A method for preparing asphalt warm mix agent by using mixed industrial by-product gypsum

Abstract

The present application relates to the technical field of asphalt warm-mixing agent, and particularly discloses a method for preparing asphalt warm-mixing agent by using mixed industrial by-product gypsum, which aims to provide a new phosphogypsum treatment method, and remove harmful impurities to prepare calcium sulfate dihydrate whiskers with high purity and high aspect ratio. The present application uses industrial solid waste phosphogypsum as raw material, and through screening and impurity removal, constant-temperature acidification modification, hot filtration and impurity removal, controlled cooling and crystallization, water washing and purification, secondary filtration and low-temperature drying process, and in combination with a specific amount of crystal form control agent, high-purity and high-aspect-ratio calcium sulfate dihydrate whisker type asphalt warm-mixing agent is prepared. The present application optimizes core processes such as solid-liquid ratio, stirring parameters and crystallization conditions, strictly controls the performance index of the finished product, and solves the problems of high cost and poor stability of traditional warm-mixing agents.

Description

Technical Field

[0001] This application relates to the field of asphalt warm mix additive technology, and specifically discloses a method for preparing asphalt warm mix additive using mixed industrial by-product gypsum. Background Technology

[0002] Warm-mix asphalt, as a green road construction technology, can complete the mixing and compaction process of asphalt mixtures at lower temperatures, offering significant energy savings and emission reduction compared to traditional hot-mix asphalt. This technology reduces the viscosity, surface energy, or coefficient of friction of the asphalt, making it easier for aggregates to be coated with asphalt, thus achieving good workability at lower temperatures. Warm-mix technology not only reduces emissions of pollutants such as carbon dioxide and nitrogen oxides but also improves the working environment and personnel health conditions at construction sites, extends construction time, and enhances compaction effectiveness. Therefore, it is widely recognized as an important means of promoting green and low-carbon highway construction.

[0003] Warm-mix asphalt technology, as a new green construction technology to replace traditional hot-mix asphalt, can reduce the mixing and compaction temperature of asphalt mixtures by 20-40℃, completing the entire construction process under low-temperature conditions. This solves the energy consumption and pollution problems of traditional hot-mix technology from the source. The core principle of this technology is to reduce asphalt viscosity, optimize aggregate interfacial bonding performance, and reduce internal frictional resistance of the mixture through physical modification and chemical doping. This allows the asphalt to fully coat the aggregates at low temperatures, ensuring excellent workability and compaction performance of the mixture. Compared with traditional hot-mix asphalt, warm-mix asphalt technology can reduce construction energy consumption by 20%-50%, significantly reducing greenhouse gas and harmful exhaust emissions. At the same time, low-temperature construction can effectively inhibit asphalt thermal aging, improve the fatigue and aging resistance of asphalt pavements, and extend the service life of roads. In addition, the low-temperature construction mode can avoid the hidden dangers of construction in the high-temperature season, extend the effective construction period throughout the year, improve the working environment at the construction site, and reduce the harm of harmful gases to the health of construction workers. With multiple environmental protection, energy saving and engineering advantages, this technology has become the core technical means to achieve low-carbon emission reduction and green construction in the highway construction field, and has been included in the key technology system for promoting green construction in the transportation industry.

[0004] Currently, mainstream warm-mix asphalt (WM) technologies are mainly divided into three categories: mechanical foaming, organic viscosity reducing, and surfactant additives. However, each type of technology has significant application shortcomings, with high cost and insufficient cost-effectiveness being the core bottlenecks restricting its widespread adoption. Mechanical foaming WM technologies require specialized equipment for water storage, air supply, and foam control, resulting in high initial investment costs for equipment modification and purchase, and complex equipment operation and maintenance processes, making it difficult for small and medium-sized construction companies to adopt them. Organic and chemically active commercial WM additives have complex preparation processes, scarce raw materials, and high market prices, significantly increasing the overall cost of road construction in engineering applications. The energy-saving and consumption-reducing economic benefits of WM technologies are limited and cannot offset the additional costs of additives and equipment. Furthermore, existing commercial WM additives generally suffer from poor storage stability, weak low-temperature adaptability, and rapid performance degradation over long-term service. Some additives can also affect the high and low temperature road performance of asphalt mixtures, making it difficult to simultaneously meet the engineering requirements of low cost, high stability, and superior performance. Therefore, developing new low-cost, high-performance, and environmentally friendly WM additives is crucial to breaking through the bottlenecks in the promotion of WM asphalt technology and driving the industrialization of green road construction technologies.

