the intermittent time is determined by the temperature falling back to a certain empirical threshold, and no quantitative correlation has been established with the heat transfer characteristic parameters of the material itself. Asphalt mixtures with different compositions, such as aggregate-absorbing type, micro powder-absorbing type, and steel slag and micro powder composite type, have fundamentally different cooling decay laws. Controlling the intermittent time based on empirical parameters cannot adapt to the heat transfer characteristics of different material systems. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method based on thermal relaxation time constant. t A method and system for self-healing asphalt pavement using microwave intermittent pulse heating. The pavement material is an asphalt mixture containing microwave absorbing material, which is selected from one or more of steel slag aggregate, magnetite aggregate, ferrite aggregate, steel slag powder, magnetite powder, and ferrite powder.

[0007] Therefore, the microwave intermittent pulse heating healing method for asphalt pavement provided by the present invention includes the following steps: Step 1, Thermal relaxation time constant t Calibration includes collecting the initial temperature of the area of ​​the road surface to be healed. T env The area to be healed was then subjected to microwave heating for 20-30 seconds at a frequency of 2.40–2.50 GHz and a power of 600–1200 W. Infrared thermal imaging was then used to collect surface temperature decay data of the heated area for at least 60 seconds. A first-order exponential decay function for the temperature decay data of the road surface material to be healed was constructed using least-squares fitting. T (t) = T env + ΔT·exp( (t / t) , ΔT For the peak temperature in the collected data and T env The difference, where the goodness of fit R of the least squares fit is... 2 ≥ 0.90; Step 2: Perform microwave intermittent pulse heating on the surface to be healed, for a total of N times, with each heating session lasting [duration missing]. t h The duration of the interval between two consecutive heating cycles t r = k·t Where 2 ≤ N ≤ 6, 30 s ≤ t h ≤ 120 s, k Take a value of 1.5 to 3.0, and the total cumulative heating time (N·m) t h ≤ 720 s; simultaneously, during each pulse heating period, the infrared thermal imaging device monitors the maximum surface temperature of the heating area in real time. T max ,when T max ≥ T safe The current pulse will automatically terminate and enter an interval period; T safe The temperature is 105-130°C.

[0008] An optional approach is that the asphalt mixture contains wave-absorbing material at both the coarse aggregate and mineral powder scales; the coarse aggregate scale is ≥4.75 mm, and the mineral powder scale is <0.075 mm; when the volume percentage of wave-absorbing material with a particle size ≥4.75 mm in the pavement material to be healed is ≥50%, kTake a value of 2.0 - 3.0; when the volume percentage of the absorbing material <0.075 mm in the road surface material is ≥50%, k Take 1.5 - 2.0.

[0009] An alternative approach is to fit the temperature decay data collected from 10 to 15 seconds after the start of the data collection to eliminate interference from unsteady radiative heat dissipation during the initial stage of heating cessation.

[0010] An alternative approach is to use an infrared thermal imaging device to monitor the standard deviation of the surface temperature distribution in the area of ​​the road surface to be healed during the intermittent period. s T ;when s T ≤ s At 0:00, the current interval ends early and the next pulse heating begins; s 0 represents 3 - 8°C.

[0011] An alternative is that the heating microwave power in step 2 is the same as the microwave power in step 1.

[0012] An alternative approach is to use a microwave power reduction strategy for N-pulse heating. The microwave power for the first to N / 2 pulse heating is 100% of the rated power, and the microwave power for the remaining pulse heating is 70%-85% of the rated power. When N is an odd number, N / 2 is rounded up.

[0013] The microwave healing heating system provided by this invention includes: A microwave transmitting device, including a magnetron and a waveguide antenna array, is used to transmit microwave radiation toward the road surface; Infrared thermal imaging device, used to acquire two-dimensional surface temperature field of heated area; The controller module controls the microwave heating device and the infrared thermal imaging device according to the above method.

