Modified bitumen targeting regulation of wax crystallization and method for preparing the same

Abstract

This invention discloses a modified asphalt with targeted regulation of wax crystallization and its preparation method, relating to the field of asphalt, and involves the preparation of matrix asphalt; purification of diatomaceous earth to obtain purified diatomaceous earth; heating random polypropylene to a molten state in an oven, then pouring it into a high-speed shear mill, adding a hindered amine light stabilizer, shearing it uniformly, and then incorporating random copolymer polypropylene, shearing it uniformly to obtain blended modified random polypropylene; the modified asphalt of this invention, through the synergistic design of materials and processes, simultaneously achieves multiple functions such as anti-photooxidation, inhibition of reversible thermal aging, and improvement of low-temperature impact resistance and cold resistance, breaking through the performance bottleneck of traditional modified asphalt in cold-region applications.

Description

Technical Field

[0001] This invention relates to the field of asphalt, and more specifically to a modified asphalt with targeted regulation of wax crystallization and its preparation method. Background Technology

[0002] Asphalt pavements often suffer from prolonged low temperatures (such as...) during their service in cold regions. This can lead to low-temperature cracking. Such cracking not only damages the structural integrity of the pavement and shortens its service life, but also significantly increases maintenance costs and threatens driving safety. Traditional research has focused on the oxidative aging of asphalt, which is an irreversible chemical change under high temperature and aerobic conditions. However, in recent years, it has been found that thermally reversible aging is another key mechanism leading to low-temperature cracking.

[0003] The so-called thermal reversible aging refers to the aging of asphalt under sustained low temperatures (such as...). Under certain conditions, reversible phase transitions (precipitation / dissolution cycles) occur in components such as wax, leading to deterioration of their rheological properties (e.g., increased creep stiffness S value and decreased creep rate m value). This deterioration can be partially recovered after heating, but repeated cycles still accumulate micro-damage. This mechanism differs from irreversible oxidative aging under high-temperature aerobic conditions. This process is partially reversible, meaning that properties can be partially recovered after heating, but repeated occurrences still lead to the accumulation of microcracks. Studies have shown that wax crystallization is one of the core factors inducing thermal reversible aging: long-chain n-alkanes (wax) in asphalt precipitate and form crystals at low temperatures, disrupting the colloidal structure stability, reducing ductility, and exacerbating brittle fracture.

[0004] Currently, the main methods for controlling wax crystallization include:

[0005] Adding pour point depressants, such as ethylene-vinyl acetate copolymer (EVA), is costly and has limited effectiveness on domestically produced high-wax asphalt.

[0006] Mineral fillers such as talc and diatomaceous earth were used, but the effects of impurities and adsorption selectivity were not considered.

[0007] Polymer modification, such as SBS and PP, is possible, but atactic polypropylene is rarely used in cold regions due to its high brittleness at low temperatures and easy oxidation at high temperatures.

[0008] Furthermore, existing modification processes often employ a "one-step incorporation method," where all admixtures are simultaneously added to the asphalt and shear-mixed. This method easily leads to interference between different functional components, making precise control difficult.

[0009] Therefore, there is an urgent need for a modified asphalt and its preparation method that can target and inhibit wax crystallization, synergistically improve high and low temperature performance, and have a controllable process. Summary of the Invention

[0010] The purpose of this invention is to provide a modified asphalt with targeted control of wax crystallization and its preparation method. By incorporating purified diatomaceous earth and blended modified atactic polypropylene in stages and steps, wax precipitation is inhibited from the source, effectively alleviating thermal reversible aging and significantly improving the crack resistance of asphalt under continuous low temperature environment, while taking into account high temperature stability and anti-aging ability.

[0011] The first objective of this invention is to provide a method for preparing modified asphalt with targeted regulation of wax crystallization, comprising the following steps:

[0012] The asphalt is placed in an oven and heated to a molten state at 110~140℃. Then it is poured into a high-speed shearing machine and stirred and mixed at 110~140℃ for 60~80 minutes to obtain the base asphalt.

[0013] The purification process of diatomaceous earth yields purified diatomaceous earth, specifically including:

[0014] The dried and crushed diatomaceous earth was dispersed in water, soaked, and then stirred. Water was then added, and stirring was continued for 0.5 hours to disperse the diatomaceous earth and obtain a slurry.

[0015] After stirring, the slurry is allowed to stand for 10 minutes. During this time, the denser minerals such as quartz and feldspar settle rapidly, while the less dense organic matter and clay remain suspended in the upper layer. The diatomaceous earth suspension that is stably suspended in the middle is extracted, which is the first suspension. The bottom sediment and the top scum are discarded. The bottom sediment is added with water and stirred again, and the above sedimentation and separation operation is repeated to obtain the second suspension. All the first and second suspensions are combined and separated into solid and liquid by filtration or centrifugation. The obtained solid is dried at 60~100℃ to obtain the preliminarily purified diatomaceous earth.

[0016] Sulfuric acid was added to the pre-purified diatomaceous earth under continuous stirring. After boiling, the mixture was filtered, washed, and dried to obtain purified diatomaceous earth.