[0006] The core component of phosphogypsum is calcium sulfate dihydrate, which naturally contains abundant water of crystallization, possessing physical properties of reducing viscosity and lubrication, thus meeting the functional requirements of warm-mix asphalt additives and exhibiting excellent potential for warm-mix applications. However, the residual free phosphorus, soluble fluorine, organic impurities, and insoluble impurities in raw phosphogypsum can severely affect the purity and performance stability of the material. Directly adding it to asphalt mixtures can easily lead to problems such as uneven dispersion, poor compatibility, and large performance fluctuations. This not only fails to guarantee the warm-mix effect but may also degrade the road performance of asphalt pavements, greatly limiting its direct application in road engineering. By treating phosphogypsum through acidification dissolution, purification, and recrystallization modification processes, harmful impurities can be effectively removed, and high-purity, high aspect ratio calcium sulfate dihydrate whiskers can be prepared. The modified phosphogypsum whiskers have multiple functions, including lubrication and viscosity reduction, interface enhancement, and filling modification, making them suitable for the construction conditions and performance requirements of warm-mix asphalt.

[0007] Applying modified phosphogypsum whiskers as a novel green warm-mix asphalt additive to road engineering can, on the one hand, replace expensive commercial chemical warm-mix agents, significantly reducing the engineering application cost of warm-mix asphalt technology and breaking through the cost barrier for industry technology promotion; on the other hand, it can realize the high-value resource utilization of industrial solid waste phosphogypsum, solving the ecological and environmental pollution problems caused by phosphogypsum stockpiling, and achieving "treating waste with waste and turning waste into treasure." This research direction perfectly aligns with the dual national strategies of green and low-carbon transformation of transportation infrastructure and resource utilization of industrial solid waste, and has significant theoretical value and engineering practical significance for promoting the large-scale popularization of warm-mix asphalt technology, improving the green road construction material system, and achieving sustainable development of road engineering.

[0008] In view of this, the inventors propose a method for preparing asphalt warm mix additives using mixed industrial by-product gypsum, in order to solve the above problems. Summary of the Invention

[0009] The purpose of this invention is to propose a new method for treating phosphogypsum, which aims to remove harmful impurities and prepare high-purity calcium sulfate dihydrate whiskers with a high aspect ratio.

[0010] To achieve the above objectives, the present invention provides the following basic solution: A method for preparing asphalt warm mix additive using mixed industrial by-product gypsum includes the following steps: S1: Select phosphogypsum from mixed industrial by-product gypsum as the raw material, and screen the phosphogypsum raw material to remove large particle impurities and obtain refined phosphogypsum raw material with uniform particle size. S2: Add hydrochloric acid solution to the reaction beaker, place the beaker in a heat-insulating jacket for constant temperature heating, and add the sieved phosphogypsum raw material and crystal control agent under continuous stirring to carry out acidification modification reaction; through the acidification reaction, the calcium sulfate dihydrate in the phosphogypsum is fully dissolved, and at the same time, the solid impurities such as phosphorus, fluorine and organic impurities contained in the raw material are converted into soluble salts and uniformly dispersed in the reaction system; S3: After the acidification reaction is completely finished, the suspension of the reaction system is subjected to hot filtration to effectively separate the insoluble solid impurities in the system, remove the undissolved inert impurities, and obtain a clear and pure acidified hot filtrate. S4: The prepared acidified hot filtrate is placed in a room temperature environment for natural cooling and crystallization treatment, so that the calcium sulfate dihydrate component dissolved in the filtrate undergoes recrystallization. After crystallization, the mixed system is filtered to obtain a crude crystalline substance containing trace amounts of soluble salt impurities. S5: Use distilled water as a cleaning agent to thoroughly wash the obtained coarse crystals, and continuously stir to dissolve them, so that the soluble salt impurities on the surface and inside of the coarse crystals are completely dissolved and removed. S6: After the solid-liquid mixture is washed, it is filtered to completely remove the salt impurities and waste liquid dissolved in the water, and obtain a high-purity calcium sulfate dihydrate whisker solid product. S7: The purified calcium sulfate dihydrate whiskers are placed in a constant temperature drying equipment for low-temperature drying to completely remove the free moisture on the surface of the product, and finally the modified phosphogypsum asphalt warm mix agent is obtained.