[0014] Furthermore, the controller module also includes a safety interlock module, which cuts off the power supply to the microwave transmitter module and issues an alarm when any of the following conditions are met: (a) T max ≥ T safe If the duration exceeds 3 seconds, it indicates an overheating risk and heating should be stopped. The controller's interlock module should then cut off the power to the microwave transmitter module. (b) Step (1) takes more than 250 seconds to execute; Explanation t Calibration timeout (interval exceeds 5τ and R is still not reached) 2 ≥0.90) indicates that the interference from the external environment is too great, or the heat dissipation characteristics of the road surface material are very abnormal, the fitting fails, and the fitting should be stopped; (c) The total cumulative heating time of the healing pulse exceeds 720 s. The heating process cannot be repeated indefinitely to avoid thermal damage to the asphalt.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1). Taking pure steel slag aggregate asphalt mixture as an example, under the same total heating time, compared with continuous heating, the intermittent pulse heating of the present invention, according to the experimentally verified multiphysics simulation model calculation, the effective healing volume ratio (40-130°C range) increases from about 70% to about 83%, and the thermal damage volume ratio (>130°C range) decreases from about 15% to about 6%.

[0016] (2) The intermittent period is not a passive waiting period, but an active means of filling the heating blind zone by conducting and converging multiple sources of waste heat. This mechanism enables the secondary distribution of heating energy.

[0017] (3). t It features material adaptability: it automatically matches the optimal intermittent strategy to different pavement materials, eliminating the need for manual parameter tuning based on experience.

[0018] (4). t It only requires a short pulse of 20-30 seconds and a cooling record of 5 minutes, which can be completed automatically on site. Attached Figure Description

[0019] Figure 1 shows the embodiment. V heal (a) and V damag (b) The variation with the intermittent coefficient k.

[0020] Figure 2 This is a comparison diagram of the temperature field of SS-100 mixture under continuous heating and intermittent pulse heating in the examples and comparative examples. ΔT max This is the difference between the peak temperature on the specimen surface and the initial temperature on the specimen surface. Detailed Implementation

[0021] Unless otherwise specified, the scientific and technical terms used in this article are intended for understanding by those skilled in the art.

[0022] Thermal relaxation time constant t It is the time required for the material to decay from the peak temperature to the ambient temperature to 1 / e (approximately 36.8%) of the initial temperature difference (i.e., the difference between the peak temperature and the ambient temperature). tThis reflects a material's comprehensive ability to resist heat loss, depending on its thermal conductivity, specific heat capacity, density, and geometric boundary conditions. The heat redistribution dominated by this parameter directly determines the rheological state of materials (such as asphalt mixtures) after heating, thereby enhancing the viscoelastic flow of asphalt to achieve physical filling and healing of cracks. Different asphalt mixture compositions correspond to different... t Value, therefore t Intermittent strategies for controlling variables have inherent material adaptability.

[0023] Based on this, the present invention, while ensuring that the material is not overheated, adjusts the thermal relaxation time constant. t As a bridge control variable between microwave heating process parameters and the internal heat transfer physical properties of materials, t Certainly t r (Interval time / interval duration) ensures that the interval after each pulse is precisely matched to the characteristic time required for the material's residual heat diffusion, thereby systematically transforming the interval from a passive waiting period into an active heat redistribution process. This enhances the viscoelastic flow of asphalt to achieve physical filling and healing of cracks.

[0024] To mitigate the risk of high-temperature thermal degradation of asphalt, this invention, in addition to utilizing the thermal relaxation time constant to set the interval duration, further controls the average surface temperature of the material during heating to not exceed 90°C and the maximum surface temperature to not exceed the temperature safety threshold by setting microwave power, heating duration, and pulse count. T safe The present invention describes T safe The temperature range is 105-130°C, determined based on the high-temperature oxidation aging limit of the asphalt mixture. To better mitigate the risk of high-temperature thermal degradation of asphalt, the solution of this invention will be used as... T safe Safety thresholds for each heating process.

[0025] In the specific solution, the size of the area to be repaired depends on the size of the waveguide port of the microwave heating vehicle, and the temperature data of this area is collected after heating.

[0026] In the present invention t Sufficient data needs to be collected during calibration (e.g., using an infrared thermal imaging model with a sampling frequency higher than 1Hz) to ensure that the first-order exponential decay least squares fitting has sufficient statistical significance and can effectively eliminate random thermal noise interference in complex natural environments.

