Asphalt pavement hot in-place recycling heating optimization method based on multi-field coupling simulation

Abstract

The invention provides an asphalt pavement hot in-place recycling heating optimization method based on multi-field coupling simulation, belongs to the field of road maintenance engineering, and solves the problems that heating parameters are set according to experience, a temperature field is difficult to quantify, local overheating aging occurs, and energy consumption is high. The method comprises the following steps: firstly, establishing an infrared heating device-air domain-three-layer asphalt pavement model in multi-physics field software, and setting construction parameters; secondly, each layer is endowed with thermophysical properties changing along with the temperature, and a pavement bottom heat insulation and air domain convective heat transfer boundary is arranged; then coupling solid heat transfer, fluid flow and surface radiation, and adopting a mobile heat source to simulate unit advancing heating to obtain a road surface transient temperature field; and finally, parameterized scanning is carried out by taking the heating power, the advancing speed, the heating height and the heating times as variables, the target depth average temperature, the road surface peak value, the temperature uniformity and the unit area energy consumption are calculated, and an optimal parameter combination is screened. The method can guide on-site heating construction, realizes uniform heating, saves energy, reduces consumption and inhibits asphalt aging.

Description

Technical Field

[0001] This invention proposes an optimized heating method for in-situ thermal recycling of asphalt pavement based on multi-field coupled simulation, which belongs to the field of road maintenance engineering. Background Technology

[0002] With the continuous improvement of my country's highway network and the sustained increase in highway mileage, a large number of asphalt pavements have entered a critical stage of periodic maintenance and repair. As a major type of pavement, asphalt pavements inevitably suffer from various defects such as cracks, ruts, loosening, and aging during their design service life due to multiple factors including traffic loads, environmental factors, and material aging. These defects not only affect driving safety and comfort but also significantly shorten the service life of the pavement. Traditional maintenance methods, such as milling and overlaying with new asphalt mixture, while technically mature, have many problems, including resource waste from discarding old materials, increased energy consumption and carbon emissions from material transportation, and long construction cycles that affect traffic flow. Against this backdrop, asphalt pavement recycling technologies, especially in-situ thermal recycling technology, which combine environmental friendliness and economy, are receiving increasing attention and are being widely applied.

[0003] In-situ thermal recycling technology is a complete process that involves heating and loosening existing asphalt pavement at the construction site, adding recycling agents or new asphalt mixtures as needed, and then mixing, paving, and compacting the mixture. This technology enables 100% recycling of old asphalt mixtures, maximizing the conservation of non-renewable resources such as aggregates and asphalt binders, and significantly reducing the environmental damage and pollution caused by aggregate mining and asphalt refining. Simultaneously, because old materials do not need to be transported to fixed sites, the demand for new materials is greatly reduced, effectively lowering energy consumption and carbon dioxide emissions.

[0004] However, despite the significant advantages of in-situ thermal recycling technology, the level of process control in its core component—the heating process—directly determines the final recycling quality and engineering benefits. Existing in-situ thermal recycling units typically employ multiple heating plates or radiant heaters, using liquefied petroleum gas or diesel fuel to heat the road surface through high-temperature flames or infrared radiation generated by combustion. This process is a complex transient heat transfer process involving convection, conduction, and radiation, and is influenced by various factors such as environmental conditions, road surface conditions, and equipment parameters.

[0005] In practical engineering applications, the heating process faces severe challenges. First, ensuring heating uniformity is difficult. Due to the uneven heat distribution of the heating equipment itself, the spatial variability of the thermal properties of road materials, and random disturbances in the environmental wind field, temperature gradients easily appear in the lateral and depth directions of the road surface. Locally low temperatures make it difficult to loosen the old asphalt mixture, resulting in uneven mixing of the recycling agent and old asphalt, weakening interlayer adhesion and creating quality hazards. Conversely, locally high temperatures accelerate asphalt aging, making it hard and brittle, reducing road performance, and even producing harmful substances such as asphalt fumes. Second, temperature control precision is insufficient. Currently, temperature control during construction relies heavily on the operator's experience, making rough judgments by observing the road surface color or using handheld thermometers, lacking real-time, precise monitoring and feedback control of the temperature field across the entire heated surface. This extensive control mode is ill-suited to complex and variable working conditions and cannot achieve precise temperature regulation. Furthermore, energy utilization efficiency is generally low. To ensure that even the coldest areas reach the minimum temperature required for construction, operators often tend to use higher heating power or slower travel speeds. This inevitably leads to overheating in other areas, resulting in a large amount of energy waste, increased construction costs, and contradicts the original intention of green and low-carbon development.