[0011] Furthermore, the chemical composition of the phosphogypsum raw material includes: 85%–90% CaSO4·2H2O, 5%–10% SiO2, 1%–1.5% F, 0.5%–2.3% P2O5, 0.1%–0.8% Al2O3, 0.03%–0.2% Fe2O3, 0.05%–0.35% K2O, 0.08%–0.2% Na2O, 0.01%–0.2% TiO2, and 0.02%–0.15% MgO.

[0012] Furthermore, the screening process uses a square-hole sieve with a aperture of 200 mesh.

[0013] Furthermore, the acidification reaction temperature is controlled at 70–90°C, the mass fraction of hydrochloric acid is 12%–20%, the stirring time is 10–30 min, and the stirring speed is controlled at 300–600 r / min; the solid-liquid ratio of phosphogypsum raw material to hydrochloric acid solution is 1:4 g / mL to 1:8 g / mL, and the temperature control adopts a corrosion-resistant thermometer and the temperature measuring wire adopts a thermocouple wire resistant to strong acids and alkalis.

[0014] Furthermore, the amount of crystal form control agent added in step S2 is 1.5% to 4.5% of the dry weight of the phosphogypsum raw material, and the crystal form control agent includes any one of calcium chloride dihydrate, copper chloride dihydrate, magnesium chloride hexahydrate, dodecyltrimethylammonium bromide, and ethylenediaminetetraacetic acid.

[0015] Furthermore, in step S3, the hot filtration process requires the installation of a buffer bottle between the filtration flask and the vacuum pump of the filtration device to block acidic vapors and waste liquid.

[0016] Furthermore, in step S4, the cooling crystallization process parameters are as follows: the cooling rate of the acidified hot filtrate is controlled at 2-5℃ / min, and the time for static crystallization at room temperature is 2-4h. In step S5, the water washing process parameters are as follows: distilled water with a mass of 3-5 times that of the coarse crystal material is used for water washing, and the continuous stirring water washing time is 10-20min.

[0017] Furthermore, in step S7, the drying process is completed using a constant temperature forced-air drying oven, with the drying temperature strictly controlled below 60°C, removing only the free water on the surface of the product while completely preserving the crystalline water structure of calcium sulfate dihydrate.

[0018] Furthermore, the performance indicators of the modified phosphogypsum asphalt warm mix agent obtained through steps S1 to S7 meet the following indicators: calcium sulfate dihydrate whisker purity ≥99%, free water mass fraction ≤1%, whisker aspect ratio ≥55. When any one of the calcium sulfate dihydrate whisker purity, free water mass fraction, or whisker aspect ratio fails to meet the standard, the temperature, hydrochloric acid mass fraction, and stirring time in the acidification reaction are readjusted, and the indicators of temperature, hydrochloric acid mass fraction, and stirring time in the acidification reaction are gradually increased.

[0019] A modified phosphogypsum asphalt warm mix agent prepared by this method can improve the workability of asphalt mixtures and reduce the construction temperature by 20℃-22℃.

[0020] The principle and effect of this solution are as follows: 1. Compared with existing technologies, this invention uses phosphogypsum, a bulk industrial solid waste, as the core raw material to replace traditional high-priced chemically synthesized warm mix agents, significantly reducing the preparation and engineering application costs of warm mix asphalt modification materials. It breaks through the cost barrier for the promotion of existing warm mix technology and is conducive to the large-scale popularization of warm mix asphalt technology.

