A polyurethane-modified thermochromic warm mix asphalt and a preparation process thereof

Abstract

The application discloses polyurethane modified thermochromic warm mix asphalt and a preparation process thereof, and relates to the technical field of materials for road engineering. The application realizes double function optimization by using polyurethane and a surface active agent type warm mixing agent, the polyurethane improves the asphalt performance while having a lower requirement on the production temperature of the asphalt, and the polyurethane has environmental friendliness; the surface active agent type warm mixing agent has the characteristics of reducing the construction temperature while having a limited influence on the original performance of the asphalt. When the adding proportion of the warm mixing agent is 0.6%, the mixing temperature reduction effect can reach 20 DEG C. The warm mixing process can effectively reduce the possible reversible thermochromic microcapsule damage problem in the mixing and compaction process, and then significantly improves the cooling effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road engineering materials, in particular to a polyurethane modified thermochromic warm mix asphalt and a preparation process thereof. BACKGROUND

[0002] Thermochromic asphalt can automatically adjust the reflection ability to solar radiation according to the change of ambient temperature, reduce the temperature of pavement structure in high temperature season, and slow down the aging rate of asphalt. However, compared with polymer modified asphalt, the physical rheological performance of thermochromic asphalt is poor, so polymers can be used to improve the road performance of asphalt. However, common polymers usually have high requirements for the production temperature of asphalt. Under the condition of continuous high temperature, thermal aging and thermal degradation of asphalt and modifier occur respectively, which affects the final performance of modified asphalt. In actual engineering, warm mix process is usually used to reduce the construction temperature. However, common organic viscosity reducing type warm mix agent usually has negative effects on the low temperature performance of asphalt.

[0003] Based on the above reasons, the present application is proposed. SUMMARY

[0004] Based on the above reasons, in view of the problems or defects in the prior art, the purpose of the present application is to provide a polyurethane modified thermochromic warm mix asphalt and a preparation process thereof, to solve or at least partially solve the above technical defects in the prior art. The present application realizes double function optimization by using polyurethane and surfactant type warm mix agent. The polyurethane improves the performance of asphalt while having lower requirements for the production temperature of asphalt, and has environmental friendliness. The surfactant type warm mix agent reduces the construction temperature while having the characteristics of limited influence on the original performance of asphalt.

[0005] In order to achieve the above first purpose of the present application, the technical scheme adopted by the present application is as follows:

[0006] A preparation method of a polyurethane modified thermochromic warm mix asphalt, the method specifically comprises the following steps:

[0007] The base asphalt is heated to a flow state, then polyurethane (PU) particles are added according to the proportion, and after uniform stirring, reversible thermochromic microcapsules (RTM) are continuously added under stirring conditions, and mixed uniformly. Then, a surfactant type warm mix agent is slowly added to the obtained mixture, and stirred uniformly to obtain the polyurethane modified thermochromic warm mix asphalt.

[0008] Further, in the above technical scheme, the mass ratio of the polyurethane to the base asphalt is 3-9:100.

[0009] Further, in the above technical scheme, the mass ratio of the polyurethane to the base asphalt is preferably 3-6:100.

[0010] Further, the above technical solution, the mass ratio of the reversible thermochromic microcapsule to the base asphalt is 6:100.

[0011] Further, the above technical solution, the mass ratio of the surface active modifier to the base asphalt is 0.6:100.

[0012] Further, the above technical solution, the polyurethane is synthesized by the following method, and the specific steps are as follows:

[0013] The polytetramethylene ether glycol (PTMG) and methylene diphenyl diisocyanate (MDI) after vacuum drying are mixed according to the ratio, the obtained mixed reactants are stirred and reacted at 75-85 DEG C for 1.5-2.5 hours, and then the temperature of the reaction system is reduced to 65-70 DEG C, and the chain extender 1, 4-butanediol (BDO) is added according to the ratio, and the reaction is continued for 1.5-2.5 hours, and if the viscosity is too large during the reaction process, a proper amount of solvent dimethylformamide (DMF) is added to reduce the viscosity; after the reaction is completed, the obtained product is poured into a mold and vacuum dried to obtain the polyurethane.

[0014] Further, the above technical solution, the vacuum drying process of the PTMG and MDI is as follows: vacuum drying at 100 DEG C-120 DEG C for 2-3 hours.

[0015] Further, the above technical solution, the molecular weight of the PTMG is 2000.

[0016] Further, the above technical solution, the molar ratio of the PTMG to MDI is 1:(1.5-2). In a preferred embodiment of the present application, the molar ratio of the PTMG to MDI is 1:1.75.

[0017] Further, the above technical solution, in a preferred embodiment of the present application, the reaction temperature of the mixed reactants is 80 DEG C, and the reaction time is 2 hours.

[0018] Further, the above technical solution, the molar ratio of the BDO to PTMG is (0.5-1):1. In a preferred embodiment of the present application, the molar ratio of the BDO to PTMG is 0.67:1.

[0019] Further, the above technical solution, in a preferred embodiment of the present application, the reaction time after adding the chain extender is 2 hours.

[0020] Further, the above technical solution, in a preferred embodiment of the present application, the temperature of the vacuum drying is 80 DEG C, and the vacuum drying time is 48 hours.

[0021] The second object of the present application is to provide a polyurethane modified thermochromic warm mix asphalt prepared by the above method.

[0022] The present application first determines the performance improvement effect of polyurethane / reversible thermochromic material on asphalt performance by testing the influence of different dosages of polyurethane on the performance indicators of thermochromic asphalt before and after aging. Then, the temperature reduction range of the surfactant warm mix agent is determined by controlling the porosity of the test piece; the change trend of the rheological properties of asphalt at different aging temperatures is compared to observe the improvement range of the warm mix agent on the performance stability of asphalt; the thermal degradation degree of the modified material in the simulated construction process is observed by using a gel chromatograph and a spectrometer. Finally, the influence of polyurethane / reversible thermochromic material on the pavement performance of asphalt is evaluated from the performance indicators of asphalt mixture, and then the influence of different construction processes on the temperature adjustment performance of thermochromic asphalt mixture is evaluated by monitoring the internal temperature of the test piece.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The thermochromic material used in the present application slightly improves the high-temperature performance, rutting resistance and fatigue performance of asphalt, but also slightly damages the low-temperature cracking resistance. Due to the alternating structure of soft and hard segments in the polyurethane structure, when the hard segment content is 20%, the high and low temperature performance of asphalt is improved, and the low temperature performance is particularly important.