[0027] The safety interlock module built into the system controller based on the method of the present invention is used to perform: If the maximum temperature of the area is detected by infrared real-time monitoring T max≥ Preset safety threshold T safe If the duration exceeds 3 seconds, the controller determines it to be a real overheating danger caused by excessive concentration of localized absorbing aggregate and immediately cuts off the power. The 3-second time delay is set here to filter out instantaneous road surface reflections or occasional artifacts from infrared sensors, preventing the system from falsely triggering a shutdown. If calibrated t The process lasted for more than 250 seconds, but still did not reach R. 2 If the goodness-of-fit requirement is ≥ 0.90, it is determined that the current environmental interference is too great or the heat dissipation characteristics of the material are abnormal. An alarm is then issued and the microwave cycle operation is terminated to prevent unnecessary energy consumption. The total cumulative time of the healing pulses for microwave heating is set to an upper limit of 720 seconds to prevent excessive heat accumulation in the deep layers of the road surface caused by multiple pulse superpositions, thereby protecting the asphalt from secondary thermo-oxidative aging damage.

[0028] The principles and features of the present invention are described below with reference to the accompanying drawings. The embodiments given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0029] In the following examples, the asphalt was 90# base asphalt, aged with steel slag for over 12 months. Basic properties are shown in Tables 1 and 2. All mixtures used AC-13 gradation, with the asphalt-aggregate ratio determined according to JTG F40-2004. The microwave equipment had a frequency of 2.45 GHz and a rated power of 700W. Infrared thermal imaging was performed using a Fluke TiS75 with a sampling frequency of 2 Hz.

[0030] Example 1: This embodiment studies and analyzes the thermal relaxation time constants of three typical asphalt mixtures. t Three typical asphalt mixtures are steel slag asphalt mixture, steel slag micro powder asphalt mixture, and steel slag and steel slag micro powder composite asphalt mixture.

[0031] This embodiment involves three types of asphalt mixtures (all three types are designed based on AC-13 mixture): SS-100: 100% volumetric replacement of limestone with steel slag in the 4.75 - 9.5 mm particle size range, with an oil-aggregate ratio of 4.8%; H-1: 50% of coarse aggregate grade steel slag replaces 4.75-9.5mm limestone + 100% of steel slag powder replaces mineral powder, with an oil-aggregate ratio of 4.9%; GSS-100: Limestone aggregate remains unchanged, steel slag powder replaces 100% of mineral powder by volume, and the oil-stone ratio is 4.9%.

[0032] Table 1 Basic Properties of Asphalt

[0033] Table 2 Basic Properties of Aggregates and Mineral Powder

[0034] Three mixtures t Calibration test and results: Marshall specimens (height 63.5 mm, diameter 101.6 mm) of the three types of mixtures were tested separately. t Calibration: After placing the specimens in an environment of 20°C for 12 h, they were heated in a 700 W microwave oven for 25 s (the highest surface temperatures of the three mixtures were SS-100: 77.3℃, H-1: 62.6℃, and GSS-100: 44.5℃). After heating was stopped, an infrared thermal imager continuously recorded the average temperature (temperature decay data) of the surface area of ​​the specimens at a sampling frequency of 2 Hz for 300 s. Constructing the first-order exponential decay function for the temperature decay data of three types of mixtures: First, determine the room temperature condition to obtain... T evn The difference between the peak temperature of the specimen and the room temperature (or the initial surface temperature of the specimen) is then obtained. ΔT Then, fitting was performed, specifically on the temperature decay data from 15 seconds to the end of the calibration (300 seconds in this example). T(t) A first-order exponential least squares fit was performed to construct the function for the three types of mixtures: SS-100: T(t) = 20 + 57.3·exp( t / 35)， H-1: T(t) = 20 + 42.6·exp( t / 48)， GSS-100: T(t) = 20 + 24.5·exp( t / 58) The common knowledge of their respective thermal relaxation times is shown in Table 3.

[0035] Table 3. Calibration results of τ for three types of mixtures

[0036] According to Table 3, the three types of mixtures tThe significant gradient differences in the values ​​are physically rooted in the different spatial topologies of the absorbers. In SS-100, the steel slag is distributed in isolated point-like patterns, with a steep near-interface temperature gradient, concentrated heat flow channels, and the fastest attenuation (τ = 35 s). In GSS-100, the micro-powder is uniformly dispersed, with minimal internal temperature difference. The cooling bottleneck is the convective heat dissipation at the thin interface layer between the aggregate and the mortar, resulting in the slowest attenuation (τ = 35 s). t = 58 s). H-1 is between the two. The results of this embodiment show t The one-to-one correspondence between the topology of the three mixed materials illustrates that... t It can be used as a control variable for microwave heating and healing of asphalt mixtures.