[0021] 2. Compared with existing technologies, this invention uses phosphogypsum, a bulk industrial solid waste, as the core raw material to replace traditional high-priced chemically synthesized warm mix agents, significantly reducing the preparation and engineering application costs of warm mix asphalt modification materials. It breaks through the cost barrier for the promotion of existing warm mix technology and facilitates the large-scale popularization of warm mix asphalt technology.

[0022] 3. This invention uses industrial solid waste phosphogypsum as raw material, and through screening for impurity removal, constant-temperature acidification modification, hot filtration for impurity removal, controlled-rate cooling crystallization, water washing purification, secondary filtration, and low-temperature drying processes, combined with a specific amount of crystal form control agent, prepares a high-purity, high aspect ratio calcium sulfate dihydrate whisker-type warm mix asphalt. This invention optimizes core processes such as solid-liquid ratio, mixing parameters, and crystallization conditions, and strictly controls the performance indicators of the finished product, solving the problems of high cost and poor stability of traditional warm mix asphalt. This warm mix asphalt can significantly improve the workability of asphalt mixtures, reduce the construction temperature by 20-22℃, realize the high-value utilization of phosphogypsum solid waste, take into account both engineering and ecological benefits, and meet the needs of green and low-carbon road construction. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1This illustration shows an XRF analysis diagram of the asphalt warm mix agent in a method for preparing asphalt warm mix agent using mixed industrial by-product gypsum according to an embodiment of this application. Figure 2 This paper shows an SEM image of the phosphogypsum warm mix agent in Example 1 of a method for preparing asphalt warm mix agent using mixed industrial by-product gypsum proposed in this application. Figure 3 This paper shows an SEM image of the phosphogypsum warm mix agent in Example 2 of a method for preparing asphalt warm mix agent using mixed industrial by-product gypsum proposed in this application. Figure 4 This paper shows an SEM image of the phosphogypsum warm mix agent in Example 3 of a method for preparing asphalt warm mix agent using mixed industrial by-product gypsum proposed in this application. Figure 5 This paper shows an SEM image of the phosphogypsum warm mix agent in Example 4 of a method for preparing asphalt warm mix agent using mixed industrial by-product gypsum proposed in this application. Figure 6 This paper shows an SEM image of the phosphogypsum warm mix agent in Example 5 of a method for preparing asphalt warm mix agent using mixed industrial by-product gypsum proposed in this application. Detailed Implementation

[0025] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0026] A method for preparing asphalt warm mix additives using mixed industrial by-product gypsum, such as Figures 1-6 As shown, it includes the following steps: S1: Select phosphogypsum from mixed industrial by-product gypsum as the raw material. Perform sieving on the phosphogypsum raw material to remove large particle impurities and obtain refined phosphogypsum raw material with uniform particle size. The sieving process is performed using a square hole sieve with a pore size of 200 mesh.

[0027] Specifically, the chemical composition of phosphogypsum raw materials includes: CaSO4·2H2O content 85%–90%, SiO2 content 5%–10%, F content 1%–1.5%, P2O5 content 0.5%–2.3%, Al2O3 content 0.1%–0.8%, Fe2O3 content 0.03%–0.2%, K2O content 0.05%–0.35%, Na2O content 0.08%–0.2%, TiO2 content 0.01%–0.2%, and MgO content 0.02%–0.15%.

[0028] S2: Add hydrochloric acid solution to the reaction beaker, place the beaker in a heat-insulating jacket for constant temperature heating, and add the sieved phosphogypsum raw material and crystal control agent under continuous stirring to carry out acidification modification reaction; through the acidification reaction, the calcium sulfate dihydrate in the phosphogypsum is fully dissolved, and at the same time, the solid impurities such as phosphorus, fluorine and organic impurities contained in the raw material are converted into soluble salts and uniformly dispersed in the reaction system.