[0025] (2) The present application finds through accelerated aging test that the reversible thermochromic microcapsule can effectively resist the aging of asphalt caused by ultraviolet radiation, however, in terms of long-term thermal oxidation aging, its anti-aging effect is limited. In addition, the addition of polyurethane can further enhance the ability of the asphalt system to resist long-term thermal oxidation and ultraviolet aging.

[0026] (3) The present application finds by controlling the porosity of asphalt mixture that when the warm mix agent is added at a proportion of 0.6%, the mixing temperature can be reduced by 20℃, and because of the reduction of mixing temperature, the performance stability of the overall asphalt system is greatly improved. That is, the aging process of asphalt is alleviated; the thermal cracking and thermal degradation of polyurethane in high temperature environment and the thermal expansion and even rupture of microcapsule are also alleviated.

[0027] (4) The present application finds through outdoor temperature measurement experiment that the internal temperature of the thermochromic asphalt mixture prepared by hot mixing is about 5℃ lower than that of the blank group, and the internal temperature of the thermochromic asphalt mixture prepared by warm mixing is about 6.5℃ lower than that of the blank group. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0029] Figure 1 Schematic diagram of constructing the master curve of the complex shear modulus of unaged 70# asphalt

[0030] Figure 2 The three major performance indicators of the asphalt samples prepared for Examples 2-4 and Comparative Examples 1-2, respectively: (a) 25℃ penetration; (b) softening point; (c) 10℃ ductility;

[0031] Figure 3 The 135℃ Brookfield viscosity of different asphalt samples prepared for Examples 2-4 and Comparative Examples 1-2, respectively;

[0032] Figure 4 G-R parameters of different asphalt samples in the black space diagram;

[0033] Figure 5 CMAI values under different aging conditions: (a) TFOT; (b) TFOT+UV; (c) TFOT+PAV;

[0034] Figure 6 Effect of warm mix agent content on the air void of AC-13 asphalt in Examples 5-7;

[0035] Figure 7 Appearance of indirect tensile fatigue test sample: (a) core drilling of rotary test sample; (b) cutting and forming;

[0036] Figure 8 Indirect tensile fatigue test;

[0037] Figure 9 Outdoor temperature measurement test;

[0038] Figure 10 Test results of Marshall stability of asphalt mixture: (a) Marshall stability; (b) flow value; (c) Marshall modulus.

[0039] Figure 11 Test results of low-temperature splitting of asphalt mixture: (a) splitting tensile strength; (b) failure tensile strain; (c) failure stiffness modulus;

[0040] Figure 12 Test results of freeze-thaw splitting of asphalt mixture;

[0041] Figure 13 Asphalt mixture freeze-thaw split tensile strength ratio

[0042] Figure 14 Relationship between fatigue life and stress level applied; wherein: (a) hot mix; (b) warm mix;

[0043] Figure 15 Outdoor temperature measurement results; wherein: (a) temperature inside different asphalt mixtures; (b) temperature difference inside modified asphalt mixture and unmodified asphalt mixture. DETAILED DESCRIPTION

[0044] The application will be further described in the following implementation cases. The implementation cases are implemented on the premise of the application technology, and the detailed implementation modes and specific operation processes are given to illustrate the creativity of the application, but the protection scope of the application is not limited to the following implementation cases.

[0045] The equipment and raw materials used in the application can be purchased from the market or are commonly used in the art. The methods in the following examples are conventional methods in the art, unless otherwise specified.

[0046] The base asphalt used in the following examples of the application is 70# asphalt produced by SK Company. The basic performance indicators of the asphalt are tested according to the experimental method in JTGE20-2011, and the basic performance indicators are listed in Table 1.

[0047] Table 1 Basic performance of 70# asphalt

[0048]

[0049]

[0050] The reversible thermochromic microcapsule (RTM) used in the following examples of the application is purchased from Guangzhou Chongyu Industrial Material Co., Ltd., with cas number 115392-27-3 (provided by the vendor). The phase transition temperature of the reversible thermochromic microcapsule is 31℃, and it presents a red appearance. The electron donor, electron acceptor, solvent and shell thereof are fluoroolefin substance, bisphenol A, methyl stearate and melamine resin, respectively. When the temperature is lower than 31℃, the appearance color of the reversible thermochromic microcapsule is red, and when the temperature is higher than 31℃, the appearance color of the reversible thermochromic microcapsule will change to colorless.

[0051] The surface active agent type warm mixing agent used in the following examples of the application is provided by Changzhou Luyou Traffic Facilities Co., Ltd., with product code LY-W3. The main components thereof are surface active agent, anti-stripping agent, etc. The basic performance indicators of the warm mixing agent are shown in Table 2.

[0052] Table 2 Basic performance indicators of warm mixing agent

[0053]

[0054] The AC-13 type asphalt used in the following examples of the present application is a mixture, the gradation table of which is shown in Table 3; the aggregate used in the asphalt mixture is limestone, which is hard, wear-resistant, and has no weathering on the surface, and the aggregate is washed of surface impurities and dried and cleaned before use. The aggregate is divided into three grades, coarse aggregate, medium aggregate, and fine aggregate, according to the particle size. The basic properties of the aggregate and the mineral powder are shown in Tables 4-6.

[0055] Table 3 AC-13 type gradation table

[0056]

[0057]

[0058] Table 4 Technical performance indicators of mineral powder

[0059]

[0060] Table 5 Quality technical indicators of fine aggregate for asphalt mixture

[0061]

[0062] Table 6 Quality technical indicators of coarse aggregate for asphalt mixture

[0063]

[0064]

[0065] Example 1

[0066] The specific steps of the polyurethane synthesis of this example are as follows: first, 100 grams of PTMG and 21.97 grams of MDI are weighed and placed in a vacuum drying oven and dried at 100-120°C for 2-3 hours to remove trace amounts of moisture in the materials. Then, the oil bath temperature is set to 80°C, and a 500-milliliter round-bottom three-neck flask is used as the reaction container. The dried PTMG and MDI are placed in the three-neck flask, the speed of the electric stirrer is set to 300 rpm, and the reaction is carried out for 2 hours. During the reaction, the viscosity of the reaction system slowly increases, and the preparation of the polyurethane prepolymer is successful. Subsequently, the system temperature is adjusted to 70°C, 3.032 grams of chain extender BDO is added, and the reaction is continued for 2 hours. At this stage, the viscosity of the reaction system increases sharply. If the viscosity is too large, an appropriate amount of solvent dimethylformamide (DMF) should be added to reduce the viscosity. Finally, the reaction mixture is poured into a mold and dried in a 80°C vacuum drying oven for 48 hours to obtain the polyurethane.