[0006] To address these issues, researchers and engineers in the industry have conducted a series of studies. Early research relied heavily on field experiments and physical engineering tests, evaluating heating effects through methods such as embedding thermocouples for temperature measurement and subsequent core sampling for performance testing. While direct, this method was costly, time-consuming, and limited in the number of test points, making it difficult to comprehensively capture the spatiotemporal distribution of the entire temperature field and impossible to predict and optimize before construction. With advancements in computer technology and numerical calculation methods, numerical simulation techniques such as the finite element method and finite volume method have been introduced into the study of asphalt pavement construction processes. Some researchers attempted to establish heat transfer models for the asphalt pavement heating process to simulate the temperature field distribution. However, early models often involved excessive simplification, such as treating the heat source as a constant and uniform heat flux density, neglecting the detailed processes of combustion, fluid flow, and heat transfer within the burner, and failing to fully consider the dynamic influence of ambient wind speed and direction on the convective heat transfer boundary, leading to significant deviations between simulation results and actual conditions.

[0007] In recent years, multi-field coupling simulation technology has provided a powerful tool for solving such complex engineering problems. Software such as COMSOL Multiphysics can establish and solve models of multiple coupled physical fields on a unified platform. The heating process of in-situ thermal recycling pavement is essentially a typical multi-physics coupling problem involving fluid dynamics and heat transfer, with each physical field closely related and influencing the others. However, existing multi-physics simulation studies on the in-situ thermal recycling heating process still have some shortcomings: First, the treatment of heat sources, flow fields, and material thermal properties is generally oversimplified, making it difficult to truly reflect the heat transfer laws during the heating process; second, simulation analysis often remains at the level of qualitative comparison of temperature fields, without establishing a clear correspondence between simulation results and controllable process parameters such as heating power, travel speed, and heating height; third, a standardized simulation and optimization process that can be used for engineering design and on-site construction has not yet been formed, making it difficult to provide a systematic and quantitative basis for the selection of heating process parameters.

[0008] Therefore, this invention proposes an optimization method for in-situ thermal recycling of asphalt pavement based on multi-field coupled simulation. By systematically applying multi-field coupled simulation technology to the heating process of in-situ thermal recycling of asphalt pavement, and constructing a coupled model that accurately reflects the characteristics of the heat source, environmental influences, and material behavior, parametric analysis and optimization are performed on process parameters such as different heating power, travel speed, heating height, and heating cycles. This allows for the pre-determination of a heating process scheme in a virtual environment that meets construction temperature requirements, has uniform temperature distribution, and low energy consumption. This provides a quantitative design basis for on-site equipment control, improves the construction quality and resource utilization efficiency of in-situ thermal recycling, and has significant theoretical and engineering application value. Summary of the Invention

[0009] (1) Technical issues

[0010] The purpose of this invention is to provide an optimization method for in-situ thermal recycling of asphalt pavement based on multi-field coupled simulation. By constructing a multi-physics field coupled model that includes solid heat transfer, fluid heat transfer, and thermal radiation, the method performs parameterized scanning and comprehensive evaluation of heating power, travel speed, heating height, and heating times. This solves the problems of existing in-situ thermal recycling heating processes that rely solely on experience to adjust process parameters, making it difficult to accurately measure the temperature field distribution across the entire thickness of the asphalt pavement. These problems include uneven heating leading to localized overheating and severe asphalt aging, low energy utilization, and a lack of optimal heating parameters that can directly guide on-site construction. The method achieves quantitative analysis and multi-objective optimization control of the process parameters for in-situ thermal recycling of asphalt pavement.

[0011] (2) Technical solution

[0012] To address the aforementioned technical problems, this invention proposes an optimized heating method for in-situ thermal recycling of asphalt pavement based on multi-field coupled simulation. The technical solution is as follows: First, a three-dimensional geometric model including an infrared heating plate, a heating cavity, an air domain, and a three-layer asphalt pavement is established in multi-physics simulation software, and the material properties and boundary conditions of each structural layer of the pavement and the air domain are set. Then, solid heat transfer, fluid heat transfer, and surface-to-surface radiation physical fields are simultaneously enabled in the model, and the dynamic heating process of the infrared heating plate moving along the direction of travel is simulated by moving the heat source or moving the mesh to obtain the transient temperature field of the entire thickness of the pavement. Next, parametric simulation calculations were performed on multiple working conditions using heating power, equipment moving speed, heating height, and heating times as parameters. The road surface temperature field distribution under different parameter combinations was obtained, and the average temperature at a specified road depth, the highest surface temperature, temperature uniformity, and energy consumption per unit area were calculated. Finally, based on the suitable temperature range, temperature uniformity, and energy-saving requirements of in-situ thermal recycling construction, the evaluation indicators of each working condition were comprehensively analyzed and ranked. The optimal combination of process parameters that meets the heating requirements of each structural layer of the road surface, provides uniform heating, low energy consumption, and low risk of asphalt aging was selected to guide on-site heating construction.