[0029] Specifically: the acidification reaction temperature is controlled at 70-90℃, the mass fraction of hydrochloric acid is 12%-20%, the stirring time is 10-30 min, and the stirring speed is controlled at 300-600 r / min; the solid-liquid ratio of phosphogypsum raw material to hydrochloric acid solution is 1:4 g / mL to 1:8 g / mL; the temperature control adopts a corrosion-resistant thermometer, and the temperature measuring wire adopts a thermocouple wire resistant to strong acids and alkalis.

[0030] In step S2, the amount of crystal form control agent added is 1.5% to 4.5% of the dry weight of phosphogypsum raw material, and the crystal form control agent includes any one of calcium chloride dihydrate, copper chloride dihydrate, magnesium chloride hexahydrate, dodecyltrimethylammonium bromide, and ethylenediaminetetraacetic acid.

[0031] S3: After the acidification reaction is complete, the suspension of the reaction system is subjected to hot filtration to effectively separate the insoluble solid impurities in the system, remove the undissolved inert impurities, and obtain a clear and pure acidified hot filtrate.

[0032] In step S3, the hot filtration process requires a buffer bottle to be installed between the filtration flask and the vacuum pump of the filtration device to block acidic vapors and waste liquid.

[0033] S4: The prepared acidified hot filtrate is placed in a normal temperature environment for natural cooling and crystallization treatment, so that the calcium sulfate dihydrate component dissolved in the filtrate undergoes recrystallization. After crystallization, the mixed system is filtered to obtain a crude crystalline substance containing trace amounts of soluble salt impurities.

[0034] In step S4, the cooling crystallization process parameters are as follows: the cooling rate of the acidified hot filtrate is controlled at 2-5℃ / min, and the static crystallization holding time at room temperature is 2-4h. In step S5, the water washing process parameters are as follows: distilled water with a mass of 3-5 times that of the crude crystal material is used for water washing, and the continuous stirring water washing time is 10-20min.

[0035] S5: Use distilled water as a cleaning agent to thoroughly wash the obtained coarse crystals, and continuously stir to dissolve them, so that the soluble salt impurities on the surface and inside of the coarse crystals are completely dissolved and removed. S6: After the solid-liquid mixture is washed, it is filtered to completely remove the salt impurities and waste liquid dissolved in the water, and obtain a high-purity calcium sulfate dihydrate whisker solid product. S7: The purified calcium sulfate dihydrate whiskers are placed in a constant temperature drying equipment for low-temperature drying to completely remove the free moisture on the surface of the product, and finally the modified phosphogypsum asphalt warm mix agent is obtained.

[0036] Specifically: In step S7, the drying process is completed using a constant temperature forced-air drying oven, with the drying temperature strictly controlled below 60°C, removing only the free water on the surface of the product while completely preserving the crystalline water structure of calcium sulfate dihydrate.

[0037] The performance indicators of the modified phosphogypsum asphalt warm mix agent obtained through steps S1 to S7 meet the following indicators: calcium sulfate dihydrate whisker purity ≥99%, free water mass fraction ≤1%, whisker aspect ratio ≥55. When any of the calcium sulfate dihydrate whisker purity, free water mass fraction, or whisker aspect ratio fails to meet the standard, the temperature, hydrochloric acid mass fraction, and stirring time in the acidification reaction are readjusted, and the indicators of temperature, hydrochloric acid mass fraction, and stirring time in the acidification reaction are gradually increased.

[0038] A modified phosphogypsum asphalt warm mix agent prepared by this method can improve the workability of asphalt mixtures and reduce the construction temperature by 20℃-22℃.

[0039] Example 1: Phospholipid gypsum, a byproduct of phosphate chemical production, was used as raw material. After drying in a drying oven, the dried phospholipid gypsum was sieved through a 0.075mm square-hole sieve to remove larger particles and impurities, obtaining phospholipid gypsum powder with uniform particle size. 500mL of a 12% hydrochloric acid solution was placed in a 1L acid-resistant glass beaker, which was then placed in an insulated jacket and heated to 90℃ and maintained at a constant temperature. The temperature was monitored using an acid- and alkali-resistant probe thermometer. Under magnetic stirring, 100g of phospholipid gypsum was slowly added, and the mixture was stirred for 30 minutes to allow the calcium sulfate dihydrate to fully dissolve and impurities to be converted into soluble salts.

