A phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavement

Abstract

A phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavements. The present invention relates to the field of asphalt pavement snow and ice removal performance evaluation and phase change material research and development technology, and specifically to a phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavements. The present invention is to solve the problem that the current evaluation is too time-consuming, has high randomness, is greatly affected by human interference, is not accurate, and cannot quickly and effectively determine whether the tested phase change material can be used for snow and ice removal on asphalt pavements. Methods: 1. Determine the thermal conductivity; 2. Determine the thermal diffusion coefficient; 3. Determine the specific heat capacity; 4. Determine the enthalpy decay rate; 5. Establish a comprehensive evaluation system for phase change asphalt mixture to melt snow and ice, and then evaluate the feasibility of the phase change asphalt mixture for snow and ice removal. The present invention is used to determine the feasibility of snow and ice removal on asphalt pavements.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt pavement deicing performance evaluation and phase change material research and development, and in particular to a phase change material evaluation method for determining the feasibility of deicing and snow removal on asphalt pavement. Background Art

[0002] In winter and spring, snow and ice will accumulate on the road, seriously affecting traffic safety and traffic efficiency. How to remove ice and snow from the road in a timely and efficient manner has become a problem that plagues the transportation department.

[0003] Among the current methods of snow and ice removal, manual and mechanical snow and ice removal is time-consuming and labor-intensive, and is prone to damage to the road surface; spreading snow-melting agents will pollute the environment and reduce the life of the road surface; thermal snow-melting road surface construction is complex and costly; elastic road surface compaction is difficult and has poor durability; salt-based snow and ice removal has poor durability. Adding phase change materials as an admixture to asphalt pavement can achieve snow and ice melting through active temperature-adjusting pavement without increasing the difficulty of road construction, and has good development prospects. Phase change materials refer to functional materials that can undergo phase changes within a certain temperature range, absorbing or releasing heat through phase changes to maintain their own temperature within a certain range.

[0004] The use of phase change materials for snow and ice removal on asphalt pavements is still in the research stage, and an accurate and efficient evaluation method is urgently needed to determine the feasibility of using various phase change materials for snow and ice melting on asphalt pavements. The current evaluation method mostly uses the method of placing ice and snow on the asphalt mixture to observe the efficiency of snow and ice melting, which is too time-consuming and has a large randomness, and does not consider the durability of phase change materials. The process of snow and ice melting is subject to environmental and snow and ice conditions (temperature, adhesion, etc. are difficult to guarantee), human interference has a great impact, the accuracy is not high, it is difficult to unify standards, and it is impossible to quickly and effectively determine whether the tested phase change material can be used for snow and ice removal on asphalt pavements. Summary of the invention

[0005] The present invention aims to solve the problems that the current evaluation is too time-consuming, has high randomness, is greatly affected by human interference, is not accurate, and cannot quickly and effectively determine whether the tested phase change material can be used for deicing and snow on asphalt pavements. A phase change material evaluation method for determining the feasibility of deicing and snow on asphalt pavements is now provided.

[0006] The present invention provides a phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavement, comprising the following steps:

[0007] Step 1: measuring the thermal conductivity of a phase change asphalt mixture specimen to obtain the thermal conductivity of the phase change asphalt mixture;

[0008] Step 2: Based on the non-steady-state heat conduction principle of a semi-infinite object, the thermal diffusion coefficient of the phase change asphalt mixture specimen is measured to obtain the thermal diffusion coefficient of the phase change asphalt mixture;

[0009] Step 3: measuring the specific heat capacity of the phase change asphalt mixture specimen to obtain the specific heat capacity of the phase change asphalt mixture;

[0010] Step 4: Determine the enthalpy decay rate of the phase change asphalt mixture specimen to obtain the enthalpy decay rate of the phase change asphalt mixture;

[0011] Step 5: Use the entropy weight method to weight the thermal conductivity, thermal diffusion coefficient, specific heat capacity, and enthalpy decay rate respectively, establish a comprehensive evaluation system for phase change asphalt mixture to melt ice and snow, and then evaluate the feasibility of the phase change asphalt mixture for removing ice and snow.