[0067] The polyurethane involved in the following examples or comparative examples is the polyurethane prepared in Example 1.

[0068] The optimal amount of polyurethane was screened, and Examples 2-4 and Comparative Examples 1-2 were set.

[0069] Example 2

[0070] A sample of asphalt in this example, abbreviated as RTM+PU3% asphalt, was prepared by the following method, and the steps were as follows:

[0071] First, 70# asphalt was heated to a flow state in an oven at 150°C. Then, 3% (relative to the mass of the base asphalt) of the polyurethane particles that had been crushed in advance were added to the asphalt. After initial stirring, the speed of the shearing machine was adjusted to 4000 rpm, and it was operated for 1 hour. Subsequently, the speed of the shearing machine was adjusted to 1000 rpm, and 6% (relative to the mass of the base asphalt) of the reversibly thermochromic microcapsules that had been weighed in advance were added, and the operation was continued for 20 minutes. After mixing, it was poured out for standby.

[0072] Example 3

[0073] A sample of asphalt in this example, abbreviated as RTM+PU6% asphalt, was prepared by the same method as in Example 1, except that the amount of polyurethane particles added in this example was 6%, i.e., 6% of the mass of the base asphalt.

[0074] Example 4

[0075] A sample of asphalt in this example, abbreviated as RTM+PU9% asphalt, was prepared by the same method as in Example 1, except that the amount of polyurethane particles added in this example was 9%, i.e., 9% of the mass of the base asphalt.

[0076] Comparative Example 1

[0077] A sample of asphalt in this comparative example was 70# asphalt, abbreviated as 70#.

[0078] Comparative Example 2

[0079] A sample of asphalt in this comparative example, abbreviated as RTM asphalt, was prepared by the same method as in Example 1, except that no PU raw material was added in the preparation process of the asphalt sample in this comparative example.

[0080] Test methods:

[0081] The softening point, penetration at 25°C, ductility at 10°C, and Brookfield viscosity at 135°C of the asphalt were tested according to the four test methods of T0606, T0604, T0605, and T0625 in the standard of JTG E20-2011.

[0082] The method for testing the anti-aging performance of the asphalt sample is as follows:

[0083] Glover-Rowe parameter (G-R parameter)

[0084] (1) Anderson et al. and Glover et al. developed a rheological parameter based on the results of DSR experiments using the Maxwell model, and the specific formula is G' / (η' / G'). This parameter has a good correlation with the failure strain obtained by the tensile experiment. Subsequently, Rowe modified this parameter. Since η' / G' can be expressed as tanδ / ω, and G' can be expressed as |G*|cosδ, the original expression is rewritten as G * (cosδ) 2 ω / sinδ. Where ω is a given constant value (0.005 rad / s) and can be ignored. The new G-R parameter can be expressed as:

[0085]

[0086] In the formula, G * and δ are expressed as the complex shear modulus and the phase angle at 15°C and 0.005 rad / s.

[0087] The change trend of the G-R parameter can be used to describe the aging characteristics of asphalt binders, and the change in the anti-cracking performance during the aging process can be directly evaluated from the black space diagram. The larger the G-R parameter, the more brittle the asphalt binder, and the greater the possibility of cracking. Because the G-R parameter only depends on G* and δ, it can be easily represented by the black space diagram. Researchers proposed two threshold conditions to determine three different material states: (1) the damage curve at G-R=180 kPa. The area below this curve is considered to be undamaged; (2) the damaged area, which is jointly determined by the damage curve and the failure curve, where the failure curve is at G-R=450 kPa; (3) G-R>450 kPa indicates that obvious cracks have occurred.

[0088] G* and δ were determined by DSR tests. All asphalt samples were subjected to frequency sweep tests at 5°C, 15°C and 25°C (angular frequency range from 0.1 to 100 Hz), with a peak strain amplitude of 0.1% to ensure that the samples were in the linear viscoelastic range. Subsequently, the master curve of each asphalt sample was constructed using the standard S-type model and the Williams-Landel-Ferry (WLF) function, from which G* and δ at 15°C and 0.005 rad / s were obtained to calculate the G-R parameter.

[0089] (2) Master curve construction

[0090] Viscoelasticity is one of the most significant properties of asphalt. Time and temperature are the key factors to determine the rheological behavior of asphalt, which will significantly affect the performance of asphalt in the linear viscoelastic range. Through the principle of time-temperature superposition (TTS), the equivalent rheological behavior of asphalt can be obtained under different experimental conditions. TTS can be achieved by the shift factor in the Williams-Lindel-Ferry (WLF) equation (formula (2)), which allows the rheological data at one temperature to be converted to the rheological data at another temperature. In order to construct the master curve, a reference temperature needs to be selected. In this invention, the reference temperature is set to 15℃ for convenience of calculating G-R parameters. The complex shear modulus and phase angle master curves are constructed using the standard S-model, and the calculation process is shown in formulas (2)-(5).

[0091]

[0092] In the formula, loga T is the shift factor; C1 and C2 are coefficients; T r is the reference temperature; ω r and ω are the reduced frequency and loading frequency, respectively; α, β and γ are coefficients.

[0093] Taking unaged 70# asphalt as an example, Figure 1 the detailed shift process of complex shear modulus and the shift factor at different temperatures are shown. All other asphalt samples use this method to construct the complex shear modulus master curve. For the construction of the phase angle master curve, the shift factor and other parameters used are the same as those in the complex shear modulus master curve.

[0094] The rheological performance indicators involved in the following examples of the invention

[0095] According to the results of previous studies, the inventors selected some rheological indicators to represent the aging degree of different asphalt samples, and the specific definitions are shown in formulas (6)-(7). The asphalt with a larger aging index indicates that its anti-aging performance is poorer.