[0017] Random polypropylene was placed in an oven and heated to a molten state at 140-160°C. Then it was poured into a high-speed shear press, and a hindered amine light stabilizer was added. The mixture was stirred and mixed at 140-160°C for 20-30 minutes. Random copolymer polypropylene was then incorporated and stirred and mixed for 40-50 minutes to obtain blended modified random polypropylene.

[0018] Purified diatomaceous earth and matrix asphalt are sheared in a high-speed shear mill at 110~140℃ for 30~60 min to obtain pre-modified asphalt.

[0019] Modified atactic polypropylene was added to pre-modified asphalt and mixed to obtain modified asphalt. The shearing rate of the high-speed shearing machine was 4000~4500 r / min.

[0020] Diatomaceous earth is purified through water washing and acid leaching, which can effectively remove impurities such as feldspar, quartz, clay minerals and organic matter, thus avoiding their negative impact on the rheological and aging properties of asphalt.

[0021] After purification, diatomaceous earth exhibits a more complete pore structure and a larger specific surface area, enabling it to efficiently adsorb lightweight components in asphalt and inhibit their high-temperature volatilization and oxidation. The adsorbed lightweight components provide directional interaction sites for subsequent blending and modification of atactic polypropylene, achieving precise intervention in wax crystallization.

[0022] Pretreatment of the base asphalt ensures sufficient homogeneity of the asphalt components, providing a stable base for the subsequent dispersion and reaction of admixtures. Temperature control at 110-140℃ avoids premature aging caused by excessively high temperatures while maintaining fluidity for shear dispersion.

[0023] Tinuvin 622LD effectively prevents the thermo-oxidative degradation of atactic polypropylene during high-temperature processing at 140-160℃, maintaining its molecular integrity. Furthermore, the introduction of 2%-4% atactic copolymer polypropylene reduces crystallinity, melting point, and embrittlement point, significantly improving the material's flexibility, impact resistance, and ductility at low temperatures. While single atactic polypropylene has relatively low tensile strength and modulus, blending it provides synergistic enhancement, giving the modified asphalt both flexibility and strength.

[0024] Furthermore, this invention obtains pre-modified asphalt by first shearing and mixing purified diatomaceous earth with matrix asphalt; then, it adds blended modified atactic polypropylene to the pre-modified asphalt to obtain modified asphalt. If added simultaneously, the diatomaceous earth may encapsulate the polymer particles, hindering their compatibility with the asphalt. Therefore, the step-by-step operation ensures that each step maximizes its function.

[0025] Furthermore, diatomaceous earth first adsorbs lightweight components to form reaction precursors, which are then targeted to the affected area by modified PP to inhibit wax crystal nucleation and growth. Parameters at each stage are independently optimized to improve reproducibility and industrial feasibility.

[0026] Furthermore, traditional polymer-modified asphalt exhibits poor high-temperature processing stability; PP is prone to thermo-oxidative degradation above 150℃, leading to molecular chain breakage and modification failure. Ordinary atactic polypropylene has high crystallinity and a glass transition temperature (Tg) close to 0℃. It becomes brittle rapidly below, and cannot effectively improve low-temperature crack resistance.

[0027] This invention protects the PP molecular chains from oxidation during high-temperature shearing by introducing 0.6%-0.8% Tinuvin 622LD; it also incorporates 2%-4% random copolymer polypropylene to disrupt the regular chain structure of PP, significantly reducing crystallinity, melting point, and embrittlement point; the blend system combines flexibility, cold resistance, and mechanical strength, overcoming the shortcomings of low tensile modulus and easy creep of single PP.

[0028] Existing modification technologies mainly improve elasticity by forming a three-dimensional network with SBS, enhance high-temperature stability with PE / PP, and reinforce with nanomaterials. However, none of these methods address the core cause of deterioration in domestically produced asphalt: wax crystallization. Especially in areas with large diurnal temperature differences or persistently low temperatures, wax in asphalt repeatedly precipitates and melts, leading to volume changes, the initiation of microcracks, and thus, reversible thermal aging.

[0029] This invention utilizes diatomaceous earth to pre-anchor lightweight components; it interferes with the orderly arrangement of wax molecules by blending and modifying PP, thereby inhibiting the formation of crystal nuclei; ultimately reducing the amount and size of wax crystals precipitated at low temperatures, thus weakening the driving force of thermally reversible aging from the source.

[0030] Therefore, by constructing a modified system that targets and regulates wax crystallization, the ordered arrangement of wax molecules and crystal growth can be inhibited at the source. Specifically, this invention utilizes the high specific surface area microporous structure of purified diatomaceous earth to preferentially adsorb light aromatic and saturated components in asphalt that act as wax solvents, forming locally enriched regions. Subsequently, blended modified atactic polypropylene is introduced. This polymer maintains its molecular integrity under the protection of antioxidants and, due to its good compatibility with the light components, preferentially enters the aforementioned adsorption regions, interfering with the van der Waals forces between wax molecules and hindering crystal nucleation and crystal growth.

[0031] Furthermore, the present invention proposes a second objective: a modified asphalt for targeted regulation of wax crystallization prepared using the above-described preparation method.