[0040] After the reaction is complete, hot filtration is performed immediately. A buffer bottle is placed between the vacuum pump and the filtration flask in the filtration system to prevent acidic solution from being drawn into the vacuum pump. After filtration, a clear, acidified hot filtrate is obtained.

[0041] The acidified hot filtrate was allowed to cool to room temperature (approximately 25°C), resulting in the precipitation of a large amount of white crystals. The crystals were collected by suction filtration to obtain a crude crystalline product. This crude crystalline product was slightly yellow and mainly composed of calcium sulfate dihydrate and a small amount of salt impurities.

[0042] Add distilled water at a volume three times the mass of the crystals and stir magnetically for 15 minutes to fully dissolve soluble salt impurities. Filter again to obtain purified crystals. Place the purified crystals in a constant temperature forced-air drying oven and dry at 59°C for 24 hours to remove free water, obtaining white, fine needle-like calcium sulfate dihydrate whiskers, which is the finished product of the phosphogypsum warm mix agent.

[0043] XRF analysis and SEM images of the phosphogypsum warm mix agent obtained in this embodiment are as follows: Figure 1 and Figure 2 As shown, the main crystalline phase of the product is calcium sulfate dihydrate, with a purity of 99.22%; the whisker aspect ratio is approximately 58; the free water mass fraction is 0.73%, and the product is a white filamentous powder. The prepared phosphogypsum warm mix agent was added to AC-13 type asphalt mixture at 0.3% of the asphalt mass, and standard specimens were formed with a designed porosity of 4% for Marshall test, rutting test, and four-point bending fatigue test.

[0044] Example 2: Following the steps of Example 1, the hydrochloric acid mass fraction was adjusted to 20%, the reaction temperature was controlled within the range of 80℃, and the stirring time was 20 min. The XRF analysis and SEM images of the phosphogypsum warm-mixing agent obtained in this example are shown below. Figure 1 and Figure 3 As shown, the main crystalline phase of the product is calcium sulfate dihydrate with a purity of 99.26%; the whisker aspect ratio is approximately 56; the free water mass fraction is 0.69%; the product is a white filamentous powder. The prepared phosphogypsum warm mix agent is added to AC-13 type asphalt mixture at 0.3% of the asphalt mass, and standard specimens are formed with a designed porosity of 4% for Marshall test, rutting test, and four-point bending fatigue test.

[0045] Example 3: Following the steps of Example 1, the hydrochloric acid mass fraction was adjusted to 16%, the reaction temperature was controlled within the range of 80℃, and the stirring time was 20 min. The XRF analysis and SEM images of the phosphogypsum warm-mixing agent obtained in this example are shown below. Figure 1 and Figure 4 As shown, the main crystalline phase of the product is calcium sulfate dihydrate with a purity of 99.44%; the whisker aspect ratio is approximately 69; the free water mass fraction is 0.39%; the product is a white filamentous powder. The prepared phosphogypsum warm mix agent is added to AC-13 type asphalt mixture at 0.3% of the asphalt mass, and standard specimens are formed with a designed porosity of 4% for Marshall test, rutting test, and four-point bending fatigue test.

[0046] Example 4: Following the steps of Example 1, the hydrochloric acid mass fraction was adjusted to 16%, the reaction temperature was controlled within the range of 70℃, and the stirring time was 10 min. The XRF analysis and SEM images of the phosphogypsum warm-mixing agent obtained in this example are shown below. Figure 1 and Figure 5As shown, the main crystalline phase of the product is calcium sulfate dihydrate with a purity of 99.05%; the whisker aspect ratio is approximately 56; the free water mass fraction is 0.57%, and the product is a white filamentous powder.