[0096]

[0097] The traditional three performance indicators of asphalt (ductility, penetration and softening point) are tested to evaluate the performance of asphalt in actual use, so as to select the material suitable for specific applications. Figure 2 The change rule of the physical performance of asphalt after the incorporation of reversible thermochromic microcapsules and polyurethane is shown. From Figure 2(a) It can be seen that the penetration of asphalt slightly decreases after the incorporation of reversible thermochromic microcapsules, because reversible thermochromic microcapsules can be regarded as a kind of filler, which increases the frictional resistance between the particles of the system when dispersed in asphalt, thereby reducing the deformation of asphalt under stress, improving its anti-deformation ability and stability. In addition, the penetration of asphalt further decreases after the introduction of polyurethane on the basis of reversible thermochromic microcapsules, indicating that both polyurethane and reversible thermochromic microcapsules improve the high-temperature performance of asphalt. In addition, the softening point increases with the incorporation of reversible thermochromic microcapsules and polyurethane, especially after the incorporation of polyurethane, which increases more significantly, which improves the high-temperature stability of asphalt. However, the ductility of asphalt decreases significantly after the incorporation of reversible thermochromic microcapsules, and the ductility is restored to some extent after the introduction of polyurethane. This may be because the microcapsules occupy part of the space, limiting the flow ability of asphalt molecules, and polyurethane partially makes up for this effect, so that the ductility of asphalt is improved.

[0098] Figure 3 The change rule of the Brookfield viscosity of asphalt at 135°C after the incorporation of reversible thermochromic microcapsules and polyurethane is shown. Reversible thermochromic microcapsules form a filler structure in asphalt, increasing the volume of asphalt binder. This volume expansion effect will cause the viscosity of asphalt to increase, because under the same volume, the movement of asphalt molecules will be limited by microcapsules, thereby increasing the viscosity. After the incorporation of polyurethane, it can be found that the viscosity of asphalt increases significantly, but when the dosage reaches 9%, the viscosity of modified asphalt is twice that of the matrix asphalt. This is because polyurethane is a high molecular material, and its molecular weight and molecular weight distribution are large. When polyurethane is incorporated into asphalt, these high molecular polyurethane molecules will increase the average molecular weight and molecular weight distribution of the mixture. Larger molecular weight will significantly increase the viscosity of the mixture, in addition, polyurethane may react with some components in asphalt, causing changes in the structure of asphalt molecules. These structural changes may lead to an increase in the interaction between asphalt molecules, making it more difficult for asphalt to flow, thereby increasing the viscosity. The SHRP asphalt binder performance specification proposes that the Brookfield viscosity of modified asphalt at 135°C should not exceed 3 Pa·s. As can be seen from the figure, the viscosity values measured for all asphalt samples are lower than this reference value, so it can be known that the workability of the prepared modified asphalt is good, within the specification requirements.

[0099] Figure 4The GR parameter for all aged and unaged asphalt samples is plotted on the same black space graph. According to its definition, a larger GR parameter value indicates a higher risk of low-temperature cracking. After accelerated indoor simulated aging, the GR parameter for all asphalt samples increased to varying degrees, indicating an increased risk of low-temperature cracking due to aging. Comparing the GR parameters of RTM and base asphalt, it was found that after TFOT+UV aging, the GR parameter value of RTM was significantly lower than that of base asphalt. This is because RTM has a higher reflectivity to solar radiation than base asphalt, which can reduce aging caused by UV radiation. However, after TFOT+PAV aging, the difference in GR parameter values ​​between RTM and base asphalt was less significant, indicating that RTM's high reflectivity is less effective in resisting thermal oxidative aging. On the other hand, after the incorporation of polyurethane, the growth trend of the GR parameter of the aged asphalt was significantly slowed, indicating that the RTM+PU combination has better aging resistance than RTM alone.

[0100] By analyzing the degree of change in the complex shear modulus of asphalt before and after aging, we can understand its aging sensitivity. If the performance index of asphalt changes less during the aging process, it means that the asphalt is less affected by aging and has better anti-aging performance. The complex shear modulus aging index (CMAI) is calculated as follows: Figure 5The matrix asphalt always shows the highest CMAI value in any aging simulation experiment, indicating that it is the most sensitive to aging. When only reversible thermochromic microcapsules are added, the asphalt sample shows excellent resistance to ultraviolet aging, and the resistance to long-term thermal oxidative aging is only slightly better than that of the matrix asphalt. The resistance of RTM to ultraviolet aging comes from the high reflectivity given by the thermochromic microcapsules, and the reason why the thermal oxidative aging is better than that of the matrix asphalt is that the solvent in the thermochromic microcapsules is methyl stearate, which is a phase change material. When the asphalt is in a short-term thermal oxidative aging environment, methyl stearate can play its own phase change endothermic function, so that the degree of asphalt aging is reduced. For asphalt samples in a long-term thermal oxidative aging environment, the melting enthalpy of methyl stearate is not enough to resist long-term thermal oxidative aging. In this process, the microcapsules in the asphalt will be broken due to long-term high temperature and high pressure, and the internal methyl stearate will be absorbed by the asphalt to supplement the light components in the asphalt system, so the performance of the RTM sample in resisting long-term thermal oxidative aging is still better than that of the matrix asphalt. On the other hand, when polyurethane is added, the anti-aging performance of the asphalt is improved to different degrees. Among them, the anti-ultraviolet aging performance of the asphalt sample (RTM+PU) is slightly enhanced, and the anti-thermal oxidative aging performance is significantly improved. This shows that in the combination of reversible thermochromic microcapsules and polyurethane, the reversible thermochromic microcapsules can improve the resistance of asphalt to ultraviolet aging, and at the same time protect the polyurethane, reduce the degree of degradation of the polyurethane under ultraviolet irradiation. The polyurethane can enhance the resistance of the asphalt to thermal oxidative aging. In addition, with the increase of the amount of polyurethane, the CMAI value of the asphalt sample first decreases and then rises, indicating that the anti-aging performance of the asphalt does not increase indefinitely with the increase of the amount of polyurethane. It can be found that when the amount of polyurethane reaches 6%, the asphalt sample shows the best anti-aging performance.

[0101] In summary, under the condition of fixed amount of reversible thermochromic microcapsules, the addition of polyurethane can enhance the resistance of asphalt to thermal oxidative aging, which is mainly due to the mutual resistance of the small molecules generated by the degradation of polyurethane polymer and the volatilization of light components in asphalt and the hardening caused by aging. Moreover, after the addition of polyurethane, the performance of asphalt binder cannot be infinitely improved, therefore, considering economic factors and practical factors, it is recommended that the best amount of polyurethane is between 3% and 6%.