[0012] Beneficial effects:

[0013] The present invention takes thermal conductivity, thermal diffusion coefficient, specific heat capacity and enthalpy decay rate as evaluation indicators from the perspective of thermodynamics, and evaluates the ice and snow melting performance of asphalt mixture based on the nature of phase change materials. It is accurate, efficient, and has unified standards, and has good applicability. The method of the present invention involves various thermal parameters such as heat absorption, heat release, energy storage, and durability related to the phase change material and ice and snow melting performance. The evaluation indicators are comprehensive, accurate, and scientific, avoiding the one-sidedness, volatility, and subjectivity of the evaluation results. The determination of the thermal diffusion coefficient for ice and snow removal is guaranteed through reasonable design of the evaluation indicators, and a method for obtaining the specific heat capacity of the phase change asphalt mixture is proposed. This method does not require prefabricated ice cubes and snow accumulation, gets rid of environmental restrictions, and shortens the experimental time. This method can theoretically and quantitatively calculate the thermal parameters of different phase change material addition amounts, greatly improving the evaluation efficiency, and also provides guidance for determining the phase change material addition amount under different environments, which is helpful to promote the research and development and application of phase change materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of heat insulation treatment of the outer surface and bottom of the phase change asphalt mixture specimen before measuring the thermal diffusion coefficient of the specimen;

[0015] Figure 2 for Figure 1 A top view of

[0016] Figure 3 : is a comparison curve of ice melting amount of asphalt mixture; wherein 1 represents 0.1% phase change doped asphalt mixture in Example 1, 2 represents 0.2% phase change doped asphalt mixture in Example 1, 3 represents 0.3% phase change doped asphalt mixture in Example 1, 4 represents 0.4% phase change doped asphalt mixture in Example 1, 5 represents 0.5% phase change doped asphalt mixture in Example 1, and 6 represents ordinary asphalt mixture in the comparative example;

[0017] Figure 4: is a thermal conductivity comparison curve of asphalt mixture; wherein 1 represents 0.1% phase change doped asphalt mixture in Example 1, 2 represents 0.2% phase change doped asphalt mixture in Example 1, 3 represents 0.3% phase change doped asphalt mixture in Example 1, 4 represents 0.4% phase change doped asphalt mixture in Example 1, 5 represents 0.5% phase change doped asphalt mixture in Example 1, and 6 represents ordinary asphalt mixture in the comparative example;

[0018] Figure 5 : is a comparison curve of thermal diffusion coefficient of asphalt mixture; wherein 1 represents 0.1% phase change doped asphalt mixture in Example 1, 2 represents 0.2% phase change doped asphalt mixture in Example 1, 3 represents 0.3% phase change doped asphalt mixture in Example 1, 4 represents 0.4% phase change doped asphalt mixture in Example 1, 5 represents 0.5% phase change doped asphalt mixture in Example 1, and 6 represents ordinary asphalt mixture in the comparative example;

[0019] Figure 6 The specific heat capacity comparison curve of asphalt mixture is shown in which 1 represents 0.1% phase change doped asphalt mixture in Example 1, 2 represents 0.2% phase change doped asphalt mixture in Example 1, 3 represents 0.3% phase change doped asphalt mixture in Example 1, 4 represents 0.4% phase change doped asphalt mixture in Example 1, 5 represents 0.5% phase change doped asphalt mixture in Example 1, and 6 represents ordinary asphalt mixture in the comparative example. DETAILED DESCRIPTION

[0020] Specific implementation method 1: A phase change material evaluation method for determining the feasibility of asphalt pavement snow and ice removal described in this implementation method includes the following steps:

[0021] Step 1: measuring the thermal conductivity of a phase change asphalt mixture specimen to obtain the thermal conductivity of the phase change asphalt mixture;

[0022] Step 2: Based on the non-steady-state heat conduction principle of a semi-infinite object, the thermal diffusion coefficient of the phase change asphalt mixture specimen is measured to obtain the thermal diffusion coefficient of the phase change asphalt mixture;

[0023] Step 3: measuring the specific heat capacity of the phase change asphalt mixture specimen to obtain the specific heat capacity of the phase change asphalt mixture;

[0024] Step 4: Determine the enthalpy decay rate of the phase change asphalt mixture specimen to obtain the enthalpy decay rate of the phase change asphalt mixture;

[0025] Step 5: Use the entropy weight method to weight the thermal conductivity, thermal diffusion coefficient, specific heat capacity, and enthalpy decay rate respectively, establish a comprehensive evaluation system for phase change asphalt mixture to melt ice and snow, and then evaluate the feasibility of the phase change asphalt mixture for removing ice and snow.

[0026] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that: the phase change asphalt mixture specimen in step 1 is a rotary compacted cylindrical specimen cut into test specimens with a diameter of 150 mm and a thickness of 10 mm; the temperature for measuring the thermal conductivity coefficient is above 0°C; the test instrument is a Hot Disk thermal constant analyzer. Others are the same as specific implementation method 1.