[0013] (3) Beneficial effects

[0014] Due to the rapid development of highway transportation, the demand for asphalt pavement maintenance is increasing. Although in-situ thermal recycling technology can realize the recycling of waste pavement materials, its core heating process has always lacked scientific and effective control methods. Existing experience-based operations not only lead to energy waste and environmental pollution, but also seriously affect the long-term performance of recycled pavements. If heating is not done properly, the pavement will quickly develop cracks, loosening, and other defects, shortening its service life and causing greater economic losses. The present invention provides an in-situ thermal recycling heating optimization method for asphalt pavements based on multi-field coupled simulation. By establishing a multi-field coupled model that includes solid heat transfer, fluid heat transfer, and surface-to-surface radiation, and introducing a moving heat source and parameterized scanning, controllable process parameters such as heating power, moving speed, heating height, and heating times are directly correlated with evaluation indicators such as pavement temperature field distribution, temperature uniformity, and energy consumption, achieving multi-objective comprehensive optimization in a virtual environment. Compared with existing methods that rely solely on experience or a single heat transfer model to determine heating parameters, this invention can pre-determine the optimal heating scheme that meets construction temperature requirements, provides uniform heating, consumes less energy, and minimizes the risk of asphalt aging. Furthermore, the optimized parameters can be directly applied to on-site heating equipment to achieve precise control of the heating process. This has significant practical and economic value for ensuring uniform heating of recycled pavement, preventing asphalt aging, improving the quality of recycled layers, extending pavement service life, saving energy, and reducing harmful gas emissions. Detailed Implementation

[0015] This invention provides an optimized heating method for in-situ thermal recycling of asphalt pavement based on multi-field coupled simulation. The specific implementation steps are as follows:

[0016] (1) In COMSOL In Multiphysics simulation software, a three-dimensional geometric model of the asphalt pavement in-situ thermal recycling heating system was established, including an infrared heating plate, a heating cavity and its guide hood, an air domain above and around the heating plate, and the upper, middle, and lower layers of the asphalt pavement. The heating plate is 2.0m long and 2.0m wide, the heating cavity is 2.0m long, 2.0m wide, and 0.30m high, and the asphalt pavement model is 3.0m long, 2.0m wide, and has a total thickness of 0.18m. The thicknesses of the upper, middle, and lower layers are 0.04m, 0.06m, and 0.08m, respectively. The model's operating parameters were set in conjunction with typical in-situ thermal recycling construction technology. The air inlet velocity was set to 2.0m / s, the inlet air temperature to 25℃, and the equivalent surface temperature of the heating plate to 450℃. This ensured that the simulation model matched the actual heating equipment and pavement structure in terms of geometric scale and operating conditions, thus simulating the actual heating influence range and realistically reflecting the heating process.

[0017] (2) Assign material properties and initial conditions to each component in the geometric model. Set the thermal conductivity, density and specific heat capacity functions that vary with temperature for the asphalt surface layer, intermediate layer and bottom layer respectively. Set the thermal conductivity and surface emissivity for the heating plate and cavity structure. Set the density, viscosity, specific heat capacity and thermal conductivity for the air domain. Set the initial temperature of the road surface and the ambient temperature to 25℃. Use the adiabatic condition for the bottom boundary of the road surface. Use the convective heat transfer boundary for the outer surface of the air domain. Set the upper boundary of the air domain at 1.0m from the road surface to reduce the influence of the outer boundary on the temperature field distribution of the calculation area.

[0018] (3) Establish a multi-physics field coupled heat transfer model for in-situ thermal regeneration of asphalt pavement. In the model, the solid heat transfer physical field is enabled in the pavement structure to simulate the heat conduction inside each structural layer. The fluid heat transfer physical field is enabled between the heating plate and the pavement and in the air domain around the heating cavity. The fluid flow module is used to simulate the movement of hot air flow and convective heat transfer generated by combustion. The surface-to-surface radiation physical field is enabled between the heating plate and the pavement. The surface emissivity, equivalent heating power and surface temperature of the heating plate are set to simulate thermal radiation. The solid heat transfer, fluid heat transfer and surface-to-surface radiation physical fields are coupled through the multi-physics field coupling node to form a multi-field coupled model of the heating process of in-situ thermal regeneration of asphalt pavement.

[0019] (4) After completing the geometric modeling and multiphysics field setting, the above multi-field coupling model is meshed. The mesh is refined in the road surface, interlayer interface, near the heating plate and air inlet area. In other areas, a relatively large unit size is used to improve the calculation accuracy and take into account the calculation efficiency. The transient solver and time step 1fs are set. The heating plate is regarded as a heat source moving along the direction of travel of the on-site thermal recycling construction unit at a set moving speed. The change of the asphalt pavement temperature field with time during the heating process is calculated.