[0102] The present application selects the best amount of surfactant warm mix agent, and sets examples 5-7.

[0103] Example 5

[0104] One asphalt sample of the present example uses AC-13 asphalt as the matrix asphalt, which is referred to as RTM+PU3%+0.3% warm mix agent, and is prepared by the following method, the steps are as follows:

[0105] First, the AC-13 asphalt is heated to a flow state in an oven at 150°C. Then, 3% (relative to the mass of the base asphalt) of the polyurethane particles that have been crushed in advance are added to the asphalt. After initial stirring, the speed of the shearing machine is adjusted to 4000 rpm and operated for 1 hour. Subsequently, the speed of the shearing machine is adjusted to 1000 rpm, and 6% (relative to the mass of the base asphalt) of the reversibly thermochromic microcapsules that have been weighed in advance are added, operated for 20 minutes, mixed uniformly, and 0.3% (relative to the mass of the base asphalt) of the surfactant-type warm-mixing agent is continuously added, mixed uniformly, and poured out for standby.

[0106] Example 6

[0107] An asphalt sample of this example, referred to as RTM+PU3%+0.6% warm-mixing agent, is prepared in the same manner as in Example 5, except that the amount of the surfactant-type warm-mixing agent added in this example is 0.6%, i.e., 0.6% of the warm-mixing agent relative to the mass of the base asphalt is added.

[0108] Example 7

[0109] An asphalt sample of this example, referred to as RTM+PU3%+0.9% warm-mixing agent, is prepared in the same manner as in Example 5, except that the amount of the surfactant-type warm-mixing agent added in this example is 0.9%, i.e., 0.9% of the warm-mixing agent relative to the mass of the base asphalt is added.

[0110] Effect of the warm-mixing agent on the temperature reduction range of the asphalt mixture:

[0111] At present, the air voids of the mixture are often used as an index to determine the mixing temperature in road construction, and thus the air voids of the warm-mixing asphalt Marshall test piece at different molding temperatures can be tested to adjust the air voids to the limit value of the target air voids, and the cooling effect of the warm-mixing technology can be determined accordingly. According to the requirements for the construction temperature of the hot-mixing asphalt pavement in the specification JTG F40-2004, the mixing and compaction temperature is set to 150°C. To determine the optimal addition ratio of the warm-mixing agent in the asphalt, the air voids of the warm-mixing asphalt mixture with different blending ratios are tested under different mixing and compaction temperatures. The mixing temperature is reduced by 10°C, 20°C, and 30°C compared to the hot-mixing asphalt mixture, and the experiments are performed. The gradation type is AC-13, the Marshall test piece is double-sidedly compacted for 75 times, and then the air voids of the Marshall test piece are tested. The change curve of the air voids of the asphalt mixture is shown in FIG. 1. Figure 6

[0112] From Figure 6 ​It can be found that the air voids of asphalt mixture decrease with the decrease of temperature. This is mainly because the viscosity of asphalt decreases and its fluidity increases with the increase of temperature. This makes asphalt better fill the voids in asphalt mixture, reducing the existence of voids. When the content of warm mix additive is increased, the air voids of the specimen gradually decrease under the same temperature condition, indicating that the warm mix additive has effective lubrication function, which can reduce the surface tension of asphalt, so that it can better wet and cover the surface of particles at a lower temperature. This helps to improve the fluidity of asphalt during mixing, making it easier to mix with aggregate, thereby promoting the compaction of the mixture. According to the recommendation of the specification "JTG F40-2004", the target air voids is 4%. When the content of warm mix additive is 0.3%, the air voids of the mixture do not meet the target requirement. When the content of warm mix additive is 0.6% and 0.9% and the mixing temperature is 130℃, the air voids of the mixture fluctuate around the target air voids. The air voids of the asphalt mixture with 0.6% warm mix additive is closer to 4%, therefore, based on road performance and economic factors, the content of warm mix additive is determined to be 0.6% and the temperature reduction range is 20℃.

[0113] The preparation process of AC-13 warm mix asphalt used in the following examples is as follows:

[0114] The mineral aggregate, mineral powder and asphalt are weighed according to the design gradation. Generally, 2-4 standard Marshall specimens are prepared (one standard Marshall specimen weighs about 1200g). The aggregate, mineral powder and mold are heated in an oven at about 140℃, and the temperature of the mixer is set to 130℃. After the asphalt is heated to a flowable state, the pre-heated aggregate is poured into the mixer, then the required amount of asphalt is added, and the mixer is started to stir for 1.5 min. The mixing is paused, the pre-heated mineral powder is added, and the mixing is continued for another 1.5 min. The mixed asphalt mixture is then properly mixed with a small shovel to obtain AC-13 warm mix asphalt.

[0115] The specimen mold should be wiped with a little lubricating oil in advance and a circular oil separator paper is placed on the mold base. The required amount of specimen is weighed and poured into the mold. A screwdriver is used to tamp 15 times around the perimeter and 10 times in the middle. After tamping, the surface of the asphalt mixture is flattened and another oil separator paper is placed on it. The mold is placed in the Marshall specimen automatic compaction instrument, and both sides are compacted for 75 times each. After compaction, the specimen is cooled and demolded for use. The height of all Marshall specimens should meet the standard of 63.5mm±1.3mm.

[0116] The preparation process of AC-13 hot mix asphalt used in the following examples is as follows:

[0117] The aggregate, filler and asphalt are weighed according to the design gradation. Generally, 2-4 standard Marshall specimens are prepared (one standard Marshall specimen weighs about 1200 g). The aggregate, filler and mold are heated in an oven at about 160°C, and the temperature of the mixer is set at 150°C. After the asphalt is heated to a flowable state, the preheated aggregate is poured into the mixer, and the required amount of asphalt is added. The mixer is started and stirred for 1.5 min. The mixing is paused, the preheated filler is added, and the mixing is continued for 1.5 min. The mixed asphalt mixture is appropriately stirred with a small shovel to obtain the AC-13 hot-mixed asphalt.

[0118] The specimen mold is prepared in the same manner as above.

[0119] Example 8

[0120] A sample of asphalt in this example, referred to as RTM+PU3%+asphalt (without incorporation of warm-mixing agent), is prepared in substantially the same manner as in Example 2, except that the asphalt used in this example is the AC-13 hot-mixed asphalt prepared in the above-described manner.