[0037] Example 2: This embodiment quantitatively evaluates the temperature field improvement effect of intermittent pulse heating based on the COMSOL multiphysics coupling model, and performs simulation analysis on different heating strategies. The model has been verified by measured temperature rise curves (R... 2 >0.99).

[0038] The heating strategy is as follows: under the premise of ensuring a basic heating power of 700W and consistent position of the specimen model in the simulated electromagnetic field, the total heating time of both the continuous group and the pulse group is set to 120s to ensure that the heat transfer advantage of intermittent pulses is rigorously demonstrated under the basis of equal energy input; secondly, three typical materials (three mixtures in Example 1) are selected to verify the adaptability of the intermittent strategy with τ as the core of the present invention to different absorber skeletons; finally, the intermittent coefficient k is scanned from 1 to 3 to explore the heat transfer physical boundary for different systems to achieve optimal heat redistribution.

[0039] In the COMSOL software simulation, based on the rheological analysis of the asphalt softening point of 46.5°C, with 40°C as the effective healing lower limit temperature and 130°C as the thermal damage threshold, the proportion of effective healing volume within the asphalt mortar domain in the 40-130°C range was statistically analyzed. V heal (This value represents the volume of asphalt that reaches the healing temperature, indicating the volume of effective healing. A higher value is better (up to 100%), indicating that the heated asphalt mixtures are in a healing state, avoiding both insufficient healing due to low temperatures and excessive heat damage.) It also includes the percentage of heat damage exceeding 130°C. V damage (This value represents the volume of asphalt damaged by high temperature, which may subsequently age and become unrepairable. A smaller value is better, indicating that the proportion of asphalt damaged by high temperature within the mixture is relatively small, preventing secondary damage to the asphalt.) The results are shown in Table 4, where T... avg ΔT represents the average surface temperature of the specimen. maxThis is expressed as the initial temperature difference, i.e., ΔT in the formula; t h Indicates: heating time. t r Indicates the duration of the interval.

[0040] Table 4. Comparison of temperature field simulation results for different heating strategies

[0041] Analyzing Table 4 and referring to Figure 1, the following key conclusions can be drawn: (1) Optimal coefficients of SS-100 k =2.0( V heal =83%, V damage =5.8%); H-1 is optimal k =1.5( V heal =87%, V damage =2.5%); GSS-100 is optimal. k =1.5( V heal =80%, V damage =2.2%).

[0042] (2) SS-100 from continuous to optimal V damage The reduction was 61% for H-1, 44% for H-1, and only 21% for GSS-100. This proves that the present invention is most effective for point-like isolated absorbing systems, and has limited effect on network-like continuous systems.

[0043] (3) Three mixtures V heal All in k =2-2.5 then it starts to decrease (SS-100 in k =3 from 83 to 80, H-1 from 87 to 83, GSS-100 from 80 to 77), the reason is that the interval is too long, causing the diffused heat to be lost to the environment, and the heat network needs to be re-established in the second pulse.

[0044] The above analysis results demonstrate that the intermittent pulse heating strategy based on the thermal relaxation time constant τ can effectively overcome the contradiction in traditional continuous microwave heating where the pursuit of increased healing rate leads to exacerbated thermal damage. The simulation data supports the proposed range of values ​​for the intermittent time coefficient k: for systems with coarse aggregate as the core heat source, the benefit reaches its peak when k is between 2 and 3; while for micro-powder heating systems, k between 1.5 and 2 is sufficient to achieve heat homogenization. Furthermore, all materials exhibited a decrease in healing rate after exceeding a specific intermittent period, which conversely confirms the scientific validity of strictly limiting the upper limit of k to 3 in this invention.

[0045] The initial surface temperature of the following examples and comparative sample mixtures (height 63.5 mm, diameter 101.6 mm) was 20°C (the samples were placed in a 20°C environment for 4 h).

[0046] Example 3: This embodiment is based on mixture SS-100. t = 35 s, and then subjected to microwave intermittent pulse heating for healing.

[0047] Heating conditions are t h = 60 s, t r = 2τ = 70 s, pulse heating times N = 2, microwave power 700 W.

[0048] The surface temperature field of the specimen after pulse heating in this embodiment is shown below. Figure 2 As shown in (b).

[0049] Example 4: This embodiment is based on mixture H-1. τ= It was subjected to microwave intermittent pulse heating for 48 seconds.

[0050] The heating parameters for healing are: t h = 60 s, t r = 1.5τ = 72 s, N = 2, microwave power 700 W.