[0032] Modified bitumen comprises the following components in parts by weight: 80-120 parts bitumen, 2-10 parts purified diatomaceous earth, and 2-10 parts blended modified atactic polypropylene. The blended modified atactic polypropylene includes atactic polypropylene, hindered amine light stabilizer, and atactic copolymer polypropylene.

[0033] The weight ratio of random polypropylene, hindered amine light stabilizer and random copolymer polypropylene is 1:0.6~0.8:2~4.

[0034] The hindered amine light stabilizer is Tinuvin 622LD.

[0035] Random polypropylene serves as the main chain backbone, providing a basic thermoplastic network. It melts at high temperatures to form a continuous phase, and partially crystallizes upon cooling, thus improving elastic recovery and high-temperature stability.

[0036] Tinuvin 622LD, whose molecular structure contains a piperidine ring, is subjected to high-temperature shearing. The process can capture alkyl free radicals generated by the thermal oxidation of aPP. and peroxy free radicals It interrupts the chain oxidation reaction; it also has light-stabilizing properties, preventing long-term aging caused by ultraviolet radiation; it has good compatibility with aPP and can be uniformly dispersed in the polymer phase to form a built-in protective layer. Random copolymer polypropylene is used as a toughening modifier: the introduction of ethylene monomers disrupts the regularity of the PP main chain and significantly reduces crystallinity;

[0037] More importantly, aPP and its copolymers have similar solubility parameters to the light components in asphalt, and therefore preferentially distribute in the light oil enrichment area formed by diatomite adsorption; its long-chain molecules are wrapped around the wax molecules, which hinders their orderly stacking, reduces the size and number of wax crystals, and changes the shape from needle-like to spherical, thereby reducing the volumetric phase transformation stress.

[0038] Traditional antioxidants (such as Irganox 1010) are small molecules that easily migrate, volatilize, or are extracted by water in asphalt, resulting in short-lived protective effects. In contrast, Tinuvin 622LD is a high-molecular-weight hindered amine that forms a stable dispersed phase after melt blending with PP. Even after undergoing double aging, it can maintain the integrity of the polymer structure, ensuring that its long-term performance does not degrade.

[0039] Ordinary mineral powder only serves as a filler and may even absorb oil, causing asphalt to harden. In contrast, purified diatomaceous earth, due to its pore size distribution matching the scale of asphalt components, can dynamically respond to temperature changes. At high temperatures, it releases some of the adsorbed oil to improve fluidity, while at low temperatures, it locks in the oil to inhibit wax precipitation, exhibiting a slow-release effect.

[0040] If only diatomaceous earth is added, the improvement at low temperatures is limited, and it may become brittle at high temperatures; if only PP is added, it is prone to aging at high temperatures and remains brittle at low temperatures; if only antioxidants are added, the wax problem cannot be solved; however, all three are indispensable in this invention, forming a closed loop of adsorption, protection, interference, and toughening, achieving a synergistic effect.

[0041] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0042] This invention relates to a modified asphalt with targeted regulation of wax crystallization and its preparation method. The modified asphalt is formed into an organic and unified functional whole through the directional adsorption of purified diatomite, the crystallization inhibition and toughening of blended polypropylene, and the molecular-level protection of a highly efficient antioxidant.

[0043] This invention utilizes the unique microporous structure of diatomaceous earth to pre-adsorb lightweight components in asphalt. This prevents oxidative aging caused by the volatilization of these components and provides conditions for the targeted reaction of subsequent admixtures. Purifying diatomaceous earth effectively enhances its adsorption capacity while reducing the harmful effects of impurities. The mixing of diatomaceous earth and asphalt is a simple physical process without any chemical reaction. Since the solubility parameters of atactic polypropylene and its copolymers are similar to those of the saturated and aromatic components in asphalt, they can spontaneously migrate to the region of concentrated lightweight oil adsorbed by diatomaceous earth in the molten state. Their long-chain molecules encapsulate potential wax crystal nuclei through entanglement, creating steric hindrance and inhibiting the orderly stacking of wax molecules through van der Waals forces, thereby effectively reducing the crystal nucleation rate and growth size.

[0044] In summary, the modified asphalt of this invention, through the synergistic design of materials and processes, simultaneously achieves multiple functions such as resistance to photo-oxidation, inhibition of reversible thermal aging, and improvement of low-temperature impact resistance and cold resistance, breaking through the performance bottleneck of traditional modified asphalt in cold-region applications. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments, but this does not limit the invention to the scope of the embodiments described. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0046] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0047] Example 1

[0048] A method for preparing modified bitumen with targeted regulation of wax crystallization includes the following steps:

[0049] Step 1, prepare the base bitumen;

[0050] The asphalt is placed in an oven and heated to a molten state at 110~140℃. Then it is poured into a high-speed shearing machine and stirred and mixed at 110~140℃ for 60~80 minutes to obtain homogenized base asphalt.