[0020] (5) By using parametric scanning, heating power, moving speed, heating height and heating times are selected as working condition parameters. Multiple working conditions are set within the given parameter range and simulation calculations are performed separately. The influence of different working condition parameter combinations on the road surface temperature field distribution is analyzed. The average temperature, maximum surface temperature, temperature uniformity index and energy consumption per unit area within the specified road surface depth range are calculated. Based on the requirements of temperature range and temperature distribution uniformity for in-situ thermal recycling of asphalt pavement, the calculation results of each working condition are comprehensively compared and analyzed to determine the optimal heating process parameter combination. This satisfies the heating temperature requirements of in-situ thermal recycling of asphalt pavement, improves the temperature field distribution uniformity, reduces energy consumption, and reduces the degree of asphalt aging, thus optimizing the heating process of in-situ thermal recycling of asphalt pavement.

Claims

1. A heating optimization method for in-situ thermal recycling of asphalt pavement based on multi-field coupled simulation, characterized in that... The specific steps of this method are as follows: (1) In COMSOL In Multiphysics simulation software, a three-dimensional geometric model of the asphalt pavement in-situ thermal recycling heating system was established, including an infrared heating plate, a heating cavity and its guide hood, an air domain above and around the heating plate, and the upper, middle, and lower layers of the asphalt pavement. The heating plate is 2.0m long and 2.0m wide, the heating cavity is 2.0m long, 2.0m wide, and 0.30m high, and the asphalt pavement model is 3.0m long, 2.0m wide, and has a total thickness of 0.18m. The thicknesses of the upper, middle, and lower layers are 0.04m, 0.06m, and 0.08m, respectively. The model's operating parameters were set in conjunction with typical in-situ thermal recycling construction technology. The air inlet velocity was set to 2.0m / s, the inlet air temperature to 25℃, and the equivalent surface temperature of the heating plate to 450℃. This ensured that the simulation model matched the actual heating equipment and pavement structure in terms of geometric scale and operating conditions, thus simulating the actual heating influence range and realistically reflecting the heating process. (2) Assign material properties and initial conditions to each component in the geometric model. Set the thermal conductivity, density and specific heat capacity functions that vary with temperature for the asphalt surface layer, intermediate layer and bottom layer respectively. Set the thermal conductivity and surface emissivity for the heating plate and cavity structure. Set the density, viscosity, specific heat capacity and thermal conductivity for the air domain. Set the initial temperature of the road surface and the ambient temperature to 25℃. Use the adiabatic condition for the bottom boundary of the road surface. Use the convective heat transfer boundary for the outer surface of the air domain. Set the upper boundary of the air domain at 1.0m from the road surface to reduce the influence of the outer boundary on the temperature field distribution of the calculation area. (3) Establish a multi-physics field coupled heat transfer model for in-situ thermal regeneration of asphalt pavement. In the model, the solid heat transfer physical field is enabled in the pavement structure to simulate the heat conduction inside each structural layer. The fluid heat transfer physical field is enabled between the heating plate and the pavement and in the air domain around the heating cavity. The fluid flow module is used to simulate the movement of hot air flow and convective heat transfer generated by combustion. The surface-to-surface radiation physical field is enabled between the heating plate and the pavement. The surface emissivity, equivalent heating power and surface temperature of the heating plate are set to simulate thermal radiation. The solid heat transfer, fluid heat transfer and surface-to-surface radiation physical fields are coupled through the multi-physics field coupling node to form a multi-field coupled model of the heating process of in-situ thermal regeneration of asphalt pavement. (4) After completing the geometric modeling and multiphysics field setting, the above multi-field coupling model is meshed. The mesh is refined in the road surface, interlayer interface, near the heating plate and air inlet area. In other areas, a relatively large unit size is used to improve the calculation accuracy and take into account the calculation efficiency. The transient solver and time step 1fs are set. The heating plate is regarded as a heat source moving along the direction of travel of the on-site thermal recycling construction unit at a set moving speed. The change of the asphalt pavement temperature field with time during the heating process is calculated. (5) By using parametric scanning, heating power, moving speed, heating height and heating times are selected as working condition parameters. Multiple working conditions are set within the given parameter range and simulation calculations are performed separately. The influence of different working condition parameter combinations on the road surface temperature field distribution is analyzed. The average temperature, maximum surface temperature, temperature uniformity index and energy consumption per unit area within the specified road surface depth range are calculated. Based on the requirements of temperature range and temperature distribution uniformity for in-situ thermal recycling of asphalt pavement, the calculation results of each working condition are comprehensively compared and analyzed to determine the optimal heating process parameter combination. This satisfies the heating temperature requirements of in-situ thermal recycling of asphalt pavement, improves the temperature field distribution uniformity, reduces energy consumption, and reduces the degree of asphalt aging, thus optimizing the heating process of in-situ thermal recycling of asphalt pavement.