[0027] This embodiment measures thermal conductivity based on the principle of transient flat plate heat source method. Phase change material is added during the mixing process of asphalt mixture and formed by rotary compaction method. The formed cylindrical specimen is cut into test specimens with a diameter of 150 mm and a thickness of 10 mm to ensure that the phase change material is the only variable. Considering the heat absorption capacity when the ice and snow are not melted, the heating starting temperature is 0°C. The cut specimen is heated using the Hot Disk thermal constant analyzer probe and the thermal conductivity at different temperatures is measured to evaluate the heat absorption capacity of the phase change asphalt mixture.

[0028] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that: the thermal diffusion coefficient of the phase change asphalt mixture specimen is determined in step two by placing the phase change asphalt mixture specimen in a low temperature constant temperature test box, and the linear relationship between temperature and time is T=b1t+b2, and the quadratic relationship between temperature and depth is T=a1z 2 +a2z+a3, the thermal diffusion coefficient is shown as follows:

[0029]

[0030] Wherein, a is the thermal diffusion coefficient of the phase change asphalt mixture, T is the phase change asphalt mixture temperature, t is the time difference, b1 and b2 are the fitting constants of the linear relationship between temperature and time, and a1, a2, and a3 are the fitting constants of the quadratic relationship between temperature and depth. The rest is the same as the first or second embodiment.

[0031] This embodiment takes into account that ice and snow are located on the upper part of the asphalt pavement, and in order to improve calculation efficiency, only the thermal diffusion coefficient of the phase change asphalt mixture along the height direction is measured.

[0032] Specific implementation method 4: This implementation method is different from specific implementation methods 1 to 3 in that: before measuring the thermal diffusion coefficient of the phase change asphalt mixture specimen, the outer surface and bottom of the specimen are first insulated: the outer surface and bottom of the specimen are wrapped with rubber-plastic insulation cotton and tin foil, and the total thickness of the rubber-plastic insulation cotton is not less than 20 mm. Others are the same as specific implementation methods 1 to 3.

[0033] This implementation method stipulates that the total thickness of the plastic insulation cotton should be no less than 20 mm to ensure that only the upper surface of the asphalt mixture specimen is left to exchange heat with the outside world.

[0034] Specific implementation method 5: This implementation method is different from specific implementation methods 1 to 4 in that the phase change asphalt mixture specimen is placed in a low temperature constant temperature test box to ensure that the temperature sensor is placed at 2 cm, 7 cm, and 14 cm of the phase change asphalt mixture specimen, and to ensure that the drilling holes at each depth are parallel, the drilling depth is 5 cm, and the hole diameter is 5 mm. Other aspects are the same as specific implementation methods 1 to 4.

[0035] This implementation method can characterize the temperature in each asphalt surface layer and monitor the temperature change of the phase change asphalt mixture during the cooling process; the temperature sensors should be buried consistently to ensure that the drilling holes at different depths are parallel.

[0036] Specific implementation method 6: This implementation method is different from specific implementation methods 1 to 5 in that: the specific heat capacity of the phase change asphalt mixture specimen is determined in step 3 by measuring the specific heat capacity of each single component material to calculate the specific heat capacity of the phase change asphalt mixture; the single component materials are aggregate, mineral powder, phase change material and asphalt; the amount of each single component material is controlled within 10 mg during measurement to ensure that it is evenly dispersed in the crucible. Others are the same as specific implementation methods 1 to 5.

[0037] In this embodiment, the aggregate is selected from fine materials with a diameter of less than 0.3 mm, and the amount is controlled within 10 mg using an electronic balance so that it is evenly dispersed in the crucible; the amount of mineral powder is controlled within 10 mg so that it is evenly dispersed in the crucible; a trace amount of asphalt in a molten state is dipped with a glass rod, and after it is cooled, it is scraped off with a knife and placed in a crucible, the amount of asphalt is controlled within 10 mg, and the crucible containing the asphalt is heated until the asphalt is in a molten state again, so that it is evenly dispersed in the crucible and cooled.

[0038] The amount of phase change material is controlled within 10 mg so that it is evenly dispersed in the crucible; the specific heat capacity of the multi-material composition substance is additive.

[0039] Specific embodiment 7: This embodiment differs from the specific embodiments 1 to 6 in that: the measurement method adopts the sapphire method and uses a differential scanning calorimeter for measurement; the specific heat capacity can be obtained by the following formula:

[0040]

[0041] In the formula, C P is the specific heat capacity of phase change asphalt mixture, m i is the mass of a single component material, C Pi is the specific heat capacity of the corresponding material, and M is the total mass of the phase change asphalt mixture. The rest is the same as that of the first to sixth embodiments.

[0042] In this embodiment, considering that the amount of phase change material added is smaller than the mass of asphalt mixture, simply analyzing the specific heat capacity of phase change material is not very meaningful, so the specific heat capacity of phase change asphalt mixture is measured. Based on the sapphire method, the specific heat capacity is measured using a differential scanning calorimeter (DSC).