[0051] Example 5: This embodiment is based on mixture SS-100. t = 35 s, and perform intermittent pulse heating with decreasing power.

[0052] t h = 60 s, t r= 2τ = 70 s, N = 2, first pulse 700 W, second pulse 530 W (75% rated).

[0053] Example 6: This embodiment is based on GSS-100. τ= Intermittent pulsed heating was performed for 58 seconds to heal the wound. 。

[0054] t r = 1.5 t = 87 s, t h = 60 s, N = 2, microwave power is 700w.

[0055] Comparative Example 1: For the SS-100 sample, a 700 W microwave was used continuously for 120 s without interruption. The surface temperature field of the specimen after continuous heating in this comparative example is shown below. Figure 2 As shown in (a).

[0056] Comparative Example 2: The SS-100 is used for fixed intermittent heating at 700 W microwave power, with intermittent heating for 2 × 60 s, but the interval is set to a fixed 60 s instead of being based on... t Calculation (of this scheme) t r ≈ 1.7τ, lower than the recommended value of 2. t ).

[0057] Comparative Example 3: H-1 was continuously heated for 120 seconds at a microwave power of 700 W.

[0058] Comparative Example 4: The GSS-100 was continuously heated for 120 seconds at a microwave power of 700 W.

[0059] SCB cyclic healing test method: The SCB specimen was placed in a 20°C environment and left to stand for 4 hours. A CMT 5105 electronic universal testing machine was used for displacement control loading to the initial peak load F1. After stopping the pressure, the specimen was bandaged and microwave-heated according to the corresponding scheme of the embodiment or comparative example. After healing at room temperature for 6 hours, the next microwave-heated healing was performed, for a total of 5 cycles. n = F n / F1× 100%, F n The peak load is the load of the nth cycle, where n is the number of cycles, n=1,2,…,5. After 5 cycles, core samples are taken to extract bitumen for FTIR measurement of the carbonyl index I. C=O .

[0060] Table 5 Test Results

[0061] Results Analysis 1 (Example 3 vs. Comparative Example 1 vs. Comparative Example 2): All three groups used SS-100 material, with a total heating time of 120 s. In Example 3, η5 = 54.3%, representing a 38.8% improvement over the continuous heating of Comparative Example 1 and a 14% improvement over the fixed intermittent heating of Comparative Example 2. Meanwhile, compared to continuous heating, I... C=O It decreased from 0.072 to 0.038; compared to fixed intermittent heating, I C=O The value decreased from 0.051 to 0.038. After three sets of comparisons, Comparative Examples 1 to 3 demonstrated that intermittent pulse heating is superior to continuous heating; Comparative Examples 2 to 3 demonstrated... t The baseline interval is superior to the empirical interval.

[0062] Furthermore, as shown in Table 5 regarding the trend of cyclic healing rate changes, the healing rate of Comparative Example 1 decreases sharply with the increase of the number of cycles, with η dropping from 75.0% to 39.1%, while the decline in Example 3 is significantly more gradual (η gradually decreases from 81.5% to 54.3%). This fully demonstrates that intermittent pulses effectively suppress the cumulative thermal damage to asphalt caused by repeated microwave heating, giving the pavement a longer lifespan of multiple healable cycles.

[0063] Results Analysis II (Example 4 vs. Comparative Example 3) For H-1 dual-scale materials, t Basal interval ( k = 1.5) further increases η5 from 60.4% to 66.5%, I C=O It decreased from 0.032 to 0.022. This indicates... t The adaptive mechanism has significant optimization effects on different material systems.

[0064] Results Analysis 3 (Example 6 vs. Comparative Example 4) For the GSS-100 micro powder system, the intermittent pulse only slightly increased η5 from 51.2% in Comparative Example 4 to 57.8%, and I C=O The thermo-oxidative aging index only decreased slightly from 0.018 to 0.016. The improvement was far less significant than that of the aggregate system. This is because the continuous mesh material itself is nearly isothermal during microwave heating, without significant spatial misalignment or localized extreme high temperatures, thus limiting the potential for heat redistribution gain during the intermittent heating period. This further demonstrates that the intermittent mechanism based on the thermal relaxation time constant of this invention primarily targets and addresses the thermal damage issues of microwave-absorbing aggregate systems containing isolated point-like structures.