[0051] Step 2: Purify the diatomaceous earth to obtain purified diatomaceous earth;

[0052] Water washing method: Disperse the dried and crushed diatomaceous earth with water, soak it for 0.5 hours, stir for 0.5 hours, add water, and continue stirring for 0.5 hours to disperse the diatomaceous earth and obtain a slurry;

[0053] After stirring, the slurry is allowed to stand for 10 minutes. During this time, the denser minerals such as quartz and feldspar settle rapidly, while the less dense organic matter and clay remain suspended in the upper layer. The diatomaceous earth suspension in the middle is extracted, which is the first suspension. The bottom sediment and the top scum are discarded. The bottom sediment is added with water and stirred again, and the above sedimentation and separation operation is repeated to obtain the second suspension. All the first and second suspensions are combined and separated into solid and liquid by filtration or centrifugation. The obtained solid is dried at 60~100℃ to obtain the preliminarily purified diatomaceous earth.

[0054] Acid leaching method:

[0055] Under continuous stirring, sulfuric acid was added to the preliminarily purified diatomaceous earth and boiled for 4 hours to remove impurities from the diatomaceous earth. , Clay mineral impurities such as CaO and MgO react with acids to form soluble salts, which are then filtered, washed, and dried to obtain purified diatomaceous earth.

[0056] Step 3: Prepare blended modified atactic polypropylene;

[0057] Random polypropylene was placed in an oven and heated to a molten state at 140-160°C. Then it was poured into a high-speed shear mill, and a hindered amine light stabilizer was added as a protective agent for atactic polypropylene (aPP). The mixture was stirred and mixed at 140-160°C for 20-30 minutes. Random copolymer polypropylene (PP-R) was then incorporated to modify the atactic polypropylene (aPP). The mixture was stirred and mixed for 40-50 minutes to obtain blended modified atactic polypropylene.

[0058] Step 4: Prepare pre-modified asphalt;

[0059] Purified diatomaceous earth and matrix asphalt are sheared in a high-speed shear mill at 110~140℃ for 30~60 min to obtain pre-modified asphalt.

[0060] Step 5: Prepare modified asphalt;

[0061] Modified atactic polypropylene is added to pre-modified asphalt and mixed to obtain modified asphalt.

[0062] In the above steps, the shearing rate of the high-speed shearing machine is 4000~4500 r / min.

[0063] The modified bitumen comprises the following components in parts by weight: 100 parts bitumen, 8 parts purified diatomaceous earth, and 7.6 parts blended modified atactic polypropylene. The blended modified atactic polypropylene includes atactic polypropylene, hindered amine light stabilizer, and atactic copolymer polypropylene.

[0064] The composition includes 2 parts by weight of atactic polypropylene, 1.6 parts by weight of hindered amine light stabilizer, and 4 parts by weight of atactic copolymer polypropylene. The hindered amine light stabilizer is Tinuvin 622LD.

[0065] Example 2

[0066] Based on Example 1, the modified asphalt comprises the following components in parts by weight: 100 parts asphalt, 2 parts purified diatomaceous earth, and 3.6 parts blended modified atactic polypropylene. The blended modified atactic polypropylene includes atactic polypropylene, a hindered amine light stabilizer, and atactic copolymer polypropylene. The atactic polypropylene comprises 1 part by weight, the hindered amine light stabilizer comprises 0.6 parts by weight, and the atactic copolymer polypropylene comprises 2 parts by weight. The hindered amine light stabilizer is Tinuvin 622LD.

[0067] Example 3

[0068] Based on Example 1, the modified asphalt comprises the following components in parts by weight: 80 parts asphalt, 10 parts purified diatomaceous earth, and 9 parts blended modified atactic polypropylene. The blended modified atactic polypropylene includes atactic polypropylene, a hindered amine light stabilizer, and random copolymer polypropylene. The atactic polypropylene comprises 2.5 parts by weight, the hindered amine light stabilizer comprises 1.5 parts by weight, and the random copolymer polypropylene comprises 5 parts by weight. The hindered amine light stabilizer is Tinuvin 622LD.

[0069] Comparative Example 1

[0070] Based on Example 1, modified bitumen was obtained by using unpurified diatomaceous earth.

[0071] Comparative Example 2

[0072] Based on Example 1, no blended modified atactic polypropylene was prepared; instead, atactic polypropylene was used to replace the blended modified atactic polypropylene.

[0073] Comparative Example 3

[0074] Based on Example 1, in steps 4 and 5, purified diatomaceous earth, blended modified atactic polypropylene, and matrix asphalt are simultaneously sheared in a high-speed shear mill at 110~140℃ for 30~60 min to obtain modified asphalt.

[0075] Comparative Example 4

[0076] Based on Example 1, the modified asphalt comprises the following components in parts by weight: 80 parts asphalt, 10 parts purified diatomaceous earth, and 6 parts blended modified atactic polypropylene. The blended modified atactic polypropylene includes atactic polypropylene, a hindered amine light stabilizer, and atactic copolymer polypropylene. The atactic polypropylene comprises 1 part by weight, the hindered amine light stabilizer comprises 4 parts by weight, and the atactic copolymer polypropylene comprises 1 part by weight. The hindered amine light stabilizer is Tinuvin 622LD.