[0047] The prepared phosphogypsum warm mix agent was added to AC-13 type asphalt mixture at 0.3% of the asphalt mass. Standard specimens were formed with a designed void ratio of 4% and subjected to Marshall test, rutting test and four-point bending fatigue test.

[0048] Example 5: Following the steps of Example 1, the hydrochloric acid mass fraction was adjusted to 20%, the reaction temperature was controlled within the range of 70℃, and the stirring time was 20 min. The XRF analysis and SEM images of the phosphogypsum warm-mixing agent obtained in this example are shown below. Figure 1 and Figure 6 As shown, the main crystalline phase of the product is calcium sulfate dihydrate with a purity of 99.16%; the whisker aspect ratio is approximately 61; the free water mass fraction is 0.46%; the product is a white filamentous powder. The prepared phosphogypsum warm mix agent is added to AC-13 type asphalt mixture at 0.3% of the asphalt mass, and standard specimens are formed with a designed porosity of 4% for Marshall test, rutting test, and four-point bending fatigue test.

[0049] Compared with Example 15, Comparative Example 1 did not add phosphogypsum warm mix agent to the asphalt mixture, but the other components and preparation methods were the same. The design gradation table of AC-13 asphalt mixture is shown in Table 1.

[0050]

[0051] Table 1. Design gradation table for AC-13 asphalt mixture The test results of the asphalt mixture prepared using the present invention are shown in Table 2.

[0052]

[0053] Table 2 Test Results of Asphalt Mixture As shown in Table 2, in Examples 1-5 using phosphogypsum warm mix additive, the mixing temperature of the asphalt mixture was reduced by approximately 23-25°C compared to Comparative Example 1, and the compaction temperature was reduced by approximately 21-23°C, effectively achieving a construction temperature reduction of over 20°C. This indicates that the phosphogypsum warm mix additive can significantly improve the workability of the asphalt mixture. Regarding dynamic stability data, the dynamic stability of the examples was significantly higher than that of Comparative Example 1 (1035 cycles / mm), with Example 2 showing the highest at 1349 cycles / mm, an increase of approximately 14%-30%. This indicates that the phosphogypsum warm mix additive helps improve the high-temperature resistance to permanent deformation of the asphalt mixture. In terms of fatigue performance, the fatigue life of the examples at the 400 με level was 75820-89070 cycles, an increase of approximately 7%-26% compared to Comparative Example 1 (70730 cycles). At the 700 με strain level, the fatigue life remained between 6650-6970 cycles, also an improvement compared to Comparative Example 1 (6510 cycles).

[0054] The phosphogypsum warm mix agent of this invention can significantly reduce the construction temperature of asphalt mixtures while improving their high-temperature stability and fatigue durability, thus having a comprehensive beneficial effect of reducing energy consumption, reducing emissions, and improving mechanical properties.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum, characterized in that, Includes the following steps: S1: Select phosphogypsum from mixed industrial by-product gypsum as the raw material, and screen the phosphogypsum raw material to remove large particle impurities and obtain refined phosphogypsum raw material with uniform particle size. S2: Add hydrochloric acid solution to the reaction beaker, place the beaker in a heat-insulating jacket for constant temperature heating, and add the sieved phosphogypsum raw material and crystal control agent under continuous stirring to carry out acidification modification reaction; through the acidification reaction, the calcium sulfate dihydrate in the phosphogypsum is fully dissolved, and at the same time, the solid impurities such as phosphorus, fluorine and organic impurities contained in the raw material are converted into soluble salts and uniformly dispersed in the reaction system; S3: After the acidification reaction is completely finished, the suspension of the reaction system is subjected to hot filtration to effectively separate the insoluble solid impurities in the system, remove the undissolved inert impurities, and obtain a clear and pure acidified hot filtrate. S4: The prepared acidified hot filtrate is placed in a room temperature environment for natural cooling and crystallization treatment, so that the calcium sulfate dihydrate component dissolved in the filtrate undergoes recrystallization. After crystallization, the mixed system is filtered to obtain a crude crystalline substance containing trace amounts of soluble salt impurities. S5: Use distilled water as a cleaning agent to thoroughly wash the obtained coarse crystals, and continuously stir to dissolve them, so that the soluble salt impurities on the surface and inside of the coarse crystals are completely dissolved and removed. S6: After the solid-liquid mixture is washed, it is filtered to completely remove the salt impurities and waste liquid dissolved in the water, and obtain a high-purity calcium sulfate dihydrate whisker solid product. S7: The purified calcium sulfate dihydrate whiskers are placed in a constant temperature drying equipment for low-temperature drying to completely remove the free moisture on the surface of the product, and finally the modified phosphogypsum asphalt warm mix agent is obtained.