[0121] Example 9

[0122] A sample of asphalt in this example, referred to as RTM+PU6%+asphalt (without incorporation of warm-mixing agent), is prepared in substantially the same manner as in Example 3, except that the asphalt used in this example is the AC-13 hot-mixed asphalt prepared in the above-described manner.

[0123] Example 10

[0124] A sample of asphalt in this example, referred to as RTM+PU9%+asphalt (without incorporation of warm-mixing agent), is prepared in substantially the same manner as in Example 4, except that the asphalt used in this example is the AC-13 hot-mixed asphalt prepared in the above-described manner.

[0125] Example 11

[0126] A sample of asphalt in this example, referred to as RTM+PU3%+warm-mixed asphalt (with incorporation of warm-mixing agent), is prepared in substantially the same manner as in Example 8, except that the sample of asphalt in this example further includes 0.6% of a surfactant-type warm-mixing agent, and the asphalt mixture used in this example is the AC-13 warm-mixed asphalt.

[0127] Example 12

[0128] An asphalt sample of this example, referred to as RTM+PU 6%+ warm mix asphalt (with warm mix agent incorporated), was prepared in substantially the same manner as in Example 9, except that 0.6% of a surfactant-type warm mix agent was added to the asphalt sample during preparation, and the asphalt mixture used in this example was AC-13 warm mix asphalt.

[0129] Example 13

[0130] An asphalt sample of this example, referred to as RTM+PU 9%+ warm mix asphalt (with warm mix agent incorporated), was prepared in substantially the same manner as in Example 10, except that 0.6% of a surfactant-type warm mix agent was added to the asphalt sample during preparation, and the asphalt mixture used in this example was AC-13 warm mix asphalt.

[0131] Comparative Example 3

[0132] The 70# warm mix asphalt (with warm mix agent incorporated) of this comparative example was prepared by weighing 2-4 standard Marshall specimens (one standard Marshall specimen weighs about 1200 g) of 70# asphalt. The asphalt and mold were placed in an oven at about 140°C, and the temperature of the mixing machine was set to 130°C. After the asphalt was heated to a flowable state, 0.6% of a surfactant-type warm mix agent was added, and the mixing machine was started and agitated for 3 minutes. The mixed asphalt mixture was then manually mixed with a small shovel to obtain a 70# warm mix asphalt.

[0133] Comparative Example 4

[0134] The RTM asphalt (with warm mix agent incorporated) of this comparative example was prepared in the same manner as in Comparative Example 3, except that 6% (relative to the mass of the base asphalt) of reversibly thermochromic microcapsules that had been previously weighed were added to the asphalt sample during preparation.

[0135] The asphalt samples prepared in Examples 2-4, Examples 8-12, and Comparative Examples 1-4 were used for road performance tests. The test methods were as follows:

[0136] (I) High temperature stability test

[0137] In engineering, Marshall stability is one of the important indicators to evaluate the high temperature stability of asphalt mixture. In this experiment, the Marshall specimens are double-sided compacted for 75 times, and then the prepared specimens and the upper and lower press heads of the Marshall tester are kept in the constant temperature water tank at the specified temperature for 30-40 minutes. During the experiment, the loading speed of the instrument is 50 mm / min ± 5 mm / min. The parallel specimens of each group are 4. After the test is completed, the maximum load during the test of the specimen and the vertical deformation of the specimen, i.e. the stability (MS) and the flow value (FL) are recorded. According to the data obtained by the test, the Marshall modulus (T) of the specimen can be further calculated,

[0138] which is defined as follows:

[0139]

[0140] (II) Low temperature cracking resistance test

[0141] Under low temperature environment, asphalt mixture will shrink, leading to increased internal stress, in addition, the elastic modulus of asphalt will increase, and the asphalt mixture will become more brittle and hard. The structure of asphalt system under low temperature environment is affected by the shrinkage stress of itself and external load, and is more prone to cracking. Therefore, low temperature splitting test is usually used in the laboratory to evaluate the low temperature performance of asphalt mixture. The experimental temperature is set at -10℃, the temperature control accuracy is ± 0.5℃, and the Poisson's ratio is 0.25. In this experiment, the Marshall specimens are double-sided compacted for 75 times, and when the constant temperature water tank reaches the required temperature, the temperature is kept for not less than 1.5h. When using a constant temperature air tank as a heat preservation medium, the heat preservation time is not less than 6h, and the distance between the specimens during heat preservation should be greater than 1cm. The parallel specimens of each group are 4. Through the experimental data, the splitting tensile strength (R T ), the failure tensile strain (ε T ) and the failure stiffness modulus (S T ) are calculated.

[0142] The evaluation indexes obtained by this experiment include: splitting strength (R T ), failure tensile strain (ε T ) and failure stiffness modulus (S T ), and the calculation process is shown in formulas 9-11:

[0143] R T = 0.006287P T / h (9)

[0144] ε T = X T (0.0307+0.0936μ) / (1.35+5μ) (10)

[0145] S T = P T (0.27 + 1.0 μ) / (h * X T ) (11)

[0146] where P T is the maximum value of the experimental load; X T is the total deformation in the horizontal direction at the maximum breaking load, h is the height of the specimen, and μ is the Poisson's ratio.

[0147] (III) Water stability evaluation method

[0148] Asphalt mixtures are required to have the ability to maintain structural and performance stability in a humid environment. This involves the properties of water erosion resistance, water resistance, and permeability resistance of asphalt mixture soil under humid conditions. If the water stability of asphalt is insufficient, water can easily penetrate into the interior of the mixture, destroy the interfacial bonding between asphalt and aggregate, and cause the internal structure of the mixture to be loose, which can easily cause deformation or damage, thereby affecting the service life and safety of the road. The Marshall specimens used in the experiments of the present application are all double-sidedly compacted 50 times. All the specimens are randomly divided into two groups, the first group is properly stored at room temperature for use, and the second group is subjected to vacuum saturation according to the procedure of the saturation experiment, under a vacuum degree of 97.3-98.7 kPa, the saturation experiment lasts for 15 minutes. Then the vacuum is removed, the normal pressure is restored, and the specimen is still stored in water for 0.5 h. After that, the specimen is placed in a sealed bag, 10 ml of water is added, after sealing treatment, the specimen is maintained in a constant temperature refrigerator (-18℃) for 16 h±1 h. After the end of the heat preservation step, the sealed bag is removed, and the specimen is immediately placed in a water tank with a constant temperature of 60℃ for 24 h. After the end of the heat preservation step, all the specimens of the first group and the second group are placed in a water tank with a stable temperature of 25℃ for not less than 2 h, and the distance between the specimens should be at least 1 cm during this period. After the test is completed, the splitting tensile strength and the freeze-thaw splitting tensile strength ratio are calculated, and the detailed calculation process is shown in the following formula:

[0149] R T1 = 0.006287P T1 / h1 (12)

[0150] R T2 = 0.006287P T2 / h2 (13)

[0151]

[0152] where R T1 and R T2 represent the splitting tensile strength of a single specimen before and after freeze-thaw cycle treatment; P T1 and P T2L is the load value of the test piece; h1 and h2 are the heights of the test piece; and respectively, are the average values of the splitting tensile strength of the two groups of effective test pieces.

[0153] (Four) Fatigue performance evaluation method

[0154] During the long-term service of asphalt pavement, vehicle traffic load and temperature change will cause fatigue stress to accumulate in the internal structure of the pavement, and eventually lead to fatigue cracks. In the present invention, the fatigue characteristics of asphalt mixture are tested by indirect tensile fatigue experiment. The experiment process refers to the specification of BS EN 12697-24:2018, and according to the specification requirements, the height of the test piece is 40mm, the diameter is 100mm±3mm, the whole test piece is formed by a rotary compactor, and the initial size of the test piece is: height 150mm, diameter 150mm. The test piece needs to be cored to obtain a 100mm sample, and then the 100mm sample is accurately cut to meet the required size of the specification, and the experimental sample is as shown in Figure 7 .

[0155] The present experiment is tested by a universal testing machine, and the experimental parameters and experimental environment conditions are set as follows: the temperature of the experimental box is constant at 25℃, the loading cycle width is 100ms, the cycle period repetition time is 400ms, the horizontal initial strain of the test piece should be in the range of 70-400με, the maximum cycle number in the experimental process is 40000, the maximum cumulative deformation of the actuator is set to 10mm, the maximum horizontal deformation is set to 5mm, and the ratio of the cycle horizontal strain to the initial strain should be greater than 2.0.

[0156] The judgment condition for the end of the experiment is that the data of the tested piece reaches the instrument setting parameter (cumulative strain reaches twice the initial strain) or a significant crack appears. Each group contains 4 parallel test pieces. The experiment ends after multiple cycle loading periods, and the number of loading periods in this stage is defined as the fatigue life value of the sample. The experimental process is as shown in Figure 8 . In this experiment, there is a certain functional relationship between the fatigue life value of the sample and the applied stress level, which is fitted according to formula 15:

[0157]

[0158] In the formula, N f and σ are the fatigue life and the applied stress level respectively; a, b are the fitting coefficients.

[0159] (Five) Outdoor temperature measurement experiment

[0160] According to the respective mixing, compaction temperature and oil-stone ratio, Marshall specimens of warm-mixed and hot-mixed 70# base asphalt, RTM and RTM+PU asphalt mixtures were prepared, all of which were AC-13 gradation. It has been found by researchers that the highest temperature of asphalt pavement structure is not the surface directly in contact with the external environment, but usually 2 cm away from the surface. All temperature sensors were inserted 2 cm below the surface of the Marshall specimen, and then all specimens were wrapped with a sponge to simulate the actual pavement light and heat boundary conditions, ensuring that only the surface of the specimen was exposed to sunlight. The internal temperature of the specimen and the external environment temperature were recorded simultaneously using a multi-channel data logger, and the outdoor field temperature measurement experiment is shown in Figure 9 .

[0161] Test result analysis:

[0162] (a) High temperature stability, Figure 10 The Marshall stability of the specimens prepared by hot mixing and warm mixing of 70# base asphalt, RTM and RTM+PU respectively was compared. From Figure 10 (a) and (b), it was found that the Marshall stability and flow value of the asphalt mixture would change to varying degrees after the reversible thermochromic microcapsules and polyurethane were added to the specimens prepared by hot mixing and warm mixing. When the microcapsules were dispersed in the asphalt as a powder filler, the filler particles increased the internal friction of the asphalt system, thereby increasing the load required for unit deformation of the asphalt mixture. Polyurethane has a certain elasticity and flexibility, which improves the strength of the asphalt mixture, which can effectively resist deformation caused by external load. From Figure 10 (c) Marshall modulus results, it can be more intuitively found that the high temperature performance of the asphalt mixture after adding polyurethane has been greatly improved compared to the base asphalt.

[0163] In addition, by comparing the experimental results of hot-mixed and warm-mixed asphalt mixtures in the figure, it can be seen that the high temperature stability of warm-mixed asphalt mixture is slightly lower than that of hot-mixed asphalt mixture, with a decrease of about 10%±3%, and the liquid warm-mixing agent will soften the asphalt, thereby slightly weakening the high temperature stability of the mixture. According to the specification requirements of hot-mixed asphalt mixture, the Marshall stability should be greater than 8 kN. Except for the warm-mixed 70# asphalt mixture, which is less than this value, the remaining asphalt mixture samples all meet the requirements of the construction specification.

[0164] (b) Low temperature crack resistance, in cold climate conditions, asphalt pavement is prone to shrinkage, hardening and brittleness due to temperature changes, thereby causing cracks and reducing the durability and safety of the pavement. Therefore, it is necessary to study the ability of asphalt mixture to resist crack formation in low temperature environment. The three indicators of low temperature splitting experiment, splitting tensile strength, failure tensile strain and failure stiffness modulus, reflect the tensile performance, deformation performance and stiffness of the mixture in low temperature environment. The experimental results are shown in Figure 11It can be found from Fig. (a) that both RTM and PU can improve the tensile strength of asphalt mixture at low temperature. The tensile strain reflects the deformation ability of the material at low temperature, and the greater the value, the better the low-temperature performance. As can be seen from Fig. (b), the strain of asphalt mixture decreases after adding reversible thermochromic microcapsules, indicating that the microcapsules affect the fluidity of asphalt, making the deformation ability of asphalt at low temperature weaken. However, after adding polyurethane, the deformation ability of asphalt mixture at low temperature is enhanced, which may be because polyurethane has lower temperature sensitivity and better flexibility, which can better adapt to external load at low temperature, making the asphalt mixture have better deformation performance at low temperature.