[0077] Comparative Example 5

[0078] Based on Example 1, the modified asphalt comprises the following components in parts by weight: 80 parts asphalt, 10 parts purified diatomaceous earth, and 6 parts blended modified atactic polypropylene. The blended modified atactic polypropylene includes atactic polypropylene, a hindered amine light stabilizer, and atactic copolymer polypropylene. The atactic polypropylene comprises 4 parts by weight, the hindered amine light stabilizer comprises 1 part by weight, and the atactic copolymer polypropylene comprises 1 part by weight. The hindered amine light stabilizer is Tinuvin 622LD.

[0079] Comparative Example 6

[0080] Based on Example 1, the blended modified atactic polypropylene was replaced with... Styrene-Butadiene-Styrene block copolymer (SBS).

[0081] Experimental Example 1

[0082] (1) The asphalt prepared in Examples 1-3 and Comparative Examples 1-6 was tested by extended bending beam rheological test.

[0083] Three qualified asphalt beam specimens were gently placed into a pre-prepared -18℃ external independent alcohol bath using tweezers, ensuring the specimens were completely submerged in the alcohol and that there was no contact between them to prevent heat transfer from affecting the hardening process. A timer was started to record the placement time of each of the three specimens, ensuring they underwent isothermal hardening treatment in the alcohol bath for 1 hour and 72 hours respectively. During the hardening process, the temperature of the alcohol bath was checked every 12 hours to ensure it remained consistently at a certain temperature. If temperature fluctuations occur within ±0.2℃, the temperature control system should be adjusted promptly. Simultaneously, check the alcohol level; if the level drops due to evaporation, add an appropriate amount. Use alcohol to ensure the sample is always submerged.

[0084] Once the sample has reached the set hardening time (1 hour or 72 hours), gently remove the sample with tweezers and quickly wipe the alcohol off the sample surface with a clean, soft cloth (the wiping process should be gentle to avoid damaging the sample). Then immediately transfer the sample to the corresponding bending beam rheometer bath to avoid prolonged exposure of the sample to air (exposure time should not exceed 30 seconds), which could cause temperature changes and affect the test results.

[0085] (2) The asphalt prepared in Examples 1-3 and Comparative Examples 1-6 was subjected to bending beam rheological testing.

[0086] Temperature testing: For asphalt beam samples that have undergone 1 hour of isothermal hardening, use tweezers to place them steadily on the pre-set temperature. On the support of the bending beam rheometer, ensure that the axis of the specimen is aligned with the center line of the support, and that the center line of the loading head coincides with the center line of the specimen, to avoid the specimen being displaced by force and generating additional bending moment.

[0087] Adjust the height of the loading head so that it gently contacts the upper surface of the sample, with the initial contact force controlled within 0.01N. Then, set the loading parameters in the instrument control system: constant load mode, loading force 100±5mN, loading time 60s, and data acquisition frequency 1 time / second.

[0088] The loading program is initiated, and the instrument automatically applies a constant load. Simultaneously, the displacement sensor records the deflection change of the specimen in real time during the 60-second loading process. The testing system automatically calculates and records the creep stiffness (S) and creep rate (m) at 60 seconds of loading. After the test is completed, the specimen's... The following test data.

[0089] Temperature test: Completed Immediately after the test, use tweezers to remove the sample from... Removed from the rheometer and quickly transferred to the pre-set... In another bending beam rheometer bath, the sample was placed stably on the support to ensure accurate positioning. Then, the timer was started to perform a 5-minute constant temperature curing of the sample, so that the sample temperature was consistent with the bath temperature. ) are completely consistent.

[0090] After the constant temperature curing is completed, follow the instructions in accordance with... The same loading parameters (constant load 100±5 mN, loading time 60 s, data acquisition frequency 1 time / second) were used to start the loading program. The creep stiffness (S) and creep rate (m) were recorded after 60 s of loading. The data of this specimen were saved. The following test data.

[0091] Following the steps described above, the remaining two 1-hour isothermal hardening asphalt beam samples were then subjected to the same conditions. Rheological testing was conducted on each specimen to ensure consistent testing procedures and complete data recording. The same steps were followed for 72-hour isothermal hardening asphalt beam specimens.

[0092] All test data were exported from the control systems of the two bending beam rheometers, including data for each specimen after 1 hour and 72 hours of hardening. and The loading time-deflection curve, creep stiffness (S), and creep rate (m) at 60 s loading were obtained. The exported data underwent preliminary screening to remove obviously abnormal data. Linear interpolation was used to calculate the temperatures at which the asphalt reached the critical stiffness (300 MPa) and critical m value (0.3), which are considered the asphalt's ultimate low-temperature performance grade. For safety, the larger of the two values ​​was taken as the ultimate low-temperature performance grade of the asphalt. The ultimate low-temperature performance grades of the asphalt samples after 1 h and 72 h of isothermal hardening were calculated, and the difference between the two is the low-temperature grading loss. This value reflects the degree of attenuation of the asphalt's low-temperature performance during long-term low-temperature hardening; the larger the value, the more obvious the physical hardening effect of the asphalt and the more significant the decrease in low-temperature crack resistance.