[0043] Since the size of phase-change asphalt mixture is large, and the mixture has many single components and poor uniformity, and the crucible and sample required for DSC thermal difference measurement are small, the specific heat capacity of the mixture cannot be directly measured. Therefore, the specific heat capacity of the phase-change asphalt mixture is calculated by measuring the specific heat capacity of each single component material (aggregate, mineral powder, phase-change material and asphalt) of the mixture and using the specific heat capacity superposition formula.

[0044] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that: in step four, the cycle method for determining the enthalpy decay rate of the phase change asphalt mixture specimen is to heat the phase change material from -20°C to 50°C at a heating rate of 10°C / min and perform a heating and cooling cycle; the formula for the enthalpy decay rate is as follows:

[0045]

[0046] Where μ is the enthalpy decay rate of the phase change material, C n is the enthalpy value of the phase change material after the temperature is increased and decreased by n times, and C0 is the initial enthalpy value of the phase change material. The rest is the same as that of the first to seventh embodiments.

[0047] The enthalpy decay rate of this embodiment reflects the reusability of the phase change material and is an indicator proposed to ensure the long-term ice and snow melting effect. The enthalpy value of the phase change material is determined by the method of step three. Considering that the service area of ​​the phase change asphalt mixture is mainly located in North China, combined with the asphalt pavement temperature in North China, the phase change material is heated from -20°C to 50°C at a heating rate of 10°C / min and a heating and cooling cycle is performed to calculate the proportion of the melting enthalpy decay.

[0048] Specific implementation method 9: This implementation method is different from specific implementation methods 1 to 8 in that: in step 5, the thermal conductivity, thermal diffusion coefficient, specific heat capacity, and enthalpy decay rate are weighted by the entropy weight method, and a comprehensive evaluation system for phase change asphalt mixture melting ice and snow is established. The specific steps are as follows:

[0049] The entropy weight method is used to determine the indicator weights, and the entropy of each indicator is:

[0050]

[0051] Where P ij represents the proportion of the i-th evaluation object under the j-th indicator. When P ij= 0, let P ij ln ij =0;

[0052] Entropy weight of each indicator ω j It is obtained by the following formula:

[0053]

[0054] The ice and snow melting score of phase change asphalt mixture is calculated by the following formula:

[0055]

[0056]

[0057]

[0058] In the formula, S represents the ice and snow melting score of the phase change asphalt mixture. S greater than or equal to 1 means that the ice and snow melting conditions are met, and S less than 1 does not meet the conditions. j Indicates the score of this indicator, η j represents the score reduction factor, The rest is the same as that of the first to eighth embodiments.

[0059] Specific implementation method 10: This implementation method is different from specific implementation methods 1 to 9 in that: considering the durability of asphalt pavement de-icing and snow removal, the score reduction coefficient is divided into six climate zones according to the climate zoning of the asphalt pavement performance and whether the temperature difference is greater than 10°C, and then the value is determined according to the six climate zones;

[0060] The first climate zone: minimum temperature <-21.5℃, temperature difference >10℃; the reduction coefficients of the scores of each index in this climate zone are: the reduction coefficient of thermal conductivity is 0.6, the reduction coefficient of thermal diffusion coefficient is 0.6, the reduction coefficient of specific heat capacity is 0.6, and the reduction coefficient of enthalpy decay rate is 0.7;

[0061] The second climate zone: the lowest temperature is -21.5~-9.0℃, and the temperature difference is >10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.7, the reduction coefficient of thermal diffusion coefficient is 0.8, the reduction coefficient of specific heat capacity is 0.7, and the reduction coefficient of enthalpy decay rate is 0.8;

[0062] The third climate zone: minimum temperature>-9.0℃, temperature difference>10℃; the reduction coefficients of the scores of each indicator in this climate zone are: the reduction coefficient of thermal conductivity is 1.1, the reduction coefficient of thermal diffusion coefficient is 1.2, the reduction coefficient of specific heat capacity is 1.1, and the reduction coefficient of enthalpy decay rate is 1;

[0063] The fourth climate zone: the minimum temperature is less than -21.5℃, the temperature difference is less than 10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.6, the reduction coefficient of thermal diffusion coefficient is 0.6, the reduction coefficient of specific heat capacity is 0.6, and the reduction coefficient of enthalpy decay rate is 0.8;

[0064] The fifth climate zone: the lowest temperature is -21.5~-9.0℃, and the temperature difference is less than 10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.8, the reduction coefficient of thermal diffusion coefficient is 0.8, the reduction coefficient of specific heat capacity is 0.8, and the reduction coefficient of enthalpy decay rate is 1;

[0065] The sixth climate zone: minimum temperature>-9.0℃, temperature difference<10℃; the reduction coefficients of the scores of the indicators in this climate zone are: the reduction coefficient of thermal conductivity is 1, the reduction coefficient of thermal diffusion coefficient is 1, the reduction coefficient of specific heat capacity is 1, and the reduction coefficient of enthalpy decay rate is 1. The rest is the same as the specific implementation methods one to nine.