[0065] Results Analysis 4 (Example 5 vs. Example 3) Comparing Example 5 and Example 3, after adopting the power reduction strategy, the healing rate η5 of Example 5 in the 5th cycle further increased slightly from 54.3% to 56.1%. More importantly, its asphalt thermo-oxidative aging index I... C=O The value further decreased from 0.038 to 0.033. This indicates that employing a power reduction strategy (such as 75% of rated power) in subsequent pulses can further reduce the excessive heat accumulation peak at the aggregate interface while maintaining the effective healing temperature, achieving a deeper level of aging protection, thus verifying the beneficial effect of the power reduction strategy of this system.

Claims

1. A method for microwave intermittent pulse heating and healing of asphalt pavement, wherein the pavement material is an asphalt mixture containing a microwave absorbing material, and the microwave absorbing material is selected from one or more of steel slag aggregate, magnetite aggregate, ferrite aggregate, steel slag powder, magnetite powder, and ferrite powder; characterized in that, The method includes the following steps: Step 1, Thermal relaxation time constant τ Calibration includes collecting the initial temperature of the area of ​​the road surface to be healed. T env The area to be healed was then subjected to microwave heating for 20-30 seconds at a frequency of 2.40–2.50 GHz and a power of 600–1200 W. Infrared thermal imaging was then used to collect surface temperature decay data of the heated area for at least 60 seconds. A first-order exponential decay function for the temperature decay data of the road surface material to be healed was constructed using least-squares fitting. T(t) = T env + ΔT·exp( t / τ) , ΔT For the peak temperature in the collected data and T env The difference, where the goodness of fit R of the least squares fit is... 2 ≥ 0.90; Step 2: Perform microwave intermittent pulse heating on the surface to be healed, for a total of N times, with each heating session lasting [duration missing]. t h The duration of the interval between two consecutive heating cycles t r = k·τ Where 2 ≤ N ≤ 6, 30 s ≤ t h ≤ 120 s, k Use a value of 1.5 to 3.0, with a total cumulative heating time of N. t h ≤ 720 s; simultaneously, during each pulse heating period, the infrared thermal imaging device monitors the maximum surface temperature of the heating area in real time. T max ,when T max ≥ T safe The current pulse will automatically terminate and enter an interval period; T safe The temperature is 105-130°C.

2. The method according to claim 1, characterized in that, The asphalt mixture contains wave-absorbing material at both the coarse aggregate and mineral powder scales; the coarse aggregate scale is ≥4.75 mm, and the mineral powder scale is <0.075 mm; when the volume percentage of wave-absorbing material with a particle size ≥4.75 mm in the pavement material to be healed is ≥50%, k Take a value of 2.0 - 3.0; when the volume percentage of the absorbing material <0.075 mm in the road surface material is ≥50%, k Take 1.5 - 2.

0.

3. The method according to claim 1, characterized in that, The temperature decay data from 10-15 seconds after acquisition to the end of acquisition were used for fitting to eliminate the interference of unsteady radiative heat dissipation in the early stage of heating cessation.

4. The method according to claim 1, characterized in that, During the interval, the infrared thermal imaging device monitors the standard deviation of the surface temperature distribution in the area of ​​the road surface to be healed. σ T ;when σ T ≤ σ At 0:00, the current interval ends early and the next pulse heating begins; σ 0 represents 3 - 8°C.

5. The method according to claim 1, characterized in that, The microwave power for heating in step 2 is the same as that in step 1.

6. The method according to claim 1, characterized in that, The N-pulse heating employs a microwave power reduction strategy. The microwave power for the first to N / 2 pulse heating is 100% of the rated power, while the microwave power for the remaining pulse heating is 70%-85% of the rated power. When N is an odd number, N / 2 is rounded up.

7. A microwave healing heating system implementing the method of claim 1, characterized in that, include: A microwave transmitting device, including a magnetron and a waveguide antenna array, is used to transmit microwave radiation toward the road surface; Infrared thermal imaging device, used to acquire two-dimensional surface temperature field of heated area; The controller module controls the microwave heating device and the infrared thermal imaging device according to the method of any one of claims 1-6.

8. The system according to claim 7, characterized in that, The controller also includes a safety interlock module, which cuts off the power supply to the microwave transmitting module and issues an alarm when any of the following conditions are met: (a) T max ≥ T safe (a) Duration exceeding 3 s; (b) Execution time of step (1) exceeding 250 s; (c) Total cumulative heating time of healing pulse exceeding 720 s.

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