[0093] The test results are shown in Table 1:

[0094] Table 1

[0095]

[0096] Experimental results show that the modified asphalt prepared in Examples 1-3 of this invention can achieve an extreme low temperature rating of up to [missing information]. to Low-temperature grading loss is only Significantly better than comparative examples 1-6 ( to ,loss Comparative Example 3 has the same chemical composition as Example 1, but due to the use of a one-step doping method, its low-temperature fractionation loss (1.9°C) is nearly twice as high as that of Example 1 (1.0°C); although Comparative Example 6 has good elasticity, its low-temperature fractionation loss is still as high as 4.0°C, which is far inferior to that of the present invention.

[0097] Domestically produced road petroleum asphalt generally contains 3% to 7% n-alkanes, i.e., "wax". When the ambient temperature drops to the wax precipitation point (usually...),... When the temperature is below a certain level, these long-chain alkanes will self-assemble through van der Waals forces to form needle-like or plate-like crystals. This process has the following characteristics: wax crystals act as rigid fillers, significantly increasing the stiffness (S value) of asphalt while reducing the stress relaxation ability (m value decreases); when the temperature rises, the wax crystals partially melt, but due to the change in recrystallization orientation, they cannot restore the original colloidal structure; repeated freeze-thaw cycles cause microcracks to initiate and propagate at the tips of the wax crystals, eventually leading to macroscopic cracking.

[0098] Therefore, low-temperature fractionation loss is essentially a quantitative indicator of the degree of physical aging caused by wax crystallization-melting cycles. The larger the loss value, the weaker the system's control over wax behavior.

[0099] After water washing and acid leaching purification, diatomaceous earth , Once the impurities are effectively removed, The content is significantly increased, and its specific surface area can typically reach [amount missing]. (Measured according to GB / T 19587), the surface is rich in silanol groups (≡Si–OH). These hydroxyl groups can be selectively adsorbed through hydrogen bonding and van der Waals forces. Light oils serve as the solvent environment during wax precipitation. Once adsorbed, the free migration ability of wax molecules decreases, the supersaturation of the system decreases, and the nucleation rate slows down significantly.

[0100] The flexible segments of the random copolymer polypropylene can insert into the leading edge of the growing wax crystals, hindering the orderly stacking of molecular chains and transforming the crystals from brittle needle-like structures into tough, spherical microcrystals (particle size <1 μm). These microcrystals are less prone to stress concentration and are easier to melt and recover upon heating. Comparative Example 2, lacking a flexible phase, experienced a low-temperature fractionation loss of 5.2°C; while Example 1 (containing 4 parts of random copolymer polypropylene) only suffered a loss of 1.0°C.

[0101] In Comparative Example 3, diatomaceous earth, blended modified atactic polypropylene, and asphalt were subjected to a one-step high-speed shearing process. The diatomaceous earth particles were rapidly encapsulated by the viscous asphalt, and the surface active sites were shielded. At the same time, the blended modified atactic polypropylene melt was easily pinned by diatomaceous earth, forming agglomerates, which could not effectively migrate to the wax crystal interface.

[0102] This invention employs a method of first preparing pre-modified bitumen to fully wet diatomaceous earth and expose adsorption sites; then, blended modified atactic polypropylene is added, causing it to preferentially accumulate at the diatomaceous earth-bitumen interface, forming a composite structure. This structure combines the adsorption capacity to capture wax precursors with the interference capacity to block crystal growth, enabling targeted wax inhibition.

[0103] While Comparative Example 6 improved the elasticity of asphalt, its styrene-butadiene block did not specifically interact with wax molecules, failing to prevent wax precipitation and recrystallization. During 72 hours of isothermal hardening, wax crystals continued to grow and pierce the SBS network, leading to irreversible accumulation of stiffness, resulting in a low-temperature grading loss as high as 4.0℃. In contrast, this invention does not rely on mechanical reinforcement but directly regulates the wax phase transformation behavior, eliminating the physical hardening inducing factors at the source. Therefore, even after prolonged low-temperature treatment, the system maintains a high creep rate (m > 0.298) with minimal grading loss.

[0104] Therefore, as can be seen from the data in Table 1, the present invention achieves fundamental inhibition of the reversible thermal aging of high-wax asphalt.

[0105] Experimental Example 2

[0106] Residual ductility (15℃, cm) test method

[0107] (1) Short-term aging simulation (RTFOT)

[0108] Samples from Experimental Examples 1-3 and Comparative Examples 1-6 were injected into clean sample bottles; the sample bottles were placed in a rotating thin-film oven, with the temperature set at 163 ± 1℃, the rotation speed at 5 ± 1 r / min, and the air flow rate at 4.0 ± 0.2 L / min; the oven was heated at a constant temperature for 85 ± 1 min; after removal, the sample was immediately poured into an aluminum pan and cooled to room temperature to obtain short-term aged asphalt.

[0109] (2) Long-term aging simulation (PAV)

[0110] Take about 50 g of aged asphalt and inject it into a stainless steel PAV sample dish; place it in a pressure aging vessel (PAV), set the temperature to 100 ± 1℃ and the pressure to 2.10 ± 0.05 MPa, and introduce compressed air; continue aging for 20 ± 0.1 h; remove and cool to room temperature to obtain double-aged (RTFOT+PAV) asphalt.