[0066] The beneficial effects of the present invention are verified by the following examples:

[0067] Example 1: A phase change material evaluation method for determining the feasibility of deicing and snow removal on asphalt pavement comprises the following steps:

[0068] Phase change asphalt mixture adopts AC-16 median gradation, and the phase change material is solid-solid phase change material sold by a company in Beijing. The phase change addition amount is 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% of the mass of the asphalt mixture. The phase change asphalt mixture is formed by rotary compaction method, and two types of diameters of 10cm and 15cm are formed respectively;

[0069] Step 1: Measure the thermal conductivity of the phase change asphalt mixture specimen to obtain the thermal conductivity of the phase change asphalt mixture: Add different masses of phase change materials during the mixing process of the asphalt mixture and form it by rotary compaction. Cut the formed cylindrical specimen into test specimens with a diameter of 150 mm and a thickness of 10 mm. There are 5 parallel test specimens of the same type to ensure that the phase change material is the only variable;

[0070] The cut samples were heated using the Hot Disk thermal constant analyzer probe and the thermal conductivity coefficients were measured at 0°C, 5°C, 10°C, 15°C, and 20°C. Figure 4: is a thermal conductivity comparison curve of asphalt mixture; wherein 1 represents 0.1% phase change doped asphalt mixture in Example 1, 2 represents 0.2% phase change doped asphalt mixture in Example 1, 3 represents 0.3% phase change doped asphalt mixture in Example 1, 4 represents 0.4% phase change doped asphalt mixture in Example 1, 5 represents 0.5% phase change doped asphalt mixture in Example 1, and 6 represents ordinary asphalt mixture in the comparative example;

[0071] Step 2: Based on the non-steady-state heat conduction principle of a semi-infinite object, the thermal diffusion coefficient of the phase change asphalt mixture specimen is measured to obtain the thermal diffusion coefficient of the phase change asphalt mixture:

[0072] The temperature sensors were placed at 2cm, 7cm, and 14cm of the asphalt mixture specimens. The temperature sensors of different specimens were buried in the same way. The holes were drilled in parallel at different depths, with a depth of 5cm and a hole diameter of 5mm to monitor the temperature changes of the phase change asphalt mixture during the cooling process.

[0073] The outer surface and bottom of the specimen are insulated, and the outer surface and bottom of the specimen are wrapped with rubber-plastic insulation cotton and tin foil. The thickness of the rubber-plastic insulation cotton is more than 2 cm to ensure that only the upper surface of the mixture specimen is left to exchange heat with the outside world;

[0074] The mixture specimen was placed in a low-temperature constant temperature test box at -20℃. The initial temperature of the specimen was 25℃. The observation began after 2 hours of placement. The total placement time was 10 hours. The analysis step was 60 minutes. The linear relationship between temperature and time was T=b1t+b2, and the quadratic relationship between temperature and depth was T=a1z. 2 +a2z+a3, the thermal diffusion coefficient is shown as follows:

[0075]

[0076] Where a is the thermal diffusion coefficient of phase change asphalt mixture, T is the phase change asphalt mixture temperature, t is the time difference, b1 and b2 are the fitting constants of the linear relationship between temperature and time, and a1, a2, and a3 are the fitting constants of the quadratic relationship between temperature and depth; finally, the thermal diffusion coefficients of each phase change asphalt are obtained as follows: Figure 5 As shown; Figure 5 : is a comparison curve of thermal diffusion coefficient of asphalt mixture; wherein 1 represents 0.1% phase change doped asphalt mixture in Example 1, 2 represents 0.2% phase change doped asphalt mixture in Example 1, 3 represents 0.3% phase change doped asphalt mixture in Example 1, 4 represents 0.4% phase change doped asphalt mixture in Example 1, 5 represents 0.5% phase change doped asphalt mixture in Example 1, and 6 represents ordinary asphalt mixture in the comparative example;

[0077] Step 3: Determine the specific heat capacity of the phase change asphalt mixture specimen to obtain the specific heat capacity of the phase change asphalt mixture:

[0078] Based on the sapphire method, a differential scanning calorimeter (DSC) is used to measure the specific heat capacity of each single component material (aggregate, mineral powder, phase change material and asphalt) that constitutes the mixture. An electronic balance is used to weigh 10 mg of each material to be measured. Among them, the aggregate is selected as fine material below 0.3 mm. When measuring asphalt, a small amount of asphalt is heated to a molten state. A trace amount of asphalt is dipped with a glass rod. After it cools and solidifies, it is scraped with a knife to make it into a mass and placed in a crucible. The amount of asphalt is controlled within 10 mg. The crucible containing the trace amount of asphalt is then heated to disperse the asphalt in the crucible and then cooled;

[0079] Based on the principle that the specific heat capacity of multi-material substances is additive, the specific heat capacity can be obtained by the following formula:

[0080]

[0081] In the formula, C P is the specific heat capacity of phase change asphalt mixture, m i is the mass of a single component material, C Pi is the specific heat capacity of the corresponding material, M is the total mass of the phase change asphalt mixture;

[0082] Step 4: Determine the enthalpy decay rate of the phase change asphalt mixture specimen to obtain the enthalpy decay rate of the phase change asphalt mixture:

[0083] The method in step 3 was used to determine the enthalpy value of a solid-solid phase change material produced by a Beijing company. The phase change material was heated from -20°C to 50°C at a heating rate of 10°C / min and a heating and cooling cycle was performed. The enthalpy decay rate was calculated according to the following formula. The results are shown in Table 1.

[0084]

[0085] Where μ is the enthalpy decay rate of the phase change material, C n is the enthalpy value of the phase change material after n cycles of heating and cooling, and C0 is the initial enthalpy value of the phase change material;

[0086] Table 1

[0087]

[0088] Step 5: The thermal conductivity, thermal diffusion coefficient, specific heat capacity, and enthalpy decay rate are weighted by the entropy weight method to establish a comprehensive evaluation system for phase change asphalt mixture to melt ice and snow, and then the feasibility of the phase change asphalt mixture to remove ice and snow is evaluated; 5 kinds of doping phase change materials are tested, and the entropy weights of thermal conductivity, thermal diffusion coefficient, specific heat capacity, and enthalpy decay rate are obtained based on the entropy method. They are 0.2401, 0.2704, 0.2608, and 0.2287 respectively; the entropy weight method is used to determine the index weights, and the entropy of each index is:

[0089]

[0090] Where P ij represents the proportion of the i-th evaluation object under the j-th indicator. When P ij = 0, let P ij ln ij =0;

[0091] Entropy weight of each indicator ω j It is obtained by the following formula:

[0092]

[0093] The ice and snow melting score of phase change asphalt mixture is calculated by the following formula:

[0094]

[0095]

[0096]

[0097] In the formula, S represents the ice and snow melting score of the phase change asphalt mixture. S greater than or equal to 1 means that the ice and snow melting conditions are met, and S less than 1 does not meet the conditions. j Indicates the score of this indicator, η j represents the score reduction factor, Indicates the base value.

[0098] Considering the durability of asphalt pavement in removing ice and snow, the score reduction coefficient is divided into six climate zones according to the climate zoning of asphalt pavement performance and whether the temperature difference is greater than 10°C, and then the value is determined according to the six climate zones;

[0099] The first climate zone: minimum temperature <-21.5℃, temperature difference >10℃; the reduction coefficients of the scores of each index in this climate zone are: the reduction coefficient of thermal conductivity is 0.6, the reduction coefficient of thermal diffusion coefficient is 0.6, the reduction coefficient of specific heat capacity is 0.6, and the reduction coefficient of enthalpy decay rate is 0.7;

[0100] The second climate zone: the lowest temperature is -21.5~-9.0℃, and the temperature difference is >10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.7, the reduction coefficient of thermal diffusion coefficient is 0.8, the reduction coefficient of specific heat capacity is 0.7, and the reduction coefficient of enthalpy decay rate is 0.8;

[0101] The third climate zone: minimum temperature>-9.0℃, temperature difference>10℃; the reduction coefficients of the scores of each indicator in this climate zone are: the reduction coefficient of thermal conductivity is 1.1, the reduction coefficient of thermal diffusion coefficient is 1.2, the reduction coefficient of specific heat capacity is 1.1, and the reduction coefficient of enthalpy decay rate is 1;

[0102] The fourth climate zone: the minimum temperature is less than -21.5℃, the temperature difference is less than 10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.6, the reduction coefficient of thermal diffusion coefficient is 0.6, the reduction coefficient of specific heat capacity is 0.6, and the reduction coefficient of enthalpy decay rate is 0.8;