[0165] In addition, by comparing warm-mixed asphalt mixture and hot-mixed asphalt mixture, it can be found that after adding warm-mixing agent, the asphalt material will be slightly softened, so the tensile strength of asphalt mixture decreases, the tensile strain at failure increases, and the stress relaxation performance at low temperature is further improved.

[0166] (c) Water stability: When asphalt pavement is in service, it often faces the working environment containing pore water. Under the influence of vehicle load, the pore water in the structure will produce hydrodynamic pressure, which will drive water to gradually penetrate into the interface between asphalt and aggregate, and eventually cause asphalt to peel off the surface of aggregate. In this section, freeze-thaw splitting experiment is used to test the water stability of asphalt mixture, and the experimental results are shown in Fig. Figure 12-13 As can be seen, after freeze-thaw cycle, the splitting strength of asphalt mixture has a significant downward trend. Reversible thermochromic microcapsules will damage the water stability of asphalt mixture, while polyurethane can improve the water stability of asphalt mixture, which may be because polyurethane can form strong chemical bonds or physical cross-linking structures in asphalt, improving the bonding force between asphalt and particles, making the structure of the mixture more compact, and the water permeability resistance is enhanced.

[0167] In addition, by comparing the experimental results of warm-mixed asphalt mixture and hot-mixed asphalt mixture, it can be found that surfactant-type warm-mixing agent can enhance the water stability of asphalt mixture, which may be because the surfactant-type warm-mixing agent contains anti-stripping agent.

[0168] (d) Durability: The indirect tensile fatigue test results of asphalt mixture are shown in Table 7, Figure 14 The relationship between the fatigue life of asphalt mixture and the applied stress level is plotted. During the experiment, according to the specification requirements, the horizontal initial strain of asphalt mixture after applying load must be in the range of 70-400με. Therefore, through the pre-loading experiment, the applied stress level is determined to be 300kPa, 400kPa and 500kPa.

[0169] Table 7 Summary of indirect tensile fatigue test results of asphalt mixture

[0170]

[0171] According to formula 15, the relationship between fatigue life and applied stress level was obtained by nonlinear function fitting, and the results are shown in Figure 14 As the applied stress level increases, the fatigue life of asphalt mixture decreases rapidly, because the greater the load, the more rapidly the material damage inside the asphalt mixture accumulates, resulting in a sharp decline in durability. Compared with the base asphalt mixture, the fatigue life of the asphalt mixture with reversible thermochromic microcapsules is slightly improved. With the continuous addition of polyurethane, the fatigue life of the asphalt mixture is greatly improved. In addition, compared with hot-mixed asphalt mixture, the fatigue life of warm-mixed asphalt mixture decreases slightly, but because of its small amount, it does not bring great adverse effects.

[0172] (e) In terms of road temperature regulation performance, the temperature data inside different asphalt mixtures irradiated by outdoor solar radiation for one day are shown in Figure 15 (a) The temperature change trend inside the sample with time is basically the same as the change trend of the ambient temperature (near-ground air temperature), reaching a peak at about 2 pm. It is difficult to observe the cooling effect of modified asphalt mixture intuitively from figure (a). According to the internal temperature difference diagram of modified asphalt mixture and unmodified asphalt mixture (70#), as shown in Figure 15 (b), the internal temperature difference of the samples is not large at the beginning of the test, and with the passage of time, the internal temperature difference of the modified asphalt mixture prepared by hot mixing and the unmodified asphalt mixture can reach a maximum difference of about 5°C, while the internal temperature difference of the modified asphalt mixture prepared by warm mixing and the unmodified asphalt mixture can reach a maximum difference of about 6.5°C, which proves that the thermochromic road material can effectively cool the road surface under high temperature conditions. The reason why the cooling range of warm-mixed thermochromic asphalt is higher than that of hot-mixed thermochromic asphalt is that the high mixing and compaction temperature of hot-mixed asphalt can cause part of the reversible thermochromic microcapsules to break during mixing and compaction, losing the cooling effect. Therefore, compared with the hot mixing method, the warm mixing method can greatly reduce the number of microcapsules broken during mixing and compaction. Through the warm mixing technology, it helps the thermochromic asphalt to effectively cool the road surface under high temperature conditions, reduces the aging effect of temperature on asphalt, and at the same time, alleviates the urban heat island effect.

Claims

1. A method for preparing polyurethane-modified thermochromic warm mix asphalt, characterized by: The method specifically comprises the following steps: heating a base asphalt to a fluid state, then adding polyurethane (PU) particles according to a proportion, stirring evenly, and then adding reversible thermochromic microcapsules under stirring conditions and mixing evenly; then slowly adding LY-W3 surfactant-type warm mix agent to the resulting mixture and stirring evenly to obtain the polyurethane-modified thermochromic warm mix asphalt; wherein: the mass ratio of the reversible thermochromic microcapsules to the base asphalt is 6:100; the mass ratio of the polyurethane to the base asphalt is 3-6:100; the mass ratio of the surfactant-type warm mix agent to the base asphalt is 0.6:100; the phase transition temperature of the reversible thermochromic microcapsules is 31° C., the microcapsules exhibit a red appearance, the CAS number of the electron donor is 115392-27-3; the electron acceptor, solvent, and shell are bisphenol A, methyl stearate, and melamine resin, respectively; The polyurethane is synthesized by the following method, specifically comprising the following steps: mixing separately dried polytetramethylene ether glycol (PTMG) and methylene diphenyl diisocyanate (MDI) in a certain ratio, stirring the resulting mixture at 80° C. for 2 hours to obtain a polyurethane prepolymer; then, lowering the temperature of the reaction system to 65-70° C., adding a chain extender, 1,4-butanediol (BDO), in a certain ratio, and continuing the reaction for 2 hours. If the viscosity is too high during the reaction, adding an appropriate amount of solvent, dimethylformamide (DMF), to reduce the viscosity; after the reaction, pouring the resulting product into a mold and vacuum drying to obtain the polyurethane; the molecular weight of the PTMG is 2000; the molar ratio of the PTMG to the MDI is 1:1.75; and the molar ratio of the BDO to the PTMG is 0.67:

1.

2. The polyurethane-modified thermochromic warm mix asphalt prepared by the preparation method according to claim 1.

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