[0111] (3) Ductility measurement

[0112] Heat the double-aged asphalt to a fluid state (approximately 150°C). The sample was poured into an "8"-shaped ductility mold; after cooling at room temperature for 30 min, it was placed in a water bath at 15 ± 0.1℃ for 90 min; it was then installed in a ductility tester and stretched at a speed of 5 ± 0.25 cm / min; the elongation length at fracture was recorded as the residual ductility (unit: cm); three samples were tested in parallel, and the average value was taken as the final result.

[0113] Storage stability ( Test methods

[0114] (1) Sample preparation

[0115] Heat the samples from Experimental Examples 1-3 and Comparative Examples 1-6 to the construction temperature (usually 160–170℃) and stir until homogeneous; pour into a clean aluminum tube (inner diameter 25 ± 0.5 mm, height 140 ± 5 mm), with the liquid level about 20 mm from the tube opening; seal the tube opening tightly with aluminum foil or a sealing cap to prevent evaporation.

[0116] (2) High temperature storage

[0117] Place the aluminum tube vertically in an oven at 163 ± 1℃ for 48 ± 0.5 h; do not shake or tilt it during this period to ensure that gravity settling occurs naturally.

[0118] (3) Determination of softening point and calculate

[0119] After storage, the aluminum tube was quickly removed and cooled to room temperature; asphalt samples were then cut from the top 1 / 3 and bottom 1 / 3 sections respectively.

[0120] The softening points of the top and bottom samples were determined separately according to GB / T 4507—2014 (or JTG E20 T 0606) using the ring and ball method, and recorded as follows: and Calculate the segregation value , ;

[0121] like The modified asphalt was deemed to have satisfactory storage stability and good compatibility with the polymer.

[0122] like This indicates significant segregation, and the product may become ineffective during high-temperature storage or transportation.

[0123] The obtained data is shown in Table 2;

[0124] Table 2

[0125]

[0126] As shown in Table 2, the residual elongation of Comparative Example 2 was only 9.5 cm, while that of Example 1 reached 18.6 cm. Atactic polypropylene (aPP) is highly susceptible to thermo-oxidative degradation during the 163°C RTFOT and 100°C PAV processes, generating alkyl radicals. This triggers an oxidation chain reaction in the aromatic hydrocarbons and resins in asphalt, leading to molecular chain breakage or cross-linking, and making the system brittle. Tinuvin 622LD, however, is a high-molecular-weight hindered amine light stabilizer (HALS) that continuously captures alkoxy radicals in a thermo-oxidative environment through the Denisov cycle—a catalytic cycle of hindered amine, nitryl radical, and regenerated hindered amine. This effectively interrupts the oxidation chain reaction, protecting aPP and asphalt components from degradation and maintaining high ductility.

[0127] Comparative Example 4, although its storage stability was poor due to insufficient PP-R ( However, its high content of Tinuvin 622LD significantly inhibited thermo-oxidative degradation, so the residual elongation (16.2 cm) was still better than that of comparative examples 2 and 5. However, its low-temperature grading loss was as high as 4.8℃ (see Table 1), indicating that anti-oxidation alone cannot solve the physical aging caused by wax crystallization, further proving the wax inhibition and anti-oxidation effects of the present invention.

[0128] Comparative Example 5 showed an elongation of only 10.8 cm, while Example 1 achieved 18.6 cm. The introduction of ethylene units in the random copolymer polypropylene (PP-R) disrupted the regularity of the polypropylene (PP) backbone, leading to reduced crystallinity and a lower glass transition temperature (Tg). Below. In the ductility test at 15℃, random copolymer polypropylene (PP-R) remained in a highly elastic state, serving as a "flexible bridge" to connect asphalt micro-regions, absorbing tensile energy and delaying fracture. Meanwhile, atactic polypropylene (aPP) approached its Tg at 15℃. It has a high modulus and poor ductility. Therefore, the proportion of random copolymer polypropylene (PP-R) in the blend system directly determines the toughness reserve of the system after aging.

[0129] Comparative Example 1 had a ductility of 12.3 cm, lower than Example 1 (18.6 cm). The original diatomaceous earth sample... , Transition metal ions are strong oxidizing catalysts that accelerate the free radical reactions in the PAV stage, leading to the conversion of more resins into asphaltenes and system hardening. Purification removes these catalytic sites, reducing the oxidation rate and helping to retain more ductile components.

[0130] Comparative Example 3 Unqualified, while Example 1 Qualified. In the single-step high-speed shearing process, the surface of diatomaceous earth particles is rapidly coated with high-viscosity asphalt, forming an "asphalt shell" that hinders their contact with the blended modified atactic polypropylene. Simultaneously, the molten blended modified atactic polypropylene, due to its lower density than asphalt, tends to float, while the diatomaceous earth sinks, resulting in bidirectional segregation. In the segmented process, however, diatomaceous earth first forms a stable suspension with asphalt, and then polypropylene is added, causing the blended modified atactic polypropylene to preferentially adsorb onto the diatomaceous earth surface, forming composite particles. These particles have a density close to that of asphalt, and their surface is wetted by asphalt, significantly improving their thermodynamic stability. Significantly reduced.