[0103] The fifth climate zone: the lowest temperature is -21.5~-9.0℃, and the temperature difference is less than 10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.8, the reduction coefficient of thermal diffusion coefficient is 0.8, the reduction coefficient of specific heat capacity is 0.8, and the reduction coefficient of enthalpy decay rate is 1;

[0104] The sixth climate zone: minimum temperature> -9.0℃, temperature difference<10℃; the reduction coefficients of the scores of each indicator in this climate zone are: the reduction coefficient of thermal conductivity is 1, the reduction coefficient of thermal diffusion coefficient is 1, the reduction coefficient of specific heat capacity is 1, and the reduction coefficient of enthalpy decay rate is 1; comparative example:

[0105] Asphalt mixture adopts AC-16 median gradation, and phase change material is solid-solid phase change material sold by a Beijing company. The phase change addition amount is 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% of the mass of asphalt mixture, respectively. Phase change asphalt mixture rutting plate specimens are formed by wheel rolling method. According to the characteristics of phase change material and the actual situation of ice melting of asphalt pavement, icicles with a diameter of 8cm and a height of 8cm are formed in a refrigerator at -20℃ for 72h. Under constant temperature environment, the rutting plates of ordinary asphalt mixture and phase change asphalt mixture are irradiated with lights with fixed heat source for 2h, and then stored in -5℃ environment. Ice columns are placed on their surface and the difference in ice melting between the two is compared within 2h. Three parallel ice columns are placed.

[0106] The indicators listed in this evaluation method include thermodynamic performance indicators, which are comprehensive and easy to measure, and are also conducive to determining the dosage of phase change materials. The detection methods proposed for each indicator are also easy to implement, getting rid of environmental restrictions and uncertainty of variables. The original evaluation method required the amount of ice and snow melting per unit area, the test preparation time was long, the road environmental conditions and road temperature were not considered, it was difficult to unify the variables, the results were too discrete, and there was only an overall evaluation, which could not make choices based on different road needs and could not guide the design of phase change materials.

[0107] This method can evaluate various indicators, and can provide guidance for the selection of phase change material types and dosages under different environmental conditions and ice and snow melting needs. It can provide guidance for the research and development of phase change materials, and is targeted, avoiding a one-size-fits-all selection.