2. The method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 1, characterized in that, The chemical composition of the phosphogypsum raw material includes: 85%–90% CaSO4·2H2O, 5%–10% SiO2, 1%–1.5% F, 0.5%–2.3% P2O5, 0.1%–0.8% Al2O3, 0.03%–0.2% Fe2O3, 0.05%–0.35% K2O, 0.08%–0.2% Na2O, 0.01%–0.2% TiO2, and 0.02%–0.15% MgO.

3. A method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 1 or 2, characterized in that, The screening process uses a square-hole sieve with a mesh size of 200.

4. The method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 3, characterized in that, The acidification reaction temperature is controlled at 70-90℃, the mass fraction of hydrochloric acid is 12%-20%, the stirring time is 10-30 min, and the stirring speed is controlled at 300-600 r / min; the solid-liquid ratio of phosphogypsum raw material to hydrochloric acid solution is 1:4 g / mL to 1:8 g / mL; the temperature control adopts a corrosion-resistant thermometer, and the temperature measuring wire adopts a thermocouple wire resistant to strong acids and alkalis.

5. The method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 4, characterized in that, The amount of crystal form control agent added in step S2 is 1.5% to 4.5% of the dry weight of phosphogypsum raw material. The crystal form control agent includes any one of calcium chloride dihydrate, copper chloride dihydrate, magnesium chloride hexahydrate, dodecyltrimethylammonium bromide, and ethylenediaminetetraacetic acid.

6. The method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 5, characterized in that, In step S3, the hot filtration process requires a buffer bottle to be installed between the filtration flask and the vacuum pump of the filtration device to block acidic vapors and waste liquid.

7. The method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 6, characterized in that, In step S4, the cooling crystallization process parameters are as follows: the cooling rate of the acidified hot filtrate is controlled at 2-5℃ / min, and the holding time for crystallization at room temperature is 2-4h. In step S5, the water washing process parameters are as follows: distilled water with a mass of 3-5 times that of the crude crystal material is used for water washing, and the continuous stirring water washing time is 10-20min.

8. The method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 7, characterized in that, In step S7, the drying process is completed using a constant temperature forced-air drying oven, with the drying temperature strictly controlled below 60°C. Only the free water on the surface of the product is removed, while the crystal water structure of calcium sulfate dihydrate is completely preserved.

9. A method for preparing asphalt warm mix admixture using mixed industrial by-product gypsum according to claim 8, characterized in that, The performance indicators of the modified phosphogypsum asphalt warm mix agent obtained through steps S1 to S7 meet the following indicators: calcium sulfate dihydrate whisker purity ≥99%, free water mass fraction ≤1%, whisker aspect ratio ≥55. When any of the calcium sulfate dihydrate whisker purity, free water mass fraction, or whisker aspect ratio fails to meet the standard, the temperature, hydrochloric acid mass fraction, and stirring time in the acidification reaction are readjusted, and the indicators of temperature, hydrochloric acid mass fraction, and stirring time in the acidification reaction are gradually increased.

10. A modified phosphogypsum asphalt warm mix agent, prepared using the method for preparing asphalt warm mix agent by mixing industrial by-product gypsum as described in any one of claims 1-9, characterized in that, The modified phosphogypsum asphalt warm mix agent can improve the workability of asphalt mixtures and reduce the construction temperature by 20℃-22℃.

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