[0131] Comparative examples 4 and 5 With a temperature range as high as 3.8~3.9℃, random copolymer polypropylene (PP-R) not only provides flexibility, but its long-chain structure can also entangle asphalt macromolecules, enhancing interfacial bonding. If the amount of random copolymer polypropylene (PP-R) is insufficient (e.g., only 1 part in Comparative Example 5), the atactic polypropylene (aPP) has poor compatibility with asphalt, easily forming an independent phase. Under gravity, it settles rapidly, leading to an increase in the softening point at the bottom and a decrease at the top. Increase.

[0132] Comparative Example 6 However, the ductility is lower than that of Example 1. Styrene-butadiene-styrene block copolymer (SBS) itself has excellent compatibility with asphalt, and the styrene blocks interact strongly with asphaltene, thus ensuring storage stability. However, it cannot suppress physical aging caused by wax. In the low-temperature ductility test after PAV, wax crystals still induce microcracks, limiting elongation. This invention, by inhibiting wax, fundamentally reduces internal defect sources, thus achieving higher ductility.

[0133] Therefore, this invention successfully constructed a modified asphalt system that does not separate during high-temperature storage and remains flexible after long-term aging by blending modified random polypropylene, purifying diatomaceous earth, and adopting a staged blending process.

[0134] The above description is merely some specific embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing modified asphalt with targeted regulation of wax crystallization, characterized in that, Includes the following steps: Preparation of matrix bitumen; The diatomaceous earth was purified to obtain purified diatomaceous earth. Random polypropylene was placed in an oven and heated to a molten state at 140~160℃. Then it was poured into a high-speed shearing machine and a hindered amine light stabilizer was added. After shearing evenly, random copolymer polypropylene was added and sheared evenly to obtain blended modified random polypropylene. Purified diatomaceous earth and base asphalt are sheared and mixed in a high-speed shearing machine. After uniform stirring, pre-modified asphalt is obtained. Modified atactic polypropylene is added to pre-modified asphalt and mixed to obtain modified asphalt.

2. The method for preparing modified asphalt with targeted regulation of wax crystallization according to claim 1, characterized in that, The purification process for diatomaceous earth specifically includes: The dried and crushed diatomaceous earth was dispersed in water, soaked, and then stirred. Water was then added, and stirring was continued for 0.5 hours to disperse the diatomaceous earth and obtain a slurry. Let the slurry stand for 10 minutes, then extract the upper first suspension and separate the sediment. Wash the sediment with water, take the upper second suspension, and separate the first and second suspensions into solid and liquid components. Dry the solid at 60~100℃ to obtain preliminarily purified diatomaceous earth. Sulfuric acid was added to the pre-purified diatomaceous earth under continuous stirring. After boiling, the mixture was filtered, washed, and dried to obtain purified diatomaceous earth.

3. The method for preparing modified asphalt with targeted regulation of wax crystallization according to claim 1, characterized in that, Purified diatomaceous earth and matrix asphalt are sheared in a high-speed shear mill at 110~140℃ for 30~60 min to obtain pre-modified asphalt.

4. The method for preparing modified asphalt with targeted regulation of wax crystallization according to claim 1, characterized in that, Random polypropylene was placed in an oven and heated to a molten state at 140-160°C. Then it was poured into a high-speed shearing machine, and a hindered amine light stabilizer was added. The mixture was stirred and mixed at 140-160°C for 20-30 minutes. Random copolymer polypropylene was then incorporated and stirred and mixed for 40-50 minutes to obtain blended modified random polypropylene.

5. The method for preparing modified asphalt with targeted regulation of wax crystallization according to claim 1, characterized in that, The shearing rate of the high-speed shearing machine is 4000~4500 r / min.

6. The method for preparing modified asphalt with targeted regulation of wax crystallization according to claim 1, characterized in that, The base bitumen includes the following steps: The asphalt is placed in an oven and heated to a molten state at 110~140℃. Then it is poured into a high-speed shearing machine and stirred and mixed at 110~140℃ for 60~80 minutes to obtain the base asphalt.

7. Modified asphalt prepared by any one of the preparation methods according to claims 1-6.

8. The modified asphalt with targeted regulation of wax crystallization according to claim 7, characterized in that, Modified bitumen comprises the following components in parts by weight: 80-120 parts bitumen, 2-10 parts purified diatomaceous earth, and 2-10 parts blended modified atactic polypropylene. The blended modified atactic polypropylene includes atactic polypropylene, hindered amine light stabilizer, and atactic copolymer polypropylene.

9. The modified asphalt with targeted regulation of wax crystallization according to claim 8, characterized in that, The weight ratio of random polypropylene, hindered amine light stabilizer and random copolymer polypropylene is 1:0.6~0.8:2~4.

10. The modified asphalt with targeted regulation of wax crystallization according to claim 8, characterized in that, The hindered amine light stabilizer is Tinuvin 622LD.

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