Claims

1. A phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavement, characterized in that: The following steps are involved: Step 1: measuring the thermal conductivity of a phase change asphalt mixture specimen to obtain the thermal conductivity of the phase change asphalt mixture; Step 2: Based on the non-steady-state heat conduction principle of a semi-infinite object, the thermal diffusion coefficient of the phase change asphalt mixture specimen is measured to obtain the thermal diffusion coefficient of the phase change asphalt mixture; Step 3: Determine the specific heat capacity of the phase change asphalt mixture specimen to obtain the specific heat capacity of the phase change asphalt mixture; the specific heat capacity of the phase change asphalt mixture specimen is determined by measuring the specific heat capacity of each single component material to calculate the specific heat capacity of the phase change asphalt mixture; the single component materials are aggregate, mineral powder, phase change material and asphalt; the amount of each single component material is controlled within 10 mg during measurement to ensure that it is evenly dispersed in the crucible; the measurement method adopts the sapphire method and is measured using a differential scanning calorimeter; the specific heat capacity can be obtained by the following formula: In the formula, C P is the specific heat capacity of phase change asphalt mixture, m i is the mass of a single component material, C Pi is the specific heat capacity of the corresponding material, M is the total mass of the phase change asphalt mixture; Step 4: Determine the enthalpy decay rate of the phase change asphalt mixture specimen to obtain the enthalpy decay rate of the phase change asphalt mixture; the cycle method in the determination of the enthalpy decay rate of the phase change asphalt mixture specimen is to heat the phase change material from -20°C to 50°C at a heating rate of 10°C / min and perform a heating and cooling cycle; the formula of the enthalpy decay rate is as follows: Where μ is the enthalpy decay rate of the phase change material, C n is the enthalpy value of the phase change material after n cycles of heating and cooling, and C0 is the initial enthalpy value of the phase change material; Step 5: Use the entropy weight method to weight the thermal conductivity, thermal diffusion coefficient, specific heat capacity, and enthalpy decay rate, and establish a comprehensive evaluation system for phase change asphalt mixture to melt ice and snow, and then evaluate the feasibility of the phase change asphalt mixture to remove ice and snow; Use the entropy weight method to weight the thermal conductivity, thermal diffusion coefficient, specific heat capacity, and enthalpy decay rate, and establish a comprehensive evaluation system for phase change asphalt mixture to melt ice and snow. The specific steps are as follows: The entropy weight method is used to determine the indicator weights, and the entropy of each indicator is: Where P ij represents the proportion of the i-th evaluation object under the j-th indicator. When P ij = 0, let P ij ln ij =0; Entropy weight of each indicator ω j It is obtained by the following formula: The ice and snow melting score of phase change asphalt mixture is calculated by the following formula: In the formula, S represents the ice and snow melting score of the phase change asphalt mixture. S greater than or equal to 1 means that the ice and snow melting conditions are met, and S less than 1 does not meet the conditions. j Indicates the score of this indicator, η j represents the score reduction factor, Indicates the base value; Considering the durability of asphalt pavement in removing ice and snow, the score reduction coefficient is divided into six climate zones according to the climate zoning of asphalt pavement performance and whether the temperature difference is greater than 10°C, and then the value is determined according to the six climate zones; The first climate zone: minimum temperature <-21.5℃, temperature difference >10℃; the reduction coefficients of the scores of each index in this climate zone are: the reduction coefficient of thermal conductivity is 0.6, the reduction coefficient of thermal diffusion coefficient is 0.6, the reduction coefficient of specific heat capacity is 0.6, and the reduction coefficient of enthalpy decay rate is 0.7; The second climate zone: the lowest temperature is -21.5~-9.0℃, and the temperature difference is >10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.7, the reduction coefficient of thermal diffusion coefficient is 0.8, the reduction coefficient of specific heat capacity is 0.7, and the reduction coefficient of enthalpy decay rate is 0.8; The third climate zone: minimum temperature>-9.0℃, temperature difference>10℃; the reduction coefficients of the scores of each indicator in this climate zone are: the reduction coefficient of thermal conductivity is 1.1, the reduction coefficient of thermal diffusion coefficient is 1.2, the reduction coefficient of specific heat capacity is 1.1, and the reduction coefficient of enthalpy decay rate is 1; The fourth climate zone: the minimum temperature is less than -21.5℃, the temperature difference is less than 10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.6, the reduction coefficient of thermal diffusion coefficient is 0.6, the reduction coefficient of specific heat capacity is 0.6, and the reduction coefficient of enthalpy decay rate is 0.8; The fifth climate zone: the lowest temperature is -21.5~-9.0℃, and the temperature difference is less than 10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 0.8, the reduction coefficient of thermal diffusion coefficient is 0.8, the reduction coefficient of specific heat capacity is 0.8, and the reduction coefficient of enthalpy decay rate is 1; The sixth climate zone: minimum temperature > -9.0℃, temperature difference <10℃; the reduction coefficients of the scores of various indicators in this climate zone are: the reduction coefficient of thermal conductivity is 1, the reduction coefficient of thermal diffusion coefficient is 1, the reduction coefficient of specific heat capacity is 1, and the reduction coefficient of enthalpy decay rate is 1.

2. A phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavement according to claim 1, characterized in that: The phase change asphalt mixture specimen in step 1 is a rotary compacted cylindrical specimen cut into test samples with a diameter of 150 mm and a thickness of 10 mm; the temperature for measuring the thermal conductivity coefficient is above 0°C; and the test instrument is a Hot Disk thermal constant analyzer.

3. A phase change material evaluation method for determining the feasibility of asphalt pavement snow and ice removal according to claim 1, characterized in that: The thermal diffusion coefficient of the phase change asphalt mixture specimen is determined in step 2 by placing the phase change asphalt mixture specimen in a low temperature constant temperature test chamber. The linear relationship between temperature and time is T t =b1t+b2, the quadratic relationship between temperature and depth is T z =a1z 2 +a2z+a3, the thermal diffusion coefficient is shown as follows: Where a is the thermal diffusion coefficient of the phase change asphalt mixture, t is the time difference, z is the longitudinal distance between the temperature measurement position of the asphalt mixture specimen and the upper surface of the asphalt mixture, b1 and b2 are the fitting constants of the linear relationship between temperature and time, and a1, a2, and a3 are the fitting constants of the quadratic relationship between temperature and depth.

4. A phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavement according to claim 3, characterized in that: Before measuring the thermal diffusion coefficient of the phase change asphalt mixture specimen, the outer surface and bottom of the specimen shall be insulated: the outer surface and bottom of the specimen shall be wrapped with rubber-plastic insulation cotton and tin foil, and the total thickness of the rubber-plastic insulation cotton shall not be less than 20mm.

5. A phase change material evaluation method for determining the feasibility of snow and ice removal on asphalt pavement according to claim 4, characterized in that: The phase change asphalt mixture specimen is placed in a low temperature constant temperature test box to ensure that the temperature sensors are placed at 2cm, 7cm, and 14cm of the phase change asphalt mixture specimen, and the drilling holes at various depths are parallel, with a drilling depth of 5cm and a hole diameter of 5mm.

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